Effect of Strain Rate Upon Plastic Flow of Steel

Abstract

Thermoplastic materials are increasingly used as a light weight replacement for metal, especially in automotive applications. Typical examples are frontends and bumpers. The loads on these structures are very often impulsive, for example in a crash situation. A high rate of loading causes a high strain rate in the material which has a major impact on the mechanical behavior of thermoplastic materials. The stiffness as well as the rigidity of polymers increases to higher strain rates. The increase of the mechanical properties is superimposed at higher rates of loading by another effect which works reducing on stiffness and rigidity, the increase of temperature caused by plastic deformation. The mechanical behavior of thermoplastic materials is influenced by temperature opposing to strain rate. The stiffness and rigidity are decreased to higher values of temperature. The effect of thermal softening on thermoplastic materials is investigated at IKV. For this purpose high-speed tensile tests are performed on a blend, consisting of Polybutylenterephthalate (PBT) and Polycarbonate (PC). In preliminary investigations the effects of strain rate on the thermomechanical behavior of thermoplastic materials was studied by different authors. Tensile impact as well as split Hopkinson pressure bar (SHPB) tests were conducted in combination with high-speed temperature measurement, though, the authors struggled especially with temperature measurement. This paper presents an approach which uses high-speed strain measurement to transpire the link between strain, strain rate and thermal softening as well as the interdependency between strain hardening and thermal softening. The results show a superimposition of strain hardening and thermal softening, which is consistent to preliminary investigations. The advantage of the presented research is that the results can be used to calibrate damage and material models to perform mechanical simulations using Finite Element Analysis.

Self-organization of shear bands in stainless steel

“…Initial perturbations lead to a non-uniform distribution of temperature, which promotes localized softening and accelerates catastrophic failure. Adiabatic shear bands have been extensively studied [1][2][3] since the mechanism was described by Zener and Hollomon [4]. A significant body of research has been carried out, correlating both the thermomechanical response and metallurgical characteristics with the sensitivity to shear localization.…”

Description of “Hot Spots” Associated with Localized Shear Zones in Impact Tests

“…1,13,14 It is instructive to compare Equations (4) and (5) with the torsional results described earlier for internal heating within a high strength steel material. 2 For this case we let nT < G/20 = 3.9 GPa, where G is the shear modulus for steel.…”

“…where b is the dislocation Burgers vector, T is the shear stress, v is the dislocation velocity and K is the thermal conductivity; C* has been defined for Equation (1). The quantity contained within…”

“…2 For this case we let nT < G/20 = 3.9 GPa, where G is the shear modulus for steel. 1 With T-= 1 GPa, n r 4. Also, for steel, k = 60J/ms OK, so 2K/C* = 3.4 = 10 -5 m 2 /s, and with a limiting value of v = 3.2 x 103 m/s which is the shear wave velocity and b = 2.5 x 10-1 0 m, then (2K/C*vb) >> 1.0.…”

Austenitic Grain Growth behavior Immediately after Dynamic Recrystallization in HSLA Steels and Austenitic Stainless Steel

“…8) Currently, the control of the as cast microstructure evolved by various continuous casting processes including a thin slab caster or strip casing has become important in steel industry. 9,10) The authors paid attention to this point, and studied refinement of the very coarse g microstructure evolved in a strand casting slab of HSLA steels by use of dynamic recrystallization.…”