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Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The influence of moisture content and density on fracture properties of unmodified and thermally modified spruce wood (Picea abies) has been investigated. Thermal modification was done at 180 °C, 200 °C, and 230 °C, and samples were conditioned at 20%, 44%, 76%,% and 88% relative humidity. Double cantilever beam specimens with TL and RL orientation were used for testing. The crack length was determined via digital image correlation, and the compliance of the specimen was determined via multiple loading-unloading cycles of the specimen. The strain energy release rate was calculated, which decreased with an increasing degree of modification and increased with increasing wood moisture content. The analysis showed that the strain energy release rate increased more with wood moisture content for unmodified samples, while the dependence of the release rate on moisture was less obvious for modified samples. The strain energy release rate values are higher in the TL orientation than in the RL orientation, while the crack length has no significant influence. The highest strain energy release rate was 0.256 N/mm for the unmodified TL specimens exposed to 88% relative humidity, and the lowest was 0.071 N/mm for the RL orientation of the thermally modified specimens at 230 °C and then exposed to 88% relative humidity. From all measurements, functions were fitted to calculate the strain energy release rate as a function of orientation, degree of modification, moisture content, and density of the spruce wood, which can be used to calculate the strain energy release rate for any combination of the factors studied. [ABSTRACT FROM AUTHOR]

In this work, the distribution of the strain energy release rate (SERR) at the crack front of carbon fiber‐reinforced polymer laminates with elastic coupling is analyzed using the edge ring crack torsion (ERCT) test configuration. The SERR at the delamination front is calculated by virtual crack closure technique (VCCT). Elastic coupling laminates, including bending‐extension (BE) and bending‐torsion (BT) ones with different stacking sequences are studied. The effect of two different loading boundary conditions on the SERR distribution of laminates is also investigated. The results demonstrate that the distribution of SERR is significantly affected by the elastic coupling and stacking sequence. In addition, elastic coupling introduces mode I and mode II components in the ERCT configuration. However, their contribution is negligible. In comparison to unidirectional laminates, better uniformity of SERR distribution can be obtained in the BE and BT laminates. Pure mode III fracture without non‐uniformity is achievable by designing the elastic coupling of laminates. The obtained results can provide guidance for the standardization of the ERCT configuration used for the measurement of mode III fracture toughness. [ABSTRACT FROM AUTHOR]

The double cantilever beam (DCB) is the most acceptable geometry to obtain the critical strain energy release rate (GIc) of adhesive joints under Mode I. However, there are still some areas of uncertainty in the standardized compliance methods recommended by the ISO and ASTM standards in terms of accuracy in estimating the compliance of a bonded double cantilever beam and, consequently, GIc. In this work, an investigation of the standardized compliance methods for fracture characterization of bonded joints under Mode I is conducted, employing a finite element model to obtain the compliance of a double cantilever beam, considering different crack lengths. The compliance values determined from the finite element model are compared with those recommended by the standards. It is concluded that the standardized compliance methods are very sensitive to issues derived from crack length measurements. The crack length correction methodology proposed by the corrected beam theory is inadequate, which can lead to a wrong interpretation of the structure's behavior and the structural integrity assessment. The best approach to obtain the compliance of a double cantilever beam in respect of crack length is to use a compliance calibration method, fitting an expression for the experimental curve. [ABSTRACT FROM AUTHOR]

The present work investigates the equivalent crack methodology by considering the Double Cantilever Beam (DCB) test to obtain the strain energy release rate of adhesive joints, using different compliance methods rather than the Compliance Based Beam Model (CBBM). This procedure allows the determination of the crack length based on the compliance of the specimen, which avoids crack growth monitoring during tests. The compliance values predicted by the analytical methods were studied and compared with a computational model, considering different crack lengths. Results showed that the preciseness of the crack length obtained by the equivalent crack method relies on the accuracy of the respective compliance method in predicting the load-displacement curve of a bonded double cantilever beam. The Euler–Bernoulli and Timoshenko beam models are not recommended to obtain an equivalent crack length based on the specimen's compliance since they overestimate the actual crack length. Best crack length predictions were obtained using compliance methods based on the beam-on-elastic foundation models, including an elastic interface to model the adhesive layer joint. Similar strain energy release rate results were found for different compliance methods when using the equivalent crack methodology. [ABSTRACT FROM AUTHOR]

A new comprehensive criterion has been presented to assess the fracture response in cracked wood as natural orthotropic material based on the maximum strain energy release rate criterion (SER) under mixed-mode I/II loading. A general off-axis case is assumed for desired crack-fiber angle. The most important purpose of the proposed paper is to accurately predict the fracture behavior of orthotropic materials. In this article, two influencing factors on fracture assessment are discussed comprehensively. The first one is employing the accurate model of the orthotropic material named as reinforcement isotropic solid (RIS) model, and the second factor is considering the effects of the T-stress term. The SER concept is extended in combination with the reinforcement isotropic solid (RIS) model for orthotropic materials. Using RIS, a mapping between the stress fields in the isotropic and orthotropic materials is established. In this article, the reinforcement coefficients are extracted using a new method called "corresponding stresses" for the desired crack-fiber angles. These coefficients depend on the mechanical properties of the orthotropic material and crack-fiber angle. The results obtained from the curves of reinforcement coefficients indicate that as the crack-fiber angle increases, the reinforcement coefficients decrease drastically. The SER around the crack tip is extracted considering the normal and shear stress fields and the non-singular T-stress term. Using extracted results, it can be shown that the T-stress term has a serious role in predicting the crack behavior of orthotropic materials. It is practically impossible to calculate the fracture toughness of pure modes I and II when the crack is not along the fibers. Based on the proposed extended maximum strain energy release rate (EMSER) criterion, a new concept called equivalent fracture toughness (EFT) is introduced as a fracture property of orthotropic materials. To validate and evaluate the accuracy of the EMSER criterion, the fracture limit curves (FLCs) for different angles between crack and fibers are compared with available experimental data from the literature. Compared to other criteria, a prominent correlation is obtained between the theoretical results evaluated by the EMSER criterion and available test data. [ABSTRACT FROM AUTHOR]

Single shear or single lap joints are the most prevalent type of adhesive joints used in advanced engineering applications, where they are exposed to fatigue loadings in their services. Although their mechanical performances under static loading have been investigated extensively, the studies related to the fatigue performances were limited. For that purpose, single lap joints' (SLJs) reaction to fatigue tensile loading was studied by varying the adherend thickness (3 mm to 6 mm) and fatigue load (3250 N to 1500 N). ABAQUS/Standard was used to create its advanced FE model. To represent the progressive damage in the adhesive layer, the fatigue damage model via the Paris Law, which links the rate of the crack expansion to the strain energy release rate (SERR), was integrated into the cohesive zone model with bi-linear traction–separation characteristics. The model was written in a UMAT subroutine. The developed model was validated using experimental data from the literature. The crack initiation cycle (Ni), the failure cycle (Nf), the fatigue load limit, the strain energy release rate, the crack propagation rate, and variation of stress components with their dependency to design parameters were investigated in depth. It was found that the service life of the SLJs with thicker adherends was more responsive to the amount of stress applied. When exposed to lesser loads, the SLJs' life span changed more noticeably. [ABSTRACT FROM AUTHOR]

The characteristics of the debonding process zone involving macroscale, microscale, and nanoscale mechanisms along CNT interface influence the fracture behavior of nanocomposites and their structural integrity. In current article, a multi‐scale and multi‐mechanism modeling approach with a cylindrical RVE comprising CNT, interphase, and matrix is developed to assess such damage progression and energy dissipation occurring at the nanoscale. The model considers the dominant damaging phenomena emerging in CNT/epoxy nanocomposites, that is, CNT debonding with an interphase zone around nanoparticles, cavitation, and plastic deformation of nanovoids. Enhancement of fracture toughness with the weight fraction of CNT is investigated with a qualitative variation of geometric and mechanical properties of the interphase, cavitation, and plastic yielding adopting strain energy release rate procedures. The fracture energy is shown to be critically influenced by the stiffness ratio of interphase to the matrix, interphase thickness, and hardening exponent. The model is validated using experimental and analytical data. Highlights: The model has harmonized the relevance of the macro‐, micro‐, and nanoscale.The multi‐scale and multi‐mechanism models have evaluated the zone shielding fracture.Dominant mechanisms, that is, CNT debonding, cavitation, and plastic yielding are studied.The interphase modulus, thickness, and hardening exponent, all impact fracture toughening. [ABSTRACT FROM AUTHOR]

Producing structured mesh at the immediate vicinity of the crack front for three-dimensional(3D)crack modelling is a very time consuming and difficult task.A geometry feature based method for 3D crack modelling based on virtual crack closure-integral method(VCCM)for the tetrahedral finite element is proposed,and the implementation details of employing tetrahedral finite elements for 3D crack modelling on the basis of ABAQUS are described.On this basis,a 3D crack analysis package is developed by applying the Python programming language combined with NumPy and SciPy to automate the whole process of crack problem analysis.The stability and robustness of the 3D crack automated modelling is improved by employing tetrahedral finite element.The numerical examples are in good agreement with the results in the literature,proving the accuracy and reliability of the modelling method.

Laminated composites with thermoset matrices are already well established in major engineering fields like automotive and aviation. The primary drawbacks of such thermoset-based composites are the high cycle times required during manufacturing and their limited potential for recycling. Providing an alternative to thermoset-based composites, thermoplastic matrix materials gained more and more momentum by addressing these previously mentioned drawbacks. The preferred manufacturing technique for these materials employs fiber-reinforced thermoplastic tapes consolidated and formed together with a compatible substrate. The most critical aspect for all these applications is the stress or load transfer between the thermoplastic tapes and the substrate. If the interface is too weak and fails prior to the substrate or tape, a high amount of theoretical mechanical performance is lost. The presented research investigates the influence of variations in manufacturing parameters, within the industrially relevant process window, on the interface strength of the final composite. The investigated composite material consists of PPGF UD tapes consolidated on a PPGF mat substrate. In particular, the influence of the consolidation parameters of pressure, temperature, and time are of special interest. The results of this work reveal a 400% increase in the measured mean strain energy release rate upon increasing the consolidation time from 60 s to 120 s at a consolidation temperature of 230 °C and a pressure of one bar. In contrast to this, an increase in the consolidation pressure, at constant temperature and time, leads to a minor improvement in the GC value of 20%. For testing and characterizing the corresponding interface properties, a mandrel peel testing setup was employed. [ABSTRACT FROM AUTHOR]

Part-through-the-width ply break followed by interfacial delamination is a common mode of failure in laminated FRP composites. Resistance to interfacial delamination being a matrix dominated property, the present work investigates the influence of adding CNTs to adhesive resin on the resistance to the delamination at the interface. A laminate with a part-through-the-width broken ply is considered with carbon fiber as the main reinforcement and epoxy mixed with CNTs as the matrix. A full 3D finite element (FE) analysis in conjunction with virtual crack closure integral (VCCI) has been carried out to determine critical strain energy release rate (SERR) as a measure of resistance to delamination growth. Properties of the matrix and the lamina corresponding to different weight percentage of CNTs in epoxy obtained using micromechanics have been used. Results show that addition of a small weight percent of CNTs to the epoxy leads to a significant enhancement of resistance to delamination at the interface of part-through-the-width broken ply and the intact ply and the enhancement is only up to a certain limit of weight percent beyond which the resistance decreases again. [ABSTRACT FROM AUTHOR]

On the basis of material and fracture mechanics theory, the flexible matrix and stiffness matrix of crack elements are derived using the strain energy release rate and the Timoshenko beam element model of six degrees of freedom. In accordance with the geometric relationship between the opening and closing of crack, time-varying centroid coordinates of the crack are fixed by neutral axis theory, and the position of the crack closing line is obtained depending on the time-varying centroid coordinates, which describe the crack's breathing characteristics. On this basis, a time-varying centroid coordinate model is proposed and compared with the sinusoidal model, the Gaozhu model, and the zero-stress intensity factor model. Results show that the proposed model has more coupling characteristics. Finally, the flexibility matrix of oblique, straight, and semielliptical crack elements is derived, and the breathing mechanism of three kinds of cracks is studied. [ABSTRACT FROM AUTHOR]

The present work illustrates the influence of bimodulus polarity and curing stress on interface delamination in skin stiffener runout. In contrast to unimodular assumptions, the bimodulus skin stiffener's fracture behavior is much more unsymmetrical depending on the sequential thermo-mechanical loading. The numerical study has been done to demonstrate debonding and delamination with the help of the Virtual Crack Closure Technique on compliant runout configuration under varying bimodular ratios. The modified design of the runout has been displayed, and different design configurations have been compared to determine the merits of the design of skin-stiffener runout: a baseline configuration, a tip-tapered configuration, and notch-tapered configuration with the functionally graded bimodular property. A three-dimensional finite element-based analysis has been performed on these configurations to evaluate the strength and damage tolerance. Also, the Strain Energy Release Rate has been assessed for non-identical loading and boundary conditions. It has been found that bimodularity significantly reduces failure growth. This analysis aims to decelerate the interfacial fracture extension rate by introducing functionally graded bimodularity in the structure. [ABSTRACT FROM AUTHOR]

In this paper, the energy release energy corresponding to the unit crack propagation obtained from the displacement-controlled load-displacement plot is equalized to the elastic energy release rate, and the variation of stiffness based on the crack length is obtained. For this purpose, instead of measuring the amount of crack mouth opening in the single edge-cracked tensile specimen, the extensometer elongation amount was taken in the middle part of the specimen. Thanks to the equality of the stiffness to the crack length, the transformation of the load-displacement curve into the material resistance curve was realized. [ABSTRACT FROM AUTHOR]

A delamination propagation analysis of a composite beam specimen was performed in this research. To estimate the displacement field of laminates the Layer wise theory was used and the Virtual Crack Closure Technique (VCCT) was developed to predict and calculate crack growth and delamination based on it. Interface elements were defined as numerical layers that existed between any two adjacent layers that there is a possibility of delamination. Double Cantilever Beam (DCB) specimens were used to determine the Strain Energy Release Rate in Mode I of the examined material. The numerical technique of predicting delamination in composite laminates was handled using MATLAB code. The Load-Displacement behavior in delamination propagation was reported. In this study it was shown that the current developed method is in good agreement with the finite element approach and Analytical solution. Finally, the influence of different factors on the Reaction Force and Strain Energy Release Rate during the delamination process and crack growth in the composite beam were studied in mode I. [ABSTRACT FROM AUTHOR]

Purpose: To assess the influence of titanium tetrafluoride (TiF4) solution on the adhesion of composite cement to commercially pure titanium (cp Ti). Materials and Methods: cp Ti plates with dimensions of 30 mm x 8 mm x 1.5 mm were machined and polished. The specimens were divided into seven groups according to the surface treatment as follows: group 1: control (machined); group 2: sandblasted with 110 μm Al2O3; group 3: hydrofluoric acid (HF); group 4: TiF4 (5%-5 min); group 5: TiF4 (5%-10 min); group 6: TiF4 (10%-5 min); and group 7: TiF4 (10%-10 min). One type of composite cement (Multilink Speed) was applied to each group for assessing the bond strength using strain energy release rate (G-value, J/m²) test. SEM analysis and surface roughness evaluation of cp Ti were carried out after treatment. The debonded specimens were examined with a stereomicroscope and SEM. Data were analyzed by the Kruskal-Wallis and Dunn's multiple comparison tests. Statistical significance was set at the 0.05 probability level. Results: All the tested groups showed significantly higher bond strengths compared with the control group (p < 0.05). Surface treatment of cp Ti with TiF4 (10%-10 min) showed higher bond strength compared with sandblasting and HF groups (p < 0.05). Surface topography of treated cp Ti showed alterations in surface roughness and morphology. Conclusion: Adhesion between composite cement and cp Ti could be improved by using TiF4 (10%-10 min) solution prior to composite cement application as an alternative technique to sandblasting and HF. [ABSTRACT FROM AUTHOR]

The wedge-loaded asymmetric double cantilever beam (WADCB) test is an experimental method to determine the mixed-mode I/II fracture toughness of composite materials by inserting a wedge into the specimen along a potential delamination path. Whilst the current closed-form solution for the ADCB test assumes identical forces acting in both specimen arms, this manuscript proposes a refined closed-form solution allowing for different forces acting on both specimen arms, which is thought to be more general and more rigorous. WADCB tests were carried out on composites made from Torayca T700SC/2592 unidirectional prepreg. Both the current and the refined closed-form solution were used to analyze the data, and some differences were found in the predictions, indicating that the forces in the two specimen arms are indeed not identical. [ABSTRACT FROM AUTHOR]

This paper presents an estimation of natural frequencies for free vibration of a cantilever beam in the presence of an inclined edge crack using linear elastic fracture mechanics. The Strain Energy Release Rate (SERR) approach is employed to compute the compliance coefficients for the edge crack inclined to the longitudinal axis at an arbitrary angle. A full compliance matrix under the general loading is presented and corresponding definitions of the compliance coefficients are given. Calculations of natural frequencies are carried out for both Timoshenko and Euler-Bernoulli beams under the influence of load P1, P3, and P5. Contribution to strain energy coming from various modes of fracture is accounted for by using stress intensity factors obtained numerically using ABAQUS 6.14 software. The effect of the crack on transverse and longitudinal natural frequencies is studied for different crack locations, depths, and inclination angles. Experiments are performed on short and long beams for a set of parameters for comparison purposes. It is found that the natural frequencies estimated by the proposed method compare well with the frequencies obtained experimentally for both beams. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Polytechnic is the property of Journal of Polytechnic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The use of composite materials is on the rise in different engineering fields. The main advantage of these materials for the aerospace industry being their low weight for excellent mechanical qualities. The analysis of failure modes, such as delamination, of these materials has received great attention from researchers. This paper proposes a method to evaluate the mode I Strain Energy Release Rate (SERR) of sandwich structures. This method associates a two-dimensional mixed finite element with virtual crack extension technique for the analysis of interfacial delamination of sandwich beams. The cases of a symmetrical Double Cantilever Beam (DCB) and a asymmetrical Double Cantilever Beam (UDCB) have been analyzed in this study.The comparison of the results obtained by this method with those found in the literature shows efficiency and good precision for the calculation of Strain Energy Release Rate (SERR).

Single shear or single lap joints are the most prevalent type of adhesive joints used in advanced engineering applications, where they are exposed to fatigue loadings in their services. Although their mechanical performances under static loading have been investigated extensively, the studies related to the fatigue performances were limited. For that purpose, single lap joints’ (SLJs) reaction to fatigue tensile loading was studied by varying the adherend thickness (3 mm to 6 mm) and fatigue load (3250 N to 1500 N). ABAQUS/Standard was used to create its advanced FE model. To represent the progressive damage in the adhesive layer, the fatigue damage model via the Paris Law, which links the rate of the crack expansion to the strain energy release rate (SERR), was integrated into the cohesive zone model with bi-linear traction–separation characteristics. The model was written in a UMAT subroutine. The developed model was validated using experimental data from the literature. The crack initiation cycle (Ni), the failure cycle (Nf), the fatigue load limit, the strain energy release rate, the crack propagation rate, and variation of stress components with their dependency to design parameters were investigated in depth. It was found that the service life of the SLJs with thicker adherends was more responsive to the amount of stress applied. When exposed to lesser loads, the SLJs’ life span changed more noticeably.

The delamination phenomenon in sandwich panels occurs in the form of face/core debonding. The grooved foams are usually employed in curved sandwich structures for easier formability and better adhesion. In this research, the debonding toughness of facesheet to the core in a sandwich beam with grooved core is investigated using numerical and experimental methods. The sandwich beam consisted of two Kevlar 49/polyester facesheets and a polyurethane foam core. To obtain the values of strain energy release rate, the Cracked Sandwich Beam (CSB) specimen along with the Modified Beam Theory (MBT) method was used for the data reduction of the test results. In the numerical part, a model based on the cohesive zone theory was employed to simulate the crack growth in the specimens. Comparison of the numerical and experimental load–displacement curves indicated that the proposed model can reasonably predict the behavior of the structure under similar loading conditions. The effect of foam-related parameters such as the number and width of core grooves on crack growth resistance was examined numerically. The results showed that increasing the number and width of the grooves enhanced the resistance of the sandwich beams against the growth of interfacial cracks. [ABSTRACT FROM AUTHOR]

The adhesive bonding strength of the membrane layers between the asphalt concrete surface layers and the decks of steel bridges has a strong influence on the fatigue life of orthotropic steel deck bridges (OSDBs). The interfacial properties between the membrane and the layers bonded to it have not been extensively studied in the current orthotropic steel deck bridge system. For the adequate characterisation of the adhesive-bonding strength of various membranes and surrounding materials on OSDBs and for the collection of the necessary parameters for finite element model, details of the membrane adhesion test (MAT) are introduced and simulated by using the adhesive traction-separation interface element which was developed in a companion paper to this contribution (Liu, X., Kasbergen, C., Li, J., & Scarpas, A. (2019). Modelling of membrane bonding response: part 1 development of an adhesive contact interface element. International Journal of Pavement Engineering). Parametric studies of the adhesive contact element utilised for modelling the membrane bonding layer in the MAT test have been performed on the basis of the combination of different critical strain energy release rates and the characteristic opening length in the constitutive model. Comparison of membrane deformation profiles and the in-time debonding force distribution between experimental observations and finite element simulations have been presented. [ABSTRACT FROM AUTHOR]

This paper comprehensively reviews the various experimental and numerical techniques, which were considered to determine the fracture characteristics of the cortical bone. This study also provides some recommendations along with the critical review, which would be beneficial for future research of fracture analysis of cortical bone. Cortical bone fractures due to sports activities, climbing, running, and engagement in transport or industrial accidents. Individuals having different diseases are also at high risk of cortical bone fracture. It has been observed that osteon orientation influences cortical bone fracture toughness and fracture mechanisms. Apart from this, recent studies indicate that fracture parameters of cortical bone also depend on many factors such as age, sex, temperature, osteoporosis, orientation, location, loading condition, strain rate, and storage facility, etc. The cortical bone regains its fracture toughness due to various toughening mechanisms. Owing to these factors, several experimental, clinical, and numerical investigations have been carried out to determine the fracture parameters of the cortical bone. Cortical bone is the dense outer surface of the bone and contributes to 80%–82% of the skeleton mass. Cortical bone experiences load far exceeding body weight due to muscle contraction and the dynamics of motion. It is very important to know the fracture pattern, direction of fracture, location of the fracture, and toughening mechanism of cortical bone. A basic understanding of the different factors that affect the fracture parameters and fracture mechanisms of the cortical bone is necessary to prevent the failure and fracture of cortical bone. This review has summarized the advancement considered in the various experimental techniques and numerical methods to get complete information about the fracture mechanisms of cortical bone. [ABSTRACT FROM AUTHOR]

To compare ceramic-coating techniques versus conventional techniques on bonding between composite cements and zirconia by means of strain energy release rate (G c , J/m2). Two sizes of zirconia bars (30 mm × 8 mm × 1.5 mm and 14.8 mm × 8 mm × 1.5 mm) were fabricated. Two smaller bars were treated and cemented to the surface of a large bar using one of the following methods: (i) AlN-nano-structured alumina coating with RelyX Unicem 2; (ii) HOT-DCM hotbond coating with G-Multi Primer and G-Cem Linkforce; (iii) LiDi-lithium disilicate glass-ceramic coating with Monobond N Primer and Multilink Speed; (iv) COJ-tribochemical silica treatment with RelyX Ceramic Primer and RelyX Unicem 2; (v) GCEM-alumina grit blasting with G-Multi Primer and G-Cem LinkForce; (vi) MUL-alumina grit blasting with Multilink Speed; and (vii) PAN-alumina grit blasting with Clearfil Ceramic Primer and Panavia F2.0. A total of 30 bilayered specimens in each group were stored in distilled water at 37 °C for 24 h and assigned to three subgroups (n = 10/test group): short-term test, thermocycling for 5000 cycles, and thermocycling for 10,000 cycles and tested in 4-point bending configuration. Results were analysed using two-way ANOVA, followed by one-way ANOVA and Games-Howell (α = 0.05). Failure mode and surfaces were analysed using optical microscopy and SEM. The bonding (J/m2) of COJ and MUL groups was significantly higher than the other groups among all aging conditions. Thermocycling affected the bonding in COJ and GCEM groups. Surface pre-treatments and artificial aging affect the bonding between composite cements and zirconia. [ABSTRACT FROM AUTHOR]

Laminated composites with thermoset matrices are already well established in major engineering fields like automotive and aviation. The primary drawbacks of such thermoset-based composites are the high cycle times required during manufacturing and their limited potential for recycling. Providing an alternative to thermoset-based composites, thermoplastic matrix materials gained more and more momentum by addressing these previously mentioned drawbacks. The preferred manufacturing technique for these materials employs fiber-reinforced thermoplastic tapes consolidated and formed together with a compatible substrate. The most critical aspect for all these applications is the stress or load transfer between the thermoplastic tapes and the substrate. If the interface is too weak and fails prior to the substrate or tape, a high amount of theoretical mechanical performance is lost. The presented research investigates the influence of variations in manufacturing parameters, within the industrially relevant process window, on the interface strength of the final composite. The investigated composite material consists of PPGF UD tapes consolidated on a PPGF mat substrate. In particular, the influence of the consolidation parameters of pressure, temperature, and time are of special interest. The results of this work reveal a 400% increase in the measured mean strain energy release rate upon increasing the consolidation time from 60 s to 120 s at a consolidation temperature of 230 °C and a pressure of one bar. In contrast to this, an increase in the consolidation pressure, at constant temperature and time, leads to a minor improvement in the GC value of 20%. For testing and characterizing the corresponding interface properties, a mandrel peel testing setup was employed.

In this research, the effects of induced delamination on the variation of the mechanical properties of composite laminates subjected to bending loads are investigated using a micromechanical model. For this purpose, the variation of the mechanical properties of delaminated laminates is determined using stress analysis of damaged ply and classical laminate theory (CLT) relationships. Using the proposed model and CLT, the fracture toughness due to induced delamination formation is presented in cross‐ply laminates. Subsequently, the variation of strain energy release rate (SERR) is calculated in terms of crack density using analytical and finite element (FE) models to detect dominant failure modes in different crack densities. The results are compared with those of matrix cracking propagation. The results obtained by the proposed analytical model are in good agreement with those obtained by existing numerical and experimental approaches. The proposed model can be utilized to predict induced delamination formation in composite laminates subjected to bending loads. Highlights: An analytical micromechanical model is adopted to predict the variation of flexural mechanical properties, for any stacking sequence.The laminates are subjected to bending loads containing matrix cracks and delamination.By using classical laminate theory (CLT), the fracture toughness required to formation of induced delamination in composite laminates has been estimated.By using the finite element (FE) method, numerical model has been introduced to predict SERR in terms of the damage modes in cross‐ply laminates. [ABSTRACT FROM AUTHOR]

This study develops a three-dimensional finite element simulation model for the prediction, propagation, and improvement of adhesion failure in an adhesively bonded laminated T-joint structure using smart piezoelectric materials. Initially, three-dimensional stresses (normal and shear) and failure locations in the composite T-joint (all the layers of the web and flange) were evaluated. In the identified failure location, Virtual Crack Closure Technique (VCCT) of fracture mechanics was employed to compute the Strain Energy Release Rate (SERR) values for different pre-embedded adhesion failure lengths. The developed coupling analysis model was employed to evaluate the SERR responses for the laminated composite T-joint with single/multiple piezoelectric layers. The efficacy and improved performance (resistance to adhesion failure) of the laminated smart T-joint structure were analyzed in detail by considering different influencing parameters, i.e., orientation schemes, material types, piezoelectric layers, thicknesses, and number of laminate layers. [ABSTRACT FROM AUTHOR]

The goal of the study was to analyze fracture properties of adhesive bond using a three-point end-notched flexure test and the compliance-based beam method. Critical strain energy release rates (GIIc) and cohesive laws were obtained for adhesive bonds made of European beech (Fagus sylvatica L.) and adhesives such as EPI, MUF, PRF and PUR. The experiments were assisted with FE analyses employing three different material models of wood: elastic (Elas), symmetric elasto-plastic (EP) and elasto-plastic with different compressive and tensile yield stresses parallel to fiber (EP+). The highest mean GIIc was achieved for PUR (5.40 Nmm−1) and then decreased as follows: 2.33, 1.80, 1.59 Nmm−1 for MUF, EPI, and PRF, respectively. The failure of bondline was brittle and occurred at bondline for EPI, MUF and PRF, and ductile and commonly occurring in wood for PUR adhesive. The FE simulations employing cohesive models agreed well with the experimental findings for all adhesives. FE model with Elas material was found accurate enough for EPI, MUF and PRF adhesives. For PUR adhesive, the model EP+ was found to be the most accurate in prediction of maximal force. The impact of friction between lamellas may be up to 4.2% when varying friction coefficient from 0 to 1. The impact of the grain angle distortion (α) with respect to longitudinal specimen axis showed its high influence on resulting stiffness and maximal force. It was found that three-point end-notched test is suitable for EPI, MUF, and PRF, while it is less appropriate for a bond with PUR adhesive due to notable plastic behavior. [ABSTRACT FROM AUTHOR]

Based on the theory of linear elastic fracture mechanics, the relationships between material constants c3, c4 required in Abaqus and constants C, m in Paris formula are derived. Then extended finite element method (XFEM) of Abaqus software is used to is used to predict the crack propagation path and life of the plate with center inclined through crack and typical stiffened wing spar with initial crack under the constant amplitude fatigue load. The results show that the predicted crack propagation path is in good agreement with the experimental results, and the crack propagation life error is less than 6.3%. It also shows that this method can accurately predict the fatigue crack growth path and life of two-dimensional and three-dimensional complex structures under constant amplitude loads. This study can provide an effective way for damage tolerance analysis of structures and has certain engineering application value.

BackgroundDuring the service period of the tritium barrier coating in the fusion reactor, the crack performance of the coating surface and the roughness of the substrate are the key factors restricting the service cycle of the coating.PurposeThis study aims to clarify the relationship between substrate roughness and coating surface cracks in SiC/316L stainless steel tritium barrier coating system.MethodBased on the Abaqus finite element software, SiC/316L stainless steel tritium penetration barrier system was established. Factors such as the strain energy release rate, amplitude of substrate and length position were investigated with emphasis on the relationship between substrate roughness and coating surface cracks.ResultsThe results show that the substrate roughness has a significant effect on the strain energy release rate of the coating surface cracks. When the crack is above the peak of the substrate, the strain energy release rate is the largest. When the crack is located directly above the valley, the strain energy release rate is the smallest. Compared with the smooth interface, the stress along the rough interface is suppressed, showing a decreasing trend.ConclusionsThis study reveals the influence of crack position on the driving force of crack growth.

The use of composite materials is on the rise in different engineering fields. The main advantage of these materials for the aerospace industry being their low weight for excellent mechanical qualities. The analysis of failure modes, such as delamination, of these materials has received great attention from researchers. This paper proposes a method to evaluate the mode I Strain Energy Release Rate (SERR) of sandwich structures. This method associates a two-dimensional mixed finite element with virtual crack extension technique for the analysis of interfacial delamination of sandwich beams. The cases of a symmetrical Double Cantilever Beam (DCB) and a asymmetrical Double Cantilever Beam (UDCB) have been analyzed in this study. The comparison of the results obtained by this method with those found in the literature shows efficiency and good precision for the calculation of Strain Energy Release Rate (SERR). [ABSTRACT FROM AUTHOR]