LIMIT LOAD AND J‐ESTIMATES FOR IDEALISED PROBLEMS OF DEEPLY CRACKED WELDED JOINTS IN PLANE‐STRAIN BENDING AND TENSION

Abstract

Using simple assumed deformation fields, approximate solutions have been obtained for tension and bending specimens containing welds for both limit loads and for fully plastic proportionality coefficients between the singular field amplitude J and the strain energy. The solutions allow for the degree of over or undermatch in the material tensile properties of the weld metal relative to the parent steel, and for the size of the weld region relative to the remaining ligament ahead of the crack.Detailed finite-element analyses have been performed for particular values of under/over-match and size of weld region. These refine the approximate analytical solutions for the particular cases examined, and show broad agreement with the trends predicted by the analytical models.The results have been used to provide guidance for testing weldments using standard, bend-type geometries. For small-specimen testing, cracks should be sufficiently deep for the remaining ligament ahead of a centrally located crack to be less than the total width of the weld. For large specimens, the weld region should be less than 20% of the size of the remaining ligament. If these guidelines are followed then standard relationships may be used to derive J from the area under the load-displacement curve.Common advice that the tensile properties of the weaker material in a weldment should be used in J-estimation techniques has been shown to be appropriate in many cases. However, the advice is likely to be overconservative when plastic deformation is predominantly in the weld even for overmatched weld properties, or predominantly in base metal even for undermatched weld properties. The results in the paper enable such cases to be identified. NOMENCLATURE a = crack length A = integration area b = thickness of the plastic mechanism c = semi-width of the punch loading of the 3PB specimen C = elastic compliance D = measure of contour dependence G = virtual extension function h = semi-width of the weld material J = crack tip integral fracture parameter k = uy/2 or 0,,/,/3 for Tresca and von-Mises effective stresses, respectively k, = k for the weld material K = stress intensity factor I = ligament length I,,, = length of the plastic mechanism l,, = reference length M = bending moment B, = thickness of the specimen 1061 1062 J. JOCH et al. nJ = component of the outward unit vector normal to contour r P = load per unit thickness P, = limit load PLr = limit load normalised by single base material limit load r = radius of the postulated plastic mechanism in bending u, = component of displacement vector u , ,~ = derivative of u, with respect of xJ U,, = strain energy U; = strain energy of elastic specimen Up, = dissipated energy Ut0 = area under the load-displacement curve ti = velocity of sliding along the plastic mechanism W = width of the studied specimen x, = component of the Cartesian coordinate system (x, is parallel to crack direction) b = angle describing the postulated plastic mechanism 8, = angle p which minimises the dissipated energy y = shear strai...

The effect of the weld mismatch on the yield load of C(T) and SE(B) fracture specimens

“…Sin embargo, la presencia de un material con propiedades diferentes, en la proximidad de una grieta, también puede alterar la distribución de tensiones en el entorno de ésta. Joch et al [3] y Burstow y Ainsworth [4] , usando el método de elementos finitos, mostraron cómo el campo de líneas de deslizamiento en probetas de flexión y tensión se altera por cambios en el límite elástico del material de base que rodea a una región de metal de soldadura que contiene una grieta.…”

Mismatch limit loads and approximate J estimates for tensile plates with constant-depth surface cracks in the center of welds

“…As the accuracy of the defect assessment methods modified for strength mismatch effects is directly related to the plastic limit load, accurate estimation of mismatch limit loads is essential for assessing cracked structures with weldments (Hao et al 1997;Joch et al 1993;Kim et al 2000;Schwalbe et al 1997; Lei and Ainsworth 1997;Kotousove and Mohmed 2006). Limit load solutions for mismatched plates have been presented by several researchers, see for instance Kim and Schwalbe (2001a, b, c), Schwalbe et al (1996), Hao et al (1997), Joch et al (1993) and Burstow et al (1998).…”

“…Limit load solutions for mismatched plates have been presented by several researchers, see for instance Kim and Schwalbe (2001a, b, c), Schwalbe et al (1996), Hao et al (1997), Joch et al (1993) and Burstow et al (1998). For instance, via extensive two-dimensional finite element (FE) analyses using elastic-perfectly plastic materials, the authors presented closed-form mismatch limit load solutions for middle cracked tension plates, single-edge-cracked plates in bending and double-edge-cracked plates in tension (Kim and Schwalbe 2001a, b, c).…”

Evaluation of Weld Homogenization Schemes Based on Plastic Loading of Single Edge Notched Tension (SE(T)) Tests

“…Researchers [12,[17][18][19][20] typically assume that the slip line pattern obtained from a notched weld is a straight line, mostly 45 0 . This consideration was based on a homogeneous body or a mismatched weld.…”