Thèses : « EFFECT OF STIFFNESS »

1

Vedam, Hima. « Short-term hypoxia and arterial stiffness ». Thesis, The University of Sydney, 2007. https://hdl.handle.net/2123/28093.

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The studies in this thesis assess the ventilatory and vascular effects of short-term awake isocapnic hypoxia in healthy subjects and those with obstructive sleep apnoea (OSA). The particular focus of this thesis is the impact of the hypoxic stimulus on indices of arterial stiffness, in particular the augmentation index (AIx) and time to reflection (Tr). The role of nitric oxide in this response in healthy subjects is also examined.

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Elshafie, Mohammed Zein Elabidin Babiker. « Effect of building stiffness on excavation-induced displacements ». Thesis, University of Cambridge, 2008. https://www.repository.cam.ac.uk/handle/1810/252093.

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Al-Hammoud, Abdullah. « Effect of joint design on vehicle bodyshell stiffness ». Thesis, Loughborough University, 1985. https://dspace.lboro.ac.uk/2134/10336.

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The work presented in this thesis is an investigation into vehicle bodyshell structural joints, with the aim of improving their stiffness. The bodyshell joint is defined to be an area or sub-structure containing the intersection of beam-type members, the behaviour of which may be defined by a matrix determined experimentally or analytically by using the finite element method. An actual bodyshell was tested on a suitably designed rig and the primary displacement modes affecting the steady state and vibration response of a bodyshell were identified and the relevant stiffness measured by using a special transducer. The joint rotational displacements were measured in these modes and the relative importance of the joints obtained. The joints were then modified by the addition of stiffening plates and the effect on the various stiffnesses noted. To assist the analyst, a similar study was performed on the effectiveness of the panels, such as roof, floor and rear quarter. A finite element beam model was established for the bodyshell and modified until a good approximation was achieved with respect to the experiments. Some practical modification of three selected joints cut from the bodyshell was done in order to improve their stiffness. A theoretical study of the influence of spot welding size and spacing on the stiffness of two plates was made. A finite element model of an actual body joint was established and the effect on stiffness of various modifications was observed.

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Toro, Andrea del Pilar. « Effect of Lateral Stiffness on Bridge Deck Performance ». UNF Digital Commons, 2015. http://digitalcommons.unf.edu/etd/587.

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The use of the empirical deck design method has increased its acceptance due to the economic advantages that it presents when compared to its counterpart, the traditional method. This can be attributed to the fact that the empirical method provides an appropriate design where the deck withstands stress not only due to the steel reinforcement but to an implicit arching membrane stress set-up as an effect of the lateral restraint surrounding the deck slab known as Compressive Membrane Action (CMA). It has been proved through research that most design codes underestimate the strength of laterally restrained slabs. However, there is still a lack of acceptance in practical bridge design codes. This thesis presents an analysis addressing the influence that the lateral stiffness of the support beams has on the overall bridge deck performance. The lateral stiffness behavior was assessed through a programmed electronic spreadsheet where a comparison with different current code requirements and an additional approach was made. Through this analysis it was determined that not only does the support beam lateral stiffness plays an important role in the overall bridge deck slab ultimate capacity, but mapping out this influence is a priority that may also be useful in setting the basis for future design criteria.

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Tatting, Brian F. « Analysis and Design of Variable Stiffness Composite Cylinders ». Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/29313.

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An investigation of the possible performance improvements of thin circular cylindrical shells through the use of the variable stiffness concept is presented. The variable stiffness concept implies that the stiffness parameters change spatially throughout the structure. This situation is achieved mainly through the use of curvilinear fibers within a fiber-reinforced composite laminate, though the possibility of thickness variations and discrete stiffening elements is also allowed. These three mechanisms are incorporated into the constitutive laws for thin shells through the use of Classical Lamination Theory. The existence of stiffness variation within the structure warrants a formulation of the static equilibrium equations from the most basic principles. The governing equations include sufficient detail to correctly model several types of nonlinearity, including the formation of a nonlinear shell boundary layer as well as the Brazier effect due to nonlinear bending of long cylinders. Stress analysis and initial buckling estimates are formulated for a general variable stiffness cylinder. Results and comparisons for several simplifications of these highly complex governing equations are presented so that the ensuing numerical solutions are considered reliable and efficient enough for in-depth optimization studies. Four distinct cases of loading and stiffness variation are chosen to investigate possible areas of improvement that the variable stiffness concept may offer over traditional constant stiffness and/or stiffened structures. The initial investigation deals with the simplest solution for cylindrical shells in which all quantities are constant around the circumference of the cylinder. This axisymmetric case includes a stiffness variation exclusively in the axial direction, and the only pertinent loading scenarios include constant loads of axial compression, pressure, and torsion. The results for these cases indicate that little improvement over traditional laminates exists through the use of curvilinear fibers, mainly due to the presence of a weak link area within the stiffness variation that limits the ultimate load that the structure can withstand. Rigorous optimization studies reveal that even though slight increases in the critical loads can be produced for designs with an arbitrary variation of the fiber orientation angle, the improvements are not significant when compared to traditional design techniques that utilize ring stiffeners and frames. The second problem that is studied involves arbitrary loading of a cylinder with a stiffness variation that changes only in the circumferential direction. The end effects of the cylinder are ignored, so that the problem takes the form of an analysis of a cross-section for a short cylinder segment. Various load cases including axial compression, pressure, torsion, bending, and transverse shear forces are investigated. It is found that the most significant improvements in load-carrying capability exist for cases which involve loads that also vary around the circumference of the shell, namely bending and shear forces. The stiffness variation of the optimal designs contribute to the increased performance in two ways: lowering the stresses in the critical areas through redistribution of the stresses; and providing a relatively stiff region that alters the buckling behavior of the structure. These results led to an in-depth optimization study involving weight optimization of a fuselage structure subjected to typical design constraints. Comparisons of the curvilinear fiber format to traditional stiffened structures constructed of isotropic and composite materials are included. It is found that standard variable stiffness designs are quite comparable in terms of weight and load-carrying capability yet offer the added advantage of tailorability of distinct regions of the structure that experience drastically different loading conditions. The last two problems presented in this work involve the nonlinear phenomenon of long tubes under bending. Though this scenario is not as applicable to fuselage structures as the previous problems, the mechanisms that produce the nonlinear effect are ideally suited to be controlled by the variable stiffness concept. This is due to the fact that the dominating influence for long cylinders under bending is the ovalization of the cross-section, which is governed mainly by the stiffness parameters of the cylindrical shell. Possible improvement of the critical buckling moments for these structures is investigated using either a circumferential or axial stiffness variation. For the circumferential case involving infinite length cylinders, it is found that slight improvements can be observed by designing structures that resist the cross-sectional deformation yet do not detract from the buckling resistance at the critical location. The results also indicate that bucking behavior is extremely dependent on cylinder length. This effect is most easily seen in the solution of finite length cylinders under bending that contain an axial stiffness variation. For these structures, the only mechanism that exhibits improved response are those that effectively shorten the length of the cylinder, thus reducing the cross-sectional deformation due to the forced restraint at the ends. It was found that the use of curvilinear fibers was not able to achieve this effect in sufficient degree to resist the deformation, but that ring stiffeners produced the desired response abmirably. Thus it is shown that the variable stiffness concept is most effective at improving the bending response of long cylinders through the use of a circumferential stiffness variation.
Ph. D.

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Karamichos, Dimitrios. « Effect of strain and stiffness on matrix remodelling genes ». Thesis, University College London (University of London), 2007. http://discovery.ucl.ac.uk/1445416/.

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Cells embedded within tissues respond to mechanical, chemical and biological signals. However, the detail of how mechanical forces are transmitted to cells is poorly understood at present and represents a key missing link in Tissue Engineering. As cells attach to the fibrils in fibroblast-seeded 3D collagen scaffolds they generate contractile forces to levels, which depend on cell type, attachment, density, growth factors and matrix stiffness. The aim of this study was to use external applied strain to increase matrix stiffness in collagen constructs. Embedded resident cells (from three different sites) were then subjected to specific mechanical loading regimes in scaffolds of increasing stiffness and matrix remodelling genes quantified as markers of mechanoregulatory cellular response. Mechanical responses of cells were also quantified as contraction profiles over time. Our findings indicated that collagen got stiffer with application of high strains and visco-elastic properties resulted in minimal transfer of applied loads as recorded by movement of indwelling markers. The mechanical and molecular responses of three different cell lineages: human dermal (HDF), neonatal foreskin fibroblasts (HNFF) and human bone marrow stem (hBMSC) cells seeded in constructs of increased stiffness was tested. Results indicated that in HNFFs contraction was predominantly attachment-dependent while in HDFs it was predominantly stiffness-dependent. hBMSCs showed differential response to serum levels. Molecular responses in progressively stiffer constructs investigated were MMP-2, MMP-3, MMP-9, TIMP- 2,COL-l,COL-3 and IGF-1. Different cell types expressed specific variations in gene regulation. The effect of specific mechanical loading (slow and fast ramp) regimes on regulation of matrix remodelling genes also showed a lineage dependent response. The major impact of this project has been the identification of a strong co-relation between substrate stiffness, mechanical loading and regulation of key ECM turnover genes. This knowledge is crucial to successful tissue engineering outcomes. The differential lineage dependent response is a key finding and will have to be tailored depending on cell source and specific outcomes desired. regimes on regulation of matrix remodelling genes also showed a lineage dependent response. The major impact of this project has been the identification of a strong co-relation between substrate stiffness, mechanical loading and regulation of key ECM turnover genes. This knowledge is crucial to successful tissue engineering outcomes. The differential lineage dependent response is a key finding and will have to be tailored depending on cell source and specific outcomes desired.

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Kelly, Darren. « Effect of particle loss on soil volume, strength and stiffness ». Thesis, Edinburgh Napier University, 2015. http://researchrepository.napier.ac.uk/Output/8865.

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Soil particle loss can occur through biodegradation, erosion and dissolution. Yet there is little understanding of the mechanical changes that accompany these phenomena, especially where the size of particle removed is concerned. This study investigated the influence of particle loss on the volumetric, strength and small strain stiffness of analogue soils. These consisted of uniform Leighton Buzzard sand with selected salt particle sizes. Particle sizes chosen for experimental tests are representative of the fines that might be lost through an erosion process called suffusion in embankment dams or the various sizes that might be degraded and/or decomposed in landfill and mining wastes. A triaxial apparatus was modified to allow the in-situ dissolution of samples under triaxial stress states. This was achieved through the circulation of water through the pore-water pressure line with ow controlled by differential pressure using a peristaltic pump. Bender elements were installed to monitor changes in shear wave velocity before, during and after dissolution. Test results showed increases in void ratio in all dissolution tests. The influence of salt size and the stress under which tests were performed was found to have a limited impact on the magnitude of void ratio increase. Salt particle size did, however, affect the initial packing density of the sand-salt mixtures with fine salt sizes resulting in lower void ratios. Therefore, these tests showed lower post-dissolution void ratios. Coarse salt sizes initially densely prepared resulted in high post-dissolution void ratios close to the maximum void ratio for the Leighton Buzzard sand. Ultimately, post-dissolution void ratios determined the large-strain shearing behaviour. Therefore the fine salt tests, in which the post-dissolution void ratios were lowest, were the only tests to show minor peak strengths prior to the critical state with a shear behaviour described as strain-softening dilative. The comparatively high void ratios obtained in coarse salt tests showed no peak strength but a strain-hardening contractive behaviour. The structural role of salt particles within sand mixtures was continually assessed with evidence suggesting that salt particles maintainedtheir structural integrity under the stresses applied through loading and subsequent shearing in this study. The influence of particle loss on the critical state was also probed. Post-dissolution samples consistently showed higher critical void ratios than sand-only samples not subjected to particle loss. Most of the findings might be explained in the context of strong force chains and their stability which is in turn influenced by the amount and size of soluble particles. Shear wave velocities were shown to decrease significantly with dissolution of 15% of weight of salt irrespective of size. Associated small-strain stiffness moduli were found to decrease even more substantially. The reported changes illustrate the significant influence that particle removal has on the mechanical properties of soil and are discussed and analysedwithin this thesis.

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Colthrust, Melissa B. « The effect of oral contraceptives on musculo-tendinous stiffness of the knee flexors ». Virtual Press, 2005. http://liblink.bsu.edu/uhtbin/catkey/1319218.

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The purpose of this study is to investigate the relationship between oral contraceptive use and the musculo-tendinous stiffness of the knee flexors. Twenty-three female participants and ten male participants (control group) ranging in age from 20 - 30 years. A uniaxial accelerometer was used to assess stiffness based on the exponential decay of the damped oscillation. Female groups had estradiol and 17 a-OH progesterone levels tested. At 30% of MVC, the Ortho-Tri Cyclen group, the Other OC group and women not using OC's had a mean stiffness of 249.3+94.5, 274.1+79.1 and 216.0+43.3 Nm/rad respectively and at 50% of MVC values of 290.2+70.7, 326.7+78.9 and 267.9+52.6 Nm/rad respectively. No significant difference in stiffness was found. Also no correlation was found between estradiol and stiffness. These results indicate that there was no significance between knee stiffness and oral contraceptives within the female groups.
School of Physical Education, Sport, and Exercise Science

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Bozorgzadeh, Azadeh. « Effect of structure backfill on stiffness and capacity of bridge abutments ». Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2007. http://wwwlib.umi.com/cr/ucsd/fullcit?p3274986.

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Thesis (Ph. D.)--University of California, San Diego, 2007.
Title from first page of PDF file (viewed October 2, 2007). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 260-265).

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Karlstrand, Nils, et Johan Neander. « After-compaction effect on the stiffness modulus of laboratory made samples ». Thesis, Linköpings universitet, Institutionen för teknik och naturvetenskap, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-97217.

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The report is written in research purpose for the Swedish National Road and Transport Research Institute (VTI). The aim has been to find out and to determine after-compaction effect on the stiffness modulus of laboratory made samples with different void content and at various temperatures. With the stiffness modulus the shear modulus can be calculated. With the shear modulus a road structure’s deformation in its different layers can be calculated. The work began with the choice of asphalt mixture (ABb16 160/220) with 5% binder content. This was compacted to sample bodies. These samples were analyzed with a number of methods from FAS (the association for asphalt pavements in Sweden). The results from these tests show among other things bulk density, void content and stiffness modulus. These results have afterwards been analyzed through different calculations developed by VTI. From the results we draw the conclusion that there is a clear connection between void and deformation, i.e. a higher void content gives a bigger deformation because of the low stiffness modulus. What happens is that after-compaction leads to a reduced void content which gives a higher stiffness modulus which gives an asphalt pavement that is more resistant against deformations. If the asphalt mixture has a void content of 5% you get a deformation during the first years that is 20% bigger than at a void content of 2% at 10°C. Is the void content 7% the deformation becomes 40% bigger that with 2% according to this study.
Rapporten är skriven i forskningssyfte för Statens väg och transportforskningsinstitut (VTI). Med syftet att ta reda på och klarlägga efterpackningens effekt på styvhetsmodulen hos laboratorietillverkade provkroppar med olika hålrum och vid olika temperaturer. Med hjälp av styvhetsmodulen kan skjuvmodulen räknas fram, under förutsättning att materialet är elastiskt, som man direkt kan härleda till en väg konstruktions deformation i de olika lagren. Arbetet började med val av asfaltmassa (ABb16 160/220) med en 5 % bindehalt, som sedan packades till provkroppar. Dessa provkroppar analyserades med ett antal metoder från FAS´(Föreningen för asfaltbeläggningar i Sverige). Resultatet från dessa metoder visar bland annat kompakt- och skrymdensitet, hålrumshalt och styvhetsmodul. Dessa resultat har sedan analyserats genom olika beräkningar framtagna av VTI. Från dessa resultat drar vi slutsatsen att det finns ett klart samband mellan hålrum och deformation (efterpackning), då en högre hålrumshalt ger en större deformation på grund av den låga styvhetsmodulen. Vad som sker är att efterpackningen leder till en minskad hålrumshalt vilket ger en högre styvhetsmodul vilket i sin tur ger en asfaltbeläggning som är mer motståndskraftig mot deformationer. Packas bindlagret till en hålrumshalt på 5 % får man en deformation under de första åren som är 20 % större än vid en hålrumshalt på 2 %, vid 10ºC. Är hålrumshalten 7 % blir deformationen istället 40 % större än vid 2 % enligt denna undersökning.

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Sue, Ji Woong. « Effect of microstructure of closed cell foam on strength and effective stiffness ». Texas A&M University, 2006. http://hdl.handle.net/1969.1/4986.

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This research is concerned with the modeling and failure analysis of closed cell foam with various scales of microstructure that is disordered due to defects. This foam material is used for the forward bipod closeout on the space shuttle external tank. Three dimensional finite element simulations of closed cell foams with various microstructures are performed to study the influence of the geometric character of the microstructure (eg. defect size and distribution) on the stiffness and failure behavior of the foam. First, regularly arrayed cells are modeled for a reference to compare with the disordered microstructure. For studying the effect of cellular microstructure, a discrete model is developed where in every edge and face of each cell are modeled. Two types of defects, point defects (void) and area defects (knot), are indicated from the examination of BX250 and BX265 polyurethane foams. However, this research is focused on the point defect. Analyzing a material with such complex microstructure is especially challenging in terms of computation power as well as required modeling techniques. A finite element model consisting of only beam and shell elements was developed. Certain complications that arise from using beam and shell elements were resolved using novel techniques. Stiffness predictions from the model agreed with data from the literature for a wide range of relative densities. Parametric studies were performed to examine the effect of different properties, such as relative densities and edge fraction, on the effective stiffness, Von Mises stress, and buckling stress. The thickness of the face plays an important role in the behavior of the foam material. Linear buckling and postbuckling analyses were performed to understand the effect of local buckling on the effective properties of the foam and stress concentrations. A distorted multicell model was developed to analyze the effect of point defects on the foam behavior. In particular, two geometric parameters, the defect size and the defect density (or the distance between two defects) were varied to find their effect on the stress concentrations and the effective stiffness of the foam. It is seen that the discrete model that accounts for the foam microstructure reveals much more about the foam behavior than a homogenous model.

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Elliott, Winston Howard. « Effect of Tissue Viscoelasticity and Stiffness on Hemodynamics and Endothelial Cell Signaling ». Doctoral thesis, Università degli studi di Trento, 2017. https://hdl.handle.net/11572/368196.

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Cardiovascular disease (CVD) is the most common cause of death in the United States of America, accounting for 24% of all deaths each year,(Anderson et al., 2003) and is projected to rise above 20% globally by 2030.(Mathers and Loncar, 2006) Options for CVD treatment do exist, but are limited by availability of healthy replant tissue from the patient or long term effectiveness and failure rates of both autologous tissue grafts and artificial implants. Grafting failure may often be attributed to the poor mimicry of the site-specific, healthy arterial tissue. While much TEVG research focuses on endothelialization of the graft lumen through chemical signaling, mechanotransduction plays a large role in forming and maintaining a healthy endothelial cell (EC) monolayer. Arteries and grafts interact with hemodynamics to determine flow pulsatility and create healthy, or pathological, mechanical signaling environments. Though arterial tissue is known to be viscoelastic,(Armentano et al., 2006; Bergel, 1961; Bia et al., 2006) the importance of this in developing healthy blood flow is undetermined. Therefore, a gap in the knowledge occurs in the importance of arterial mechanics affecting graft outcomes. To address this we attempt to examine specific shortcomings: 1) Determine whether pathological flow is capable of maintaining EC monolayer in a low arterial compliance model, 2) Establish methods of catering protein hydrogel frequency-dependent properties towards establishing biodegradable materials intended for TEVG, 3) Determine benefits of viscous wall damping in improving hemodynamics towards improved cell response. This proposal centers on improving cell response to pathological hemodynamics through catered viscoelastic material response at the arterial wall. To address this, we hypothesize that maintaining healthy EC monolayer is predicated on hemodynamic mechanotransduction, which results from both graft compliance and viscous damping of the material. To validate this hypothesis, we examine healthy and pathological hemodynamic effects on EC monoculture, and systematically determine the role of viscoelastic material response in maintaining healthy hemodynamics.

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Elliott, Winston Howard. « Effect of Tissue Viscoelasticity and Stiffness on Hemodynamics and Endothelial Cell Signaling ». Doctoral thesis, University of Trento, 2017. http://eprints-phd.biblio.unitn.it/3011/1/WinstonElliott_Dissertation(Final-2).pdf.

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Cardiovascular disease (CVD) is the most common cause of death in the United States of America, accounting for 24% of all deaths each year,(Anderson et al., 2003) and is projected to rise above 20% globally by 2030.(Mathers and Loncar, 2006) Options for CVD treatment do exist, but are limited by availability of healthy replant tissue from the patient or long term effectiveness and failure rates of both autologous tissue grafts and artificial implants. Grafting failure may often be attributed to the poor mimicry of the site-specific, healthy arterial tissue. While much TEVG research focuses on endothelialization of the graft lumen through chemical signaling, mechanotransduction plays a large role in forming and maintaining a healthy endothelial cell (EC) monolayer. Arteries and grafts interact with hemodynamics to determine flow pulsatility and create healthy, or pathological, mechanical signaling environments. Though arterial tissue is known to be viscoelastic,(Armentano et al., 2006; Bergel, 1961; Bia et al., 2006) the importance of this in developing healthy blood flow is undetermined. Therefore, a gap in the knowledge occurs in the importance of arterial mechanics affecting graft outcomes. To address this we attempt to examine specific shortcomings: 1) Determine whether pathological flow is capable of maintaining EC monolayer in a low arterial compliance model, 2) Establish methods of catering protein hydrogel frequency-dependent properties towards establishing biodegradable materials intended for TEVG, 3) Determine benefits of viscous wall damping in improving hemodynamics towards improved cell response. This proposal centers on improving cell response to pathological hemodynamics through catered viscoelastic material response at the arterial wall. To address this, we hypothesize that maintaining healthy EC monolayer is predicated on hemodynamic mechanotransduction, which results from both graft compliance and viscous damping of the material. To validate this hypothesis, we examine healthy and pathological hemodynamic effects on EC monoculture, and systematically determine the role of viscoelastic material response in maintaining healthy hemodynamics.

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Gioux, Gaël 1974. « Effect of properties of metallic foams on stiffness and strength of sandwich beams ». Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/85270.

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McDonnell, Barry John. « The effect of diabetes, ethnicity, impaired fasting glucose and exercise on arterial stiffness ». Thesis, Cardiff University, 2007. http://orca.cf.ac.uk/54056/.

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The "first study" compared 3 methods of assessing arterial stiffness and found that: each method of assessment was comparable to the other and that reproducibility was similar throughout the systems. Since there are conflicting data associated with arterial stiffness and type-2 diabetes, the "second study" therefore assessed arterial stiffness, using pulse wave analysis and pulse wave velocity and found there to be increased arterial stiffness in a group of type-2 diabetics compared to healthy controls. The second study also found that South Asians had significantly lower arterial stiffness in the femoral vascular bed compared to the Caucasians. Although diabetes is known to increase arterial stiffness, the effect of impaired fasting glucose on arterial stiffness is unclear. The effect of impaired fasting glucose on arterial stiffness has therefore been investigated in the "third study" and the findings demonstrate that individuals with impaired fasting glucose have increased arterial stiffness compared to individuals with normal fasting glucose. Similar findings were observed when comparing diabetics and individuals with normoglycaemia. Finally, therapeutic intervention targeted at increased arterial stiffness should be of benefit in reducing the prevalence of cardiovascular disease. The "fourth study" has therefore also examined the effect of regular aerobic exercise on arterial stiffness and found that in older individuals, arterial stiffness was significantly lower in a group of individuals who exercised regularly compared to sedentary controls. Therefore, suggesting the potential benefit of aerobic exercise as a non-pharmacological intervention to decrease arterial stiffness and cardiovascular disease.

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Williams, Brian O. « Effect of isokinetic resistance training on ulnar stiffness in young, college-aged women ». Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/33025.

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Bone mineral content (BMC) and bone mineral density (BMD), measured by dual x-ray absorptiometry are used clinically to diagnose osteoporosis and estimate risk for fragility fractures. Bone mineral explains up to 70% of bone strength; however, it does not take into account bone geometry. Mechanical Response Tissue Analysis is a method of non-invasively measuring the bending stiffness (EI) of bone which is determined by the product of Young's modulus of elasticity (E) and the areal cross sectional moment of inertia (I). The aim of the current study was to determine if high intensity strength training will increase ulnar bending stiffness in young women. Forty-nine women aged 19.9 Â± 1.7 yrs, trained their nondominant arm either concentrically or eccentrically in the Isokinetic modality on the BiodexÂ® system III 3d/wk for 32 wks. The dominant arm served as the control limb (untrained). Analysis of all subjects regardless of training mode demonstrated a significant increase in ulnar EI (22% â , P=0.01) with no significant difference in the untrained arm. When EI results were assessed by training mode, subjects who trained eccentrically showed a significant increase for ulnar EI in the trained limb (40% â , P=0.01) with no significant effect on the untrained limb while concentric training demonstrated no significant gain in either the trained or untrained arm. There was no effect of time x mode of training interaction for either the trained or untrained limb. Bone mineral density and bone mineral content of the ulna increased significantly in the trained arm in both concentric and eccentric training modes (P<0.05). These findings suggest support for the hypothesis that a critical threshold of mechanical bending loads may be necessary to effect an adaptation in bone strength and thus, eccentric training may be a novel approach to increase ulnar EI in young women.
Master of Science

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Conners, Terrance E. « The effect of moisture gradients on the stiffness and strength of yellow-poplar ». Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/74713.

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Wood with a uniform moisture distribution is known to have different mechanical properties compared to wood with a non-uniform moisture distribution. Moisture gradients are likely to develop in full-size members tested in the In-Grade Testing Program and might therefore affect the test results. The purpose of this study was to mathematically model the effect of desorption moisture gradients on the stiffness and strength of yellow-poplar beams. An additional objective was to experimentally determine gradient effects in yellow-poplar beams. Three-dimensional finite-element modeling was employed and several subsidiary models were developed. Among these was a three-parameter segmented model for fitting digitized tension and compression stress-strain curves. Unlike previous models (such as the Ramberg-Osgood model), this model has a linear slope up to the point approximately corresponding to the proportional limit. A methodology was also devised whereby most hardwood and softwood elastic constants can be estimated at any moisture content. Data are required at one moisture content. Equilibrated uniaxial testing was conducted at four moisture contents to acquire data for the finite-element model. It was found that the longitudinal Young's moduli in tension and compression were approximately equal at 6% and 18% moisture content; the compression modulus was greater at 12%, but the tension modulus was greater for green specimens. Intersection points for tension and compression mechanical properties may be different. Tests of small clear yellow-poplar beams indicated that moisture gradients induced at 12% equilibrium moisture content had little effect on the modulus of rupture up to 19% average moisture content. At higher moisture contents, gradient-containing beams were significantly stronger than equilibrated beams when comparisons were made at identical moisture contents. Modulus of elasticity data exhibited a similar trend, although differences between equilibrated and non-equilibrated beams were observed below 19% moisture content. The finite-element program was moderately successful in predicting the effects of moisture gradients on the strength and stiffness of yellow-poplar beams. Computer time and storage constraints limited the accuracy of the solutions. Predicted trends were verified by the experimental data. Modeling of full-size lumber indicated that significant moisture gradients will likely influence the stiffness and strength of higher quality lumber.
Ph. D.

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18

Li, Xiaoming. « The effect of stiffness and mass on the dynamic response of wood floors ». Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-06112009-063311/.

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Swann, Anthony Charles. « The effect of mechanical stress on the stiffness of articular cartilage and its role in the aetiology of osteoarthrosis ». Thesis, University of Leeds, 1988. http://etheses.whiterose.ac.uk/363/.

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Although a substantial amount is known about the pathogenesis of osteoarthrosis, its aetiology and in particular the role that mechanical factors play, remains unclear. One particular hypothesis suggests that cartilage adapts mechanically so that it may transmit, without sustaining damage, the stresses to which it is predominantly subjected, and that damage to the cartilage is caused by infrequent high stresses in excess of the predominant level. As a corollary, it was suggested that highly stressed cartilage should be stiffer than lowly stressed cartilage. A survey of the mechanical properties of normal articular cartilage from unembalmed cadaveric knee and ankle joints was undertaken to test this hypothesis. For this purpose, a specially developed indentation test apparatus was commissioned. Tests of the machine's measurement capabilities indicate that coefficients of variation of 2.14% and 1.20% for indentation and cartilage thickness measurement could be expected. The maximum percentage errors in the calculated creep modulus value which could result from these typical measurement errors, were 4.2% and 2.9% respectively. Creep modulus values, calculated from these measurements, were used in topographical comparisons of cartilage stiffness. The stiffest areas of cartilage in the knee joint were the femoral condyles and areas of the tibia covered by the menisci. Cartilage on the patellar surfaces of the femur and in areas exposed by the menisci was significantly softer. Cartilage from the ankle joint was considerably stiffer than cartilage from the knee. Comparisons between the cartilage stiffness and levels of stress which act in the knee and ankle joints during normal ambulatory activity, showed the stiffest areas of cartilage to be subjected to the greater stresses. Correlations of averaged data values indicated a significant (p < 0.01) direct relationship between cartilage stiffness and stress. This relationship and the consistency with which osteoarthrotic lesions were found in areas subjected to damaging patterns of stress supported the hypothesis under examination. The lack of correlation found between the proteoglycan content and cartilage stiffness suggested that structural rather than compositional factors may be more important in influencing the compressive stiffness of normal articular cartilage.

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Kocak, Umut, Karljohan Palmerius, Camilla Forsell et Matthew Cooper. « The Effect of the Stiffness Gradient on the Just Noticeable Difference between Surface Regions ». Linköpings universitet, Medie- och Informationsteknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-79905.

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Numerous studies have considered the ability of humans to perceive differences in forces and how this affects our ability to interpret the properties of materials. Previous research has not considered the effect of the rate of change of the material stiffness in our ability to perceive differences, however, an important factor in exploration processes such as a doctor’s palpation of the skin to examine tissues beneath. These effects are the topic of this research which attempts to quantify the effects of stiffness gradient magnitude and form on the discernment of changes in stiffness.

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Rothsching, Norman. « The effect of shaft stiffness on the performance of the ice hockey slap shot ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0001/MQ43940.pdf.

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Jacobson, Erik Andrew. « Effect of ski pole stiffness on upper body power output in cross-country skiers ». Thesis, Montana State University, 2008. http://etd.lib.montana.edu/etd/2008/jacobson/JacobsonE0508.pdf.

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The purpose of this study was to determine whether increased pole stiffness corresponds with higher measures of upper body power in competitive cross-country skiers. Fifteen elite/college level cross-country ski racers (8 men, 7 women) tested UBP on a custom-built double-poling ergometer. Ski poles tested were two models of the same brand with different factory-specified stiffness ratings. Subjects underwent three 10 s UBP tests (W10, W) and one 60 s UBP test (W60, W) for each pole type. UBP measures were defined as the average power output over the length of each test. Video recordings of the 10 s and 60 s tests were analyzed with digital imaging software to determine the maximum bend angle for each pole type. Ergometer and kinematic measures were compared by ski poles tested (stiff vs. less stiff) using a multivariate RMANOVA (Î±=0.05).

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Baker, Matthew W. « Effect of Pallet Deckboard Stiffness and Unit Load Factors on Corrugated Box Compression Strength ». Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/79367.

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Corrugated paper boxes are the predominant packaging and shipping material and account for the majority of packaging refuse by weight. Wooden pallets are equally predominant in shipping, transportation and warehousing logistics. The interaction between these two components is complex and unexplored leaving industry to compensate with outdated component specific safety factors. Providing a focused exploration of the box and pallet interaction will open the door for holistic design practices that will reduce cost, weight, damage, and safety incidents. This study was separated into four chapters exploring different aspects of the corrugated box to pallet interaction. The first chapter evaluates the support surface provided by a pallet consists of deckboards spaced perpendicular to the length of the pallet. The resulting gaps between deckboards reduce the support to the box. Gaps were limited to 55% of box sidewall length for practical reasons. The effect of gaps was significant and produced a nonlinear reduction in box strength. Small boxes were more susceptible to gaps than larger boxes. Moving the gap closer to the corner increased its effect while increasing the number of gaps did not increase the effect. A modification to the McKee equation was produced that was capable of predicting the loss in strength due to gaps. The equation is novel in that is modifies a widely used equation and is the first such equation capable of handling multiple box sizes. This study also has practical implications for packaging designers who must contend with pallet gap. Chapter 2 explores the relationship between deckboard deflection and box compression strength. Testing found that reducing the stiffness of the deckboard decreases the compression strength of the box by 26.4%. The location of the box relative to the stringer also had varying effects on the box strength. A combination of deckboard stiffness and gaps produced mixed with results with gaps reducing the effect of stiffness. It was observed that lower stiffness deckboards not only deflect but also twist during compression. The torsion is suspected to have a significant influence on compression but further exploration is needed. The third chapter tests the effect of box flap length on box compression strength under various support conditions. Variables included four flap lengths, gaps between deckboards, low stiffness deckboards, column stacking and misaligned stacking. The results show that the box flaps can be reduced by 25% with no significant effect of box strength under any support condition tested. Furthermore, the box flap can be reduced by 50% with less than 10% loss in compression strength under all scenarios. These results have significant sustainability implication as 25% and 50% reduction in box flap reduce material usage by approximately 12% and 24%, respectively. In the fourth and final chapter, the theory of beam-on-elastic foundation is applied to deckboard bending and corrugated boxes. In this model the corrugated box acts and the foundation and the deckboard is the beam. Rotational stiffness, load bridging, and foundation stiffness changes required the development of novel testing solution and model development. The model was capable of predicting the distribution of force along the length sidewall but was not capable of predicting the ultimate strength of the box. The model developed in the study will be applicable in determining potential weakness in the unit load in addition to optimizing those that are over designed. These four chapters represent a considerable contribution of applicable research to a field that relied on outdated safety factors over thirty years. These safety factors often lead to costly over design in an industry where corrugated box and pallets volumes make event the smallest improvements highly beneficial. Furthermore, this research has opened the door for significant additional research that will undoubtedly provided even greater economic and sustainability benefits.
Ph. D.

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K, C. Ashim. « SLAB AND TRANSVERSE BEAM STIFFNESS EFFECT ON THE SEISMIC DESIGN OF MOMENT FRAME STRUCTURE ». OpenSIUC, 2021. https://opensiuc.lib.siu.edu/theses/2817.

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Structures experience a dynamic nature of the load, different from ordinary design loads during earthquake excitation. The response of the structure to earthquake loads depends on the properties of its structural as well as non-structural components. The objective of this study is to examine the effect of the slab and transverse beams on the dynamic response of the structure using the seismic design provisions of the latest building design codes. Structural analysis and design (Staad.Pro) software is used in this study to perform seismic analysis of four building models having identical sectional properties and loading conditions with a variation on structural properties to find out the fundamental period, bending moment, axial force, and deformations. The results of this study imply that the building model without slabs and transverse beams have a higher value of the fundamental period and more effect of lateral loads as the bending moment, and lateral deflection values are larger than those on models with transverse beams and slabs.

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Sakaue, Takahiro. « Conformational transition of a semiflexible polymer chain : effect of chain length, stiffness and electrostatics ». 京都大学 (Kyoto University), 2004. http://hdl.handle.net/2433/147792.

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Werner, Timothy Jason. « Effect of Nebivolol and Lifestyle Modification on Large Artery Stiffness in Middle-Aged and Older Hypertensive Adults ». Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/23316.

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For more than half a century cardiovascular disease has been the leading cause of death in the United States. Aging, hypertension, and obesity are major risk factors for cardiovascular disease and clearly associated with arterial stiffness. Arterial stiffness generates higher afterloads and diminishes coronary perfusion thereby causing ventricular hypertrophy and ischemia. Importantly, arterial stiffness is an independent predictor of cardiovascular disease risk and all-cause mortality. Current strategies such as inhibition of angiotensin II or angiotensin converting enzyme, reduction of smooth muscle tone, blood volume, or inflammatory mediators, and improving glucose homeostasis are effective destiffening options. Nebivolol, a third generation beta-blocker, has unique vasodilatory characteristics and may be particularly efficacious as a destiffening agent. Only a few studies have addressed this issue while relying on indirect, blood pressure-dependent stiffness indices precluding clear understanding of study outcomes. There remains a need to determine the potential utility of nebivolol therapy as an arterial destiffening strategy. Thus, we hypothesized that the combination of nebivolol and lifestyle modification would reduce central arterial stiffness in middle-aged and older hypertensive adults more than either intervention alone. To test this hypothesis, we randomized 45 hypertensive adults to receive lifestyle modification, nebivolol, or combination for 12 weeks. Î"-stiffness index, pulse wave analysis, and arterial compliance were measured at baseline and following the intervention. No baseline differences in variables of interest were observed between groups. In contrast to our hypothesis, lifestyle modification, nebivolol, and combination groups had similar (P>0.05) reductions in beta-stiffness index (-1.87±0.83; -2.03±0.60; and -2.51±0.90 U), respectively, while carotid-femoral pulse wave velocity declined only in the nebivolol and combination groups. Our findings suggest combination of nebivolol and lifestyle modification reduces arterial stiffness to a similar degree as either intervention alone in middle-aged and older hypertensive adults. Further studies are needed to determine if the changes in arterial stiffness continue to occur or remain clinically significant over longer durations.
Ph. D.

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Cilingir, Ulas. « A Model Study On The Effects Of Wall Stiffness And Surcharge On Dynamic Lateral Earth Pressures ». Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606215/index.pdf.

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A model study on laterally braced sheet pile walls retaining cohesionless soil was conducted using 1-g shaking table. Lateral dynamic earth pressures, backfill accelerations and dynamic displacement of walls were measured. Input accelerations were kept between 0.03g to 0.27g. A data acquisition system consisting of dynamic pressure transducers, accelerometers, displacement transducer, signal conditioning board and a data acquisition card compatible with a personal computer was used during the study. Three different walls with thicknesses of 6.6, 3.2 and 2.0 mm were used in order to investigate the effects of changing wall stiffness value on lateral seismic pressures developed on the wall. In addition to that, steel blocks were placed on top of the backfill in order to simulate a surcharge effect of 1.57 kPa to 3.14 kPa during shaking. Amplification of input acceleration, incremental seismic lateral thrusts and corresponding maximum dynamic pressures, application point of the resultant, effect of stiffness and surcharge on maximum seismic lateral thrust and dynamic wall deflections were calculated by processing raw data stored. The results were compared to previous model studies and some analytical methods available.

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Wojtowitz, Gabrielle. « The effect of heterogeneity on the overall stiffness and seismic velocity of hydrate-bearing sediments ». Thesis, University of Southampton, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.543381.

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Rees, Emily V. L. « Methane gas hydrate morphology and its effect on the stiffness and damping of some sediments ». Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/79442/.

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Gas hydrates are ice–like compounds found in deep sea sediments and permafrosts. Concise detection and quantification of natural methane gas hydrate deposits, will allow for a more robust assessment of gas hydrate as a potential energy resource or natural geohazard. Current seismic methods, used to identify and quantify gas hydrates, have proved to be unreliable in providing accurate information on the extent of natural gas hydrate deposits, due to the lack of understanding on how gas hydrate affects the host sediment. Direct measurement of some hydrate bearing sediment properties has been made possible in recent years through advances in pressure coring techniques, but methods for dynamically testing these samples at in–situ pressures are still unavailable. Laboratory tests on synthetic hydrate bearing sediments have shown that factors such as formation technique, sediment type and use of hydrate former affects the form and structure of hydrate in the pore space and how it interacts with the sediment. The aim of this research was therefore to create methane hydrate in sediments under a variety of conditions, so that the influence of hydrate morphology could be investigated. A number of experiments were conducted using two distinct formation techniques. The first technique formed methane hydrate from the free gas phase in almost fully water saturated conditions. Five sand specimens, with a range of hydrate contents from 10% to 40% were formed and tested in the gas hydrate resonant column (GHRC). Results from these tests were compared with previous results from tests where methane hydrate had been formed from free gas in partially saturated conditions. It was found that formation method had a significant influence on the properties of the hydrate bearing sand, and therefore the morphology of the hydrate in the pore space. The second set of experiments formed methane hydrate from free gas within partially saturated sediments, but where the sediments were made up of coarse granular materials with a variety of particle size and shape. As it had been established that hydrate acts as a cement when formed under partially saturated conditions, the experiments aimed to observe the effect of particle size and shape on hydrate bonding mechanisms. The results showed that the influence of disseminated hydrate on the physical properties of the specimens was affected by both mean particle size and by particle shape, with the surface area of the sediment grains influencing the volume and distribution of hydrate throughout a material and therefore it’s bonding capabilities. In addition to the experiments on synthetic hydrate specimens, five core sections containing naturally occurring gas hydrate in fine grained sedimentsweremade available to the University of Southampton from the Indian National Gas Hydrate Program (NGHP) 01 expedition. High resolution CT imaging of the core sections observed large volumes of methane hydrate as a network of veins throughout the specimens. Due to sample disturbance caused during the depressurisation and subsequent freezing of the samples prior to delivery, dynamic testing in the gas hydrate resonant column apparatus was not feasible. Therefore, the hydrate was dissociated and a number of geotechnical tests were undertaken on the remaining host sediment. Results from these tests suggested that hydrate dissociation could affect host sediment properties, due to a change in water content, salinity and structure.

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Koval, Lidia. « Investigating the effect of internal fixation stiffness on metaphyseal fracture healing in a mouse model ». Thesis, Queensland University of Technology, 2014. https://eprints.qut.edu.au/75644/1/Lidia_Koval_Thesis.pdf.

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This project examined the differences in healing of metaphyseal bone, when the implants of variable stiffness are used for fracture fixation. This knowledge is important in development of novel orthopaedic implants, used in orthopaedic surgery to stabilise the fractures. Dr Koval used a mouse model to create a fracture, and then assessed its healing with a combination of mechanical testing, microcomputed tomography and histomorphometric examination.

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Khaled, Alhaifi. « Numerical and experimental studies of a nonlinear vibration system ». Thesis, Brunel University, 2015. http://bura.brunel.ac.uk/handle/2438/10545.

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The objective of this research is to show that nonlinearity can be used to improve vibration absorption and suppression of unwanted vibrations in a main system due to external excitation. This was shown by investigating two systems a SDOF (with hardening nonlinearity) and a 2DOF (with softening nonlinearity). The aim of carrying out these investigations was to introduce a passive nonlinear system that can update itself and self-regulate to suppress undesired oscillations. To fulfil the desired gaol, various types of springs were considered and investigated. A commercially available spring called Mag-spring has been chosen and a function for its nonlinearity has been investigated. Mag-Spring is a newly invented spring which is designed to exhibit constant force at its operating range. However, this spring has a special non-linear behaviour before reaching to the constant force domain which is the main focus of the investigation presented in this thesis. The nonlinear behaviour of Mag-spring encouraged the idea that vibration design is possible by the advantages that can be gained from magnetic technology. The added benefit through this new Mag-spring, is that it solved some of the concerns assotiated with old available ones. The most concern norrowing the usage of magnetic springs, is the air gap between the two magnets, which make the attraction or repulsive force unstable through the spring’s working range. Linmot Company, introduced a solution to this concern by introducing a teflone that works as a bearing between the two magnets, which fixed the distance between them while they are sliding againest each other. In the first scenario of this study, a hardening nonlinear spring was added in parallel to a system with a single degree of freedom. The system will remain single degree of freedom as the spring was added in parallel without additional mass. The hardening spring shows low stiffness at low amplitude and high stiffness at higher amplitude. In this study, it was shown that nonlinearity affects the dynamic performance of a system and makes the natural frequency amplitude dependant. As the amplitude of vibration increases, consequently, stiffness increases and the natural frequency shifts away from the excitation frequency. For this investigation, a vibrating system with one degree of freedom has been built based on a mathematical model simulated and tested in Matlab software. Mag-spring was used to introduce the nonlinear stiffness to the system. Unbalance mass mounted to a disc fixed to a rotational machine has been used to create a forced vibration system with variable frequency. The response of the system with and without nonlinearity effect was monitored with an accelerometer. Simulation and experimental results showed that nonlinearity could shift the resonance frequency of the SDOF system by 10% (hardening of the system), without affecting the stiffness of the system at normal working condition. In the second scenario, a softening nonlinear spring was added as a vibration absorber to a system with a single degree of freedom, to make the system with two degree of freedom. The softening spring shows high stiffness at low amplitude and low stiffness at high amplitude. The rationale behind this is to introduce a spring which is hard at high frequency and soft at low frequency, which as a result will make the ratio √(k_a/m_a ) of the absorber follows the excitation frequency (ω) allowing the system to update itself and self-regulate providing vibration cancellation at more than one frequency value and widen the vibration cancellation range (ω_n2-ω_n1). It was shown that the Mag-spring could show a softening behaviour in a limited domain if its operating position is shifted. A program has been written to simulate the behaviour of all nonlinear system with two degree of freedom (nonlinear absorber). At this program, the maximum amplitude of each time domain was used to produce the frequency domain of the amplitude of the system. The amplitude of the vibration for a linear and a nonlinear absorber was compared. The results showed that the nonlinear absorber suppresses and reduces the vibration amplitude of the main system better than the linear absorbers with up to 60% reduction in magnification ratio and from 5% to 10% in widening the cancellation range (ω_n2-ω_n1). In the last scenario of this study, 4 different ideal softening stiffness curves were introduced based on theoretical methods. Their vibration response was calculated and compared to the nonlinear absorber (Mag-spring) and a linear absorber. This study shows that when nonlinearity is designed properly, it could provide a distinguished vibration cancellation response resulting more than 60% vibration cancellation improvement. This study demonstrated the possibility of developing a passive self-regulating tuned mass system involving the usage of nonlinearity. Nonlinearity will enhance the vibration cancellation by allowing the system to update itself and as a result will make the vibration absorption to be effective within a frequency range rather than single frequency unlike the classical tuned mass system. This study, to the best knowledge of the author, can be classified as an uncommon study in vibration systems investigations.

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Chong, Song Hun. « The effect of subsurface mass loss on the response of shallow foundations ». Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/54271.

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Subsurface volume loss takes place in many geotechnical situations, and it is inherently accompanied by complex stress and displacement fields that may influence the performance of engineered geosystems. This research is a deformation-centered analysis, it depends on soil compressibility and it is implemented using finite elements. Soil stiffness plays a central role in predicting ground deformation. First, an enhanced Terzaghi’s soil compressibility model is proposed to satisfy asymptotic conditions at low and high stress levels with a small number of physically meaningful parameters. Then, the difference between small and large strain stiffness is explored using published small and large-strain stress-strain data. Typically, emphasis is placed on the laboratory-measured stiffness or compressibility; however, there are pronounced differences between laboratory measurements and field values, in part due to seating effects that prevail in small-thickness oedometer specimens. Many geosystems are subjected to repetitive loads; volumetric strains induced by drained repetitive ko-loads are experimentally investigated to identify shakedown and associated terminal density. The finite element numerical simulation environment is used to explore the effect of localized subsurface mass loss on free-surface deformation and shallow foundations settlement and bearing capacity. A stress relaxation module is developed to reproduce the change in stress associated to dissolution features and soft zone formation. The comprehensive parametric study is summarized in terms of dimensionless ratios that can be readily used for engineering applications. Field settlement data gathered at the Savannah River Site SRS are back-analyzed to compare measured values with predictions based on in situ shear wave velocity and strain-dependent stiffness reduction. The calibrated model is used to estimate additional settlements due to the pre-existing cavities, new cavities, and potential seismic events during the design life of the facility.

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Falck, Josefina. « Effect of side windows, stiffening plate and roof sheet on the stiffness of the bus body ». Thesis, KTH, Medicinsk teknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-125893.

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As a bus developer, Scania focus to construct a safe vehicle for the passengers, i.e. high strength of the bus structure and good comfort, which is also profitable for the operator, i.e. high passenger capacity and low fuel consumption. The trade-off when developing a bus body structure is to get both high stiffness and low weight. The bus body including exterior panels plays together with the chassis an important role for the stiffness of the bus. By gathering knowledge about how various exterior panels affects the stiffness of the bus body, the design of the panels can be optimized with respect to high stiffness and low weight. Also from a calculation point of view is it of interest to know how important different panels are for the stiffness of the bus body, in order to make conscious simplifications in the calculation model. The aim with this master thesis was to investigate how the stiffening plate, side windows and roof sheet influence the strength of the bus body. How the thickness of the side windows affects the stiffness of the bus body is also investigated. The investigations were made as a relative comparison between a complete bus and comparison models. The results showed that exterior panels participate in distributing load. By distributing the load, the load uptake gets more efficient since a bigger part of the bus structure is used to take up the load. The side windows affect the stiffness for all tested load cases, with increased importance for the load case where a gravity field is applied in the longitudinal direction, for the torsion load case and when a load is applied to the power train in vertical direction. The roof sheet has a high impact on the stiffness in the torsion load case, but has negligible influence on the stiffness of the bus body for the other tested load cases. The stiffening plate has little influence on the stiffness of the bus body in general and is negligible for all tested load cases except for when a lateral load is applied as either a gravity field or locally to the power train. Thinner side windows are shown to have a positive influence on the stiffness of the bus body.

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Addis, Pauline Robina. « The effect of tendon stiffness on the development and degeneration of locomotion in the sport horse ». Thesis, University of Newcastle Upon Tyne, 2011. http://hdl.handle.net/10443/1374.

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Introduction Injury to the flexor tendon is unfortunately a common cause of retirement of the sport horse, leading to concerns for equine welfare and economic loss. Maximising the quality of the tendon is only possible before tendon matrix synthesis ceases at around three years old. This cease is reflected in a change in tendon stiffness from an increase to a plateau. Throughout the rest of the horse’s life, repeated loading cycles gradually weaken the tendon and lead to decrease in stiffness. Since the two flexor tendons support the joint of the distal limb, this change in stiffness is likely to be reflected in the joint angles, which could be used to determine both when tendon matrix synthesis has ceased and if degenerative changes are normal. A second area of investigation is into the development and deterioration of stride parameters such as length and frequency. Since these depend on both leg length and on the input of the central nervous system (CNS), normalising to leg length allows investigation of the influence of the CNS alone. Method The distal limbs of 57 horses from three months to 17.5 years old were videoed over one complete stride. Horses were divided into three age groups; young horses up to 35 months whose tendon stiffness and leg length was assumed to increase; adult horses 36 to 99 months old whose tendon stiffness and leg length was assumed to remain constant; and finally horses over 100 months old whose deteriorating tendons were assumed to show a decrease in stiffness but whose leg length would not change. To determine joint angles, the videos were processed with a new marker-free tracking system that was found to show comparable results to previously-published data. Since joint angles of the passive equine distal limb depend not only on tendon stiffness but also mass of the horse, angles were normalised to calculated mass to allow investigation of tendon stiffness alone. Results Maximum normalised angles decreased in the young horse, remained constant in the adult horse and increased towards old age; consistent with changes in tendon stiffness. Most stride parameters changed during growth, and all except velocity showed a change when normalised to leg length. Towards old age, two parameters showed a slight decrease but there was no change in the normalised parameters. Conclusion In terms of joint angle, a trend was seen that was consistent with previously-reported trends in tendon stiffness. An owner could track their horse’s joint angles from birth to identify the characteristic change that accompanies the cease of matrix synthesis and therefore the limit of adaptive ability of the tendon. Tracking joint angles towards old age would also allow early identification of any abnormal change before the injury becomes severe enough to cause an overt change in the horse’s gait. The change seen in normalised stride parameters in the young horse indicates that these parameters are influenced by CNS maturation as well as a simple increase in leg length. Any abnormal change in stride parameters could indicate a lack of stability and the risk of a fall.

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Quesenberry, Chandler Blake. « The Effect of Pallet Top Deck Stiffness on the Compression Strength of Asymmetrically Supported Corrugated Boxes ». Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/104965.

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During unitized shipment, the components of unit loads are interacting with each other. During floor stacking of unit loads, the load on the top of the pallet causes the top deck of the pallet to bend which creates an uneven top deck surface resulting in uneven, or asymmetrical support of the corrugated boxes. This asymmetrical support could significantly affect the strength of the corrugated boxes, and it depends on the top deck stiffness of the pallet. This study is aimed at investigating how the variations of pallet top deck stiffness and the resulting asymmetric support, affects corrugated box compression strength. Pallet top deck stiffness was determined to have a significant effect on box compression strength. There was a 27-37% increase in box compression strength for boxes supported by high stiffness pallets in comparison to low stiffness pallets. The fact that boxes were weaker on low stiffness pallets could be explained by the uneven pressure distribution between the pallet deck and bottom layer of boxes. Pressure data showed that a higher percentage of total pressure was located under the box sidewalls that were supported on the outside stringers of low stiffness pallets in comparison to high stiffness pallets. This was disproportionately loading one side of the box. Utilizing the effects of pallet top deck stiffness on box compression performance, a unit load cost analysis is presented showing that a stiffer pallet can be used to carry boxes with less board material; hence, it can reduce the total unit load packaging cost.
Master of Science
Packaged products are primarily shipped as unit loads that consist of packaged products restrained to a platform, commonly a pallet. Paying particular attention to the design of the unit loads' components is necessary to safely ship products while still maintaining low packaging costs and sustainability initiatives. Stacking unit loads is a common practice to effectively use warehouse space, but warehouse stacking causes large amounts of weight for packaging to support. Pallets are not completely rigid and will deform because of this weight. The purpose of the study was to investigate the effect of pallet stiffness on the compression strength of corrugated boxes. Compression tests were completed on boxes supported by pallet designs having different deck stiffnesses. The top deck stiffness of a pallet was determined to have up to a 37% effect on the strength of corrugated boxes. Pressure data recorded between the bottom layer of boxes and the top deck of the pallet showed a larger percentage of pressure was located towards the outside edges of the unit load for boxes carried by a flexible pallet. Effectively, one side of the box was stressed more than the other causing package failure. Utilizing the effects of pallet top deck stiffness on box compression performance, a unit load cost analysis is presented showing that a stiffer pallet can be used to carry boxes with less board material; hence, it can reduce the total unit load packaging cost.

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Phanthanousy, Samantha. « The Effect of the Stiffness of Unit Load Components on Pallet Deflection and Box Compression Strength ». Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/86203.

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Currently, pallets are designed assuming that the load is distributed evenly on the top of the pallet. When pallets are loaded with packages such as corrugated boxes or returnable plastic containers, due to their physical shape, packages, are not capable of deforming freely with the pallet and a bridging phenomenon occurs. During this load bridging phenomenon, a portion of the vertical forces are redistributed as horizontal forces which causes the redistribution of the vertical compression stresses on the pallet towards the support. As a result, the deflection of the pallet can decrease and the load capacity of the pallet can increase significantly. The second chapter of this paper investigates the effect of package content on pallet deflection. The study concluded that package content did not have a significant effect on pallet deflection within the boundary conditions of the experiment. The third part of this paper considers how a specific pallet characteristic could affect the way a corrugated box performs. Standard box design procedures include adjustments of estimated compression strength for relative humidity, overhang on pallets, vibration, and alignment of boxes. However, there is no adjustment factor for pallet stiffness. The objective of the study described in this thesis is to find an answer for how the compression strength of a box is affected by pallet stiffness and top deckboard twist. The study concluded that the pallet stiffness and top deckboard twist do not have an effect on the compression strength of the box until less than 12% of the area box is supported.
Master of Science

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Payne, Rupert Alistair. « Pulse transit time and the pulse wave contour as measured by photoplethysmography : the effect of drugs and exercise ». Thesis, University of Edinburgh, 2009. http://hdl.handle.net/1842/5950.

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Photoplethysmography (PPG) is a simple means of measuring the pulse wave in humans, exploitable for the purposes of timing the arrival of the pulse at a particular point in the arterial tree, and for pulse contour analysis. This thesis describes a methodology for measuring arterial pulse transit time (PTT) from cardiac ejection to pulse arrival at the finger. It describes the effect on PTT of drug and exercise induced changes in BP. The nature of the relationship between the PPG and arterial pressure is also examined, and the PTT technique extended to assessment of conduit vessel pulse wave velocity (PWV) during exercise. PTT measured from ECG R-wave to PPG finger wave (rPTT) had a negative correlation (R2=0.39) with systolic BP (SBP), unaffected by vasoactive drugs in some but not all persons. rPTT showed similar beat-to-beat variability to SBP, unaffected by drugs. rPTT correlated weakly with diastolic (DBP) and mean (MAP) pressure. Cardiac pre-ejection period (PEP) formed a substantial and variable part of rPTT (12% to 35%). Transit time adjusted for PEP (pPTT) correlated better with DBP (R2=0.41) and MAP (R2=0.45), than with SBP. The PPG wave tracked changes in the peripheral pressure wave. Drugs had little effect on the generalised transfer function (GTF) describing the association between arterial and PPG waves. Strenuous exercise induced a large decrease in rPTT, mainly accounted for by decreases in PEP (53% of the total change in rPTT) and in transit time from aorta to distal brachial artery (33%). In contrast, minimal change in transit time from wrist to finger tip occurred with exercise. Simultaneous ear-finger PPG signals were used to measure conduit artery PWV during exercise. Ear-finger PWV (PWVef) overestimated carotid-radial PWV throughout exertion (overall bias 0.81±1.05ms-1, p<0.001), but the degree of difference remained constant. The increase in PWVef with exercise, was greater (1.18±0.54ms-1, p=0.035) in healthy subjects with a positive cardiovascular family history compared to those without. PPG enables analysis of the pulse contour during exercise, but estimation of the radial pressure wave from finger PPG by use of a GTF derived at rest, resulted in inaccuracy following exertion. These effects were variable and relatively short-lived. Furthermore, a resting GTF used to determine central pressure from the peripheral wave, resulted in underestimation of SBP (-5.9±2.1mmHg) and central pressure augmentation index (-8.3±2.9%), which persisted for 10 minutes post-exercise. rPTT had a negative linear association with SBP (R2=0.94) during strenuous exercise, slightly stronger than during recovery (R2=0.85). Differences existed in area-undercurve of the rPTT/SBP relationship between exercise and recovery, due to discrepancies in rate and degree of recovery of SBP and PEP. The linear relationship between the rPTT/SBP during exercise was affected by aerobic capacity, and the regression slope was less in the anaerobic compared to aerobic phase of exercise due to minimal change in PEP during anaerobic exertion. The correlation between rPTT/SBP did not change with prolonged aerobic exercise. Finally, measures of baroreflex sensitivity during exercise, were not significantly different between actual beat-to-beat SBP and SBP estimated using rPTT. In conclusion, absolute BP cannot be reliably estimated by measurement of rPTT following administration of drugs and during exercise. However, rPTT may have a role in measuring BP variability and in the assessing exercise capacity. PPG may also be useful in determining the effects of exercise on arterial stiffness, and for estimating the pressure wave contour, although its use during exercise for the latter purpose must be treated with caution.

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Strömberg, Frida. « Humidity’s effect on strength and stiffness of containerboard materials : A study in how the relative humidity in the ambient air affects the tensile and compression properties in linerboard and fluting mediums ». Thesis, Karlstads universitet, Institutionen för ingenjörs- och kemivetenskaper, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-43474.

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The aim of this thesis was to investigate the difference between containerboard materials strength and stiffness properties in tension and compression, how the mechanisms behind compressive and tensile properties are affected by the relative humidity of the ambient air and how the relative humidity affects the compressive response of the fibre network. These properties are used to predict the lifetime performance of corrugated boxes and to prevent early collapses of the boxes and thereby waste or harm of the transported goods inside. The work also discusses the methods used to evaluate the different properties and how reliable the results are. The experimental part includes testing of linerboard and fluting materials from both virgin and recycled fibres, which have been conditioned at 50% and 90% relative humidity. The compression tests were filmed to evaluate if different compression failure modes can be related to the strength and stiffness of the material. The results indicated that the compressive strength and stiffness differ from the strength and stiffness values in tension at 90% relative humidity. Compressive strength is lower in both 50% and 90% relative humidity compared with the tensile strength. However, the compression stiffness shows a higher value than the tensile stiffness at 90% relative humidity. The study of the method for evaluating the compressive behaviour of the paper does not present a complete picture on what type of failure the paper actually experience.

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Wass, Brittney. « The Effect of Substrate Stiffness on VCAM-1 Expression and Monocyte Adhesion in Rat Lung Microvascular Endothelial Cells ». Master's thesis, Temple University Libraries, 2016. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/420946.

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Bioengineering
M.S.
The overall goal of this research is to elucidate the effects of stiffness on the activation of pulmonary endothelial cells by inflammatory cytokines. The hypothesis tested is that increasing matrix stiffness in the (patho) physiological range will exacerbate the response of cultured endothelial cells to inflammatory stimuli. To test this hypothesis, we are culturing control and TNF-a stimulated rat lung microvascular endothelial cells (RLMVECs) on hydrogels with tunable stiffnesses of 5, 20, and 45 kPa (measured using compression testing), modeling the stiffness of healthy, intermediate and fibrotic lung tissue respectively. The cellular readout was assessed through RT-qPCR, microscopy, and monocyte adhesion for basal expression and upregulation of vascular cell adhesion molecule-1 (VCAM-1) in quiescent and TNF-a stimulated cultured endothelial cell. This model of microvascular pulmonary inflammation, mimicking a normal, intermediate, and fibrotic lung, is aimed at establishing a correlation between substrate stiffness and inflammation. This research demonstrates the significant increase of basal VCAM-1 gene expression as well as monocyte adhesion as substrate stiffness increases. When using inhibition, it was also found that VCAM-1 is partially activated through the Rho/ROCK, YAP/TAZ, and NF-kB pathway. Our results contribute to a mechanistic understanding of disease pathologies such as idiopathic pulmonary fibrosis, in which treatment is just about limited to a full lung transplant and facilitate testing of new drug therapies.
Temple University--Theses

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Bircan, Mehmet. « A Study On The Effect Of Pipe - Soil Relative Stiffness On The Behaviour Of Buried Flexible Pipes ». Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/2/12611562/index.pdf.

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In this study, the effect of pipe-soil relative stiffness on the behaviour of buried flexible pipes was investigated considering the pipe size, material type, stiffness, pipe-soil and natural soil-backfill interfaces and geometry of the trench using the finite element method. For this purpose, a parametric study was conducted to examine the effect of different variables on the resulting earth loads and deformations imposed on the buried pipes. Various types of trench pipe-soil cases were analysed for a certain natural ground and backfill material by the PLAXIS finite element code which allows simulating non-linear soil behaviour, the stages of construction as well as the pipe-soil interaction aspects of the problem. Loads and deformations obtained by the finite element method were compared with those calculated by the conventional approaches for different pipe-soil stiffness ratios. The finite element results obtained for the deformation of typically flexible Polyethylene pipes were then used to back-calculate the range of modulus of soil reaction, E'
, values for various pipe-soil relative stiffness and they were compared with the suggested value proposed by Howard (1977).

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Wiebe, Bradley J. « The effect of confining pressure, temperature, and suction on the shear strength and stiffness of unsaturated buffer ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq23549.pdf.

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Syk, Annelie, et Erik Axelsson. « Effect of axle load spreading and support stiffness on the dynamic response of short span railway bridges ». Thesis, KTH, Bro- och stålbyggnad, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-137118.

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In this thesis the effect of axle load spreading through ballast and the effect of support stiffness has been investigated on short span railway bridges. Two types of bridges, simply supported bridges and bridges with integrated backwalls, have been modeled with 2D beam elements. When analyzing the load spreading effect, two types of load shapes have been considered. The first one is the load shape proposed in Eurocode where the axle load is modeled with three point loads where 50% of the axle load acts on the sleeper located underneath the wheel and 25% on the two adjacent sleepers, respectively. Therefrom the loads are further distributed through the sleepers and the ballast. The second load shape that has been studied is a triangular load shape. These two load shapes have been modeled both with different numbers of point loads and as distributed line loads to see how the dynamic response of the bridges is affected and thereby find what level of accuracy that is required to capture the full effect of the load spreading. For the bridges with integrated backwalls the supports were also modeled as springs with varying stiffness to see how the dynamic response was affected. The response was measured in terms of vertical acceleration and bending moment. From the simulations the conclusion can be drawn that the triangular load shape gives significantly lower bridge responses than the Eurocode load shape. It is further found that modeling the axle loads with point loads can give spurious acceleration peaks, which in the case of bridges with integrated backwalls often are critical. For these bridges it is necessary to enhance the accuracy of the load spread, either by increasing the number of point loads or using a distributed line load. From the spring support simulations, it can be seen that support stiffness has great influence on the dynamic response of bridges with integrated backwalls. For certain values the response is increased, whereas for other values a large reduction is obtained.

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Harris, Stephen Alan. « Effect of aging and habitual aerobic exercise on endothelial function, arterial stiffness, and autonomic function in humans ». Thesis, University of Iowa, 2014. https://ir.uiowa.edu/etd/1465.

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Lin, Yu-An, et 林育安. « Effect of bearing properties on spindle stiffness ». Thesis, 2016. http://ndltd.ncl.edu.tw/handle/76859291802898057825.

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碩士
國立中興大學
機械工程學系所
104
In the present machine tool industry, the calculation process of the bearing stiffness through a spindle''s dynamic state is still under development. Bearing stiffness is determined by the elastic deformation between bearing raceway surface and rolling element when bearing at force condition. The actual bearing stiffness can be known by inversing the natural frequency of the spindle through spindle dynamic experiment. Angular contact ball bearings are usually used in high-speed spindle. Bearing usually add preload to increase its stiffness. According the operation condition to select the preload force is important. The study is given different preload levels and used three simulation methods to discuss the bearing properties. The spindle/shaft natural frequencies are predicted by the Rayleigh-Ritz method and the finite element method. The commercial software of BEARINX is used to predict the bearing life, bearing stiffness and spindle/shaft natural frequencies. The difference between the Rayleigh-Ritz method and the finite element method are assumptions. One is assumed as a rigid body and another is assumed as a beam. The experiment of spindle are the rotation experiment and modal testing. Find the actual spindle natural frequencies and compare the simulation results.

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Tsai, Yuan-Yu, et 蔡元毓. « Effect of Sprinting Distance on Leg Stiffness ». Thesis, 2016. http://ndltd.ncl.edu.tw/handle/95357608174067667324.

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碩士
國立彰化師範大學
運動學系應用運動科學碩士班
104
The purpose of this study is to investigate the effect of sprinting distance on kinetic, kinematic, and also on stiffness and the modulation of leg stiffness. Nine healthy male high school sprinters volunteered for this investigation and all of them were trained for over 6 month. The participants’ physical characteristics were the following: height, 172.9  4.197 cm; body mass, 62  7.01 kg; and age, 15.51  2.86 years (mean ± SD). The participants performed the tasks of 5m, 15m, 25m, and 35m sprint. Seven Kistler force plates to prevent the incoordination from aiming one single plate and eight well placed VICON FX40 cameras to collect kinematic data. The rapeated measures of one-way ANOVA, and the HSD post-hoc were used for the statistical testing of the conditions for the sprints (α = .05). The results showed that the knee-extention moment and knee stiffness had significant differences on the distance variation (p < .05); the hip and ankle extention moment and stiffness and leg stiffness had no significant differences on the distance variation (p > .05).

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(7332803), Andrea Ardila Quiroga. « Effect of Climatic Changes on Subgrade Stiffness ». Thesis, 2019.

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There is consistent research evidence that shows improvement of the engineering properties of subgrade soils treated with lime or cement. However, limited information is available on the effect of climatic changes on the subgrade stiffness. The thesis studies the effects of changes in soil moisture content and temperature on the resilient modulus of treated and untreated subgrades in Indiana. Two types of soils were tested: A-6 and A-7-6, from two locations in Indiana: Hartford City and Bloomington, respectively. When existing standards ASTM D559/559-15 and ASTM D560/560-16 for wetting/drying (WD) and freezing/thawing (FT) processes, respectively, were followed, the treated and untreated samples failed through the process of preparation due to the stringent procedures in the standards. Appropriate test conditions were investigated, as part of the research, to develop new protocols more appropriate to the field conditions in Indiana. Two new test protocols were developed and successfully applied to the treated soils. A total of 26 resilient modulus, M_R, tests were conducted following the standard AASHTO T307-99. The M_R results showed that the repeated action of WD and FT cycles reduced the stiffness of the chemically-treated soils down to values similar to or lower than those of the untreated soils. However, when the amount of chemical was doubled, with respect to the optimum, the M_R of the treated soils improved over that of the untreated soils, even after the wetting-drying cycles.

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Liu, Guang-Yu, et 劉光宇. « MEMS Structure With Tunable Stiffness Using Magnetorheological Effect ». Thesis, 2013. http://ndltd.ncl.edu.tw/handle/66328187975686404189.

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TEWARI, MAMTA. « EFFECT OF STIFFNESS IN THE BEHAVIOUR OF FRAMED BUILDINGS IN EARTHQUAKES ». Thesis, 2016. http://dspace.dtu.ac.in:8080/jspui/handle/repository/15306.

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The purpose of this project work is to study the effect of stiffness in the behaviour of framed buildings in earthquakes. The lateral stiffness of a framed structure does play a significant role in defining its response to the seismic forces. As per the studies sufficient lateral stiffness is a requisite for all the structures so that they function well under minor earthquake forces and give full resistance to such forces without any structural failure. Main objective of this research work is to study the effect of the lateral stiffness on the response of a G+4 storey building [3-D frame], subjected to seismic forces. The building frame model has been analyzed by Response Spectrum method, with the help of STAAD Pro software as per IS 1893:2002. Changes in various parameters have been considered to bring a change in the stiffness of the building model and conclusions have been drawn.

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Orendurff, Michael. « The effect of mountain bicycle fork stiffness on impact acceleration ». Thesis, 1996. http://hdl.handle.net/1957/34273.

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Mountain bike suspension forks have been developed to reduce the accelerations transmitted to the rider. However, the effectiveness of suspension forks has not been systematically investigated. It was the goal of this project to quantify the amount of impact acceleration damping afforded by three stiffness settings of suspension forks compared to rigid mountain bike forks. Seven experienced mountain bike riders gave their informed consent to participate in the study. The subjects coasted down a ramp and impacted a bump at 5.4 m/s located about 2.3 m past the ramp end. Accelerometers were placed on the axle and frame of the bicycle which was fitted with either a rigid fork (FR) or suspension forks set on soft (F1), medium (F3), or firm (F6) stiffness. Bumps were either small (B1), medium (B2) or large (B3). Accelerometer data were telemetered to a computer, sampled at 1000 Hz and smoothed with Butterworth filter with 50 Hz cutoff. Peak acceleration during impact (P1) and landing (P2) as well as the slope of the impact acceleration peak (jerk, J) were extracted from the data and analyzed using a 2 x 3 x 4 repeated measures ANOVA for each of the dependent variables (P1, P2, J), and with linear contrasts as follow-up tests. A significance level of p<.01 was chosen. All forks were found to produce similar impact acceleration (P1) at the axle and frame on the small bump (B1). On larger bumps (B2 and B3), softer suspension forks (F1 and F3) significantly reduced acceleration transmitted to the rider during bump impact (P1), while maintaining significantly higher axle acceleration than other forks (p<.001); Jerk was significantly reduced at the frame compared to the axle for each suspension fork with the larger bumps. Landing impacts (P2) were of similar magnitude for most fork conditions at both the axle and frame. It appears from these data that suspension forks with moderate stiffness may provide the best impact acceleration damping for mountain bikes encountering impacts with characteristics similar to the bumps and velocity used in this study. It is unclear how these results generalize to other conditions encountered while riding.
Graduation date: 1997

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FaNg, Li De, et 方立德. « The Effect of Contact Stiffness for Shear Strength of Granule ». Thesis, 1998. http://ndltd.ncl.edu.tw/handle/22420310654970873730.

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