Institute of Fundamental Technological Research

In this paper, the thermo-viscoplastic behaviour of DH-36 and Weldox-460-E steels is analyzed at wide ranges of strain rates and temperature. These materials are commonly used for naval applications. Thus, the may be subjected to a wide range of exploitation temperature and at the same time to high strain rates due to accidental impact or explosion. The thermo-viscoplastic behaviour of these materials has been modeled by application of RK (Rusinek-Klepaczko) constitutive relation. The comparison with other models well known in the literature has been studied.

constitutive modelling, thermo-viscoplasticity, DH-36 steel, Weldox-460-E steel, impact processes, FE numerical simulations, perforation process

In this paper the thermo-visco-plastic behaviour of six high strength steels is analyzed in a wide range of strain rates and temperature. The steels belong to two well-known versions of steels: three ferritic steels: HSLA-65, DH-36 and Wedox 460-E and three austenitic steels: Nitronic-50, Uranus B66 and Al-6XN.
Micro-mechanism of plastic deformation in the case of ferritic steels is dominated by dislocation's gliding. In the case of austenitic steels the twinning appears that modifies the material's plastic properties. In the present paper the RK (Rusinek-Klepaczko) constitutive relation is evaluated for modelling of the plastic behaviour of six steels which represent these two different deformation mechanisms.

ferritic steels, austenitic steels, RK Rusinek - Klepaczko model, dislocation glide, twining, thermo-visco-plasticity

In this paper an extension of the Rusinek-Klepaczko (RK) constitutive relation is presented. The new formulation proposed, allows defining the phase transformation effect observed on macroscopic scale using a phenomenological approach. The key point is to introduce in the original formulation of RK model a new stress component based on evolution of martensite, which takes into account strain, strain rate and temperature effects. Analytical predictions of the xtended constitutive relation are compared with experimental results for 301Ln2B steel.

RK model, phase transformation, austenitic steel

A modified miniaturized version of the Direct Impact Compression Test (DICT) technique is described in this paper. The method permits determination of the rate-sensitive plastic properties of materials up to strain rate∼105s−1. Miniaturization of the experimental setup with specimen dimensions: diameter dS=2.0 mm and thicknesslS=1.0 mm, Hopkinson bar diameter 5.2 mm, with application of a novel optical arrangement in measurement of specimen strain, makes possible compression tests at strain rates from∼103s−1to∼105s−1. In order to estimate the rate sensitivity of a low-alloy construction steel, quasi-static, Split Hopkinson Pressure Bar (SHPB) and DICT tests have been performed at room temperature within the rate spectrum ranging from 5*10−4s−1to5*104s−1. A diabatic heating and friction effects are analyzed and the final true stress versus true strain curves at different strain rates are corrected to a constant temperature and zero friction. The results have been analyzed in the form of true stress versus the logarithm of strain rate and they show two regions of a constant rate sensitivity β¼Δσ.log": relatively low up to the strainrate threshold∼50 s−1, and relatively high above the threshold, up to strain rate∼4.5*104s−1.

Direct Impact Compression Test (DICT), Dynamic plasticity, Mild Steel, High strain rate

An experimental study of the strain rate behavior of technically pure iron in pure shear is reported in this work. As is well known, most experimental results have been obtained from tension or compression tests; few results on strain rate behavior in pure shear.

Furthermore, dynamic tests on thin tubular specimens show several advantages over tension or compression tests.

Neglecting strain rate history effects the surface τ = τ(φ, gh) has been experimentally obtained, where τ is the shear stress, φ and η are the shear strain and strain rate respectively. This surface was obtained over the following ranges of strain and strain rate 0 ⩽ φ ⩽ 0.42; 1 × 10−5sec−1 ⩽ η ⩽ 1 × 102sec−1.

In addition, a comparison between the effect of strain rate in pure shear, tension and compression tests has been carried out. This comparison enables preliminary data on the strain rate behavior in biaxial states of stress to be obtained.

Finally, the basic assumptions of the visco-plasticity theory for complex states of stress have been examined in the light of this experimental evidence.

In this paper an analysis of instability in tension tests is presented. It is assumed that the flow stress is a unique function of strain, strain-rate and temperature. For such a type of constitutive equation the three following cases have been analysed. First, when the temperature of a specimen is maintained constant, i.e. an isothermal process; for this case the relationship between uniform elongation, temperature and strain-rate has been obtained. The second case is related to instability under adiabatic conditions; this case has been numerically investigated for copper and aluminium. Finally, in the third case, the critical impact velocity in tension tests is discussed and some theoretical predictions are compared with experimental results.

This work presents an application of the dislocation theory of intersections to the experimental results obtained at changed strain rates under conditions of pure shear for polycrystalline aluminium. Simultaneously, strain-rate history effects have been shown, and discussed in terms of dislocation behaviour.