Crack initiation and fatigue life prediction on aluminum lug joints using statistical volume element–based multiscale modeling

2012 ◽  
Vol 24 (17) ◽  
pp. 2097-2109 ◽  
Author(s):  
Jinjun Zhang ◽  
Kuang Liu ◽  
Chuntao Luo ◽  
Aditi Chattopadhyay
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Multiscale Modeling ◽  
Life Prediction ◽  
Volume Element ◽  
Fatigue Life Prediction ◽  
Lug Joints

Fatigue Life Prediction Under Biaxial FALSTAFF Loading Using Statistical Volume Element Based Multiscale Modeling

2012 ◽  
Author(s):  
Jinjun Zhang ◽  
Kuang Liu ◽  
Aditi Chattopadhyay
Keyword(s):  
Fatigue Life ◽  
Root Mean Square ◽  
Life Prediction ◽  
Element Model ◽  
Fatigue Tests ◽  
Volume Element ◽  
Fatigue Life Prediction ◽  
Mean Square ◽  
Damage Criterion ◽  
Micro Cracks

This article presents the fatigue life prediction in a cruciform specimen of 2024-T351 aluminum alloy subjected to biaxial FALSTAFF loading. An energy- and slip-based multiscale damage criterion is developed to capture the fatigue crack formation in crystalline metallic materials. In these materials, there are two stages in crack initiation: nucleation of micro cracks and coalescence of micro cracks into major cracks. In the first stage, micro cracks generate from intermetallic particles and extend into surrounding grains. For the FCC crystalline structure, fatigue damage increments in four dependent slip planes are calculated and accumulated to measure micro crack. In the second stage, the micro cracks grow and coalesce into major cracks. Subsequently, a meso-statistical volume element model is developed to represent the microstructure of the material. Finally, a root mean square method is introduced to take into account FALSTAFF loading. Using the root mean square (RMS) method, the loading history for tests is analyzed to determine the RMS maximum and minimum stresses. The multiscale damage criterion, statistical volume element and RMS method were validated using previously conducted fatigue tests on cruciform samples. The fatigue life and crack direction predicted using the developed model correlate well with the experiments.

Study on Anisotropic Fatigue Damage Model of Metal Component

2011 ◽  
Vol 21 (4) ◽  
pp. 599-620 ◽  
Author(s):  
Zhang Miao ◽  
Meng Qingchun ◽  
Hu Weiping ◽  
Zhang Xing
Keyword(s):  
Fatigue Life ◽  
Damage Evolution ◽  
Life Prediction ◽  
Damage Mechanics ◽  
Evolution Equations ◽  
Prediction Method ◽  
Volume Element ◽  
Fatigue Life Prediction ◽  
Repeated Loading ◽  
Damage Evolution Equation

First of all, the boom–panel model is constructed to describe the anisotropic damage evolution of continuum volume element. The constitutive relation of continuum volume element is represented by damage extent of the booms and panels. Furthermore, based on irreversible thermodynamics, damage evolution equations of boom and panel are constructed. The fatigue life prediction method for smooth specimen under the repeated loading with constant strain amplitude is constructed. By the theory of conservative integral in damage mechanics, the fatigue life prediction method for notched specimen under the repeated loading with constant amplitude is obtained. Using these methods, the material parameters of LC4CS aluminum alloy in the damage evolution equation can be obtained by the mean values of experimental fatigue curves of standard specimens with KT = 1, K T = 3, and K T = 5. The computational results are in accordance with the experiment data.

Fatigue Life Prediction for Short Dents in Petroleum Pipelines

2002 ◽  
Author(s):  
Adam J. Rinehart ◽  
Peter B. Keating
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Crack Propagation ◽  
External Force ◽  
Life Prediction ◽  
Fatigue Behavior ◽  
Contact Region ◽  
Fatigue Cracking ◽  
Fatigue Life Prediction ◽  
Crack Initiation Life

Pipeline dent fatigue behavior has been shown to be strongly dependent upon dent length and external force dent restraint characteristics. Full-scale laboratory tests have shown that short dents that are unrestrained by an external force typically experience fatigue cracking in the dent periphery outside of the dent contact region. A fatigue life prediction method for short dents is presented here. In order to assess method accuracy, predictions are made for cases in which fatigue life has been measured experimentally. The predictions account for both crack initiation life and crack propagation life. Stress concentration values used in the predictions are determined using finite element modelling on a case-by-case basis for comparison purposes. Appropriate crack initiation life estimates, stress intensity factor predictions, and crack propagation models are taken from existing literature. Predicted and measured fatigue lives are compared for the cases studied.

A New Extreme-Value Probabilistic Framework for Predicting Fatigue Crack Initiation Life of Notched Components

2011 ◽  
Author(s):  
Gbadebo Owolabi ◽  
Horace Whitworth
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Crack Initiation ◽  
Strain Field ◽  
Life Prediction ◽  
Notch Root ◽  
Fatigue Crack Initiation ◽  
Fatigue Life Prediction ◽  
Probabilistic Framework ◽  
Notched Components

Traditional deterministic methods for predicting the fatigue life of notched components require a number of approximations based on heuristics and phenomenological data rather than solid theoretical underpinning and still yield unsatisfactory and inconsistent results when applied to complex components under service loads. Microstructural inhomogeneities in the materials are still an important issue, but are not explicitly accounted for in the traditional deterministic methods. Recent developments in computational crystal plasticity and microstructure-scale modeling have provided deeper understanding of the complex correlations between properties and structures and further indicate the limitations of conventional fatigue life prediction approaches. These modeling approaches have the potential to substantially reduce the need for costly large scale experimental programs to determine scatter in fatigue, for example. At present, however, there is a lack of simulation-based strategy for considering interactive effects of stress/strain field gradients at the notch-root and microstructure-scale behavior in predicting notch-root fatigue crack initiation. In this paper, the distribution of a shear-based fatigue indicator parameter computed within a well-defined fatigue damage process zone at the notch are used along with a novel probabilistic mesomechanics approach to obtain the probability distribution of fatigue crack initiation of notched components, thus extending fatigue life prediction to explicitly incorporate microstructure sensitivity via probabilistic arguments. The new probabilistic framework presented in this paper takes into account the complete plastic shear strain field around the notch root and also links the variation in the materials microstructure and associated slip activations to observable scatter in fatigue strength of the notched component. The use of such probabilistic approach can be beneficial as it avoids conservatism that may result from the use of deterministic approach for fatigue life prediction.

Short Crack Propagation Law and Fatigue Life Prediction Method for Structural Alloy Steel

2011 ◽  
Vol 197-198 ◽  
pp. 1400-1405
Author(s):  
Zan Zhi Wang
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Life Prediction ◽  
Prediction Method ◽  
Short Crack ◽  
Fatigue Life Prediction ◽  
Structural Alloy ◽  
Propagation Law ◽  
Alloy Steels

35CrMo and 42CrMo are the two main structural alloy steels in China, and are widely used in making important structural components subjected to heavy loads. In order to search after their fatigue properties under cyclic loads, 33 specimens were tested, under different stress level and different stress ratio from each other, to observe their crack initiation lives and the failure lives, together with the growing short crack lengths at various cycles. All tests were conducted using the MTS 810-22 material testing system. Based on the results from the tests, the relationships between the maximum stress range at crack tip and the number of cycles prior to crack initiation were determined, and in the meanwhile, the small crack propagation laws and the threshold stresses for fatigue crack initiation were obtained. In the end, the fatigue life prediction method for the two structural alloy steels was carried out.

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