Papers by Keyword: Mixed-Mode Loading

Abstract: The creep crack problem in damaged materials under mixed mode loading is considered. The class of the self-similar solutions to the plane creep crack problems in a damaged medium under mixed-mode loading is given. With the similarity variable and the self-similar representation of the solution for a power-law creeping material and the power-law damage evolution equation the near crack-tip stresses, creep strain rates and continuity distributions for plane stress conditions are obtained. The self-similar solutions are based on the hypothesis of the existence of the completely damaged zone near the crack tip. It is shown that the asymptotical analysis of the near crack-tip fields gives rise to the nonlinear eigenvalue problems. The technique permitting to find the eigenvalues numerically is proposed and numerical solutions of the nonlinear eigenvalue problems arising from the mixed-mode crack problems in a power-law medium under plane stress conditions are obtained. Using the approach the eigenvalues different from the eigenvalues corresponding to the Hutchinson-Rice-Rosengren (HRR) problem are found. Having obtained the eigenspectra and eigensolutions the geometry of the completely damaged zone in the vicinity of the crack tip can be found for all values of the mixity parameter.

Abstract: The experiments of mixed-mode I-II fatigue crack growth under stress redistribution at crack tips were conducted with compact specimens made of 16MnR steel. This test consisted of the 1st, the 2nd and 3rd step. When the crack reached a certain length in 1st step, the loading direction was switched to a certain angle. Finally, the loading direction was returned to the original orientation. The stress redistribution of mixed-mode fatigue was formed by altering the loading direction at propagating crack tips. A finite element analysis was also conducted to obtain the and values, and then mixed-mode crack growth parameters were adopted to evaluate the crack growth rate and crack paths. The crack growth paths had a tendency perpendicular and across to the loading axis. Right after the loading direction was changed, the crack growth rate was decreased rapidly, and crack growth paths under the stress redistribution zone (SRZ) were affected.

Abstract: Several hypotheses and concepts exist for the prediction of crack deflection angles from the analysis of the undisturbed stress distribution at the crack front. In this paper, a finite element analysis of small penny shaped secondary cracks with deflection angles ψ₀ = π/4 at a pure mode III loaded crack front is presented. The results are compared with the solutions of the well-known 3D fracture criteria. The fracture mechanical analysis is performed by the highly effective MVCCI-method.

Abstract: Fracture studies of components involving mode III loading are rare. This paper concentrates on mixed-modes I, II and III fracture testing of brittle PMMA material and summarises an extensive experimental investigation. Karpour and Zarrabi have developed a special pair of grips for which they have received a patent. These grips allow the application of various mixtures of modes, including mode III, using a universal testing machine. To measure the three-dimensional crack-tip opening and sliding displacements, Karpour and Zarrabi have also developed a novel stereo machine vision system whose description is included in the paper. The measured critical crack-opening displacements presented in normalised format with potential of being used to assess the integrity of any component against elastic fracture and they compare well with limited pertinent data available from literature.

Abstract: Some authors proposed to combine a torsional loading of cylindrical specimens with surface semi-elliptical cracks (the principal axes along the axial direction) with superimposed static axial compression in order to eliminate kinking or branching of shear cracks from the shear plane. To authors’ knowledge, however, no precise numerical analysis of such a loading configuration is currently available. The aim of this article is to calculate stress intensity factors KI, KII and KIII along the semi-elliptical crack front using the ANSYS code. The problem is solved for a semi-circular crack front and various crack inclination angles. The results reveal that the compressive loading cannot eliminate the branching process. The inclination of the crack plane induces a rather high opening mode which means that the microscopically tortuous fatigue cracks observed in experiments grew under mixed-mode I+II+III.

Abstract: In this paper a detailed 3D-finite element analyses results of modified compact tension shear (MCTS)-specimens with an inclined crack plane or crack front under mixed-mode loading conditions are presented. It is found that under mixed-mode loading, a superposition of all fracture modes I, II and III can be generated along the straight crack front of MCTS-specimens, and the maximum of the total SERR along the crack front of two different MCTS-specimens is found at right hand side of crack front corner，where the risk of crack initial growth is highest. The computational fracture analysis is based on the calculation of separated energy release rates GI, GII and GIII along the crack front by the numerically highly effective modified virtual crack closure integral(MVCCI)-method.