Journal Sciences News
Theoretical and Applied Fracture Mechanics
August 2018
Flutter of multi-cracked laminated composite beams subjected to a non-conservative compressive load
Publication date: August 2018
Source:Engineering Fracture Mechanics, Volume 199 Author(s): H. Alidoost, J. Rezaeepazhand Free vibration and buckling instability of laminated composite beams and flutter instability of an isotropic beam with different defects have been investigated before, however, still dynamic stability of laminated composite beam with weak section subjected to follower forces has not considered. This paper presents a simple semi-analytical solution to the flutter instability of a laminated composite beam with multi open-edge cracks subjected to a tip follower force. Using classical lamination theory and Euler-Bernoulli beam theory, equation of motion of the beam is derived analytically and characteristic eigenvalue equations of the cracked laminated composite beam are obtained. A Matlab code is used to solve these equations numerically. After validating the results, a numerical study is performed to investigate the effect of crack depth and stacking sequences on the dynamic stability of the cracked beam.
August 2018
An interaction factor to estimate the over-constraining effect in plates with co-planar cracks
Publication date: August 2018
Source:Engineering Fracture Mechanics, Volume 199 Author(s): Teik Tian Seah, Xudong Qian This paper reports an over-constraining effect on the near-tip stress field caused by the presence of a nearby coplanar crack, through detailed numerical investigations. The crack driving force, measured by the leading term in the near-tip stress solution, underestimates the stresses near the coplanar crack fronts. This study thus proposes a crack interaction factor based on the average Q-stress over a finite distance from the crack tip. The proposed interaction factor provides a close estimate of the near-tip stress for the coplanar cracks, and predicts successfully the interaction among coplanar elliptical crack-front locations, using an equivalent through-thickness coplanar crack model.
August 2018
Fatigue life prediction of nickel-based GH4169 alloy on the basis of a multi-scale crack propagation approach
Publication date: August 2018
Source:Engineering Fracture Mechanics, Volume 199 Author(s): Shen Ye, Cheng-Cheng Zhang, Peng-Yue Zhang, Xian-Cheng Zhang, Shan-Tung Tu, Run-Zi Wang This paper was concerned with an approach to predict fatigue life based on a multi-scale crack propagation model. The expressions of crack propagation rates in microstructurally small crack (MSC), physically small crack (PSC) and long crack (LC) stages were unified in the multi-scale crack propagation model. Its integral form presented a fatigue life prediction approach. The nickel-based GH4169 alloy was employed to validate the prediction capacity of present approach. The prediction results of lives of specimens with different initial defects sizes were compared with the experimental data.
August 2018
An efficient FE-implementation of implicit gradient-enhanced damage models to simulate ductile failure
Publication date: August 2018
Source:Engineering Fracture Mechanics, Volume 199 Author(s): Andreas Seupel, Geralf H
August 2018
Effect of fiber orientation on Mode-I delamination resistance of glass/epoxy laminates incorporated with milled glass fiber fillers
Publication date: August 2018
Source:Engineering Fracture Mechanics, Volume 199 Author(s): K. Saravanakumar, Nibras Farouk, V. Arumugam The present work is focused on improving the Mode-I delamination resistance of glass/epoxy composite laminates with milled glass fiber fillers. The influence of the interface fiber orientation and also the effect of fillers on the Mode-I interlaminar fracture toughness was experimentally investigated and the results were correlated with the baseline glass/epoxy samples. It was observed that the dispersion of milled glass fiber fillers by weight of 5% of the epoxy matrix into the resin rich domain improved the fracture toughness efficiently, in all the cases of interface fiber orientation. This improvement in interlaminar fracture toughness was due to additional toughening mechanisms through crack deflection, filler debonding, filler interlocking/bridging and filler pullout. The results showed that incorporation of milled glass fiber filler enhanced the GIC Initiation and GIC Propagation fracture toughness by 102% and 50% in 00 interply orientations over the baseline glass/epoxy samples. Besides, fracture surface analysis of the samples using Scanning Electron Microscope (SEM) indicates that the different damage mechanisms correspond to the deviation in fracture toughness.
August 2018
A Voronoi element based-numerical manifold method (VE-NMM) for investigating micro/macro-mechanical properties of intact rocks
Publication date: August 2018
Source:Engineering Fracture Mechanics, Volume 199 Author(s): Quansheng Liu, Yalong Jiang, Zhijun Wu, Jun He In this study, a two-dimensional Voronoi element based-numerical manifold method (VE-NMM) was developed as a new approach to investigate the micro- and macro- mechanical properties of intact rocks. The Voronoi technique was used to generate a polygonal grain assemblage to approximate the microstructure of sandstone samples from Gubei colliery of Huainan mining area in China. A modified contact model incorporating cohesion and tensile strength was adopted to interpret the interactions between rock grains. A series of laboratory tests, i.e. scanning electron microscope tests, uniaxial compression and Brazilian tests were carried out to obtain the microstructural information and macro-mechanical properties of the sandstone samples. To verify the proposed VE-NMM, simulations of Brazilian tensile splitting and uniaxial compressive tests were carried out and the results, in terms of strength, elastic constant and crack distribution, were compared to those of the laboratory tests. To investigate the effects of grain size on the micro-mechanical parameters and the representative elementary volume (REV) size, numerical uniaxial compression tests with different grain sizes (2mm, 3
August 2018
Characteristic damage state of symmetric laminates subject to uniaxial monotonic-fatigue loading
Publication date: August 2018
Source:Engineering Fracture Mechanics, Volume 199 Author(s): Hamed Pakdel, Bijan Mohammadi Experimental and variational investigation of the onset of matrix crack saturation and induced delamination initiation are performed in laminates containing mid-ply matrix cracks. An evolution criterion is developed based on energy release rate to predict the crack density at saturation which is argued to be a characteristic damage state (CDS) independent of loading. A unit cell based analysis is established upon variational principles to derive the stress state and strain energy of [
July 2018
Acoustic emission and kinetic fracture theory for time-dependent breakage of granite
Publication date: August 2018
Source:Engineering Fracture Mechanics, Volume 199 Author(s): Ryan A. Winner, Guanyi Lu, Romain Prioul, Gallyam Aidagulov, Andrew P. Bunger Earthquakes, mine failures, and initiation of hydraulic fractures have all been associated with time-delayed breakage of rocks subjected to loads insufficient to incur instantaneous failure. To better model and identify failure precursors for rocks under these so-called static fatigue conditions, Acoustic Emission (AE) was monitored in beams of Coldspring Charcoal Granite subjected to constant three point loading. As a result of varying the magnitude of the loading, the times to failure range from O ( 10 1 ) to O ( 10 5 ) seconds. The experiments show a number of consistencies in the AE data. In all cases the event rate exponentially declines for a period that is about 0.40.6 of the total time to failure. This period is followed by a period in which the event rate exponentially increases. The total number of events generated during these two periods is also consistent among the experiments. Motivated by these observations, we propose a modified kinetic fracture theory that captures both the period of event rate decline and the period of event rate increase. It does this by firstly accounting for early time depletion of available bonds for breakage, similar to previous models. The model also accounts for generation of critically stressed bonds in the vicinity of previous bond breakages due to stress redistribution, thereby also predicting the event rate increase and further providing consistency with the observed tendency of the events to become increasingly concentrated around the eventual plane of failure as time progresses.
July 2018
Editorial Board
Publication date: July 2018
Source:Engineering Fracture Mechanics, Volume 198

July 2018
Foreword
Publication date: July 2018
Source:Engineering Fracture Mechanics, Volume 198 Author(s): Georgios Savaidis, H. Thomas Beier, Uwe Zerbst
July 2018
Fatigue strength and fracture mechanics A general perspective
Publication date: July 2018
Source:Engineering Fracture Mechanics, Volume 198 Author(s): U. Zerbst, M. Madia, M. Vormwald, H.Th. Beier Common fracture mechanics based fatigue considerations are usually limited to the residual lifetime determination of so-called long cracks. The extension of this concept to the total lifetime, as in the S-N curve approach, requires an adequate description of short crack propagation which cannot be based on the
July 2018
Cyclic J-integral: Numerical and analytical investigations for surface cracks in weldments
Publication date: July 2018
Source:Engineering Fracture Mechanics, Volume 198 Author(s): D. Tchoffo Ngoula, M. Madia, H.Th. Beier, M. Vormwald, U. Zerbst The cyclic J-integral (
July 2018
The cyclic R-curve Determination, problems, limitations and application
Publication date: July 2018
Source:Engineering Fracture Mechanics, Volume 198 Author(s): J
July 2018
Numerical analysis of residual stresses and crack closure during cyclic loading of a longitudinal gusset
Publication date: July 2018
Source:Engineering Fracture Mechanics, Volume 198 Author(s): D. Tchuindjang, W. Fricke, M. Vormwald The fatigue strength of welded joints is determined by crack initiation and propagation, the latter forming in several cases the major part of the fatigue life. Failure is usually assumed when the fatigue crack has penetrated the adjacent plate or as specimen fracture in case of fatigue tests. Crack propagation is influenced by crack closure effects, slowing down crack propagation mainly in case of load cycles partly in compression. However, it is well-known that tensile residual stresses occurring particularly in welded joints can decrease crack closure and lead to fatigue behaviour independent of the applied stress ratio, i. e. mean stress. This has been observed for example with welded longitudinal gussets. On the other hand, recent measurements have shown that tensile residual stresses at the weld toe are smaller than further away and that they are relaxed or even become compressive after the first load cycle. Insofar, the role of residual stresses is still unclear. For this reason, numerical investigations have been performed in addition to fatigue tests to clarify the matter further. After describing a numerical model to investigate the crack closure behaviour by the example of a center crack in a plate originally studied by Newman, the crack closure behaviour of a semi-elliptical crack in front of a longitudinal steel gusset is analysed for depths between 5 and 50% of the plate thickness. In addition to the stress-relieved state, also welding-induced residual stresses were generated with a simplified model, calibrated by measurements, and used for the analysis of crack closure. It is shown that the residual stresses strongly affect the crack closure although these are compressive at the weld toe after the first load cycle. The simulations are performed for different load levels and stress ratios.
July 2018
Fracture-mechanics based prediction of the fatigue strength of weldments. Material aspects
Publication date: July 2018
Source:Engineering Fracture Mechanics, Volume 198 Author(s): P. Kucharczyk, M. Madia, U. Zerbst, B. Schork, P. Gerwien, S. M
July 2018
The effect of the local and global weld geometry as well as material defects on crack initiation and fatigue strength
Publication date: July 2018
Source:Engineering Fracture Mechanics, Volume 198 Author(s): B. Schork, P. Kucharczyk, M. Madia, U. Zerbst, J. Hensel, J. Bernhard, D. Tchuindjang, M. Kaffenberger, M. Oechsner The paper provides an application of the IBESS approach to the investigation of the influence of various parameters of the global and local weld geometry as well as material defects on the fatigue strength of weldments. For this purpose, the global weld parameters, such as the weld toe radius, the flank angle, the excess weld metal, local secondary notches (in the present study as a measure of surface imperfections) and inclusions sizes have been determined as statistical distributions for different joint types and geometries and two steels of different strengths. The results are in line with literature data and reveal the potential of the theoretical approach to predict the correct trends. The combination with an advanced weld quality system has been demonstrated to be possible.
July 2018
Welding residual stresses as needed for the prediction of fatigue crack propagation and fatigue strength
Publication date: July 2018
Source:Engineering Fracture Mechanics, Volume 198 Author(s): J. Hensel, T. Nitschke-Pagel, D. Tchoffo Ngoula, H.-Th. Beier, D. Tchuindjang, U. Zerbst Welding residual stresses have an impact on the performance of welded structures, on their fracture resistance, their resistance against fatigue crack propagation and, most important, their fatigue strength and fatigue lifetime. The present paper provides an overview on the issue mainly from the point of view of the application of fracture mechanics to the determination of the fatigue strength as the topic of this Special issue. Besides own experimental and theoretical data a comprehensive discussion is provided in that context which includes the definition and interaction of short- and long-range (or reaction) residual stresses, the effect of cyclic mechanical loading and its treatment in fracture and fatigue analyses.
July 2018
Micromechanical investigation and numerical simulation of fatigue crack formation in welded joints
Publication date: July 2018
Source:Engineering Fracture Mechanics, Volume 198 Author(s): Carla Beckmann, Tobias Kennerknecht, Johannes Preu
July 2018
Development of integrated framework for fatigue life prediction in welded structures
Publication date: July 2018
Source:Engineering Fracture Mechanics, Volume 198 Author(s): Takayuki Shiraiwa, Fabien Briffod, Manabu Enoki A new fatigue prediction method for wide range of welded structures has been developed by integrating several advanced computational techniques such as thermo-mechanical finite element method, crystal plasticity model and extended finite element method. The method consists of the following procedures: (i) computation of materials properties; (ii) analysis of temperature field, microstructure and residual stress generated during a welding process; (iii) stress distribution analysis under cyclic loading; (iv) fatigue crack initiation analysis by the Tanaka-Mura model; (v) fatigue crack propagation analysis. Using the proposed methodology, the fatigue life of butt joint was evaluated and compared with the experimental data.
Available online 22 June 2018
The IBESS model Elements, realisation and validation
Publication date: July 2018
Source:Engineering Fracture Mechanics, Volume 198 Author(s): M. Madia, U. Zerbst, H. Th. Beier, B. Schork The work presents the procedure developed within the German research project IBESS, which allows for the fracture mechanics-based prediction of the fatigue strength of welded joints under constant amplitude loading. Based on the experimental observations of the crucial failure mechanisms, the approach focuses on the short crack propagation, where elastic-plastic fracture mechanics and the build-up of closure effects must be considered, as well as the variability of the local geometry at the weld toe and the modelling of multiple crack interaction. Analytical solutions are provided for the approximation of the through-thickness stress profiles at the weld toe and for the determination of the crack driving force in the form of a plasticity-corrected stress intensity factor range
Available online 22 June 2018
Thermo-mechanical responses of cracked quasi-transparent film to laser irradiation
Publication date: Available online 22 June 2018
Source:Engineering Fracture Mechanics Author(s): Qing Peng, Chen-Wu Wu, Chen-Guang Huang Thermal and mechanical responses of a cracked transparent conducting film to laser irradiation were investigated. A representative coin-shaped crack was modeled in the transparent conducting film and the case of vertical incidence of laser beam considered. Firstly, the multiple reflections, transmissions as well as absorptions are formulated in the quasi-multilayer media due to the effect of inner crack. Then, the temperature characteristics generated by the dissipated light energy are computed for the film of typical thermal boundary conditions. Finally, the thermal stress and stress intensity factors around the crack tip are particularly analyzed. The effects of the coin-shaped crack are discussed on the multi-physical responses of the film to laser irradiation.
Available online 21 June 2018
Comparison of J-integral methods for the characterization of tough polypropylene grades close to the glass transition temperature
Publication date: Available online 22 June 2018
Source:Engineering Fracture Mechanics Author(s): Anja Gosch, Florian J. Arbeiter, Michael Berer, Gerald Pinter The fracture mechanical characterization of very tough Polypropylene at room temperature is of great interest for many technical applications. Precision and validity of obtained values can significantly be influenced by notching and crack length determination, which has thoroughly been shown in literature. Additionally, the proximity to the glass transition temperature can induce further uncertainties. The aim of this study is to compare different J-integral methods of elastic plastic fracture mechanics to determine J-R curves for tested materials. Methods consist of the classical multi-specimen, a single specimen method (load separation) and a statistical approach (Weibull). Specific data reduction procedures based on physical principles were applied to reduce scattering and achieve reliable values. In this way, a reliable fracture mechanics characterization of Polypropylene at room temperature was achieved with a critical verification of the used methods. Finally, the determined fracture toughness value showed a good agreement with the surface texture of inspected fracture surfaces.
Available online 21 June 2018
New acoustic parameter characterizing loading history effects
Publication date: Available online 21 June 2018
Source:Engineering Fracture Mechanics Author(s): L.R. Botvina, M.R. Tyutin A new parameter of acoustic emission (TAE ) is proposed, which determines the period of acoustic gap before the final fracture under tension of specimens of low- and medium-carbon steel after preliminary cyclic loading. Values of the bAE and the total number of acoustic signals
Available online 21 June 2018
Effect of phase coarsening on the mechanical properties of alloys: II. Mechanism analysis
Publication date: Available online 21 June 2018
Source:Engineering Fracture Mechanics Author(s): J.C. Li, K.G. Wang For alloys strengthened by precipitates, the precipitate size and distribution within the inner structure will change significantly during phase coarsening. Correspondingly the alloys will behave as different deformation and failure manners, and their mechanical properties will show a considerable variation. In this paper, we investigate in detail the variations of the mechanical properties of alloys with various microstructures, including the hardness, strength, ductility, and fracture toughness, etc., based on the deformation and failure characteristics under different deformation conditions. Especially we focus on the evolution of related internal variables in alloys and the mechanism analysis. Our analysis demonstrates that degradations for the mechanical properties of alloys during phase coarsening are sensitive to the change of their microstructures, i.e., the precipitate size and distribution in the alloys. The microstructural evolution in alloys alters the manners of the nucleation, multiplication, and movement of dislocations in the material, which further results in different macroscopic mechanical behaviors of alloys. The corresponding mechanism analysis is helpful for the design of material microstructure.
Available online 21 June 2018
Influence of rice husk ash on the fracture characteristics and brittleness of self-compacting concrete
Publication date: Available online 21 June 2018
Source:Engineering Fracture Mechanics Author(s): Elias Molaei Raisi, Javad Vaseghi Amiri, Mohammad Reza Davoodi The application of self-compacting concrete (SCC) has recently been more common in practice. SCC is a highly flowable type of concrete that spreads into the formwork itself without any mechanical vibration. In addition, fracture characteristics and brittleness of SCC can be modified by application of supplementary cementitious material (SCM) due to concrete internal structure densification. One of the highly reactive SCM is rice husk ash (RHA). The main purpose of this study is to determine the influence of adding RHA on the fracture characteristics and brittleness of SCC using 75-notched beams. The specimens were prepared from mixes with various RHA replacement ratios (0%, 5%, 10%, 15%, and 20%). The fracture parameters were determined using two main methods, the size effect method (SEM) and the work of fracture method (WFM). For all mixes, fracture toughness (KIC), fracture energies (Gf in SEM and GF in WFM), brittleness number (
Available online 21 June 2018
Comparison of numerical predictions with experimental burst pressures of tubes with multiple surface cracks
Publication date: Available online 21 June 2018
Source:Engineering Fracture Mechanics Author(s): Myeong-Woo Lee, Ji-Seok Kim, Jun-Young Jeon, Yun-Jae Kim, Jin-Weon Kim, Jong-Sung Kim This paper compares numerical predictions with experimental burst pressures of Alloy 690TT steam generator tubes with multiple surface cracks of forty-one different cases at two different temperatures. For numerical prediction, the simplified multi-axial fracture strain model is used. The damage model is determined from tensile tests of smooth and notched tubes. Predicted maximum pressures are in good agreement with experimental data of steam generator tubes with multiple surface cracks.
Available online 21 June 2018
Effect of phase coarsening on the mechanical properties of alloys: I. Numerical simulations
Publication date: Available online 21 June 2018
Source:Engineering Fracture Mechanics Author(s): J.C. Li, K.G. Wang To study process-structure-property relationships, the multiparticle diffusion simulation and the finite element method simulation are linked together in this paper. The mechanical properties of alloys during phase coarsening are analyzed with this linkage. The correlation between microstructural evolutions and the corresponding variations of mechanical properties during phase coarsening in alloys is investigated. We study how the resultant hardness, strength, ductility, and fracture toughness of the alloy depend on the microstructural evolution driven by phase coarsening in alloys. Related analysis demonstrates that considerable degradations occur for the mechanical properties of alloys during phase coarsening, which are sensitive to microstructures in the alloys. Our work shows that the linkage of multiparticle diffusion simulation to finite element method simulation provides a practical approach to investigate process-structure-property relationships. Our simulation results can predict the microstructural evolution, the main deformation and failure characteristics of alloys.
Available online 20 June 2018
Application of acoustic emission monitoring and signal analysis to the qualitative and quantitative characterization of the fracturing process in rocks
Publication date: Available online 21 June 2018
Source:Engineering Fracture Mechanics Author(s): Patricia Rodr
Available online 19 June 2018
Evaluation of Fracture Toughness Test under Hydrogenation Condition and Microstructural Aspects using Unloading Compliance Technique
Publication date: Available online 20 June 2018
Source:Engineering Fracture Mechanics Author(s): Marcella Araujo Lage, Daniela de Figueiredo Cavalcante, Kioshy Santos de Assis, Oscar Rosa Mattos Unloading compliance technique in fracture toughness tests according to ASTM E1820 standard is used to obtain the resistance curve (R-curve) of metallic materials in air tests. Even in this situation, there are aspects inherent to work hardening around the crack-tip that could affect the unloading compliance technique and that are not well discussed. .Another important aspect is the application of this methodology in conditions involving corrosive environments. Indeed, the presence of hydrogen around the crack-tip can promote significant changes in the strain and stress around the process zone, leading to the phenomenon called subcritical crack growth. This phenomenon can affect the compliance increasing the divergence between the crack sizes obtained by the unloading compliance technique and the correct crack sizes measured after the test. The aim of this paper is to analyse the influence of subcritical crack growth and to present a methodology to correct crack sizes and the influence of work hardening during fracture.
Available online 19 June 2018
Direct comparison of anisotropic damage mechanics to fracture mechanics of explicit cracks
Publication date: Available online 19 June 2018
Source:Engineering Fracture Mechanics Author(s): John A. Nairn Because damage mechanics modeling involves damage initiation followed by propagation that releases energy, it is often uncritically assumed to be an alternative implementation of fracture mechanics. This paper tests that claim by running side-by-side damage mechanics and explicit crack fracture mechanics simulations within the same code on three separate problems. For a center-notched specimen loaded in tension, damage mechanics can reproduce all features of fracture mechanics, but with three restrictions. First, damage mechanics must implement anisotropic damage mechanics rather then simpler isotropic or scalar damage methods. Second, initiation stress and toughness used in damage mechanics must be calibrated before damage mechanics can reproduce either fracture mechanics or experimental results. Third, damage mechanics properties must scale with absolute size of discretization elements. Two other problems considered were mixed-mode, dynamic fracture and cracking of a brittle coating on a substrate. In each case, anisotropic damage mechanics can be made consistent with fracture mechanics by suitable calibration of properties. An advantage of damage mechanics is its potential to model certain complicated issues better then explicit crack fracture mechanics. Two examples are dealing with a transition to shear failure and modeling of fracture events such as periodic cracking in coatings.
15 June 2018
Understanding the tensile strength of ceramics in the presence of small critical flaws
Publication date: Available online 19 June 2018
Source:Engineering Fracture Mechanics Author(s): E. Martin, D. Leguillon, O. Sevecek, R. Bermejo The effect of small critical flaws on the strength of polycrystalline ceramic materials is analyzed with the help of an initiation criterion combining both a stress and an energy conditions. If the size of the defect is smaller than the characteristic material length, numerical predictions reveal that the defect (either sharp or blunt) has no effect on the strength. This result is in a good agreement with experimental results obtained from the strength measurements of ceramic materials with controlled flaws. Combining two fracture tests after introducing flaws with controlled sizes enables to identify the fracture parameters of the ceramic material.
15 June 2018
Editorial Board
Publication date: 15 June 2018
Source:Engineering Fracture Mechanics, Volume 197

15 June 2018
Experimental study on mechanical properties and failure modes of low-strength rock samples containing different fissures under uniaxial compression
Publication date: 15 June 2018
Source:Engineering Fracture Mechanics, Volume 197 Author(s): Yanlei Wang, Jianxin Tang, Zhangyin Dai, Ting Yi Uniaxial compressive tests (UCS) were carried out to investigate the influence of pre-existing fissure geometry parameters (various dip angles, lengths, widths, and numbers) on the mechanical properties and deformation failure modes of low-strength rock samples. The results suggested that UCS, elastic modulus and axial peak strain were reduced by pre-existing fissures, but the reduction degree was strongly associated with the pre-existing fissure geometry. In addition, the UCS and elastic modulus of the low-strength rock samples were very sensitive to fissure dip angle and number, while the fissure number had the greatest effect on both of them. The axial peak strain was mainly influenced by the fissure dip angle. Moreover, due to the influence by the pre-existing fissures, the stress-strain curves of low-strength rock specimens usually changed from rapid drop to multistage decline, and even to horizontal extension slow decline. This indicated that low-strength specimens usually can change from brittle failure to ductile failure, and even had ductile flow deformation damage occurring under the influence of the pre-existing fissures. This change did not occur in high-strength rock mass. The fracture morphology of low-strength rock specimens was primarily affected by the fissure dip angle, and the influence of the fissure number on the fracture morphology was constrained by the fissure dip conditions, while the fissure length and width had fairly little effects on the fracture morphology of low-strength rock samples. This paper may provide new insights into the principle features of rock failure under uniaxial compression for future studies.
15 June 2018
On crack band model in finite element analysis of concrete fracture in engineering practice
Publication date: 15 June 2018
Source:Engineering Fracture Mechanics, Volume 197 Author(s): J.
15 June 2018
A novel approach to evaluate mixed-mode SIFs for a through-thickness crack in a welding residual stress field using an effective welding simulation method
Publication date: 15 June 2018
Source:Engineering Fracture Mechanics, Volume 197 Author(s): Ramy Gadallah, Naoki Osawa, Satoyuki Tanaka, Seiichiro Tsutsumi This paper accurately evaluates mixed-mode SIFs (MM-SIFs) for cracks in welding residual stress (WRS) fields using a novel approach based on finite element method (FEM). For this reason, the interaction integral method (IIM) available in WARP3D, an open source code, was developed to include normal and shear stress components in MM-SIF solutions. The effectiveness of the developed WARP3D-IIM was verified based on the superposition method and by means of well-established analytical and numerical reference solutions using an inclined through-thickness cracked FE model. After validating the adequacy of the developed WARP3D-IIM, different welding simulations were conducted using JWRIAN (Joining and Welding Research Institute ANalysis). JWRIAN, a sophisticated welding simulation in-house code, was adopted as a welding simulation tool to predict WRS. Different weld line (WL) orientations, as well as different perpendicular distances between WLs, were performed to investigate their influence on the behavior of MM-SIFs. The developed WARP3D-IIM and superposition method were thereafter employed to evaluate MM-SIF solutions for an inclined through-thickness crack in the simulated WRS fields. Different crack angles were also employed to examine the effect of the induced WRS on calculated MM-SIFs. SIF solutions resulting from WRS were validated with analytical reference solutions. Results showed that WRS has a considerable influence on the behavior of MM-SIFs. Moreover, WL orientation as well as the perpendicular distance between WLs revealed a significant influence on the induced WRS and thus MM-SIF solutions. On the other hand, the crack angle showed a remarkable effect on the behavior of MM-SIFs. MM-SIFs calculated at through-thickness crack fronts were influenced by the induced WRS distribution as well as crack angle.
15 June 2018
On power-law tail distribution of strength statistics of brittle and quasibrittle structures
Publication date: 15 June 2018
Source:Engineering Fracture Mechanics, Volume 197 Author(s): Zhifeng Xu, Jia-Liang Le Understanding the tail behavior of the probability distribution of structural strength is of paramount importance for reliability-based design of engineering structures. For brittle and quasibrittle structures, the tail distribution not only determines the design strength at a low failure probability, but also governs the functional form of the strength distribution of large-size structures. There exists clear evidence that the Weibull distribution is applicable to brittle structures. Based on the theory of extreme value statistics, the applicability of Weibull distribution suggests that the tail distribution must follow a power law. The justification of the power-law tail distribution was first proposed by Freudenthal based on an assumed type of flaw statistics and linear elastic fracture mechanics of non-interacting flaws. A series of recent studies suggested that the power-law tail can be explained by the transition rate theory governing the statistics of material failure at the nano-scale. In this study, we investigate the tail distribution by considering the randomness in both material strength and applied stress field. The present analysis adopts a nonlocal strength-based failure criterion, in which the spatial variability of the material strength is represented by an autocorrelated random field. The failure statistics of the structure is calculated as a first passage probability. We analyze this problem in 1D, 2D and 3D settings, and the results indicate that in all cases the tail distribution of the nominal structural strength follows a power law. It is shown that the power-law tail behavior of strength distribution stems from the tail distribution of material strength. The flaw statistics introduces additional randomness to the nominal structural strength, but does not dictate the power-law form of its tail distribution.
15 June 2018
Thermomechanical peridynamic analysis with irregular non-uniform domain discretization
Publication date: 15 June 2018
Source:Engineering Fracture Mechanics, Volume 197 Author(s): Yile Hu, Hailong Chen, Benjamin W. Spencer, Erdogan Madenci Irregular non-uniform discretization of the solution domain in models based on peridynamic theory can improve computational efficiency by allowing local refinement and remove mesh bias effects on crack initiation and propagation. However, the use of such discretizations generally requires adjustment of the classical peridynamic material parameters and usage of a variable horizon which results in the so-called ghost force effect in the interactions between differing horizons. This study presents a generalization of the original bond-based and ordinary state-based peridynamic models to permit the use of irregular non-uniform domain discretizations, in which the strain energy and thermal potential associated with a bond between two material points is split into two parts based on volumetric ratios. This division is potentially different for each bond due to the presence of irregular non-uniform discretization. The validity and accuracy of this proposed approach is established using several benchmark examples, and its applicability to real engineering problems is demonstrated by modeling thermally induced cracking in a three-dimensional nuclear fuel pellet.
15 June 2018
Tensile and explosive properties of current carrying wires
Publication date: 15 June 2018
Source:Engineering Fracture Mechanics, Volume 197 Author(s): A. Widom, J. Swain, Y.N. Srivastava, Georges de Montmollin A statistical thermodynamic viewpoint is employed towards the electro-mechanical properties of current carrying wires under tension. In particular, we consider the loss in the tensile strength of the wire and the tendency to fracture into small segments explosively, in terms of the electronic (relativistic) kinetic energies contributing to the pressure tensor and weakening the metallic chemical binding. A sufficiently violent explosion from a strong current pulse is a conventional manufacturing method for fabricating metallic nano-particles. Such high current fracture explosions are known to often be accompanied by low energy nuclear reactions. We consider the strength of threshold currents for some explicit nuclear reactions from the conventional thermodynamic theory of reaction chemical potentials. Numerical values are provided for important threshold currents.
15 June 2018
A theoretical method to determine the tortuous crack length and the mechanical parameters of concrete in direct tensionA particle size effect analysis
Publication date: 15 June 2018
Source:Engineering Fracture Mechanics, Volume 197 Author(s): Dong Li, Liu Jin, Xiuli Du, Jingbo Liu Cementitious materials, mainly in the form of concrete, belong to a class of macroscopically heterogeneous materials. The building technology of mass concrete structures enables large-sized coarse aggregate to be used. The maximum coarse aggregate size, in conjunction with the mechanical properties of the interfacial transition zone (ITZ), have great influences on the mesoscopic crack path and the macroscopic mechanical behavior of concrete. Herein this study, based on some pioneering work (Stroeven, 2000; Rossell
15 June 2018
Determining indentation fracture toughness of ceramics by finite element method using virtual crack closure technique
Publication date: 15 June 2018
Source:Engineering Fracture Mechanics, Volume 197 Author(s): Liang Sun, Dejun Ma, Lizhi Wang, Xinzheng Shi, Jialiang Wang, Wei Chen Based on indentation cracks produced by Vickers indentation tests on Silicon Nitride and Fused Silica, fracture toughness (K IC) of the two materials was determined by a Vickers indentation finite element model using virtual crack closure technique (VCCT). The elastic modulus and yield stress of the materials needed in finite element simulation were determined by using dimensionless expressions specially established for ceramic materials, which revealed the approximate numerical relationship between indentation responses and elastoplastic properties of ceramic materials. Computed K IC was obtained by calculating the stress intensity factor (K I) at crack tip. Considering that the calculated stress intensity factor (K I) varied distinctly along an ideal semi-circle crack front, the equi-K I crack front was acquired through successive simulation and adjustment. By comparison, the computed K IC values of equi-K I crack fronts were in good consistence with the reference K IC of the two materials, while those of the semi-circle crack fronts presented significant errors. The results indicated that indentation fracture toughness could be well determined by employing finite element method (FEM) and VCCT, and the obtainment of equi-K I crack front was crucial to the accuracy of computed fracture toughness.
15 June 2018
A machine learning approach for the identification of the Lattice Discrete Particle Model parameters
Publication date: 15 June 2018
Source:Engineering Fracture Mechanics, Volume 197 Author(s): Mohammed Alnaggar, Naina Bhanot Concrete is a composite material that is governed by complex constitutive behavior under various loading and environmental conditions. Only comprehensive computational models can represent such behavior and capture the effects of heterogeneity, crack coalescence and damage localization. Such models are usually governed by a large set of parameters that require, correspondingly, multiple experimental tests for their proper calibration. In many experimental campaigns, not all of the needed tests are performed. In this case, the uniqueness of the calibration results cannot be guaranteed. In this research, a Machine Learning (ML) approach is proposed to solve this problem by predicting the unknown characteristics of the concrete based on a statistical interpolation of large concrete testing databases and by using these interpolated data to identify the model parameters. The ML framework is demonstrated using the Lattice Discrete Particle Model (LDPM), which is a comprehensive concrete model that successfully replicates concrete behavior under multi-axial stresses in both static and dynamic loading conditions. The ML approach consists of an initial training of an Artificial Neural Network (ANN) to reverse engineer LDPM using pilot concrete data that represent common concrete properties. Next, an adaptive updating technique is implemented to improve the parameter identification capabilities and to allow continuous learning. The paper discussed multiple validations performed by using both original and updated ANNs. The results show the excellent parameter identification capabilities of the framework and its ability to adaptively update and improve its predictions. Additionally, the proposed ML approach improves convergence, accuracy and speed of other parameter identification methods, such as the nonlinear least square method, when used to provide the initial guess values of the parameters to be identified.
15 June 2018
On the fatigue performance and residual life of intercity railway axles with inside axle boxes
Publication date: 15 June 2018
Source:Engineering Fracture Mechanics, Volume 197 Author(s): S.C. Wu, Y.X. Liu, C.H. Li, G.Z. Kang, S.L. Liang Railway axles with inside axle boxes have a great potential in modern urban railway system due to good dynamic performance on small-radius track. However, because of entirely different loading nature from widely-used one, a challenging problem of the fatigue performance and damage endurance arises in the case of defects from various external sources. In this paper, a stepwise fatigue assessment framework composed of safe life as the first level and damage tolerance as the second level was tentatively proposed for the wheelset with inside axle boxes. An assumed load spectrum was employed to estimate the remaining life for a damaged axle made of the EA4T steel. Calculated results show that the critical safety region has been transferred to the axle center in contrast to classical axles, where a 1.0
15 June 2018
Frictional behaviour of the interface between concrete and rubber: Laboratory shear test and its elastoplastic model
Publication date: 15 June 2018
Source:Engineering Fracture Mechanics, Volume 197 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.
15 June 2018
Determination of crack tip stress intensity factors by singular Voronoi cell finite element model
Publication date: 15 June 2018
Source:Engineering Fracture Mechanics, Volume 197 Author(s): Rui Zhang, Ran Guo A singular Voronoi cell finite element model (SVCFEM) is proposed for estimation of the mixed-mode stress intensity factors (SIFs) of crack tip in this paper. Formulation of a singular Voronoi cell finite element is based on a modified complementary energy principle. To satisfy the stress singularity at the crack tip, we enrich stress solution in assumed stress hybrid model. In addition to polynomial and reciprocal terms, singular stress terms of Williams expansion are added for elliptical crack to capture crack-tip stress concentrations. After obtaining the stress, SIFs of model I and model II were calculated using linear least-squares method. Comparisons of SVCFEM solution with analytical solution for crack are made to demonstrate the efficiency of SVCFEM.
15 June 2018
A comparative study on stress intensity factor-based criteria for the prediction of mixed mode I-II crack propagation in concrete
Publication date: 15 June 2018
Source:Engineering Fracture Mechanics, Volume 197 Author(s): Wei Dong, Zhimin Wu, Xuchao Tang, Xiangming Zhou Combined with the fictitious crack model, the stress intensity factor (SIF)-based criteria are widely adopted to determine the crack propagation of mixed mode I-II fracture in normal strength concrete. However, less research is reported on the applicability of the different SIF-based criteria when they are used to analyze the crack propagation process of concrete with different strength grades. With this objective in mind, three-point bending and four-point shear tests were conducted in this study on C20, C50 and C80 grade concrete to measure the initial fracture toughness, fracture energy, load-crack mouth opening/sliding displacement (CMOD/CMSD). Four SIF-based criteria, including two initial fracture toughness-based (with/without mode II component of SIF K II) and two nil SIF-based (with/without K II), were introduced to determine crack propagation and predict the P-CMOD/CMSD curves for the notched concrete beams under four-point shear loading. The results indicated that the difference between the peak loads from experiment and from the analysis based on the nil SIF criterion with K II approximately increases with the increase of the concrete strength. By contrast, the predicted peak load and P-CMOD/CMSD curves adopting the initial fracture toughness-based criterion with K II showed better agreement with experimental results for the different concrete strength. Meanwhile, in the case of the initial fracture toughness-based criteria, the predicted initial load was underestimated if the component of K II was not considered. However, the fracture mode transformed from mixed mode I-II to mode I after the crack initiation, meaning the K II component in the criterion had a less significant effect on the crack propagation process.
15 June 2018
Simple mechanics model and Hertzian ring crack initiation strength characteristics of silicon nitride ceramic ball subjected to thermal shock
Publication date: 15 June 2018
Source:Engineering Fracture Mechanics, Volume 197 Author(s): Shinya Matsuda, Takeshi Nakada This study investigated the ring crack initiation strength characteristics of silicon nitride ceramic balls subjected to thermal shock. Sphere indentation tests were conducted on ceramic balls following water quenching and furnace cooling operations performed in air and vacuum. The ring crack radius was significantly smaller because of the very thin silicon oxide (SiO2) layer formed owing to heat treatment in air at high temperatures. In addition, the ring crack initiation load and Weibull shape parameter of water-quenched ceramic balls decreased with increasing temperature difference and remained relatively unaffected by the high-temperature oxidation. This phenomenon was mainly due to microscopic damage, which occurs near the surface of ceramic balls, caused by transient thermal stress developed during water quenching. A simple mechanics model based on the constant energy release rate criterion has been proposed for comparing experimental results obtained in this study against theoretical predictions, and results of the said comparison adequately verify strength characteristics of the aforementioned ceramic balls subjected to thermal shock.
15 June 2018
A novel test configuration designed for investigating mixed mode II/III fracture
Publication date: 15 June 2018
Source:Engineering Fracture Mechanics, Volume 197 Author(s): Behnam Saboori, Majid R. Ayatollahi In this paper, a novel test setup is introduced to investigate mixed mode II/III fracture (fracture under combined in-plane and out-of-plane shear loadings) in components weakened by crack. The designed loading fixture can exert the full range of mixed mode II/III loading conditions, from pure mode II to pure mode III, to a single edge cracked test specimen. The proposed test rig has a simple configuration as well as a low manufacturing cost and it is easy to be utilized and installed in conventional loading machines for performing fracture experiments. Three-dimensional finite element analysis has been employed for evaluating the performance and effectiveness of the test configuration in different mixed mode loading cases. The computational results demonstrate that the designed loading apparatus can appropriately create various mode mixities from pure mode II to pure mode III and is capable of assessing the mode II/III fracture behaviour of the materials experimentally.
15 June 2018
Homogenization coarse graining (HCG) of the lattice discrete particle model (LDPM) for the analysis of reinforced concrete structures
Publication date: 15 June 2018
Source:Engineering Fracture Mechanics, Volume 197 Author(s): Erol Lale, Roozbeh Rezakhani, Mohammed Alnaggar, Gianluca Cusatis In this study, a coarse-graining framework for discrete models is formulated on the basis of multiscale homogenization. The discrete model considered in this paper is the Lattice Discrete Particle Model (LDPM), which simulates concrete at the level of coarse aggregate pieces. In LDPM, the size of the aggregate particles follows the actual particle size distribution that is used in experiment to produce concrete specimens. Consequently, modeling large structural systems entirely with LDPM leads to a significant number of degrees of freedom and is not feasible with the currently available computational resources. To overcome this limitation, this paper proposes the formulation of a coarse-grained model obtained by (1) increasing the actual size of the particles in the finescale model by a specific coarsening factor and (2) calibrating the parameters of the coarse grained model by best fitting the macroscopic, average response of the coarse grained model to the corresponding fine scale one for different loading conditions. A Representative Volume Element (RVE) of LDPM is employed to obtain the macroscopic response of the fine scale and coarse grained models through a homogenization procedure. Accuracy and efficiency of the developed coarse graining method is verified by comparing the response of fine scale and coarse grained simulations of several reinforced concrete structural systems in terms of both accuracy of the results and computational cost.
15 June 2018
Long term availability of raw experimental data in experimental fracture mechanics
Publication date: 15 June 2018
Source:Engineering Fracture Mechanics, Volume 197 Author(s): Patrick Diehl, Ilyass Tabiai, Felix W. Baumann, Daniel Therriault, Martin Levesque Experimental data availability is a cornerstone for reproducibility in experimental fracture mechanics, which is crucial to the scientific method. This short communication focuses on the accessibility and long term availability of raw experimental data. The corresponding authors of the eleven most cited papers, related to experimental fracture mechanics, for every year from 2000 up to 2016, were kindly asked about the availability of the raw experimental data associated with each publication. For the 187 e-mails sent: 22.46 % resulted in outdated contact information, 57.75 % of the authors did received our request and did not reply, and 19.79 replied to our request. The availability of data is generally low with only 11 available data sets ( 5.9 %). The authors identified two main issues for the lacking availability of raw experimental data. First, the ability to retrieve data is strongly attached to the possibility to contact the corresponding author. This study suggests that institutional e-mail addresses are insufficient means for obtaining experimental data sets. Second, lack of experimental data is also due that submission and publication does not require to make the raw experimental data available. The following solutions are proposed: (1) Requirement of unique identifiers, like ORCID or ResearcherID, to detach the author(s) from their institutional e-mail address, (2) Provide DOIs, like Zenodo or Dataverse, to make raw experimental data citable, and (3) grant providing organizations should ensure that experimental data by public funded projects is available to the public.

Phase-field regularized cohesive zone model (CZM) and size effect of concrete
Publication date: 15 June 2018
Source:Engineering Fracture Mechanics, Volume 197 Author(s): De-Cheng Feng, Jian-Ying Wu A phase-field regularized cohesive zone model (CZM) was recently proposed for both brittle fracture and cohesive failure within the framework of the unified phase-field damage theory. Motivated from the fact that this model gives length scale and mesh independent global responses for problems with or without elastic singularities, we further apply it in this work against the size and boundary effects of concrete under both mode-I and mixed-mode failure. More specifically, for the two independent experimental campaigns of three-point bending notched and unnotched concrete beams under mode-I failure, the quality of data-fitting is, at least, comparable to the best results reported in the literature. For another series of eccentrically notched concrete beam tests, the size effect with transition from mode-I fracture to mixed-mode failure is also predicted. In all numerical examples, not only the peak loads but also the softening regimes agree well with the experimental results using a single set of material parameters for a specific series of tests. Being accompanied with other merits, e.g., generic softening laws, no lateral widening, no need of extrinsic crack tracking nor the penalty stiffness, etc., the presented phase-field regularized CZM can be used as a promising approach in the modeling of damage and failure in solids and structures.
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