Spall Behavior of Cast Iron with Varying Microstructures

Abstract

The spall strength of five cast irons with varying microstructures have been investigated with the use of plate impact experiments conducted in a vacuum. A single stage gas gun was utilized to drive projectiles to velocities between 100 and 300 m/s, resulting in low to moderate shock loading of the cast iron samples. Measurement of the stress histories were made with the use of commercial manganin stress gauges that were imbedded between the back face of the cast iron specimen and a low impedance backing of polycarbonate. Spall strength values were calculated utilizing the measured peak stress and pullback stress signals captured in the stress history. Strength values were found to vary between 0.44 and 1.6 GPa respectively as a function of the damage evolution from initiation of micro-cracks to complete spall fracture. Post mortem analysis of spalled samples has shown the graphite phase to be the primary factor influencing the failure process. SEM micrographs indicate that initial failure occurs due to the debonding of graphite from the metal matrix. It has been noted that subsequent coalescence of initiated cracks into a complete fracture plane is correlated to both the microstructural components of the metal matrix and relative spacing of the graphite phase.