scholarly journals Numerical Analysis of Fatigue Crack Growth Path and Life Predictions for Linear Elastic Material

Materials ◽  
2020 ◽  
Vol 13 (15) ◽  
pp. 3380
Author(s):  
Abdulnaser M. Alshoaibi ◽  
Yahya Ali Fageehi
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Crack Propagation ◽  
Crack Growth ◽  
Mixed Mode ◽  
Compact Tension ◽  
Compact Tension Specimen ◽  
Growth Path ◽  
Linear Elastic ◽  
Crack Growth Path

The main objective of this work was to present a numerical modelling of crack growth path in linear elastic materials under mixed-mode loadings, as well as to study the effect of presence of a hole on fatigue crack propagation and fatigue life in a modified compact tension specimen under constant amplitude loading condition. The ANSYS Mechanical APDL 19.2 is implemented for accurate prediction of the crack propagation paths and the associated fatigue life under constant amplitude loading conditions using a new feature in ANSYS which is the smart crack growth technique. The Paris law model has been employed for the evaluation of the mixed-mode fatigue life for the modified compact tension specimen (MCTS) with different configuration of MCTS under the linear elastic fracture mechanics (LEFM) assumption. The approach involves accurate evaluation of stress intensity factors (SIFs), path of crack growth and a fatigue life evaluation through an incremental crack extension analysis. Fatigue crack growth results indicate that the fatigue crack has always been attracted to the hole, so either it can only curve its path and propagate towards the hole, or it can only float from the hole and grow further once the hole has been lost. In terms of trajectories of crack propagation under mixed-mode load conditions, the results of this study are validated with several crack propagation experiments published in literature showing the similar observations. Accurate results of the predicted fatigue life were achieved compared to the two-dimensional data performed by other researchers.

scholarly journals Fatigue Crack Growth Analysis with Extended Finite Element for 3D Linear Elastic Material

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 397
Author(s):  
Yahya Ali Fageehi
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Fatigue Life ◽  
Crack Propagation ◽  
Crack Growth ◽  
Mixed Mode ◽  
Propagation Path ◽  
Loading Conditions ◽  
Extended Finite Element ◽  
Linear Elastic

This paper presents computational modeling of a crack growth path under mixed-mode loadings in linear elastic materials and investigates the influence of a hole on both fatigue crack propagation and fatigue life when subjected to constant amplitude loading conditions. Though the crack propagation is inevitable, the simulation specified the crack propagation path such that the critical structure domain was not exceeded. ANSYS Mechanical APDL 19.2 was introduced with the aid of a new feature in ANSYS: Smart Crack growth technology. It predicts the propagation direction and subsequent fatigue life for structural components using the extended finite element method (XFEM). The Paris law model was used to evaluate the mixed-mode fatigue life for both a modified four-point bending beam and a cracked plate with three holes under the linear elastic fracture mechanics (LEFM) assumption. Precise estimates of the stress intensity factors (SIFs), the trajectory of crack growth, and the fatigue life by an incremental crack propagation analysis were recorded. The findings of this analysis are confirmed in published works in terms of crack propagation trajectories under mixed-mode loading conditions.

Morphology Analysis of Mixed Mode Fatigue Crack Growth in a Low Alloy Steel

2013 ◽  
Vol 787 ◽  
pp. 745-749
Author(s):  
Hui Fang Li ◽  
Xiao Ju Sun ◽  
Lan Qing Tang ◽  
Cai Fu Qian
Keyword(s):  
Fatigue Crack ◽  
Fracture Surface ◽  
Crack Growth ◽  
Alloy Steel ◽  
Mixed Mode ◽  
Low Alloy Steel ◽  
Growth Path ◽  
Fatigue Fracture Surface ◽  
Final Fracture ◽  
Crack Growth Path

In this paper, I+II mixed mode fatigue crack propagation in a low alloy steel 16MnDR was experimentally investigated. Morphologies of crack growth path and fracture surface are analyzed. It is found that upon initiation from the inclined pre-crack, the newly formed crack grows in a direction to be perpendicular to the applied load, making crack mode transformation from I+II mixed mode to mode I. The crack growth is transgranular and no clear branches are presented. Striations and dimples are found on the fatigue fracture surface and the final fracture surface, respectively, showing that the material is ductile in nature.

Research on Microstructure Dependence of Near-Threshold Fatigue Crack Propagation by Combined Analyses of Fracture Surface and Fatigue Crack Growth Path

2009 ◽  
Author(s):  
Ming-Liang Zhu ◽  
Fu-Zhen Xuan ◽  
Guo-Zhen Wang ◽  
Zheng-Dong Wang
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Crack Advance ◽  
Growth Path ◽  
Austenite Grain Size ◽  
Fatigue Crack Growth Resistance ◽  
Crack Growth Path ◽  
Near Threshold

Near-threshold fatigue crack growth behavior was investigated in a newly developed steel 25Cr2NiMo1V with different heat treatments to meet different property requirements of high-pressure (HP) and low-pressure (LP) parts in the combined steam turbine rotor. The load-shedding method was adopted in the near-threshold fatigue crack growth experiment at room temperature with a constant load ratio of 0.1. Combined analyses of crack surface and fatigue crack growth path were carried out to identify the dominant crack growth mechanisms in both HP and LP. Results show that in the threshold regime, fatigue crack growth resistance of the HP is clearly superior to that of LP and hence shows strongly dependence on the microstructure of 25Cr2NiMo1V. The distributed bainitic microstructures and larger prior austenite grain size in HP result in more tortuous crack propagation path than that in LP. Compared with ferritic blocks in HP, the tempered martensitic laths in LP do not play a dominate role in stopping the fatigue crack advance.

scholarly journals Computational Simulation of 3D Fatigue Crack Growth under Mixed-Mode Loading

2021 ◽  
Vol 11 (13) ◽  
pp. 5953
Author(s):  
Abdulnaser M. Alshoaibi
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stress Intensity Factors ◽  
Mixed Mode ◽  
Intensity Factors ◽  
Linear Elastic ◽  
Growth Studies

The purpose of this research was to present a simulation modelling of a crack propagation trajectory in linear elastic material subjected to mixed-mode loadings and investigate the effects of the existence of a hole and geometrical thickness on fatigue crack growth and fatigue life under constant amplitude loading. For various geometry thickness, mixed-mode (I/II) fatigue crack growth studies were carried out to utilize a single edge cracked plate with three holes and compact tension shear specimens with various loading angles. Smart Crack Growth Technology, a new feature in ANSYS, was used in ANSYS Mechanical APDL 19.2 to predict the cracks’ propagation trajectory and their consequent fatigue life associated with evaluating the stress intensity factors. The maximum circumferential stress criterion is implemented as a direction criterion under linear elastic fracture mechanics (LEFM). According to the hole position, the results demonstrate that the fatigue crack grows towards the hole due to the unbalanced stresses on the hole induced crack tip. The results of this simulation are verified in terms of crack growth paths, stress intensity factors, and fatigue life under mixed-mode load conditions, with several crack growth studies published in the literature showing consistent results.

scholarly journals Adaptive Finite Element Prediction of Fatigue Life and Crack Path in 2D Structural Components

Metals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 1316
Author(s):  
Abdullateef H. Bashiri ◽  
Abdulnaser M. Alshoaibi
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Stress Intensity ◽  
Crack Propagation ◽  
Crack Growth ◽  
Mixed Mode ◽  
Equivalent Stress ◽  
Circumferential Stress ◽  
Mixed Mode Loading ◽  
Linear Elastic

The existence of a hole near a growing fatigue crack can cause the crack trajectory to deviate. Unless the hole is too close to the crack, the crack is arrested at the edge of the hole and does not progress further. The purpose of this paper was to predict the crack propagation and lifetime of two-dimension geometries for linear elastic materials in mixed-mode loading using a finite element source code program written in Visual Fortran language. The finite element mesh is generated using the advancing front method. The onset criterion of crack propagation was based on the equivalent stress intensity factor which provides the most important parameter that must be accurately estimated for the mixed-mode loading condition. The maximum circumferential stress theory was used as a direction criterion. The modified compact tension (MCTS) was studied to demonstrate the influence of the hole’s presence on the direction of crack growth and fatigue life for different configurations. The Paris’ law model has been employed to evaluate the mixed-mode fatigue life for MCTS in different configurations under the linear elastic fracture mechanics (LEFMs) assumption. The framework involves a progressive crack extension study of stress intensity factors (SIFs), crack growth direction, and fatigue life estimation. The results show that the fatigue growth was attracted to the hole either changes its direction to reach the hole or floats by the hole and grows as the hole is missed. The results of the study agree with several crack propagation experiments in the literature revealing similar crack propagation trajectory observations.

Analysis of a main fatigue crack interaction with multiple micro-cracks/voids in a compact tension specimen repaired by stop-hole technique

2018 ◽  
Vol 53 (8) ◽  
pp. 648-662 ◽  
Author(s):  
Mohammad Malekan ◽  
Hermes Carvalho
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Crack Growth ◽  
Growth Period ◽  
Compact Tension ◽  
Compact Tension Specimen ◽  
Tension Specimen ◽  
Extended Finite Element ◽  
Forming Process ◽  
Micro Cracks

Fatigue is a process in engineering materials in which damage accumulates due to the fluctuating loading. One solution for a component under the fatigue process is to arrest the crack propagation before the final failure using different available retardation methods, such as drilling/stop-hole technique. In addition, structural components may also suffer from the existence of micro-cracks or voids due to their forming process or service lives. These micro-cracks/voids are very critical to study, since they can effectively play an important role in the behavior of the existing main crack in a component. This article aims to investigate the effect of the stop-hole retardation technique and multiple micro-cracks/voids with different characteristic lengths and geometries on the fatigue crack propagation in a compact tension specimen. A modified Forman equation, the so-called NASGRO equation is used to define the transition between crack initiation and crack growth period. Also, the extended finite element method is adapted in the crack propagation phase in order to model crack path in the geometry eliminating the need for remeshing procedure. The whole analyses are conducted in a commercial package through a user-written code that handles all fatigue crack growth analysis. The reference solutions from the literature are used to compare and to validate results obtained from current work.

scholarly journals Two- and Three-Dimensional Numerical Investigation of the Influence of Holes on the Fatigue Crack Growth Path

2021 ◽  
Vol 11 (16) ◽  
pp. 7480
Author(s):  
Yahya Ali Fageehi
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Propagation ◽  
Crack Growth ◽  
Three Dimensional ◽  
Real Life ◽  
Growth Path ◽  
Crack Growth Path

Problems in fracture mechanics are difficult when the appropriate analysis is unspecified, which is very common in most real-life situations. Finite element modeling is thus demonstrated to be an essential technique to overcome these problems. There are currently various software tools available for modeling fracture mechanics problems, but they are usually difficult to use, and obtaining accurate results is not an obvious task. This paper illustrates some procedures in two finite element programs to solve problems in two- and three-dimensional linear-elastic fracture mechanics, and an educational proposal is made to use this software for a better understanding of fracture mechanics. Crack modeling was done in a variety of ways depending on the software. The first is the well-known ANSYS, which is usually utilized in industry, and the second was a freely distributed code, called FRANC2D/L, from Cornell University. These software applications were used to predict the fatigue crack growth path as well as the associated stress intensity factors. The predicted results demonstrate that the fatigue crack is turned towards the hole. The fatigue crack growth paths are influenced by the varying positions and sizes of single holes, while two symmetrically distributed holes have no effect on the fatigue crack growth direction. The findings of the study agree with other experimental crack propagation studies presented in the literature that reveal similar crack propagation trajectory observations.

Pre-Strain Effects on Mixed-Mode Fatigue Crack Propagation Behaviour of the P355NL1 Pressure Vessels Steel

2018 ◽  
Author(s):  
João Ferreira ◽  
José A. F. O. Correia ◽  
Grzegorz Lesiuk ◽  
Sergio Blasón González ◽  
Maria Cristina R. Gonzalez ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Mixed Mode ◽  
Pressure Vessels ◽  
Mode I ◽  
Pure Mode

Pressure vessels and piping are commonly subjected to plastic deformation during manufacturing or installation. This pre-deformation history, usually called pre-strain, may have a significant influence on the resistance against fatigue crack growth of the material. Several studies have been performed to investigate the pre-strain effects on the pure mode I fatigue crack propagation, but less on mixed-mode (I+II) fatigue crack propagation conditions. The present study aims at investigating the effect of tensile plastic pre-strain on fatigue crack growth behavior (da/dN vs. ΔK) of the P355NL1 pressure vessel steel. For that purpose, fatigue crack propagation tests were conducted on specimens with two distinct degrees of pre-strain: 0% and 6%, under mixed mode (I+II) conditions using CTS specimens. Moreover, for comparison purposes, CT specimens were tested under pure mode I conditions for pre-strains of 0% and 3%. Contrary to the majority of previous studies, that applied plastic deformation directly on the machined specimen, in this work the pre-straining operation was carried out prior to the machining of the specimens with the objective to minimize residual stress effects and distortions. Results revealed that, for the P355NL1 steel, the tensile pre-strain increased fatigue crack initiation angle and reduced fatigue crack growth rates in the Paris region for mixed mode conditions. The pre-straining procedure had a clear impact on the Paris law constants, increasing the coefficient and decreasing the exponent. In the low ΔK region, results indicate that pre-strain causes a decrease in ΔKth.

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