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.

Augmenting Generic Fatigue Crack Growth Models Using 3D Finite Element Simulations and Gaussian Process Modeling

2019 ◽  
Author(s):  
Adrian Loghin ◽  
Shakhrukh Ismonov
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Propagation ◽  
Gaussian Process ◽  
Crack Growth ◽  
Life Assessment ◽  
Growth Path ◽  
3D Fem

Abstract Assessing the crack propagation life of components is a critical aspect in evaluating the overall structural integrity of a mechanical structure that poses a risk of failure. Engineers often rely on industry standards and fatigue crack growth tools such as NASGRO [1] and AFGROW [2] to perform life assessment for different structural components. A good understanding of material damage tolerant capabilities, and the component’s loading mission during service conditions are required along with the availability of generic fracture mechanics models implemented in the lifing tools. Three-dimensional (3D) linear elastic fracture mechanics (LEFM) finite element modeling (FEM) is also a viable alternative to simulate crack propagation in a component. This method allows capturing detailed geometry of the component and representative loading conditions which can be crucial to accurately simulate the three dimensionality of the propagating crack shape and further determine the associated loading cycles. In comparison to a generic model, the disadvantage of the 3D FEM is the extended runtime. One feasible way to benefit from 3D modeling is to employ it to understand the crack front evolution and growth path for the representative loading condition. Mode I stress intensity factors (KI) along the predetermined crack growth path can be generated for use in fatigue crack growth tools such as NASGRO. In the current study, such a 3D FEM lifing process is presented using a classical bolt-nut assembly, components that are commonly used in engineering design. First, KI solutions for a fixed crack aspect ratio a/c = 1 are benchmarked against a similar solution available in NASGRO. Next, a predefined set of crack shapes and sizes are simulated using 3D FEA. A machine learning model Gaussian Process (GP) was trained to predict the KI solutions of the 3D model, which in turn was used in the crack propagation simulation to accelerate the life assessment process. Verification of the implemented procedure is done by correlating the crack growth curves predicted from GP to the results obtained directly from 3D FE crack propagation method.

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.

A research on fatigue crack growth monitoring based on multi-sensor and data fusion

2019 ◽  
pp. 147592171986572
Author(s):  
Chang Qi ◽  
Yang Weixi ◽  
Liu Jun ◽  
Gao Heming ◽  
Meng Yao
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Data Fusion ◽  
Crack Propagation ◽  
Finite Element Model ◽  
Crack Length ◽  
Crack Growth ◽  
Lamb Wave ◽  
Element Model

Fatigue crack propagation is one of the main problems in structural health monitoring. For the safety and operability of the metal structure, it is necessary to monitor the fatigue crack growth process of the structure in real time. In order to more accurately monitor the expansion of fatigue cracks, two kinds of sensors are used in this article: strain gauges and piezoelectric transducers. A model-based inverse finite element model algorithm is proposed to perform pattern recognition of fatigue crack length, and the fatigue crack monitoring experiment is carried out to verify the algorithm. The strain spectra of the specimen under cyclic load in the simulation and experimental crack propagation are obtained, respectively. The active lamb wave technique is also used to monitor the crack propagation. The relationship between the crack length and the lamb wave characteristic parameter is established. In order to improve the recognition accuracy of the crack propagation mode, the random forest and inverse finite element model algorithms are used to identify the crack length, and the Dempster–Shafer evidence theory is used as data fusion to integrate the conclusion of the two algorithms to make a more accountable and correct judge of the crack length. An experiment has been conducted to demonstrate the effectiveness of the method.

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.

Numerical simulation of fatigue crack propagation in mixed-mode (I+II) using the program BemCracker2D

2019 ◽  
Vol 10 (4) ◽  
pp. 497-514
Author(s):  
Pedro G.P. Leite ◽  
Gilberto Gomes
Keyword(s):  
Numerical Simulation ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Propagation ◽  
Crack Growth ◽  
Mixed Mode ◽  
Mode I ◽  
Post Processing ◽  
Content Type

Purpose The purpose of this paper is to present the application of the boundary element method (BEM) in linear elastic fracture mechanics for analysis of fatigue crack propagation problems in mixed-mode (I+II) using a robust academic software named BemCracker2D and its graphical interface BemLab2D. Design/methodology/approach The methodology consists in calculating elastic stress by conventional BEM and to carry out an incremental analysis of the crack extension employing the dual BEM (DBEM). For each increment of the analysis, the stress intensity factors (SIFs) are computed by the J-Integral technique, the crack growth direction is evaluated by the maximum circumferential stress criterion and the crack growth rate is computed by a modified Paris equation, which takes into account an equivalent SIF to obtain the fracture Modes I and II. The numerical results are compared with the experimental and/or BEM values extracted from the open literature, aiming to demonstrate the accuracy and efficiency of the adopted methodology, as well as to validate the robustness of the programs. Findings The paper addresses the numerical simulation of fatigue crack growth. The main contribution of the paper is the introduction of a software for simulating two-dimensional fatigue crack growth problems in mixed-mode (I+II) via the DBEM. The software BemCracker2D coupled to the BemLab2D graphical user interface (GUI), for pre/post-processing, are very complete, efficient and versatile and its does make relevant contributions in the field of fracture mechanics. Originality/value The main contribution of the manuscript is the development of a GUI for pre/post-processing of 2D fracture mechanics problems, as well as the object oriented programming implementation. Finally, the main merit is of educational nature.

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