The Fatigue Life Prediction Methodology Based on the Unigrow Model

Abstract

This paper is concerned with the problem of prediction of the total life of an engineering structure based on the fatigue crack growth model. The life of an engineering component is generally modeled as a combination of the time required for a crack to initiate and then the time required for crack to propagate till the final fracture. Unfortunately the crack initiation size is a vaguely defined parameter. In order to overcome this ambiguity it is proposed to model the total life of an engineering structure by using the UniGrow fatigue crack growth model with assumption of the intrinsic material parameter ρ* as an initial crack size. The method to overcome the small crack problem in fatigue crack modeling is presented as well. The proposed model was successfully used to predict fatigue lives of misaligned cruciform welded joints under a constant amplitude loading. Results from the analysis and experiment are in a good agreement.

A modification of UniGrow 2‐parameter driving force model for short fatigue crack growth

“…27,33,54 To overcome this limitation of the UniGrow model, Bogdanov et al 44 proposed a modification of the Creager-Paris-based SIF solution. However, it could not provide accurate FCG predictions for crack sizes close to the parameter, ρ * , in the SC regime because of the fact that FCG rates of short cracks are greater than those of long cracks under the same applied driving force.…”

“…The authors 44 corrected the Creager-Paris-based SIF solution so that actual stresses at the crack tip of a short crack, that is larger than those for long cracks, can be accounted for. Bogdanov et al 44 presented the proposed methodology by combining the UniGrow model with the Monte Carlo simulation to assess probability distributions of FCG coefficients and initial crack size; however, the validity of the proposed method for predicting short crack propagation behaviours in HCF was not specifically presented and reported. To make a comprehensive assessment of the UniGrow model with its current form for estimating fatigue lives of materials resulted from short crack propagations, 2 improvement FIGURE 4 A, Residual stress intensity factor as a function of the maximum stress intensity factor and the stress intensity factor range.…”

“…However, it could not provide accurate FCG predictions for crack sizes close to the parameter, ρ * , in the SC regime because of the fact that FCG rates of short cracks are greater than those of long cracks under the same applied driving force. 27,33,54 To overcome this limitation of the UniGrow model, Bogdanov et al 44 proposed a modification of the Creager-Paris-based SIF solution. The authors 44 corrected the Creager-Paris-based SIF solution so that actual stresses at the crack tip of a short crack, that is larger than those for long cracks, can be accounted for.…”

“…However, all these efforts only focused on analyzing fatigue crack propagation behaviours using the UniGrow model in the LC regime. Bogdanov et al 44 applied the UniGrow model to estimate fatigue crack propagation in the SC regime. The authors 44 corrected the stress intensity factor range by modifying stresses obtained from the Creager-Paris solution with the solution of boundary problem using an elliptical notch.…”

Fracture mechanics based estimation of fatigue lives of laser welded joints

“…One of the major challenges with the conventional LEFM approach is that the initial crack size is needed as the input, which is difficult to obtain experimentally. The UniGrow FCG model based on total fatigue life approach [19][20][21] has been utilized in this work which requires among others a material characteristic property, ρ* as input rather than the initial crack size. As per the total fatigue life approach the entire fatigue life can be estimated using ACCEPTED MANUSCRIPT…”