Dissertations / Theses: 'Residual Stresses'

1

Blanchard, Pierre. "Residual stresses and indentation." Thesis, KTH, Hållfasthetslära (Avd.), 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-92586.

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The correlatioin between residual stresses and the global properties from an indentation test, i.e. hardness and size of the contact area, has been studied frequently in recent years. The investigations presented have been based on experimental, theoretical and numerical methods and as a result, the basic features of the problem are fairly well understood in the case of residual equi-biaxial surface stresses. The more general case, when the principal surface stresses are not necessarily equi-biaxial, has received nuch less attention and it is therefore the aim of the present study to remedy this shortcoming. In doing so, qualitative results are of immediate interest in this initial study but possible ways of quantitative descriptions are also discussed for future purposes. The present analysis is based on numerical methods and in particular the finite element method (FEM) is relied upon. Classical Mises elastoplastic material behavior is assumed throughout the investigation.

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Pascual, Joan. "Residual stresses in sandwich components." Thesis, KTH, Lättkonstruktioner, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-121312.

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High residual stresses are likely to develop in honeycomb sandwichparts after autoclave co-curing and can lead to manufacturing defects.By using finite element unit cell models, these stresses have been calculatedfor standard panels and for panels where different core blocksare joined with adhesive. Failure criteria are given for three types ofaluminum honeycombs under combined thermal and shear loads, allowingto calculate the residual strength of the cores. Residual stressvalues are also calculated for adhesive joints between different coreblocks, they being about the same order of magnitude as the strengthof the adhesive regardless of geometry or core combination. Last, it isshown that the effect of the sandwich plate chamfered edges in preventingthe core expansion during the heating cycle may cause corecrushing when high and low density honeycombs are combined.

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3

Lingois, Philippe. "Residual stresses in dental composites." Licentiate thesis, Luleå tekniska universitet, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-17853.

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In several European countries, dental composites are replacing mercury-containing amalgams as the most common restorative materials. The problems with dental composites are they can induce pain for the patient, fracture of the tooth, gap between the tooth and the filling what will induce secondary caries. The main reason is residual stresses. The factors affecting residual stresses are known; it is Young's modulus, volume changes, relaxation, geometry, but their importance is unknown. A model approach has been chosen in order to determine what are the main factors. An experimental set-up, shown in the second paper, to measure residual stresses has been made based on the bimetallic experiment. The dental composite is cured on an aluminum substrate and two strain gages register the bending of the substrate. From this experiment, the residual stresses in the composite could be determined. The modeling, treated in the second paper of this thesis, can be divided in sub-models. The first one is the cure kinetics in order to obtain the degree of cure. From this sub-model, the volume change and the Young's modulus can be determined. From the two last sub-models and the geometry, the stresses can be calculated. The chemical shrinkage was considered as linearly dependent on the degree of conversion. A simple pseudo-autocatalytic model was used for the cure kinetics. In order to do the calculation the change of modulus as a function of degree of cure has to be model. The viscoelastic properties of pure resin samples light-cure at different degree of conversion were determined using dynamic mechanical analysis and time-temperature superposition. The viscoelastic Young's modulus has been represented by a discrete exponential series and it has been observed that time-cure superposition works, what means that the weight factors do not depend on the degree of cure. Only the relaxed modulus, the unrelaxed modulus, and the principal relaxation time (time at which the relaxation spectrum has its maximum) depend on the degree of cure. A linear relation was found between the logarithm of these parameters and the degree of cure. An elastic Young's modulus model was done by taking the same expression as for viscoelasticity, but replacing the time by 1s what corresponds to the change of the 1Hz modulus as a function of degree of cure. The calculations were done for 2D-constraint geometry like for the bimetallic experiment. Finite difference was used for the calculations. The changes of physical properties as a function of degree of cure were done on pure resin, but we need the changes for different filler content. This is the reason why the first paper deals with micro-mechanical models to predict the effect of filler on the Young's modulus and the chemical shrinkage. The Young's modulus is well described by the upper bound of Hashin's sphere model. Whereas the chemical shrinkage is well described by a modified Rosen and Hashin's model that was developed for the thermal coefficient expansion. Since this two models work well they were used for the calculation of the composite chemical shrinkage and the calculation of relaxed and unrelaxed Young's modulus considering that the weight factors and relaxation time were the same as for the resin. Two isothermal models have been done: one elastic and one viscoelastic. The viscoelastic model gives stresses that are 15% lower than elastic case. The viscoelastic model gives good results at the beginning compare to the experimental data, but after it overestimates a lot the stresses. There are two main reasons. First the modeling of shrinkage is inadequate, it is believed that the shrinkage decreases near vitrification so the linear relation do not hold and induce an overestimation of stresses. The second factor is the fact that there is an exotherm from room temperature to 55ºC in the case of pure resin, so the isothermal conditions are not fulfilled. This study shows us the validity of time-cure superposition. It also demonstrates that the modeling of shrinkage should be done more carefully and that the non-isothermal conditions should certainly be taken into account. The results of this thesis are presented in following papers: P. Lingois and L. Berglund, "Modeling Young's modulus and volume shrinkage of dental composites" P. Lingois, L. Berglund, A. Mafezzoli, and A. Greco, "Chemically induced residual stresses in dental composites"
Godkänd; 2000; 20070318 (ysko)

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Moeller, Gregory V. "Residual stresses due to grinding." Thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-05022009-040807/.

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Lora, Ruben, and Jayesh Namjoshi. "Simulation of Residual Stresses in Castings." Thesis, Jönköping University, JTH, Mechanical Engineering, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-1587.

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This work presents a study and implementation of the simulation of residual stresses in castings. The objects of study are a cast iron truck Hub part (provided by the company Volvo 3P) and an optimized version of the Hub resulting from the application of a topology optimization process. The models are solved through an uncoupled thermo-mechanical solidification analysis, performed both in the FE commercial software Abaqus and the FD commercial software Magmasoft and the results are compared. First, a thermal analysis is carried out where the casting is cooled down from a super-heated temperature to room temperature. The thermal history obtained, is then used as an external force to calculate the residual stresses by means of a quasi-static mechanical analysis, using a J2-plasticity model. The simulation procedures are explained through a simplified model of the Hub and then applied to the geometries of interest. A results comparison between the original Hub and its optimized version is also presented. The theoretical base is given in this work as well as detailed implementation procedures. The results shows that the part subjected to the topology optimization process develop less residual stresses than its original version.

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Stephens, D. G. "Residual stresses in ring stiffened cylinders." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384531.

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Leaity, Grant Philip. "Residual stresses and fatigue crack propagation." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293635.

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Gill, Stephen Charles. "Residual stresses in plasma sprayed deposits." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386108.

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9

Liou, Ming Jaw. "Minimizing residual stresses in molded parts." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/17213.

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Mahmoudi, Amir Hossein. "Influence of residual stresses on fracture." Thesis, University of Bristol, 2005. http://hdl.handle.net/1983/4026a13c-3d83-49a6-815c-1bdf50e37f0a.

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This thesis presents numerical and experimental research concerned with developing laboratory test specimens containing well-characterised residual stress fields. These specimens were then used to examine how residual stresses influenced fracture conditions. Three different materials were used in this work; an A508 ferritic steel, and two aluminium alloys, 2650 and 2024. Residual stresses were generated using a technique called local compression on both uncracked plates and cracked compact tension, C(T), specimens. Residual stresses introduced by single punching tools on the uncracked specimens were examined theoretically and numerically to benchmark further developments. Also residual stresses were measured using three techniques, deep-hole drilling (DHD), centre-hole drilling (ICHD) and synchrotron diffraction (HEXRD) and excellent agreement between measurement methods was obtained. A parametric study was carried out to determine the features of the residual stress field generated in cracked specimens. The position of single and double pairs of punching tools relative to the crack tip as well as the size of the punches were examined systematically. The numerical analyses revealed that positioning a single punching tool tangentially to the crack tip resulted in the generation of a tensile residual stress field ahead of a crack. Furthermore, double pairs of punching tools were shown to generate either tensile or compressive residual stresses normal to the crack plane depending on the relative position of the tools to the crack tip. The numerical findings were confirmed experimentally through HEXRD measurements and fracture tests. Local compression and prior overloading were applied to C(T) specimens to generate a residual stress field, either independently or in combination. It was found that tensile residual stresses reduced the apparent fracture toughness and that compressive residual stresses resulted in increased the fracture toughness. The shift in the apparent fracture toughness depended on the magnitude of the residual stresses and material, with the aluminium alloys being more susceptible to the presence of tensile residual stresses. A local approach based on the Beremin model was used to predict failure in the presence of residual stress fields in terms of fracture toughness for cleavage fracture in steel specimens. The overall trends from predictions were similar to the experiments, but there remain limitations in the model. For aluminium specimens, a method based on the William's series was employed to predict the stress intensity corresponding to a residual stress field (Kres). The measured changes in initiation toughness matched the predicted values of K1es.

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Stranart, Jean-Claude E. "Mechanically induced residual stresses, modelling and characterisation." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0028/NQ49944.pdf.

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Greving, Daniel James. "Residual stresses and thermal spray coating performance /." Access abstract and link to full text, 1995. http://0-wwwlib.umi.com.library.utulsa.edu/dissertations/fullcit/9610608.

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Free, J. A. "Residual stresses in welded tubular Y-joints." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384462.

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Wilks, Martin David Bernard. "The influence of residual stresses on fatigue." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240439.

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Parkyn, A. T. "Residual stresses in laminated thermoplastic matrix composites." Thesis, University of Reading, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234355.

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Payne, J. G. "Residual stresses in welded tubular T-joints." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384523.

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17

Sun, Xing. "Estimation of residual stresses in marine structures." Thesis, University of Strathclyde, 2013. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=18980.

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A finite element model that is capable of simulating the thermo-mechanical welding process was developed by using full thermal-elasto-plastic computational analysis and validated by comparison with experimental data. It shows that distortions predicted by the finite element model agree well with measured data from previous literature and that the numerically obtained residual stress distribution is compared and agreed by both ANSYS and VrWeld software. After that, a simple method for predicting butt-welding residual stresses based on force and moment equilibrium was derived in this section. The results calculated from this simple method were a good match with the FE results. Then the author performed detailed analysis for the distribution of transverse and longitudinal residual stresses of 2D butt welding process by using 3D elements, which illustrated how the butt-welding residual stresses were distributed and accumulated during the welding process and how the boundary conditions affect the final results. A detailed parametric study for butt welding residual stresses based on 2D butt-welding by using 3D element was demonstrated. The factors carried out in the parametric study involved cut-off temperature effect, welding power effect, welding velocity effect, plate length effect and plate width effect. Lastly, the author also presented a simulation and an optimization of welding sequences for residual stress and distortion of a typical, fatigue sensitive, ship's side shell connection detail under different welding sequences.

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18

Lingois, Philippe. "Modeling of residual stresses in dental composites." Doctoral thesis, Luleå tekniska universitet, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-16835.

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In several European countries, dental composites are replacing mercury- containing amalgams as the most common restorative materials. The problems with dental composites are that they can induce pain for the patient, fracture in the tooth, and gaps between the tooth and the filling which will induce secondary caries. One reason for these problems is residual stress. The factors affecting residual stress are known; it is Young's modulus, volume change, stress relaxation, light absorption, and geometrical constraint, but their relative importance is unclear. A combined modeling and characterization approach has been chosen to determine and quantify the main factors. The material studied was a model composite of known methacrylate resin composition, where the filler fraction was varied. An experimental set-up to measure residual stress was developed based on the bimaterial experiment. The dental composite is cured on an aluminum substrate and two strain gauges register strains in the substrate. From this experiment, the residual stresses in the composite during curing are determined. The numerical master model is divided in submodels. The first one is the cure kinetics model, in order to obtain the degree of conversion of the matrix as a function of time. From this sub-model, the volume change and the Young's modulus of the matrix are obtained from separate submodels. Micromechanical models are then used to determine composite shrinkage and Young's modulus. From composite properties, substrate properties, and geometry, the stresses in the composite can be predicted from a stress model. To simplify the problem isothermal conditions were supposed. Modeling of the vitrification event is critical as well as the influence of geometrical constraint on vitrification, through free volume. For this reason, special efforts have been put to accurately describe the influence of vitrification on the different submodels. For this reason, a modified pseudo-autocatalytic model was used for the cure kinetics model. A chemical shrinkage model based on viscoelasticity was developed in order to take into account the non-linear shrinkage with degree of conversion during vitrification. A viscoelastic model for the Young's modulus is also needed, which was obtained using the time-cure superposition principle. The good agreement between experimental data and the model predictions support our model and indicates that the essential physics of the residual stress development process has been captured. The model shows the necessity of a non-linear shrinkage model and the influence of free volume induced by geometrical constraints on all the others properties during vitrification. The parametric study shows the complex interactions between cure kinetics, volume change, modulus development, free volume effects, and rate of volume change. Obviously, shrinkage, modulus, and geometrical constraint are important parameters. But the width of the relaxation spectrum has also strong effects. Light power density has also some effects on the stress level, but much less than expected. This is due to the complex interactions between the different submodels and the fact that some factors, like light absorption or non-isothermal conditions, are not taken into account. The influence of the cavity design and the filling procedure were not studied. I. P. Lingois and L. Berglund, "Modeling Elastic Properties and Volume Change in Dental Composites" submitted to J. Mat. Sci. II. P. Lingois, L. Berglund, A. Greco, and A. Mafezzoli, "Chemically Induced Residual Stresses in Dental Composites" submitted to J. Mat. Sci. III. P. Lingois and L. Berglund, "Modelling of Chemically Induced Residual Stresses in Dental Composites Including Free Volume Effects" IV. P. Lingois and L. Berglund, "Factors Affecting Residual Stresses in Dental Composites: A Parametric Study"
Godkänd; 2002; 20061110 (haneit)

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Hossain, Sayeed. "Residual stresses under conditions of high triaxiality." Thesis, University of Bristol, 2005. http://hdl.handle.net/1983/7b464389-6e62-4232-9373-ea0978d6360b.

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The present study was motivated by a need to model and understand creep in an ageing power plant particularly when residual stresses are present. A number of methods of generating residual stress in laboratory specimens are presented. Both numerical and experimental studies were conducted. The finite element (FE) analysis used in the numerical study was validated with an extensive experimental study of residual stress field characterisation in the test specimens. Two novel means of generating highly triaxial residual stress field in the laboratory specimens were identified and were followed up with design and manufacture. The specimens with internal residual tensile stresses of high triaxiality were used in the subsequent creep study. Using specimens containing residual tensile stress field with variable triaxiality and plastic strain the influence of prior straining in the creep cavitation initiation was also highlighted. A mechanical strain relief deep-hole (DH) drilling residual stress measurement technique used in residual stress measurement of specimens with high triaxiality highlighted a potential difficulty in using a simple elastic approach to data reduction in the DH measurement method. A comprehensive FE study modelling the DH using an elasto-plastic analysis and an incremental trepanning process in contrast to a previous elastic analysis with a single-step trepanning process [George 2000] was carried out to study further the influence of DH process on the residual stress field. The reconstructed residual stress distribution obtained in the DH FE analysis considering the influence of the electro-discharge machining (EDM) trepanning showed a good correlation with the DH measured residual stress distribution in the components with residual stress field with high triaxiality. A further DH FE study of the repair welded pipe three material models were considered and the result was found to be highly sensitive to the material model selected. The DH FE study of repair weld revealed that the original residual stress distribution was generated even considering the cutting process of the DH method. Consequently the deep hole drilling technique was used to characterise the residual stress field in a number of selected locations in practical components including thick-section steel welds consisting of a welded nozzle component which was thermally aged at 550�C for 19,644 hours and a pipe with repair weld.

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Lundin, Emma. "Simulation of Residual Stresses in Cemented Carbide." Thesis, KTH, Teknisk mekanik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-295154.

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Cemented carbides are used in a multitude of applications within machining as they can withstand tough conditions. Therefore, the stress state in a virgin material is of interest. After cooling from the sintering stage during cemented carbide production, the large difference in coefficients of thermal expansion of the constituents results in thermal residual microstresses. These may be of significant magnitude that could influence the material's performance in later applications. The present work is therefore concerned with these thermal residual microstresses and deals with them through 2D finite element calculations in ANSYS APDL. The geometry was chosen to try to emulate different conditions that could happen within a cemented carbide grain. The tungsten phase was modeled as fully elastic and the cobalt phase as elastic-plastic with linear hardening. The results show that the stress levels reach such magnitudes that the simple material models used in this work, as well as in previous works, are not sufficient to accurately capture the behavior of the material. The stress levels far exceed the strength of the materials, which would cause them to fail. However, that is not the case in reality. Further, the simulations showed that the microgeometry plays a large role in the distribution of the stresses within each phase. In general, the cobalt phase is subjected to tension and the tungsten phase to compression. However, under certain conditions parts of the tungsten phase can also show tensile stresses.
Hårdmetaller används i många tillämpningar inom skärande bearbetning på grund av dess egenskaper. De klarar av de stora belastningar som uppstår under kontakter i processerna. På grund av obesvarade frågor när det gäller till exempel sprickbildning är spänningstillståndet i ett obelastat material av intresse. Under tillverkningen av hårdmetaller, måste kompositen kylas ned efter sintringen. Kobolt och wolframkarbid har mycket olika värmeutvidgningskoefficienter, vilket resulterar i att termiska restspänningar uppstår. Dessa kan nå en betydande storlek vilket kan påverka materialets prestation under senare användning. Detta arbete behandlar dessa termiska restspänningar genom finita elementberäkningar i ANSYS APDL. Geometrin gjordes i 2D, och valdes för att försöka efterlikna de förhållanden som kan råda inuti ett korn av hårdmetall. Wolframkarbiden modellerades som helt elastisk medan kobolten modellerades som elastisk-plastisk med linjärt hårdnande. Resultaten visar att spänningsnivåerna når sådana nivåer att materialet inte borde klara av belastningen. Materialmodellerna i detta arbete, och tidigare arbeten, är för enkla för att korrekt beskriva materialens beteende. Spänningsnivåerna överstiger materialets styrka, vilket skulle orsaka brott. Detta överensstämmer inte med verkligheten. Vidare visar simuleringarna att mikrogeometrin har spelar stor roll för spänningsfördelningen inom varje fas, där det kan vara stor skillnad inom samma fas. Generellt sett, hamnar kobolten i ett dragtillstånd och wolframkarbiden i tryck. Det finns dock vissa förutsättningar som leder till dragspänningar inom vissa delar av wolframkarbiden.

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Omatuku, Emmanuel Ngongo. "Modelling of Residual Stresses of Blood Vessels." Thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/21604.

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The diagnosis of vascular diseases can be achieved with a suitably determined circumferential stress at arterial walls. The stress distribution over arterial walls in blood vessels is affected by residual stresses and stresses due to blood pressure. However, residual stresses are still not reliably determined. For this reason, a suitable incorporation of these stresses is required in order to establish the wall stress as a reliable diagnostic indicator. Thus this study aims to model residual stresses by incorporating them into the wall stress distribution, and to investigate the effect that parameters defining the study constitutive model have on the stress distribution. The constitutive model makes use of the Cosserat fibre continuum in order to account for mechanics of arterial walls. It was developed for cardiac tissues by Skatulla et al. (2014), but it can also be used for a preliminary investigation on arterial tissues as these two types of tissues exhibit comparable mechanics. Residual stresses are incorporated by using three problem definitions, which are derived from the opening angle method, into a three dimensional two-layer artery consisting of the media and adventitia. The first problem incorporates residual stresses that are locked within individual load-free layers. The second problem continues the first problem by incorporating residual stresses acting at the interface surface between arterial layers, and then determine the artery wall stress distribution under blood pressure. The third problem determines the wall stress in the stress-free artery under blood pressure. On the other hand, the effect of parameters defining the constitutive model is investigated by varying the size of parameters in these problems. However, the second problem is not analysed in this study because it requires an analysis implementation that could not be achieved within the study timeline. Similarly, model parameters of problems are not calibrated to available experimental data. Therefore, this study only provides qualitative results. The investigation results on the incorporation of residual stresses into the stress distribution are found to be inconclusive as they provide contradictory results. The characteristic scaling parameters are found to influence the magnitude and gradient of the stress distribution. However, these results are not conclusive to clearly define the influence. Thus it is recommended that further research be conducted in order to gain conclusive results.

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Shih, Yi-Pu. "The stress patterns and residual stresses developed in curved die upsetting." Ohio : Ohio University, 1993. http://www.ohiolink.edu/etd/view.cgi?ohiou1175883679.

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Afsaridis, Kimon. "Investigation of residual stresses generation in aluminum flywheel." Thesis, Jönköping University, Jönköping University, JTH. Research area Product Development, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-9255.

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Quality of the castings is affected by several factors which the designer should take into consideration during the product development process. Although residual stress is one of those, it is often not considered in practical computations. Hence residual stresses are one of the forgotten areas in designing of machine parts. This master thesis is focused on the investigation of residual stresses in a high pressure die casted component, with the aim of extending its service life, by taking results from the study as a feedback.

The investigation of residual stresses was done on a variety of specimens, cast aluminum flywheel, provided by Husqvarna AB. This flywheel is a component in a product of the same company.In evaluating the residual stresses in the part, two tools-simulation and physical measurement were used. Moreover, comparison with these two methods is also done at an area of interest on the flywheel. The simulation was carried out by using MAGMAhpdc-a module for high pressure die casting process, from the commercial software package MAGMAsoft; while for the physical measurements, the hole drilling method was used, a method believed to be less accurate at low stresses areas.

The findings obtained from this study show that the results from both procedures are close, with small deviations observed, which reveals the reliability of the hole drilling method even when the stress levels are low. It is also found that the compressive residual stresses dominate in the component-a preferred phenomenon with regards to residual stress.

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Anyi, Janan Toma. "Residual strength of clay at low normal stresses." Thesis, Loughborough University, 1990. https://dspace.lboro.ac.uk/2134/28319.

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Nagaralu, Ramesh. "Fatigue Crack Growth Under Residual Stresses Around Holes." MSSTATE, 2005. http://sun.library.msstate.edu/ETD-db/theses/available/etd-11112005-143754/.

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Compressive residual stresses induced by tensile overloads, compressive under loads, or by a cold-expansion process in specimens containing a circular hole and their influence on subsequent fatigue crack growth in aluminum alloys are studied. The finite element method is used to calculate residual stresses. The superposition method, which uses crack-tip stress intensity factors for cases involving remote loading and residual stresses, is used to calculate crack growth life for three kinds of tests from the literature: (1) fatigue of a circular hole specimen after an overload or under load, (2) single crack growing from a circular hole after a severe tensile overload, and (3) single crack growing from a circular hole after cold-working, reaming and notching. All specimens were subjected to subsequent constant amplitude loading. The superposition method worked fairly well for most cases, but tended to over predict fatigue life for small cracks and for cracks growing under residual stresses, which produce compressive (maximum and minimum) stress intensity factors.

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Clarin, Mattias. "High strength steel : local buckling and residual stresses." Licentiate thesis, Luleå, 2004. http://epubl.luth.se/1402-1757/2004/054.

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Paździor, Przemyslaw. "Development of residual stresses during electron beam processing." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=83922.

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In order to further the comprehension of the electron beam (EB) processing of polymers and composites, it is necessary to better understand the development of residual stresses during processing. In-situ measurement of stress development during EB irradiation is a challenging task. The instrumentation has to be adequately shielded from the high-energy electron beam. In this work, a special fixture was designed specifically to measure the warpage of a specimen throughout the EB curing process. The specimen consisted of a thin layer of epoxy resin (Tactix 123 or CAT B) embedded in a layer of glass scrim cloth, sandwiched between layers of steel and aluminum plates and also antisymmetric unidirectional carbon-epoxy laminates. The warpage of the specimens was monitored during and after irradiation at different constant dose rates. The results confirmed that the experimental instrumentation was not affected by the EB exposure and that it was possible to monitor the specimen warpage during the EB process. The results show that the EB cured specimens have lower stress-free temperature compared to equivalent thermally cured specimens. It was also shown that an increase in dose rate increased the level of residual stresses. Furthermore, the results suggest that there is a direct relation between the stress free temperature (TSF) and the temperature of the specimen at gelation (TGEL). Also, the stress free temperatures for CAT B specimens were 5ºC higher than the Tactix 123 specimens cured under the same curing conditions. Finally, a cure kinetics model for Tactix 123 was used to predict the degree of cure (~0.32) at onset of residual stress development and the results proved to be valid when compared to parallel plate rheology results.

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Preston, R. V. "Modelling of residual stresses in welded aerospace alloys." Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272727.

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Wain, Nick. "Oxide matrix nanocomposites : residual stresses and mechanical properties." Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.410715.

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Hosseinzadeh, Foroogh. "Residual Stresses in Shrink Fits and Quenched Components." Thesis, University of Bristol, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.525438.

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Amjad, K. "Study of residual stresses around cold-expanded holes." Thesis, University of Liverpool, 2018. http://livrepository.liverpool.ac.uk/3017530/.

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Split sleeve cold expansion is one of the most widely used methods in the aerospace industry to enhance the fatigue performance of fastener holes in airframe structures. The initial motivation, which led to this research programme, was to develop an understanding of the behaviour of fatigue cracks emanating from cold-expanded holes, with a particular emphasis on the influence of these cracks on the surrounding compressive residual stresses. There are two strands of the research presented in this thesis: first being related to the study of hole deformation resulting from split sleeve cold expansion; and the second one focused on the fatigue behaviour of cracks emanating from cold-expanded holes. The strain fields developed from cold expansion were measured using stereoscopic digital image correlation (DIC) technique in aluminium specimens of two different thicknesses giving thickness to hole diameter ratio of 0.25 and 1. The capability of DIC in providing full-field strain data was exploited to determine the shape and size of the plastic zones developed from cold expansion. The results showed that the existing split sleeve cold expansion process is not as effective in creating an axisymmetric compressive residual elastic stress zone around the fastener holes in thin as it is in the thick specimens. The thin specimens used in this investigation were equivalent in thickness to sheet material commonly used in an aircraft fuselage or wing skins and the results indicate that there is a need to review the use of cold expansion process using a split sleeve and mandrel for holes in thin sheets. A simple approach utilising DIC was presented to analyse the strain fields resulting from cold expansion in stacked specimens. The results showed that stacking offers some improvement in the cold expansion of thin sheet components. They also demonstrated the workability of this approach which can be applied effectively to analyse cold expansion of fastener holes associated with a real joint configuration in an airframe. The propagation of fatigue cracks initiating from the cold-expanded holes was investigated by employing the thermoelastic stress analysis (TSA) technique and their influence on the surrounding residual stresses was determined using synchrotron x-ray diffraction (SXRD) technique. A long-standing ambiguity in the literature regarding the potential relaxation of beneficial compressive residual stresses, as a result of fatigue crack propagation, was addressed; and it was established, from TSA and SXRD results, that the formation or propagation of a fatigue crack does not cause any significant relaxation of these residual stresses. The results also clearly identify the loading conditions under which the residual stresses are expected to relax. This information is important in improving the theoretical models for fatigue life assessment of cold-expanded holes. The results should also be useful for the engineers in the aerospace industry to realise the full potential of the cold expansion process and to utilise it more effectively in the manufacturing of airframes leading to improved fatigue endurance under different loading conditions.

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Sun, Xiaodan. "Residual stresses, cracking and stress intensity factors for Vickers indentations in ceramics." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:71f1d3ed-8163-4487-a81e-df09d50710ed.

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Vickers hardness indentations on AI2O3 were studied comprehensively. Beneath indentation, there is a well-defined interface between the plastic zone and the elastic region and the radius of the plastic zone is close to half the indentation diagonal length. The residual stress field around the indentations has been measured by optical fluorescence microscope (FLM) scans. Yoffe's stress model predicted higher stresses than the experimental stress results. the radial crack lengths were measured by FLM scans, and the optical microscope (OM) and SEM methods for crack length measurements were found to significantly underestimate the crack lengths. Post indentation slow crack growth was found on the radial cracks were determined. The radial-median crack system was found for alumina indentations. Lateral cracks were also found for all the indentations, and their depths were close to the half diagonal lengths. the lateral cracks joined the tips of the radial cracks and had the similar growth rates to the radial cracks. The indentation parameters of SiC and 3Y-TZP indentations were also measured. Lateral cracking was observed beneath in SiC indentations but not in case of 3Y-TZP. The depth of the lateral crack of the SiC indentation was found to be close to the half diagonal length. the residual stresses and surface profiles around SiC and 3Y-TZP indentations were measured. the lateral crack lengths of the SiC determined from the surface profiles were close to the radial crack lengths. For TZP indentations, the highest volume fraction of the monoclinic zirconia phase was found near the edge of the indentations. Surface uplifts around indentations were found to have the profiles matching with distributions of the volume fraction of the monoclinic phase. A new Vickers indentation residual stress model has been presented using assumptions based on the experimental findings on alumina indentations. The main novelty of the model is that it predicts the stresses in the presence of cracking, and is therefore testable. The residual stress model has successfully predicted the stress fields around the polycrystalline alumina and SiC indentations but failed on TZP indentations because of the lack of lateral cracking and the tetragonal-to-monoclinic phase transformation. From the residual stress model, a new formula for the indentation stress intensity factor K was derived, which provided good results for threshold stress intensity factor, K10, on alumina, and fracture toughness, KIC, for SiC, and Si3N4. Three adjustable parameters can be added to strengthen existing model.

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Sham, Man-Lung. "Underfill adhesion characteristics, residual stresses and analysis of thermal stresses in flip chip packages /." View Abstract or Full-Text, 2003. http://library.ust.hk/cgi/db/thesis.pl?MECH%202003%20SHAM.

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Farajian, Majid [Verfasser]. "Stability and Relaxation of Welding Residual Stresses / Majid Farajian." Aachen : Shaker, 2011. http://d-nb.info/1080764895/34.

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35

Wineman, Sarah J. (Sarah Johannah). "Residual stresses and web fracture in roller-straightened rail." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/26829.

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Kesler, Olivera E. (Olivera Elizabeth). "Residual stresses and properties of layered and graded coatings." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/85368.

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Lee, Beom No. "Effect of residual stresses on fracture behavior of weldments /." The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486399451960546.

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38

Erlingsdotter, Stridsman Rebecca, and Felicia Månsson. "Residual Stresses Induced by Welding in High Performance Steel." Thesis, Luleå tekniska universitet, Byggkonstruktion och brand, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-72015.

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Today, high performance steel as a construction material is treated as conventional steel in the European standards. Referring to the Eurocodes, the buckling curves for dimensioning of steel constructions only presents values up to steel grade S460, meaning that the full potential of high performance steel is not considered. If the amplitude of the residual stresses in high performance steel can be confirmed to be smaller than in conventional steel, more slender cross sections could be obtained when using high performance steel, HPS. One challenge with the residual stress patterns for HPS is its variation obtained in different studies, where new resulting residual stress patterns are found depending on plate thickness and manufacturing methods for the steel. Residual stresses in steel are stresses not associated with external forces. The stresses are instead caused by internal forces, such as differencing temperature. Residual stresses can therefore be connected to stresses due to welding. Considering HPS, it is distinctive from conventional steel in the way that it has higher performance in tensile strength, toughness, weldability, corrosion and cold formability. This study has been performed by Finite Element Modelling in the software Abaqus and by performing an experiment. The objective of this study was to find residual stress patterns and to compare the results with existing residual stress patterns according to the European Convention for Constructional Steel (ECCS) and the Swedish handbook for steel constructions provided by Boverket (BSK 07), but also to compare the results with previous studies. The influence of temperature changes due to welding was studied for a L-section made of steel S690QL, where only the longitudinal stresses were considered during the research. The numerical analysis in Abaqus was performed using a DFlux subroutine, which is written in Fortran language. Furthermore, the analysis was divided into subparts; one heat transfer analysis and two three-dimensional stress analyses for two different boundary conditions, with the purpose of obtaining results in terms of temperature and stresses for further analysis. The experimental work was performed on three specimens using Gas Metal Arc Welding, where thermocouples and strain gages were used for measuring temperature and strains respectively. Conclusions of this study were that the resulting residual stress pattern obtained the experiment was similar to the stress pattern for a L-section in BSK 07, while the resulting residual stress pattern obtained in the numerical analysis was mostly comparable to ECCS, but with similarities to BSK 07 and a previous study by Cherenenko & Kennedy (1990). Moreover, the resulting residual tensile stresses obtained in the study had the same amplitude or lower than what is specified in BSK 07.

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Lundberg, Mattias. "Residual Stresses and Fatigue of Shot Peened Cast Iron." Licentiate thesis, Linköpings universitet, Konstruktionsmaterial, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-99842.

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The complex geometry of cylinder head in heavy-duty diesel engine makes grey cast iron or compact graphite iron a perfect material choice due to its castability, thermal conductivity and damping capacity. To increase the efficiency of the engine, the fatigue property of the material needs to be improved. Shot peening is often used to increase the fatigue strength of components. The benefits are associated with the compressive stresses induced and with surface hardening. In this research project, these effects on grey and compact iron have been analyzed for different shot peening parameters using XRD, SEM and fatigue testing methods. The ultimate aim of the project is to increase the fatigue strength of cast irons by optimization of residual stresses. The XRD measurements and SEM examinations revealed that the shot peening parameters including shot size and peening intensity had significant influences on the resulted residual stresses and strain hardening while changing the coverage made little difference. Also differences in the peening results between the two materials were observed, which were ascribed to an effect of the different graphite morphology. Nevertheless, a residual stress profile similar to the one general considered to improve the fatigue strength in steels could be obtained in both grey and compact iron after shot peening. The axial fatigue testing with R=-1 on the grey iron showed that peening using large shot size and high peening intensity (heavy shot peening) resulted in a fatigue strength reduction of 15-20% in comparison with the mechanically polished surface. The negative effects are likely related to surface damage and relatively high tensile residual stresses in subsurface induced by the heavy peening. Grey cast iron has low ductility in tension and therefore tensile residual stresses may promote multiple cracking and crack networking during cyclic loading. Shot peening using much smaller shots and lower intensity (gentle shot peening) which resulted in a much smaller residual stress field gave no significant changes in fatigue strength. However, a short time annealing at 285°C of specimens being gently shot peened increased the fatigue strength roughly by 10%. The improvement could be an effect of precipitates formed due to the heat treatment, which lock the dislocation movement under cyclic loading.

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Su, Jiann-Cherng. "Residual stress modeling in machining processes." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/14030.

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Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2007.
Committee Chair: Liang, Steven Y.; Committee Member: Garmestani, Hamid; Committee Member: Huang, Yong; Committee Member: Melkote, Shreyes N.; Committee Member: Neu, Richard W. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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41

Altenkirch, Jens. "Stress engineering of friction stir welding : measurement and control of welding residual stresses." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.505389.

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Friction stir welding (FSW) is a maturing welding technique using a rotating tool for simultaneous heating and stir deforming th~ material interface to form a solid bond. Significant tensile residual stresses (RS) and component distortion may be produced even with optimized FSW parameters. Recent stress engineering techniques such as global mechanical or roller tensioning may reduce tensile RS and distortion. This dissertation reports on the first systematic investigation into the efficiency of insitu global mechanical tensioning (IS GMT) as well as roller tensioning applied in-situ (ISRT) and post welding (PWRT) for mitigation of tensile RS and plate distortion in high strength aluminium alloy plates joined by FSW. The techniques were evaluated by measuring the distribution of RS across the weld-line by means of neutron and synchrotron X-ray diffraction as well as' the levels of plate distortion. In each case the weld microstructure and hardness distribution were characterised. The data were rationalised against the ISGMT load and roller tensioning down force respectively. The results have shown that ISGMT and PWRT significantly mitigate longitudinal tensile RS and component distortion. ISGMT was found to decrease the tensile RS by an amount approximately equal to that of the load applied. Consequently, a stress free weld is produced with an ISGMT load equal to the magnitude of the weld-line RS in the as-welded condition~ PWRT decreases the tensile RS as the rolling down force increases and significant compression may be introduced once a certain magnitude is exceeded. ISRT, at least for the range tested, was found to be less effective. The component distortion reduced along with RSÇ'ú mitigation. No effects on the microstructure or hardness distribution due to mechanical stress engineering were observed. Furthermore, it was demonstrated that in order to make accurate stress measurements by diffraction, the effect of precipitation on the stress free lattice spacing must be taken into account for age hardening alloys. In order to complete this study an automated robotic sample manipulation system was developed. Finally, the degree of stress relaxation occurring on cutting down large welds was evaluated by progressively shortening test welds and determining the RS for each length. The amount of stress relaxation for each weld follows the same behaviour and appears to depend on the width of the tensile weld zone only.

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Chipanga, Tendai. "Determination of the accuracy of non-destructive residual stress measurements methods." Thesis, [S.l. : s.n.], 2009. http://dk.cput.ac.za/cgi/viewcontent.cgi?article=1100&context=td_cput.

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43

Guo, Sheng. "Fluorescence microscopy investigation on residual stresses in alumina-based ceramics." Thesis, University of Oxford, 2008. http://ora.ox.ac.uk/objects/uuid:d617f5b2-e432-4890-b3bc-3c8d93381cf6.

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Grinding/polishing and indentation induced residual stresses were measured by confocal Cr³⁺ fluorescence microscopy with high spatial resolution (~2 μm),obtaining local stress variation information rather than the mean stress averaged over a large sampling volume as is measured by other techniques. Due to the translucency of alumina materials, a substantial portion of the fluorescence signal comes from beneath the surface of the specimen. A probe response function (PRF) was developed taking account of microscope resolution, refraction, absorption and scattering, to quantitatively describe where the collected signal came from. It described the fluorescence intensity variations against defocus distance very well for a range of materials including sapphire, ruby, polycrystalline alumina and AI₂O₃/SiC nanocomposites. Large variations in the residual stresses on ground and polished surfaces were observed, owing to the surface fracture and pullouts. The broad peaks and narrow peaks separated from the spectra collected near the ground/polished surfaces physically represented the two distinct regions in the ground region: a plastically deformed surface layer and the elastically deformed material underneath. A model for the residual stress field taking into account the pullout was proposed using an array of virtual dislocations. The model agreed with the experimental results well when the PRF was included. Tensile stresses were detected on the ground surfaces of polycrystalline aluminas and 2 vol.% SiC nanocomposite, but not on the polished surfaces of polycrystalline aluminas or ground surfaces of 5 and 10 vol.% SiC nanocomposites. This was explained in terms of difference in the amount of pullouts on the surfaces. The depth of deformation was deeper in the ground polycrystalline alumina compared to the polished condition; the depth of deformation in alumina and the AI₂O>sub>3/SiC nanocomposites were similar (~1 μm) while the compressive stresses in the nanocomposites were greater owing to the reduction in pullout. The main difference between ground alumina and AI₂O₃/SiC nanocomposites was the brittle fracture behavior rather than the plastic deformation. Line scans and area mapping were carried out on 1 kg loaded Vickers indentations of alumina-based ceramics. Tensile stresses were found at the tips of radial cracks and lateral cracks and compressive stresses were found around the indent impression. The line scan results in the elastic regions agreed qualitatively with Yoffe's model and the quantitative discrepancy was attributed mainly to the cracking that relaxed the stresses. The differences in residual stresses between alumina and AI₂O₃/SiC nanocomposites were small if measured with high spatial resolution but it would be exaggerated with lower resolution.

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44

Östlund, Magnus. "Residual stresses in paperboard and the influence of drying conditions." Doctoral thesis, KTH, Solid Mechanics (Div.), 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-469.

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The drying sequence in the manufacturing process for paperboard involves evaporation of water, primarily from within the fibres. The vapour is then transported out of the web by pressure or concentration gradients. As the moisture transport from the paper web to the ambient is quicker than the moisture transport within the fibre network to the surfaces of the web, moisture gradients develop through the thickness of the web. This work concerns effects on the mechanics of paper drying from the variation in moisture through the relatively thin structures of paper and paperboard.

Distributions of inplane residual stresses through paper materials in the unloaded state after drying are believed to be caused by the varying moisture through the thickness during drying. The distributions in general exhibit compressive stress near the board surfaces and tensile stress in the interior of the board. This may be modified after drying and is also affected by structural variation in the material between different plies of multi-ply paperboards.

The stress development during drying is important because it influences the resulting material properties of the paper and because it can lead to curl, which is a quality problem. The residual stresses themselves are an error source in simulation or evaluation of the mechanical behaviour of paper.

In this work, residual stress distributions in paperboard were determined experimentally, to clarify the mechanisms of residual stress build-up. An experimental method for such tests was also developed. Based on the experimental findings, the mechanics of paper drying was modelled and the stress build-up simulated. Simulation offers a way of studying how the properties of paper develop during drying of wet paper webs.

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45

Aleong, Chris J. "Experimental determination of residual stresses in filament wound composite rings." Thesis, University of Ottawa (Canada), 1986. http://hdl.handle.net/10393/4818.

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46

Östlund, Magnus. "Residual stresses in paperboard and the influence of drying conditions /." Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-469.

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47

Shah, Syed Mushtaq Ahmed. "Prediction of residual stresses due to grinding with phase transformation." Phd thesis, INSA de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00679816.

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Grinding is a commonly used finishing process to produce components of desired shape, size and dimensional accuracy. The ultimate goal is to have the maximum workpiece quality, minimum machining time and high economic efficiency by making a selective adaptation of the possible process strategy and chosen parameter selection. The focus of this study arose from a limitation that challenges the grinding industry. The production rate of the ground parts is generally constrained by surface topography and subsurface damage appearing as residual tensile stress, localized burns, and phase transformation induced micro and macro-cracking. This motivates the need for a reliable numerical modelling to simulate the grinding process. The numerical model sought should be able to predict not only the required grinding residual stresses but also the deformation history. The objective of this thesis is to build up a reliable finite element model for grinding-induced residual stress analysis and thus to explore thoroughly the mechanisms in terms of grinding conditions. The variations of the residual stresses and strains at integration points have been examined, and the effects of the friction coefficient (µ), Peclet number (Pe), non dimensional heat transfer coefficient (H) and different magnitudes of input heat flux (Q) on both the microstructure and the residual stress state are analyzed. Finally, based on the new findings in this research, a more comprehensive methodology is suggested for further study.

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Zheng, Tieyu. "A study of residual stresses in thin anisotropic (silicon) plates." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17516.

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Rahimzadeh, Tanaz. "Finite element modelling of residual stresses due to shot peening." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=40773.

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Shot peening is a surface enhancement process used to improve the fatigue strength of metals by introducing beneficial compressive residual stresses on the surface. Shot peening is widely used in a number of industrial applications, including gas turbine engines. However, the fatigue life improvement gained via shot peening is not explicitly accounted for in current engine components life prediction processes. Therefore, there is a significant potential for increasing the predicted damage tolerance capabilities of engine components if beneficial residual stress considerations are incorporated into the life prediction methodology. In this work, a finite element model was developed to apply residual stresses from shot peening as initial stresses to the finite element mesh. The proposed technique was validated using a simple numerical example and the sensitivity of the resulting stress distribution in the model was investigated. The capability of the proposed strategy was also demonstrated on a fatigue test specimen containing high stress concentration features, broadly used in gas turbine engine applications. With the proposed technique, the applied residual stress profile is not self-equilibrating. Therefore, a redistribution of stresses was found in the model after the application of the boundary conditions. The depth and magnitude of the tensile residual stresses had a significant influence on the resulting redistribution of stresses.
Le grenaillage est un traitement de surface visant à améliorer la résistance en fatigue des métaux en introduisant des contraintes résiduelles en compression sur la surface. Le grenaillage est largement utilisé dans de nombreuses applications industrielles particulièrement dans les moteurs à turbine à gaz. Cependant, l’effet des contraintes résiduelles de n’est pas explicitement inclus dans les analyses de la prédiction de la résistance en fatigue des composantes. Ceci entraîne des prédictions très conservatrices de la vie en fatigue des pièces. Dans ce travail, un modèle d'analyse par éléments finis a été développé en applicant les contraintes induites par le grenaillage comme contraintes initiales dans le modèle. La méthode d’analyse proposée a été validée par un exemple numérique unidimensionnel. L’effet de la distribution des contraintes initiales sur la répartition des contraintes finales à été étudié. Un exemple de calcul a été effectué pour un échantillon utilisé pour mesurer la vie en fatigue des matériaux utilisés dans les moteurs à turbine à gaz. Avec la technique proposée, la contrainte initiale appliquée n’est pas en équilibre et ceci provoque une redistribution des contraintes dans la pièce. Ainsi, la profondeur et l’amplitude des contraintes résiduelles ont un effet important sur la redistribution des contraintes initiales dans la pièce.

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Tropsa, Vlado. "Predicting residual stresses due to solidification in cast plastic plates." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271561.

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Dissertations / Theses on the topic 'Residual Stresses'

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