70,000 cycles 30,000 cycles 10,000 cycles с S Webmail SA = 160 Mpa SB = 210 Mpa SC = 260 Mpa B R=0 Time A very wide thin plate (plane stress) made of low carbon steel with a center crack length 2a = 6 mm and material properties Sy = 350 MPa, Sut = 550 MPa, K=110 MPa Vm, and AK = 5 MPa Vm is subjected to variable amplitude loading as shown in the figure above. For loading shown, treat R=0. Fatigue da crack growth rate is governed by: = 6.9x10-AK', where da/dN is in m/cycle and AK in MPa Vm. IN Answer the following questions: (a) Determine Ki at time A (first cycle of loading and compare with AK, and K. Will the crack grow? (6) What value of Smax will not cause crack growth at time A? (c) Find the crack length at times B, C and D. (d) Find Ki at times B, C and D and compare with ke (e) Find the plane stress plastic zone size / at A, B, C and D. (f) Find the total number of cycles to cause fracture if Sma=260 MPa is continued beyond D until fracture (B) IS LEFM applicable in (a) through ? Substantiate your answer.
You can directly integrate Paris law or use the equation below for FCGR Paris Law da dN =c (CΔσ πα)" Ao PRE Fatigue cycles for crack growth from a to aj. N- 2 (m -2)C,C" (Ac)" " 1 -212 for m2 (a)-2 (a)(-2) a N 1 In CC (Δσ) π form = 2
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