Fatigue crack closure model

Crack closure is a phenomenon in fatigue loading, where the opposing faces of a crack remain in contact even with an external load acting on the material. Modified ccs fatigue crack growth model for the aa2019. The causes of crack closure are typically associated with crack tip plasticity and residual plastic deformation, oxide debris, and surface roughness. Pdf crack closure effects on fatigue crack propagation rates. In this model, a stripyield methodology was used to simulate creep fatigue crack growth and to quantify the influence of hold time on plasticityinduced crack closure during creep fatigue crack growth. The purpose of this paper is to model analytically fatigue crack growth with a plasticityinduced crack closure effect in constant amplitude loading. A simple crack closure model for prediction of fatigue crack. At the same time, the first damage24 and geometrical deformation models2, 3, 4, 5 were proposed to explain the fatigue crack propagation.

The results showed a good agreement between the proposed modification of the ccs fatigue crack propagation model taking into account the plasticityinduced crack closure model with the boundary correction factor and experimental results of the fatigue crack propagation data for the 2219t851 aluminium alloy. Fatiguelife prediction methodology using a crackclosure model j. Crack closure is a phenomenon in fatigue loading, where the opposing faces of a crack remain. Mechanics of materials branch, nasa langley research center, hampton, va 23681. The present paper is concerned with the development and application of an analytical model of cyclic crack growth that includes the effects of crack closure. A geometric model for fatigue crack closure induced by fracture surface roughness. Crack closure effects on fatigue crack propagation rates. The model results also indicate that increased creep deformation at the crack tip caused by longer hold time leads to a diminishing influence of the plasticityinduced crack closure on the crack growth, thus an acceleration of the crack growth rate during the cyclic portion of a creep fatigue cycle. A crack closure model of fatigue crack growth in plates of finite. The crack closure and opening effects can be estimated using an elastoplastic analysis based on analytical 3, 19 or numerical, 14 approaches. This model advances the idea that a decrease of plasticityinduced crack closure is experienced by the crack during fatigue loading when a longer hold time is applied each creepfatigue cycle. Materials whenever subjected to fatigue cracking may exhibit mean stress effects as well as crack closure effects. The implications of crack closure on fatigue crack are considered. Key words suggested by authors fatigue crack growth crack closure ti6al4v titanium.

A fatigue crack closure model is developed that includes the effects of, and interactions between, the three closure mechanisms most likely to occur at threshold. His work is currently published in international journal of fatigue. Fatigue life prediction methodology using a crackclosure model j. A geometric model for fatigue crack closure induced by. Crack closure occurs from the presence of material propping open the crack faces and can arise from many sources including plastic deformation or. A crackclosure model for predicting fatiguecrack growth under. A closure model for predicting crack growth under creep. Fatiguelife prediction methodology using a crackclosure. Crack closure is the most used mechanism to model thickness and load interaction effects on fatigue crack propagation. A crack closure model for predicting fatigue crack growth. On the dominant role of crack closure on fatigue crack growth. In the present paper, a geometric model is presented for crack closure induced by fracture surface roughness. In this paper, a theoretical model based on the same initial assumptions of the analytical models proposed by hudak and davidson and ellyin is.

The occurrence of crack closure was directly measured by an electricalpotential method, and indirectly by loadstrain measurement. Mechanisms for fatigue crack closure under plane strain conditions have recently been identified at very low nearthreshold stress intensities in terms of effects of excess corrosion deposits or fracture surface roughness in promoting premature closure of the crack. Consequently, the crack tip experiences an increase in the effective stress intensity factor range causing faster growth rate during the fatigue loading. Fatigue crack closure analysis and crack propagation estimation.

Modified geometry effects on plane stress fatigue crack closure 485 stripyield model predictions of crack opening loads are often presented as being independent of crack size. Wei lehigh university bethlehem, pennsylvania summary crack closure phenomenon in fatigue was studied by using a ti6a14v titanium alloy. This model, herein referred to as the crop model for closure, roughness, oxide, and plasticity, also includes the effects of out. These experiments have shown that crack closure is a significant factor in causing loadinteraction effects retardation and acceleration on crack growth rates under variableamplitude loading. A geometric model for fatigue crack closure induced by fracture surface. An assessment of geometry effects on plane stress fatigue. The experimental results show that crack closure cannot fully account for the effect of stress ratio, r, on crack growth, and that it cannot be regarded as the sole cause for delay. A loading stage for the scanning electron microscope has been used in conjunction with the stereoimaging technique to study fatigue crack closure for a. Crack closure effects on fatigue crack propagation rates hindawi. Fatigue crack growth resistance and crack closure behavior in two.