F W a f(a/w) 2.0 20 1.5 1.0 0 0.1 0.2 a/w b Figure 10.17. (A) Support shape. (B) Variation of f with a/w. 0.3 0.4 3. The support in Figure 10.17a is to be constructed from a 4340 steel plate tempered at 800F. The yield strength of the steel is 228 ksi and its value of Kic is 51 ksi√(in). The width of the support, w, is 4 in., the length, L, is 36 in. and the thickness, t, is 0.25 in. Figure 10.17b gives f(a/w) in the equation σ = Kic/[f(a/w)/(a)]. A. If the crack length, a, is small enough, will the support yield before it fractures? What is the size of the largest crack for which this is true (i.e., what is the largest value of a for which general yielding will precede fracture)? Assume that any fracture would be in mode I (plane strain). Discuss critically the assumption of mode I. B. If it is guaranteed that there are no cracks longer than a length equal to 80% of that in A, does this assure that failure will occur by yielding rather than fracture? Explain briefly.