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Article
Publication date: 1 January 1987

T.K. Hellen and W.S. Blackburn

A review is made of methods for calculating parameters characterizing crack tip behaviour in non‐linear materials. Convenient methods of calculating J‐integral type quantities are…

Abstract

A review is made of methods for calculating parameters characterizing crack tip behaviour in non‐linear materials. Convenient methods of calculating J‐integral type quantities are reviewed, classified broadly into two groups, as domain integrals and virtual crack extension techniques. In addition to considerations of how such quantities may be calculated by finite elements, assessment methods of conducting the actual incremental analyses are described.

Details

Engineering Computations, vol. 4 no. 1
Type: Research Article
ISSN: 0264-4401

Article
Publication date: 31 March 2020

Imad Barsoum, Hamda Almansoori, Aaesha Ahmed Almazrouei and Ebru Gunister

The main aim of this study is to determine the fracture toughness and accordingly to predict the fracture initiation, crack propagation and mode of crack extension accurately in…

Abstract

Purpose

The main aim of this study is to determine the fracture toughness and accordingly to predict the fracture initiation, crack propagation and mode of crack extension accurately in polypropylene subsea pipes subjected to internal pressure.

Design/methodology/approach

Tensile test was performed following the ISO 527–1 standard. An elastic-plastic constitutive model was developed based on the tensile test results, and it is implemented in the FEA model to describe the constitutive behaviour of the polypropylene material. Three-point bend tests with linear-elastic fracture mechanics (LEFM) approach were conducted following ISO-13586 standard, from which the average fracture toughness of the polypropylene pipe material in crack-opening mode was found as KIc = 3.3 MPa√m. A numerical model of the experiments is developed based on the extended finite element method (XFEM), which showed markedly good agreement with the experimental results.

Findings

The validated XFEM modelling approach is utilised to illustrate its capabilities in predicting fracture initiation and crack propagation in a polypropylene subsea pipe subjected to an internal pressure containing a semi-elliptical surface crack, which agrees well with existing analytical solutions. The XFEM model is capable of predicting the crack initiation and propagation in the polypropylene pipe up to the event of leakage.

Originality/value

The methodology proposed herein can be utilised to assess the structural integrity and resistance to fracture of subsea plastic pipes subjected to operational loads (e.g. internal pressure).

Details

International Journal of Structural Integrity, vol. 12 no. 2
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 9 April 2018

S.A. Krishnan, G. Sasikala, A. Moitra, S.K. Albert and A.K. Bhaduri

The purpose of this paper is to present a methodology to assess material damage parameters for ductile crack initiation and growth ahead of a crack/notch tip in high hardening…

Abstract

Purpose

The purpose of this paper is to present a methodology to assess material damage parameters for ductile crack initiation and growth ahead of a crack/notch tip in high hardening steel like AISI type 316L(N) stainless steel.

Design/methodology/approach

Ductile damage parameter and far field J-integral have been obtained from standard FEM analysis for a crack/notch tip undergoing large plastic deformation and resulting in crack initiation/growth. In conjunction with experimental results, the damage variable for low strength and high hardening material has been derived in terms of continuum parameters: equivalent plastic strain (εeq) and stress triaxiality (φ). The material parameters for damage initiation and growth in 316LN SS have been evaluated from tensile and fracture tests. With these material tensile/fracture parameters as input, elastic-plastic eXtended Finite Element Method (X-FEM) simulations were carried out on compact tension (CT) specimen geometry under varying initial stress triaxiality conditions.

Findings

The material parameters for damage initiation and growth have been assessed and calibrated by comparing the X-FEM predicted load-displacement responses with the experimental results. It is observed that the deviations in the predicted load values from the experimental data are within 6 percent for specimens with a/W=0.39, 0.55, 0.64, while for a/W=0.72, it is 17 percent.

Originality/value

The present study is a part of developing methods to obtain calibrated material damage parameters for crack growth simulation of components made of AISI 316L(N) stainless steel. This steel is used for fast breeder reactor-based power plant being built at Kalpakkam, India.

Details

International Journal of Structural Integrity, vol. 9 no. 2
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 17 July 2019

Feizal Yusof and Karh Heng Leong

Crack tip stresses are used to relate the ability of structures to perform under the influence of cracks and defects. One of the methods to determine three-dimensional crack tip…

Abstract

Purpose

Crack tip stresses are used to relate the ability of structures to perform under the influence of cracks and defects. One of the methods to determine three-dimensional crack tip stresses is through the J-Tz method. The J-Tz method has been used extensively to characterize the stresses of cracked geometries that demonstrate positive T-stress but limited in characterizing negative T-stresses. The purpose of this paper is to apply the J-Tz method to characterize a three-dimensional crack tip stress field in a changing crack length from positive to negative T-stress geometries.

Design/methodology/approach

Elastic-plastic crack border fields of deep and shallow cracks in tension and bending loads were investigated through a series of three-dimensional finite element (FE) and analytical J-Tz solutions for a range of crack lengths ranging from 0.1⩽a/W⩽0.5 for two thickness extremes of B/(Wa)=1 and 0.05.

Findings

Both the FE and the J-Tz approaches showed that the combined in-plane and the out-of-plane constraint loss were differently affected by the T-stress and the out-of-plane size effects when the crack length changed from deep to shallow cracks. The conditions of the J-Tz dominance on the three-dimensional crack front tip were shown to be limited to positive T-stress geometries, and the J-Tz-Q2D approach can extend the crack border dominance of the three-dimensional deep and shallow bend models along the crack front tip until perturbed by an elastic-plastic corner field.

Practical implications

The paper reports the limitation of the J-Tz approach, which is used to calculate the state of three-dimensional crack tip stresses in power law hardening materials. The results from this paper suggest that the characterization of the three-dimensional crack tip stress in power law hardening materials is still an open issue and requires other suitable solutions to solve the problem.

Originality/value

This paper demonstrates a thorough analysis of a three-dimensional elastic-plastic crack tip fields for geometries that are initially either fully constrained (positive T-stress) or unconstrained (negative T-stress) crack tip fields but, subsequently, the T-stress sign changes due to crack length reduction and specimen thickness increase. The J-Tz stress-based method has been tested and its dominance over the crack tip field is shown to be affected by the combined in-plane and the out-of-plane constraints and the corner field effects.

Details

International Journal of Structural Integrity, vol. 10 no. 5
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 2 February 2015

A. Krasovskyy and A. Virta

Even though modern welding technology has improved, initial defects on weld notches cannot be avoided. Assuming the existence of crack-like flaws after the welding process, the…

Abstract

Purpose

Even though modern welding technology has improved, initial defects on weld notches cannot be avoided. Assuming the existence of crack-like flaws after the welding process, the stage of a fatigue crack nucleation becomes insignificant and the threshold for the initial crack propagation can be used as a criterion for very high cycle fatigue whereas crack growth analysis can be applied for the lifetime estimation at lower number of cycles. The purpose of this paper is to present a mechanism based approach for lifetime estimation of welded joints, subjected to a multiaxial non-proportional loading.

Design/methodology/approach

The proposed method, which is based on the welding process simulation, thermophysical material modeling and fracture mechanics, considers the most important aspects for fatigue of welds. Applying worst-case assumptions, fatigue limits derived by the weight function method can be then used for the fatigue assessment of complex welded structures.

Findings

An accurate mechanism based method for the fatigue life assessment of welded joints has been presented and validated.

Originality/value

Compared to the fatigue limits provided by design codes, the proposed method offers more accurate lifetime estimation, a better understanding of interactions between welding process and fatigue behavior. It gives more possibilities to optimize the welding process specifically for the considered material, weld type and loading in order to achieve the full cost and weight optimization potential for industrial applications.

Details

International Journal of Structural Integrity, vol. 6 no. 1
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 1 November 2022

Yongliang Wang and Xin Zhang

Hydrofracturing technology has been widely used in tight oil and gas reservoir exploitation, and the fracture network formed by fracturing is crucial to determining the resources…

Abstract

Purpose

Hydrofracturing technology has been widely used in tight oil and gas reservoir exploitation, and the fracture network formed by fracturing is crucial to determining the resources recovery rate. Due to the complexity of fracture network induced by the random morphology and type of fluid-driven fractures, controlling and optimising its mechanisms is challenging. This paper aims to study the types of multiscale mode I/II fractures, the fluid-driven propagation of multiscale tensile and shear fractures need to be studied.

Design/methodology/approach

A dual bilinear cohesive zone model (CZM) based on energy evolution was introduced to detect the initiation and propagation of fluid-driven tensile and shear fractures. The model overcomes the limitations of classical linear fracture mechanics, such as the stress singularity at the fracture tip, and considers the important role of fracture surface behaviour in the shear activation. The bilinear cohesive criterion based on the energy evolution criterion can reflect the formation mechanism of complex fracture networks objectively and accurately. Considering the hydro-mechanical (HM) coupling and leak-off effects, the combined finite element-discrete element-finite volume approach was introduced and implemented successfully, and the results showed that the models considering HM coupling and leak-off effects could form a more complex fracture network. The multiscale (laboratory- and engineering-scale) Mode I/II fractures can be simulated in hydrofracturing process.

Findings

Based on the proposed method, the accuracy and applicability of the algorithm were verified by comparing the analytical solution of KGD and PKN models. The effects of different in situ stresses and flow rates on the dynamic propagation of hydraulic fractures at laboratory and engineering scales were investigated. when the ratio of in situ stress is small, the fracture propagation direction is not affected, and the fracture morphology is a cross-type fracture. When the ratio of in situ stress is relatively large, the propagation direction of the fracture is affected by the maximum in situ stress, and it is more inclined to propagate along the direction of the maximum in situ stress, forming double wing-type fractures. Hydrofracturing tensile and shear fractures were identified, and the distribution and number of each type were obtained. There are fewer hydraulic shear fractures than tensile fractures, and shear fractures appear in the initial stage of fracture propagation and then propagate and distribute around the perforation.

Originality/value

The proposed dual bilinear CZM is effective for simulating the types of Mode I/II fractures and seizing the fluid-driven propagation of multiscale tensile and shear fractures. Practical fracturing process involves the multi-type and multiscale fluid-driven fracture propagation. This study introduces general fluid-driven fracture propagation, which can be extended to the fracture propagation analysis of potential fluid fracturing, such as other liquids or supercritical gases.

Article
Publication date: 10 August 2015

Jirí Behal, Petr Homola and Roman Ružek

The prediction of fatigue crack growth behaviour is an important part of damage tolerance analyses. Recently, the author’s work has focused on evaluating the FASTRAN retardation…

94

Abstract

Purpose

The prediction of fatigue crack growth behaviour is an important part of damage tolerance analyses. Recently, the author’s work has focused on evaluating the FASTRAN retardation model. This model is implemented in the AFGROW code, which allows different retardation models to be compared. The primary advantage of the model is that all input parameters, including those for an initial plane-strain state and its transition to a plane-stress-state, are objectively measured using standard middle-crack-tension M(T) specimens. The purpose of this paper is to evaluate the ability of the FASTRAN model to predict correct retardation effects due to high loading peaks that occur during variable amplitude loading in sequences representative of an aircraft service.

Design/methodology/approach

This paper addresses pre-setting of the fracture toughness K R (based on J-integral J Q according to ASTM1820) in the FASTRAN retardation model. A set of experiments were performed using specimens made from a 7475-T7351 aluminium alloy plate. Loading sequences with peaks ordered in ascending-descending blocks were used. The effect of truncating and clipping selected load levels on crack propagation behaviour was evaluated using both experimental data and numerical analyses. The findings were supported by the results of a fractographic analysis.

Findings

Fatigue crack propagation data defined using M(T) specimens made from Al 7475-T7351 alloy indicate the difficulty of evaluating the following two events simultaneously: fatigue crack increments after application of loads with maximum amplitudes that exceeded J Q and subcritical crack increments caused by loads at high stress intensity factors. An effect of overloading peaks with a maximum that exceeds J Q should be assessed using a special analysis beyond the scope of the FASTRAN retardation model.

Originality/value

Measurements of fatigue crack growth on specimens made from 7475 T7351 aluminium alloy were carried out. The results indicated that simultaneously evaluating fatigue crack increments after application of the load amplitude above J Q and subcritical increments caused by the loads at high stress intensity factors is difficult. Experiments demonstrated that if the fatigue crack reaches a specific length, the maximal amplitude load induces considerable crack growth retardation.

Details

International Journal of Structural Integrity, vol. 6 no. 4
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 2 October 2017

Rachman Setiawan and Musthafa Akbar

Integrity assessment is used to ensure reliability operation of a pressurized equipment containing defects. Based on data of cylindrical shell dimensions, operation conditions…

Abstract

Purpose

Integrity assessment is used to ensure reliability operation of a pressurized equipment containing defects. Based on data of cylindrical shell dimensions, operation conditions, material properties and crack dimensions, an assessment can be carried out, using either Level 1, Level 2 or Level 3 procedure. Assessment using Level 3 procedure within the code requires a finite element simulation in order to generate both the evaluation point and the failure assessment diagram (FAD) that serves as the acceptance criteria. The purpose of this paper is to provide the numerical data which are used for integrity assessment of a pressure vessel containing crack. Here, a parametric study has been carried out to generate such result for the cases of longitudinal crack defect in a cylindrical shell for a number of common cases, in terms of thickness-to-radius ratio, crack size ratio and crack aspect ratio.

Design/methodology/approach

The evaluation of stress intensity factor is determined through J-integral parameter found using a finite element analysis with a specially meshed strategy incorporating the crack. A comparison is made against stress intensity factor provided by the code.

Findings

A good agreement is obtained with percent error of 2.13 percent for low aspect ratio crack, and 0.57 percent for high aspect ratio crack. Furthermore, a study has been carried out using the methodology for 160 cases, covering both cases already available in the code and other cases of crack in cylindrical shells. The result can be used as a complement to the existing tabular data available in the code for Level 2 assessment, to be used for integrity analysis of damaged cylindrical shells based on the FAD criteria.

Originality/value

The result can be used as a complement to the existing tabular data available in the API 579 code for Level 2 assessment, to be used for integrity analysis of damaged cylindrical shells based on the FAD criteria. New equations were generated based on finite element analysis and can be used for Level 3 assessment of the code.

Details

International Journal of Structural Integrity, vol. 8 no. 5
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 17 January 2022

Xintian Liu, Que Wu, Shengchao Su and Yansong Wang

The properties of materials under impact load are introduced in terms of metal, nonmetallic materials and composite materials. And the application of impact load research in…

Abstract

Purpose

The properties of materials under impact load are introduced in terms of metal, nonmetallic materials and composite materials. And the application of impact load research in biological fields is also mentioned. The current hot research topics and achievements in this field are summarized. In addition, some problems in theoretical modeling and testing of the mechanical properties of materials are discussed.

Design/methodology/approach

The situation of materials under impact load is of great significance to show the mechanical performance. The performance of various materials under impact load is different, and there are many research methods. It is affected by some kinds of factors, such as the temperature, the gap and the speed of load.

Findings

The research on mechanical properties of materials under impact load has the characteristics as fellow. It is difficult to build the theoretical model, verify by experiment and analyze the data accumulation.

Originality/value

This review provides a reference for further study of material properties.

Details

International Journal of Structural Integrity, vol. 13 no. 2
Type: Research Article
ISSN: 1757-9864

Keywords

Article
Publication date: 8 June 2015

S. A. Krishnan, A. Moitra, G. Sasikala, S.K. Albert and A.K. Bhaduri

The purpose of this paper is to present a methodology to predict initial crack growth behavior of crack or notch like stress raisers in AISI 316L(N) stainless steel material…

Abstract

Purpose

The purpose of this paper is to present a methodology to predict initial crack growth behavior of crack or notch like stress raisers in AISI 316L(N) stainless steel material subjected to monotonic loading condition.

Design/methodology/approach

The methodology for critical crack blunting corresponding to crack initiation in crack or notch like stress raisers is based on critical plastic strain (Epc) at a characteristic distance (lc), where uniform strain (Eu) is considered as Epc and two grain diameter is considered as lc. Further crack growth is based on parabolic crack tip opening displacement (CTOD) scheme established based on coupled experimental and FEM analysis of compact tension (CT) specimen subjected to mode-I loading condition. The FEM predicted load-displacement plots is compared with experimental result of CT specimens with different a/W ratios. It has shown that the proposed methodology could account initial crack blunting appropriately and predict the fracture load and load-displacement plots for initial crack growth regime.

Findings

The results show that for crack growth with near straight crack front, experimental data from a CT specimen of particular a/W ratio coupled with plane strain 2D FEM analysis could predict load vs displacement plots for different a/W ratios when initial crack blunting is accounted appropriately with a local damage model.

Originality/value

The present study is a part of developing methods to analyse fracture behavior of AISI 316L(N) SS material components used for fast breeder reactor-based power plant being built at Kalpakkam, India.

Details

International Journal of Structural Integrity, vol. 6 no. 3
Type: Research Article
ISSN: 1757-9864

Keywords

1 – 10 of 283