Crack Opening Stress Research Articles

Fatigue crack closure at stress intensity threshold level

Recently, the application of fracture mechanics to metal fatigue has proven to be quite successful, that is, the fatigue crack propagation rate da/dn has been known to be expressed well by a power function of the range of stress intensity factor AK [I]. This expression, however, is not applicable to the case of very low crack propagation rate, and there is the stress intensity threshold level AK.. below which fatigue crack propagation becomes insignificant [2]. tn On the other hand, the stress ratio R(=o . /a =K . /K ) has been _. I mln _max mln max _ . found to influence the Xa~lgue crack propagation rate and the stress intensity threshold level [2-4]. Furthermore, observations of the tip of crack have revealed that the fatigue cracks are partially closed, even though loading is tension-tension. By considering the effective stress intensity range AK ~. which is calculated from the el crack opening stress, the effect of stress ratlo on the crack propagation rate has been explained [5]. The authors have suggested by a result of measurement on very low propagation rates for various stress ratios that the fatigue crack closure at the stress intensity threshold level shows a particular behavior [4]. To clarify this phenomenon further, the behavior of fatigue crack closure at AK _ was investigated for R of -i, -0.5, 0, 0.4, 0.6, and 0.8 in HTS0 stee~

Elastic-Plastic Analysis of a Propagating Crack under Cyclic Loading

Fatigue cracks have been experimentally shown to close at positive stresses during constant-amplitude load cycling. The crack-closure phenomenon is caused by residual plastic deformations remaining in the wake of an advancing crack tip. This paper is concerned with the development and application of a two-dimensional finiteelement analysis to predict crack-closure and crack-opening stresses during specified histories of cyclic loading. An existing finite-element computer program which accounts for elastic-plastic material behavior under cyclic loading was modified to account for changing boundary conditions—crack growth and intermittent contact of crack surfaces. This program was subsequently used to study the crack-closure behavior under constantamplitude and simple block-program loading. a [B]

An elastic-plastic finite element analysis of crack tip fields under biaxial loading conditions

A square plate containing a central crack and subjected to biaxial stresses has been studied by a finite element analysis. An elastic analysis shows that the crack opening displacement and stress of separation ahead of the crack tip are not affected by the mode of biaxial loading and therefore the stress intensity factor adequately describes the crack tip states in an elastic continuum.

Compatibility of linear elastic ( k1 c) and general yielding (COD) fracture mechanics

An investigation of the applicability of the general yielding fracture mechanics concept of crack opening displacement is made in relation to the well established concepts of linear elastic fracture mechanics. The nature of the relationship between crack opening displacement and stress intensity factor is explored using the concepts of linear elasticity and model analyses proposed by Dugdale. Tests on C/Mn steel, a low alloy steel and a manual metal arc weld deposit define the nature of this relationship in the stress region for which the theoretical compatibility is no longer to be expected. Based on this relationship a single fracture test procedure may be used to determine COD or K 1 c (depending on the stress conditions at failure). The results of the tests analysed in terms of J, the contour integral, determine the significance of J as a fracture characterising parameter. Defect tolerance parameters for the assessment of the significance of flaws in welded structures are also introduced.