THE EFFECT OF RESIDUAL STRESSES IN FILLET WELDS ON THE FATIGUE BEHAVIOR: A LEFM APPROACH

2014 ◽  
Vol 1 (1) ◽  
Author(s):  
Wim Nagy ◽  
Hans De Backer ◽  
Philippe Van Bogaert
Keyword(s):  
Residual Stresses ◽  
Crack Propagation ◽  
Fatigue Behavior ◽  
Growth Direction ◽  
Steel Bridge ◽  
Civil Structures ◽  
Linear Elastic ◽  
Real Behavior ◽  
Crack Growth Direction ◽  
Elastic Fracture

Residual stresses are present in many civil structures due to manufacturing actions causing plastic deformations. Nevertheless, these stresses are not often taken into account when considering the design of these structures, especially when assessing fatigue problems. This remains true for orthotropic steel bridge decks. Due to their many complex welding details, these decks are sensitive to fatigue. To increase the understanding of the fatigue behavior of welded details, an improved analyzing tool using linear elastic fracture mechanics is proposed in this paper. Apart from the fatigue life of the weld detail, the crack propagation and crack growth direction are also evaluated with an XFEM model. Application of this method to the case of the orthotropic steel Temse Bridge in Belgium results in crack propagation very similar to reality. It also demonstrates that the fatigue calculations need to include residual stresses to comply with the real behavior of crack propagation.

Numerical Simulation of Fatigue Crack Growth of New-Material Track Rollers

2012 ◽  
Vol 157-158 ◽  
pp. 1471-1476
Author(s):  
Chang Liu ◽  
Xu Hong Guo ◽  
Xin Xin Gao
Keyword(s):  
Crack Propagation ◽  
Crack Growth ◽  
Growth Direction ◽  
Maximum Principal Stress ◽  
Fem Modeling ◽  
Stress Theory ◽  
Linear Elastic ◽  
New Material ◽  
Crack Growth Direction ◽  
Elastic Fracture

Because of the excellent mechanical properties of Austempered Ductile Iron (ADI), track rollers can be made out of this material. The casting may lead to cracks forming inside rollers and there will also be some scratches in the surface when rollers work, which will greatly affect the lifespan of rollers. It is helpful to use crack propagation method based on the Finite Element Method (FEM) to simulate the crack growth. Firstly, define the position and the value of the force imposed on rollers. If the load is compressive, contact pairs should be set between the crack surfaces. After the model is established, Stress Intensity Factors (SIF) KI and KII can be calculated with the node displacement theory by using the commands of FEM software. With the maximum principal stress theory, crack growth direction can be determined. Since the values of KI and KII calculated by the software are positive, we should judge weather the values are positive or negative to get a right propagating angle. The analysis applies linear elastic fracture mechanics and FEM modeling the crack propagation in the elastic state.

Influence of the Interface and Residual Stresses on the Apparent Fracture Toughness of Layered Ceramic Composites Based on Alumina-Zirconia

2014 ◽  
Vol 606 ◽  
pp. 209-212
Author(s):  
Luboš Náhlík ◽  
Bohuslav Máša ◽  
Pavel Hutař
Keyword(s):  
Residual Stresses ◽  
Crack Propagation ◽  
Ceramic Composites ◽  
Layered Composites ◽  
Material Interfaces ◽  
Linear Elastic ◽  
Apparent Fracture Toughness ◽  
Elastic Fracture ◽  
Layered Ceramic ◽  
Good Agreement

This paper deals with the fracture behaviour of layered ceramic composite with residual stresses. The main goal is to investigate the effect of residual stresses and material interfaces on crack propagation by more complex 3D finite element models. The crack behaviour was described by analytical procedures based on linear elastic fracture mechanics (LEFM) and generalized LEFM. The influence of laminate composition with residual stresses on critical values for crack propagation through the laminate interfaces was also determined. Good agreement has been found to exist between numerical results and experimental data. The results obtained can be used for a design of new layered composites with improved resistance against crack propagation.

Finite Element Analysis for the Fatigue Behavior of Steel Plates Strengthened with CFRP Plates

2006 ◽  
Vol 324-325 ◽  
pp. 359-362 ◽  
Author(s):  
Zheng Yun ◽  
Lie Ping Ye ◽  
Xin Zheng Lu ◽  
Qing Rui Yue
Keyword(s):  
Finite Element ◽  
Crack Propagation ◽  
Fatigue Behavior ◽  
Steel Plates ◽  
Intensity Factors ◽  
Element Analysis ◽  
Linear Elastic ◽  
Paris Law ◽  
Numerical Predictions ◽  
Elastic Fracture

The experimental research on six steel plates strengthened with CFRP plates, loaded in tension, shows that their fatigue lives can be greatly increased compared with un-strengthened specimens. Linear elastic fracture mechanics (LEFM) is adopted to explain the mechanism of CFRP plates strengthening. The stress intensity factors of the steel plates are calculated with finite element method (FEM), and Paris law on crack propagation is used to predict the fatigue life of strengthened specimens. The comparison between experimental results and numerical predictions shows good agreements on the fatigue crack propagation.

Description of Strengthening Mechanism in Layered Ceramic Composites

2015 ◽  
Vol 665 ◽  
pp. 93-96 ◽  
Author(s):  
Kateřina Štegnerová ◽  
Luboš Náhlík ◽  
Pavel Hutař
Keyword(s):  
Residual Stresses ◽  
Crack Propagation ◽  
Ceramic Composite ◽  
Strengthening Mechanism ◽  
Ceramic Composites ◽  
Zirconia Ceramic ◽  
Linear Elastic ◽  
Density Factor ◽  
Elastic Fracture ◽  
Layered Ceramic

The aim of this paper is to describe specific crack behaviour in the layered alumina-zirconia ceramic composite with strong interfaces and its strengthening mechanism. Different coefficients of thermal expansion of individual constituents of ceramic composite cause high residual stresses inside the layers during the sintering process. Compressive residual stresses can significantly influence the crack propagation through the laminate hereby improve the resistance of the material to the crack propagation. Estimation of crack behaviour in laminate was performed assuming the validity of linear elastic fracture mechanics using the criterion based on the strain energy density factor derived by Sih. This paper describes the strengthening mechanism in layered ceramic composites and prediction of their failure which contributes to better understanding of the fracture behaviour of the layered ceramic composites.

The Use of Classification Zones for Fatigue Behavior in Steels—2

1993 ◽  
Vol 115 (4) ◽  
pp. 380-384 ◽  
Author(s):  
M. P. Weiss
Keyword(s):  
Crack Propagation ◽  
Fatigue Behavior ◽  
Evaluation Criteria ◽  
Real Life ◽  
Stress Intensity Factor Range ◽  
Design Problems ◽  
Linear Elastic ◽  
Fatigue Design ◽  
Elastic Fracture ◽  
Fatigue Evaluation

This is the second and updated version of a paper with a similar name, that was published in this journal in [1], 1977. The basic idea of classification of the Fatigue Regime is implemented again, using updated fatigue studies, and the result is a new and updated diagram. Numerous studies on Fatigue Damage and Fatigue Crack Propagation dealt with these problems either by the cumulative damage approach, or by using crack propagation equations based on linear elastic fracture mechanics. Although these two approaches are not compatible, each is useful for predicting fatigue behavior with acceptable scatter, but only within defined limits. This study updates the “Fatigue Diagram,” which classifies different combinations of stresses and crack lengths in a given specimen, as zones in which different fatigue evaluation criteria govern. The whole fatigue regime is divided into six zones, that fit to known and to new prediction methods. For the more problematic zone, where the stress amplitude is higher than the fatigue limit, and the stress intensity factor range is higher than the threshold, a superposition of two prediction procedures is shown to match closely to test results in AISI 4XXX types of steel specimens. The fatigue diagram is shown to be a useful tool for dealing with real life, fatigue design problems. The “Threshold Crack Length” is reintroduced, and directions for additional studies are indicated.

The Use of Classification Zones for Fatigue Behavior in Steels

1977 ◽  
Vol 99 (1) ◽  
pp. 23-25 ◽  
Author(s):  
M. P. Weiss
Keyword(s):  
Phase Diagram ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Fatigue Behavior ◽  
Evaluation Criteria ◽  
Linear Elastic ◽  
Elastic Fracture ◽  
Initiation Stage ◽  
Definition Of ◽  
Fatigue Evaluation

Numerous studies on fatigue damage and fatigue crack propagation in the past dealt with these problems, either by a cumulative damage approach, or using crack propagation equations based on linear elastic fracture mechanics. Although these two approaches are not compatible, each is useful for predicting fatigue behavior correctly, but only within defined limits. This study introduces the “fatigue phase diagram”, which classifies different combinations of stresses and crack lengths in a given specimen, as zones in which different fatigue evaluation criteria, and possibly different fatigue mechanisms govern. Furthermore, a definition of the “threshold crack length” is proposed for consideration as the end of the crack initiation stage. It is suggested that most stress-intensity-range-threshold studies in the literature, were performed with stress range under the fatigue limit of the material, and therefore no crack initiation or propagation could have been measured. Any additional study should specify the zone of the tests on the fatigue phase diagram, so that correlations between different tests could be done with the proper data only.

Application of Multi-Parameter Fracture Mechanics to Study of Crack Propagation Angle in Selected Mixed-Mode Geometry

2013 ◽  
Vol 592-593 ◽  
pp. 209-212 ◽  
Author(s):  
Lucie Šestáková Malíková ◽  
Václav Veselý
Keyword(s):  
Fracture Mechanics ◽  
Crack Propagation ◽  
Mixed Mode ◽  
Initial Crack ◽  
Propagation Angle ◽  
Linear Elastic ◽  
Higher Order Terms ◽  
Elastic Fracture ◽  
Cracked Specimens ◽  
Crack Propagation Angle

The multi-parameter fracture mechanics becomes more and more significant, because it is shown that it can help to describe fracture processes occurring in cracked specimens more precisely than conventional linear elastic fracture mechanics. In this paper, the concept based on the Williams expansion derived for approximation of stress/displacement crack-tip fields is presented and applied on a mixed-mode configuration. Two fracture criteria for estimation of the initial crack propagation angle are introduced. A parametric study is performed in order to investigate the dependence of the crack propagation angle on the stress intensity factors ratio. Influence and importance of taking into account the so-called higher-order terms of the Williams expansion are discussed and some recommendations are stated.

Estimation of the Crack Propagation Direction of a Crack Touching the Interface between Two Elastic Materials

2007 ◽  
Vol 567-568 ◽  
pp. 225-228 ◽  
Author(s):  
Luboš Náhlík ◽  
Lucie Šestáková ◽  
Pavel Hutař
Keyword(s):  
Crack Propagation ◽  
Protective Coatings ◽  
The Body ◽  
Elastic Behavior ◽  
Layered Composites ◽  
The Finite Element Method ◽  
Elastic Materials ◽  
Linear Elastic ◽  
Composites Materials ◽  
Elastic Fracture

The objective of the paper is to investigate the direction of a further crack propagation from the interface between two elastic materials. The angle of crack propagation changes when the crack passes the interface. The suggested procedure makes it possible to estimate an angle of propagation under which the crack will propagate into the second material. The assumptions of linear elastic fracture mechanics and elastic behavior of the body with interfaces are considered. The finite element method was used for numerical calculations. The results obtained might contribute to a better understanding of the failure of materials with interfaces (e.g. layered composites, materials with protective coatings) and to a more reliable estimation of the service life of such structures.

scholarly journals Subcritical crack propagation as a mechanism of crevasse formation and iceberg calving

2004 ◽  
Vol 50 (168) ◽  
pp. 109-115 ◽  
Author(s):  
Jérôme Weiss
Keyword(s):  
Crack Propagation ◽  
Subcritical Crack Growth ◽  
Body Wave ◽  
Critical Crack ◽  
Ice Shelves ◽  
Wave Speeds ◽  
Linear Elastic ◽  
Iceberg Calving ◽  
Elastic Fracture ◽  
Natural Way

AbstractRecent investigations of crevassing on alpine glaciers and ice shelves have been based on linear elastic fracture mechanics (LEFM). However, LEFM is unable to explain some aspects of crevasse formation such as the initiation of crevasse propagation from crystal-scale (mm) microcracks, the slow propagation of large fractures in ice shelves, and the acceleration of crevasse opening before breaking of the ice terminus. Here another mechanism to account for these observations is proposed: subcritical crevassing. Subcritical crack growth, documented in many materials though not yet explored in ice, is characterized by a crack velocity that scales as a power of the tensile stress intensity factor, but is much less than that associated with critical crack propagation. This mechanism allows crevasse propagation from mm-scale microcracks at velocities much lower than body wave speeds, and explains crevasse-opening accelerations in a natural way. Subcritical crevassing is theoretically explored for several simplified situations but is limited by a lack of available data on crevasse evolution.

The Influence of Notch Geometric Size in the Fatigue Strength of Steel

2014 ◽  
Vol 602-605 ◽  
pp. 167-171
Author(s):  
Yong Zhuang Yuan
Keyword(s):  
Fatigue Strength ◽  
Fatigue Behavior ◽  
Stress Gradient ◽  
Fatigue Crack Initiation ◽  
Estimation Method ◽  
Size Factor ◽  
Linear Elastic ◽  
Factor Effect ◽  
Geometric Size ◽  
Elastic Fracture

The fatigue behavior of notch specimens has been investigated in this manuscript. It is shown that notch geometric size has apparent effect for fatigue strength of specimens. The blunt notch is used in test. It is concluded that geometric size effect depends on the stress gradient and can be estimated with the help of the linear elastic fracture mechanics. The influence of notch size for fatigue strength can be explained with geometric factor. The plastic strain play an important role in fatigue crack initiation with notch gets sharper reach certain magnitude limit, and fatigue strength is lower than the predicted by geometric size factor effect. The method does not apply fatigue strength of the sharper notch. Another estimation method shall be used to that kind of notches.

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