Dynamic Compressive And Tensile Mechanical Properties Of A QP Steel

This paper studies on the dynamic compressive and tensile mechanical behavior of a QP steel,the main results are as follows:1. Dynamic compressive constitutive equation of QP steel cylinder specimens was determinedand calibrated1) Uniaxial compression tests were performed on QP steel cylinder specimens, using810material test system (MTS) and split Hopkinson pressure bar (SHPB) tests. Based on the stress-strain data obtained from quasi-static (Q-S) tests and first loading in SHPB tests at different strainrates and temperatures, this study determined J-C type and Z-A type compressive constitutiveequations for QP steel.2) The determined compressive constitutive equations of QP steel were calibrated, innumerically simulating the stress waves on the bars recorded by strain gages and the deformationsof the cylinder specimens recorded by a high speed camera and generated by single-compression inSHPB tests.3) The results of3D Super Depth Digital Microscope (SDDM) and scanning electronmicroscope (SEM) investigation of recovered QP steel cylinder specimens in SHPB tests atdifferent strain rates and temperatures were presented. Examinations of residual microstructuresover the range of strain rates and temperatures for this paper attest to the fact that themicrostructures do not change abruptly, nor do they change characteristically.2. Dynamic tensile constitutive equation of QP steel sheet specimens was determined andcalibrated1) Q-S uniaxial tensile tests for two scales of QP steel sheet specimens with gauge lengthorientation (GLO) of0°,45°,90°relative to the RD at ambient temperature were performed onMTS. It was indicated that the Q-S stress-strain data of smaller sheet specimens with GLO of0°,45°,90°relative to the RD appropriate to tensile split Hopkinson bar (TSHB) tests are approximateto that of ASTM standard sheet specimens for QP steel.2) Optimization of TSHB tests were performed by numerical simulation to obtain the effecttensile properties of QP steel at different strain rates and ambient temperature. The effects ofspecimen length-width ratio on the stress and strain uniformity in specimens were revealed. The geometry of the sheet specimens was designed to deduce ring-up time, inertial effects, and to resultin approximate uniaxial stress and uniform stress and strain in QP steel sheet specimens.3) Dynamic tensile stress-strain data of QP steel sheet specimens with GLO of0°,45°and90°relative to the RD were obtained by using optimized TSHB tests at different strain rates andtemperatures. Based on the stress-strain data in Q-S tension tests on MTS and in dynamic tensiontests on TSHB, J-C type tensile constitutive equations of QP steel sheet specimens with GLO of0°,45°,90°relative to the RD and Z-A type tensile constitutive equation of QP steel sheet specimenswith GLO of0°relative to the RD were determined.4) The determined tensile constitutive equations of QP steel sheet specimens with GLO of0°relative to the RD were calibrated, in numerically simulating the stress waves on the bars generatedby single-tension and recorded by strain gages and the deformations of specimens generated bymulti-tension and recorded by a high speed camera in TSHB tests.5) Different scales of sheet specimens with GLO of0°relative to the RD were adopted toinvestigate the effects of specimen scale on stress-strain data in Q-S uniaxial tensile testing for QPsteel material. The effects of specimen scale on the stress-strain data in TSHB testing wereanalysed by using numerical simulation.3. The dynamic fracture mechanism of QP steel sheet specimens was investigated1) The diffuse necking of QP steel sheet specimens with GLO of0°relative to the RD inTSHB tests were analyzed by using Batra and Wei’s instability criterion and the calibrated J-C typetensile constitutive equation.2) The effects of strain rate and temperature on fracture strain of QP steel sheet specimenswith GLO of0°relative to the RD were explored. The results of SEM investigation of the rupturedzones in Q-S tensile tests and TSHB tests of QP steel sheet specimens with GLO of0°,45°,90°relative to the RD were presented.3) Dynamic experimental verification of void coalescence criteria was conducted for QP steel.Thomason’s criterion, Brown-Embury’s criterion and Ma and Chen’s criterion were assessed bythe comparison between experimental evolution of drilled void in the QP steel sheet specimenswith GLO of0°relative to the RD and the results of numerically simulation performed by thedetermined J-C type constitutive equation which involve void coalescence criteria.