ABSTRACT
This chapter focuses on primarily the porosity, and secondarily the micro-crack, dependence of fracture energy and fracture toughness nominaiJy at -22°C, where the bulk of the data is. It shows that overall fracture energy and toughness trends, and frequently individual data sets, are consistent with minimum solid model (MSA) and E-P trends, but there are significant variations which must be considered when evaluating the porosity dependence of these properties. The chapter demonstrates that variations are mainly due to crack interactions with various combinations of larger grains and pore distributions on a scale substantially larger than that of the microstructure. It also show that porosity and microcracks often have similar effects, but issues of pore-microcrack interactions, stress/crack-generated versus preexisting microcracks, and behavior of some micro-cracks remain. Correlation with Young's modulus and its porosity dependence and direct applicability of MSA models thus provides an important basis for evaluating the porosity dependence of fracture energy and toughness.
