Stationary shocks in periodic highly nonlinear granular chains

We study the existence of stationary shock waves in uniform and periodic heterogeneous highly nonlinear granular chains governed by a power-law contact interaction, comparing discrete and continuum approaches, as well as experiments. We report the presence of quasisteady shock fronts without the need for dissipative effects. When viscous effects are neglected, the structure of the leading front appears to be solely the result of dispersive effects related to the lattice wave dispersion and, for heterogeneous bead chains, to the impedance mismatch between material domains. We report analytically and numerically the shock-width scaling with the variation in the particles periodicity (cell size) and compare the obtained results with experiments. We check the state (−) behind the shock front via quasistatic compression analysis and report a very good agreement between theory and numerical data

Thermomechanical modeling of orthogonal cutting including the effect of stick-slide regions on the rake face

An orthogonal cutting model including the primary and secondary shear zones is pre-sented in this study. The primary shear zone is modeled by a thermomechanical model where the rake contact is represented by two regions of respectively sticking and sliding friction. The model is compared with experimental results in terms of shear stress, shear angle, and cutting force predictions. Overall a good agreement is observed

Numerical and analytical modeling of orthogonal cutting : The link between local variables and global contact characteristics

The response of the tool–chip interface is characterized in the orthogonal cutting process by numerical and analytical means and compared to experimental results. We study the link between local parameters (chip temperature, sliding friction coefficient, tool geometry) and overall friction characteristics depicting the global response of the tool–chip interface. Sticking and sliding contact regimes are described. The overall friction characteristics of the tool are represented by two quantities: (i) the mean friction coefficient qualifies the global response of the tool rake face (tool edge excluded) and (ii) the apparent friction coefficient reflects the overall response of the entire tool face, the effect of the edge radius being included. When sticking contact is dominant the mean friction coefficient is shown to be essentially the ratio of the average shear flow stress along the sticking zone by the average normal stress along the contact zone. The dependence of overall friction characteristics is analyzed with respect to tool geometry and cutting conditions. The differences between mean friction and apparent friction are quantified. It is demonstrated that the evolutions of the apparent and of the mean friction coefficients are essentially controlled by thermal effects. Constitutive relationships are proposed which depict the overall friction characteristics as functions of the maximum chip temperature along the rake face. This approach offers a simple way for describing the effect of cutting conditions on the tool–chip interface response. Finally, the contact length and contact forces are analyzed. Throughout the paper, the consistency between numerical, analytical and experimental results is systematically checked

On the longitudinal impact of two phase transforming bars. Elastic versus a rate-type approach. Part II: The rate-type case

AbstractWe study the propagation of phase transformation fronts induced by the longitudinal impact of two shape memory alloy bars modeled by a general form of a rate-type approach to non-monotone elasticity. We illustrate that such a rate-type law should be seen like a kinetic law for phase transformation. This investigation continues in a comparative way the analysis of the dynamic theory of elastic bar considered in Part I in relation with a viscosity criterion. We focus here on mathematical, thermodynamical and experimental aspects related with the wave structure which accompanies both the forward and reverse transformation. We analyze the propagation of disturbances in a pure phase near and far from their sources, that is the instantaneous waves and the delayed waves as well as the traveling wave solutions and the accompanying dissipation. In the numerical experiments one focuses on the influence of the impact velocity on the way the phase boundary propagates and on the results which can indicate indirectly the existence of a phase transformation like the time of separation, the velocity–time profile at the rear end of the target and the stress history at the impact face

Usinage à Grande Vitesse - Modélisation analytique de la coupe orthogonale et validation expérimentale

Nous présentons dans cette étude le modèle analytique de la coupe orthogonale développé au LPMM. La modélisation de la bande primaire de cisaillement est couplée à une analyse thermique à l'interface outil-copeau. Une loi de frottement dépendante de la température moyenne est introduite afin de reproduire les observations expérimentales. En effet, lorsque la vitesse de coupe ou l'avance augmentent, la température tend à croître et ainsi, à réduire le coefficient de frottement, et les efforts de coupe. Pour toutes les conditions de coupe, un bon accord est observé entre la modélisation et les résultats expérimentaux pour l'acier AISI 1050

Stability analysis for forging of porous bodies

The continuum theory of sintering is used for the analysis of the stability of forging of a cylindrical powder specimen. The constitutive properties of the powder material are assumed to follow a power-law creep relationship. Temperature-coupled linear non-uniform stability analyses are carried out. Stability maps are obtained for forging of copper powder components

Identification of the critical wavelength responsible for the fragmentation of ductile rings expanding at very high strain rates

This work examines the mechanisms governing the fragmentation of ductile ringsexpanding at very high strain rates. Based on previous works three different methodologies have been addressed, namely: fully 3D finite element computationsof the radial expansion of ductile rings, numerical simulations of unitary axisymmetric cells with sinusoidal spatial imperfections subjected to tensile loading and a linear perturbation technique derived within a quasi-1D theoretical framework. The results derived from these three different approaches allow for identification of a critical wavelength which dictates the fragmentation of ductile rings expanding at very high strain rates. This critical wavelength is revealed quite independent of the material properties but closely related to the ratio (L0/Ø0) critical ≈1:5 where L0 is the fragment size and Ø0 is the diameter of the circular section of the ring. This work highlights the fundamental role played by material inertia in the fragmentation at very high strain rates, setting aside the mechanisms associated to the classical statistical theories.Comunidad Autónoma de Madrid (Project CCG10-UC3M/DPI-5596) and to the Ministerio de Ciencia e Innovación de España (Project DPI/2011-24068) for the financial support received which allowed conducting part of this work.Publicad

Multiple necking pattern in nonlinear elastic bars subjected to dynamic stretching: the role of defects and inertia

In this paper we explore the inception and development of multiple necks in incompressible nonlinear elastic bars subjected to dynamic stretching. The goal is to elucidate the role played by a spatial-localized defect of the strain rate field in the necking pattern that emerges in the bars at large strains. For that task, we have used two different approaches: (1) finite element simulations and (2) linear stability analyses. The finite element simulations have revealed that, while the defect of the strain rate field speeds up the development of the necking pattern in the late stages of the localization process, the characteristic (average) neck spacing is largely independent of the defect within a wide range of defect amplitudes. The numerical results have been rationalized with the linear stability analyses, which enabled to explain the average spacing characterizing the necking pattern at high strain rates. Moreover, the numerical calculations have also shown that, due to inertia effects, the core of the localization process occurs during the post-uniform deformation regime of the bar, at strains larger than the one based on the Considère criterion. This phenomenon of neck retardation is shown to have a meaningful influence on the necking pattern.AVR and JARM are indebted to the Ministerio de Economía y Competitividad de España (Projects EUIN2015-62556 and DPI2014- 57989-P ) for the financial support which permitted to conduct part of this work. AM and JARM acknowledge the support by the French State through the program Investment in the future operated by the National Research Agency (ANR) and referenced by ANR-11-LABX- 0 0 08-01 (LabEx DAMAS). The research leading to these results has received funding from the European Union’s Horizon2020 Programme (Excellent Sci- ence, Marie Sklodowska-Curie Actions) under REA grant agreement 675602 (Project OUTCOME)

Proteomic profile determination of autosomal aneuploidies by mass spectrometry on amniotic fluids

<p>Abstract</p> <p>Background</p> <p>Prenatal diagnosis of chromosomal abnormalities by cytogenetic analysis is time-consuming, expensive, and requires highly qualified technicians. Rapid diagnosis of aneuploidies followed by reassurance of women with normal results can be performed by molecular analysis of uncultured foetal cells. In the present study, we developed a proteomic fingerprinting approach coupled with a statistical classification method to improve diagnosis of aneuploidies, including trisomies 13, 18, and 21, in amniotic fluid samples.</p> <p>Results</p> <p>The proteomic spectra obtained from 52 pregnant women were compiled, normalized, and mass peaks with mass-to-charge ratios between 2.5 and 50 kDa identified. Peak information was combined together and analysed using univariate statistics. Among the 208 expressed protein peaks, 40 differed significantly between aneuploid and non aneuploid samples, with AUC diagnostic values ranging from 0.71 to 0.91. Hierarchical clustering, principal component analysis and support vector machine (SVM) analysis were performed. Two class predictor models were defined from the training set, which resulted in a prediction accuracy of 92.3% and 96.43%, respectively. Using an external and independent validation set, diagnostic accuracies were maintained at 87.5% and 91.67%, respectively.</p> <p>Conclusion</p> <p>This pilot study demonstrates the potential interest of protein expression signature in the identification of new potential biological markers that might be helpful for the rapid clinical management of high-risk pregnancies.</p

Rate Dependent Adhesion Energy and Nonsteady Peeling of Inextensible Tapes

Elastomer based pressure sensitive adhesives used in various peeling applications are viscoelastic and expected to be rate sensitive. The effects of varying peel velocity on adhesion energy and its dependence on the peel angle and rate of peeling are investigated. Experiments are conducted on an adhesive tape using a displacement-controlled peel test configuration. By adjusting the peel arm length, the peel velocity can be continuously varied though the extremity of the film is displaced at a constant rate, which results in nonsteady peeling. Constant peel rate tests are performed over a wide range of peeling rates for a fixed peeling angle, which results in steady state peeling. Based upon the experimental data, a power law relation for the adhesive energy of a packaging tape and its dependence on the rate of peeling is presented. The applicability of the rate dependent law for adhesion energy based upon the steady state experiments to the nonsteady peeling process is critically examined