Polyurea, a reaction product of isocyanates and an amine blend has been reported to be highly strain rate sensitive, which responds in its own unique way when subjected to increasing strain rates. The amine blend comprise of a long chain amine, forming the soft segments, chain extender, which brings the urea linkages closer and a crosslinker, which serves as a chemical bond between the chains. In this work, we attempt to tune the viscous contribution in polyurea, by increasing crosslinking density, while keeping the amount of chain extender more or less constant. The viscoelastic behavior and its effect on the time dependant behavior was established by extensive dynamic studies. Quasi-static tests and Split Hopkinson testing was performed over large deformation rates (10(-4) to 10(3) s(-1)). It was observed that polyureas with larger viscous contribution (tan delta), were capable of exhibiting larger strain rate sensitivity.

Experimental and numerical studies were conducted to determine the impact response of 15 mm thick AA2014-T652 forged plates in the velocity region from 800 m/s to 1300 m/s. Spherical projectiles (10 mm diameter) of hardened steel and soft iron were launched from propellant gun of 30 mm bore diameter and their impact and residual velocities were measured by capturing the impact phenomena with a high speed camera. Residual velocities of projectiles were in good agreement with Recht-Ipson analytical model, when kinetic energy of the fragments ejected from the target was accounted for in the energy balance. Failure in target plates occurred due to a combination of failure mechanisms such as hydrodynamic flow, spalling, ductile hole growth and scabbing. A comprehensive material characterization program was executed to study the plastic flow and failure of the material. Tensile tests were carried out on target and projectile materials at different stress triaxialities, strain rates and temperatures. The experimental data of stress-strain curves were used to calibrate the material parameters of Johnson-Cook constitutive model, which relates the flow stress of the material to effective plastic strain, strain rate and temperature. Fracture strain values were used to calibrate the material parameters of Johnson-Cook failure model, which relates the fracture strain of a material to stress triaxiality, strain rate and temperature. Finite element analyses of all the impact experiments were carried out using a two dimensional axisymmetric model. Numerical results overestimated the ballistic limit velocities as the quasi-brittle fracture of target could not be captured using Johnson-Cook failure model. Limitations of Johnson-Cook failure model were analyzed and numerical simulations were repeated using hydrostatic tensile stress failure model. A non-linear equation of state was also introduced in the model for more accurate calculations of hydrostatic stress. These modifications resulted in an excellent correlation between experimental and numerical results.

Experimental and numerical studies were conducted to analyze the ballistic penetration of high strength aluminium alloy 2014-T652. Hardened steel balls were launched using a propellant gun at velocities ranging from 800 to 1300 m/s to cover regions below and above the ballistic limit. Failure in target plates occurred due to a combination of failure mechanisms such as hydrodynamic flow, spalling, ductile hole growth and scabbing. Tensile tests were conducted at different stress triaxialities, strain rates and temperatures to calibrate the material parameters of Johnson-Cook plasticity and fracture model. Finite element analyses of all the impact experiments were carried out using a two dimensional axisymmetric model. Johnson-Cook fracture model was not able to simulate the quasi-brittle fracture of material and numerical ballistic limit velocity was overestimated. Numerical simulations were repeated using hydrostatic tensile stress failure model along with non-linear equation of state, which resulted in excellent correlation with experimental results.

The Deccan trap is a large igneous rock province located on the Deccan plateau of west-central India. There are several important structures located on Deccan trap basalt like Koyna dam hydropower project, Konkan railways, Katraj twin tunnels to name a few. In order to safeguard the structures from dynamic loading arising from manmade or natural disastrous circumstances, it becomes necessary to characterize the dynamic behavior of rocks. In the present work, experimental studies have been performed to determine the dynamic stress-strain behavior of Deccan trap basalt rock as the same is not yet available in literature. The rock samples have been collected from various regions spread along the Western Ghats in Maharashtra. Tests have been performed to determine the physical and static mechanical properties. The dynamic tests have been carried out using 20 mm diameter split Hopkinson pressure bar (SHPB) at different strain-rates. From the analysis of results, the dynamic stress-strain response of the rocks, force equilibrium and dependence of dynamic strength on the strain rate have been examined for the first time.

This paper presents the static and dynamic experimental characterization of dolomite subjected to static unconfined compressive strength test and dynamic split Hopkinson pressure bar (SHPB) tests. The dynamic compression tests on rock samples are performed at strain rates from 500/sec to 1500/sec. It is observed from the results that the rocks exhibit significant strain rate sensitive behaviour and the peak stress increases with increasing strain rate. In the present work, the force equilibrium at the incident and transmission bar ends of the rock samples has been studied. Dynamic increase factor (DIF), i.e. the ratio of the dynamic to static peak stress has been calculated at different strain rates. Based on the calculated DIF values, an empirical correlation equation has been proposed for the DIF of the rock with the strain rate induced.

In the present work, dynamic stress–strain response of five sedimentary and three metamorphic rocks from different regions of India, e.g. Kota sandstone, Dholpur sandstone, Kota limestone, Himalayan limestone, dolomite, quartzite, quartzitic gneiss and phyllite have been investigated through split Hopkinson pressure bar test at different strain rates. The dry density, specific gravity, static compressive strength and tensile strength values of the rocks have also been determined. Petrological studies of the rocks have been carried out through X-ray diffraction test and scanning electron microscope test. It is observed from the stress–strain response of the rocks that the peak stress increases with increasing strain rate. Dynamic increase factors for the strength of these rocks have been determined by comparing the dynamic and the static peak compressive stresses and correlation equations are proposed.

This paper presents the experimental results to analyze the strain rate sensitivity of aluminium alloy AA-5052 H34. The experiments were carried out under uniaxial tension as well as compression. Tensile tests were carried out with UTM (Zwick Z-250) in the strain rate range of 10-4 to 10-1 s-1 using standard ASTM specimen with gauge length 50mm. Compression tests were carried out in the strain rate range of 10-4 to 103 s-1 using UTM and Split Hopkinson Pressure Bar. Cylindrical specimens of 10mm diameter and 10mm thickness were used for compression experiments. The material showed negative strain rate sensitivity in strain rate from 10-4 to 1 s-1 but showed positive strain rate sensitivity when strain rate increased to 103 s-1. The material was found to be susceptible to Portevin–Le Chatelier effect.

The paper summarizes the experimental observations and simulation studies of damage potential of tungsten alloy cubes on relatively thin mild steel spaced armour target plates in the velocity regime 1300 – 4000 ms−1 using Two Stage Light Gas Gun technique. The cubes of size 9.5 mm and 12 mm having mass 15 g and 30 g respectively were made to impact normally on three target plates of size 300 mm × 300 mm of thickness 4, 4 and 10 mm at 100 mm distance apart. Flash radiography has been used to image the projectile-target interaction in the nitrogen environment at 300 mbar vacuum at room temperature. The results reveal clear perforation by 9.5 mm cube in all the three target plates up to impact velocity of about 2000 m/s. While 12 mm cube can perforate the spaced armour upto impact velocity of 4000 m/s. This shows that 9.5mm tungsten alloy cube is not effective beyond 2000 m/s while 12 mm tungsten alloy cube can defeat the spaced armour upto 4000 m/s. The simulation studies have been carried out using Autodyn 3D nonlinear code using Lagrange solver at velocities 1200 – 4000 m/s. The simulation results are in good agreement with the experimental findings.