Fracture Mechanics Approach to Fatigue Analysis in Design

1978 ◽  
Vol 100 (2) ◽  
pp. 113-120 ◽  
Author(s):  
R. P. Wei
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Environmental Variables ◽  
Life Prediction ◽  
Fatigue Analysis ◽  
Growth Data ◽  
Engineering Structures ◽  
The Relationship

Many engineering structures are subjected to cyclically varying (fatigue) loads during service. Fatigue analysis, or the estimation of fatigue lives on such structures, is therefore an essential part of engineering design. In this paper, the fracture mechanics approach to fatigue analysis is described. This approach has evolved over the last decade, and is based on the assumptions (i) that there are preexisting flaws or cracks in a structural component, or that cracks are initiated early in the life of the component, and (ii) that the fatigue life of the component is determined principally by the rate of growth of these cracks under cyclic loading. Characterization of the rate of fatigue crack growth in terms of fracture mechanics parameters is discussed. The relationship between these parameters and those commonly used in fatigue analysis is identified. A procedure for estimating fatigue lives from crack growth data is outlined. The importance of various loading and environmental variables on fatigue life prediction is considered. A number of example problems are given to illustrate the procedure and the various effects.

scholarly journals Recent Developments on the Unified Fatigue Life Prediction Method Based on Fracture Mechanics and its Applications

2020 ◽  
Vol 8 (6) ◽  
pp. 427 ◽  
Author(s):  
Fang Wang ◽  
Weicheng Cui
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Life Prediction ◽  
Structural Reliability ◽  
Influential Factors ◽  
Fatigue Life Prediction ◽  
Model Parameters ◽  
Sensitivity Index ◽  
Marine Structure

Safety analysis and prediction of a marine structure is of great concern by many stakeholders and the general public. In order to accurately predict the structural reliability of an in-use marine structure, one needs to calculate accurately the fatigue crack growth at any service time. This can only be possible by using fracture mechanics approach and the core of fracture-mechanics-based method is to establish an accurate crack growth rate model which must include all the influential factors of the same order of sensitivity index. In 2011, based on the analysis of various influencing factors, the authors put forward a unified fatigue life prediction (UFLP) method for marine structures. In the following ten years of research, some further improvements of this method have been made and the applications of this UFLP are carried out. In this paper, these progresses are reported and its underlying principles are further elaborated. Some basic test data used to determine model parameters are also provided.

Influence of Hold Time on Creep-Fatigue Life and Metallurgical Degradation at High Temperature

2006 ◽  
Vol 306-308 ◽  
pp. 1013-1018 ◽  
Author(s):  
Byeong Soo Lim ◽  
Bum Joon Kim
Keyword(s):  
Fatigue Life ◽  
Crack Growth ◽  
Life Prediction ◽  
Hold Time ◽  
Creep Damage ◽  
Crack Growth Behavior ◽  
Delta Ferrite ◽  
Austenite Grain ◽  
Creep Fatigue ◽  
The Relationship

This paper investigates the influence of various hold times on creep-fatigue life at 600oC. The relationship between the crack growth behavior and hold time was studied, and a metallurigical investigation to examine the effect of creep was performed. To examine the relationship between creep-fatigue life and microvoids, the fraction of micro-voids/cavity area was analyzed at the crack tip. The crack growth rate of the HAZ was found to be faster than that of base metal while creep-fatigue life was found to be shorter. Finally, it can be stated that the fraction of cavity area, Fca could be utilized for the life prediction under creep-fatigue interaction. As the hold time increased, the creep damage was observed along the prior austenite grain boundaries and inside and boundaries of delta-ferrite.

Effect of Simulation Methodology on Solder Joint Crack Growth Correlation and Fatigue Life Prediction

2002 ◽  
Vol 124 (3) ◽  
pp. 147-154 ◽  
Author(s):  
Robert Darveaux
Keyword(s):  
Fatigue Life ◽  
Solder Joint ◽  
Constitutive Model ◽  
Crack Growth ◽  
Life Prediction ◽  
Plastic Work ◽  
Growth Data ◽  
Worst Case ◽  
Modeling Procedure ◽  
Growth Constants

A generalized solder joint fatigue life model for surface mount packages was previously published in [1,2]. The model is based on correlation to measured crack growth data on BGA joints during thermal cycling. It was subsequently discovered by Anderson et al. that the ANSYS™1 5.2 finite element code used in the model had an error in its method for calculating plastic work [3]. It was shown that significant error in life prediction could result by using a recent version of the code where the bug has been fixed. The error comes about since the original crack growth constants were derived based on plastic work calculations that had the bug. In this paper, crack initiation and growth constants are recalculated using ANSYS™ 5.6. In addition, several other model related issues are explored with respect to the crack growth correlations. For example, 3D slice models were compared to quarter symmetry models. Anand’s constitutive model was compared with Darveaux’s constitutive model. It was shown that the crack growth rate dependence on strain energy density always had an exponent of 1.10+/−0.15. This is in the range of the original correlation. The model was applied to several data sets of tape-based and laminate-based BGAs. The accuracy of absolute predictions is mostly within +/−2X. The accuracy of relative predictions is within +/−25%. However, the accuracy of absolute predictions could be off by a factor of 7 in the worst case, if the analyst uses a modeling procedure that is not consistent with that used for the crack growth correlation. The key to good accuracy is to maintain consistency in the modeling procedure.

Adaptive Neural Network Modelling in Fatigue life Prediction under Load History effects

2011 ◽  
Vol 284-286 ◽  
pp. 1266-1270
Author(s):  
M. Abdul Razzaq ◽  
Kamal A. Ariffin ◽  
Ahmed El Shafie ◽  
Shahrum Abdullah ◽  
Z. Sajuri ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Crack Growth ◽  
Life Prediction ◽  
Experimental Tests ◽  
Fatigue Life Prediction ◽  
Load History ◽  
Adaptive Neural Network ◽  
Network Modelling ◽  
History Effects ◽  
Point Bend

Artificial intelligence (AI) techniques and in particular, adaptive neural networks (ANN) have been commonly used in order to Fatigue life prediction. The aim of this paper is to consider a new crack propagation principle based on simulating experimental tests on three point-bend (TPB) specimens, which allow predicting the fatigue life and fatigue crack growth rate (FCGR). An important part of this paper is estimation of FCG rate related to different load histories. The effects of different load histories on the crack growth life are obtained in different representative simulation and experiments.

Fracture Mechanics Based Mooring Fatigue Analysis for a Semi-Submersible Subjected to Triple Narrow-Band Loading Processes

2019 ◽  
Author(s):  
Xutian Xue ◽  
Nian-Zhong Chen ◽  
Yongchang Pu
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Fatigue Analysis ◽  
Second Order ◽  
Combination Method ◽  
Mooring System ◽  
Initial Surface ◽  
Loop Current ◽  
Mooring Lines ◽  
First Order

Abstract In the general offshore operating locations, mooring systems are normally considered to be primarily affected by environmental loadings induced by waves, wind and current. WF motion induced by first-order waves, LF motion induced by second-order waves and wind would make the most contribution to the fatigue damage of mooring lines. However, it was reported recently that in the Gulf of Mexico (GoM), the fatigue life of mooring lines can be significantly affected by the vortex induced motion (VIM) induced by loop current. The aim of this presented paper is to address the influence of VIM on fatigue life of the mooring system operating at the central of the GoM through performing a fracture mechanics (FM) based fatigue analysis for an offshore mooring system. A frequency-domain mooring analysis for the semi-submersible is conducted where WF motion induced by first-order waves, LF motion induced by second-order waves and wind, and VIM induced by loop current are taken into account. WF motion, LF motion and VIM are treated as three independent loading processes. A wide-band loading combination method is then used for predicting the loading processes acting on the mooring system combining WF motion, LF motion and VIM. A fracture mechanics based analysis is performed to examine the fatigue life of mooring system, in which initial surface cracks in previous existence are assumed to grow from the surfaces of mooring chain links connecting to the fairleads. The stress intensity factor ranges to estimate the crack growth in the FM based analysis are obtained from a finite element (FE) analysis.

Life Prediction of Solder Joints by Damage and Fracture Mechanics

1996 ◽  
Vol 118 (4) ◽  
pp. 193-200 ◽  
Author(s):  
S. H. Ju ◽  
B. I. Sandor ◽  
M. E. Plesha
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Damage Mechanics ◽  
Solder Joints ◽  
Continuum Damage Mechanics ◽  
Computer Time ◽  
Initial Crack ◽  
Continuum Damage ◽  
Growth Path

Much research has been done on Surface Mount Technology (SMT) using the Finite Element Method (FEM). Little of this, however, has employed fracture mechanics and/or continuum damage mechanics. In this study, we propose two finite element approaches incorporating fracture mechanics and continuum damage mechanics to predict time-dependent and temperature-dependent fatigue life of solder joints. For fracture mechanics, the J-integral fatigue formula, da/dN = C(δJ)m, is used to quantify fatigue crack growth and the fatigue life of J-leaded solder joints. For continuum damage mechanics, the anisotropic creep-fatigue damage formula with partially reversible damage effects is used to find the initial crack, crack growth path, and fatigue life of solder joints. The concept of partially reversible damage is especially novel and, based on laboratory tests we have conducted, appears to be necessary for solder joints undergoing cyclic loading. Both of these methods are adequate to predict the fatigue life of solder joints. The advantage of the fracture mechanics approach is that little computer time is required. The disadvantage is that assumptions must be made on the initial crack position and the crack growth path. The advantage of continuum damage mechanics is that the initial crack and its growth path are automatically evaluated, with the temporary disadvantage of requiring a lot of computer time.

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