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This paper proposes a rate-dependent cohesive zone model for simulating the evolution and growth of cracks under dynamic loading. This model takes into consideration the effects of cohesive separation rate and crack growth speed on the cohesive traction-separation relationship to reflect the rate-dependent characteristics of both material viscosity and energy dissipation of micro-crack branches. The evolution algorithm of the cohesive law is presented, wherein separation rate and crack growth speed are evaluated using the backward difference method explicitly in incremental computation, leading to the determination of rate-dependent critical traction and fracture toughness. The proposed model was implemented in ABAQUS software via UEL subroutine and utilized in an example of interfacial crack growth simulation, with satisfactory agreement found among the present results, experimental data, and numerical results from the literature. The effectiveness of the rate-dependent model and numerical algorithm in simulating high speed crack growth is validated through further numerical tests. [ABSTRACT FROM AUTHOR]

To evaluate the peel resistance of a device wherein a polyimide (PI) sheet is bonded to a curved surface with a pressure-sensitive adhesive (PSA) experimentally and analytically, we applied a mechanical simulation considering the viscoelasticity of the pressure-sensitive adhesive (PSA) and the fracture energy of the bonding interface. The mechanical behavior against the local load applied on the PI sheet surface was evaluated using this simulation. To verify the accuracy of this simulation, we fabricated a local load tester that could apply a load to a local area of 8 mm in diameter and compared the mechanical behavior with the simulation results. Dynamic mechanical analysis of the PSA with a film thickness of 19 μm was performed using the nanoindentation technique. The generalized Maxwell model parameters were estimated by fitting the relaxation elastic modulus E(t) to conduct a mechanical simulation. For the double cantilever beam test to derive the interfacial fracture energy, soft PI sheets were reinforced with Al substrates. As a result of these analyses, it was confirmed that the relationship between the displacement and load obtained by this simulation agrees well with the actual local load test. This technique is useful for predicting the bonding strength of complex-shaped devices fabricated using soft adherends and adhesives. [ABSTRACT FROM AUTHOR]

Adhesive bonding is a commonly used technology for joining dissimilar materials. However, production-related effects on the performance of the bondline have to be considered for an accurate joint design. In case of an adhesive joint in an automotive multi-material body in white, these effects arise from the so-called mismatch in thermal expansion coefficients, which leads to distortions of the adhesive in an uncured state or even damage in the cured one. The distortion of the uncured adhesive in the normal direction is called the 'viscous fingering effect', which reduces the adhesively bonded cross section by changing the adhesive bondline's shape to thin 'fingers' and therefore influences the materials properties. To investigate the effect of viscous fingering on the modulus, strength and energy release rate, linear butt bonded specimens and Tapered Double Cantilever Beams (TDCB) with different elongations of the adhesive bondline in the viscous state are investigated. The results are used to parameterize a cohesive zone model (CZM) and perform numerical analysis of the TDCB specimen for validation and to build up a model of a dissimilar joint consisting of a steel hatprofile and an adhesively bonded aluminum panel subjected to thermal distortions. [ABSTRACT FROM AUTHOR]

Tensile cracks significantly influence stability of mining, tunneling, and other geotechnical engineering scenarios. Discontinuous deformation analysis (DDA) is widely employed to analyze, predict, and prevent the deformation and progressive failure of such geomaterials. However, an accurate and efficient simulation of the cracking process remains a challenge, requiring appropriate fracture models. This study presents an improved DDA algorithm featuring a nonlinear cohesive zone model (CZM) designed for the intricate deformation and fragmentation analysis of geotechnical structures composed of quasi-brittle materials. Building upon fracture mechanics theory, an exponential-type CZM that accounts for both post-peak softening behaviors and nonlinear relations inherent in quasi-brittle materials is introduced. This exponential-type CZM is integrated into the original DDA method, addressing the co-edge blocks connected with cohesive springs. The ensuing unbalanced force in normal contact arising from the nonlinear cohesive spring is mitigated using a nonlinear iterative algorithm. The formulation, the implementation, and the iteration of the exponential-type CZM within the DDA framework are elucidated. Finally, the feasibility and the accuracy of the improved DDA for analyzing quasi-brittle crack propagation are demonstrated and validated by comparing several examples with experimental and numerical results. Highlights: An improved DDA, incorporating an exponential-type CZM, is presented to simulate the nonlinear fracture behaviors in geomaterials. A nonlinear iterative algorithm is proposed to address the solution of nonlinear equilibrium equations in the improved DDA. The effectiveness and the accuracy of the improved DDA are validated and verified through typical examples. [ABSTRACT FROM AUTHOR]

This paper aims to examine the behavior of cracked adhesive joints experimentally and numerically when they are subjected to quasi-static and dynamic loads using the tensile and falling-wedge impact tests, respectively. Double cantilever beam (DCB) specimens were manufactured and tested under impact loading with varying impact energies to analyze the adhesive joint mode-I dynamic fracture response. To determine quasi-static and dynamic mode-I fracture energies, the compliance-based beam method (CBBM) was utilized accounting for the axial force exerted by the wedge. It was found that by changing the loading condition from quasi-static to impact, the maximum force and fracture energy of adhesively bonded joints were considerably increased by 275% and 452%, respectively. However, within the impact test conditions, increases of 10% and 22% were obtained in maximum force and fracture energy when the impact energy was tripled. The adhesive joints tested under static loading experienced a mixed interfacial/cohesive failure pattern, whereas by shifting the loading condition to impact, the failure pattern turned fully cohesive. The quasi-static and dynamic fracture responses of adhesive joints were modeled using the cohesive zone model employing a triangular traction-separation law. The numerical and experimental results exhibited reasonable correlation. [ABSTRACT FROM AUTHOR]

Damages in composite structures are typically repaired using external bonded patches. In this work, the damage tolerance within external patches is studied using double strap joint (DSJ) with carbon fibre reinforced plastic (CFRP) specimens. The damage tolerance in this work refers to bond-line manufacturing-related defects such as debond or dry area. Both intact and pre-cracked DSJ specimens are numerically analysed using experiments for comparisons. DSJ specimens' adherends were CFRP laminates with AS4/3501–6 plies and bonded using adhesive film FM 300–2. The pre-cracked specimens are monitored during experiments using high-speed digital image correlation to visualize damage propagation. The unsymmetric pre-crack influences in a clear way as shown by experiments. The numerical analyses reveal the effect of failure mechanisms on final failure and the maximum force during a test. The included parametric sensitivity analysis is performed using statistical methods. The normally distributed parameters are sampled using separate distributions for each analysed interface and fracture mode. UNCLASSIFIED Based on Foreground Information under EDA Contract No B.PRJ.RT.670 covering the Ad Hoc Project entitled "PATCHBOND II". [ABSTRACT FROM AUTHOR]

This study investigates the propagation of surface cracks in bearings under oscillating conditions. Voronoi elements are employed to simulate the microstructure of bearings and combined with a cohesive zone model of continuum damage mechanics to simulate the propagation of cracks. A new type of oscillating contact fatigue test machine was designed to conduct experiments on contact crack propagation under oscillating conditions, and the experimental results were analyzed. By comparing the simulation results with experimental data, the validity of the theoretical analysis was confirmed. [ABSTRACT FROM AUTHOR]

Rubber concrete (RC) has been used in fatigue-resistant components due to its durability, yet the numerical simulation of its fatigue properties remains in its early stages. This study proposes a cohesive zone model (CZM) that accounts for the accumulation of fatigue damage at the mesoscale to investigate the fatigue performance of RC. The model integrates static and fatigue damage in the CZM, effectively capturing damage caused by fatigue loading. Validation was conducted using experimental data from the existing literature. Based on this validation, four concrete beams with varying rubber replacement rates (0%, 5%, 10%, and 15%) were tested. The CZM was employed to describe the mechanical behavior of the interface transition zones (ITZs) and the mortar interior, which were simulated and analyzed under different stress levels. The results demonstrate that the model accurately simulates crack propagation paths, interface damage evolution, and the fatigue life of RC beams under fatigue loading. A functional relationship between fatigue life and stress level was established for various rubber replacement rates. This study provides a reference model for numerical simulations of RC under fatigue loading conditions and introduces new approaches for analyzing the fatigue performance of other materials. [ABSTRACT FROM AUTHOR]

Highlights The extensive use of multidirectional composite laminates requires to understand the delamination behavior at interfaces between plies with different fiber orientations. In this study, double cantilever beam testing was performed to investigate the mode I interlaminar fracture of carbon fiber reinforced polymer laminates with different central interfaces (0//0, 0//+45 and +45//−45). X‐ray microtomography revealed the curved crack front shape that was incorporated to calculate fracture toughness. The fracture toughness varies with the crack length in a typical delamination resistance curve, which can be quantified by an empirical equation. Incorporation of variable fracture toughness into a cohesive zone model can better predict the delamination fracture of the laminate, compared to constant toughness. It was found that the delamination mechanism is independent of central interfaces. However, compared to unidirectional laminates, multidirectional laminates are less resistant to crack initiation, but more resistant to propagation with higher toughness and shorter fiber bridging zone. Mode I interlaminar fracture of CFRP laminates with different central interfaces was investigated experimentally and numerically. Curved crack front shape was incorporated to calculate fracture toughness. Incorporation of variable fracture toughness into a cohesive zone model can better predict the delamination fracture of the laminate. Multidirectional laminates are less resistant to crack initiation but more resistant to propagation with higher toughness and shorter fiber bridging zone. [ABSTRACT FROM AUTHOR]

This is Part II of a series of two papers in which the effect of fiber bridging on fatigue delamination propagation is assessed. In Part I, unidirectional double cantilever beam specimens composed of the carbon fiber‐reinforced polymer prepreg AS4/8552 were tested by means of fatigue cycling. Fiber bridging in beam specimens composed of unidirectional plies causes the apparent fatigue delamination curves to exhibit growth which is slower than that for the case when fiber bridging does not occur. Generally, fiber bridging does not occur in laminate structures. In Part II of this study, a cohesive zone model (CZM) is developed and used to carry out finite element analyses to simulate the experiments. The CZM is employed to quantify and eliminate the contribution of fiber bridging to the fatigue delamination growth curves. In this way, more realistic results are obtained. These results are compared to an upper bound curve determined in Part I. Highlights: Effect of fiber bridging on fatigue delamination propagation is quantified.To this end, a cohesive zone model is developed.Fatigue delamination propagation tests were numerically simulated.Fiber bridging was seen to increase the fatigue fracture toughness by about 22%. [ABSTRACT FROM AUTHOR]

The efficiency of a repair strategy applied to a honeycomb/carbon-epoxy sandwich beam was analyzed in this work. Experimental tests were performed considering three-point bending loading of undamaged, damaged and repaired specimens. In the damaged case, the central part of the core and of one of the skins were removed. The repair scheme consists of bonding a plug of honeycomb into the core and repairing the carbon-epoxy skin considering a scarf patch. A finite element analysis incorporating cohesive zone mixed-mode I + II analysis was performed. The resultant load-displacement numerical curves were compared with the experimental ones. It was verified that the repair procedure is efficient regarding recovery of the initial stiffness and strength of the undamaged case, and it was concluded that the proposed numerical model is a valid tool to deal with repair of sandwich beams. [ABSTRACT FROM AUTHOR]

Finite element (FE) simulations of adhesively bonded composite joints were conducted using the cohesive zone model (CZM). To clarify the effect of fracture criteria on the accuracy of the CZM simulation, two types of mixed-mode criteria including the -linear summation model of Modes I and II energy release rates, G I / G IC + G II / G IIC = 1 , and the nonlinear power-law, ( G I / G IC ) n + ( G II / G IIC ) n = 1 , were employed. A CZM formulation using the power-law fracture criterion was developed in this study. The load–displacement curves calculated by the two models were compared with the experimental results obtained from mixed-mode Fernlund–Spelt-type double cantilever beam tests, and the Mode II end-notched flexure (ENF) tests. Calculations using the nonlinear fracture criterion were closer to the experimental results. Consequently, it is concluded that nonlinear fracture modeling is of vital importance for accurate strength analysis of mixed-mode adhesive joints. [ABSTRACT FROM AUTHOR]

In this paper, the multi-linear cohesive zone model has been extended to simulate the mixed-mode I/II delamination growth in composite laminates. In the extended multi-linear cohesive zone model, inclined spring elements have been used to consider the fracture process zone effects so that when the crack starts to grow, the spring stiffness changes based on the material's traction–separation curve with any arbitrary shape of softening law. To apply mode II loading in addition to mode I, the angle of spring elements in each desired mixed-mode ratio has been calculated using analytical equations and applied in the finite element model. The simulation results as load–displacement curves at different mixed-mode ratios are compared with the available experimental results to investigate the validity and accuracy of the newly proposed model. The maximum load values in three different mixed-mode ratios have been well predicted with an average error of less than 6%. After that, the applicability of the extended multi-linear cohesive zone model is evaluated to estimate the mixed-mode I/II delamination R-curve behavior and an analytical relation for the R-curve is presented based on the spring elements' energy. A good agreement has been obtained between the R-curves extracted by the new model and the available experimental R-curves. The results show that the extended multi-linear cohesive zone model in combination with the proposed analytical R-curve can accurately predict the mixed-mode I/II delamination growth in composite laminates by considering the effects of the fracture process zone. [ABSTRACT FROM AUTHOR]

This article presents a detailed analysis of a numerical model for studying the failure of masonry structures that have been retrofitted with timber solutions. The model accurately reproduces the failure mechanisms of masonry and evaluates the effectiveness of timber-based retrofitting. The study validates the model through comparisons with experimental and numerical results and assesses its efficacy through nonlinear static analysis. The article also discusses the use of a timber frame system as a retrofitting strategy for masonry walls, highlighting its significant enhancement of the wall's load-bearing capacity against lateral forces. However, the post-peak behavior of the retrofitted cases reveals potential weaknesses in the timber frame system, which can lead to sudden drops in resistance. The article concludes by emphasizing the importance of preventing simultaneous failure of multiple bracing elements in the retrofitting system and the need for further research to improve its design and mitigate brittle behavior. [Extracted from the article]

Concrete cover separation (CCS) is a common type of delamination failures that occurs at the plate end in reinforced concrete (RC) beams strengthened in flexure using fiber-reinforced polymer (FRP) materials. The effectiveness of FRP U-wrap anchorage has been demonstrated in mitigating CCS failure, resulting in increased utilization of FRP composites for strengthening purposes. The current study presents the development of a nonlinear three-dimensional finite element (FE) model using ABAQUS software in order to simulate the flexural behavior and debonding failure of FRP-strengthened RC beams end-anchored with vertical FRP U-wraps. The cohesive zone model (CZM) is used in the developed FE model to predict the debonding failure of the anchored beams, considering the influence of relevant parameters. The validation of the FE model was achieved through comparisons with experimental data from the literature, which demonstrated good agreement. A parametric study was then conducted to investigate the impact of the design parameters of FRP U-wrap on the behavior of the anchored beams. The examined parameters included the width, layout, and height of the vertical FRP U-wraps. The findings of the FE parametric study have revealed that to successfully prevent plate-end debonding, it is critical to not only use the required area of vertical FRP U-wrap but also carefully consider the U-wrap layout. The FRP U-wrap should be placed at the plate-end region covering the concrete tooth created by the shear cracks, and the U-wrap layout should consider the detailing recommended in this study. [ABSTRACT FROM AUTHOR]

Gas-wave refrigerators are widely used devices that utilize gas pressure to produce wave motion inside an oscillating tube for high-power refrigeration. This paper manufactures the core component of gas-wave refrigerators—the oscillating tubes—using hub and blade brazing. The tensile strength and fatigue life of the brazed joints were obtained through experiments. A finite element simulation based on the cohesive zone model determined that the critical damage stress of the brazed-joint brazing seam was 525 MPa. Under cyclic displacements of U = [0.4 mm, 0.5 mm, 0.6 mm], the errors between the simulated and experimental values of fatigue life are 9.09%, 4.38%, and 4.44%, respectively, which verifies the accuracy of the VUMAT subroutine of the cyclic CZM. The fatigue life relationship formula for the butt-brazed joints was fitted as y = 5458.97 x − 3.545 . Through the simulation analysis of the impact of the butt-joint angles on the fatigue life of brazed joints, it was found that as the butt-joint angle increased, the fatigue damage decreased, and the fatigue life increased. A finite element model of an oscillating tube with a DN (Nominal Diameter) of 285 × 450 mm was established to analyze the fatigue life of the butt-brazed structure of the rotor blade. The fatigue life of the brazed structure with a butt-joint angle of α = 45° increased by over 102.92% than that of α = 0°. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature 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.)

In this study, an in-depth analysis is carried out to simulate the failure mechanism of T700 carbon fiber-reinforced polymer composite (CFRP) joints with a layup sequence of [45/-45/0/90]3 s when subjected to tensile loading, both experimentally and numerically. We compared the mechanical performance of three different edge-to-bolt diameter ratios (E/d) of bonded, bolted, and hybrid single lap joints subjected to tensile loading. A finite element-based progressive damage method (PDM) along with the bilinear triangular cohesive zone model (BTCZM) is developed to predict the damage evolution and failure mechanism for all joint configurations. By juxtaposing the simulation outcomes and the experimental data, we observed the failure morphology and assessed the bearing capacity of the joint under tensile loading. The comparison results revealed a minor discrepancy of merely 5.5% in terms of joint load capacity between simulations and experiments, which indicates the high accuracy of our model. The strength of the adhesive and mechanical joints increases with E/d from 3 to 5; however, the strength of the hybrid joints decreases. At E/d = 3, hybrid joints performed significantly better than bonded ones, with a remarkable enhancement of 41.53%. However, for E/d ratios of 4 and 5, both simulation results and test data showed that hybrid joints were inferior to bolted joints. The analytical methodology presented in this paper offers a valuable reference for future analysis and design of composite joints. [ABSTRACT FROM AUTHOR]

Copyright of Micronanoelectronic Technology is the property of Micronanoelectronic Technology Editorial Office 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.)

Introduction: The precise mechanism of rupture in abdominal aortic aneurysms (AAAs) has not yet been uncovered. The phenomenological failure criterion of the coefficient of proportionality between von Mises stress and tissue strength does not account for any mechanistic foundation of tissue fracture. Experimental studies have shown that arterial failure is a stepwise process of fibrous delamination (mode II) and kinking (mode I) between layers. Such a mechanism has not previously been considered for AAA rupture. Methods: In the current study we consider both von Mises stress in the wall, in addition to interlayer tractions and delamination using cohesive zone models. Firstly, we present a parametric investigation of the influence of a range of AAA anatomical features on the likelihood of elevated interlayer traction and delamination. Results: We observe in several cases that the location of peak von Mises stress and tangential traction coincide. Our simulations also reveal however, that peak von Mises and intramural tractions are not coincident for aneurysms with Length/Radius less than 2 (short high-curvature aneurysms) and for aneurysms with symmetric intraluminal thrombus (ILT). For an aneurysm with (L/R = 2.0), the peak σ vm moves slightly towards the origin while the peak T t is near the peak bulge with a separation distance of ~ 17 mm. Additionally, we present three patient-specific AAA models derived directly from CT scans, which also illustrate that the location of von Mises stress does not correlate with the point of interlayer delamination. Conclusion: This study suggests that incorporating cohesive zone models into clinical based FE analyses may capture a greater proportion of ruptures in-silico. [ABSTRACT FROM AUTHOR]

Flax fiber/epoxy composites have attracted extensive attention in aviation applications due to the advantages of low density，remarkable mechanical properties and environmental friendliness. However，the interface compatibility between hydrophilic flax fiber and hydrophobic epoxy resin matrix is poor, which makes the lamination resistance of the composite insufficient, and affects the bearing capacity and service life of the material. Chopped fiber interlaminar toughening is an effective method to improve the interlaminar fracture toughness of composites. Besides，the numerical simulation based on cohesive zone models has also become an effective tool for analyzing interlaminar toughening in the composites. In this study，three different cohesive zone models，including bilinear，exponential and trilinear cohesive zone laws，are used to simulate the mode Ⅰ interlaminar fracture behavior of chopped aramid fiber interleaved flax fiber/epoxy composites. The numerical results are analyzed and compared with the double cantilever beam（DCB）experimental results and digital image correlation（DIC）observations，summarizing the influence of different cohesive zone laws. The results show that bilinear and exponential cohesive zone models are unsuitable for simulating the interlaminar toughening effect of chopped fiber interleave due to the numerical results with no laddered or fluctuated descent. The trilinear cohesive zone model can effectively present the chopped fiber interlaminar toughening effect and behavior by including the toughening effects of fiber bridging and matrix failure so that fiber bridging failure mode and crack propagation behavior are similar to those observed with the DIC method. This research provides a rational basis for the chopped fiber interlaminar toughening design of flax fiber/epoxy composites.

The CRTS II ballastless track is sensitive to temperature due to its longitudinal continuity. The application of reflective insulation coating can efficiently lower the temperature of the track slab, thereby decelerating track deterioration. Given the considerable length of high-speed railway lines, the application of reflective insulation coatings leads to numerous transitions between coated and uncoated sections. This study investigates the influence of reflective insulation coatings on the structural damage of coated-uncoated transition zones in railways. To this end, a CRTS II slab track model involving the bilinear cohesive zone model and the concrete plastic damage model is established. The model examines the combined impact of high temperature and train loading, aiming to investigate the damage patterns within the coated-uncoated transition zone of the track. The results indicate: (1) During high temperature loading, the center of the track slab layer is predisposed to warping compared to the sides. (2) If the cohesion parameter falls below 0.04 MPa, augmenting the cohesion model parameter effectively alleviates track slab arching. (3) In instances where the track slab lacks complete coverage of reflective insulation coatings, train loading may shift the location of the maximum vertical displacement and interface failure mode. [ABSTRACT FROM AUTHOR]

The cohesive zone model (CZM) is widely employed for simulating delamination and debonding behaviour in engineering structures. However, the choice of CZM shape impacts the accuracy of simulation results. Therefore, the selection of a suitable Traction-Separation Law (TSL) with appropriate cohesive parameters is crucial. This study focuses on simulating the mode II delamination of unidirectional carbon/epoxy composites under varying moisture content levels (0%, 2.2%, 3.8%, and 5.3%) using the End Notched Flexure (ENF) test. Trapezoidal TSL (TTSL) with varying pseudo-plasticity parameter (Γ) was implemented and compared. A guideline was proposed in this study to aid in the selection of cohesive parameters, and a relationship between these parameters and moisture content was established. The results indicate that Γ = 0.99 yields a more accurate force-displacement response compared to Γ = 0. The estimated cohesive zone length falls within the range of 2.0–2.4 mm. During crack growth, the analysis reveals that, at the peak force, a region approximately 0.5–0.6 mm ahead of the crack tip undergoes total failure. Simultaneously, damage initiation occurs in the region 2.3–2.4 mm beyond the complete failure zone.

Abstract Rock mass deformation and failure are macroscopic manifestations of crack initiation, propagation, and coalescence. However, simulating the transition of rocks from continuous to discontinuous media under cyclic dynamic loading remains challenging. This study proposes a hybrid finite-discrete element method (HFDEM) to model crack propagation, incorporating a frequency-dependent cohesive-zone model. The mechanical properties of standard sandy mudstone under quasi-static and cyclic dynamic loading were simulated using HFDEM, and the method's reliability was verified through experimental comparison. The comparative analysis demonstrates that HFDEM successfully captures crack interaction mechanisms and accurately simulates the overall failure behavior of specimens. Additionally, the effects of pre-existing flaw inclination angle and dynamic loading frequency on rock failure mechanisms were investigated. The numerical results reveal that rock samples exhibit significantly higher compressive strength under dynamic loading compared to quasi-static loading, with compressive strength increasing with higher cyclic dynamic load frequencies. Furthermore, by analyzing the strength characteristics, crack propagation, and failure modes of the samples, insights into the failure mechanisms of rocks under different frequency loads were obtained. This study provides valuable insights into crack development and failure of rocks under seismic loads, offering guidance for engineering practices.

Sandwich structures are often prone to catastrophic failure due to premature separation between the core and skin layers. Geometric parameters, such as the thickness of the skin and core, along with the materials used in their manufacturing, directly influence the resistance to separation between the skin and core. This study explores how variations in skin thickness affect both failure modes and maximum load capacity in sandwich structures, utilizing both experimental testing and numerical simulations. Specimens were categorized as intact and pre-debonded samples. Each specimen featured four different skin thicknesses (3, 6, 8, and 10 layers of composite laminated skins, with corresponding thicknesses of 0.68, 1.33, 1.73, and 2.1 mm respectively). The specimens incorporated a foam-filled square corrugated core and underwent 3-point bending tests. Results revealed a significant shift in the failure mode: initially observed as upper skin fracture (V-shaped failure), it transitioned to separation between skins and cores with increased skin thickness, particularly in the presence of pre-debonding. Notably, the predominant failure mode did not involve separation between the skin and core in specimens without a pre-existing crack. Furthermore, numerical simulations effectively demonstrated the accurate capture of failure modes and loads using the Hashin and cohesive zone model (CZM). [ABSTRACT FROM AUTHOR]

A thermo-mechanical progressive analysis model is proposed for predicting fatigue-driven delamination in composite laminated plates. The delamination is simulated based on extended layerwise method (XLWM). The traction-separation law is employed to the heat flux transfer and mechanical load transfer across the delamination front. A thermo-mechanical cohesive zone model (TM-CZM) is developed by Peerlings damage law to simulate the fatigue characteristic of delamination front. In the numerical examples, the effects of mesh lengths, acceleration multipliers, interface strengths, and cyclic temperature load magnitudes on the delamination expansion process are investigated, and the temperature-life curves of composite laminates are determined as well. [ABSTRACT FROM AUTHOR]

Highlights This study delved into the Mode I fracture behavior of laser‐assisted automated fiber placement (AFP) in situ consolidated thermoplastic composite laminates under different curing pressures. In compliance with ASTM D5528 standards, T700 carbon fiber reinforced polyether ether ketone (T700‐CF/PEEK) double cantilever beam (DCB) specimens were fabricated and segregated into three test groups subjected to distinct roller pressures: DCB‐100N, DCB‐500N, and DCB‐1500N. The fracture toughness of these specimens was then inversely characterized by employing an optimized ASTM‐based data reduction methodology. A kind of tri‐linear cohesive zone model (CZM) incorporating the fracture process zone (FPZ) length was developed to simulate delamination behavior, showing good agreement between experimental results and simulation predictions. Compared with the other two test groups, DCB‐1500N specimens have more inter‐laminar bridging fibers and higher propagated toughness. Although the length of fiber bridging area is shorter, the fiber bridging density is higher, so the influence of fiber bridging on toughness is more pronounced in the DCB‐1500N specimens. This study provides theoretical guidance for the impact resistance design of thermoplastic composites (TPCs), offering valuable insights into the intrinsic relationship between material processing and fracture damage mechanisms. Explore the characteristic interlaminar fracture behavior of thermoplastic laminates made by AFP under different curing pressures. Develop a more accurate tri‐linear CZM model to describe the plastic deformation at crack tips and fiber bridging during the delamination process. Unveil the intrinsic relationship between AFP curing pressure and ductile fracture mechanism of thermoplastic composites. [ABSTRACT FROM AUTHOR]

The cohesive zone model (CZM) has been used widely and successfully in fracture propagation, but some basic problems are still to be solved. In this paper, artificial compliance and discontinuous force in CZM are investigated. First, theories about the cohesive element (local coordinate system, stiffness matrix, and internal nodal force) are presented. The local coordinate system is defined to obtain local separation; the stiffness matrix for an eight-node cohesive element is derived from the calculation of strain energy; internal nodal force between the cohesive element and bulk element is obtained from the principle of virtual work. Second, the reason for artificial compliance is explained by the effective stiffnesses of zero-thickness and finite-thickness cohesive elements. Based on the effective stiffness, artificial compliance can be completely removed by adjusting the stiffness of the finite-thickness cohesive element. This conclusion is verified from 1D and 3D simulations. Third, three damage evolution methods (monotonically increasing effective separation, damage factor, and both effective separation and damage factor) are analyzed. Under constant unloading and reloading conditions, the monotonically increasing damage factor method without discontinuous force and healing effect is a better choice than the other two methods. The proposed improvements are coded in LS-DYNA user-defined material, and a drop weight tear test verifies the improvements. [ABSTRACT FROM AUTHOR]

A micromechanical model with realistic initial fiber misalignment (IFM) was developed to simulate the longitudinal compression behavior of unidirectional carbon fiber/aluminum composites. The matrix and fiber were modeled using ductile damage law and brittle fracture model, respectively. The interfacial properties were firstly determined by the single‐fiber push‐out and transverse tensile tests, and the cohesive zone model was adopted to capture the interfacial behavior. The calculated compressive response curve is in alignment with the experimental data. Compression failure can be attributed to fiber kinking, possibly triggered by the matrix shear damage. The increase of IFM angle makes the failure mode being transformed from fiber crushing to fiber kinking, along with a significant decrease in compressive strength. With the fiber content increasing, the compressive strength increases first and then decreases, while the compressive modulus increases monotonically. Increasing interfacial strength significantly improves the compressive strength, but this is limited by the matrix properties. Highlights: Micromechanical modeling with realistic fiber misalignment of UD‐Cf/Al composites.Identifying interface parameters via single‐fiber push‐out tests and numerical methods.Experimental and numerical investigation into longitudinal compression failure process.Effects of misalignment, fiber fraction, and interface strength on compressive behavior. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department 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.)

In this study, an improved discontinuous deformation analysis method with sub-block strategy is introduced to numerically simulate mixed-mode fractures. This approach partitions the material domain into continuum and potential discontinuum regions, applying specialized modeling techniques to each. In the continuum region, penalty-like bonding springs are employed to glue the sub-blocks together to capture the elastic behavior of the material. In the potential discontinuum region, the cohesive springs with the stiffness based on the cohesive zone model are implemented between sub-blocks to reproduce the process of crack nucleation and propagation. The primary advantage of this method is its capability to effectively model the transition of quasi-brittle solids from a continuous to a discontinuous stage through the degradation of cohesive springs. This accurately represents material failure while maintaining stability and consistency along uncracked interfaces. Another significant benefit is the method's efficiency, as it avoids complex contact operations along sub-block interfaces before the cohesive spring between them fails. Validation through various benchmark numerical examples, such as cantilever beam-bending and diverse fracture simulations, demonstrates the method's accuracy and robustness by comparing the results with analytical solutions. These comparisons show that the proposed method effectively captures the interplay between tensile and shear traction components in the mixed-mode crack propagation process. [ABSTRACT FROM AUTHOR]

Quasi-brittle materials such as composite laminates, concrete, and toughened ceramics are subject to size effects in which the nominal strength decreases with increasing specimen size. Analyzing the joining of such materials is very important. Mechanically bolted joints are a widely used and suitable method for joining composite laminates in aircraft materials. Two-parameter cohesive laws—linear, constant, and exponential—were implemented analytically to analyze tearing, bearing stress, and remotely applied stress. An extended 2-D finite element model was created to validate the remote applied stress. The model provides reasonably acceptable results that can be used as fast design data for the selection of such materials and optimization of composite bolted joints. [ABSTRACT FROM AUTHOR]

This work investigated the effects of moisture absorption treatment on composite−to−metal double−lap shear joints (DLSJs) bonded with epoxy adhesive film through experiments and simulations. The composite−to−metal DLSJ can be divided into five parts (the interface between the composite and adhesive, the interface between the adhesive and metal, the composite adherend, the metal adherend, and the adhesive layer). First, the wet−dependent properties of the adhesive and interfaces were obtained through adhesive tensile tests and GC tests, which showed that the properties of the adhesive and interfaces were significantly affected by the moist environment. Then, tensile tests of the composite−to−metal double−lap shear joints were carried out in dry and wet environments. Finally, based on the experimental investigations, a finite element (FE) model that considered cohesive damage was established for simulating damage evolution and predicting the failure loads and failure modes of the DLSJs. The results of both the experimental and numerical tests show that the DLSJ failure load decreases significantly after immersion in 95 °C water, and the major failure mode transfers from adhesive failure to interface failure. The research results provide a theoretical basis or basic data for the structural design of adhesively bonded composite−to−metal. [ABSTRACT FROM AUTHOR]

Currently, microscopic research on the tensile fracture properties of recycled brick coarse aggregate concrete has mainly adopted microscopy techniques, which can clearly observe the actual damage situations of each phase material but are unable to individually analyze the effect of a specific material factor on the tensile properties of recycled concrete. This brings much uncertainty to the practical application of recycled concrete. Therefore, this study proposes a cohesive zone model (CZM) for simulating the tensile fracture of recycled brick coarse aggregate (RBCA) concrete. To this end, the study explores the effects of various critical factors on the fracture mode and bearing capacity of recycled brick aggregate concrete, including the replacement rate of recycled brick coarse aggregate, pore structure, interfacial transition zone (ITZ) strength, mortar strength, and volume fraction of brick aggregate. The results indicate that, when the minor to major axis ratio of elliptical pores is 0.5 ≤ K < 1, the following order of influence can be observed: random convex polygonal pores, circular pores, and elliptical pores. Moreover, excessively strengthening the ITZ and mortar does not significantly enhance the tensile performance of RBCA concrete. The distribution location of aggregate has a significant impact on the crack shape of recycled concrete, as does the pore structure, due to their randomness. Therefore, this article also discusses these. These findings contribute to a comprehensive understanding of the tensile properties of recycled brick coarse aggregate and provide insights into optimizing its behavior. [ABSTRACT FROM AUTHOR]

The continental shale reservoirs of Jurassic Lianggaoshan Formation in Sichuan Basin contain thin lamina, which is characterized by strong plasticity and developed longitudinal shell limestone interlayer. To improve the production efficiency of reservoirs by multi-cluster fracturing, it is necessary to consider the unbalanced propagation of hydraulic fractures and the penetration effect of fractures. This paper constructed a numerical model of multi-fracture propagation and penetration based on the finite element coupling cohesive zone method; considering the construction cluster spacing, pump rate, lamina strength and other parameters studied the influencing factors of multi-cluster fracture interaction propagation; combined with AE energy data and fracture mode reconstruction method, quantitatively characterized the comprehensive impact of the strength of thin interlayer rock interfaces on the initiation and propagation of fractures that penetrate layers, and accurately predicted the propagation pattern of hydraulic fractures through laminated shale oil reservoirs. Simulation results revealed that in the process of multi-cluster fracturing, the proportion of shear damage is low, and mainly occurs in bedding fractures activated by outer fractures. Reducing the cluster spacing enhances the fracture system's penetration ability, though it lowers the activation efficiency of lamina. The high plasticity of the limestone interlayer may impact the vertical propagation distance of the main fracture. Improving the interface strength is beneficial to the reconstruction of the fracture height, but the interface communication effect is limited. Reasonable selection of layers with moderate lamina strength for fracturing stimulation, increasing the pump rate during fracturing and setting the cluster spacing reasonably are beneficial to improve the effect of reservoir stimulation. [ABSTRACT FROM AUTHOR]

The advent of digital image and volume correlation has attracted wide use in fracture mechanics. The full‐field nature of digital image and volume correlation allows for the integration of computational fracture mechanics to analyse cracked samples quantitatively. This review provides a comprehensive overview of current methods used to extract fracture properties from full‐field displacement data. The term full‐field fracture mechanics is introduced to highlight the uniqueness of using inherently noisy experiential data to extract fracture properties. The review focuses on post‐processing‐based approaches rather than integrated approaches, as these have less limitations and are more commonly employed. There are four approaches that are discussed in extracting fracture properties from experimentally computed displacement data: field‐fitting, integral, crack‐opening and cohesive zone modelling approaches. This is further developed to discuss problems associated with using digital image and volume correlation to extract properties, including application examples. [ABSTRACT FROM AUTHOR]

Adhesive joints play a crucial role in enhancing the structural integrity and performance of 3D printed parts. The purpose of this study is to investigate the failure load and behavior of polycarbonate (PC) single lap joints (SLJs) produced by fused deposition modeling (FDM) using experimental and finite element analysis (FEA) methods. The FEA of joints presents a new approach by integrating PC substrates with Hill yield criterion, transversely isotropic material and adhesive layer with cohesive zone modeling (CZM). The study focused on the effect of printing angles (0°, 45°, and 90°) and overlap lengths (12.5 and 25 mm) on the performance of SLJs. The influence of 3D printing parameters on the mechanical behavior of PC joints was investigated by tensile testing of SLJs. The experimental failure load was 1586 N for a 12.5 mm joint at 90° and 4115 N for a 25.4 mm joint at 0°. Comparison of the experimental and FEA failure loads of the joints showed maximum and minimum differences of 11.98% and 1.34%, respectively. This result showed that the proposed model is applicable for determining the joint strength as a function of the printing angle and monitoring the joint damage behavior. [ABSTRACT FROM AUTHOR]

Fatigue and fracture prediction in composite materials using cohesive zone models depends on accurately characterizing the core and facesheet interface in advanced composite sandwich structures. This study investigates the use of machine learning algorithms to identify cohesive zone parameters used in the fracture analysis of advanced composite sandwich structures. Experimental results often yield non-unique solutions, complicating the determination of cohesive parameters. Numerical determination can be time-consuming due to fine mesh requirements near the crack tip. This research evaluates the performance of Support Vector Regression (SVR), Random Forest (RF), and Artificial Neural Network (ANN) machine learning methods. The study uses features extracted from load–displacement responses during the fracture of the Asymmetric Double-Cantilever Beam (ADCB) specimen. The inputs include the displacement at the maximum load (δ*), the maximum load ( P m a x ), the total area under the load–displacement curve ( A t ), and the initial slope of the linear region of the load–displacement curve (m). There are two objectives in this research: the first is to investigate which method performs best in identifying the interfacial cohesive parameters between the honeycomb core and carbon-epoxy facesheets, while the second objective is to reduce the dimensionality of the dataset by reducing the number of input features. Reducing the number of inputs can simplify the models and potentially improve the performance and interpretability. The results show that the ANN method produced the best results, with a mean absolute percentage error (MAPE) of 0.9578% and an R-squared (R²) value of 0.7932. These values indicate a high level of accuracy in predicting the four cohesive zone parameters: maximum normal contact stress ( σ I ), critical fracture energy for normal separation ( G I ), maximum equivalent tangential contact stress ( σ I I ), and critical fracture energy for tangential slip ( G I I ). [ABSTRACT FROM AUTHOR]

This contribution focuses on understanding the bedding effect of coal rocks under the Brazilian splitting test. First, multiple Brazilian splitting tests were performed on coal rocks with various bedding angles to systematically investigate the influence of stratification. Subsequently, numerical models with stratified structures were constructed, and a continuous-discontinuous numerical analysis method based on the cohesive zone model (CZM) was employed to conduct the corresponding numerical investigations. Results indicate that the load-displacement curves of coal rock specimens with different bedding angles can be classified into four stages: initial compaction stage, elastic deformation stage, crack rapid coalescence stage, and final destruction stage. With increase in the bedding angle, the failure patterns of coal rock specimens can be categorized into three groups: 1) stretching damage along bedding planes; 2) mixed tension and shear failure along the bedding planes and the coal matrix; and 3) stretching failure passing through the coal matrix. Furthermore, the tensile strength and cumulative acoustic emission (AE) energy-displacement relations are significantly influenced by the bedding angle. The numerical model can effectively predict the mechanical responses and fracture behavior of coal rock specimens, providing empirical parameters for the simulation of similar rock engineering. [ABSTRACT FROM AUTHOR]

Rock mass deformation and failure are macroscopic manifestations of crack initiation, propagation, and coalescence. However, simulating the transition of rocks from continuous to discontinuous media under cyclic dynamic loading remains challenging. This study proposes a hybrid finite-discrete element method (HFDEM) to model crack propagation, incorporating a frequency-dependent cohesive-zone model. The mechanical properties of standard sandy mudstone under quasi-static and cyclic dynamic loading were simulated using HFDEM, and the method's reliability was verified through experimental comparison. The comparative analysis demonstrates that HFDEM successfully captures crack interaction mechanisms and accurately simulates the overall failure behavior of specimens. Additionally, the effects of pre-existing flaw inclination angle and dynamic loading frequency on rock failure mechanisms were investigated. The numerical results reveal that rock samples exhibit significantly higher compressive strength under dynamic loading compared to quasi-static loading, with compressive strength increasing with higher cyclic dynamic load frequencies. Furthermore, by analyzing the strength characteristics, crack propagation, and failure modes of the samples, insights into the failure mechanisms of rocks under different frequency loads were obtained. This study provides valuable insights into crack development and failure of rocks under seismic loads, offering guidance for engineering practices. [ABSTRACT FROM AUTHOR]

Accurate description of concrete crack propagation is of great significance to practical engineering. This paper adopts the cohesive zone model (CZM) to investigate both the macro‑mechanical properties and the micro‑cracking damage behavior of concrete beams in a three-point bending test. Throughout the study of damage under loading in the three-point bending test, parametric examinations are conducted on five key factors controlling the cracking of cohesive elements regarding the case of circulate aggregate, namely type I fracture energy, type II fracture energy, shear strength, tensile strength and elastic modulus (stiffness). Through the test results of macro-mechanical properties and micro-cracking, the test results of a group of specimens and the results of parametric models are reversely analyzed, and the applicable parameter range of control factors in three-point bending simulation is obtained. Three computation models with different aggregate areas are established by taking account of the quantitative aggregate data from specimens with different mix proportions. The parameter range is then applied to derive quantitative results related to crack propagation. Eventually, the accuracy of the parameter range is validated against both the mechanical properties and quantitative crack data obtained from simulations and experiment. [ABSTRACT FROM AUTHOR]

Asphalt concrete impervious facings, widely adopted as the impervious structures for rockfill dams and upper reservoirs in pumped storage power stations, typically have a multilayer structure with a thin sealing layer, a thick impervious layer, and a thick leveling bonding layer. The properties of the interfaces between these layers are crucial for the overall performance of the facings. This paper develops a model to investigate the complex interface damage behavior of the facing under static water pressure and gravity. The model considers two damage origins: one is the interface adhesion–decohesion damage, which is described by the cohesive zone model (CZM) combined with the Weibull-type random interface strength distribution, and the other is the bulk damage of each layer, described by Mazars' model. Primarily, a comparison between numerical simulation and indoor direct shear tests validates the reliability of the CZM for the asphalt concrete layer interface. Then, the damage distribution of the two interfaces is simulated, and the characteristics of the interface stress are analyzed in detail. The interface shear stresses of the ogee sections, which have different curvatures, all show an interesting oscillation between the thin sealing layer and the impervious layer, and the interface damage at this interface exhibits high heterogeneity. Furthermore, tension stress exists in the local zones of the ogee section, and the damage in this section is significantly greater than in other parts of the facings. [ABSTRACT FROM AUTHOR]

Determining the behavior of joints under a specific load and estimating the damage potential is essential for ensuring the durability of joints in engineering structures. Defects might occur at the adhesive layer, which causes a reduction in the durability of joints. This work aims to examine the effects of the defect presence, defect volume fraction, defect position, and random distribution of defects at the adhesive layer on the durability of the butt joint. A finite element (FE) model of the butt joint was constructed using the commercially available FE software Abaqus/Standard. The validation of the FE model was conducted by comparing its results with experimental finding reported in existing literature. Numerical and experimental results showed strong agreement, with relative errors of 2.46% and 2.95% at peak force and displacement at peak force, respectively. Defect presence significantly influences the durability of the butt joint. Defect volume fraction and defect location are the dominant parameters affecting the durability of the butt joint. The square defects at the center of the bonding layer, with volume fractions of 0.05, 0.10, and 0.15, lowers the peak force by 5.08%, 10.56%, and 15.73%, respectively. When the defect is positioned at the center of the bonding layer, adhesive failure starts at the edges of the defects. However, relocating the defect from the center to the left or upper side of the bonding layer results in adhesive failure initiation at the corresponding edges of the adhesive. Random defect distribution in the adhesive layer doesn't affect joint durability. [ABSTRACT FROM AUTHOR]

Strain localization frequently occurs in cohesive materials with friction (e.g., composites, soils, rocks) and is widely recognized as a fundamental cause of progressive structural failure.Nonetheless, achieving high-fidelity simulation for this issue, particularly concerning strong discontinuities and tension-compression-shear behaviors within localized zones, remains significantly constrained. In response, this study introduces an integrated algorithmwithin the finite element framework, merging a coupled cohesive zonemodel (CZM) with the nonlinear augmented finite elementmethod (N-AFEM). The coupledCZMcomprehensively describes tension-compression and compressionshear failure behaviors in cohesive, frictional materials, while the N-AFEM allows nonlinear coupled intraelement discontinuities without necessitating extra nodes or nodal DoFs. Following CZM validation using existing experimental data, this integrated algorithm was utilized to analyze soil slope failure mechanisms involving a specific tensile strength and to assess the impact of mechanical parameters (e.g., tensile strength, weighting factor, modulus) in soils. [ABSTRACT FROM AUTHOR]

Here, two single-lap adhesive joints (SLJs) of dissimilar materials were subjected to static and cyclic loading tests. A2017 aluminum alloy was used as an adherend for one, and carbon fiber reinforced plastic (CFRP) was used as the adherend for the other. Four types of orthogonal laminated CFRPs with different laminate stacking sequences were used as adherends to investigate the effect of adherend stiffness on the strength properties of the joints. Furthermore, the results of the finite element analysis of the dissimilar SLJs revealed that when the tensile load was applied to them, the out-of-plane deformation asymmetry increased with increasing difference in stiffness between both adherends. This asymmetry affected the peel and shear stress distributions. Furthermore, the experiments revealed that the static tensile strength of the SLJs increased with increasing stiffness of the CFRP adherend. Additionally, fracture simulation using cohesive-zone modeling (CZM) revealed that the SLJs with higher CFRP stiffness exhibited higher strength, qualitatively agreeing with the experimental results. CZM analysis and adhesion strain measurements during the tests indicated that failure occurred at the A2017 adherend–adhesive interface. In contrast, no differences were observed between the fatigue strengths of the different types of adherends in the short-life region, with a number of cycles to failure (Nf) being ≤ 2 × 105. However, in the long-life region, beyond Nf = 2 × 105, the SLJ bearing the unidirectional CFRP adherend exhibited lower fatigue strength than the others. The anodizing process on A2017 was found to improve fatigue strength by a factor of two or more.

It is important to clarify the uniaxial compressive mechanical properties and fracture mechanism of recycled aggregate concrete (RAC) from a mesoscale perspective for its further application in engineering. In this study, the cohesive zone model (CZM) based on the Benzeggagh–Kenane (B–K) criterion was used to simulate the RAC's complex fracture behavior. Meanwhile, the effects of cohesive element parameters and mechanical properties of mesoscale components on macroscopic mechanical properties and damage modes of RAC were investigated. The results show that the CZM based on the B–K criterion can be used to characterize the whole fracture process of RAC. The RAC's compressive strength has an exponential relationship with the shear strengths of the mortars as well as the ITZs and is quadratically related to the logarithm of cohesive element stiffness. The RAC's damage morphology is more sensitive to the change of element stiffness, Mode II fracture energy and hybrid fracture energy ratio.