Dynamic Strain Aging, Negative Strain-Rate Sensitivity and Related Instabilities

We give in this paper a possible mechanical interpretation to the development of L¨uders front and Portevin-Le-Chatelier effect based on a band analysis for an elastic- viscoplastic material with negative strain-rate sensitivity. This negative strain rate sensitivity allows for jumps for the plastic strain rate which in turns permits the existenceof localization bands for the elastic-viscoplastic material. The classical band analysis for an infinite solid does not predict the direction of the band. However, we show that this direction is determined in some circumstances if one considers the boundary conditions

Characterization of High Carbon Steel C68 at Elevated Temperatures and Different Strain Rates

This paper presents high-temperature tensile testing. This method is used to characterize the mechanical behaviour of a high-carbon steel C68 at temperatures up to 720°C. Samples are heated by an induction system controlled with a pyrometer. A high-speed camera (500 fps) is used to determine the displacement field with a digital image correlation software. For such tests a specific marking procedure of the sample is applied. Stress-strain curves are given from room temperature up to 720°C at strain rates ranging from 10-3/s to 10-1/s. Elastic parameters of the material are measured at room temperature using cyclic tests. Bridgman’s method is used to determine the equivalent stress-plastic strain curve during the necking phase

Numerical modelling of magnesium die-castings using stochastic fracture parameters

Quasi-static material tests using specimens cut from a generic cast component are performed to study the behaviour of the high-pressure die-cast magnesium alloy AM60 under different stress states. The experimental data set is applied to establish a validated probabilistic methodology for finite element modelling of thin-walled die-castings subjected to quasi-static loading. The test specimens are modelled in the explicit finite element (FE) code LS-DYNA using shell elements. The cast magnesium alloy AM60 is modelled using an elasto-plastic constitutive model including a high-exponent, isotropic yield criterion, the associated flow law and isotropic hardening. To simulate fracture, the Cockcroft-Latham fracture criterion is adopted, and the fracture parameter is chosen to follow a modified weakest-link Weibull distribution. Comparison between the experimental and predicted behaviour of the cast magnesium specimens gives very promising results. (C) 2009 Elsevier Ltd. All rights reserved

Effect of pre-straining on localisation and fracture of dual-phase steel at elevated rates of strain

The present paper is aimed at studying the effect of pre-straining on the localisation and fracture in dual-phase steel under dynamic loading conditions. This study was conducted by using tensile tests at elevated rates of strain.A dual-phase steel DP800 sheet of thickness 1.5 mm was pre-deformed to three different levels of effective strain 1%, 4% and 8%. Thereafter, sub-size tensile specimens were machined from the pre-deformed sheets in the pre-strained direction. Tensile tests at elevated rates of strain in the range of 10−3 s−1 to 103 s−1 were conducted by using a conventional servo-hydraulic machine and a split-Hopkinson tension bar. A high-speed video camera was used to record the sequence of deformation during testing. A full-field measurement technique, namely digital image correlation, was utilized to measure the local strains up to fracture from the recorded digital images. It was found out that the pre-straining and dynamic loading have a marked effect on the strain localisation and subsequent fracture

Cross-sectional classification for Aluminium beams-parametric study

March 200

A Parametric Study on the Rotational Capacity of Aluminium Beams Using non-linear FEM.

International Conference on Steel and Aluminium Structures, Espoo, Finland, 20-23 Jun