Within the limit of relatively short arrested crack, the static approximation appling linear fracture mechanics has yielded basis for theoretical investigation and practical application of currently used brittle fracture propagation and arrest test. But later experimental investigation using very wide specimens have revealed that the simple interpretation based on the arrest toughness concept fails to have a consistency with the case of long arrested crack. It is considered that the inadequacy of the arrest theories comes from the fact that dynamics aspects associated with fast crack propagation have been disregarded. In search of a more relevant theory and to see how the neglection of dynamic aspects affects the interpretation of unstable crack propagation arrest test and philosophy of crack arrest design, dynamic fracture mechanics analysis was made with the use of the finite-difference method to solve the equation of motion for the two dimensional elastic problem. This report gives preliminary results of some numerical examples showing applicability of the numerical method as a useful tool to analyze experimental observations in terms of dynamic fracture mechanics with a focus on energetics aspect of the crack propagation and arrest processes.