Question

S.,kpsi The bar shown in Fig. 6-16 is subjected to a repeated moment 0 <M<1200 lbf in. The bar is AISI 4430 steel with Sut = 185 kpsi, Sy=170 kpsi, and Kic=73 kpsiin. Material tests on various specimens of this material with identical heat treatment indicate worst-case constants of C = 3.8(10-1)(in/cycle)/(kpsiVin) and m= 3.0. As shown, a nick of size 0.004 in has been discovered on the bottom of the bar. Estimate the number of cycles of life remaining. The stress range Ao is always computed by using the nominal (uncracked) area. Thus I bh? 0.25(0.5)2 -= 0.01042 in? Č66 Therefore, before the crack initiates, the stress range is ** 1/0 0.01042 4 = 115.2(10%) psi = 115.2 kpsi 40 AM 1200 a = c(SK Κ = Υσπα *assume Y = B = 1 - Ni= 1 a da = c) (BAO V ta) 16-6)

Answer 1

Given, Number of life cycles to failure ? da I (B - suam СВД — ут)т. Ć ! 2,; Tajm da ¿ CB Ao Doim do (a)m/ I am of amla da Nf = (Borstjan Nf = 1 fm 2h yag Ĉ (Boo FT) M L cm + 1 to ao =0, af = 0.004 in c= 3.8810-1 ian/cycle (kp si dinim ai B =1 a = 115.2kpsi m = 3.0 - (-₂) H 0.004 IXIS No = 3,091.250 x 60.004)*7 Ng = 97,75 3.914 Cycles (or) - 9.7753 x 104 cycles