Viscoplastic flow of functional cellular materials with use of peridynamics

The subject of the study is the deformation of the oxygen-free high conductivity copper. The copper sample is given in the form of a foam. The sample undergoes an impact into an elastic wall. The strain rate hardening effect is investigated. The numerical model of the open-cell foam skeleton is prepared in the framework of the peridynamics method. The dynamic process of compression with different impact velocities is simulated. It has been found that the strain rate hardening effect is essential for the load-carrying capacity of the material under study. Taylor impact test of solid cylinder analysis precedes the analysis of the metallic foam.

Strain rate dependency of dislocation plasticity

Dislocation glide is a general deformation mode, governing the strength of metals. Via discrete dislocation dynamics and molecular dynamics simulations, we investigate the strain rate and dislocation density dependence of the strength of bulk copper and aluminum single crystals. An analytical relationship between material strength, dislocation density, strain rate and dislocation mobility is proposed, which agrees well with current simulations and published experiments. Results show that material strength displays a decreasing regime (strain rate hardening) and then increasing regime (classical forest hardening) as the dislocation density increases. Accordingly, the strength displays universally, as the strain rate increases, a strain rate-independent regime followed by a strain rate hardening regime. All results are captured by a single scaling function, which relates the scaled strength to a coupling parameter between dislocation density and strain rate. Such coupling parameter also controls the localization of plasticity, fluctuations of dislocation flow and distribution of dislocation velocity.

Dynamic finite element simulation of wheel–rail contact response for the straight track case

The dynamic effects, mainly including the inertia effect and strain-rate effect, on the dynamic wheel–rail contact behavior become more and more serious as the train speed increases. The inertia effect can be automatically taken into account in explicit finite element analysis codes, while the strain-rate effect needs to be considered via inputting the related material parameters. In the present paper, the influence of strain rate on the dynamic wheel–rail contact response for the straight track case was explored, based on a 3D wheel–rail rolling contact finite element model, via LS-DYNA/explicit algorithm. Effects of the axle load and train speed on typical dynamic wheel–rail responses were discussed, and the results indicate that the coupled train speed with strain rate has a non-negligible influence on dynamic contact responses. The strain rate hardening effect increases the maximum contact pressure and stress, and inhibits the plastic deformation of the wheel–rail system. A rate-sensitive factor (RSF) was then introduced to describe the strain rate hardening effect, confirming that the rail is more sensitive to strain rate compared to the wheel. Finally, an error analysis of the wheel–rail Hertz contact theory was conducted, which further verify the differences between elastic and elastic-plastic contact solutions.

The Effect of Material Behaviour on the Surface Roughness during Machining of H13 Tool Steel

The aim of the present study is to know the effect of material properties on surface roughness during dry turning of H13 tool steel. Machining was performed using Tungaloy made carbide insert. Chip reduction coefficient (CRC) and surface roughness values (Ra) were experimentally determined. Twenty seven experiments were conducted following 33 factorial design. Subsequently, chip samples were examined under scanning electron microscope. Surface roughness values were found to be influenced by strain hardening and strain rate hardening of the material depending upon the values of speed, feed and depth of cut (d.o.c). Surface quality improves because of strain rate hardening at higher cutting speed.

Investigation of the strain rate hardening behaviour of glass fibre reinforced epoxy under blast loading

This work investigates the use of blast loadings and inverse modeling for the identification of the strain rate hardening model parameters of fibre reinforced polymers. An experimental setup allowing the generation of known and predictable blast waves, leading to repeatable dynamic response in composite plates and the measurement of the displacement and strain fields, is developed. The dynamic response of the plates is measured by means of high-speed cameras and a 3D digital image correlation technique. A suitable numerical model that is able to reproduce the experimental conditions and predict the blast response of the plates is developed. Finally, the experimental measurements and the numerical calculation are combined through an inverse method in order to identify the strain rate hardening model parameters of the tensile and shear strengths of glass fibre reinforced epoxy.

Acquisition and Evaluation of Theoretical Forming Limit Diagram of Al 6061-T6 in Electrohydraulic Forming Process

The current study examines the forming limit diagram (FLD) of Al 6061-T6 during the electrohydraulic forming process based on the Marciniak–Kuczynski theory (M-K theory). To describe the work-hardening properties of the material, Hollomon’s equation—that includes strain and strain rate hardening parameters—was used. A quasi-static tensile test was performed to obtain the strain-hardening factor and the split-Hopkinson pressure bar (SHPB) test was carried out to acquire the strain rate hardening parameter. To evaluate the reliability of the stress–strain curves obtained from the SHPB test, a numerical model was performed using the LS–DYNA program. Hosford’s yield function was also employed to predict the theoretical FLD. The obtained FLD showed that the material could have improved formability at a high strain rate index condition compared with the quasi-static condition, which means that the high-speed forming process can enhance the formability of sheet metals. Finally, the FLD was compared with the experimental results from electrohydraulic forming (EHF) free-bulging test, which showed that the theoretical FLD was in good agreement with the actual forming limit in the EHF process.

Effect of Alloy Composition and Pre-Ageing on the Stretch Formability of 6xxx Automotive Sheet Alloys

In this study, the effect of Mg/Si ratio, Cu content and/or pre-ageing treatment (e.g. 100 °C for 2 h and/or 200 °C for 20 s) on the stretch formability of 6xxx alloys was investigated through their influence on the work hardening and strain-rate hardening behaviour using tensile testing and forming limit diagram tests. The results showed that a high Mg/Si ratio, a low Cu content and/or the employment of pre-ageing could deteriorate the stretch formability due to the decrease in work hardening and/or strain rate hardening capabilities. Moreover, the stretch formability was observed to have an opposite correlation with the paint-bake response of the alloys studied.