疲労きれつ伝播速度に関する研究(第1報)

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In this paper, phenomenon of fatigue crack propagation is considered as continuous fatigue crack initiation at crack tip. It is assumed that fatigue crack initiation life is used up when damage caused by cyclic strain near crack tip is accumulated and magnitude of the damage is reached to a certain critical value at ΔN strain cycles and size of the crack length Δa is average grain size of material. Using the above assumptions and proposed cumulative damage law, crack propagation rate da/dN under fully reversed loading is expressed by the following equation. [numerical formula] where Δε_p : cyclic plastic strain range at a point situated Δa apart from crack tip ε_f : monotonic true fracture strain ε_0 : maximum strain at 1 st cycle d : average grain size α : exponent in equation Δε_p^α・N_c=constant The above equation can be transformed in to the following form. [numerical formula] where ΔK : range of stress intensity factor E : Young's modulus Z : (1-n)/(1+n) n : exponent in equation of cyclic stress-strain curve with strain hardening effect _Y' : yield stress in the cyclic stress-strain curve Further, the above equation may be expressed by the well known power low formula approximately in the range where K is 50 kgmm^<-3/2>500 kgmm^<-3/2>. [numerical formula] There is the following relation between coefficients C and m. [numerical formula] Crack propagation rates calculated by these equations agree with experimental ones of mild steel quite well, and then these equation may be used for estimation of crack propagation life with good accuracy.
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疲労きれつ伝播速度に関する研究(第1報)

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