An experimental investigation of the behaviour of steels over large temperature and strain rate ranges

Abstract

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. During forging and machining manufacturing processes, the material is subject to large strains at high strain rates which provoke local heating and microstructural changes. Modelling of these phenomena requires precise knowledge of the stress-strain constitutive equations for a large range of strains, strain rates and temperatures. An experimental study of the rheology of both hyper-and hypo-eutectoid steels (with different microstructures) over a temperature range from 20 1C to 1000 1C and with strain rates from 10 À2 to 10 5 s À1 has been undertaken. These tests were performed in compression on cylindrical specimens and in shear using hat-shaped specimens. Both a GLEEBLE 3500 thermomechanical testing machine and a Split-Hopkinson Pressure Bar apparatus were used. From these tests, three deformation domains have been identified as a function of the material behaviour and of the changes in the deformed microstructure. Each domain was characterized by its behaviour, including the competition between hardening and softening, strain rate sensitivity on the flow stress and the softening phenomenon (i.e. recrystallisation or recovery, etc.). Finally, based on thermodynamical considerations, the conditions of thermoplastic instability (i.e. shear bands, twinning, heterogeneities, etc.) and microstructural changes are highlighted using process maps of the dissipated power repartition.

Modelling, identification and application of phenomenological constitutive laws over a large strain rate and temperature range

“…a b s t r a c t A review of the different phenomenological thermo-viscoplastic constitutive models often applied to forging and machining processes is presented. Several of the most common models have been identified using a large experimental database (Hor et al, 2013). The latter consists of the tests were done in compression on cylindrical shaped specimens and in shear using hat-shaped specimens.…”

Towards cutting force evaluation without cutting tests

“…5, while complementary specifications can be found in [15]. These dimensions have been selected regarding past studies [10,[13][14] and should result in a cylindrical shear band of 0.1 mm thickness (shown in Fig. 5) when compressing the hat-shaped specimen.…”

“…Even if hat-shaped experiments are more representative of the cutting process, Changeux [11] noted that there are some differences considering the hydrostatic stress, the shear strain rate -even in high-speed experiments -, and mostly the dimensions of the deformed volume introducing scaling and thermal effects. Despite these differences, these tests are quite simple and were widely used for the last twenty years to characterise the behaviour of work materials, especially for metal cutting simulations [12,13]. At a macroscopic scale, Hofmann and El-Magd [14] observed that the deformation work (or strain energy) per unit volume and the shear strain at fracture obtained by hat-shaped tests can be correlated with the chip breakability of the machined material.…”

Numerical investigation on ballistic resistance of aluminium multi-layered panels impacted by improvised projectiles

“…Pothnis et al [40] found that for both aluminium alloy 7075 T651 and IS 2062 mild steel tensile yield strength was enhanced when different strain rates were applied, if compared to quasi-static loading. Hor et al [41] conducted a number of compression and shear tests involving a wide range of temperatures (20-1000 • C) and strain rates (10 −2 -10 5 1/s). They found strong coupling of three main phenomena: effect of the temperature, effect of the strain rate and the strain hardening-softening.…”