Effect of Microcracks on the Toughness of Particulate Composites

The crack tip region in an elastic composite can be separated into three different regions. based on a simple rate-independent phenomenological constitutive model, the path independence of the J-integral and the concept of cracktip shielding, the maximum radii R of the damage saturation zone is obtained. Damage isotropy in the largest saturated damage zone is expressed by utilizing the Monte-Carlo technique to create the uniform distributions of microcrack location and orientation. With the assumption of dilute microcrack concentration, interaction among microcracks are neglected, and the stress intensity factor produced by interaction between main-crack and each microcrack can be superposed. Two sources of loading are analyzed, one is for the main-crack microcrack interaction under an applied remote load, and the other is for the main-crack microcrack interaction accompanied by the relief of residual stresses on the microcrack surfaces. The results show that two sources of loading can shield the main-crack tip, and microcracks behind the main-crack tip can make the most shielding whereas microcracks ahead of the main-crack tip play no role in shielding.