Journal articles on the topic 'Stiffness under stresses'
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1
Philippidis, T. P., and A. P. Vassilopoulos. "Stiffness Reduction of Composite Laminates under Combined Cyclic Stresses." Advanced Composites Letters 10, no. 3 (May 2001): 096369350101000. http://dx.doi.org/10.1177/096369350101000302.
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Stiffness reduction due to fatigue of a [0/(±45)2/0]T Glass/Polyester (GRP) laminate under combined cyclic stress is investigated in this experimental study. Stress states combining all three components of in-plane stress tensor are induced by uniaxially testing specimens cut off-axis at various angles from the principal material coordinate system. Modulus reduction is related to the various failure modes exhibited under different states of combined stress. It is verified that shear and transverse normal stress induce more severe stiffness degradation compared to stress states where normal stress in the main fibre direction is dominant. For every loading condition and stress state, it is observed in general that stiffness decrease is more pronounced under lower stress levels than these inducing low cycle fatigue.
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Topkaya, Cem, and Özer Zeybek. "Application of ring beam stiffness criterion for discretely supported shells under global shear and bending." Advances in Structural Engineering 21, no. 16 (February 20, 2018): 2404–15. http://dx.doi.org/10.1177/1369433218758476.
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Silos in the form of a cylindrical metal shell are commonly elevated to provide access to the space beneath. In general, a few discrete column supports at evenly spaced intervals are commonly utilized. The presence of discrete supports results in circumferential non-uniformity in the axial compressive stress above the support. Depending on the size of the structure, several different support arrangements may be chosen. A stiff ring beam is utilized in larger silos to transfer and evenly distribute the discrete forces from the supports into the cylindrical shell wall. A stiffness criterion was developed by Rotter to assess the degree of non-uniformity in axial compressive stresses around the circumference. The stiffness criterion is based on the relative stiffnesses of the ring beam and the cylindrical shell and was verified for loading conditions that produce circumferentially uniform axial stresses around the circumference. A study has been undertaken to investigate the applicability of the stiffness criterion to cylindrical shells under global shear and bending. Pursuant to this goal, extensive finite element analyses were conducted where different ring beam and cylindrical shell combinations are subjected to global shearing and bending actions. The results revealed that the stiffness criterion can be extended to shells under this loading condition. The degree of non-uniformity in axial stresses is quantified and presented as simple formulas that can be readily adopted by design standards.
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Pervan, Nedim, Elmedin Mešić, Adis J. Muminović, Muamer Delić, Enis Muratović, Mirsad Trobradović, and Vahidin Hadžiabdić. "Biomechanical Performance Analysis of the Monolateral External Fixation Devices with Steel and Composite Material Frames under the Impact of Axial Load." Applied Sciences 12, no. 2 (January 12, 2022): 722. http://dx.doi.org/10.3390/app12020722.
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This paper describes comparative analysis of the biomechanical performances conducted on the external fixation devices whose frames are made out of two different material (stainless steel and composite material). Biomechanical properties were determined with experimental and FEM (finite element method) models which are used to study the movement of the fracture crack, establish stiffness of the design solutions and monitor generated stresses on the zones of interest. Geometric modeling of two fixation devices configurations B50 and C50 is used as a basis for structural analysis under the impact of axial load. Structural analysis results are confirmed with an experimental setup. Analyzed deflection values in the load and fracture zones are used to define the exact values of the stiffness for the construction design and fracture, respectively. The carbon frame device configuration has 28% lower construction stiffness than the one with the steel frame (for B50 configuration), i.e., 9% (for C50 configuration). In addition, fracture stiffness values for the composite frame application are approximately 23% lower (B50 configuration), i.e., 13% lower (C50 configuration), compared to steel frame. The carbon frame device has about 33% lower stresses at the critical zones compared to the steel frame at the control zone MM+ and, similarly, 35% lower stresses at the control zone MM-. With an exhausting analysis of the biomechanical properties of the fixation devices, it can be concluded that steel frame fixation device is superior, meaning it has better biomechanical characteristics compared to carbon frame fixation device, regarding obtained data for stresses and stiffnesses of the frame construction and fracture. Considering stresses at the critical zones of the fixation device construction, the carbon frame device has better biomechanical performances compared to steel frame devices.
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Hsu, Thomas T. C., and Mohamad Y. Mansour. "Stiffness, Ductility, and Energy Dissipation of RC Elements under Cyclic Shear." Earthquake Spectra 21, no. 4 (November 2005): 1093–112. http://dx.doi.org/10.1193/1.2044828.
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A new Cyclic Softened Membrane Model (CSMM) was recently developed to predict the stiffness, ductility, and energy dissipation of reinforced concrete (RC) elements subjected to reversed cyclic shear. Using the nonlinear finite element analysis, we can integrate these responses of elements to predict the behavior of a whole structure, such as a low-rise shear wall, subjected to earthquake action. This study of CSMM summarizes systematically the effects of the two primary variables: the steel bar angle with respect to the direction of the applied principal stresses and the steel percentage. The results clearly show that RC structures under cyclic shear stresses could be designed to be very ductile, have large stiffness, and possess high energy-dissipation capacities (just like flexural-dominated elements), if the steel bars are properly oriented in the directions of principal stresses and if the steel percentages are kept within certain limits.
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Terrell, Ronald G., Brady R. Cox, Kenneth H. Stokoe, John J. Allen, and Dwayne Lewis. "Field Evaluation of the Stiffness of Unbound Aggregate Base Layers in Inverted Flexible Pavements." Transportation Research Record: Journal of the Transportation Research Board 1837, no. 1 (January 2003): 50–60. http://dx.doi.org/10.3141/1837-06.
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Unbound aggregate base layers in a quarry haul road in Georgia were characterized using embedded sensors and in situ seismic testing. Two sections of the road were constructed as inverted pavements, one using a South African Roads Board method and the other using a conventional Georgia Department of Transportation method. A third was constructed using a traditional method. Miniaturized versions of traditional cross-hole and downhole seismic tests were conducted to determine the stiffnesses of each base layer. Horizontally propagating compression and shear waves were measured under four different loading conditions to determine Young’s moduli and Poisson’s ratios of the base. An increase in stiffness with an increase in load was measured. Additionally, it was found that the Georgia and South Africa sections had similar stiffnesses. Surprisingly, the traditional section was found to be somewhat stiffer than the other sections. This higher stiffness is thought to be caused by a prolonged period of compaction before construction of the unbound aggregate base layer, which essentially transforms the traditional section into an inverted pavement. Using the vertical total normal stresses computed from ILLI-PAVE, a value of 0.3 for the earth pressure coefficient was found to be reasonable for this material in determining the radial total normal stresses. The radial effective normal stresses were calculated from the radial total normal stresses and experimentally determined pore water pressures. Additionally, the negative pore water pressures in the partially saturated granular base had a significant impact on the stiffness of the unbound aggregate base layer, especially under small load levels.
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Shen, Jun Min, Yu Min Zhou, and Xiao Zhang. "Finite Element Analysis of Asphalt Overlays on Existing PCC Pavement under Heavy Traffic Loading." Advanced Materials Research 361-363 (October 2011): 1472–75. http://dx.doi.org/10.4028/www.scientific.net/amr.361-363.1472.
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This study models the thermal stresses and load stresses of Xia-Feng expressway asphalt overly on an existing PCC pavement by using finite element method. The sensitiveness of different influence factors on thermal stresses and load stresses are discussed. Research results show that asphalt overlay deflection and load stresses increase with the decreasing of weakening of subgrade strength index λk and when a soft interlayer with low level of spring stiffness is adopted, the thermal stress of asphalt overlay is quite small compared with load stresses.
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Tong, Li Li, Zhen Qing Wang, and Bao Hua Sun. "Numerical Simulation of Unidirectional Hoop Composite Laminates under Flexural Loads." Key Engineering Materials 334-335 (March 2007): 217–20. http://dx.doi.org/10.4028/www.scientific.net/kem.334-335.217.
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Numerical simulation for unidirectional hoop composite laminates under flexural loads was finished. The change of tensile and compressive stresses, the position of local crush and delamination and stiffness degradation were analyzed with parametric program compiled by APDL language in ANSYS. The results showed that composite laminate could bear the load continually after local crush and delamination. Displacements of calculated result with stiffness degradation model matched test results well.
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He, Jun, Yu Qing Liu, Chen Zhao, Ai Rong Chen, and Teruhiko Yoda. "Mechanical Behavior of Composite Girder with Perfobond Shear Connector under Hogging Moment." Advanced Materials Research 446-449 (January 2012): 1046–53. http://dx.doi.org/10.4028/www.scientific.net/amr.446-449.1046.
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The mechanical behavior of the support regions for continuous composite girders with tensile stresses in the concrete slab and compressive stresses in the lower steel profile becomes strongly nonlinear under negative bending moments. A static test on four half-scale model of a steel and concrete composite girders with different shear connectors including studs and PBL under hogging moments was conducted and observed to evaluate the influence of shear connector on inelastic behavior such as flexural stiffness reduction, crack initiation and development in concrete slab. From the test results, the flexural stiffness and loading capacity of the composite girders were improved by PBL shear connector. Higher initial cracking load and crack resistance stiffness of composite girders with PBL shear connector under serviceability limit state was obtained during crack development process. The test specimen could be assumed as full composite section until the ultimate state from load-slip relationship of shear connector. Analytical and experimental studies can serve as a basis for continuous composite bridges design.
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Liu, Guangsheng, Xiaocong Yang, and Lijie Guo. "Stiffness Determination of Backfill-Rock Interface to Numerically Investigate Backfill Stress Distributions in Mine Stopes." Advances in Civil Engineering 2021 (October 19, 2021): 1–13. http://dx.doi.org/10.1155/2021/6460764.
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Numerical modeling is an effective and efficient method to investigate the stress distributions of backfill in stopes, which should be well understood in underground mining. Interface elements between backfill and rock in simulated stopes had been proved to be essential components, for which the stiffness parameters need to be assessed and assigned. However, few reports have revealed the effects of interface stiffness on backfill stress distributions, and there is not yet a clear solution to determine the interface stiffness to simulate stresses in backfilled stopes, except an empirical method for simply applying a high value suggested in FLAC manual. In this study, a new solution is first proposed to determine the normal stiffness and shear stiffness of interface elements, respectively, in numerical modeling of backfill stresses. The applicability of the solution has been verified by investigating backfill stress distributions in mine stopes of two widely used mining methods with variable stiffness values. The results show that the newly proposed method leads to totally the same backfill stress distributions with models applying the interface stiffness by the method in FLAC manual based on a “rule-of-thumb” but will save at least 20%–30% calculation time to improve modeling efficiency under the same simulation conditions and will carry much clear physical meanings corresponding to the interaction between backfill and rock walls in mine stopes. In addition, the vertical and horizontal stresses show good agreements with the analytical stresses predicted by the Marston equation under the at-rest state, which validates the reliability of the proposed solution for interface stiffness. Moreover, the plotting methods of stress distributions and the coefficient of lateral earth pressure of backfill in simulated stopes with proposed interface stiffness were discussed to further clarify the reasonable methods to investigate the backfill stresses in mine stopes, especially after considering the effects of the convergence from rock walls, which is a very significant and common phenomenon in practical mining engineering.
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Zhang, Peng, Dan Shen, and Shi Rong Li. "Analysis of Stress Distribution of Externally Pre-Stressed Beams under Transverse Loads." Applied Mechanics and Materials 166-169 (May 2012): 3065–70. http://dx.doi.org/10.4028/www.scientific.net/amm.166-169.3065.
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The size, the position and the arrangement of external restraint will significantly affect the mechanical properties of the structures with the external restraint. Based on classical beam theory, the stress distribution of a simply supported beam with externally reinforcing steel bars under transverse loads is analyzed in this presentation. By assuming that the stresses in both the beam and the external constrains are less than their proportional limits, an analytical formulation of normal stress in the cross section of the beam was derived by considering two cases that the externally reinforcing steel bars are pre-stressed and are not pre-stressed. Influences of the parameters of the stiffness and the position of the externally reinforcing steel bars on the stress of the beam are discussed.
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Jalonen, Kimmo, Joonas Tulonen, and Anssi Laaksonen. "Influence of Cracking on Effects of Restrained Deformations in a Post-tensioned Concrete Bridge." Nordic Concrete Research 59, no. 1 (December 1, 2018): 95–110. http://dx.doi.org/10.2478/ncr-2018-0017.
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Abstract Imposed and restrained deformations cause stresses in continuous concrete bridges, and in analyses of the superstructure these stresses are usually reduced to some degree due to creep and cracking of concrete. This study examines cracking and redistribution of stresses in a bridge superstructure under the loads and load combinations used in the original bridge design. The subject of this study is a three-span post-tensioned continuous concrete cantilever beam bridge. The bridge was analysed with non-linear calculation utilising the general force method and moment-curvature relationships. The analysis yielded the bending stiffness of the post-tensioned bridge superstructure as a function of bridge length under different loads. It was discovered that the secondary moment from prestressing force increased as the bending stiffness of the central span decreased due to cracking under external loads, which is not normally considered in design. The bending moment effects of linear temperature difference and support settlement decreased as expected as the superstructure bending stiffness decreased. The analysis provided new information on the effects of secondary moment from the prestressing force and on the difference between the cracked state and the linear elastic analysis of the concrete bridge superstructure.
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Timchenko, Radomir, Dmytro Krishko, and Iryna Khoruzhenko. "Mathematical modeling of the folded foundation interaction with the base by varying the structure stiffness." ACADEMIC JOURNAL Series: Industrial Machine Building, Civil Engineering 2, no. 51 (October 12, 2018): 145–50. http://dx.doi.org/10.26906/znp.2018.51.1306.
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The article describes a practice of using software system based on the finite element method for calculating shell foundations. It considers the peculiarities of the folded foundation interaction with subsoil mathematical modeling . It is found that during modeling, special attention should be paid to a purpose of the system initial parameters, to a choice of finite elements type, and to an optimal model of subsoil. Mathematical modeling of the folded foundation interaction with subsoil is performed under conditions of a plane problem. The foundation operation under various conditions of interaction with subsoil and with different stiffness parameters of the foundation is analyzed. Correlation between stiffness of a foundation structure and resulting equivalent stresses in subsoil under different conditions of interaction is determined. It is concluded that the obtained results represent a benchmark for subsequent calculations and modeling the interaction between a foundation and subsoil under a volumetric stressed condition.
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Mohd Tobi, Abdul Latif, M. A. Harimon, A. A. Saad, and A. A. Azalan. "Fretting Wear of Coated Substrate with Interlayer: Substrate Stress Behaviour." Applied Mechanics and Materials 372 (August 2013): 516–21. http://dx.doi.org/10.4028/www.scientific.net/amm.372.516.
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Finite element analysis of a coated SCMV (high-strength alloy steel) substrate with interlayer has been studied with the emphasized of stresses behaviour predicted in the substrate region due to the fretting wear surface profiles modification. The analysis is simulated using a simple cylinder-on-flat contact geometry under gross sliding condition for a given surface profile on a specific number of fretting cycles. The effect of interlayer stiffness on the stresses predicted in the substrate region is studied. It is found that the stresses in the substrate region are generally predicted to reduce with the increase of interlayer stiffness and with the advancement of wear.
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Lin, C. C., and C. D. Mote. "The Wrinkling of Thin, Flat, Rectangular Webs." Journal of Applied Mechanics 63, no. 3 (September 1, 1996): 774–79. http://dx.doi.org/10.1115/1.2823362.
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A web is termed wrinkled when one of the in-plane principal stresses is tensile and the other is sufficiently compressive. A criterion is derived that predicts wrinkling of isotropic, compressible rectangular webs under uniform in-plane principal stresses. The compressive stress at impending wrinkling depends on the flexural stiffness, and it equals zero in the case of a membrane. A criterion of wrinkling is also derived using isotropic, incompressible membrane theory. This criterion predicts an infinite number of wrinkle waves in a wrinkled region. With small flexural stiffness, the number of wrinkle waves becomes finite at wrinkling and it is predictable along with the shape and the size of the wrinkled region. The number of the wrinkle waves increases as the aspect ratio of the rectangular web increases, as the in-plane principal tension increases, and as the flexural stiffness decreases. Analyses of wrinkling of a rectangular web under simple shear and under uniform longitudinal stretching illustrate the above predictions.
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Kumara, Wasantha, Mang Tia, Chung-Lung Wu, and Bouzid Choubane. "Evaluation of Applicability of Ultrathin Whitetopping in Florida." Transportation Research Record: Journal of the Transportation Research Board 1823, no. 1 (January 2003): 39–46. http://dx.doi.org/10.3141/1823-05.
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A three-dimensional (3-D) finite element model for stress analysis of pavements with ultrathin whitetopping (UTW) under critical loading conditions was developed. The 3-D model developed was used to analyze the UTW test pavement sections at the Ellaville Weigh Station in Florida, which had less than satisfactory performance. The poorly performing UTW sections at the Ellaville Weigh Station were found to have relatively higher maximum computed stresses under critical loading conditions, which appeared to explain their poor performance and high percentages of cracked slabs. The 3-D model developed was also used to perform a parametric analysis to determine the effects of asphalt thickness, asphalt modulus, concrete thickness, concrete modulus, base stiffness, subgrade stiffness, slab dimension, temperature differential in the concrete, and applied load on the maximum stresses in UTW pavements under typical Florida conditions.
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Avery, W. B., and C. T. Herakovich. "Effect of Fiber Anisotropy on Thermal Stresses in Fibrous Composites." Journal of Applied Mechanics 53, no. 4 (December 1, 1986): 751–56. http://dx.doi.org/10.1115/1.3171854.
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An elasticity solution is utilized to analyze an orthotropic fiber in an isotropic matrix under uniform thermal load. The analysis reveals that stress distributions in the fiber are singular in the radial coordinate when the radial fiber stiffness (Crr) is greater than the hoop stiffness (Cθθ). Conversely, if Crr < Cθθ the maximum stress in the composite is finite and occurs at the fiber-matrix interface. In both cases the stress distributions are radically different than those predicted assuming the fiber to be transversely isotropic (Crr=Cθθ). It is also shown that fiber volume fraction greatly influences the stress distribution for transversely isotropic fibers, but has little effect on the distribution if the fibers are transversely orthotropic.
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Karasu, Adem, Cüneyt Vatansever, and Haluk Emre Alçiçek. "An investigation of the behavior of header end-plate connections under monotonic loading." Challenge Journal of Structural Mechanics 4, no. 3 (September 4, 2018): 108. http://dx.doi.org/10.20528/cjsmec.2018.03.004.
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In seismically active regions such as Turkey, the context of the nonlinearity provided by a building is based on the behaviors of structural components; beams, columns and their connections constituting the seismic force resisting system of the structure. Of these members, beam-to-column connections can play a considerably important role even if they have a capability of limited stiffness and flexural strength. Structural steel connections are mainly classified as a pinned or a moment connection. However, some beam-to-column connections having limited stiffness and flexural strength, which are called semi-rigid connections such as header end-plate connections designed so as to transmit only shear forces, can be characterized by moment-rotation relationship. This paper investigates the behavior of header end-plate connections using finite element (FE) modeling. The FE models include material, geometrical and contact nonlinearities. FE modeling technique was first verified through the test results of the experimental research performed by Aggarwal (1990). Then the effect of header end-plate thickness upon moment-rotation relationship was investigated. According to the analyses results, in addition to shear stresses, axial tensile stresses have been observed to occur in the bolts at the tension side and thickness of the header end-plate and beam web play a governing role in the development of initial rotational stiffness and the flexural strength of header end-plate connections.
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Cai, Xiaoguang, Jiayu Feng, Sihan Li, Honglu Xu, Weiwei Liu, and Xin Huang. "Study on Interface Interaction between Uniaxial Geogrid Reinforcement and Soil Based on Tensile and Pull-Out Tests." Sustainability 14, no. 16 (August 20, 2022): 10386. http://dx.doi.org/10.3390/su141610386.
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The interaction between reinforcement and soil is a key problem in the application of geosynthetics as reinforcement in geotechnical engineering. In this study, tensile and pull-out tests on a uniaxial geogrid were carried out using self-designed tensile and pull-out test equipment. The tensile test evaluated the tensile load–strain characteristics of a geogrid. Under the condition of lateral confinement, the tensile force and secant tensile stiffness of the geogrid increased with an increase in the normal stress when the strain was constant, and the secant tensile stiffness decreased with a decrease in the tensile rate. The stiffness coefficient was used to quantitatively describe the change in the stiffness of the reinforcement. Using the pull-out test, the variation laws of the pull-out force of the geogrid under different normal stresses and different longitudinal rib percentages were obtained. When the geogrid was broken, the pull-out force of the same type of geogrid was not significantly different under different normal stresses. With an increase in the longitudinal rib percentage, the pull-out force of the geogrid under the same normal stress gradually increased, and the apparent friction coefficient was obtained by analysis. The results of the apparent friction coefficient obtained by the analytical method in accordance with French specifications (NF P94-270-2020) are relatively safe compared to the experimental values.
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Mohd Tobi, Abdul Latif, M. A. Harimon, A. A. Saad, and R. M. Karim. "Investigation on the Fretting Wear of a Coated Substrate with Interlayer." Applied Mechanics and Materials 315 (April 2013): 909–13. http://dx.doi.org/10.4028/www.scientific.net/amm.315.909.
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The fretting wear of coated SCMV (high-strength alloy steel) substrate with interlayer is studied with the focus on stresses associated with the coating failure under gross sliding condition. The analysis is simulated using finite element based method for a given number of cycles of worn half cylinder-on-flat geometry. The effect of interlayer stiffness on the stress distributions in the coating is studied. The maximum tensile stress at the trailing edge and the maximum compressive stress at the leading edge are reducing with increasing interlayer stiffness. The maximum shear stress at the coating-interlayer interface is predicted to have negligible effect with the change of interlayer stiffness. All the stresses are generally predicted to reduce with cycle. In general, stiffer interlayer will reduce the risk of coating failure.
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Rivera-Santana, J. A., A. Guevara-Morales, and U. Figueroa-López. "Micromechanics of Cracked Laminates under Uniaxial Load: A Comparison between Approaches." Advances in Materials Science and Engineering 2017 (2017): 1–12. http://dx.doi.org/10.1155/2017/3707329.
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This paper compares stiffness degradation models of cross-ply glass fiber/epoxy laminates based on four of the most commonly used approaches to micromechanical modelling: shear-lag, variational, McCartney, and synergistic damage mechanics (SDM). All of these include the process of defining 0/90s laminate unit cell, from which governing differential equations and corresponding boundary conditions are stated. Afterwards, these boundary value problems (BVP) are solved in order to obtain a stress function which couples the initial and perturbation stresses, the latter being in function of crack density, thus related to material stiffness reduction. When compared against experimental results, shear-lag model presented accurate results however, additional differentiation and integration steps were required in order to obtain the final stress field. Hashin’s variational method predicts correctly the boundary conditions at crack surfaces and gives out the complete stress field. McCartney’s approach shows further improvement over the previous two models, taking into account thermal strains and stresses. Finally, SDM, which is designed for numerical experimentation, implying a more economical alternative in comparison to traditional physical experimentation, also presented very good agreement with experimental results and can be extended to arbitrary laminate stackings, going beyond the classical cross-ply.
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Mohd Tobi, Abdul Latif, M. A. Harimon, Al Emran Ismail, A. A. Saad, and A. A. Azalan. "Investigation on the Fretting Wear of a Coated Substrate: Interlayer Stress Behaviour." Applied Mechanics and Materials 699 (November 2014): 311–17. http://dx.doi.org/10.4028/www.scientific.net/amm.699.311.
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The effect of surface modification due to fretting wear behaviour of coated SCMV (High Strength Alloy Steel) with interlayer is investigated by simulation using ABAQUS Software on a cylinder on flat contact configuration under gross sliding conditions. The effect of interlayer stiffness and the surface modification are analysed with the focus on the interlayer stress failures and its associated stresses behaviour. Tangential stress and shear stress are predicted to reduce with the increase of numbers of wear cycles due to the effect of contact conforming. Stresses in the interlayer are predicted to increase with the interlayer stiffness due to the function of the interlayer as the load bearer.
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Hashin, Z. "Analysis of Orthogonally Cracked Laminates Under Tension." Journal of Applied Mechanics 54, no. 4 (December 1, 1987): 872–79. http://dx.doi.org/10.1115/1.3173131.
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The problems of stiffness reduction and stress analysis of cross-ply fiber composite laminates, where all plies are cracked in fiber directions, are treated by a variational method on the basis of the principle of minimum complementary energy. The Young’s modulus obtained is a strict lower bound but is expected to be close to the true value on the basis of experience with a previous analysis. Approximate values of Poisson’s ratio and internal stresses have been obtained. The latter reveal important tendencies of continued failure by delamination.
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Bareišis, Jonas, Danas Garuckas, Alvydas A. Mikulskas, and Danguolė Striukienė. "STRAINS AND STRESSES OF THREE—LAYER COMPOSITE BARS AND BEAMS/TRISLUOKSNIŲ KOMPOZITINIŲ STRYPŲ IR SIJŲ DEFORMACIJOS BEI ĮTEMPIMAI." JOURNAL OF CIVIL ENGINEERING AND MANAGEMENT 3, no. 10 (June 30, 1997): 5–11. http://dx.doi.org/10.3846/13921525.1997.10531677.
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New composite anisotropic materials (CM) glass, carbon and boric plastics are more and more frequently used in engineering construction. By tuning strength and stiffness characteristics of CM under tension or bending with their density or price it is possible to get laminated construction of maximum strength and stiffness and minimum mass or price. The purpose of this work is to analyse regularity of distribution of stiffness or strains and stresses in three-layer bars, subjected to tension or bending by changing geometric characteristics of layer, materials and their position in cross-section of bars. The bar layers were formed of carbon plastic (A), hot (Sk) and cold hardening (Sc) glass plastics and epoxy resin (D). Equations were obtained describing the alteration of bar and beam stiffness and the alteration of normal stresses, all depending on relative thichness Ψ of bar or beam. The relative thickness Ψ is the ratio of middle layer height to the whole height. It has been shown that maximum stresses in exterior and middle layers (with elasticity modules E1 and E2accordingly) become equal when Ψ = E1 /E2 . The intensity of stiffness alteration depends on the magnitude of | E2 —E1 |. In the case of positive magnitude, the bar or beam stiffness increases while increasing Ψ. In the opposite case the stiffness decreases with decrease of Ψ. For the example of structure A-Sk—A and Ψ = 0,5, the price economy for 42% and mass reduction for 4% have been shown and compared with carbon plastic beam.
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Rasool, Mehnaz, and Maloy K. Singha. "Aeroelastic analysis of pre-stressed variable stiffness composite panels." Journal of Vibration and Control 26, no. 9-10 (December 31, 2019): 724–34. http://dx.doi.org/10.1177/1077546319889865.
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The effect of in-plane stresses on the stability behaviors of constant stiffness and variable stiffness composite panels, exposed to aerodynamic pressure, is studied using the finite element method. The dynamic pressure from the high velocity airflow is evaluated from the first-order piston theory, and the eigenvalue analysis is performed to investigate the flutter or divergence type of instabilities in such composite panels under combined mechanical and aerodynamic loads. Attempt is made to understand the effect of the lamination parameter on the stability characteristics of edge-supported and cantilever composite trapezoidal panels. Finally, the limit cycle oscillation of variable stiffness plates subjected to aerodynamic pressure is investigated.
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Wang, Y., and R. K. N. D. Rajapakse. "An Exact Stiffness Method for Elastodynamics of a Layered Orthotropic Half-Plane." Journal of Applied Mechanics 61, no. 2 (June 1, 1994): 339–48. http://dx.doi.org/10.1115/1.2901450.
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A method is presented in this paper to compute displacements and stresses of a multilayered orthotropic elastic half-plane under time-harmonic excitations. The half-plane region under consideration consists of a number of layers with different thicknesses and material properties. Exact layer stiffness matrices describing the relationship between Fourier transforms of displacements and tractions at the upper and bottom surface of each layer are established explicitly by using the analytical general solutions for displacements and stresses of a homogeneous orthotropic elastic medium. The global stiff ness matrix which is also symmetric and banded is assembled by considering the traction continuity conditions at the interface between adjacent layers of the multilayered half-plane. The numerical solution of the global stiffness equation results in the solutions for Fourier transform of displacements at layer interfaces. Thereafter displacements and stresses of the multilayered plane can be obtained by the numerical integration of Fourier integrals. Only negative exponential terms of Fourier transform parameter are found to appear in the elements of layer stiffness matrices. This ensures the numerical stability in the solution of the global stiffness equation. In addition, the size of the final equation system is nearly onehalf of that corresponding to the conventional matrix approach for layered media based on the determination of layer arbitrary coefficients. The present method provides accurate solutions for both displacements and stresses over a wide range of frequencies and layer thicknesses. Selected numerical results are presented to portray the influence of layering, material orthotropy, and frequency of excitation on the response of five layered systems. Time-domain solutions are also presented to demonstrate the features of transient surface displacements due to a surface loading pulse applied to layered orthotropic half-planes.
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Tarntira, Kanin, Teerapong Senjuntichai, and Suraparb Keawsawasvong. "Multilayered Elastic Medium under Axisymmetric Loading and Surface Energy." Key Engineering Materials 814 (July 2019): 320–26. http://dx.doi.org/10.4028/www.scientific.net/kem.814.320.
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This paper presents a solution scheme for analysis of a multilayered elastic medium under axisymmetric loading and surface energy effects by adopting Gurtin-Murdoch surface elasticity theory. Love’s strain function and Hankel integral transform are employed to derive the general solutions, and the obtained solutions are employed in the determination of the stiffness matrix for each layer. The global stiffness equation of a multi-layered system is assembled by considering the continuity of traction and displacements at each layer interface. The numerical solutions to the global equation yield displacements and stresses at the interfaces of the layered medium under axisymmetric loading. The accuracy of the proposed solution scheme is verified by comparing with existing solutions. Selected numerical results are presented to demonstrate a significant influence of surface energy on elastic fields of a multilayered elastic medium under axisymmetric loading.
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Chen, Tei-Chen, Horng-I. Jang, and Ampere A. Tseng. "Transient Thermal Stresses in a Multilayered Anisotropic Medium." Journal of Applied Mechanics 62, no. 4 (December 1, 1995): 1067–69. http://dx.doi.org/10.1115/1.2896045.
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A transient thermoelasticity problem of a multilayered anisotropic medium under the state of generalized plane deformation is considered in this note. The flexibility/stiffness matrix method is adopted here to obtain the complete solution of the entire layered medium by introducing the thermal and mechanical boundary and layer interface conditions in the Fourier and Laplace transform domains. As a numerical illustration, the distributions of transient temperatures and thermal stresses in a laminated anisotropic slab subjected to a uniform surface temperature rise are presented for some stacking sequences of fiber-reinforced layers.
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Thangjitham, Surot, and Hyung Jip Choi. "Thermal Stresses in a Multilayered Anisotropic Medium." Journal of Applied Mechanics 58, no. 4 (December 1, 1991): 1021–27. http://dx.doi.org/10.1115/1.2897677.
Full textAbstract:
A steady-state thermoelasticity problem of a multilayered anisotropic medium under the state of generalized plane deformation is considered in this paper. By utilizing the Fourier transform technique, the general solutions of thermoelasticity for layers with transversely isotropic, orthotropic, and monoclinic properties are derived. The complete solution of the entire layered medium is then obtained through introducing the thermal and mechanical boundary and layer interface conditions. This is accomplished via the flexibility/stiffness matrix method. As a numerical illustration, the distributions of temperature and thermal stresses in a laminated anisotropic slab subjected to a uniform surface temperature rise are presented for various stacking sequences of fiber-reinforced layers.
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Zhu, Wangang, Wei Sun, and Hao Wu. "Vibration and Stress Response of High-Speed Train Gearboxes under Different Excitations." Applied Sciences 12, no. 2 (January 12, 2022): 712. http://dx.doi.org/10.3390/app12020712.
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The vibration data of the gearbox on a high-speed train was measured, and the vibration characteristics were analyzed in this paper. The dynamic stress of the gearbox under the internal and external excitation was examined by a railway vehicle dynamic model with a flexible gearbox and a flexible wheelset. The ideal 20th polygonal wear was considered, and dynamic stresses of the gearbox under different polygonal wear amplitudes were calculated. The gear transmission model was established to study the dynamic stress of the gearbox under the influence of the time-varying stiffness of the gear meshing. Based on the rigid–flexible coupling model, and considering the influence of wheel polygonization, gear meshing time-varying stiffness, and wheelset elastic deformation, the dynamic stress of the gearbox was investigated with consideration of the measured polygonal wear and measured rail excitation. The results show that the dynamic stress of the gearbox is dominated by the wheel polygonization. Moreover, not only the wheel polygonization excites the resonance of the gearbox, but also the flexible deformation of the wheelset leads to the deformation of the gearbox, which also increases the dynamic stress of the gearbox. Within the resonant bandwidth of the frequency, the amplitude of the dynamic stresses in the gearbox will increase considerably compared with the normal case.
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Horbelt, Nils, John W. C. Dunlop, Luca Bertinetti, Peter Fratzl, and Michaela Eder. "Effects of moisture and cellulose fibril angle on the tensile properties of native single Norway spruce wood fibres." Wood Science and Technology 55, no. 5 (July 5, 2021): 1305–18. http://dx.doi.org/10.1007/s00226-021-01315-4.
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AbstractIsolated single wood fibres with cellulose fibril angles from 10 to 43° were tested in microtensile tests under controlled temperature and relative humidity of 5, 50, 75, 90% and in the wet state. This systematic study provides experimental stiffness and strength data, calculated on cell wall cross sections. It has been shown that stiffness reduction with increasing moisture content is more pronounced in fibres with large cellulose fibril angles. Interestingly, stiffness reduction in fibres with low cellulose fibril angles has been observed for the fully hydrated state only. The experimental dataset was fed into a model to determine moisture dependent stiffness of the hemicellulose-lignin-matrix and the stresses acting on the fibrils and the matrix.
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Sujan, D., L. Vincent, and Y. W. Pok. "Material Selection for Interfacial Bond Layer in Electronic Packaging." MATEC Web of Conferences 202 (2018): 01005. http://dx.doi.org/10.1051/matecconf/201820201005.
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In electronic packaging, typically two or more thin dissimilar plates or layers are bonded together by an extremely thin adhesive bond layer. Electronic assemblies are usually operated under high power conditions which predictably produces a high temperature environment in the electronic devices. Therefore, thermal mismatch shear and peeling stress inevitably arise at the interfaces of the bonded dissimilar materials due to differences in Coefficient of Thermal Expansion (CTE) typically during the high temperature change in the bond process. As a result, delamination failure may occur during manufacturing, machining, and field use. As such, these thermo-mechanical stresses play a very significant role in the design and reliability of the electronic packaging assembly. Consequently, critical investigations of interfacial stresses under variable load conditions in composite structure can result in a better design of electronic packaging with higher reliability and minimize or eliminate the risk of functional failure. In order to formulize bond material selection, analytical studies are carried out in order to study the influence of bond layer parameters on interfacial thermal stresses of a given package. These parameters include Coefficient of thermal expansion (CTE), poison’s ratio, temperature, thickness, and stiffness (compliant and stiff) of the bond layer. From the study, stiffness and bond layer thickness are identified as the key parameters influencing interfacial shearing and peeling stresses. The other parameters namely CTE, poisons ratio has shown insignificant influence on interfacial stresses due to the very thin section of bond layer compared to the top and bottom layers. The results also show that the interfacial stresses increases proportionally with the increase of temperature in the layers. Therefore, it is very important that the temperature is maintained as low as possible during the chip manufacturing and operating stages. Since only two parameters namely stiffness and bond layer thickness are identified as the key parameters, the interface thermal mismatch stresses can be reduced or eliminated by controlling these two parameters only. Therefore the identification of suitable bond layer parameters selection with reasonable accuracy is possible even without performing optimization process. Finally, this paper proposes a Metal Matrix Composite (MMC) bond material selection approach using rule of mixture material design. The outcome of this research can be seen in the forms of practical and beneficial tools for interfacial stress evaluation and physical design and fabrication of layered assemblies. The Engineers can utilize this research outcome in conjunction with guidelines for electronic packaging under variable thermal properties of layered composites.
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Baltov, Anguel, and Ana Yanakieva. "Local Deplanation Of Double Reinforced Beam Cross Section Under Bending." Journal of Theoretical and Applied Mechanics 45, no. 4 (December 1, 2015): 31–40. http://dx.doi.org/10.1515/jtam-2015-0022.
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Abstract Bending of beams, double reinforced by means of thin composite layers, is considered in the study. Approximate numerical solution is proposed, considering transitional boundary areas, where smooth quadratic transition of the elasticity modulus and deformations take place. Deplanation of the cross section is also accounted for in the areas. Their thickness is found equalizing the total stiffness of the cross section and the layer stiffness. Deplanation of the cross section of the transitional area is determined via the longitudinal deformation in the reinforcing layer, accounting for the equilibrium between the internal and the external moment, generated by the longitudinal stresses in the cross section. A numerical example is given as an illustration demonstrating model’s plausibility. The model allows the design and the calculation of recycled concrete beams double reinforced by means of thin layers. The approach is in agreement with modern design of nearly zero energy buildings (NZEB).
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Liu, Xiao Gen, and Yi Wang Bao. "Theoretical and Experimental Studies on Strength and Stiffness of Vacuum Glazing." Key Engineering Materials 544 (March 2013): 265–70. http://dx.doi.org/10.4028/www.scientific.net/kem.544.265.
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In order to understand the carrying capacity and deformation characteristics of vacuum glazing, experimental and theoretical research were carried out on load bearing capacity of four sides supported vacuum glazing, the load-displacement and load-stress curves of the test samples under uniform load were obtained. The experimental result indicated that under the test samples have the same thickness, the capacity of resisting wind load of the vacuum glazing is not so strong as common glass plate. To design methods of the vacuum glazing plate, one of those is to calculate the stresses and the deflection with the equivalent thickness as an integral model. The equivalent thickness coefficient of the vacuum glazing is about 0.85~0.9, and the magnitudes of the equivalent thickness coefficient of the vacuum glazing is decreases with increasing of the glass thickness, but not been influenced by the length and width dimensions of the glass plate. Take into account the influence of long term tensile stresses in vacuum glazing due to atmospheric pressure on the glass strength, the calculation formula of resistance to wind load for the vacuum glazing was given.
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Ahmad, Kamran, Yasir Baig, Hammad Rahman, and Hassan Junaid Hasham. "PROGRESSIVE FAILURE ANALYSIS OF HELICOPTER ROTOR BLADE UNDER AEROELASTIC LOADING." Aviation 24, no. 1 (April 23, 2020): 33–41. http://dx.doi.org/10.3846/aviation.2020.12184.
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Unlike metal structure, composite structures don’t give any clue till the fatal final collapse. The problem is more complicated when applied load on the structure is aeroelastic in nature. Under such loading, composite laminate experiences stresses. The first layer failure happens when stresses in the weakest ply exceed the allowable strength of the laminate. This initial layer-based failure changes overall material characteristics. It is important now to degrade the composite laminate characteristics for the subsequent failure prediction. The constitutive relations are required to be updated by the reduction in stiffness. The rest of the undamaged laminates continue to take the load till the updated strength is reached. In the present work, layer wise progressive failure analysis under aeroelastic loading has been performed by the inclusion of different failure criteria which allow for the identification of the location of the failure. ANSYS APDL environment has been used to model geometry of helicopter rotor. Under the loading conditions, stresses are calculated in the blade. Using stress tensor and failure criteria, failure location and modes have been predicted. It has been found that failure starts at higher speeds and failure starts from the root chord and tend towards the tip chord.
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Nelson, Gregory S., Ezzeldin Y. Sayed-Ahmed, Carol A. Gibbons Kroeker, Yi-Hui Sun, Henk E. D. J. Ter Keurs, Nigel G. Shrive, and John V. Tyberg. "Compression of interventricular septum during right ventricular pressure loading." American Journal of Physiology-Heart and Circulatory Physiology 280, no. 6 (June 1, 2001): H2639—H2648. http://dx.doi.org/10.1152/ajpheart.2001.280.6.h2639.
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The interventricular septum, which flattens and inverts in conditions such as pulmonary hypertension, is considered by many to be an unstressed membrane, in that its position is assumed to be determined solely by the transseptal pressure gradient. A two-dimensional finite element model was developed to investigate whether compression and bending moments (behavior incompatible with a membrane) exist in the septum during diastole under abnormal loading, i.e., pulmonary artery (PA) constriction. Hemodynamic and echocardiographic data were obtained in six open-chest anesthetized dogs. For both control and PA constriction, the measured left ventricular and right ventricular pressures were applied to a residually stressed mesh. Adjustments were made to the stiffness and end-bending moments until the deformed and loaded residually stressed mesh matched the observed configuration of the septum. During PA constriction, end-bending moments were required to obtain satisfactory matches but not during control. Furthermore, substantial circumferential compressive stresses developed during PA constriction. Such stresses might impede septal blood flow and provoke the unexplained ischemia observed in some conditions characterized by abnormal septal motion.
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Wu, Chong Fu, and Shu Hong Liu. "Interaction Analysis of the Superstructure and Raft Foundation for Tall Building with Podium." Applied Mechanics and Materials 71-78 (July 2011): 1720–23. http://dx.doi.org/10.4028/www.scientific.net/amm.71-78.1720.
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Based on the three-dimensional computation model, the actual project ,a high-rise building with podiums on the jointless raft foundation, is made nonlinear numerical analysis, which aims at studying the characters of superstructure-foudation-soil’s interaction, and analyzing the stress features in raft foundations under the former interaction , the distribution of stresses on foundation plate，and the range of stress dispersion about subgrade reaction. Through the factors, which can affect superstructure-foudation interaction, are analyzed , such as superstructure’s stiffness, foundation’s stiffness and soil’s stiffness. Then, the distribution rule of stress and deformation about superstructure-foudation interaction. Which can provide some calculation basis for this kind of foundation design.
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Liu, Si Hong, Yan Qiao Wang, Jiao Rong Gao, and Yuan Zheng Jin. "Cyclic Simple Shear Tests on Base Isolation Using Soilbags." Advanced Materials Research 243-249 (May 2011): 893–96. http://dx.doi.org/10.4028/www.scientific.net/amr.243-249.893.
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Soilbags have been understood to have the effect of vibration reduction and can be used as a kind of base isolation in building foundations. In this paper, a series of cyclic simple shear tests were carried out on soilbags filled with three kinds of soils under different vertical stresses to investigate the damping and stiffness characters of the soilbags. The results show that soilbags have a relatively high damping ratio and variable horizontal stiffness so that they can be used as base isolation materials.
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Shahar, R. "Evaluation of Stiffness and Stress of External Fixators with Curved Acrylic Connecting Bars." Veterinary and Comparative Orthopaedics and Traumatology 13, no. 02 (2000): 65–72. http://dx.doi.org/10.1055/s-0038-1632633.
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SummaryThe use of acrylic connecting bars in external fixators has become widespread in veterinary orthopaedics. One of the main advantages of an acrylic connecting bar is the ability to contour it into a curved shape. This allows the surgeon to place the transcortical pins according to safety and convenience considerations, without being bound by the requirement of the standard stainless steel connecting bar, that all transcortical pins be in the same plane.The purpose of this study was to evaluate the stiffness of unilateral and bilateral medium-sized external fixator frames with different curvatures of acrylic connecting bars. Finite element analysis was used to model the various frames and obtain their stiffness under four types of load: Axial compression, four-point medio-lateral bending, fourpoint antero-posterior bending and torsion. The analysis also provided the maximal pin stresses occurring in each frame for each loading condition.Based on the results of this study, curvatures of acrylic connecting bars of up to a maximal angular difference between pins of 25° will result in very similar stiffness and maximal pin stresses to those of the equivalent, uniplanar stainless steel system. In both unilateral and bilateral systems the stiffness decreases slightly as angulation increases for axial compression and medio-lateral bending, increases slightly for torsion and increases substantially for antero-posterior bending.External fixator systems with curved acrylic connecting bars are commonly used in veterinary orthopaedics. This paper evaluates the biomechanical performance of such systems by applying the finite element analysis method. It shows that external fixators with curved acrylic connecting bars exhibit stiffness and maximal pin stresses which are similar to those of the standard stainless steel system.
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Prioul, Romain, Andrey Bakulin, and Victor Bakulin. "Nonlinear rock physics model for estimation of 3D subsurface stress in anisotropic formations: Theory and laboratory verification." GEOPHYSICS 69, no. 2 (March 2004): 415–25. http://dx.doi.org/10.1190/1.1707061.
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We develop a rock physics model based on nonlinear elasticity that describes the dependence of the effective stiffness tensor as a function of a 3D stress field in intrinsically anisotropic formations. This model predicts the seismic velocity of both P‐ and S‐waves in any direction for an arbitrary 3D stress state. Therefore, the model overcomes the limitations of existing empirical velocity‐stress models that link P‐wave velocity in isotropic rocks to uniaxial or hydrostatic stress. To validate this model, we analyze ultrasonic velocity measurements on stressed anisotropic samples of shale and sandstone. With only three nonlinear constants, we are able to predict the stress dependence of all five elastic medium parameters comprising the transversely isotropic stiffness tensor. We also show that the horizontal stress affects vertical S‐wave velocity with the same order of magnitude as vertical stress does. We develop a weak‐anisotropy approximation that directly links commonly measured anisotropic Thomsen parameters to the principal stresses. Each Thomsen parameter is simply a sum of corresponding background intrinsic anisotropy and stress‐induced contribution. The stress‐induced part is controlled by the difference between horizontal and vertical stresses and coefficients depending on nonlinear constants. Thus, isotropic rock stays isotropic under varying but hydrostatic load, whereas transversely isotropic rock retains the same values of dimensionless Thomsen parameters. Only unequal horizontal and vertical stresses alter anisotropy. Since Thomsen parameters conveniently describe seismic signatures, such as normal‐moveout velocities and amplitude‐variation‐with‐offset gradients, this approximation is suitable for designing new methods for the estimation of 3D subsurface stress from multicomponent seismic data.
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Linder-Ganz, E., and A. Gefen. "Mechanical compression-induced pressure sores in rat hindlimb: muscle stiffness, histology, and computational models." Journal of Applied Physiology 96, no. 6 (June 2004): 2034–49. http://dx.doi.org/10.1152/japplphysiol.00888.2003.
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Pressure sores affecting muscles are severe injuries associated with ischemia, impaired metabolic activity, excessive tissue deformation, and insufficient lymph drainage caused by prolonged and intensive mechanical loads. We hypothesize that mechanical properties of muscle tissue change as a result of exposure to prolonged and intensive loads. Such changes may affect the distribution of stresses in soft tissues under bony prominences and potentially expose additional uninjured regions of muscle tissue to intensified stresses. In this study, we characterized changes in tangent elastic moduli and strain energy densities of rat gracilis muscles exposed to pressure in vivo (11.5, 35, or 70 kPa for 2, 4, or 6 h) and incorporated the abnormal properties that were measured in finite element models of the head, shoulders, pelvis, and heels of a recumbent patient. Using in vitro uniaxial tension testing, we found that tangent elastic moduli of muscles exposed to 35 and 70 kPa were 1.6-fold those of controls ( P < 0.05, for strains ≤5%) and strain energy densities were 1.4-fold those of controls ( P < 0.05, for strains ≥5%). Histological (phosphotungstic acid hematoxylin) evaluation showed that this stiffening accompanied extensive necrotic damage. Incorporating these effects into the finite element models, we were able to show that the increased muscle stiffness in widening regions results in elevated tissue stresses that exacerbate the potential for tissue necrosis. Interfacial pressures could not predict deep muscle (e.g., longissimus or gluteus) stresses and injuring conditions. We conclude that information on internal muscle stresses is required to establish new criteria for pressure sore prevention.
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Tejchman, J. "Finite element investigations of granular material behaviour during cyclic wall shearing under a constant normal stiffness condition." Canadian Geotechnical Journal 47, no. 9 (September 2010): 985–98. http://dx.doi.org/10.1139/t10-001.
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The behaviour of dry and cohesionless sand during quasi-static cyclic wall shearing under a constant normal stiffness (CNS) condition was studied. Numerical calculations were carried out using a finite element method based on a hypoplastic constitutive model extended by micropolar quantities: rotations, curvatures, and couple stresses. The mean grain diameter was used as the characteristic length of the microstructure. The constitutive model takes into account the effects of pressure, void ratio, and direction of deformation rate on the material’s behaviour. Calculations were performed for several shear cycles in a direct wall shear tester. The initial void ratio, mean grain diameter of sand, and vertical normal stiffness were varied. The numerical results with medium density sand were compared with corresponding laboratory tests.
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Conard, B. E., R. A. Lohnes, F. W. Klaiber, and T. J. Wipf. "Boundary Effects on Response of Polyethylene Pipe Under Simulated Live Load." Transportation Research Record: Journal of the Transportation Research Board 1624, no. 1 (January 1998): 196–205. http://dx.doi.org/10.3141/1624-23.
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The objective of this paper is to evaluate the deflection response of polyethylene pipes when loaded near their ends. Tests were conducted on pipes loaded at the center and near their ends to simulate loading of a vehicle at the center of a roadway and on the shoulder. The tests were performed on 900-mm (36-in.) and 1200-mm (48-in.) diameter polyethylene pipes with 610-mm (2 ft) cover and a variety of backfills. Loads were applied through a 93 025-mm2 (1-ft2) plate that provides very severe loading conditions. At high contact stresses, the load test plate punched into the soil cover so that the crown of the pipe was subjected to stresses in excess of those that would have occurred if the soil surface were paved or stabilized or a less severe loading condition better representing a truck tire had been used. At contact stresses equivalent to moderate highway tire pressures, pipe deflections are slightly higher near the ends of the pipes than at the center. Except for low-density till, the percent deflections are not excessive and the pipe-soil systems have adequate stiffness. For contact stresses near the upper limit of truck tire pressures and when loaded near the ends, the pipes with sand and till backfills fail by local wall bending. For flowable-fill backfill, the ultimate capacity of the pipes is nearly twice that for the soil backfills.
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Zhang, Qing Zhao, and Ming Rong Shen. "Study on the Mechanical Properties of Discontinuity under Shearing." Advanced Materials Research 261-263 (May 2011): 900–904. http://dx.doi.org/10.4028/www.scientific.net/amr.261-263.900.
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This paper presents a fundamental research in the mechanical properties of the regular jagged discontinuity under various normal stresses in the shear test. The mechanical properties of the regular jagged discontinuity under shear stress and their principal regularities are described. The strength and roughness of discontinuity under shear stress are investigated by the analysis of the data obtained. The calculation of shear stiffness of discontinuity and an empirical formula between the slope angle and roughness coefficient of discontinuity are proposed. The changing regularity of the parameters of the shear strength of discontinuity under shear stress is investigated, and an empirical formula is established to evaluate the shear strength of discontinuity.
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Pekau, O. A., and V. Cistera. "Behaviour of nonlinear coupled shear walls with flexible bases." Canadian Journal of Civil Engineering 16, no. 1 (February 1, 1989): 45–54. http://dx.doi.org/10.1139/l89-006.
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This paper examines the importance of base flexibility on the nonlinear behaviour of coupled shear walls subjected to pseudo-static lateral loading. The classic continuum method is adopted, with the base flexibility modelled by effective rotational and vertical elastic stiffnesses, Kθ and Kv, respectively. Since the magnitudes of these stiffnesses depend on the properties of the supporting soil and also on the characteristics of the foundation itself, different soils as well as the type of foundation are considered. The latter consists of separate footings under each wall as well as a single combined foundation under the coupled walls. In general, the results show that base flexibility becomes especially important for the overall lateral stiffness at all load levels, whereas internal stresses are affected in only the lower portion of the structure for service loading. Key words: shear walls, coupled, nonlinear, continuum method, flexible bases, separate footings, combined foundation.
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Chen, T. C., and H. I. Jang. "Thermal Stresses in a Multilayered Anisotropic Medium With Interface Thermal Resistance." Journal of Applied Mechanics 62, no. 3 (September 1, 1995): 810–11. http://dx.doi.org/10.1115/1.2897018.
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This note is concerned with thermoelastic analysis of a multilayered anisotropic medium under the state of generalized plane deformation with interlayer thermal contact resistance. The powerful flexibility/stiffness matrix method is adopted here to obtain the complete solution of the entire layered medium by introducing the thermal and mechanical boundary and layer interface conditions including interlayer imperfect thermal contact conditions. As a numerical illustration, the effects of interlayer thermal resistance on the distributions of temperatures and thermal stresses in a laminated anisotropic slab subjected to a uniform surface temperature rise are presented.
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Filipe Veloso Marques, Sérgio, Nilo Cesar Consoli, and Lucas Festugato. "Effects of curing stress on the stiffness of a cement-mixed sand." E3S Web of Conferences 92 (2019): 04006. http://dx.doi.org/10.1051/e3sconf/20199204006.
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Research into naturally cemented soils (e.g. sandstones) has increased considerably, mostly be-cause of growing interest in offshore oil wells at depths that can, at times, exceed 1000 m. Performing tests directly with on-site soil samples is ideal. However, it's acquisition, transportation and preservation are in-credibly difficult. In order to perform the tests required for this study, the samples were made to simulate the bonding found in naturally cemented soils. Artificially cemented sands were cured under stresses of either 500, 2000 and 4000 kPa, or simply under atmospheric pressure. These specimens were then subjected to drained triaxial compression tests. The results have shown that the curing type has influence over the artifi-cially cemented sand's yield surface and stiffness. The stiffness was vastly superior in specimens cured under higher levels of stress
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Verdino, Alessia, Oscar Arena, Osvaldo Bottiglieri, Francesco Cafaro, and Enrico Dini. "Performance of Lunar Regolith Shield under Meteoroid Impact: Uncertainties of a Numerical Prediction." Applied Sciences 12, no. 21 (October 27, 2022): 10885. http://dx.doi.org/10.3390/app122110885.
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The protection of the future lunar base from radiation, thermal stresses and impacts of meteoroids can be achieved by several options, generally consisting in a shielding system, made of either regolith or combined materials. In the present paper, the incidence of two sources of uncertainty on the FEM calculation of stress propagation through the covering regolith layer has been assessed. First, the investigation has pointed out, for a given impact and a given constitutive model, the uncertainty in the stress prediction related to the strain interval adopted for the soil stiffness measurement. Thereafter, calculation has been performed, for a given stiffness value, changing the assumed collision duration of one order of magnitude for equal impact momentum, that is, changing the maximum impact force too, correspondingly. The simulation has been performed based on physical and mechanical parameters of DNA-1A lunar simulant. The results provide indication of the relative importance of the calculation assumptions, which could address the design of a regolith shield.
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Swanson, S. R., and A. P. Christoforou. "Progressive Failure in Carbon/Epoxy Laminates Under Biaxial Stress." Journal of Engineering Materials and Technology 109, no. 1 (January 1, 1987): 12–16. http://dx.doi.org/10.1115/1.3225924.
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Despite a number of previous investigations, the question of what criterion to use to predict ultimate failure in fiber composite laminates is still open to question, and particulary so when the overall loading involves biaxial stresses. We have addressed this question by developing a progressive failure model, and comparing the model to experiments on biaxial loading of tubular specimens of quasi-isotropic AS4/3501-6 carbon/epoxy laminates. The progressive failure model uses a modified Tsai-Wu criterion for initial ply cracking, a rule for softening the ply stiffness coefficients with continued straining, and an ultimate failure criterion. It was found that a maximum fiber strain criterion agreed very well with the experiments.
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Just, Koch, Brod, Jansen, Gude, and Rolfes. "Influence of Reversed Fatigue Loading on Damage Evolution of Cross-Ply Carbon Fibre Composites." Materials 12, no. 7 (April 9, 2019): 1153. http://dx.doi.org/10.3390/ma12071153.
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Microcrack formation and delamination growth are the main damage mechanisms in thefatigue of composites. They lead to significant stiffness loss, introduce stress concentrations andcan be the origin of subsequent damage events like buckling or fibre breakage, especially in case ofshear and compression stresses during load reversal. Fatigue experiments of carbon fibre reinforcedlaminates were conducted at several stress ratios and analysed in terms of crack and delaminationgrowth. These investigations were accompanied by microscopic imaging, digital image correlationand finite element modelling to take into account the effects of residual stresses and crack closure.It was found that residual stresses significantly change the local stress ratio in off-axis layers andlead to residual crack opening of inter fibre cracks. These cracks remain open and close under highcompression loadings only. Furthermore, crack formation under pulsating compression loadingturned out to be driven by residual stresses leading to perpendicular cracks as observed underpure tension loading. The experimental findings further confirm the severe detrimental effect oftension-compression loading on crack formation and delamination growth compared to pulsatingtension-tension or compression-compression loads.
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Govindaraj, Moorthy, HN Narasimha Murthy, Shivkumar Patil, Sudarsan K., Nandagopan O.R, Ajith Kumar K., and Krishna Munishaiah. "Buckling behaviour of underwater vessels by experimental, numerical and analytical approaches." Journal of Naval Architecture and Marine Engineering 11, no. 1 (June 10, 2014): 15–28. http://dx.doi.org/10.3329/jname.v11i1.16087.
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This paper reports the buckling behaviour of glass/vinylester polymer composite filament wound shells of underwater vessels. The shells were tested for buckling under hydrostatic loading and microstrains as a function of applied hydrostatic pressure were measured. Numerical analysis was performed for critical buckling pressure based on Block Lancoz buckling analysis and for Von-Mises stresses and strains based on static analysis using ANSYS. Von-Mises stresses corresponding to hydrostatic pressures were computed analytically by Reduced Stiffness Matrix method. The numerical results of critical buckling pressure for 10 mm thick vessels showed 7.12 % deviation from the experimental results. The microstrains predicted by FEA were in good agreement with the experimental strains. Von-Mises stresses predicted by FEA agreed well with the analytical computations.DOI: http://dx.doi.org/10.3329/jname.v11i1.16087