Spall response of single-crystal copper

Abstract

We performed a series of systematic spall experiments on single-crystal copper in an effort to determine and isolate the effects of crystal orientation, peak stress, and unloading strain rate on the tensile spall strength. Strain rates ranging from 0.62 to 2.2 × 106 s−1 and peak shock stresses in the 5–14 GPa range, with one additional experiment near 50 GPa, were explored as part of this work. Gun-driven impactors, called flyer plates, generated flat top shocks followed by spall. This work highlights the effect of crystal anisotropy on the spall strength by showing that the spall strength decreases in the following order: [100], [110], and [111]. Over the range of stresses and strain rates explored, the spall strength of [100] copper depends strongly on both the strain rate and shock stress. Except at the very highest shock stress, the results for the [100] orientation show linear relationships between the spall strength and both the applied compressive stress and the strain rate. In addition, hydrodynamic computer code simulations of the spall experiments were performed to calculate the relationship between the strain rate near the spall plane in the target and the rate of free surface velocity release during the pullback. As expected, strain rates at the spall plane are much higher than the strain rates estimated from the free surface velocity release rate. We have begun soft recovery experiments and molecular dynamics calculations to understand the unusual recompression observed in the spall signature for [100] crystals.

Stress and Strain Rate Effects on Incipient Spall in Tantalum

“…The factor of 1/2 results from the approximation that the particle velocity is half the free-surface velocity. It is important to note that this is a simple, although widely used, approximation; it is useful for comparison between samples, assuming that any errors are systematic and similar for all experiments [11]. From the columns for peak stress and strain-rate in Table 2 it is clear that the four experiments can be grouped into two low stress and two high stress shots, with a low strain-rate and a high strain-rate example in each.…”

Spallation Characteristics of Single Crystal Aluminum with Copper Nanoparticles Based on Atomistic Simulations

“…The predictive modeling of the experimentally observed behavior of metallic materials under shock loading conditions (wave structures, spall strengths) is a critical challenge toward the design of next-generation structural materials [3]. Earlier studies revealed that spallation is a complex multi-scale process [1,4], affected by many factors such as shock pressure [5], loading waveform [6], strain rate [7,8], temperature [9,10], and heterogeneity in the microstructure [11][12][13]. Compared to the loading conditions that can be directly controlled, it is more difficult to study the effect of microstructure on spallation due to the lack of high resolution and ultra-fast in-situ diagnostic technology.…”

Atomistic Simulations on Metal Rod Penetrating Thin Target at Nanoscale Caused by High-Speed Collision

“…Abundant work related to damage or spallation has been successfully conducted using MD simulations [10][11][12][13][14][15]. Many factors, such as the shock intensity [16], loading rate [17], crystalline orientation [18,19], intrinsic defect [20,21] impurity [22] and grain size [23,24], have been considered.…”