Question 5.3: Failure of Cracked Materials Under Static Loading Problem A ...
Failure of Cracked Materials Under Static Loading
Problem A steel support strap designed to hold a 60 000-N static load in axial tension was accidently sawcut during production and now has an edge crack in it. Determine the safety factor of the original, uncracked strap based on yielding and its new “cracked” safety factor based on fracture mechanics. How large could the crack get before it fails? Would heat-treating the part compensate for the loss of strength due to the crack?
Given The material is steel with S_{y} = 540 MPa and K_{c} = 66 MPa-m^{0.5}. The length l = 6 m, width b = 80 mm, and thickness t = 3 mm. The crack width a = 10 mm. The crack is completely through the thickness at one edge of the 80-mm width, similar to Figure 5-19c (p. 269).
Assumptions The load is static and the assembly is at room temperature. The ratio a/b is < 0.13, which allows use of equation 5.14d (p. 269).
K=1.12 \sigma_{\text {nom }} \sqrt{\pi a} \quad a \ll b (5.14d)
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