Journal Sciences News
Theoretical and Applied Fracture Mechanics
15 May 2018
A super crack front element for three-dimensional fracture mechanics analysis
Publication date: 1 June 2018
Source:Engineering Fracture Mechanics, Volume 196 Author(s): Xue-Cheng Ping, Chun-Guang Wang, Li-Peng Cheng, Meng-Cheng Chen, Jin-Quan Xu A super crack front element containing a part of a curved crack front is established to solve the stress intensity factors of three-dimensional curved cracks by using the numerical series eigen-solutions. The element can be directly incorporated into the existing three-dimensional linear brick elements without using transition elements. The intensity of singular stress fields is determined as the system unknowns appearing as nodal displacement values. Numerical studies are conducted to demonstrate the simplicity and effectiveness of the proposed technique in handling typical three-dimensional fracture problems of curved cracks. It is proved that the super crack front element can avoid mesh refinement near the crack front domain without loss of calculation accuracy and velocity of convergence, and can be used to deal with interfacial and anisotropic fracture problems directly.
15 May 2018
Finite element modeling of crack growth in thin-wall structures by method of combining sub-partition and substructure
Publication date: 15 May 2018
Source:Engineering Fracture Mechanics, Volume 195 Author(s): Chen Xing, Chuwei Zhou A combination of sub-partition and substructure methods in finite element is developed to simulate the crack propagation in plate and shell structures. This method allows modeling arbitrary shape crack independent of element mesh and only the elements overlapping crack need to be operated. An element cut apart by a crack is sub-partitioned into ordinary sub-elements while an element enveloping crack tip is sub-partitioned into several singular sub-elements. The whole sub-elements constitute a substructure and the additional nodal freedom degrees introduced by element sub-partition are condensed to nodes of original mesh. In this way global re-meshing is avoided when the crack grows or new crack nucleates. Good accuracy of the crack tip fields prediction and good adaptability of moving crack simulation by the proposed method are proven through designed examples.
15 May 2018
Dominant mode of planar fractures and the role of material properties
Publication date: 15 May 2018
Source:Engineering Fracture Mechanics, Volume 195 Author(s): Huai-Zhong Liu, Jeen-Shang Lin, Jiang-Da He, Hong-Qiang Xie This study is aimed at determining the regions where different planar fracture modes would prevail in the k
15 May 2018
Axial-torsional high-cycle fatigue of both coarse-grained and nanostructured metals: A 3D cohesive finite element model with uncertainty characteristics
Publication date: 15 May 2018
Source:Engineering Fracture Mechanics, Volume 195 Author(s): Q.Q. Sun, X. Guo, G.J. Weng, G. Chen, T. Yang In this study the combined axial–torsional fatigue life and damage evolution of both coarse-grained (CG) and nanostructured metals are modeled by a 3D cohesive finite element method with uncertainty characteristics. To account for the random nature of metal fatigue, we combine the Monte Carlo simulation with the three-parameter Weibull statistical distribution function. For both CG and nanostructured metals, we find that the axial load levels have greater effects than random fields on the amplitude of specimen rotation. Compared with the CG metals, the nanostructured metals are found to exhibit an improved fatigue resistance, for the reason that their damage process initiates from the subsurface beneath the nanograined layer and then extends to the exterior surface. Good agreements between the numerical results and experimental data are also observed. It shows the applicability of the 3D cohesive finite element method for the analysis of damage evolution and prediction of fatigue life in these two classes of metals.
15 May 2018
Failure criterion of titanium alloy irregular sheet specimens for vibration-based bending fatigue testing
Publication date: 15 May 2018
Source:Engineering Fracture Mechanics, Volume 195 Author(s): Wei Xu, Xianfeng Yang, Bin Zhong, Yuhuai He, Chunhu Tao The failure moments of vibration-based fatigue tests are usually defined based on the natural frequency drops of specimens. But the selections of the critical values of the frequency drop have been very arbitrary in the previous tests, lacking of convincing reasons. The present paper aims to propose a failure criterion of titanium alloy irregular sheet specimens tested in a vibration-based bending fatigue experiment. A novel three-dimensional finite element model of the specimen is built, with a cohesive zone model employed to simulate the fatigue dangerous zone (FDZ) and the semi-elliptic crack propagation process of the specimen. A failure criterion to define the critical natural frequency drop is subsequently proposed based on the obtained computational results. Furthermore, a vibration-based bending fatigue test for the specimens is conducted to verify the computational model and the proposed failure criterion. After comparing the present testing results with the results of a similar bending fatigue test, the two types of the testing results are found very close. The vibration-based bending fatigue test with the proposed failure criterion provides an effective way for obtaining accurate fatigue life of irregular specimens.
15 May 2018
Development of new
15 May 2018
Plasticity-induced crack closure from surface to deep interior locations – A three-dimensional finite element study
Publication date: 15 May 2018
Source:Engineering Fracture Mechanics, Volume 195 Author(s): Chien-Yuan Hou The remeshing technique has been proved to be useful in saving numerous elements for two-dimensional finite element crack closure analysis. The computer code employing this technique was further developed for three-dimensional problems. Using this technique, the crack closure phenomenon of specimens with various thicknesses was studied, with emphases on the closure transition from specimen surface to deep interior locations. It was found that, at the specimen surface, the loading-direction stress distribution, and the crack tip plastic zone differ from those obtained under plane stress condition. However, the surface and the plane stress opening stresses are close. When a specimen is thick enough, the stress state, plastic zone and crack opening stresses at the deep interior locations are close to those under plane strain condition. The surface effects on crack opening behavior reach to a depth that is approximately 1.34 times of the Irwin’s plane stress plastic zone size.
15 May 2018
Evaluation of fracture toughness in different regions of weld joints using unloading compliance and normalization method
Publication date: 15 May 2018
Source:Engineering Fracture Mechanics, Volume 195 Author(s): Jiankai Tang, Zheng Liu, Shouwen Shi, Xu Chen Both unloading compliance method and normalization method specified in ASTM E1820-16 were conducted on the API 5L X70 and X80 pipeline steels. Extensive experimental measures of fracture toughness for different regions of weld joints were carried out. For comparison, the JR curves and initiation fracture toughness determined using the normalization method are compared with those obtained by the elastic unloading compliance method for two different weld joints. The results show that good agreements exist between the two methods, and an average difference less than 10% is detected. Moreover, the comparison indicates that the JR curves from the unloading compliance method are lower at the initial stage of crack extension, and as the crack grows, the JR curves are higher compared with those of the normalization method. For different regions in weld joints, there is clear distinction of differences between the corresponding results from above two methods. A ductile brittle mixed fracture mechanism is found in weld metal and coarse grained heat affected zone, and a corresponding higher deviation is detected.
15 May 2018
Creep characteristics and deformation analysis of service-exposed material using small punch creep test
Publication date: 15 May 2018
Source:Engineering Fracture Mechanics, Volume 195 Author(s): Sisheng Yang, Yangyan Zheng, Yejuan Duan, Xiang Ling In this study, the creep characteristics and deformation analysis of service-exposed Cr5Mo are performed. Similar creep curves and deformation trends are found in both the uniaxial creep test and small punch creep test; however, the transient and tertiary creep stages are more apparent in the small punch test. The contribution of secondary creep time to the overall creep life is proven to be greater in the small punch creep test, corresponding to the tertiary stage which occupied most of the creep strain in the uniaxial creep test. When the creep deflection continues to increase, the percentages of low-angle grain boundaries and local misorientation increase, and the largest value appears in the necking region. On the basis of the microstructure analysis, a creep cavity model for the small punch creep is proposed for service-exposed Cr5Mo. The results demonstrate that the growth of creep damage has a stage from the constant speed to the accelerated speed creep. Ductile fracture behaviour is characterized. Finally, the Larson-Miller method is introduced and applied to predict the creep life of service-exposed material from shorter rupture time data.
15 May 2018
Review and evaluation of weight functions and stress intensity factors for edge-cracked finite-width plate
Publication date: 15 May 2018
Source:Engineering Fracture Mechanics, Volume 195 Author(s): X.R. Wu, D.H. Tong, X.C. Zhao, W. Xu Various analytical and numerical weight functions (WFs) for the edge-cracked finite-width plate (ECFWP) configuration have been developed in the literature for efficient fracture mechanics analyses involving complicated/arbitrary load conditions. The objective of this paper is to make a comprehensive review and critical evaluation of the existing WFs determined by using various approaches, e.g. singular integral equation methods; one/two reference load case(s) based analytical approaches; fitting and interpolation to handbook solutions; numerical methods such as the complex Taylor series expansion and finite element analysis. The accuracy levels of existing WFs are assessed in rigorous manner by benchmarking the corresponding Green’s functions (GFs) against well-recognized accurate solutions. A highly accurate and wide-ranging analytical ECFWP WF is presented in closed form. Stress intensity factor and crack opening displacement solutions for various load cases of practical interest are easily determined with high accuracy by using the well-verified analytical ECFWP WF for this crack configuration to demonstrate the methods.
15 May 2018
A state-based peridynamic analysis in a finite element framework
Publication date: 15 May 2018
Source:Engineering Fracture Mechanics, Volume 195 Author(s): Erdogan Madenci, Mehmet Dorduncu, Atila Barut, Nam Phan This study presents a PeriDynamic (PD) element to perform deformation and fracture analysis within a finite element framework. The PD interactions among the finite element nodes are achieved through a truss element. This element permits non-uniform discretization with an irregular shape domain of interaction and a variable horizon. The size and shape of the interaction domain dictates the element connectivity. Such connectivity results in a sparsely populated global system stiffness matrix. The solution of such a system of equations is achieved by employing the BiConjugate Gradient Stabilized (BICGSTAB) method within the in-house program. The explicit analysis is performed by constructing a global lumped mass matrix along with a hybrid implicit/explicit time integration scheme. The solution of resulting system of equations is achieved through an implicit solver until crack initiation, and it continues with an explicit time integration algorithm during crack growth. Crack nucleation and its growth occur when the maximum principal stress in an element exceeds the uniaxial tensile strength of the material or the visibility criteria is not satisfied. The capability of this truss element and failure criteria is established by considering four distinct geometric configurations with and without a crack, and loading conditions. In the absence of crack propagation, the peridynamic truss element predictions are compared with those of analytical and finite element results. In presence of crack propagation, the PD damage predictions are compared with the available experimental observations.
15 May 2018
Atomistic modelling of crack-inclusion interaction in graphene
Publication date: 15 May 2018
Source:Engineering Fracture Mechanics, Volume 195 Author(s): M.A.N. Dewapriya, S.A. Meguid, R.K.N.D. Rajapakse In continuum fracture mechanics, it is well established that the presence of crack near an inclusion leads to a significant change in the crack-tip stress field. However, it is unclear how atomistic crack-inclusion interaction manifests itself at the nanoscale where the continuum description of matter breaks down. In this work, we conducted molecular dynamics simulations to investigate the interactions of an atomic-scale boron nitride inclusion with an edge crack in a graphene sheet. Numerical simulations of nanoscale tensile tests were obtained for graphene samples containing an edge crack and a circular inclusion. Stress analysis of the samples show the complex nature of the stress state at the crack-tip due to the crack-inclusion interaction. Results reveal that the inclusion results in an increase (amplification) or a decrease (shielding) of the crack-tip stress field depending on the location of the inclusion relative to the crack-tip. Our numerical experiments unveil that inclusions of specific locations could lead to a reduction in the fracture resistance of graphene. Results of the crack-inclusion interaction study were compared with the corresponding results of crack-hole interaction problem. The study also provides an insight into the applicability of well-established continuum crack-microdefect interaction models for the corresponding atomic scale problems.
15 May 2018
Underwater burst tests for evaluating unstable ductile crack arrestability in offshore pipelines
Publication date: 15 May 2018
Source:Engineering Fracture Mechanics, Volume 195 Author(s): Takahiro Hosoe, Kazuki Shibanuma, Hikaru Yamaguchi, Masatoshi Tsukamoto, Katsuyuki Suzuki, Shuji Aihara We conducted a series of short pipe burst tests with and without water backfill to investigate the difference in crack arrestability between offshore and onshore pipelines. The results clearly showed that the crack arrest lengths in underwater pipes were shorter than those of pipes with no backfill. Although underwater pipes have characteristics that both enhance and suppress crack arrestability, the effects of arrest-enhancing factors are considerably greater in water as shallow as 2.0
15 May 2018
Effect of meso-structure on strength and size effect in concrete under compression
Publication date: 15 May 2018
Source:Engineering Fracture Mechanics, Volume 195 Author(s): Sachin Rangari, K. Murali, Arghya Deb The effect of heterogeneity in meso level geometric and material properties on compressive strength and size effect in concrete cylinders is investigated. Crucial meso geometric parameters are identified by studying specimens belonging to three distinct gradations and spanning a range of sizes. A statistical analysis is used to account for dependencies between the parameters. Compressive strength and size effect are seen to depend on the degree of heterogeneity of critical meso parameters. For moderately sized specimens, major trends in the size effect are seen to be almost entirely explained by heterogeneity in the meso geometry; heterogeneity in meso level material properties is seen to be of comparatively less importance.
15 May 2018
Fracture behaviour of cemented tailing backfill with pre-existing crack and thermal treatment under three-point bending loading: Experimental studies and particle flow code simulation
Publication date: 15 May 2018
Source:Engineering Fracture Mechanics, Volume 195 Author(s): Wenbin Xu, Peiwang Cao The three-point bending test was performed on cemented tailing backfill prepared with different offset notches by a loading system with high-speed camera. And the effect of heated temperature on CTB fracture behavior has been investigated. These results indicate that the influence of pre-existing notch and temperature on CTB fracture feature is obvious. The peak load increases linearly with the increasing of the offset ratio when the depth-height ratio of notch is fixed at the same value, while the fracture peak loading decreases sharply with the increase of the notch depth when the offset ratios are the same level. The fracture toughness decreases by 63.5% as the heated temperature rises from 20
15 May 2018
Towards a physics-based relationship for crack growth under different loading modes
Publication date: 15 May 2018
Source:Engineering Fracture Mechanics, Volume 195 Author(s): Lucas Amaral, Ren
1 May 2018
J-integral expression for mixed mode I/II ductile failure prediction of U-notched Al 6061-T6 plates under large-scale yielding regime
Publication date: 15 May 2018
Source:Engineering Fracture Mechanics, Volume 195 Author(s): H.R. Majidi, A.R. Torabi, M.E. Golmakani The main purpose of the present research is to check if the Equivalent Material Concept (EMC) is capable of being combined with the J-integral failure criterion to form a new ductile failure model, called EMC-J criterion, to predict the load-carrying capacity (LCC) of U-notched aluminum plates under mixed mode I/II loading. To achieve this purpose, first, a set of experimental results on LCC of some tested U-notched Al 6061-T6 rectangular specimens, failed by large-scale yielding (LSY) regime, are taken from the recent literature. Due to the elastic–plastic behavior of the tested Al 6061-T6, EMC is utilized to avoid complex and time-consuming non-linear failure analyses for LCC predictions. Then, a new combined ductile failure model is proposed in which J-integral criterion, as a well-established brittle fracture criterion, is combined with EMC to predict theoretically the experimental results of the tested U-notched aluminum plates. Finally, it is shown that EMC-J criterion can predict the experimental results well.
1 May 2018
Editorial Board
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194

1 May 2018
Estimating fracture toughness of various matrix structured ductile iron using circumferentially notched tensile bars
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): G
1 May 2018
A microcrack growth-based constitutive model for evaluating transient shear properties during brittle creep of rocks
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): Xiaozhao Li, Chengzhi Qi, Zhushan Shao A novel microcrack growth-based constitutive model is proposed to evaluate the transient shear properties of intact rocks during brittle creep. This process of brittle creep focuses on the steady-state and accelerated stages, in which the initial state during creep is equivalent to the damage state at peak point (
1 May 2018
A methodology for fretting fatigue life estimation using strain-based fracture mechanics
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): Eduardo Martins Fontes do R
1 May 2018
Fatigue crack growth rates of X100 steel welds in high pressure hydrogen gas considering residual stress effects
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): Joseph A. Ronevich, Christopher R. D'Elia, Michael R. Hill Fatigue crack growth rate (FCGR) data were measured in high pressure hydrogen gas versus stress intensity factor range (
1 May 2018
Effect of type of coarse aggregate on the strength properties and fracture energy of normal and high strength concrete
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): K.P. Vishalakshi, V. Revathi, S. Sivamurthy Reddy An attempt has been made in the present work to study the effect of type of coarse aggregate on the strength properties and fracture energy of M30, M50 and M80 grade of concretes. The aggregate used in this study includes Grey Granite (GG), Anorthosite (AS) Charnockite (CK) Limestone, (LS) and Gneiss (GS). The result shows that the strength of concrete is greatly influenced by the aggregate types in high strength concrete. However, the aggregate has not impacted the Normal Strength Concrete as the strength is governed by the characteristics of interfacial transition zone, rather than aggregate. Among all aggregates, the Grey Granite aggregate has produced concrete with highest compressive strength followed by Anorthosite, Charnockite, Limestone and Gneiss indicating that the surface texture, structure and mineralogical composition played a dominant role. The similar trend was noticed even in fracture energy and modulus of elasticity of high strength concrete.
1 May 2018
Effect of thermal misfit stress on steam-driven delamination in electronic packages
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): Xian Zhang, Haoran Meng, Hehui Wang, Fenglin Guo In this study, circular interfacial defects or delaminations between the die-attach layer and the substrate in electronic packages are analytically modeled to investigate the effect of thermal misfit stress on the steam-driven delamination during the solder reflow process. Based on Love-Kirchhoff plate theory, analytical solutions of strain energy and strain energy release rate of circular delaminations under the combined action of steam pressure and thermal stress are derived. By comparing the energy release rates of circular delamination under steam pressure with and without thermal stress, the contribution of thermal stress to the strain energy release rate is assessed quantitatively. Further, the contribution of thermal stress to the extension of elliptic delaminations is studied numerically. This study brings new understanding on the role that thermal stress plays in facilitating steam-driven delamination during the solder reflow process in electronic packages.
1 May 2018
Characterization of concrete matrix/steel fiber de-bonding in an SFRC beam: Principal component analysis and k-mean algorithm for clustering AE data
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): Sena Tayfur, Ninel Alver, Saeed Abdi, Sel
1 May 2018
Strength distribution of Ti/SiC metal-matrix composites under monotonic loading
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): Sivasambu Mahesh, Ashish Mishra The strength of metal matrix composites shows wide scatter on account of variability in the strengths of individual fibres. The relationship between the strength distribution of the fibres, and that of the composite is also affected by the non-linear matrix and fibre/matrix interfacial responses. The present study aims to describe the strength distribution of 2D and 3D commercial Ti/SiC composites. This is accomplished by performing Monte Carlo failure simulations of these composites, comprised of up to 128 fibres. A detailed deformation theory based model, developed and validated against experimental data in previous work, is used to calculate load redistribution in the course of each simulation. The empirical composite strength distribution obtained from the simulations follows weakest-link scaling. A stochastic model for the clustered propagation of fibre breaks, akin to a model proposed for polymer matrix composites in the literature, captures the empirical weakest-link strength distribution. A scaling relationship is derived between the composite strength and composite size for a number of reliability levels.
1 May 2018
Ring cracks at the surface of a half-space
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): J.P. Lopes, D.A. Hills This paper uses a distribution of ring dislocations to determine the crack tip stress intensity factors for a ring crack at the surface of a half-space subjected to a point force at the axis of symmetry. Three cases are considered: a short crack (relative to its radius), fully open to its root; a longer crack open at the surface but closed and slipping to the root; and a longer crack open at the surface and slipping to some self-determining point in the closing region. The stress intensity factors and points of closure and stick are determined.
1 May 2018
Investigation of effects of fracturing fluid on hydraulic fracturing and fracture permeability of reservoir rocks: An experimental study using water and foam fracturing
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): W.A.M. Wanniarachchi, P.G. Ranjith, M.S.A. Perera, T.D. Rathnaweera, D.C. Zhang, C. Zhang Hydraulic fracturing is a promising technique to enhance gas production from deep geological formations by enhancing reservoir rock permeability. However, permeability enhancement may vary with reservoir conditions and fracturing fluid. The main objective of this study is to investigate the effect of fracturing fluid on the fracture pattern and permeability of fractured rock. Fracturing experiments were conducted on siltstone specimens with water and foam (N2 + water) as the fracturing fluids, using a high-pressure triaxial apparatus. CT scanning and 3-D scanning technology were used to examine the fracture pattern and the fracture surface of the fractured specimens. The fractured specimens were then used to conduct permeability experiments for five different confining pressures (5 – 25
1 May 2018
The experimental and numerical study on the effect of PVB nanofiber mat thickness on interlaminar fracture toughness of glass/phenolic composites
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): P. Kheirkhah Barzoki, A.M. Rezadoust, M. Latifi, H. Saghafi Delamination is one of the main problem in laminated composite materials especially in phenolic laminated composites. Recently, the potential of nanofibers to improve the fracture toughness of laminated composites has been proved. Therefore, in this study, the effect of (Polyvinyl butyral) PVB-nanoweb and its thickness on mode-II fracture toughness of laminated phenolic composite is considered using experimental and numerical methods. For experimental investigation, the fracture behavior of laminated composites has been determined by end notched flexure (ENF) tests using three different thicknesses of nanoweb (25, 45 and 65
1 May 2018
Experimental and discrete element modeling on cracking behavior of sandstone containing a single oval flaw under uniaxial compression
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): Sheng-Qi Yang, Wen-Ling Tian, Yan-Hua Huang, Zhan-Guo Ma, Li-Feng Fan, Zhi-Jun Wu In the rock engineering, it is very significant to focus on the failure mechanical behavior of rocks containing all kinds of flaws. In this research, the strength, deformation and crack evolution behavior of sandstone containing a single oval flaw under uniaxial compression were evaluated by experiment and numerical simulation using a two-dimension particle flow code (PFC2D). The experimental results show that the peak strength and elastic modulus first decrease and subsequently increase with increasing oval flaw angle (
1 May 2018
Numerical ductile fracture prediction of circumferential through-wall cracked pipes under very low cycle fatigue loading condition
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): Hyun-Suk Nam, Jong-Min Lee, Yun-Jae Kim, Jin-Weon Kim In this paper, a method to simulate ductile crack growth under very low-cycle fatigue loading condition is given and simulation results are compared with published test data of compact tension specimens and circumferential through-wall cracked pipes. The damage model in simulation is based on the multi-axial fracture strain energy. Two parameters in the damage model are determined from tensile and fracture toughness data under the monotonic loading condition. The determined damage model is then used to simulate ductile crack growth in compact tension specimens subjected to cyclic loading with large-amplitudes and in full-scale through-wall cracked pipes subjected to monotonic and cyclic loading with two different load ratios. Predicted results show a good agreement with experimental results.
1 May 2018
Examination of two regularized damage-plasticity models for concrete with regard to crack closing
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): Adam Wosatko, Aikaterini Genikomsou, Jerzy Pamin, Maria Anna Polak, Andrzej Winnicki Continuum models of fracture should be equipped with a localization limiter to prevent pathological discretization sensitivity of finite element simulations. Moreover, stiffness recovery, called also crack closing effect, should be reproduced in the modelling of quasi-brittle materials when reversed loading is applied. In this paper the efficiency of two different established damage-plasticity models for concrete is assessed from the viewpoint of the two above-mentioned aspects. The first description is the so-called concrete damaged plasticity model, available in the ABAQUS package. In this model the plasticity theory is not only augmented with stiffness degradation and recovery, but also with the crack band approach and viscoplastic regularization. The gradient-enhanced damage description, which is the second one considered, can also be coupled to plasticity. In this model additional averaging equation prevents the pathological discretization sensitivity of fracture simulations. Two fields, displacements and averaged strain measure, are interpolated and suitable finite elements are programmed by the authors in the FEAP package. Basic concepts of the numerical analysis of the crack closing phenomenon are reviewed. Both models are capable of avoiding mesh-sensitivity, but it is achieved in a different manner and it is shown in the paper that the users of ABAQUS should employ the crack band options with particular care. Representative examples in the context of the examined issues are demonstrated: uniaxial tension of a bar and a cantilever beam. The results obtained using both the models are compared and the effects of regularization and crack closing are illustrated.
1 May 2018
Dynamic-weighted ensemble for fatigue crack degradation state prediction
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): Hoang-Phuong Nguyen, Jie Liu, Enrico Zio This paper proposes a prognostic framework for online prediction of fatigue crack growth in industrial equipment. The key contribution is the combination of a recursive Bayesian technique and a dynamic-weighted ensemble methodology to integrate multiple stochastic degradation models. To show the application of the proposed framework, a case study is considered, concerning fatigue crack growth under time-varying operation conditions. The results indicate that the proposed prognostic framework performs well in comparison to single crack growth models in terms of prediction accuracy under evolving operating conditions.
1 May 2018
Understanding of fatigue crack growth behavior in welded joint of a new generation Ni-Cr-Mo-V high strength steel
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): Qiang Wang, Zhongjie Yan, Xuesong Liu, Zhibo Dong, Hongyuan Fang This study was mainly concerned with the long fatigue crack growth rate (FCGR) of a new generation Ni-Cr-Mo-V high strength steel and its welded joints used in modern marine environment. Several major factors, including stress ratio, microstructure, welding residual stresses (WRSs) and specimen thickness were investigated. Results showed that the weld metal (WM) possessed better resistance to crack propagation relative to the base material (BM) under each stress ratio owing to the interlocking acicular ferrite microstructure and the resultant higher crack closure level. WRSs partly retained in the extracted fracture mechanics samples and noticeably affected FCGR of the WM. Post-welding heat treatment could never eliminate the WRSs and might generate new residual stress distribution. Both the crack closure model and the two-parameter model yielded fairly good consolidation for the R-ratio effect of the BM whereas they failed to correlate the data for the WM because of the retained WRSs. Accelerated FCGR with increased specimen thickness was measured for both the BM and the WM. The fracture mechanism was scrutinized by means of fractography and fatigue trajectory map. The results obtained in the present work are helpful in shedding light on the damage tolerance design of the Ni-Cr-Mo-V high strength steel welded joints employed in modern marine structures.
1 May 2018
Adaptive floating node method for modelling cohesive fracture of composite materials
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): X. Lu, B.Y. Chen, V.B.C. Tan, T.E. Tay The cohesive element has been widely employed to model delamination and matrix cracking in composite materials. However, an extremely fine mesh along the potential crack path is required to achieve accurate predictions of stresses within the cohesive zone. A sufficient number of cohesive elements must be present within the cohesive zone ahead of the crack tip, resulting in very high computational cost and time for application to practical composite structures. To mitigate this problem, an adaptive floating node method (A-FNM) with potential to reduce model size and computational effort is proposed. An element with adaptive partitioning capabilities is designed such that it can be formulated as a master element, a refined element and a coarsened element, depending on the damage state in the progressive damage process. A relatively coarse overall mesh may be used initially, and by transforming the element configurations adaptively, the local refinement and coarsening schemes are applied in the analysis. The localized stress gradient ahead of the crack front within the refinement zone is captured by the refined elements. The refinement and coarsening operations are performed at the elemental level with fixed nodal connectivity, so that global successive remeshing in adaptive mesh refinement (AMR) techniques is avoided; this is the key difference between AMR and A-FNM. It is demonstrated that, without loss of accuracy, the present method simplifies the modelling procedure and reduces computational cost.
1 May 2018
Residual fatigue life analysis and comparison of an aluminum lithium alloy structural repair for aviation applications
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): Yashi Liao, Yibo Li, Qing Pan, Minghui Huang, Chuang Zhou A method for residual-fatigue-life estimation of repaired aluminium–lithium alloy structures designed for use in aerospace applications is presented. Crack propagation was investigated using the Abaqus software package while the stress intensity factor was calculated using the FRANC3D package. Paris equation was applied to estimate the fatigue-crack growth rate. The residual fatigue life of and corresponding a–N curve for the repaired structure were obtained via post-processing under varying conditions of repair-structure shape, size, position, and stress levels. Results demonstrate that structural repairs possessing relative width, height, and thickness values of 35.7%, 50%, and 83.3%, respectively, tend to increase the residual fatigue life of the overall structure.
1 May 2018
Using acoustic emission to understand fatigue crack growth within a single load cycle
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): J.A. Pascoe, D.S. Zarouchas, R.C. Alderliesten, R. Benedictus Current methods for prediction of fatigue crack growth are based on empirical correlations which do not take the crack growth behaviour within a single cycle into account. To improve these prediction methods, more understanding of the physical mechanisms of crack growth is required. In this research the acoustic emission technique was used to investigate the crack growth behaviour during a single fatigue cycle. It was found that crack growth can potentially occur both during loading and unloading, but only while the strain energy release rate is above a crack growth (CG) threshold value. The results suggest this CG threshold value is the same in both quasi-static and fatigue loading. Further work is necessary to fully understand the link between the received acoustic emission signals and the actual crack growth processes. Nevertheless, the paper shows the potential of acoustic emission to provide more insight into the physics of crack growth.
1 May 2018
Ductile fracture of an ultra-high strength steel under low to moderate stress triaxiality
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): C. Defaisse, M. Mazi
1 May 2018
A path-following technique implemented in a Lagrangian formulation to model quasi-brittle fracture
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): Nicol
1 May 2018
Numerical analysis of reinforced concrete structures with oriented steel fibers and re-bars
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): Janis Sliseris In this study, a new strength and stiffness numerical analysis approach of fiber reinforced concrete with oriented fibers and re-bars is proposed. The model is based on discrete lattice simulation that is obtained from standard tetrahedron mesh. Area of cross section of lattice members is obtained by homogenization of each tetrahedron finite element. A non-linear material constitutive model that takes into account fiber orientation, concrete damage and plasticity of re-bars is proposed. Re-bars are embedded in fiber concrete lattice by using a special joint elements that are consistent with re-bar’s surface pattern. The numerical model is validated by using four-point bending test results of high performance fiber concrete with oriented fibers. Moreover, the model showed a good agreement with re-bar pull-out test results for ultra-high performance concrete with oriented fibers. The proposed model is used to analyze a ribbed concrete panel with oriented fibers and best optimal fiber orientation for three-point bending is proposed.
1 May 2018
Effects of nanofiber orientations on the fracture toughness of cellulose nanopaper
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): Qinghua Meng, Bo Li, Teng Li, Xi-Qiao Feng Cellulose nanopaper exhibits superior mechanical properties with both high strength and toughness, and the crack bridging mechanism of nanofibers makes the most significant contribution to its fracture toughness. In this paper, we investigate the fracture toughness of a mode-I crack in cellulose nanopaper by using a modified crack-bridging model. Different from previous crack-bridging models, we account for the effect of nanofibers inclined to the crack surfaces. Particular attention is given to the dependence of fracture toughness on the orientation distribution of nanofibers in the cellulose nanopaper. We use a cohesive law to account for the interfacial shear stress of nanofibers, which involve self-healing of hydrogen bonds at their interfaces. Two representative orientation distributions are considered, in which nanofibers are aligned or randomly oriented, respectively. The theoretical results agree well with relevant experiments. This work helps understand the structure–property relationship of cellulose nanopaper and design other fiber-reinforced nanocomposites.
Available online 25 April 2018
The influences of mode II loading on fracture process in rock using acoustic emission energy
Publication date: 1 May 2018
Source:Engineering Fracture Mechanics, Volume 194 Author(s): Qing Lin, Dengtian Mao, Shan Wang, Shiyuan Li The influences of mode II loading on fracture process in Berea sandstone were investigated by comparing mode I and mixed-mode fractures that were created by center and eccentric notch beams under three-point bending. Fracture process was characterized by Acoustic Emission (AE) and related energy. Experimental results show mode II loading does not affect the length of fully-developed fracture process zone and maximum value of AE energy. However, it affects the zone from reaching fully-developed stage, i.e., mixed-mode fracture before or at peak load, and mode I after the peak. It also breaks the similarity and symmetry of AE events pattern.
Available online 24 April 2018
Acoustic emission detection of damage induced by simulated environmental conditioning in carbon fiber reinforced composites
Publication date: Available online 25 April 2018
Source:Engineering Fracture Mechanics Author(s): Dionysios E. Mouzakis, Dimitrios G. Dimogianopoulos High performance composites for structural applications in aviation are sensitive to aging from altering environmental conditions. For instance, the stiffening behavior of glass fiber/ polyester composites used by the wind turbine industry has already been demonstrated in previous work of the authors. Now, passenger aircrafts from such composites are increasingly entering into service. It is crucial, thus, to study the exposure of high performance materials to aging-inducing environmental conditions such as varying temperature, humidity, ultraviolet radiation, and assess their impact on mechanical response of such composites. In this work we have applied acoustic emission analysis to study the effects of simulated environmental aging on carbon fiber reinforced composites. Signals collected from three point bending testing of pristine specimens as well from thermally shocked and environmentally aged ones. Signal parameters were afterwards plotted and studied in correlation with the specimens’ mechanical response.
Available online 24 April 2018
Frictional behaviour of the interface between concrete and rubber: Laboratory shear test and its elastoplastic model
Publication date: Available online 24 April 2018
Source:Engineering Fracture Mechanics Author(s): Zhenyu Zhang, Shanyong Wang, Jili Feng This study focuses on the shear-friction behaviour of concrete interfaces (joints) with rubber between concrete segments or rings from the perspective of experiment and theoretical analysis. A number of direct shear concrete specimens with and without rubber cushions were tested under conditions of different normal loads. The shear test results of the concrete interfaces without rubber show that the slip or shear displacements can be divided into elastic and perfectly plastic phases. The post-peak shear strengths hold almost a constant with increasing shear slip, which can be described by the Coulomb frictional law. However, when concrete interface is pasted with rubber, the slip failure behaviour of the interfaces under pressure-shear loads is more appropriately characterized by hyperbolic failure criterion. The shear tests of the interfaces with rubber show that rubber materials significantly reduce the shear strength of the interfaces, which indicate that thin rubber can accommodate the mechanical response of the tunnel concrete lining, particularly by reducing the stress level of concrete segments surrounding joints due to the rubber material pasted to the joints. An elasto-plastic constitutive model for describing the three-dimensional mechanical behaviour of concrete joint with rubber is developed and also verified by means of the shear tests of concrete joints with rubber mentioned above. The predictions by the present interface model are well in agreement with the shear tests.
Available online 23 April 2018
Modelling of femur fracture using finite element procedures
Publication date: Available online 24 April 2018
Source:Engineering Fracture Mechanics Author(s): Miguel Marco, Eugenio Giner, Ricardo Larra
Available online 20 April 2018
Damage evolution and void coalescence in finite-element modelling of DP600 using a modified Rousselier model
Publication date: Available online 23 April 2018
Source:Engineering Fracture Mechanics Author(s): Iman Sari Sarraf, Daniel E. Green, Arash Jenab Numerical simulations of uniaxial tensile deformation of DP600 steel were carried out using a modified Rousselier ductile damage model at different strain rates ranging from 0.1 to 100 s
Available online 19 April 2018
A theoretical model for hydraulic fracturing through a single radial perforation emanating from a borehole
Publication date: Available online 20 April 2018
Source:Engineering Fracture Mechanics Author(s): Zhuo Dong, Shibin Tang, Pathegama Gamage Ranjith, Yingxian Lang This paper considers the problem of the plane-strain fluid-driven fracture propagation of a single radial perforation emanating from a borehole. A maximum tangential strain criterion is proposed to study crack propagation during hydraulic fracturing; this criterion considers the changes in not only the mode-I stress intensity factor caused by the pore pressure but also the mode-II stress intensity factor caused by the anisotropy of the far-field stress. The critical water pressure and the critical initiation angle at the onset of crack propagation are studied using the proposed theoretical method. The effects of the stress anisotropy coefficient, the borehole radius, the perforation length, the ratio of the water pressures inside the fracture to that of the borehole, Biot’s coefficient and Poisson’s ratio on both the critical water pressure and the critical initiation angle are discussed. The parameter analysis indicates that the perforation length, the borehole radius and the stress anisotropy coefficient significantly affect the critical water pressure and the critical initiation angle. The critical water pressure decreases as the ratio of the water pressure inside the fracture to that of the borehole and Biot’s coefficient increase, whereas the critical initiation angle is not affected by these parameters. The critical water pressure increases and the critical initiation angle decreases as the Poisson’s ratio increases. During high-pressure water injection, the fracture initiation angle decreases with increases in the water injection pressure, Biot’s coefficient and the ratio of the water pressure inside the fracture to that of the borehole; however, the angle is not affected by Poisson’s ratio. The theoretical model provides a comprehensive understanding of the characteristics of hydraulic fracturing under complex loading conditions. The results also provide a basis for quantitative investigations of the engineering design of hydraulic fracturing treatments.
Available online 19 April 2018
Study of anisotropic crack growth behavior for aluminum alloy 7050-T7451
Publication date: Available online 19 April 2018
Source:Engineering Fracture Mechanics Author(s): Jun Cao, Fuguo Li, Xinkai Ma, Zhankun Sun Hill's normalized plastic zone at crack tip under mode-I and mixed-mode loadings were studied in compact-tension-shear specimen. Effects of the parameters of Hill’s criterion on the normalized plastic zone were analyzed. Moreover, the shapes of normalized plastic zones for distortional and total strain-energy-density were investigated. To analyze the crack growth behavior by different normalized plastic zones, fatigue crack growth tests of AA7050-T7451 were performed using digital image correlation technique. The initiation angle predicted by anisotropic R-criterion under mixed-mode loading is closest to experimental data.
Available online 17 April 2018
Static strength and damage evaluation of high speed drilled composite material using acoustic emission and finite element techniques
Publication date: Available online 19 April 2018
Source:Engineering Fracture Mechanics Author(s): Naeim Akbari Shahkhosravi, Jalal Yousefi, Mehdi Ahmadi Najfabadi, Giangiacomo Minak, Hossein Hosseini-Toudeshky, Fariborz Sheibanian In this paper, a very promising procedure to evaluate damage initiation and propagation of high speed drilled composite laminates base on Acoustic Emission (AE) and Finite Element (FE) techniques is proposed. First, the extent of delamination after high speed drilling was measured in unidirectional and woven composite specimens under different feed rate and cutting speed parameters. Three point bending tests were then performed to investigate the effect of drilling-induced delamination on static strength and the damage mechanisms in the drilled specimens. FE simulation including Cohesive Zone Modeling (CZM) and an improved Continuum Damage Mechanics (CDM) approaches was conducted to predict damage initiation and propagation of each distinct damage. Besides, AE was also used to notice the damage emergence and investigate these damage mechanisms. The results showed that the effect of drilling parameters on static strength is insignificant, however the main accomplishment of this work is illustrating a good consistency between experimental procedure, exhaustive FEM and AE techniques. FEM and AE can be used as efficient ways to predict damage initiation and failure of composite structures and also to evaluate damage mechanisms in drilled composite materials with two kinds of lay-up. Consequently, it is feasible to understand the effect of lay-up on occurring different damage mechanisms.

An experimental-finite element method based on beach marks to determine fatigue crack growth rate in thick plates with varying stress states
Publication date: Available online 17 April 2018
Source:Engineering Fracture Mechanics Author(s): Jingxia Yue, Yan Dong, C. Guedes Soares The relation between the fatigue crack growth rate and stress state is significant for fatigue life estimation, especially for thick-welded structures with complex stress states. This paper proposes a hybrid Experimental-Finite Element Method aimed to obtain the fatigue crack growth rate corresponding to plane stress and plane strain states. A static load marking method is proposed to mark a series of crack fronts in a single edge notched bending specimen at known numbers of cycles, which is analysed by nonlinear finite element method to evaluate the stress state by a local constraint factor. Stress intensity factor at the center of the thickness and the surface position where plane strain and plane stress states approximately exist and remain unchanged with crack propagation, is calculated by the 1/4-node displacement method with consideration of non-orthogonal mesh influence. The J-integral method and the virtual crack closure technique are also applied to check the performance of the methods in dealing with the actual cracked body problem. Crack length increments are determined based on the crack front profiles. The da/dN-
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