Papers by Keyword: Thermomechanics

Abstract: Ti-6Al-4V ELI is one of the titanium alloys commonly used as an implant material for its good biocompatibility. However, it has problems related to its corrosion behavior, especially when it is used for a long time. This study aimed to analyze the corrosion behavior of the implant material Ti-6Al-4V ELI in Hanks’ Balanced Salt Solution (HBSS) for a certain period, using the weight loss method in HBSS as the corrosive medium at 37°C. The immersion time was varied from two, four, until six weeks. Before immersion, the sample was thermomechanically treated with a combination of solution heat treatment at a temperature of 950°C and a holding time of 1 hour, water quenching, plastic deformation with deformation variations of 10%, 15%, and 20%, and, finally, aging heat treatment at a temperature of 550°C and holding time for 1.5 hours. The study results show that thermomechanical treatment and increased plastic deformation could reduce the corrosion rate and the metal ions released into the solution. These findings were evidenced by the corrosion rates of the pre-thermomechanical and the thermomechanical Ti-6Al-4V ELI with deformations of 10%, 15%, and 20% at the 6-week immersion of 6.57 x 10^-6 mmpy, 4.27 x 10^-6 mmpy, 3.89 x 10^-6 mmpy, and 2.76 x 10^-6 mmpy, respectively, and the metal ions released of 7.3 μg/L, 7 μg/L, 6.3 μg/L, and 6 μg/L, respectively. The corrosion rate of Ti-6Al-4V ELI under thermomechanical treatment, namely 2.76 x 10^-6 mmpy, was the lowest compared to other materials in HBSS, while the highest one was that of Ti-6Al-7Nb of 3.05 x10^-2 mmpy. In addition, the study results show that Ti-6Al-4V ELI under thermomechanical treatment is the best material compared to others for biomedical applications, based on corrosion resistance and metal ions released into HBSS.

Abstract: The threshold shear strain is a fundamental property of the soil behavior subjected to cyclic loading. Starting from the unloading and reloading hysteretic curves of dynamic Ramberg-Osgood model, construct small-strain dynamic dissipation function and explain small-strain dynamic characteristics by use of the skeleton curve back stress assumption. The plotting results of yield curves in true stress space indicate that there exist two threshold shear strains which are defined as the first threshold shear strain and the second threshold shear strain respectively which represent boundaries between fundamentally different dynamic characteristics of cyclic soil behavior. The yields of soil are controlled by the constant friction coefficient, the variable friction coefficient and dilatancy-related microstructural changes respectively. Both the first threshold shear strain and the second threshold shear strain do depend significantly on the maximum dynamic shear modulus coefficient and exponent. Comparison between the two threshold shear strain values and shear modulus reduction curves obtained on exactly the same soils confirms that the soil behavior is considerably at nonlinear at , the secant shear modulus, Gs, of the four soils studied is between 0.6 and 0.8 of its maximum value.

Abstract: This work deals with a methodology to evaluate residual stresses within microelectronic devices by using MOS (Metal Oxide Semiconductor) rosette stress sensors. The stress tensor was evaluated by carrying out electrical measurements on test vehicle: the bridge from electrical to stress values was ensured by the piezoresistive relations and, prior to further in-house calibration, coefficients from literature were employed. For correlation purpose, numerical simulations were performed in order to evaluate stresses induced by TSV (Through Silicon Via). In this paper, the whole framework is described, and stress fields evaluated from in-situ electrical measurements on CMOS65 rosette sensor are compared to simulated ones. Some of the ultimate targets of this work are to develop a validated framework to deeply understand TSV induced thermo-mechanical stresses and to allow design rules definitions for products reliability and transistor performances.

Abstract: Shape memory polymers (SMPs) possess the capability of shape frozen and recovery via thermomechanical processing. Over the last decades, great work has focused on their macro-properties. In order to have a better understanding of the micro-deformation mechanisms of this class of functional materials, the thermomechanical behaviors of three types of epoxy SMPs with varied curing agent contents were simulated by the molecular dynamics (MD) method. Special attention was paid on the different responses of the materials in the rubbery and glassy states. Moreover, structure-property analyses were presented.

Abstract: In order to construct a constitutive model taking into the effect of both the fabric tensors and their evolution modes, this paper links modern ideas of thermomechanics opinion to the theory of fabric tensors. The anisotropic dissipation incremental function of modified Cam-clay constitutive model considering the effect of fabric characteristic can be obtained by establishing the relation between microstructure and plastic volume strain. After discussing the yield surfaces in the dissipative and the true stress space from the viewpoint of the evolution mode of the fabric tensors, the results indicate that the slope of the normal consolidation line and the critical state line will be governed by changes of void fabric. The model successfully captures most salient behaviors of granular materials related to fabric issues. In the dissipative stress space, the void of granular materials can rearrange and show more anisotropic. In the true stress space, fabric not only affects the deflection of the yield surface, but also affects the hardening rule.

Abstract: Significant advances in the mechanical design of ceramic parts were realized since the pioneer works of Kingery and Hasselman to define thermal shock resistance. But for high heterogeneous refractories and contrasted local phase properties the use of these criteria is not always convincing because the assumptions made are too simplicist. First, we underline how thermal shock resistance parameters helped to improve the global performance of ceramics and make some comments on their limitations for refractory materials. Then we show how numerical tools are useful for the design of refractory structures at high temperatures through several approaches we have developed for refractory structures: prediction of macroscopic thermal shock resistance of heterogeneous refractories using multi-scale analysis, finite element methods applied to a specific structure considering either a two-scale approach to describe the thermo-elastic quasi brittle behavior of heterogeneous materials, at the macroscopic scale approach considering homogeneous microstructure.