Prediction of Crack Initiation and Crack Propagation Life of Carbon Steel Subjected to Repeated Impact Tensile Loads

Abstract

In order to study the effect of the loading time of impact tensile loads on the crack propagation rate, impact fatigue tests were carried out on circumferential V-notched specimens of 0.2% carbon steel by using a repeated impact tensile loading apparatus.
Based on the experimental data, the crack initiation life and the crack propagation life for circumferential V-notched specimens were estimated empirically.
The results obtained were summarized as follows;
(1) The relation between the striation spacing (S) and the stress intensity factor (ΔKI) is given empirically by,
S=C0TnsΔKIms
where C0, ns, and ms are experimental constants, and T is the loading time of impact tensile loads.
(2) The crack propagation life (Np) and the crack initiation life (Nc) can be estimated by the following formulas and the estimated values were found to agree with the experimental results.
Np=∫afaida/C0TnsΔKIms
Nc=(D*/σ)1/m*T-n*/m*-∫afaida/C0TnsΔKIms
where D*, m*, and n* are experimental constants, ai is the initial crack size, and af is the final crack size.