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Concept
Spallation
Summary
Spallation is a process in which fragments of material (spall) are ejected from a body due to impact or stress. In the context of impact mechanics it describes ejection of material from a target during impact by a projectile. In planetary physics, spallation describes meteoritic impacts on a planetary surface and the effects of stellar winds and cosmic rays on planetary atmospheres and surfaces. In the context of mining or geology, spallation can refer to pieces of rock breaking off a rock face due to the internal stresses in the rock; it commonly occurs on mine shaft walls. In the context of anthropology, spallation is a process used to make stone tools such as arrowheads by knapping. In nuclear physics, spallation is the process in which a heavy nucleus emits numerous nucleons as a result of being hit by a high-energy particle, thus greatly reducing its atomic weight. In industrial processes and bioprocessing the loss of tubing material due to the repeated flexing of the tubing within a peristaltic pump is termed spallation.
Spallation can occur when a tensile stress wave propagates through a material and can be observed in flat plate impact tests. It is caused by an internal cavitation due to stresses, which are generated by the interaction of stress waves, exceeding the local tensile strength of materials. A fragment or multiple fragments will be created on the free end of the plate. This fragment known as "spall" acts as a secondary projectile with velocities that can be as high as one third of the stress wave speed on the material. This type of failure is typically an effect of high explosive squash head (HESH) charges.
Laser induced spallation is a recent experimental technique developed to understand the adhesion of thin films with substrates. A high energy pulsed laser (typically Nd:YAG) is used to create a compressive stress pulse in the substrate wherein it propagates and reflects as a tensile wave at the free boundary. This tensile pulse spalls/peels the thin film while propagating towards the substrate.
Official source
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