Jh Kim

Fatigue crack opening stress based on the strip-yield model

Abstract The modified strip-yield model based on the Dugdale model and two-dimensional approximate weight function method were utilized to evaluate the effect of in-plane constraint, transverse stress, on the fatigue crack closure. The plastic zone sizes and the crack opening stresses considering transverse stress were calculated for four specimens: single edge-notched tension (SENT) specimen, single edge-notched bend (SENB) specimen, center-cracked tension (CCT) specimen, double edge-notched tension (DENT) specimen under uniaxial loading. And the crack opening behavior of the center-cracked specimen under biaxial loading was also evaluated. Normalized crack opening stresses σop/σmax for four specimens were successfully described by the normalized plastic zone parameter Δω′rev/ω′ considering transverse stress, where Δω′rev and ω′ are the size of the reversed plastic zone at the moment of first crack tip closure and the size of the forward plastic zone for maximum stress, respectively. The normalized plastic zone parameter with transverse stress also was satisfactorily correlated with the behavior of crack closure for CCT specimen under biaxial loading.

Calculation of stress intensity factor using weight function method for a patched crack with debonding region

A patched crack with a debonded region is treated with a crack-bridging model: assuming continuous distribution of springs acting between crack surfaces. Adopting weight function method, the stress intensity factor for the patched crack within infinite plate is successfully obtained by numerical calculation. As the crack length a increases, the restraint on the relative displacement of the crack faces for a given value r0 is increased. The constant relative displacement (or crack surface displacement) did explain the reason for the constant stress intensity factors being independent of the crack length. A simple asymptotic solution was proposed for estimating the reduction of patching eAciency due to debonding and compared with numerical solution obtained by weight function method. ” 2000 Published by Elsevier Science Ltd.

Prediction of crack opening stress for part-through cracks and its verification using a modified strip-yield model

Abstract Newman’s crack opening stress equation [Newman JC. Jr. A crack opening stress equation for fatigue crack growth. Int. J. Fract. 1984;24:R131–R135.] was extended to predict the crack opening stress of part-through cracks within a finite body. The extended equation was obtained by replacing the normalized maximum applied stress S max / σ 0 as the normalized stress intensity factor (SIF) K max / K 0 , where K max is the SIF including the geometry correction factor F , and K 0 is the stress intensity factor for flow stress. In order to verify the crack opening stress obtained from the extended equation, the modified strip-yield model using a slice synthesis technique [Daniewicz SR. A modified strip-yield model for prediction of plasticity-induced closure in surface flaws. Fatigue Fract. Engng. Mater. Struct. 1998;21:885–901.] was utilized and the approximate weight function was modified to consider the effect of the restraint due to the uncracked area. For a corner crack or surface crack within a finite body, the crack opening stresses obtained from this model were correlated well with the results of the extended equation. Additionally, the crack shape evolutions of surface crack subjected to uniaxial constant amplitude loading or four-point bending loading were predicted by the extended crack opening stress equation and compared with experimental data for aluminium alloy specimens with R =0.1. The predictions were in good agreements with experimental data.

Stress intensity factors and crack initiation directions for ceramic/metal joint

Abstract Four points bending tests for Si3N4/Cu/S45C joint specimen showed that the bending strengths depend on the residual stresses that originated from joining process. The residual thermal stresses caused an edge sub-interface crack to initiate in the ceramic. The stress intensity factors (SIFs) of the edge sub-interface crack located at distance h from the interface with or without interlayer metal were calculated by the Greens function obtained from a finite element analysis. The crack path at the joint specimen under four points bending loading with the influence of residual stresses was also evaluated by the maximum tensile stress criterion. Finally the effect of residual stress on the crack path was found numerically; the interlayer metal decreases the deflection angle of crack from interface by reducing the residual stress.