Calorimetric consequences of thermal softening in Johnson–Cook’s model

At high loading rates, the development of adiabatic shear bands in metals is conventionally attributed to the strong interactions induced by viscoplastic dissipation within the bands and thermal softening effects. The rheological equation proposed by Johnson and Cook takes both viscoplastic hardening and thermal softening into account. The present paper reviews and includes this equation into a thermodynamic framework in order to analyse the energy impacts of thermal softening. Indeed this latter implies the existence of a ther-momechanical coupling source, probably non-negligible and which must be considered when estimating temperature variations induced by shear band development

The role of MYC-EGR1 Pathway in Colorectal Cancer Development and its Relationship to Wnt Signaling

Lexi Chrysochoos, Emily Abdoney, and Erick Spears The Role of MYC-EGR1 Pathway in Colorectal Cancer Development and its Relationship to Wnt Signaling Colorectal tumors show high levels of Wnt pathway activity, most often due to an initiating mutation in critical Wnt pathway components. Wnt pathway activation leads to b-catenin-driven expression of genes that generally stimulate cell cycle progression. One such Wnt pathway target gene is MYC, a well described oncogene involved in many cancers, including colorectal. MYC is known to stimulate proliferation but in certain cellular contexts, can stimulate apoptosis by stimulating the expression of EGR1. This is termed a noncanonical MYC target gene because EGR1 lacks typical MYC binding elements in its promoter. This unique MYC-EGR1 pathway is activated in specific cellular contexts, lacking appropriate p53 activity, often associated with colorectal tumorigenesis. In these experiments, sister HCT116 human colorectal cancer cell lines were treated with shRNA to employ RNA interference targeting MYC or EGR1 to assess the roles these genes might play in colorectal cancer cell proliferation. b-catenin wildtype and mutant HCT116 cells were treated with a non-targeting (scramble, control) shRNA, MYC shRNA, and EGR1 shRNA to specifically and temporarily target the expression of these gene. After transduction, cultures were grown, and cells were counted to assess proliferation of these cell lines with the specific interruptions in gene expression. The goal of our experiment was to evaluate the proliferation of these cells after transduction with targeted shRNAs and assess any impact that MYC and EGR1 have on proliferation in this cellular context. As the MYC-EGR1 pathway has also been shown to stimulate apoptosis in cells lacking functional p53, we also performed an apoptosis analysis and evaluated the propensity of the cell lines to apoptosis. These experiments give further insight into the role of the MYC-EGR1 pathway in colorectal cancer development and its relationship in to the Wnt signaling pathway in colorectal cancer cells

Effect of time and thermo-mechanical couplings on polymers

National audienceAnalysis of the thermo-mechanical behaviour of polymers has been and still is the subject of many rheological studies both experimentally and theoretically. For small deformations, the modelling framework retained by rheologists is often of linear visco-elasticity, which led to the definition of complex modules and used to identify the glass transition temperature as the so called rule of time-temperature superposition. In this context, the effects of time are almost unanimously associated with viscous effects. It has also been observed that the dissipative effects associated with viscous effects are often very small compared to the coupling of sources indicating a high sensitivity of polymeric materials to temperature variations. This work is mainly focused on establishing the exact role of coupling effects, which also induce the effect of time. Using traditional experimental methods of visco-analysis (DMTA) and via an energy analysis of the behaviour, the goal of the thesis is to try to restate the time-temperature equivalence rule under the Thermodynamics of Irreversible Processes, taking into account the dissipative effects and coupling induced process deformation

POD preprocessing of IR thermal data to assess heat source distributions

International audienceInfrared thermography is a useful imaging technique for analyzing the thermomechanical behaviour of materials. It allows, under certain conditions, surface temperature monitoring and, via a diffusion model, estimation of heat sources induced by dissipative and/or thermally coupled deformation mechanisms. However, the noisy and discrete character of thermal data, the regularizing effect of heat diffusion and heat exchanges with the surroundings complicate the passage from temperature to heat source. The aim of this paper is to show that the prior use of reduced-basis projection of thermal data improves the signal-to-noise ratio before estimating the heat source distributions. The reduced basis is generated by proper orthogonal decomposition (POD) of physically-admissible thermal fields. These fields are solutions of ideal diffusion problems related to a set of putative heat sources. preprocessing is applied to different direct methods (finite differences, spectral solution, local least-squares fitting) already used in the past. The gain of this preprocessing is determined using a numerical penalizing benchmark test. The methods are finally compared using data extracted from a dynamic cyclic test on a pure copper specimen

10/08/1996 - EIU Homecoming Features Movie Theme.pdf

During the high cycle fatigue of aluminium alloys, an energy dissipation occurs. This dissipation is hard to be estimated because of the high diffusivity of such alloys and the importance of the thermoelasticity effects in comparison with others standard metallic materials (e.g., steels). Nevertheless the study of the energy balance gives valuable information about the nature of deformation mechanisms facilitating the construction of constitutive models associated with the microplasticity and damage of the aluminium alloy. In this work, the different energies involved in the energy balance were deduced from two complementary imaging techniques. The dissipation and thermoelastic sources were derived from an infrared thermography system, while the deformation energy was estimated from a digital image correlation system. Three tests with various loading blocks were carried out and a comparison between deformation and dissipation energies was systematically performed. (C) 2009 Elsevier Ltd. All rights reserved

Fracture of heterogeneous graded materials : from microstructure to structure

10.1016/j.engfracmech.2007.07.017This paper presents a new computational approach dedicated to the fracture of nonlinear heterogeneous materials. This approach extends the standard periodic homogenization problem to a two field cohesive-volumetric finite element scheme. This two field finite element formulation is written as a generalization Non-Smooth Contact Dynamics framework involving Frictional Cohesive Zone Models. The associated numerical platform allows to simulate, at finite strain, the fracture of nonlinear composites from crack initiation to post-fracture behavior. The ability of this computational approach is illustrated by the fracture of the hydrided Zircaloy under transient loading

Damage analysis and fracture toughness evaluation in a thin woven composite laminate under static tension using infrared thermography

This work deals with the issue of damage growth in thin woven composite laminates subjected to tensile loading. The conducted tensile tests were monitored on-line with an infrared camera, and tested specimens were analysed using Scanning Electron Microscopy (SEM). Combined with SEM micrographs, observation of heat source fields enabled us to assess the damage sequence. Transverse weft cracking was confirmed to be the main damage mode and fiber breakage was the final damage leading to failure. For cracks which induce little variation of specimen stiffness, the classic “Compliance method” could not be used to compute energy release rate. Hence, we present here a new procedure based on the estimation of heat source fields to calculate the energy release rate associated with transverse weft cracking. The results are then compared to those computed with a simple 3D inverse model of the heat diffusion problem and those presented in the literature

Influence of Dissipated Energy on Shear Band Spacing in HY100 Steel

International audienceTo analyze the formation of multiple shear bands in HY-100 steel, we consider an infinitely extended layer of finite thickness subjected to shear loading. The perturbation approach, associated with numerical methods, is used to determine the instability modes. The criteria of Wright-Ockendon and Molinari are used to determine the shear band spacing. The hypothesis consisting in considering the proportion of plastic work dissipated as heat (quantified by the Taylor-Quinney coefficient B) as independent of the loading path is now recognized as highly simplistic. The present work attempts to provide a systematic approach to the inelastic heat fraction evolution for a general loading within the framework of thermoviscoplastic standard modeling including a number of material parameters as strain hardening, strain rate sensitivity, thermal softening. The effect of each material parameter on the shear band spacing is determined by using a power law constitutive relation. The Johnson Cook and power law models are used to illustrate the influence of the constitutive relation on the results for the adiabatic shear band spacing, by studying the response of HY-100 steel. We have compared our results with available experimental results in the literature over a very wide range of strain rate (103 -105 s-1) . In this study, we show that the variation of the Taylor-Quinney parameter, B(y), as a function of shear strain is an important parameter that plays a significant role in the calculation of the shear band spacing

Addendum to 'The equivariant spectral function of an invariant elliptic operator'

Let $M$ be a compact boundaryless Riemannian manifold, carrying an effective and isometric action of a torus $T$, and $P_0$ an invariant elliptic classical pseudodifferential operator on $M$. In this note, we strengthen asymptotics for the equivariant (or reduced) spectral function of $P_0$ derived previously, which are already sharp in the eigenvalue aspect, to become almost sharp in the isotypic aspect. In particular, this leads to hybrid equivariant $L^p$-bounds for eigenfunctions that are almost sharp in the eigenvalue and isotypic aspect.Comment: 14 pages. arXiv admin note: text overlap with arXiv:1512.0219