Narinder Kumar Gupta

Dynamic Tensile and Compressive Behaviors of Mild Steel at Wide Range of Strain Rates

AbstractThe purpose of the present paper is to investigate the mechanical behavior of mild steel at quasi-static (0.001 s−1) and different rates of dynamic tensile (5–750 s−1) and compressive (125–2,350 s−1) strain rates. Quasi-static experiments are conducted on a universal testing machine to study the stress-strain behavior of mild steel. A hydropneumatic machine and a modified Hopkinson bar are used to investigate the dynamic tensile behavior of mild steel specimens at medium and high strain rates, respectively, whereas the specimens are tested on a split Hopkinson pressure bar to acquire understanding of the strain rate sensitivity of mild steel under dynamic compression. The effects of a pulse shaper and gauge length of the specimen in the dynamic compression tests are investigated. High-speed photography has been used to monitor the deformation of the specimen at high strain rate experiments. The applicability of the existing Cowper-Symonds and Johnson-Cook material models to represent the mechanica...

Quasi-Static and Dynamic Tensile Behavior of CP800 Steel

An experimental investigation on the tensile behavior of Complex Phase 800 (CP800) steel at different strain rates (0.001 to 750 s−1) is reported here. The material is tested on a ZWICK universal testing machine to obtain the stress-strain relationship under quasi-static condition, and on a Hydro-Pneumatic machine and modified Hopkinson bar to study the mechanical behavior at medium and high strain rates, respectively. The failure surfaces of the tested specimens at different strain rates are studied from their fractographs. Finally, the applicability of the existing Cowper-Symonds and Johnson-Cook material models to represent the mechanical behavior of CP800 is examined.

Strain Rate Sensitivity of an Aluminium Alloy under Compressive Loads

An experimental investigation on the dynamic compressive behaviour of the aluminium alloy, AA6063-T6 in the strain rate range from 0.001s-1 to 850s-1 is reported here. Cylindrical specimens of AA6063-T6 are tested under universal testing machine at quasi-static (0.001s-1) condition, whereas, experiments at high strain rates (110s-1,400s-1,550s-1,700s-1 and 850s-1) are conducted on the traditional split Hopkinson pressure bar setup. The strain hardening in the material is found to increase with increasing strain rate. It is observed that the existing Johnson-Cook material model with appropriate material parameters predicts the dynamic compressive flow stress of AA6063-T3 aluminium alloy precisely.

Mechanical Behavior of a Structural Steel at Different Rates of Loading

The purpose of this chapter is to investigate the mechanical properties of a structural steel under quasi-static and dynamic loads. Specimens of as-received low-carbon mild steel are tested on universal testing machine to study their stress-strain behavior under quasi-static tension (0.001s−1) and compression (−0.001 s−1). Then, the specimens are tested under split Hopkinson pressure bar (SHPB) and modified Hopkinson bar (MHB) to study their material properties under dynamic compressive (−550, −800s−1) and tensile (250, 500s−1) loading, respectively. The material parameters of the existing Johnson-Cook model are determined. Finally, the applicability of the existing Johnson-Cook material model to represent the mechanical behavior of mild steel in plastic zone is examined.

Mechanical and thermal properties of MoS2 reinforced epoxy nanocomposites

The effects of molybdenum disulfide (MoS2) on thermal expansion and mechanical properties of epoxy composites were investigated. MoS2 nanosheets were exfoliated by ultra-sonication and reinforced into epoxy as nanofiller by mechanical stirring. Transmission electron microscopy observations demonstrated that MoS2 exhibited better dispersion in epoxy matrix. Thermal expansion measured by dilatometer has revealed that increasing MoS2 fractioninepoxy matrix significantly reduced the coefficient of thermal expansion (CTE). The 0.5wt% MoS2 incorporated epoxy composites shows 35.8% reduction in CTE as compared to neat epoxy. The addition of small fraction of MoS2(0.1wt%) in the composites increased the tensile and flexural strength 39.2% and 9.0% respectively. The glass transition temperature (Tg ) of 0.1wt% MoS2 incorporated epoxy composites shows 7.39% increase in Tg .

Mechanical Characterization of Multi Phase Steel at Different Rates of Loading

The purpose of the present paper is to investigate the mechanical properties of multi phase 800 high yield strength (MP800HY) steel under compressive loading at different strain rates (-4700s-1 to-0.001s-1). Specimens of MP800HY steel are tested on universal testing machine to study their stress-strain behavior under quasi-static (-0.001s-1) condition. Then, the specimens are tested under split Hopkinson pressure bar (SHPB) to study the strain rate sensitivity of the material under different rates of compressive loading (-4700s-1, -4300 1/s, -3800 1/s, -2900s-1 and-1600s-1). The effect of pulse shaper in SHPB experiments has been studied. Thereafter, the applicability of the existing Johnson-Cook material model to represent the flow stress of MP800HY is examined.

Strain Rate Sensitivity of Die Steel under Compressive Loads

An experimental investigation on the strain rate sensitivity of die steel (D3) has been presented in this paper at different rates (0.001-2500s-1) of uni-axial compression. Quasi-static tests (0.001s-1) of the material are conducted on universal testing machine (UTM), whereas, the experiments at high strain rates are performed on split Hopkinson pressure bar (SHPB) apparatus. The effects of gauge length of the specimen on the material properties of the material are studied at different strain rates. The material parameters of existing Cowper-Symonds and Johnson-Cook material models are determined and the suitability of the models is examined.

Mechanical Behavior of Advanced High Strength Steel at High Strain Rates

This paper presents the mechanical behavior of advanced high strength steel, Dual Phase 1200 steel (DP1200) at high strain rates (250s-1 - 750s-1) under tensile loading. The mechanical behavior of materials depends on the loading rates. The accurate knowledge of the mechanical behavior of materials at high strain rates is essential in order to improve the safety against crash, impacts and blast loads. High strain rate experiments are performed on modified Hopkinson bar (MHB) apparatus; however, some quasi-static (0.001s-1) tests are also conducted on electromechanical universal testing machine at tensile loads. Based on the experimental results, the material parameters of the existing Cowper-Symonds and Johnson-Cook models are determined. These models fit the experimental data well and hence can be recommended for the numerical simulation of the problems involving this material at high strain rates.

Lateral Collapse of Woven-Fabric Composite Tubes under Quasi-Static and Impact Loads

An experimental investigation on the lateral collapse behaviour of woven fabric glass/epoxy composite tubes under quasi-static and impact loads are presented here. Composite tubes of different diameter to thickness ratios (D/t = 5.33 - 20.67) were compressed between two flat platens or by a short width square indenter. Impact tests were performed at the gravity drop hammer test setup. The fracture process and the energy absorption capability of the composite tubes under quasi-static and impact loads were studied. It was observed that, the lateral collapse mechanism of thick composite tubes (D/t < 10) was different from thinner tubes (D/t > 10). Finally, the progressive failure analysis of the composite tube was performed in finite element software ABAQUS. Good agreement was observed between the experimental results and numerical predictions.