Crack-tip stresses and their effect on stress intensity factor for crack propagation (original) (raw)
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A numerical study of non-linear crack tip parameters
Frattura ed Integrità Strutturale, 2015
Crack closure concept has been widely used to explain different issues of fatigue crack propagation. However, different authors have questioned the relevance of crack closure and have proposed alternative concepts. The main objective here is to check the effectiveness of crack closure concept by linking the contact of crack flanks with non-linear crack tip parameters. Accordingly, 3D-FE numerical models with and without contact were developed for a wide range of loading scenarios and the crack tip parameters usually linked to fatigue crack growth, namely range of cyclic plastic strain, crack tip opening displacement, size of reversed plastic zone and total plastic dissipation per cycle, were investigated. It was demonstrated that: i) LEFM concepts are applicable to the problem under study; ii) the crack closure phenomenon has a great influence on crack tip parameters decreasing their values; iii) the ?Keff concept is able to explain the variations of crack tip parameters produced by...
A numerical study of non-linear crack tip parameters.PDF
Crack closure concept has been widely used to explain different issues of fatigue crack propagation. However, different authors have questioned the relevance of crack closure and have proposed alternative concepts. The main objective here is to check the effectiveness of crack closure concept by linking the contact of crack flanks with non-linear crack tip parameters. Accordingly, 3D-FE numerical models with and without contact were developed for a wide range of loading scenarios and the crack tip parameters usually linked to fatigue crack growth, namely range of cyclic plastic strain, crack tip opening displacement, size of reversed plastic zone and total plastic dissipation per cycle, were investigated. It was demonstrated that: i) LEFM concepts are applicable to the problem under study; ii) the crack closure phenomenon has a great influence on crack tip parameters decreasing their values; iii) the Keff concept is able to explain the variations of crack tip parameters produced by the contact of crack flanks; iv) the analysis of remote compliance is the best numerical parameter to quantify the crack opening level; v) without contact there is no effect of stress ratio on crack tip parameters. Therefore it is proved that the crack closure concept is valid.
WIT Transactions on the Built Environment, 1970
Linear fracture mechanics gives possibility for assessment of the fatigue crack propagation. The difficulties in obtaining of the strict solution for stress intensity factor and uncertainties in results can be overcome by using a numerical calculation. The discussion on theoretical approach for part of such model is performed and captures of the screen of the computer program using this approach are plotted.
Residual Stress-induced Crack-tip Constraint: A Parametric Study
Ecf17 Brno 2008, 2013
In this work, the effect of residual stress on the crack-tip constraint is studied under mode I, plane strain conditions. The modified boundary layer simulations are performed with the remote boundary conditions controlled by the stress intensity factor K and T-stress. The eigenstrain method was used to introduce a two-dimensional residual stress field near the crack-tip. It is found that the residual stress field can significantly elevate the crack-tip constraint and thus enhance the probability for cleavage fracture. The constraint parameter R is defined to characterize the residual stress-induced crack-tip constraint. Results also show that the R value decreases with the increase in the external load. The effect of residual stress on the crack-tip constraint is smaller for weaker hardening materials. The R value was also calculated for different geometry constraint level, and the results indicate that the R becomes smaller for the case with higher geometry constraint.
Effect of Crack Length to Plate Width Ratio on Stress Intensity Distribution at the Crack Tip
Industrial Engineering Letters, 2017
To start the comprehending of the materials fracture, first must understand the stress fields and deformation distribution at the crack tips. Analysis the behavior of crack for a solid plate may be extensive importance of the plate design to evade the failure. The crack is small when rivalled to the dimension of solid plate and the smallest crack ligament to the exterior plate region is greatly than the crack can be estimated for an infinite plate with finite crack. The variant of the stress field and stress intensity distribution is not great in profile compared with the variation in values. The result evaluated using finite element method to analysis by using Ansys Parametric Design Language (APDL) code in Ansys v.11 with static analysis at two different cases for carbon steel material alloy. In the first case, tension load applied at the upper edge of the plate model and in the second case, shear load applied at the upper edge. The results extracted from the current study show in...
Characterisation of crack tip fields under non_uniform fatigue loading.PDF
The paper analyses previously reported work, which uses digital image correlation to measure fatigue crack closure. As well as determining crack opening loads, the information on crack shape may be used to estimate the stress intensity factor, as well as other parameters in more complex models of crack tip fields. A number of specimens were subjected to single overload cycles, which produced a significant retardation in crack growth rate. The method previously applied to the analysis of constant amplitude loading is here used to analyse the single overload case. The stress intensity factor history is found to be very different in the two cases and the consequences of this observation for analysis of fatigue crack propagation are discussed.
International Journal of Modelling, Identification and Control, 2008
A modified strip-yield model has been developed to simulate the plasticity-induced crack closure under the constant amplitude (CA) and a single overload loading conditions. The paper focuses on the simulation of the near tip crack profiles and stress distributions during the fatigue process. Detailed information on near-tip stress and displacement fields at the maximum load (P max), the minimum load (P min), and the crack opening load (P op) of a fatigue load cycle have been presented. The correlation of the crack closure to the near-tip material fatigue damage has been investigated and used to rationalise the crack growth behaviour under the CA and a single overload loading conditions.
MACROSCOPIC RESIDUAL STRESS DISTRIBUTION AT A FATIGUE CRACK TIP
Fatigue & Fracture of Engineering Materials and Structures, 1979
Residual stress distribution in the vicinity of fatigue cracks was determined experimentally by means of the X-ray method and theoretically calculated by finite element analysis. Both the intensity and the extent of residual stress increase with the increasing stress intensity factor amplitude. There is good agreement between experimental and theoretical results.
Journal of Theoretical and Applied Mechanics
This paper deals with the influence of initial crack-tip shape, plastic compressibility and material or strain softening on near-tip stress-strain fields for mode I crack when subjected to fatigue loading with an overload event under plane strain and small scale yielding conditions. A finite strain elastic-viscoplastic constitutive equation with a hardening-softening-hardening hardness function is taken up for simulation. For comparison, a bilinear hardening hardness function is also considered. It has been observed that the near-tip crack opening stress σ yy , crack growth stress σ xx , and hydrostatic stresses are noticeably controlled by the initial crack tip shape, plastic compressibility, material softening as well as the overload event. The distribution pattern of different stresses for a plastically compressible hardening-softening-hardening solid appears to be very unusual and advantageous as compared to those of traditional materials. Therefore, the present numerical results may guide material scientists/engineers to understand the near-tip stress-strain fields and growth of a crack in a better way for plastically compressible solids, and thus may help to develop new materials with improved properties.