Effects of pre-fatigue on the strain localization during tensile tests of DP 500 steel at low and high strain rates

Abstract

The analysis involved subjecting DP 500 steel to pre-fatigue loads, and then tension at high strain rates using Hopkinson bar. Digital image correlation method was used to investigate how the pre-fatigue loads change the strains' distribution on the surface of the sample subjected to tension. The analysis involved both films recorded at low rates of deformation (1.0 3 10 22 s 21) using ARAMIS system and the images captured with a high-speed camera during dynamic deformations with a Hopkinson bar (6.0 3 10 2 s 21). It was noted, based on the micro-structural analysis, that pre-fatigue loads cause the formation of micro-damages in the examined material. Thus, macroscopically observed stress-strain characteristic as well as Huber-Mises substitute strains' distribution determined locally by the image correlation method is also subject to changes. The observed effects include the following: reduction of deformation corresponding to the tensile strength, decrease in elongation at break, and increase in yield limit and tensile strength. The observed effects are intensified with an increased stress value and pre-fatigue cycles' number. Furthermore, these phenomena are more intensive in the conditions of dynamic deformation.

Energy absorbing properties of a steel profile made of dual phase steel

“…Firstly, tensile tests were carried out to obtain mechanical characteristics of the dual phase steels. Since short specimens (5 mm width and 10 mm length of gauge) were applied during mechanical testing, therefore novel methodology of true stress and true strain estimation was employed [5][6]. This methodology is based on the use of digital image correlation to determine local strain distribution after necking point.…”

“…Constitutive equation was used to describe viscoplastic behaviour of the profiles made of dual phase steel during finite element method calculations. Methodology of true stress and true strain determining on the basis of tensile test was already shown in previous papers [5][6].…”

Anisotropic fracture criterion of Ti6Al4V titanium alloy under wide range of strain rates

“…The specimens were cut using electro-discharge machining (EDM). Tensile tests were carried out at quasi-static and dynamic loading regime using, respectively, with a servo-hydraulic testing machine and split Hopkinson tensile bar (Moćko et al, 2015(Moćko et al, , 2016. Simultaneously, plastic deformation was recorded and analysed using a digital image correlation software to determine strain distribution.…”

Analysis of the Dual-phase Steel DP500 Stress-strain Characteristics During the Plane Shear Test

“…The parameters and material characteristics measured during this type of loading can be further used as important input to numerical simulations, which through the aforementioned computational models will provide a more detailed and accurate description of the entire sheet metal stamping process. The following chapters focus on the description and evaluation of this type of mechanical material testing [1][2][3][4][5][6][7][8][9].…”