Study on the Dynamic Behavior of Tungsten Alloy at Strain Rates up to 5 000 s^(-1)

The dynamic stress-strain curves of 93% tungsten (W) alloy in the forged state at strain rates up to (5 000 s^(-1)) and in the temperature range from 223 K to 473 K were measured with the split Hopkinson pressure bar (SHPB) technique. Based on the above experimental data a dynamic constitutive equation considering the effects of strain rate, temperature and the special microstructure of such a kind of W-alloy was proposed. The numerical simulation for the experimental process with this constitutive equation was also carried out, the results show that the constitutive relationship constructed in this paper is very satisfactory for representing the dynamic responsive behavior of material..

Extension of Flow Behaviour and Damage Models for Cast Iron Alloys with Strain Rate Effect

Cast iron alloys with low production cost and quite good mechanical properties are widely used in the automotive industry.To study the mechanical behavior of a typical ductile cast iron(GJS-450)with nodular graphite,uni-axial quasi-static and dynamic tensile tests at strain rates of 10^(-4),1,10,100,and 250 s^(-1)were carried out.In order to investigate the influence of stress state on the deformation and fracture parameters,specimens with various geometries were used in the experiments.Stress strain curves and fracture strains of the GJS-450 alloy in the strain rate range of 10^(-4)to 250 s^(-1)were obtained.A strain rate-dependent plastic flow model was proposed to describe the mechanical behavior in the corresponding strain-rate range.The available damage model was extended to take the strain rate into account and calibrated based on the analysis of local fracture strains.Simulations with the proposed plastic flow model and the damage model were conducted to observe the deformation and fracture process.The results show that the strain rate has obviously nonlinear effects on the yield stress and fracture strain of GJS-450 alloys.The predictions with the proposed plastic flow and damage models at various strain rates agree well with the experimental results,which illustrates that the rate-dependent plastic flow and damage models can be used to describe the mechanical behavior of cast iron alloys at elevated strain rates.The proposed plastic flow and damage models can be used to describe the deformation and fracture analysis of materials with similar properties.

Influence of Specimen Size on Compression Behavior of Cement Paste and Mortar under High Strain Rates

Static and dynamic compression tests were carried out on mortar and paste specimens of three sizes（Ф68 mm×32 mm,Ф59 mm×29.5 mm and Ф32 mm×16 mm）to study the influence of specimen size on the compression behavior of cement-based materials under high strain rates.The static tests were applied using a universalservo-hydraulic system,and the dynamic tests were applied by a spilt Hopkinson pressure bar（SHPB）system.The experimentalresults show that for mortar and paste specimens,the dynamic compressive strength is greater than the quasi-static one,and the dynamic compressive strength for specimens of large size is lower than those of smallsize.However,the dynamic increase factors（DIF）has an opposite trend.Obviously,both strain rate and size effect exist in mortar and paste.The test results were then analyzed using Weibull,Carpinteriand Ba？ant＇s size effect laws.A good agreement between these three laws and the test results was reached on the compressive strength.However,for the experimentalresults of paste and cement mortar,the size effect is not evident for the peak strain and elastic modulus of paste and cement mortar.