EMBRYO-DAMAGE INDUCED NUCLEATION OF MICROCRACKS IN AN ALUMINUM-ALLOY UNDER IMPACT LOADING

The nucleation of microdamage under dynamic loading was investigated t hrough planar impact experiments accomplished with a light gas gun. Th e microscopic observation of recovered and sectioned specimens showed that microcracks were nucleated only by cracking of brittle particles inside material. However, for comparison the in situ static tensile te sts on the same material conducted with a scanning electron microscope showed that the microcracks were nucleated by many forms those were f racture of ductile matrix, debonding particles from matrix and crackin g of brittle particles. The quantitative metallographic observations o f the specimens subjected to impact loading showed that most of the cr acked particles were situated on grain boundaries of the aluminium mat rix. These facts suggested the concept of critical size and incubation time of submicroscopic cavities in the dynamic case and the mechanism of embryo-damage induced nucleation by fracture of brittle particles in the aluminium alloy under impact loading was proposed.