In a Charpy impact test a notched bar with the dimensions given below is struck by a hammer as shown in the diagram. In this problem the sample is a heat treated steel with a plane strain fracture toughness of only 10 ksi-in2. This steel is brittle enough so that plane strain conditions prevail during cracking. Make a lower bound estimate of the force P needed to cause fracture. Explain why the actual force might be larger than this estimate. -2 in Hammer 32 F in o ku