Journal Sciences News
Theoretical and Applied Fracture Mechanics
Available online 17 January 2018
Neuber fictitious notch rounding approach reformulated for orthotropic materials
Publication date: Available online 19 January 2018
Source:Engineering Fracture Mechanics Author(s): Michele Zappalorto, Paolo Andrea Carraro In this short contribution, the fictitious notch rounding concept is applied to U-shaped notches in orthotropic bodies. Using the normal stress criterion, the fictitious notch radius is determined in closed form. It is found that the fictitious radius strictly depends on the actual notch radius, the microstructural support length and the elastic properties of the material, the latter playing a crucial role.
Available online 17 January 2018
The stiffness matrix of cracked finite elements: Introducing shortcomings in applying stiffness approach and proposing a solution
Publication date: Available online 17 January 2018
Source:Engineering Fracture Mechanics Author(s): A. Kamali Yazdi, A. Shooshtari Several cracked finite elements have been introduced and implemented by researchers to analyze structures with cracks. In the formulation of these elements, the elastic strain energy caused by the crack is added to the elastic strain energy of the non-cracked element. Afterwards, the required relations are obtained by using Castigliano’s second theorem (flexibility approach) or the first one (stiffness approach). In this paper, the two above-mentioned formulations of cracked elements are discussed. As a result, this study demonstrates shortcomings in applying stiffness approach. Therefore, this paper introduces a step by step method to improve the utilization of Castigliano’s first theorem in producing the stiffness matrix of cracked elements. Finally, the topics discussed in this paper are numerically examined.
Available online 12 January 2018
Estimation of C
Available online 12 January 2018
An improved crack propagation model for plain concrete under fatigue loading
Publication date: Available online 12 January 2018
Source:Engineering Fracture Mechanics Author(s): Sonali Bhowmik, Sonalisa Ray Fatigue crack growth phenomenon in concrete is complex in nature and is characterised by various parameters. Important crack growth characterizing parameters must be considered in the analysis for accurate crack propagation and fatigue life prediction. In the present work, an analytical formulation has been developed to predict the propagation of crack in plain concrete members subjected to repetitive nature of loading. Dimensional analysis approach for fatigue crack growth problems has been adopted in conjunction with the theory of intermediate asymptotic for the development of the proposed model. The model has been derived considering the effect of critical energy dissipation in fatigue called fatigue fracture energy which can capture the observed size effect in concrete fatigue. Other important crack growth characterizing parameters considered in the present formulation are, change in energy release rate, maximum energy release rate, initial crack length, tensile strength, and ratio of maximum aggregate size to characteristic size of the structure. Further, the influence of fracture process zone has been incorporated in the proposed formulation through the loading parameter. The developed closed form expression has been calibrated with the available experimental results. The applicability of the mathematical model has been verified using the existing experimental results following both deterministic and statistical approach. The dependence of various governing parameters on fatigue life has been demonstrated through sensitivity study.
Available online 12 January 2018
Further improvement of the Prometey model and unified curve method part 2. Improvement of the unified curve method
Publication date: Available online 12 January 2018
Source:Engineering Fracture Mechanics Author(s): B.Z. Margolin, A.G. Gulenko, V.N. Fomenko, V.I. Kostylev An engineering Unified Curve (UC) method is considered in terms of its advantages and disadvantages for the temperature dependence of fracture toughness KJC(T) to be predicted. Based on the advanced model of brittle fracture (referred as the Prometey-M model) presented in the first part of this paper, the UC method has been improved. This method is referred to as the Advanced Unified Curve (AUC). Relying on a large database on the fracture toughness of materials with various degrees of embrittlement, a comparison was made between AUC and UC as well as AUC and the Master Curve considered as the most widely-used engineering method. AUC, UC and MC were compared using different mathematical statistics methods.
Available online 11 January 2018
Observations on the role of fracture mechanics in biology and medicine
Publication date: Available online 12 January 2018
Source:Engineering Fracture Mechanics Author(s): David Taylor Fracture mechanics has been of great benefit in the fields of biology and medicine. Biological materials have low fracture toughness and often fail by cracking, so the knowledge which has been developed for engineering materials can usefully be applied to study the failure of bone, cartilage and many other natural materials. Medical devices such as artificial joints and stents experience complex failure modes owing to their interactions with the human body: materials science and fracture mechanics experts have played an important role in the development and validation of new materials for these applications. It is also true that the fields of biology and medicine have been very good for fracture mechanics, presenting us with new and interesting challenges such as the inclusion of repair processes in theoretical models of fracture. This article describes some examples of work in this area, including the development of low modulus titanium alloys, the application of fracture concepts to study human bone and the wide range of biological materials which Nature has evolved for load-bearing applications.
Available online 9 January 2018
Acoustic emission investigation of the effect of graphene on the fracture behavior of cement mortars
Publication date: Available online 11 January 2018
Source:Engineering Fracture Mechanics Author(s): Ilias
Available online 3 January 2018
Modelling of creep rupture of ferritic/austenitic dissimilar weld interfaces under mode I fracture
Publication date: Available online 9 January 2018
Source:Engineering Fracture Mechanics Author(s): Jia-nan Hu, Takuya Fukahori, Toshihide Igari, Yasuharu Chuman, Alan C.F. Cocks Dissimilar metal welded structures (DMWs) have been used extensively in conventional and nuclear power generation plants. Evaluation of creep rupture properties of DMWs is critical to the structural integrity assessment. Failure of DMWs can occur in the base metal, the heat-affected zone (HAZ), or the dissimilar interface between the two welded materials, depending on the operating stress and temperature. The primary focus of this work is on interface failure in systems consisting of a ferritic steel (P91 or P22) and an Inconel filler material, which has an austenitic structure. A planar damage zone is introduced within a finite element (FE) framework to model the response of the interface. A traction-separation constitutive law with a Kachanov-type damage accumulation relationship is employed to describe the interface response, with the material parameters calibrated against available creep rupture data in which failure occurred at the dissimilar weld interface. It is found that the difference in damage accumulation along the interface of different DMW systems can be attributed to the mismatch in creep properties of the continuum materials either side of the interface. Diversion of the crack path into the HAZ is also captured as a result of damage accumulation in the heat affected zone (HAZ). The relationship between the empirical damage accumulation model and the major microstructural features that are responsible for interface failure is also discussed.
Available online 3 January 2018
Prediction of ductile fracture for metal alloys using a shear modified void growth model
Publication date: Available online 3 January 2018
Source:Engineering Fracture Mechanics Author(s): Yazhi Zhu, Michael D. Engelhardt Shear stress ratio have recently been recognized as an important parameter, in addition to stress triaxiality, that influences the initiation of ductile fracture in metals. In this paper, the roles of stress triaxiality and shear stress ratio in the micro-mechanisms of ductile fracture are first discussed. A modified ductile fracture model coupling both stress triaxiality and shear stress ratio is then proposed. The model is developed based on the Rice-Tracey and modified maximum shear stress models. Parametric studies are performed to demonstrate the behaviors of the model parameters. The proposed model is applied to construct the fracture loci of four types of metal alloys: aluminum 2024-T351, aluminum 6061-T6, ASTM A572 Gr. 50 steel and AISI 1045 steel. The predicted results are in good agreement with the experimental data over a wide range of triaxialities. Comparison between the proposed model and several popular fracture criteria is also provided, and the results indicate that the proposed model has significant potential to predict ductile fracture at both low and high triaxialities.
Available online 3 January 2018
Experimental and simulation studies on fracture and adhesion test of laminated glass
Publication date: Available online 3 January 2018
Source:Engineering Fracture Mechanics Author(s): Ajitanshu Vedrtnam, S.J. Pawar The present work includes fracture and adhesion testing of laminated glasses (LGs) with different inter-layers (Polyvinyl butyral (PVB), Ethyl vinyl acetate (EVA)) and their different critical thicknesses (0.38, 0.76, 1.52
Available online 2 January 2018
Theoretical analysis of fracture in double overlap bonded joints with FRP composites and thin steel plates
Publication date: Available online 3 January 2018
Source:Engineering Fracture Mechanics Author(s): Hugo C. Biscaia, Carlos Chastre The effective stress transfer between the fiber reinforced polymers (FRP) and the steel substrate is crucial for the successful retrofit of existing steel structures with FRP composites. However, there are no standard tests for FRP-to-steel interfaces, wherefore different test configurations have been used in recent years to assess the bond behaviour in these interfaces. The present study shows that the choice of test configuration is highly important and leads to different transfer stresses between the FRP and steel composites and consequently, has a direct influence on the strength of the bonded joint. Therefore, it is important to understand the debonding process that occurs in each test and avoid misinterpretations, erroneous analyses and dangerous characterizations of the interfacial behaviour of these interfaces. The current study presents a new analytical approach for the prediction of the debonding of FRP-to-steel interfaces when double-lap pull or double-strap tests are used.

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Available online 30 December 2017
Experimental and numerical investigation of skin/lattice stiffener debonding growth in composite panels under bending loading
Publication date: Available online 2 January 2018
Source:Engineering Fracture Mechanics Author(s): Farshid Kamareh, Amin Farrokhabadi, Gholamhossein Rahimi In the present paper, a comparative study on the debonding growth between skin and the lattice stiffeners is performed using both numerical and experimental procedures. To this end, two prevalent types of stiffener arrangement in designing of the lattice composite panels (orthogrid pattern) are considered. Furthermore, the detailed effects of the initial debonding pattern on the mechanical behavior of the structure are investigated. Then, finite element method (FEM) is chosen as the numerical approach and the interface debonding growth is simulated in the Abaqus software based on the bilinear CZM. In the experimental investigation, composite skin and stiffener ribs are manufactured using E-glass fibers and the prepared specimens are supposed to three-point bending loading and the debondig growth is detected experimentally. Generally the obtained results proved that the initial debonding pattern and stiffeners arrangement have a crucial effect on the bending behavior of the structure.
Available online 30 December 2017
The moving least squares based numerical manifold method for vibration and impact analysis of cracked bodies
Publication date: Available online 30 December 2017
Source:Engineering Fracture Mechanics Author(s): Wei Li, Hong Zheng, Guanhua Sun In the numerical manifold method (NMM), the mathematical patches composing the mathematical cover can take on any shape in addition to finite elements. In this study, the influence domains of those scattered nodes in the moving least squares (MLS) approximation serve as the mathematical patches. And accordingly, the MLS based NMM, designated by MLS-NMM, is derived, which owns the advantages of both NMM and MLS. Then, MLS-NMM is applied to analyze cracked bodies under dynamic loading, and a mass lumping scheme fit for MLS-NMM is proposed. The dynamic analyses of some typical cracked bodies are carried out, indicating MLS-NMM equipped with the proposed mass lumping scheme has more excellent numerical properties than that with the consistent mass formulation in the analysis of the time domain as well as the frequency domain.
Available online 30 December 2017
Numerical Simulations and Experimental Validations of a Proposed Ductile Damage Model for DIN1623 St12 Steel
Publication date: Available online 30 December 2017
Source:Engineering Fracture Mechanics Author(s): F. Haji Aboutalebi, M. Poursina, H. Nejatbakhsh, M. Khataei In this research, first, a ductile damage model for DIN1623 St12 steel is proposed. Then, the damage parameters of the material are numerically and experimentally determined, using the various tensile tests on flat-grooved, pure tension, and shear-tension specimens. Based on the experimental and numerical results, the relation between the equivalent fracture strain vs. the stress triaxiality is obtained. Finally, to validate the fracture locus, the determined damage parameters, and the damage model, two experimental tensile tests are performed on the notched specimens and compared with the numerical simulations. Comparison of the numerical simulations and empirical observations reveals good adaptation.
Available online 30 December 2017
XFEM analysis of a 2D cracked finite domain under thermal shock based on Green-Lindsay theory
Publication date: Available online 30 December 2017
Source:Engineering Fracture Mechanics Author(s): Navid Roshani Zarmehri, Mohammad Bagher Nazari, Masoud Mahdizadeh Rokhi In this paper, the extended finite element method is implemented to extract stress intensity factors (SIFs) for a stationary crack in an isotropic 2D finite domain under thermal shock. The fully coupled generalized thermoelasticity theory based on Green-Lindsay (G-L) model is considered. The interaction integral is developed to compute the stress intensity factors in which the dissipated part of the strain energy density is accounted to preserve domain-independency of. The Newmark time integration scheme is used to solve semidiscrete governing equations. According to the results, the speed of stress and temperature waves controls the time variations of stress intensity factors especially at early times of the thermal shock.
Available online 28 December 2017
Comparative study on prediction of fracture toughness of CFRP laminates from size effect law of open hole specimen using cohesive zone model
Publication date: Available online 30 December 2017
Source:Engineering Fracture Mechanics Author(s): Mohammed Y. Abdellah Carbon fibre reinforced polymer laminates (CFRPs) are widely used in the aerospace industry. However, the longitudinal fracture toughness of this composite material is a major factor that causes its failure. Here, physical linear and exponential softening laws are used to predict the fracture toughness of CFRPs. The model estimates the predicted strength of an open hole specimen of the material by using the cohesive law and the limiting value of the critical crack opening and unnotched strength obtained using a simple tension test. The critical crack opening is calculated based on a thickness formula. The model results are in good agreement with the experimental results, with errors of 6.39% and 11.29% for the linear and exponential cohesive laws, respectively.
Available online 26 December 2017
A review of lattice type model in fracture mechanics: theory, applications, and perspectives
Publication date: Available online 28 December 2017
Source:Engineering Fracture Mechanics Author(s): Zichao Pan, Rujin Ma, Dalei Wang, Airong Chen The lattice model is a discrete model that is typically used to simulate the fracture process of brittle materials. This review summarizes the main achievements during the development history of the state-of-the-art lattice model during the past 80
Available online 26 December 2017
Failure predictions of DP600 steel sheets using various uncoupled fracture criteria
Publication date: Available online 26 December 2017
Source:Engineering Fracture Mechanics Author(s): Niloufar Habibi, Ali Ramazani, Veera Sundararaghavan, Ulrich Prahl Dual-phase (DP) steel sheets have high potential for utilization as automotive structures due to theirgood combination of strength and ductility. As sheet metal forming processes induce complicated stress-strain states, determination of forming limit is vital, particularly using numerical approaches. This current study aims to examine the fracture behavior of DP600 steel sheets through several ductile fracture criteria in a wide range of stress states. For a better and more accurate understanding of the experimental tests, parallel numerical simulations were performed. First, the models were calibrated using the results of Nakazima tests, and then the fracture loci in principal strains, and equivalent strain-stress triaxiality spaces were predicted by each model. The capability of the criteria was verified through cross-die and bulge tests. Also, errors were quantified for the calculated results using correlation coefficient and relative error methods. The results reveal that Maximum Shear Stress, Modified Mohr Coulomb, and Lou fracture models were able to predict the onset of fracture with acceptable accuracy. However, Maximum Shear Stress required only one experimental test to be calibrated.
Available online 24 December 2017
Effects of additive amount, testing method, fabrication process and sintering temperature on the mechanical properties of Al2O3/3Y-TZP composites
Publication date: Available online 26 December 2017
Source:Engineering Fracture Mechanics Author(s): Alireza Moradkhani, Hamidreza Baharvandi In this research, samples of Alumina (Al2O3) along with 5, 10, 15 and 20 vol. % of 3 mol. % Y2O3-stabilized zirconia (3Y-TZP) have been prepared by different green processing techniques (conventional slip-casting or novel tape-casting) and subsequently sintered at temperatures of 1550 and 1650 °C. The mechanical properties of these composites have then been studied. To measure the hardness, Young’s modulus and fracture toughness (KIC ) values of the prepared samples, two different methods have been used and their results have been compared with each other. The findings indicate that by increasing the volume percentage of 3Y-TZP additive phase in the composites, their relative density, hardness, Young’s modulus and flexural strength are reduced, but their KIC value is increased. Also, in most of the cases, choosing a particular fabrication process (slip-casting or tape-casting), sintering temperature, or a method of measuring the mechanical properties does not lead to a significant change in the obtained results.
Available online 24 December 2017
A softening-healing law for self-healing quasi-brittle materials: analyzing with strong discontinuity embedded approach
Publication date: Available online 24 December 2017
Source:Engineering Fracture Mechanics Author(s): Yiming Zhang, Xiaoying Zhuang Quasi-brittle materials such as concrete suffer from cracks during their life cycle, requiring great cost for conventional maintenance or replacement. In the last decades, self-healing materials are developed which are capable of filling and healing the cracks and regaining part of the stiffness and strength automatically after getting damaged, bringing the possibility of maintenance-free materials and structures. In this paper, a time dependent softening-healing law for self-healing quasi-brittle materials is presented by introducing limited material parameters with clear physical background. Strong Discontinuity embedded Approach (SDA) is adopted for evaluating the reliability of the model. In the numerical studies, values of healing parameters are firstly obtained by back analysis of experimental results of self-healing beams. Then numerical models regarding concrete members and structures built with self-healing and non-healing materials are simulated and compared for showing the capability of the self-healing material.
Available online 22 December 2017
The fatigue failure study of repaired aluminum plates by composite patches using Acoustic Emission
Publication date: Available online 24 December 2017
Source:Engineering Fracture Mechanics Author(s): Abdullah Maleki, Milad Saeedifar, Mehdi Ahmadi Najafabadi, Dimitrios Zarouchas The aim of this study is to investigate the failure of cracked aluminum plates repaired by one-side composite patches under fatigue loading using Acoustic Emission (AE) and fractography images. Rectangular specimens made of 6061 aluminum alloy with central through thickness pre-cracks were repaired using glass/epoxy laminated patches. The specimens were subjected to the fatigue loading and AE technique was employed to monitor the effect of the repair patch on the damage progression. First, different stages of damage evolution were studied based on the mechanical data and fractography images. Then, the AE energy utilized to characterize failure process of the specimens. To this aim, AE signals of the aluminum cracking and adhesive layer failure were discriminated according to their energy content. The effect of patch thickness and layup on the failure behavior of the specimens were also studied. Finally, it is concluded that AE is a powerful technique to characterize the failure process of a repaired cracked aeronautic structure by composite patches.
Available online 21 December 2017
A Lode-dependent Gurson model motivated by unit cell analyses
Publication date: Available online 22 December 2017
Source:Engineering Fracture Mechanics Author(s): Lars Edvard D
Available online 21 December 2017
Continuum thermodynamics of unusual domain evolution-induced toughening effect in nanocracked strontium titanate
Publication date: Available online 21 December 2017
Source:Engineering Fracture Mechanics Author(s): Le Van Lich, Takahiro Shimada, Jie Wang, Kairi Masuda, Tinh Quoc Bui, Van-Hai Dinh, Takayuki Kitamura This work is concerned with the analysis of both unusual mechanical and electric behaviors of nanoscale pre-cracked incipient ferroelectric of SrTiO3 at room temperature. A nonlinear thermodynamic model based on the Ginzburg-Landau theory is thus constructed and employed, which takes into account the appropriate mechanical boundary conditions, the electromechanical coupling between the polarization and the mechanical strain, and the self-strains of the ferroelastic and ferroelectric phase transformations. A large toughening effect is explored as a consequence of a softening nonlinear mechanical behavior, which characterizes for nanoscale SrTiO3, despite of the brittleness of bulk SrTiO3 ceramic. Depending upon applied strain, the large toughening and nonlinear mechanical behavior are attributed to unusual domain evolution of strain-induced polarization from the crack tip, in which a local-to-global transition of ferroelectric phase takes place from polarization vortex to hybrid structure of vortex and stripe domains, and finally to stripe domain structure with N
Available online 21 December 2017
Traction-Separation Relationship for Polymer-Modified Bitumen Under Mode I Loading: Double Cantilever Beam Experiment with Digital Image Correlation
Publication date: Available online 21 December 2017
Source:Engineering Fracture Mechanics Author(s): Sreehari Rajan, Michael A. Sutton, Ryan Fuerte, Addis Kidane The traction-separation law under Mode I loading for a polymer modified bitumen commonly used as an adhesive for 3 – tab roofing shingles is quantified. Double cantilever experiments are performed at three different loading rates (0.03 mm/min, 0.3 mm/min and 3 mm/min). Load-displacement measurements are synchronized with speckle image acquisition and the data analyzed to determine (a) J-integral, (b) cohesive zone end opening displacement and (c) the crack opening displacement (COD) as a function of crack extension. Imaging is performed using two stereo vision systems equipped for capturing speckle images of the DCB specimen at two different magnifications with fields of view of (a) 14 mm x 12 mm and (b) 170 mm x 140 mm. The stereo vision system used to acquire data at higher magnification is mounted on a translation stage and focused on a region close to the crack tip as the crack propagated. This stereo vision system is used to measure the strain fields near the crack tip and for measurement of crack opening displacement (COD) at 1 mm behind the current crack tip for a range of crack extensions. The second stereo vision system is used to visualize the process zone size and measure the strain fields over larger fields of view ahead of the crack tip. Assessment of the fracture surface for lower loading rates (0.03 mm/min and 0.3 mm/min) revealed a ductile type fracture (rough surface due to void growth in the process zone). For the highest loading rate (3 mm/min), the fracture surface is typical of the type seen during brittle fracture (shiny surface with striations), with intermittent rapid crack propagation events followed by crack arrest along clearly visible arrest fronts. Analysis of the data obtained for the two slower loading rates that exhibited ductile fracture throughout the entire growth process shows that the energy release rate Gc d = 70 J/m2, and the final separation,
Available online 19 December 2017
The Beneficial Effect of Full or Partial Autofrettage on the Combined 3-D Stress Intensity Factors for Inner Coplanar Crack Arrays and Ring Cracks in a Spherical Pressure Vessel
Publication date: Available online 21 December 2017
Source:Engineering Fracture Mechanics Author(s): M. Perl, M. Steiner The distributions of the combined 3-D Stress Intensity Factor (SIF), KIN=KIP +KIA , due to both internal pressure and autofrettage along the front of coplanar crack arrays as well as ring cracks emanating from the bore of an overstrained spherical pressure vessel are evaluated. The 3-D analysis is performed using the finite element (FE) method employing singular elements along the crack front. A novel realistic autofrettage residual stress field incorporating the Bauschinger effect is applied to the vessel. The residual stress field is simulated using an equivalent temperature field in the FE analysis. Numerous coplanar crack array configurations are analyzed as well as ring cracks of various depths. SIFs distributions are evaluated for coplanar crack arrays of densities
Available online 16 December 2017
Prediction of creep crack initiation behavior considering constraint effects for cracked pipes
Publication date: Available online 19 December 2017
Source:Engineering Fracture Mechanics Author(s): J.Z. He, G.Z. Wang, S.T. Tu, F.Z. Xuan The creep crack initiation (CCI) location and time of axial surface cracks with different sizes in cracked pipes have been comparatively predicted by finite element calculations based on creep ductility exhaustion model and creep fracture mechanics considering constraint effects by using two new creep constraint parameters (R
Available online 16 December 2017
Tearing energy and path-dependent J-integral evaluation considering stress softening for carbon black reinforced elastomers
Publication date: Available online 16 December 2017
Source:Engineering Fracture Mechanics Author(s): Mohammed El Yaagoubi, Daniel Juhre, Jens Meier, Thomas Alshuth, Ulrich Giese For carbon black reinforced Ethylene-Propylene-Diene Monomer Rubber (EPDM) fracture mechanics investigations by using a Single Edge Notched Tension sample (SENT) are presented. Filled elastomers under cyclic loading typically display inelastic effects like permanent set, strong nonlinear S-shaped stress-strain behaviour and stress induced softening (discontinuous damage) as well as cyclic softening (continuous damage) better known as Mullins effect. These unique properties give this material class an interesting and a complex aspect regarding the experimental observations and numerical modelling of fracture mechanics. In simulations with homogenous material, the J-integral given as the evaluation of the Eshelby stress tensor along a path integral around the crack shows no dependency on the chosen integration path. In contrast, dissipative materials show strong path dependency of the J-integral. When the chosen path is near to the crack tip, this effect is pronounced, due to the inelastic effects, which are very high at the crack tip compared to the rest of the sample. In the process zone, the J-integral value depends strongly on the chosen path around the crack tip. This phenomenon occurs due to the intensity of inelastic effects near the crack tip. The path-dependency of J-integral using the variational formulation of a crack problem in a dissipative material has been given in [16]. Stumpf and Le have proposed a new formulation of the boundary value problem for elastoplastic cracked body using variational formulation, where the finite deformation was considered. For cyclic displacement controlled loading, the elastomers show typical stress softening behaviour, i.e. the force-displacement curve of each cycle is lower than the previous cycle and higher than the following cycle. This occurs due to the continuous damage, whereby the bondings between polymer chains and the filler particles are partially damaged. At small external amplitudes, the stress softening effect is significant only in the vicinity of the crack tip, because of the hysteresis which is large compared to the rest of the sample. The evaluation of the J-integral for an SENT sample under cyclic displacement controlled loading shows clearly that the resulting energy flux at the crack tip decreases from the virgin curve until the last repetition. The values found are in good agreement with experimentally evaluated tearing energy. Hence J-integral evaluation while considering a stress softening reflecting material model can be a promising approach used for estimation of the crack propagation or for lifetime prediction.
Available online 16 December 2017
Mixed-mode fracture of a superelastic NiTi alloy: Experimental and numerical investigations
Publication date: Available online 16 December 2017
Source:Engineering Fracture Mechanics Author(s): B. Katanchi, N. Choupani, J. Khalil-Allafi, R. Tavangar, M. Baghani The evolution of mixed-mode fracture in a superelastic NiTi (50.8
Available online 16 December 2017
Modelling laminated glass beam failure via stochastic rigid body-spring model and bond-based peridynamics
Publication date: Available online 16 December 2017
Source:Engineering Fracture Mechanics Author(s): Siro Casolo, Vito Diana The failure of a laminated glass beam is investigated by two full discrete numerical approaches: a Rigid Body-Spring Model (RBSM) and a mesh-free numerical method arising from bond-based Peridynamics (PD). The brittle nature of the failure has been modelled and investigated by exploiting the discrete nature of these models, and specifically the PD which allows the bond/spring strengths to be explicitly related with the size and orientation of the defects in the structure. Strength values have been assigned randomly, within the beam, by a Monte Carlo simulation, according to Weibull statistical distributions calibrated on experimental results obtained from literature. For the first time, the differences and analogies of the two discrete approaches are shown and discussed together with the analysis of variability of the load capacity of the beam related to the statistical presence of flaws in the structure. Results show that, due to the heterogeneous strength properties of the numerical models and mechanical features of the inter-layer, multiple cracking stages can be distinguished for the structural element, thus different cumulative distribution function of limit load can be obtained.
Available online 15 December 2017
Investigations on fracture toughness and fracture surface energy of 3D random fibrous materials at elevated temperatures
Publication date: Available online 16 December 2017
Source:Engineering Fracture Mechanics Author(s): Datao Li, Wenshan Yu, Wei Xia, Qinzhi Fang, Shengping Shen In this study, model
Available online 15 December 2017
An Efficient Mixed-Mode Rate-Dependent Cohesive Fracture Model Using Sigmoidal Functions
Publication date: Available online 15 December 2017
Source:Engineering Fracture Mechanics Author(s): Oliver Giraldo-Londo
Available online 14 December 2017
On the validation of integrated DIC with tapered double cantilever beam tests
Publication date: Available online 15 December 2017
Source:Engineering Fracture Mechanics Author(s): Thiago Melo Grabois, Jan Neggers, Laurent Ponson, Fran
Available online 14 December 2017
A local approach to cleavage fracture modeling: An overview of progress and challenges for engineering applications
Publication date: Available online 14 December 2017
Source:Engineering Fracture Mechanics Author(s): Claudio Ruggieri, Robert H. Dodds This paper provides an overview of recent progress in probabilistic modeling of cleavage fracture phrased in terms of a local approach to fracture (LAF) and the Weibull stress concept. Emphasis is placed on the incorporation of plastic strain effects into the probabilistic framework by approaching the strong influence of constraint variations on (macroscopic) cleavage fracture toughness in terms of the number of eligible Griffith-like microcracks which effectively control unstable crack propagation by cleavage. Some recent results based on a modified Weibull stress model to predict specimen geometry effects on J c -values for pressure vessel grade steels are summarized in connection with an engineering procedure to calibrate the Weibull stress parameters. These results are compared against corresponding fracture toughness predictions derived from application of the standard Beremin model. Finally, the robustness of LAF methodologies, including specifically the Weibull stress approach, is critically examined along with a discussion of key issues and challenges related to engineering applications in fracture assessments of structural components.
Available online 13 December 2017
An analytical study of wave propagation in a peridynamic bar with nonuniform discretization
Publication date: Available online 14 December 2017
Source:Engineering Fracture Mechanics Author(s): Shank Kulkarni, Alireza Tabarraei In this paper, we use an analytical approach to study the propagation of a plane wave and its spurious reflection in a peridynamic bar using two different methods. In the first method, a coupled peridynamic–finite element approach is used in which peridynamic formulation is used in one part of the domain and finite element is used in the other part. In the second method, peridynamic formulation is used in the entire domain but the bar is discretized by two grids of different sizes. In both cases, the size of the grid of each zone does not change and the two grids share one node with each other. The incident wave travels from the finer grid toward the coarser grid. For the case when peridynamics is used on the entire domain, the size of the peridynamics horizon changes based on the size of the gird. For both cases, we investigate the impact of the relative size of the girds on the amplitude and energy of the transmitted and reflected waves. Our analytical and numerical results show that more spurious reflections occur when the size mismatch between the two grids is larger. In both cases, the issue of spurious wave reflection becomes more severe when the peridynamic horizon size increases. For the case of coupled peridynamic–finite element, even when the size of the two grids are the same, spurious wave reflection occurs which is due to the change in the formulation from a nonlocal to a local continuum. The spurious reflection reduces when the wavelength of the incident wave is large compared with the coarse grid.
Available online 13 December 2017
A Virtual Crack Extension Method for Thermoelastic Fracture using a Complex-variable Finite Element Method
Publication date: Available online 13 December 2017
Source:Engineering Fracture Mechanics Author(s): Daniel Ramirez Tamayo, Arturo Montoya, Harry Millwater A virtual crack extension (VCE) technique using the complex-variable finite element method (ZFEM) has been developed and demonstrated for thermoelastic fracture problems. This VCE approach provides an accurate computation of the energy release rate (G) as a byproduct of the complex-variable finite element analysis and obviates the use of energy conservation integrals such as the J-integral. The crack extension is induced using imaginary coordinates and a single global estimate of G is obtained as a sum of the element contributions. Numerical examples are provided for 2D, including a bimaterial cracked plate, axisymmetric, and 3D structures. The results indicate that the complex-variable VCE approach is of the same accuracy as the J-integral formulation.
Available online 12 December 2017
Evaluation of the energy release rate in mode I of asymmetrical bonded composite/metal assembly
Publication date: Available online 13 December 2017
Source:Engineering Fracture Mechanics Author(s): G. Zambelis, T. Da Silva Botelho, O. Klinkova, I. Tawfiq, C. Lanouette Composite structures assembled by bonding are widely found in different areas of high performance applications such as aeronautics. The energy release rate (G) is mainly used to predict fracture. However, in some special cases, this parameter serves to investigate the propagation, the rate or the stability of a crack. The main issue resides in the calculation of this energy release rate because it strongly depends on the crack geometry and the loading mode. An energetic criterion based on the compliance method was chosen, assuming that the release of potential energy is transformed in surface energy due to the creation of wider cracks (new surfaces). To investigate the properties of an asymmetrical composite/metal bonded structure, modified Double Cantilever Beam (DCB) specimens were tested in mode I. The fracture toughness and the fatigue behavior were evaluated by experimental means, finite elements modeling (FEM) and linear elastic fracture mechanics (LEFM) theories. Timoshenko and Kanninen theories, experimental and FEM results were compared on an R-curve. A modified Kanninen theory was then proposed, to take into account the specific assembly design. As a result, the Paris’ law was built for that situation. The objective of this work was to adapt and validate a non-standard fatigue compliance methodology which calculates the energy release rates in mode I, for asymmetrical bonded structures.
Available online 12 December 2017
Axisymmetric thermo-elastic field in an infinite one-dimensional hexagonal quasi-crystal space containing a penny-shaped crack under anti-symmetric uniform heat fluxes
Publication date: Available online 12 December 2017
Source:Engineering Fracture Mechanics Author(s): P.-D. Li, X.-Y. Li, G.-Z. Kang This paper is dedicated to investigating the problem of an infinite one-dimensional hexagonal quasi-crystal medium weakened by a penny-shaped crack and subjected to a pair of anti-symmetric and identical uniform heat fluxes. In view of the anti-symmetry with respect to the crack plane, this problem is formulated by a mixed boundary value problem of the half-space. Based on the general thermo-elastic solution, the mixed boundary value problem is solved by means of the generalized potential theory method. The thermo-elastic field variables in the entire three-dimensional space are explicitly expressed in terms of elementary functions. Some important physical quantities on the crack plane, e.g., temperature, crack slip displacement, shear stress and stress intensity factor, are also presented in closed-forms. Numerical calculations are carried out to validate the present analytical solution and to graphically show the distribution of the thermo-elastic coupling field around the crack. The present solution may be served as a benchmark for the experimental investigations by infrared-thermography technique.
Available online 12 December 2017
Experimental and variational-based analytical investigation of multiple cracked angle-ply laminates
Publication date: Available online 12 December 2017
Source:Engineering Fracture Mechanics Author(s): Bijan Mohammadi, Hamed Pakdel A unit cell based method is developed based on variational principles to derive the stress state and effective mechanical properties of angle-ply laminates of type [
Available online 12 December 2017
EMTSN criterion for evaluating mixed mode I/II crack propagation in rock materials
Publication date: Available online 12 December 2017
Source:Engineering Fracture Mechanics Author(s): M.M. Mirsayar, A. Razmi, M.R.M. Aliha, F. Berto This paper investigates the results of brittle fracture in rock materials subjected to the mixed mode I/II loading using different fracture criteria. Two sets of mixed mode fracture test data in the entire range of mode mixity, from pure mode I to pure mode II, reported in the literature for semi-circular and triangular shape specimens and subjected to three point bend loading (i.e. SCB and ECT specimens) are utilized to study the brittle fracture in two marble rocks. First, the onset of fracture initiation is examined by different conventional fracture criteria including Maximum Tangential Stress (MTS) and Maximum Tangential Strain (MTSN) criteria. It is shown that these two conventional fracture criteria, which only consider singular crack tip stress/strain terms, are not able to accurately predict the mixed mode fracture test data. The experimental mixed mode fracture toughness data are then predicted by an extended version of the maximum tangential strain (EMTSN) criterion which takes into account the effect of first nonsingular strain term as well as the singular strain components. It is found that both mixed mode fracture toughness results of the investigated rock materials and the crack propagation direction can be predicted successfully by the EMTSN criterion.

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Available online 11 December 2017
An investigation of non-straight fissures cracking under uniaxial compression
Publication date: Available online 12 December 2017
Source:Engineering Fracture Mechanics Author(s): G.W. Ma, Q.Q. Dong, L.F. Fan, J.W. Gao Prediction of cracking is greatly important when evaluating the stability and safety of underground engineering projects. In this paper, 3D-printed samples with a single non-straight fissure are uniaxially compressed, and the effects of the inclination angle and effective curvature on the cracking are observed. A simplified approach is proposed for the determination of tip cracking and non-tip cracking of the non-straight fissure. The accuracy of the prediction is validated by the uniaxial tests. The results show that the cracking behavior of non-straight fissures is different from that of straight fissures with respect to the occurrence of non-tip cracking. Moreover, cracking is significantly influenced by the geometric parameters of the non-straight fissure. In addition, the proposed approach can be utilized to predict the cracking of non-straight fissures with acceptable accuracy.
Available online 9 December 2017
A phenomenological approach to fatigue with a variational phase-field model: The one-dimensional case
Publication date: Available online 11 December 2017
Source:Engineering Fracture Mechanics Author(s): Roberto Alessi, Stefano Vidoli, Laura De Lorenzis We propose a new variational fatigue phase-field model. The basic idea of the model is to let the fracture energy decrease as a suitably defined accumulated strain measure increases, which is obtained by introducing a dissipation potential which explicitly depends on the strain history. This amounts to a phenomenological description of a multitude of microscopic material degradation mechanisms, that are responsible for the macroscopic evidence of fatigue effects. In this first step of a longer term project, the analysis is limited to the simplest possible setting, namely: linear elasticity, brittle material behavior, symmetric response in tension and compression. However, in this variational framework, the extension to include additional material phenomena, such as plasticity, is straightforward. We show the results of numerical simulations based on a solution strategy devised from the variational approach. Already with the choice of simple constitutive functions, based on few key constitutive parameters, the present model is capable to describe typical
Available online 9 December 2017
Analytical flaw assessment
Publication date: Available online 9 December 2017
Source:Engineering Fracture Mechanics Author(s): U. Zerbst, M. Madia The paper provides a review on analytical flaw assessment methods with the focus on fracture under monotonic loading and fatigue crack propagation. The first topic comprises linear elastic as well as elastic-plastic fracture mechanics approaches. It essentially follows their historical development. Topics which are separately discussed are reference/limit loads, the treatment of secondary stresses, strength mismatch, constraint, unstable crack propagation (monotonic R-curve analyses) and statistical aspects. With respect to fatigue crack propagation the analytical treatment of crack closure and constraint and the determination of the cyclic elastic-plastic crack driving force is discussed. Finally, cyclic R-curve analyses are briefly addressed.
Available online 9 December 2017
Applications of fracture mechanics in assessing integrity of hydrogen storage systems
Publication date: Available online 9 December 2017
Source:Engineering Fracture Mechanics Author(s): Ashok Saxena, Kevin Nibur, Amit Prakash This paper addresses the challenges in designing high pressure, durable, safe, and cost-effective vessels for storage of gaseous hydrogen and the role of fracture mechanics in meeting those challenges. The design life limiting material property for vessels made from tempered martensitic steel is the environment assisted fatigue crack growth rate (FCGR) that depends on
Available online 9 December 2017
Molecular dynamics modeling of crack propagation in titanium alloys by using an experiment-based Monte Carlo model
Publication date: Available online 9 December 2017
Source:Engineering Fracture Mechanics Author(s): Xiangguo Zeng, Tixin Han, Yang Guo, Fang Wang Based on extensive experiments at the microscopic level, it was found that the grain sizes of TA1 titanium alloys exhibited a statistical nature, and in turn, the resultant distribution was achieved by a data fit. The Monte-Carlo method was employed to obtain a model size for molecular dynamics simulations. The melting point and lattice constants of the alloys were calculated using LAMMPS software with the model dimension. A comparison of numerical results and published experimental results was presented to demonstrate that such a method provides a reasonable domain that is beneficial to molecular dynamics modeling. Afterwards, a cohesive element model along the effective simulation region was established, and then the relationship between the traction and crack opening displacement for alloys was presented. The characteristic parameters obtained from the resultant curve were utilized to embed cohesive elements, and the real-life crack propagation behavior was further mimicked through finite element analysis. The results showed that the predicted fracture toughness agreed well with the experimental data, highlighting the suitability of the new analytical approach for predicting crack growth behavior.
Available online 9 December 2017
Effect of displacement rate and subcritical crack growth on J-R curves of API X65 steels in sour environment
Publication date: Available online 9 December 2017
Source:Engineering Fracture Mechanics Author(s): C. Finamore, E.M. Castrodeza, J.E. Perez Ipi
Available online 9 December 2017
Resistance curves of short-fiber reinforced methacrylate-based biomedical composites
Publication date: Available online 9 December 2017
Source:Engineering Fracture Mechanics Author(s): Michael Wendler, Renan Belli, Martina Schachtner, Gudrun Amberger, Anselm Petschelt, Tobias Fey, Ulrich Lohbauer
Available online 9 December 2017
Averaged strain energy density criterion for rupture assessment of cracked rubbers: A novel method for determination of critical SED
Publication date: Available online 9 December 2017
Source:Engineering Fracture Mechanics Author(s): M. Heydari-Meybodi, M.R. Ayatollahi, F. Berto In the present study, the application of averaged strain energy density (ASED) criterion has been extended to hyperelastic materials. Because of the material and geometry nonlinearities, commonly known for rubber-like materials, the use of conventional relations for determining the criterion parameters is no longer allowable. Therefore, by taking the advantage of a simple uniaxial state of stress field ahead of the crack tip in hyperelastic materials, a novel method has been proposed for determining the critical value of strain energy density. The sound agreement between the theoretical estimates based on the employed ASED criterion and the experimental data, taken from the literature, confirms the suitability of the proposed method.
Available online 9 December 2017
Brittle crack propagation/arrest behavior in steel plate – Part III: Discussions on arrest design
Publication date: Available online 9 December 2017
Source:Engineering Fracture Mechanics Author(s): Kazuki Shibanuma, Fuminori Yanagimoto, Katsuyuki Suzuki, Shuji Aihara The brittle crack arrest design of a steel plate is discussed based on systematic model simulations. The simulation results show that an essential crack arrest temperature (ECAT) exists in the temperature dependence curve of arrest toughness. Based on the investigations of the possible factors influencing the temperature dependence of the arrest toughness and the ECAT, an estimation formula is proposed for the required arrest toughness at the design temperature for arbitrary values of the plate strength and thickness. The prediction results obtained using the estimation formula are consistent with the experimental results obtained from past wide duplex crack arrest tests.
Available online 7 December 2017
Estimation of crack initiation stress and local fracture toughness of Ni-alloys 945X (UNS N09946) and 718 (UNS N07718) under hydrogen environment via fracture surface topography analysis
Publication date: Available online 9 December 2017
Source:Engineering Fracture Mechanics Author(s): Dhinakaran Sampath, Robert Akid, Roberto Morana The variation in mechanical properties of Ni-alloys 945X (UNS N09946) and 718 (UNS N07718) during slow strain rate tests (SSRTs) under two different test protocols, both involving hydrogen (H) charging, was examined through fracture surface analyses. The test protocols used were: H pre-charging of the specimen prior to in-situ H charging during SSRT (P1) and in-situ H charging during SSRT without pre-charging (P2). The ductility (elongation to failure) of Ni-alloy 945X was observed to be inferior to the ductility of Ni-alloy 718 under given SSRT conditions. FRActure Surface Topography Analysis (FRASTA) was applied to evaluate the fracture events during SSRT from crack initiation to final fracture. The fracture events were then correlated with the stress-elongation response to define the stress at which crack initiation occurs. Crack initiation occurs below the material’s yield stress under P1 and above its yield stress under P2 for alloy 945X. On the other hand, crack initiation stress for alloy 718 was found to be higher than the material’s yield stress under both test protocols. The local fracture toughness was estimated by measuring the Crack Tip Opening Displacment (CTOD) obtained from line profile analysis, based on fracture surface topography data, over the H induced fracture surface area. The average local fracture toughness of alloys 945X and 718 under H decreases significantly when compared with their in-air fracture toughness values and the reduction is higher for alloy 945X than that for alloy 718. Under a H environment, the inferior ductility of Ni-alloy 945X, compared to that of Ni-alloy 718, may be due to significant reduction in the fracture toughness of alloy 945X. The operative mechanism of H assisted cracking in these Ni-alloys is explained based on the effect of microstructural condition on H enhanced - slip localisation and decohesion.

T-stress effects on fatigue crack growth – Theory and experiment
Publication date: Available online 7 December 2017
Source:Engineering Fracture Mechanics Author(s): M.R. Ayatollahi, M. Rashidi Moghaddam, F. Berto The effects of specimen geometry on the fatigue crack growth rate and the number of elapsed cycles have been investigated experimentally and theoretically for Al 7075-T6 using four different cracked specimens with positive and negative T-stresses. All the specimens have been tested under high cycle fatigue loading. An energy-based method, namely the generalized strain energy density (GSED) criterion has been proposed to estimate the fatigue crack growth rate and the number of elapsed cycles by considering the T-stress effects. It is shown that the proposed criterion can provide significantly improved predictions for the fatigue crack growth behavior of the pre-cracked specimens.
view: 183

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