Abstract
The Council for Scientific and Industrial Research (CSIR) conducts research on explosive blast load effects for the development of protection solutions for armoured vehicles. This research includes the design and development of blast test rigs which are used to experimentally simulate the dynamic mechanical response of various protection materials that are used in armoured vehicles. The materials typically used to develop protection technologies against blast and ballistic threats usually result in mechanical failure, due to the high impact loads they are subjected to during a blast event. The failure of these materials usually occurs at high strain rates in the region of 102 to 104 s-1 and at ultra-high strain rates in the region of 104 to 106 s-1.
General material properties of metals and alloys are easily accessible from, but not limited to, mechanical design handbooks, material datasheets from steel, manufacturing suppliers, published and pre-reviewed scientific publications, and materials testing laboratories. These tests are usually conducted using conventional testing machines under quasi-static loading conditions at low strain rates in the region of 10-4 to 102 s-1. Most of the materials testing laboratories do not have the facilities to dynamically characterise materials at high strain rates, thus there is a need to characterise various materials that are commonly used in the metals and alloys manufacturing industries for the development of reliable protection technologies.
The CSIR in conjunction with the University of Pretoria developed a conventional split Hopkinson pressure bar (SHPB) apparatus to characterise various materials at high strain rates in the region of 102 – 104 s-1. The apparatus was initially designed to characterise materials in compression, and the design has recently been upgraded to characterise materials in tension as part of the scope of this research project.
Mechanical properties of aluminium 6068-T6 and S355 mild steel and VRG Copper materials were obtained from the tensile split Hopkinson pressure bar (TSHPB) apparatus for experiments carried out in the region of 102 – 103 s-1. The recorded mechanical properties were extracted using Microsoft Excel® and MATLAB TM.
These properties were also used as inputs for the construction of Finite Element Analysis (FEA) computational models to predict the mechanical response of a circular metal blast plate when subjected to blast loads in the LSTC (Ansys,Inc) LS-Dyna computational modelling and simulation software. The Johnson-Cook and Cowper Symonds material models were used to
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specify the material characteristics of the materials and the computational results were compared to the experimental results to confirm if the developed free-in-air blast model could be used as a dynamic mechanical response predictive tool.
Keywords: striker bar, incident bar, transmitter bar, stress, strain, high strain rate, material model, SHPB.