Jožef Predan

Semi-analytical approaches to assess the crack driving force in periodically heterogeneous elastic materials

When a crack propagates in a heterogeneous elastic material, its crack driving force depends strongly on the distribution of the local stiffness near the crack tip. In materials with periodic spatial variations of the Young’s modulus, shielding and anti-shielding effects appear, i.e. the crack driving force is reduced or enhanced, compared to a homogeneous material. The effect is of great practical relevance, since it may lead to a strong increase of the fracture resistance. The concept of configurational forces (CCF) offers an established procedure for calculating the crack driving force. A very general relation for the periodic variation of Young’s modulus is applied, allowing the description of both harmonically varying and layered microstructures. Numerical results are presented. Two semi-analytical approximation concepts, based on either the CCF or the moduli perturbation concept, are introduced and discussed. Comparisons are provided and recommendations given.

Comparison between Fracture Behaviour of Pipe-Line Ring Specimens and Standard Specimens

Thethin walled structures as pipe-line are often unsuitable for standard testingof fracture toughness. One possibility is applying non-standard modifiedspecimens with simple testing procedure, but measured fracture behaviour isconsequence of loading conditions and geometry of specimen. In this paper thedifferences in fracture behaviour of single edge notch bending (SENB) and ringpipe-line bended specimens are discussed. Especially uneven fatigue crack frontas consequence of complex fatigue loading caused different fracture behaviour,than standard single edge notch bending (SENB) specimens. The stress-strainconditions at the crack tip are analysed by finite element modelling. Thecritical crack tip opening displacement has been determined as a crack tipsurface strain-relaxation by using stereo-optical grading method. Comparisonbetween CTOD-R curves of both types of specimens shows difference in crackdriving force.

Application of the european SINTAP procedure to the failure analysis of a broken forklift

Abstract The recently developed European flaw assessment procedure SINTAP was applied to the failure analysis of a broken fork of a forklift. Based on the service load at failure critical crack sizes were determined at different analysis levels of the procedure. It was shown in the present case study that the reason of the failure was defective design.

On configurational forces at boundaries in fracture mechanics

Configurational forces invariably appear at the external boundaries of cracked bodies (including the crack faces), but it is unclear whether they influence crack growth. Also, it is unclear how such boundary configurational forces are related to the J-integrals calculated in the body. In this brief note, we (i) derive expressions for the surface configurational forces and determine their values on regions of the external boundaries with prescribed tractions or displacements, (ii) determine the relation between the far-field J-integral and the surface configurational forces, and (iii) show that surface configurational forces on the crack faces do not alter the relation between the near-tip and far-field J-integrals.

Effect of Strength of Mismatch Interface on Crack Driving Force

Abstract. A welded joint is a critical part of a welded structure with respect to defects, pores, geometry, misalignments, and mechanical anisotropy. Differences in the mechanical properties appear between weld metals, heat affected zone, and base metal. Crack growth resistance curves, e.g., determined in terms of crack tip opening displacement (CTOD), exhibit variations in the crack growth resistance of the welded joint as a consequence of the local variations in the material properties. Theoretical investigations have shown that also the local near-tip crack driving force (CDF) may deviate strongly from the far-field CDF, if the material properties vary locally. The reason is that the material inhomogeneity induces an additional CDF-term, called the material inhomogeneity term, Cinh, which leads to a shielding or anti-shielding of the crack tip. A model developed by Simha et al. is applied to evaluate the magnitude of Cinh in a welded joint with a strength mis-match interface. Both a stationary and a propagating crack are considered.

On problems with the determination of the fracture resistance for materials with spatial variations of the Young’s modulus

The paper considers the near-tip J-integral

Influence of Crack Length on Ductile Fracture Initiation in Welded Joints with one and Two Weld Metals

\text {J}_{\mathrm{tip}}

Analysis of deformation induced martensite in AISI 316L stainless steel

Jtip, the far-field J-integral