Effects of Bonded Crack Retarders on Fatigue Parameters of FSWed Integral Panel

2014 ◽  
Vol 891-892 ◽  
pp. 627-632
Author(s):  
Yu E Ma ◽  
Pan Fu Xu
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Stress Intensity ◽  
Stress Intensity Factors ◽  
Damage Tolerance ◽  
Weld Zone ◽  
Finite Element Models ◽  
Cohesive Elements ◽  
Intensity Factors ◽  
Friction Stir

As known, friction stir welded (FSWed) joints are mature to be applied in aircraft structure. However, the weld creates local discontinuity in property and local tensile residual stress, which harm the damage tolerance of welded panels. So crack retarders were bonded in the weld zone to improve damage tolerance. Finite element method was used to calculate stress intensity factors by ABAQUS software. Finite element models were built to simulate the function of bonded retarder. Cohesive elements were used between the substrate panel and bonded retarder. A Fortran program was made to input residual stress to finite element models. Stress intensity factors from residual stress with and without bonded retarders were calculated and compared. Effects of residual stress on stress intensity factors and redistribution of residual stress were taken into considered. Effective R ratios were calculated with crack growing through the weld. Effects of bonded retarder on stress intensity factors were calculated. The results were compared with the experimental findings.

Stress Intensity Factors and Weight Functions for Longitudinal Semi-Elliptical Surface Cracks Inside Thick-Walled Cylinders Using Highly-Refined Finite-Element Models

2010 ◽  
Author(s):  
Adam R. Hinkle ◽  
James E. Holliday ◽  
David P. Jones
Keyword(s):  
Finite Element ◽  
Stress Intensity ◽  
Crack Growth ◽  
Stress Intensity Factors ◽  
Weight Functions ◽  
Finite Element Models ◽  
Surface Cracks ◽  
Intensity Factors ◽  
Surface Flaws ◽  
Field Singularity

Fracture mechanics and fatigue crack-growth analysis rely heavily upon accurate values of stress intensity factors. They provide a convenient, single-parameter description to characterize the amplitude of the stress-field singularity at the crack tip, and are used to correlate brittle fracture and crack growth in pressure vessel and piping applications. Mode-I stress intensity factors that have been obtained for longitudinal semi-elliptical surface flaws on the inside of thick-walled cylinders using highly-refined finite element models are investigated. Using these results, weight function solutions are constructed and selected geometries are validated.

The evaluation of stress intensity factors for plane cracks in residual stress fields

1993 ◽  
Vol 28 (3) ◽  
pp. 145-152 ◽  
Author(s):  
M D B Wilks ◽  
D Nowell ◽  
D A Hills
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Stress Intensity ◽  
Residual Stresses ◽  
Crack Closure ◽  
Efficient Method ◽  
Stress Intensity Factors ◽  
Stress Fields ◽  
Intensity Factors ◽  
Distributed Dislocations

A reliable, efficient method is described for modelling plane cracks in arbitary residual stress fields, using the technique of distributed dislocations. This allows correctly for re-distribution of residual stresses as the crack grows. Problems where crack closure occur are discussed, and implications for solution by finite element procedures are inferred and confirmed by comparison.

Weight Functions and Stress Intensity Factors for Eccentric through Cracks in a 3-D Rectangular Plate Subjected to In-Plane Loading

2016 ◽  
Vol 853 ◽  
pp. 8-14
Author(s):  
Xu Teng Hu ◽  
Xu Jia ◽  
Ying Dong Song
Keyword(s):  
Finite Element ◽  
Stress Intensity ◽  
Rectangular Plate ◽  
Stress Intensity Factors ◽  
Interpolation Method ◽  
Unknown Coefficient ◽  
Weight Functions ◽  
Finite Element Models ◽  
Intensity Factors ◽  
Aspect Ratios

Three unknown coefficient weight functions for eccentric through cracks in a 3-D rectangular plate subjected to in-plane loading are proposed. 3-D finite element models of cracked rectangular plates within the whole range of crack aspect ratios, i.e., 0≤e/W≤0.8, 0.08≤a/(W-e)≤0.9, were established to obtain a reference SIF database for both crack points A and B, rather than 2-D finite element models. To improve the accuracy of the weight function, the coefficients were derived from this database using the Binary Lagrange Interpolation Method instead of Curve-Fitting Expression. Comparisons of stress intensity factors calculated using the present weight functions with finite element data for the high-order power law and residual stress distributions show high accuracy of the present weight functions.

Insulated Railroad Joint Design Evaluation by Coordinated Test and Finite Element Analysis

2013 ◽  
Author(s):  
Amir H. Iranmanesh ◽  
Robert L. West ◽  
Mehdi Ahmadian
Keyword(s):  
Finite Element ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Stress Intensity Factors ◽  
Experimental Tests ◽  
Parametric Modeling ◽  
Finite Element Models ◽  
Intensity Factors ◽  
Joint Design ◽  
Stress Analyses

The railroad industry faces challenges with bonded insulated joint designs in the present practice. A program initiated by Virginia Tech and the Transportation Technology Center Incorporated (TTCI) has been in progress to analyze and test a class of insulated joint designs featuring non-adhesive bolted connections. A hierarchical approach to finite element modeling with a parametric model maintaining essential mechanics of the joints has been applied to develop a bolted insulated joint design. The current paper reports on the recent phase of the program including development of experimental tests along with finite element analyses on scaled simplified insulated rail joint models. Two baseline rail joint configurations with simplified sections were considered for studying dominant mechanics under the AREMA (American Railway Engineering and Maintenance-of-Way Association) rail joint acceptance standard test loading and boundary conditions. The finite element models developed based on three-dimensional continuum elements incorporated bolt preloads and full-contact analysis. In the experimental tests, the strain analyses on 1/4 scaled polycarbonate rail joint specimens were performed by means of an array of strain gauge transducers mounted on the joint bars and a photoelasticity technique. The results of the experimental stress analyses were employed to validate the finite element models quantitatively and qualitatively in terms of load transfer mechanics and stress distribution. The validated models serve as baseline insulated joint configurations for developing fracture-mechanics-based fatigue-failure analysis. To investigate the role of cracks on the performance and reliability of joint bars, a damage tolerant analysis is performed on the rail joints utilizing linear elastic fracture mechanics. The locations of most critical type defects are estimated based on high stress/strain regions from stress analyses along with past experiences on failure of rail joints. To characterize the severity of theses defects under alternating loading conditions, stress intensity factors are computed as a function of crack length. Cracks of different lengths are introduced in the vicinity of the most fatigue-prone locations of the joint bar in a parametric modeling fashion. The fatigue-crack-growth-rate properties in terms of Paris Law scaling constants are selected from a survey of available material data. The number of loading cycles to failure is obtained by employing the computed stress-intensity factors as well as initial and final crack sizes. Predicted lifetimes as a function of pre-existing crack sizes and geometry of joint configuration can be used as a fracture-mechanics-based function for more accurate design of the rail joints.

Effect of Welding Residual Stress on Stress Intensity Factors for Semi-Elliptical Surface Cracks in a Butt-Welded Steel Plate

2018 ◽  
Author(s):  
Bin Qiang ◽  
Xin Wang
Keyword(s):  
Residual Stress ◽  
Finite Element ◽  
Stress Intensity ◽  
Compressive Stress ◽  
Stress Intensity Factors ◽  
Steel Plate ◽  
Welding Residual Stress ◽  
Surface Cracks ◽  
Intensity Factors ◽  
Longitudinal Residual Stress

The through-thickness distribution of welding residual stress in a 30-mm-thick butt-welded Q345qD steel plate has been investigated through experimental measurements and finite-element simulations. In this paper, the weight function and finite element methods are used to investigate the stress intensity factors (SIFs) at the surface and deepest points of the semi-elliptical surface cracks, subjected to a combination of external tensile load and through-thickness welding residual stress. Different crack aspect ratios and relative depths are analyzed. The results reveal that the longitudinal residual stress is always tensile through the plate thickness, which makes the SIFs of the surface and deepest points larger than those without considering the longitudinal residual stress. However, the transverse residual stress through the thickness presents tension–compression–tension, with the tensile transverse residual stress causing the SIFs to increase. When the crack tip enters the compressive stress region, the compressive stress offsets the external load and causes the SIFs to decrease.

A Coupled SBFEM-FEM Approach for Evaluating Stress Intensity Factors

2013 ◽  
Vol 353-356 ◽  
pp. 3369-3377 ◽  
Author(s):  
Ming Guang Shi ◽  
Chong Ming Song ◽  
Hong Zhong ◽  
Yan Jie Xu ◽  
Chu Han Zhang
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Stress Intensity ◽  
Stress Intensity Factors ◽  
Complex Geometry ◽  
Stress Singularity ◽  
Intensity Factors ◽  
Finite Element Software ◽  
Scaled Boundary Finite Element ◽  
Element Method

A coupled method between the Scaled Boundary Finite Element Method (SBFEM) and Finite Element Method (FEM) for evaluating the Stress Intensity Factors (SIFs) is presented and achieved on the platform of the commercial finite element software ABAQUS by using Python as the programming language. Automatic transformation of the finite elements around a singular point to a scaled boundary finite element subdomain is realized. This method combines the high accuracy of the SBFEM in computing the SIFs with the ability to handle material nonlinearity as well as powerful mesh generation and post processing ability of commercial FEM software. The validity and accuracy of the method is verified by analysis of several benchmark problems. The coupled algorithm shows a good converging performance, and with minimum additional treatment can be able to handle more problems that cannot be solved by either SBFEM or FEM itself. For fracture problems, it proposes an efficient way to represent stress singularity for problems with complex geometry, loading condition or certain nonlinearity.

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