3-D characterization of incipient spallation response in cylindrical copper under sweeping detonation
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Chen Jixiong School of Material Science and Engineering, Central South University, Changsha 410083, China
Guo Zhaoliang, Tang Tiegang, and Hu Haibo Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, China
Fu Yanan Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China (Received 15 August 2016; accepted 10 January 2017)
The effect of peak shock stress on the incipient spallation damage in a cylindrical sample under sweeping detonation is presented. The free surface velocity curve was measured by photon Doppler velocimetry and the quantitative investigation of voids in a spalled sample was performed using X-ray computer tomography. The results revealed that the maximum volume and the mean volume of voids in the spalled sample increased with increasing shock stress. The sphericity of voids decreases with the increasing of shock stress. The rod voids were the result of the independent growth of voids along the grain boundaries in samples with lower shock stress, while the rod shaped voids in sample with higher shock stress were formed due to coalesce. The rod voids can be found in a cylindrical sample, while the voids in plate samples were in the shape of spheres or ellipsoids, and the difference of stress state induced by the curvature in the geometry of samples may be the main reason.
I. INTRODUCTION
In shock loading processes like high-speed crash or detonation shock, the failure of metals subjected to this extreme loading condition is a series of complex phenomena, and one of the predominant modes of failure in shock loading is dynamic tensile damage (spallation). Spallation damage occurs when the interaction of two release waves leads to tensile stresses in a metal in excess of the threshold required for damage initiation. It has been verified that the spall process is due to void nucleation, growth, and coalescence during tensile loading in ductile metals, ultimately resulting in the formation of a spall layer.1 Researches over the past decades have obtained ample experimental data concerning the influence of the shock stress, pulse duration, and microstructure on spallation response.2,3 Gray4,5 investigated Ta using plate impact and sweeping detonation and demonstrated that the spall strength remains similar with different shock stresses under the same loading type, whereas Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.25
a lower spall strength than that in plate impact loading was obtained in Ta when the loading condition changes into sweeping detonation-wave instead. Historically, the experimental quantifications of spallation evolution were limited to two-dimensional (2-D) metallographic level using conventional techniques like optical microscopy (OM) as well as electron back-scattered diffraction (EBSD). With the development of technology, the widespread usage of X-ray computer tomography (XRCT) into the investigation of spallation affords a direct way
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