Characterizing Fatigue Crack Closure by Numerical Analysis

2008 ◽  
Vol 33-37 ◽  
pp. 273-278 ◽  
Author(s):  
Ya Zhi Li ◽  
Jing He ◽  
Zi Peng Zhang ◽  
Liang Wang
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Numerical Analysis ◽  
Fatigue Crack Growth ◽  
Crack Length ◽  
Crack Growth ◽  
Crack Closure ◽  
Crack Opening ◽  
Crack Tip ◽  
Fatigue Crack Closure

The crack closure phenomenon has attracted great attention in the prediction of fatigue crack growth. The finite element analysis of fatigue crack growth has been conducted by many researchers mainly emphasized on the technique implementation of the simulation. In this paper the behavior of plasticity induced fatigue crack closure was analyzed by the elastic-plastic finite element method for middle crack tension (MT) specimen. The material was assumed as linear-kinematic hardening. The crack growth was simulated by releasing the “bonded” node pairs ahead of crack tip in stepwise. The calculations focused on the effects of load cases and crack length on crack opening/closure levels. For constant amplitude cyclic loadings with different load ratios, the crack opening/closure levels increases for a while and then decreases continuously, with the increase of crack length. For the loadings with invariable maximum stress intensity factors (briefly the constant-K loading), however, the crack tip plastic zone sizes at different crack lengths remain unchanged and the crack opening and closing load levels normalized by the maximum load levels keep constants as well. The results indicate that the crack length does not affect the relative opening and closure levels and numerical analysis for the constant-K loading case should play a key role in characterizing the fatigue crack growth behavior.

Fatigue Life Estimation of Welded Joints Including the Effects of Crack Closure Phenomena

2011 ◽  
Author(s):  
Diego Felipe Sarzosa Burgos ◽  
Claudio Ruggieri ◽  
Leonardo Barbosa Godefroid ◽  
Gustavo H. B. Donato
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Crack Opening ◽  
Weld Strength ◽  
Operating Life ◽  
Mechanical Heterogeneity

The integrity of mechanical components, particularly when they experience considerable fatigue damage during its operating life, can be strongly influenced by the presence of residual stress fields and mechanical heterogeneity. Premature closure of crack flanks greatly influences fatigue crack growth rate. Extensive elastic-plastic finite element analyses have been carried out to investigate detailed crack closure behavior in center cracked welded compact tension (CT) specimens with one level of weld strength mismatch. The finite element results show that homogeneous, soft material has higher crack opening loads than heterogeneous material with 50% overmatch conditions. Fracture testing conducted on C(T) specimens to measure fatigue crack growth rates for an ASTM A516 Gr. 70 steel weldment provide the experimental data to support such behavior. The fatigue life can be reduced by more than 100% for a condition of 50% overmatch when compared with the evenmatch condition. It was verified that most of time spent in fatigue propagation life is consumed at the beginning of the propagation life.

Fatigue Crack Growth Prediction of Elliptical Corner Crack Using 3D FEM

2012 ◽  
Vol 248 ◽  
pp. 469-474
Author(s):  
M.H. Gozin ◽  
M. Aghaie-Khafri
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Crack Front ◽  
Crack Opening ◽  
3D Fem ◽  
Corner Crack ◽  
Closure Method

Plasticity induced crack closure (PICC) simulation using finite element analyses has been concerned by many researchers. In the present investigation elliptical corner fatigue crack growth from a hole was predicted using PICC method. An elastic-plastic finite element model is built with a suitably refined mesh and time-dependent remote tractions are applied to simulate cyclic loading. In a 3D geometry the crack opening value will vary along the crack front. For simplicity this shape evolution is neglected and the crack front is extended uniformly. Predicted fatigue life using crack closure method for elliptical corner crack is in good agreement with the experimental data. The results obtained highlighted the sensitivity of crack closure method to the opening stress intensity values.

Modeling of Fatigue Crack Closure by Finite Element Method

2012 ◽  
Vol 544 ◽  
pp. 145-150
Author(s):  
Zhen Yu Ding ◽  
Xiao Gui Wang ◽  
Zeng Liang Gao
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Crack Closure ◽  
Fe Simulation ◽  
Crack Tip ◽  
Cyclic Plasticity ◽  
Stress And Strain

Crack closure concept is often used to explain the crack propagation behavior in cracked components. The effective stress intensity factor range is considered as a driving force of fatigue crack growth based on the traditional crack closure concept. The crack closure process and the plastic deformation near the crack tip were discussed in this paper. The standard compact tension specimen with the plane-stress condition was used to study the crack closure. A dynamic crack propagation method was proposed to simulate the effect of previous fatigue crack growth on the successive crack growth behavior. To obtain the accurately numerical results of stress and strain components, the Jiang and Sehitoglu cyclic plasticity model was implemented into ABAQUS as UMAT. With the detailed stress and strain response taken from the finite element (FE) simulation, the whole process of crack closure was described by the load curve. The load corresponding to maximum crack closure length is firstly proposed to describe the effect of fatigue damage. According to the results of FE simulation, the cyclic plasticity of the material near the crack tip persists during the crack closure period and should not be ignored.

Finite Element Simulation of Stable Fatigue Crack Growth Using Critical CTOD Determined by Preliminary Finite Element Analysis

2014 ◽  
Vol 891-892 ◽  
pp. 1675-1680
Author(s):  
Seok Jae Chu ◽  
Cong Hao Liu
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Finite Element Simulation ◽  
Crack Growth ◽  
Crack Tip ◽  
Stress Intensity Factor Range ◽  
Crack Tip Opening Displacement ◽  
Element Analysis ◽  
Element Simulation

Finite element simulation of stable fatigue crack growth using critical crack tip opening displacement (CTOD) was done. In the preliminary finite element simulation without crack growth, the critical CTOD was determined by monitoring the ratio between the displacement increments at the nodes above the crack tip and behind the crack tip in the neighborhood of the crack tip. The critical CTOD was determined as the vertical displacement at the node on the crack surface just behind the crack tip at the maximum ratio. In the main finite element simulation with crack growth, the crack growth rate with respect to the effective stress intensity factor range considering crack closure yielded more consistent result. The exponents m in the Paris law were determined.

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 Revisiting Classical Issues of Fatigue Crack Growth Using a Non-Linear Approach

Materials ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 5544
Author(s):  
Micael F. Borges ◽  
Diogo M. Neto ◽  
Fernando V. Antunes
Keyword(s):  
Plastic Deformation ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Crack Tip ◽  
Maximum Load ◽  
Numerical Approach ◽  
Load Range ◽  
Definition Of

Fatigue crack growth (FCG) has been studied for decades; however, several aspects are still objects of controversy. The objective here is to discuss different issues, using a numerical approach based on crack tip plastic strain, assuming that FCG is driven by crack tip deformation. ΔK was found to control cyclic plastic deformation at the crack tip, while Kmax has no effect. Therefore, alternative mechanisms are required to justify models based on ΔK and Kmax. The analysis of crack tip plastic deformation also showed that there is crack tip damage below crack closure. Therefore, the definition of an effective load range ΔKeff = Kmax − Kopen is not correct, because the portion of load range below opening also contributes to FCG. Below crack closure, damage occurs during unloading while during loading the crack tip deformation is elastic. However, if the maximum load is decreased below the elastic limit, which corresponds to the transition between elastic and elasto–plastic regimes, there is no crack tip damage. Additionally, a significant effect of the crack ligament on crack closure was found in tests with different crack lengths and the same ΔK. Finally, the analysis of FCG after an overload with and without contact of crack flanks showed that the typical variation of da/dN observed is linked to crack closure variations, while the residual stresses ahead of crack tip are not affected by the contact of crack flanks.

scholarly journals An Integral Formulation of Two-Parameter Fatigue Crack Growth Model

2018 ◽  
Vol 2018 ◽  
pp. 1-12
Author(s):  
Jianguo Wu ◽  
Shan Jiang ◽  
Wei Zhang ◽  
Zili Wang
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Propagation ◽  
Crack Growth ◽  
Crack Closure ◽  
Crack Tip ◽  
Integral Form ◽  
Crack Growth Behavior ◽  
Crack Growth Model ◽  
Two Parameter

A two-parameter fatigue crack growth algorithm in integral form is proposed, which can describe the continuous crack growth process over the time period. In this model, the fatigue crack propagation behavior is governed by the temporal crack-tip state including the current applied load and the physical condition due to the previous load sequence. The plasticity-induced crack closure, left by the historical loading sequence, controls the following fatigue crack growth behavior and typically leads to the interaction effects. In the proposed method, a modified crack closure model deriving from the local plastic deformation is employed to account for this load memory effect. In general, this model can simulate the fatigue crack growth under variable amplitude loading. Additionally, this model is established on the physical state of crack tip in the small spatial and temporal scale, and it is used to evaluate the macroscopic crack propagation and fatigue life under irregular tension-tension loading. A special superimposed loading case is discussed to demonstrate the advantage of the proposed model, while the traditional two-parameter approach is not proper functional. Moreover, the typical various load spectra are also employed to validate the method. Good agreements are observed.

An Efficient Way to Characterize the Fatigue Crack Growth Based on Numerical Analysis

2009 ◽  
Vol 417-418 ◽  
pp. 653-656
Author(s):  
Ya Zhi Li ◽  
Jing He ◽  
Zi Peng Zhang
Keyword(s):  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Length ◽  
Crack Growth ◽  
Crack Closure ◽  
Load Ratio ◽  
Specimen Thickness

The behavior of plasticity induced fatigue crack closure (PICC) in middle tension specimen was analyzed by the elastic-plastic finite element method. For the constant-K (CK) loading cases, the opening stress intensity factor are independent of crack length. The level of increases with the maximal applied stress intensity factor for given load ratio and increases with for fixed . The in plane strain state is much smaller than that in plane stress state. The results under CK loadings can be deduced to constant amplitude cyclic loading case during which the load ratio, maximal load level, crack length and specimen thickness are all the factors affecting the crack closure effect. The phenomena revealed in the analysis are beneficial in understanding the driving force mechanism of the fatigue crack growth.

scholarly journals A Novel Methodology for Calculating Crack Opening Stress under Tension-Compression Cyclic Load

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Lin Zhang ◽  
Xiaohui Wei
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Crack Opening ◽  
Compressive Load ◽  
Load Effect ◽  
Compression Load ◽  
Fatigue Crack Growth Life ◽  
Crack Opening Stress

Crack closure model has been used in several applications on the prediction of fatigue crack growth life, with expression of crack opening stress often serving as milestones. A typical difficulty in calculating the crack opening stress is the phenomenon of crack closure caused by the compressive load effect. Compressive load effect, resulting in the change of residual stress status at the unloading stage and the decrease of crack opening stress, is a long-term challenge for predicting fatigue crack growth life. We propose the expression of crack opening stress to predict fatigue crack growth life based on the analysis of compact tensile specimen with elastoplastic element method. It combines the characteristics of material and load to deal with the phenomenon of crack closure and uses stress ratio and normalized maximum applied load variable to construct the expression of crack opening stress. In the study of tensile-compression fatigue crack growth experiments, the proposed expression is proved to improve, by comparative analysis, the predictive ability on the whole range of experiment data. The novel expression is accurate and simple. Consequently, it is conducive to calculate the crack opening stress under tension-compression load.

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