Mines ParisTech

About: Mines ParisTech is a education organization based out in Paris, France. It is known for research contribution in the topics: Finite element method & Microstructure. The organization has 6564 authors who have published 11676 publications receiving 359898 citations. The organization is also known as: École nationale supérieure des mines de Paris & École des mines de Paris.

Efficient chaotic iteration strategies with widenings

Abstract: interpretation is a formal method that enables the static and automatic determination of run-time properties of programs. This method uses a characterization of program invariants as least and greatest fixed points of continuous functions over complete lattices of program properties. In this paper, we study precise and efficient chaotic iteration strategies for computing such fixed points when lattices are of infinite height and speedup techniques, known as widening and narrowing, have to be used. These strategies are based on a weak topological ordering of the dependency graph of the system of semantic equations associated with the program and minimize the loss in precision due to the use of widening operators. We discuss complexity and implementation issues and give precise upper bounds on the complexity of the intraprocedural and interprocedural abstract interpretation of higher-order programs based on the structure of their control flow graph.

Video-controlled tensile testing of polymers and metals beyond the necking point

Abstract: A novel technique has been developed to record the intrinsic plastic behaviour of ductile materials by monitoring the effective strain and the effective stress in the mid-plane of hour-glass-shaped tensile specimens. The method utilizes a computer-aided video extensometer which analyses the sample profile in real time. The effective strain is computed automatically from the minimum diameter, and the effective stress is deduced from the applied load by taking into account the stress triaxiality corresponding to the local radius of curvature of the sample profile. Furthermore, a digital closed-loop system controls the ram speed of the hydraulic tensile testing machine in such a way that the local effective strain rate is maintained at a constant value. It is shown that most polymeric and metallic materials are entitled to be investigated by this method, which gives access in real time to the constitutive plastic equation, up to strains far beyond the necking point. The capabilities of the technique are illustrated and discussed critically, with more details for two polymers of different structures: polyethylene and polycarbonate.