![\"spall\"](\"http:\/\/labs.engineering.asu.edu\/pperaltawp-content\/uploads\/sites\/15\/2013\/10\/spall.png\")
<\/a><\/p>\nFigure 1: Examples of a) incipient spall [Peralta et. al, Int. J. Damage Mechanics, 2009], b) intermediate spall [S. DiGiacomo, 2008], and c) spall fracture [S. Hashemian, 2008].<\/p>\n
The incipient stage of spall damage (Figure 1-a) is necessary in order to characterize the intrinsic strength of microstructural characteristics (i.e. grain boundary misorientation, grain boundary type, Taylor factor mismatch, etc.) that are either more susceptible or resistant to damage nucleation.<\/p>\n
Three dimensional studies are performed via serial sectioning coupled with electron backscattering diffraction (EBSD), scanning electron microscope (SEM) imaging and optical microscopy, and 3-D X-ray tomography to achieve a comprehensive 3-D analysis of spall damage and the surrounding microstructure. Figure 2 shows a shocked copper multicrystal with 3-D reconstructions of both the spall damage and the microstructure from serial sectioning techniques.<\/p>\n
Figure 2: a) Spall zone in shocked sample, b) superimposed with the microstructure. Colors in (b) represent crystallographic directions parallel to the shock in each grain, as per the standard stereographic triangle inset.<\/p>\n X-ray tomography is used to acquire much higher resolutions of voids than from serial sectioning in order to understand how processing conditions, and thus various microstructures, affect the size and shapes of the voids. The void shapes and sizes may then be studied in conjunction with the surrounding microstructure to draw conclusions on what local features are indicative of void nucleation and growth.<\/p>\n Figure 3: X-ray tomography of a copper polycrystal. The \u201csheet-like\u201d shapes are indicative of intergranular damage nucleation and growth.<\/p>\n Characterization of damage induced by shock waves requires good fidelity models of the dynamics of shock wave propagation through a material. Examples of time of evolution of pressure, damage and particle velocity during a plate impact test obtained using finite element models that account for for elastic, plastic, hydrodynamic and damage behavior can be seen by using the links shown below :<\/p>\n PRESSURE<\/a>\u00a0 \u00a0\u00a0VELOCITY<\/a>\u00a0 \u00a0DAMAGE<\/a><\/p>\n Constitutive crystal plasticity models with and without damage criterion are run in ABAQUS to study the effects of stress concentration and strain localization on the damage initiation and evolution in FCC multicrystals using the actual microstructure obtained from 3-D characterization. Figure 4 shows how finite element models can be used to simulate experimental data.<\/p>\n<\/a><\/p>\n<\/a><\/p>\n