The Effect of the Size and Position of the Crack on the Normalized Stress Intensity Factor (original) (raw)
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ESTIMATION OF STRESS INTENSITY FACTOR (SIF) ON CRACK COMPONENT BY USING FINITE ELEMENT ANALYSIS
Theoretical solutions are available for idealized cases such as Infinite flat plate with edge crack, central crack etc. However main limitation of these theoretical solutions is they are very restrictive and while analyzing a normal component, a lot of assumptions go into it. Finite Element Analysis on the other hand provides good tool to determine Stress Intensity Factor. Cracks generally initiate at geometric discontinuities (such as notches, holes, weld toes, voids etc.) that induce large stress (stress concentration). Since crack growth is related to the effective stress intensity factor (SIF) which is at crack tip, the evaluation of Stress Intensity Factors. The present work would aim to fulfill this gap and generate more information thereby increased understanding on fracture behavior in 3D Components. Finite element analysis has been performed to support the results on fracture parameters like Location and Size of Cracks and results has been compared with available theoretical solutions. It is concluded that magnitude of critical Stress Intensity Factor can be used as a fracture criterion for thin Plates. Same procedure has been adapted for Analysis of connecting rod to find Stress Intensity Factor at various lengths of crack
2019
This paper proposes a combination of FRANC2D/L (2D crack growth simulation program) and ANSYS mechanical program (3D structural analysis for fracture mechanic analysis. The comparisons between the two software were performed for different case studies for stress intensity factors (SIFs) as well as crack growth trajectory. Crack growth was numerically simulated by a step-by-step 3D and 2D finite element method. The SIFs were calculated by using the displacement correlation technique. The procedure consists of computing SIFs, the crack growth path, stresses, and strain distributions via an incremental analysis of the crack extension, considering two and three-dimensional analysis. The finite element analysis for fatigue crack growth was performed for both software based on Paris's law as well as the crack orientation was determined using maximum circumferential stress theory. The simulation results obtained in this study using finite element method provide a good agreement with ex...
Stress intensity factor evaluation for central oriented cracks by stress dead‐zone concept
Material Design & Processing Communications
The concept of the stress dead zone (SDZ) at the crack vicinity of a plate submitted to a uniform tensile condition is key in the simplification of fracture characterization, in particular, in the calculation of the stress intensity factor (SIF). The stress field close to a crack face can be negligible in any structure, and thus, the corresponding region would be discarded from the initial structural component contributing to suppress the crack tip singularity. The computation of the Griffith compliance method based on disregarding this area can thereby be done with simple analytical formulations following linear elastic fracture mechanics principles. In this study, the SDZ concept was considered, together with the compliance function, to formulate the SIF analytical solution.
Crack-tip stresses and their effect on stress intensity factor for crack propagation
Engineering Fracture Mechanics, 2008
In this paper, analytical and numerical simulations of the crack-tip stresses are presented. Analytical calculations are performed utilizing modified Rice and elastic equations. 2D finite element analyses (FEA) are conducted in parallel using ANSYS. Results from both methods are compared and discussed in terms of the crack-tip compressive residual stresses. Then, the effect of the compressive residual stresses is quantified in terms of the stress intensity factor for crack propagation, K PR , using 'clamping force' method. The comparison between the calculated K PR values and those obtained experimentally by Lang demonstrates a fairly good agreement. Both the present results and Lang data independently support a two-parameter, K maxTH and DK TH , description of the threshold condition for fatigue crack propagation.
International Journal of Fracture, 2004
Linear elastic fracture mechanics (LEFM) integrated with the interference of fracture surface asperities has been formulated. The asperities are considered to simulate the influence of the microstructures and possibly oxide debris. The applied stress/load-crack opening displacement (COD) relationships in several cases have been derived. In the original LEFM, the stress-COD relationship is represented by a straight line passing through the origin of the stress-COD plot. The insert of one asperity results in a deviation of the stress-COD response from the LEFM relationship, leading to the exhibition of an inflection point (first contact point, σop), a larger slope, and a residual COD. In the case of two asperities, the slope and the residual COD of the stress-COD relationship become further larger, and two inflection points emerge. A general stress-COD expression in the case of multiple asperities has been derived. The slope of the stress-COD equation, the residual COD, and the minimum COD all increase with increasing number of asperities for a given loading condition, resulting in a smaller ΔCOD and Δσeff. The number of the inflection points is the same as that of the asperities. To the authors' knowledge, this paper is the first to derive analytically an applied stress-COD curve with a gradual variation below σop, caused by the asperity-/roughness-, or oxide-induced crack closure.
2012
A comparison between six models, calculating stress intensity factor (SIF) mode I for central cracked plate with uniform tensile stress, is made in order to select the suitable model. These models are three theoretical models (i.e. classical model) and three numerical models. The three numerical models are half ANSYS model, quarter ANSYS model (finite element method) and weight function model. The geometry of the cracked plate (the width of the plate, the length of the plate and the crack length) and applied stress are the parameters that used to compare between the models. The three theoretical models can recognize the effect of the width of the plate, the crack length and applied stress but they failed to recognize the effect of the length of the plate. The three numerical models are success to recognize the effect of geometry and loading parameters. But the half ANSYS model gives a different response to the variation of the (H/W) ratio and that occurs due to finding the stress in...
Evaluation of stress intensity factors using finite elements
The paper describes a suitability of Virtual Crack Extension (VCE) method for numerical simulation of crack propagation under mixed mode loading. The suitability of VCE method was determined using The Compact-Tension-Shear (CTS), which is subjected to fracture Mode I, Mode II or mixed mode (Mode I + Mode II) loading. In mixed mode the crack kinks when fracture crack growth occurs. Kink angle is determined with VCE method, which is an energy method, maximum tangential stress (MTS) criterion, strain energy density (SED) criterion and experimental results. Determination of crack propagation angle using MTS and SED criterion is based in regard to the stress intensity factors K I and K II . Stress intensity factors are determined using the maximum energy release rate theory using complex J integral, crack opening displacement method and method of stresses extrapolation. Bigger is the rate between K II and K I , crack path, determined with VCE method, propagates more slowly to the kink angle, determined with experiment. The computational results show that the VCE method is suitable for crack propagation, when K I around the crack tip is dominant. In case where K II is dominant, crack does not kink immediately as in other two criteria. When K II dominates around a crack tip, MTS criterion is the most appropriate for determination of kink angle.
Stress intensity factors for cracks in structures under different boundary conditions
Engineering Fracture Mechanics, 1990
In calculating stress intensity factor solutions for standard cases, the weight function and superposition technique have been used extensively. These solutions although valid for simple specimens present a problem in the case of statically indeterminate structures. The work described in this paper investigates the effect of boundary conditions on the stress intensity factor solution for an edge cracked plate, edge cracked ring and a surface cracked plate using the finite element technique.
Stress Intensity Factors For Plates With Collinear And Non-Aligned Straight Cracks
2012
Multi-site damage (MSD) has been a challenge to aircraft, civil and power plant structures. In real life components are subjected to cracking at many vulnerable locations such as the bolt holes. However, we do not consider for the presence of multiple cracks. Unlike components with a single crack, these components are difficult to predict. When two cracks approach one another, their stress fields influence each other and produce enhancing or shielding effect depending on the position of the cracks. In the present study, numerical studies on fracture analysis have been conducted by using the developed code based on the modified virtual crack closure integral (MVCCI) technique and finite element analysis (FEA) software ABAQUS for computing SIF of plates with multiple cracks. Various parametric studies have been carried out and the results have been compared with literature where ever available and also with the solution, obtained by using ABAQUS. By conducting extensive numerical stud...
Evaluation of Critical Stress Intensity Factor (Kci) For Plates Using New crack Extension Technique
Published in the Engineering and Technology Journal, University of Technology, Baghdad ,Iraq
The technique of crack extension is applied to the computation of critical stress intensity factor in linear elastic fracture mechanics for cracked plates in tension for different crack configuration (i.e. central crack, edge crack, and double edge crack). The new technique uses the Brown approximate solutions for stress intensity factors and the Westergaard analytical solutions for stress and displacement near a crack tip in finite plate to calculate crack extension during each load step and then calculating the critical stress intensity factor using an incremental procedure. A matlab program was developed for the purpose of this work, which proved to be a good tool for the computation of critical stress intensity factors for cracked plates. The results were in good agreement with results of other methods available in the literature.