FIGURE P7.21 7.22 The initial design of a bolt loaded in tensile impact is shown in Figure P7.22a. The bolt fractures. next to the nut, as shown. A proposed redesign, Figure P7.22b involves drilling an axial hole in the unthreaded portion and incorporating a larger fillet radius under the bolt head a. What is the theoretically optimum diameter of the drilled hole? b. Using this hole size, by what approximate factor do the modifications increase the energy- absorbing capacity of the bolt? K=2.2 Hole dia., d K = 1.5 250 mm (Fracture location) dia. 36 mm A-800 mm² K 3.8 Assume that hole drilled to this depth, does not significantly change the K 3.8 factor at the thread. 3 mm (negligible) Original design Modified design CH