Stress Wave Attenuation in Aluminum Alloy and Mild Steel Specimens Under SHPB Tensile Testing
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JMEPEG https://doi.org/10.1007/s11665-017-3120-x
Stress Wave Attenuation in Aluminum Alloy and Mild Steel Specimens Under SHPB Tensile Testing J.R. Pothnis, G. Ravikumar, H. Arya, Chandra S. Yerramalli
, and N.K. Naik
(Submitted May 11, 2017; in revised form October 5, 2017) Investigations on the effect of intensity of incident pressure wave applied through the striker bar on the specimen force histories and stress wave attenuation during split Hopkinson pressure bar (SHPB) tensile testing are presented. Details of the tensile SHPB along with Lagrangian x–t diagram of the setup are included. Studies were carried out on aluminum alloy 7075 T651 and IS 2062 mild steel. While testing specimens using the tensile SHPB setup, it was observed that the force calculated from the transmitter bar strain gauge was smaller than the force obtained from the incident bar strain gauge. This mismatch between the forces in the incident bar and the transmitter bar is explained on the basis of stress wave attenuation in the specimens. A methodology to obtain force histories using the strain gauges on the specimen during SHPB tensile testing is also presented. Further, scanning electron microscope images and photomicrographs are given. Correlation between the microstructure and mechanical properties is explained. Further, uncertainty analysis was conducted to ascertain the accuracy of the results. Keywords
Lagrangian x–t diagram, photomicrograph, strain measurement, stress wave attenuation in specimens, tensile high strain rate testing, uncertainty analysis
1. Introduction High strain rate characterization of materials is an important area of research. Several test techniques have been developed over the years to evaluate the behavior of materials under dynamic loading conditions (Ref 1). Split Hopkinson pressure bar (SHPB) setup is commonly used to test materials at high strain rates (Ref 1-6). The SHPB method is very versatile and is used to evaluate compressive, tensile and torsional properties of materials using different variants of the SHPB apparatus. SHPB test is based on the assumption of one-dimensional wave theory. Specimen stress equilibrium is a critical assumption in the SHPB data analysis and has been discussed in the literature (Ref 7-12). Axial equilibrium of the specimen is estimated by comparing the axial stress at the incident bar– specimen interface with the specimen–transmitter bar interface. Most of the studies available in the literature are on wave propagation and wave intensity and do not consider damage mechanics aspects. The effect of permanent deformation and influence of damage evolution on stress equilibrium is an important subject. Typical studies are available on high strain rate tensile behavior of materials in the literature (Ref 13-46). Specifically, studies are presented on aluminum alloys (Ref 13-15, 18-20, 22, 25, 29, 31, 36, 37, 39, 43-45) and aluminum alloy foams (Ref 46), steels (Ref 13, 15, 16, 18, 22, 24, 27, 28, 30, 33-35, 39), magnesium alloy (Ref 41), molybdenum (Ref 13), titanium J.R. Po
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