1. Central crack loaded with stress.

(A) The stress intensity factor for a central line crack in an infinite plate is found to be  

 K=p(πa)^.5

where p is the pressure exerted along the crack line. (A) Does this formula imply a stable or an unstable crack propagation when p reaches the critical stress level? (B)  Present an experiment to support your answer in (A). Specify your experiment in details.