Papers by Keyword: Failure Strain

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Authors: Seung Bum Kwak, Nak Sam Choi
Abstract: Coolant rubber hoses for automobile radiators under thermal and mechanical loadings can be degraded and thus failed due to the influences of contacting stresses of air, coolant liquid and to the locally formed electricity. In this study, degradation behavior of the radiator hose made of EPDM rubber was evaluated. The thermo-oxidative aging test showed that the surface hardness IRHD of the rubber increased together with a reduction of failure strain. By the electro-chemical test it was shown that the penetration of coolant liquid into the skin of the rubber hose arose inducing an increase in weight of specimens as well as a decrease in failure strain and IRHD hardness. The penetration of coolant liquid altered considerably the micro-structure and the micro-hardness distribution along the depth in the rubber hose. On the basis of the above results failure mechanisms of degraded EPDM rubbers were suggested according to the kinds of contacting stresses.
Authors: Xiang Tian Xu, Cai Xia Fan, Jun Hong Yuan
Abstract: The uniaxial compressive tests on frozen loess with different ice content under loading rate of 1.25mm/min at-6°C are carried out to investigate the effects of ice content on the mechanical behavior of ice. The influence of ice content on stress-strain, elastic modulus, strength and failure strain of frozen loess are analyzed based on the experimental data. The results show that strength and failure strain increase with increasing of ice content. The elastic modulus first increase and then decrease with increasing of ice content.
Authors: Omid Azadegan, Jie Li, S. Hadi Jafari, Gang Ren
Abstract: Construction on problematic and soft soils has always been considered a challenging task by the geotechnical engineers. Such soils can be treated with traditional lime and cement stabilization. However in some cases using geogrid reinforced lime and cement treated materials can be very effective, especially in case of seismic or dynamic loads. In this research, a series of laboratory testing has been carried out to investigate mechanical properties of lime and cement treated granular materials with and without geogrid reinforcing layers. The results of the unconfined compressive tests show that geogrid reinforcement improves the ductility of the treated materials. However, it would not develop the compressive strength in many of used mix Designs. The investigations reveal that the mix design for lime and cement treatment must be selected accurately by considering the natural beds conditions to achieve the best possible results from stabilization procedure.
Authors: Song Gao, Ya Bin Wang, Xiu Feng Li
Abstract: Penetration is an important topic in the military and protection engineering field. Based on *MAT_PLASTIC_KINEMATIC of LS-DYNA program, this report studies effects of failure strain of the material parameters on structure of penetrating projectile. By establishing a group of numerical models about 45 steel hemispherical projectile penetrating semi-infinite concrete targets, this research aimed at analyzing effects of different failure strain values related to the destruction of the internal bracket structures of this projectile. At the same time, it studied the criterion of failure on finite dynamic program. The numerical results show that the use of failure strain in this model can well simulate damage of internal bracket structures of the projectile. Test was carried on based on this conclusion, which showed that bracket plate is subjected to shear failure in process of penetration, and numerical simulation was consistent with the experimental results.
Authors: Matthieu De Beule, Peter Mortier, Jan Belis, Rudy Van Impe, Benedict Verhegghe, Pascal Verdonck
Abstract: A common treatment to restore normal blood flow in an obstructed artery is the deployment of a stent (i.e. small tube-like structure). The vast majority of stents are crimped on a folded balloon and laser cut from 316L stainless steel tubes. Although, several numerical studies (exploiting the Finite Element Method) are dedicated to the mechanical behaviour of balloon expandable stents, there seems to be no consensus regarding the mechanical properties to describe the inelastic material behaviour of SS316L. Moreover, as the typical dimensions of stent struts (e.g. 100 μm for coronary stents) are of a similar order of magnitude as the average grain size in stainless steel (i.e. 25 μm), continuum approaches relying on macroscopic material properties may be questionable. In addition, an experimental study on stainless steel stent strut specimens showed a size-dependency of the failure strain. In this study the impact of the magnitude of the yield stress on the stent expansion behavior is examined. An increase in the yield stress (from 205 N/mm² to 375 N/mm²) results in an increase of the pressure (from about 0.3 N/mm² to approximately 0.4 N/mm²) which the clinician needs to exert for the balloon to unfold and to reach its cylindrical expanded shape. Furthermore, the effect of the size dependency behavior of the material is studied by monitoring the nominal strain during stent expansion. The maximum value of the nominal strain in the expanded stent (e.g. εn = 23 %) does not exceed the critical value of the failure strain, (i.e. εn = 33 %), moreover the critical values are nowhere exceeded in the whole stent during the expansion. Our numerical results - accounting for the presence of the balloon in its actual folded shape - correspond very well with pressure/diameter data supplied by the manufacturer. Consequently, this study shows that the free expansion of new generation balloon-expandable stents can be studied accurately with computational analysis based on the Finite Element Method (FEM) and relying on macroscopic material properties. In this context, there is no need to implement a size-based constitutive material model, but before accepting the results of the study, one should check in any case the maximum strain against the limit as shown above.
Authors: Michael Schütze, Mario Rudolphi
Abstract: A new model concept for predicting mechanical oxide scale failure is applied to Al2O3, Cr2O3, Fe3O4 and NiO. The calculated critical strain values are plotted versus the physical defect size using a simplified version of the original h-w-concept. A limited number of experimental data existing in the literature were entered into the plots and yield satisfactory agreement with the model data. Future efforts should focus on extending the experimental data basis and converting these data into h-values for the model.
Authors: D.A. Cendón, Jose M. Atienza, Manuel Elices Calafat
Abstract: The stress-strain curve of a material is usually obtained from the load-displacement curve measured in a tensile test, assuming no strain localisation up to maximum load. However, strain localisation and fracture phenomena are far from being completely understood. Failure and strain localisation on plane tensile specimens has been studied in this work. A deeply instrumented experimental benchmark on steel specimens has been developed. Surface strain fields have been recorded throughout the tests, using an optical extensometer. This allowed characterisation of the strain localisation and failure processes. Tests have been numerically modelled for a more detailed analysis. Preliminary results show a substantial influence of geometrical specimen defects on the strain localisation phenomena that may be critical on the stress-strain curves obtained and in the failure mechanisms.
Authors: Kunio Takekoshi, Kazukuni Niwa
Abstract: High-speed tensile tests were carried out to investigate strain rate effect on both yield stress and failure strain using ASTM D1822 Type-S specimens made of polycarbonate. Based on test results, parameters for a material model suitable for polymers are determined, and numerical analysis is carried out to simulate test results. The material model is used to simulate tensile test using a dog-bone specimen and Charpy test other than the tensile test of Type-S specimens. It is found that good predictions can be obtained when rate dependent material parameters are used. Further, the high-speed tensile test considered in the present study is suitable for selection of parameters for material modeling of polymers for impact analysis.
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