• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.4
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• pp.353-362
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• 2016

An accurate hysteresis model of an elastomer is important for quantifying viscoelastic energy loss. We suggest a highly nonlinear hyper-viscoelastic constitutive model of elastomers. The model captures a nonlinear viscoelastic characteristic by combining Yeoh's hyperelastic model and Hoofatt's hysteresis model used Neo-Hookean hyperelastic model. Analytical and numerical models were generated from uniaxial cyclic tests of an elastomer under a sinusoidal load with a mean strain of 150%, amplitudes of 20~80%, and frequencies of 0.02~0.2Hz. The viscoelastic model can highly capture the viscoelastic energy loss up to a strain of 230%.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2002.05a
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• pp.79-84
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• 2002

The bottom-leaded plastic(BLP) packages have attracted substantial attention since its appearance in the electronic industry. Since the solder materials have relatively low creep resistance and are susceptible to low cycle fatigue, the life of the solder joints under the thermal loading is a critical issue for the reliability The represent study established a finite element model for the analysis of the solder joint reliability under thermal cyclic loading. An elasto-plastic constitutive relation was adopted for solder materials in the modeling and analysis. A 28-pin BLP assembly is modeled to investigate the effects of various epoxy molding compound, leadframe materials on solder joint reliability. The fatigue life of solder joint is estimated by the modified Coffin-Hanson equation. The two coefficients in the equation are also determined. A new design for lead is also evaluated by using finite element analysis. Parametric studies have been conducted to investigate the dependence of solder joint fatigue life on various package materials.

• Tunnel and Underground Space
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• v.11 no.3
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• pp.225-236
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• 2001

The roughness of rock joint is one of the most important parameters in developing the shear resistance and the tendency of dilation. Due to the damage accumulated with shearing displacement, the roughness angle is lowered continuously. It is known that dilation, shear strength hardening, and softening are directly related to the degradation of asperities. Much effort has been directed to incorporate the complicated damage mechanism of asperities into a constitutive model fur rock joints. This study presents an elasto-plastic formulation of joint behavior including elastic deformability, dilatancy and asperity surface damage. It is postulated that the plastic portion of incremental displacement 7an be decomposed into contributions from both sliding along the asperity surface and damage of asperity. Numerical cyclic shear tests are presented to illustrate th? performance of the derived incremental stress-displacement relation. A laboratory cyclic shear test is also simulated. Numerical examples reveal that the elasto-plastic joints model is promising.

• Geomechanics and Engineering
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• v.9 no.6
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• pp.729-742
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• 2015

The aim of the present work was the study of instability in a loose sand from Les Dunes beach in Ain Beninan, Algeria, where the Boumerdes earthquake occurred in 2003. This earthquake caused significant structural damages and claimed the lives of many people. Damages caused to infrastructures were strongly related to phenomena of liquefaction. The study was based on the results of two drained and six undrained triaxial tests over a local sand collected in a region where liquefaction occurred. All the tests hereby analyzed followed compression stress-paths in monotonic conditions and the specimens were isotropically consolidated, since the objective was to study the instability due to static loading as part of a more general project, which also included cyclic studies. The instability was modeled with the second-order work increment criterion. The definition of the instability line for Les Dunes sand and its relation with yield surfaces allowed the identification of the region of potential instability and helped in the evaluation of the susceptibility of soils to liquefy under undrained conditions and its modeling. The dilatancy rate was studied in the points where instability began. Some mixed tests were also simulated, starting with drained conditions and then changing to undrained conditions at different time steps.