Interfacial Fracture Mechanics Research Articles

Study on the interfacial microstructure and fracture mechanism of Al/Mg composites with Zn interlayer by cyclic hot pressing

Using the cyclic hot pressing method, Al/Mg laminated composites with a Zn interlayer were prepared, and the effect of temperature on the composite interfaces was studied. At 420℃, the composites interface is composed of HCP-Zn solid solution near the Al side and Laves phase near the Mg side. At 460℃, FCC-Al phase and τ-phase appear near the Al side, while τ-phase and HCP-Mg solid solution appear near the Mg side. Above 500℃, the interface is mainly composed of Al-Mg intermetallic compounds. The change of solubility during the formation of the composite causes the polarization of solute atoms in Zn and Al solid solutions, resulting in defects, such as increased grain boundary stress and lattice distortion. These defects lead to failure of the interface near the aluminum side of the composites. Composites prepared at 420℃ show the best ductile fracture properties. With the increase of preparation temperature, the fracture mode is transformed into brittle fracture induced by β-phase.

Interfacial microstructure and fracture mechanism of Cu/Al composite plate jointing process assisted by pulsed current-melted Al spheres: Finite element analysis and experimental studies

In this work, a novel method based on pulsed-current-assisted vacuum sintering processes was employed to fabricate the Cu/Al laminated metal composites (LMCs) with outstanding mechanical properties. The microstructural evolution, interfacial characteristics, phase composition, mechanical properties, and fracture behavior of Cu/Al composites prepared by the melted Al spheres induced with high-frequency pulsed current were investigated. Results show that robust interfacial bonding without micropores and cracks, and the grain structure consists mainly of recrystallized and substructured grains characterized by high angular grain boundaries. Meanwhile, interfacial analysis identifies melted Al and Al2Cu phases within the transition layer, exhibiting distinctive features such as "Al+Al2Cu" corrugated interfaces and island eutectic structures. Additionally, mechanical properties demonstrate superior strength (210 ± 13 MPa) and elongation (27 % ± 0.7 %) in specimens with corrugated interfaces compared to those with flat interfaces. Finite element analysis further elucidates stress redistribution and fracture behavior, emphasizing the enhanced coordinated deformation in specimens featuring corrugated interfaces. These findings underscore the significance of interface engineering and microstructural refinement in optimizing the mechanical performance of Cu/Al composite materials, offering valuable insights for their application in diverse engineering domains.

Evolution of Atomic-Level Interfacial Fracture Mechanics in Magnesium-Zinc Compounds Used for Bioresorbable Vascular Stents.

Bioresorbable magnesium-metal vascular stents are gaining popularity due to their biodegradable nature and good biological and mechanical properties. They are also suitable candidate materials for biodegradable stents. Due to the rapid degradation rate of Mg metal vascular scaffolds, a Mg/Zn bilayer composite was formed by a number of means, such as magnetron sputtering and physical vapor deposition, thus delaying the degradation time of the Mg metal vascular scaffolds while providing good radial support for the stenotic vessels. However, the interlaminar compounds at the metal interface have an essential impact on the mechanical properties of the bi-material interface, especially the cracking and delamination of the Mg matrix Zn coating vascular stent in the radially expanded process layer. Intermetallic compounds (IMCs) are commonly found in dual-layer composites, such as Mg/Zn composites and multi-layer structures. They are frequently overlooked in simulations aiming to predict mechanical properties. This paper analyses the interfacial failure processes and evolutionary mechanisms of interfacial fracture mechanics of a Mg/Zn interface with an intermetallic compound layer between coated Zn and Mg matrix metallic vascular stents. The simulation results show that the fracture mode in the Mg/Zn interface with an intermetallic compound involves typical ductile fracture under static tensile conditions. The dislocation line defects mainly occur on the side of the Mg, which induces the Mg/Zn interfacial crack to expand along the interface into the pure Mg. The stress intensity factor and the critical strain energy release rate decrease as the intermetallic compound layer's thickness gradually increases, indicating that the intensity of stress and the force of the crack extending and expanding along the crack tip are weakened. The presence of intermetallic compounds at the interface can significantly strengthen the mechanical properties of the material interface and alleviate the crack propagation between the interfaces.

CFRP-RC fracture strength prediction: A novel approach using deep learning

Externally bonded carbon fiber-reinforced polymer (CFRP) composites have been widely adopted for strengthening and repairing aging concrete structures. However, premature fracture at the CFRP-concrete interface remains a significant concern, necessitating a better understanding of the interfacial bond behavior and fracture mechanisms. Traditional experimental studies and numerical simulations have limitations in accurately capturing the complex nonlinear factors influencing this fracture behavior. This paper explores the novel application of machine learning (ML), specifically artificial neural networks (ANNs), for predicting the fracture strength of CFRP-reinforced concrete (CFRP-RC) members. ANNs enable mapping the intricate relationships between input parameters (e.g., CFRP/concrete properties, geometric configurations) and fracture responses through iterative training on experimental data. Key aspects include comprehensive data collection, preprocessing techniques, feature selection methods like mean impact value (MIV) analysis, and neural network architecture design. The paper highlights successful ANN applications in predicting CFRP-RC bond strength, shear capacity, and overall fracture behavior. A systematic approach is proposed for developing robust ANN models tailored to CFRP-RC fracture prediction, encompassing data curation, input variable screening, network training/validation, and model interpretability analyses. By leveraging ML’s ability to handle multifaceted nonlinearities, this data-driven framework offers a powerful alternative to traditional methods, potentially enhancing the design, analysis, and performance evaluation of CFRP-strengthened concrete structures.

Shear behavior of Cu/Al/Cu trilayered composites prepared by high-temperature oxygen-free rolling

The interfacial microstructure, interfacial shear properties, and shear fracture morphology of Cu/Al/Cu trilayered composites prepared by high-temperature oxygen-free rolling were studied, and the interfacial shear fracture mechanism was revealed. The results showed that the Cu/Al/Cu trilayered composites have a good metallurgical bonding interface. The interfacial microstructure is composed of Al2Cu, AlCu, and Al4Cu9. The intermetallics (IMCs) parallel to the rolling direction show discontinuous distribution, while the IMCs perpendicular to the rolling direction have mainly continuous distribution and occasional discontinuous distribution. The interfacial shear strength at room temperature can reach 68 MPa, and when the test temperature rises to 350 °C, the interfacial shear strength drops sharply to 16.9 MPa. The interfacial shear fracture mainly occurs in the low-strength Al layer due to the good metallurgical bonding interface. The IMCs near the shear fracture exhibit clear signs of cracking, and there is a phenomenon where the Cu layer embeds into the Al layer in a "sawtooth" shape. Meanwhile, shear fracture also occurs in the IMCs layer, and a small amount of Al will attach to the surface of the IMCs. However, the high bonding strength resulting from the excellent metallurgical bonding of the interface makes this type of shear fracture rare. The shear fracture of Cu/Al/Cu trilayered composites is mainly dominated by the fracture of the low-strength Al layer and the occasional fracture of the IMCs.

First-principles calculation on the interfacial stability, electronic structure and fracture mechanism of NbN/AlN interface

The interfacial stability of NbN(111)/AlN(0001) including interfacial energy, Wad(work of adhesion) and electronic structure were studied by first-principles calculation. The N1-Nb-cen interface(constructed with N1-terminated AlN(0001) and Nb-terminated NbN(111)) is determined to be the most stable interface which has the smallest interfacial distance(1.11 Å) and largest Wad(15.04 J/m2) among the 28 considered interface models. The electronic structure and ideal tensile stress of the N1-Nb-cen, N2-Nb-top, Al2-N-top and Al1-Nb-cen interfaces were also investigated. The AlN surface has stronger ionic bond than that in NbN surface according to the analysis of Mulliken charges. The bonding feature of N1-Nb-cen interface is ionic with strong covalent, while the other three interfaces have mainly ionic bond. The ideal tensile stress of the N2-Nb-top interface is the largest (22.88 GPa) at the strain of 17 %, which is larger than that of N1-Nb-cen interface. The fracture will occur at the interface for the Al2-N-top and Al1-Nb-cen interfaces, while it occurs at the AlN interior for the N1-Nb-cen and N2-Nb-top interfaces, due to the Wad of the N1-Nb-cen and N2-Nb-top interfaces are larger than the other two interfaces and atomic stacking of AlN surface.

Research on the deformation law of ultra-thin fiber metal laminates under the synergistic effect of nano-reinforcement and scale effect

At present, titanium alloy/carbon fiber reinforced polymer (TA1/CFRP) laminates, representing the latest fourth generation of fiber metal laminates (FMLs), are predominantly applied in the field of aerospace. The miniaturization of traditional FMLs in thickness or plane size to the micron level for the study of structural properties of ultra-thin laminates will further expand the application of FMLs in the field of micro-devices. Given that carbon nanotubes have a strengthening mechanism in polymers. However, most existing studies have focused on the effect of carbon nanotubes on the properties of macro-scale FMLs, while the enhancement mechanism of the interfacial and mechanical properties of ultra-thin micro-scale FMLs has not been studied, leaving the mechanism still unclear. Based on this, this paper explores the interfacial deformation mode, damage fracture and performance enhancement mechanism of the ultra-thin TA1/CFRP laminates by comparing the parameters of tensile strength and elongation under quasi-static conditions and different process parameters of multi-walled carbon nanotubes content, test temperature, geometry size and grain size. Meanwhile, the correlation law between high-speed tension and quasi-static tension is determined, a 29.3 % increase in tensile strength as the strain rate rises from 0.001 s−1 to 100 s−1, yielding the basic deformation law of ultra-thin FMLs.

Non-oscillatory fracture mode partition for interface crack under mixed-mode loading

The oscillatory crack-tip field in the classical interface fracture mechanics solution often leads to complications in identifying the mode mixity in bimaterial interface fracture problems. In this paper, a non-singular series solution for the continuum problem of a crack on the cohesive-spring interface under mixed-mode loading is presented and compared to the classical oscillatory solution. A Gaussian process regression model was also developed to enable quick evaluation of the phase angle for interface delamination characterization by using mixed-mode bending fracture test.

Development of single‐stream resin transfer molding using in‐situ anionic polymerization of ε‐caprolactam with preprocessing on carbon fibers

AbstractThermoplastic resin transfer molding (T‐RTM) is one of the composites manufacturing processes using anionic ring‐opening polymerization of ε‐caprolactam (CPL). Because of very fast reaction among materials, traditional T‐RTM requires two different channels before transferring resin into the mold cavity. Single‐stream method has been researched for robust and simple process, which has several advantages in aspect of manufacturing process. Carbon fibers were preprocessed including polyamide sizing, plasma treatment and activator sizing for modified single‐channel T‐RTM. Through quantitative calculation of required sizing content, concentration of sizing agent was controlled. Thermal stability of preprocessed carbon fibers during molding was measured by TGA. Crystallinity of anionic‐polyamide 6 (A‐PA6) manufactured by single‐stream T‐RTM was measured by DSC and 3.0% lower than traditional T‐RTM. Mechanical properties were measured, which are short‐beam strength and flexural strength/modulus. The short‐beam strength and flexural strength of the composites fabricated through single‐stream T‐RTM were 29.7% and 17.0% higher than those fabricated through conventional T‐RTM while strain and toughness decreased. Fracture surface of carbon fibers/A‐PA6 composites manufactured by single‐stream T‐RTM showed more adhesive bonding between carbon fiber and matrix.Highlights Surface treatment on carbon fibers to develop single‐channel T‐RTM process. Effects of surface treatment researched by thermal, quantitative, and IR analysis. Improved interfacial fracture mechanisms due to higher adhesion at the interface.

Microstructure and Mechanical Properties of IN690 Ni-Based Alloy/316LN Stainless-Steel Dissimilar Ring Joint Welded by Inertia Friction Welding.

Inertia friction welding (IFW) was used to join large-diameter hollow bars made of Inconel 690 and 316LN successfully. The interfacial characteristics, microstructure, mechanical properties and fracture mechanism of welded joints under different process parameters were investigated. The results indicated that a joining mechanism with mechanical interlocking and metallurgical bonding was found in IFW joints. There was a significant mechanical mixing zone at the welding interface. The elemental diffusion layer was found in the "wrinkles" of the mechanical mixing zone. A tiny quantity of C elements accumulated on the friction and secondary friction surfaces. The tensile strength and impact toughness of the joints increased with the total welding energy input. Increasing the friction pressure could make the grain in all parts of the joint uniformly refined, thus enhancing the mechanical properties of welded joints. The maximum tensile strength and impact toughness of the welded joint were 639 MPa and 146 J/cm2, reaching 94% and 68% of that for Inconel 690, respectively, when the flywheel was initially set at 760 rpm, 200 MPa for friction pressure, and 388 kg/m2 for rotary inertia. Due to the Kirkendall effect in the welded joint, superior metallurgical bonding was at the welding interface close to the Inconel 690 side compared to the 316LN side.

Interfacial regulation and fracture mechanism of Al–Si/SiC composites infiltrated under super-gravity field

We reported a novel method to prepare Al–Si/SiC composites infiltrated under super-gravity field without Mg addition. Noted that centrifugal force acted as the main driving force to overcome the penetration resistance, making it feasible to obtain the Al–Si/SiC composite with high relative density (≥99.3 %). The interfacial reaction between Al and SiC was retarded by Si addition under super-gravity field. Interestingly, the rod-like eutectic Si was detected at Al–SiC interface with semi-continuous distribution, leading to the excellent bending strength (342.6 ± 1.0 MPa), enhanced thermal conductivity (173 W/m K at 373 K), and relatively low coefficient of thermal expansion (8.90 × 10−6 K−1 ranged from 323 to 373 K). The interfacial regulation and fracture mechanism were discussed in details.

Prediction of crack growth at trailing edge bondlines of a wind turbine rotor blade for the assessment of remaining service life

Debonding along trailing-edge joint of a wind turbine rotor blade is one of the often reported failure modes during the rotor blade maintenance inspections. This study focuses on buckling-induced debonding along the trailing edge under in-plane compressive loads due to the gravity forces on the rotor blade. With a priori known debond crack length, an analytical model is used for predicting debond growth rate and assessing the time that takes the crack to reach a critical length. For the growth rate prediction, required input parameters are size of the initial debonding, laminate and adhesive layer thicknesses, elastic and interfacial fracture mechanics properties, gravitational load distribution and position of the initial debonding. The damage model is implemented in excel spreadsheet tool. The predictions of the analytical model were compared with the results from 3D finite element simulations and the difference between the results (energy release rate) was 8%. This study demonstrates how damage specific tools can be developed for predicting remaining useful life of rotor blades.

Micro-nano interface structure and mechanical characteristics of thin wall Cu/Al composite tubes prepared by strong staggered spinning

In this paper, a method of stamping first and then strong staggered spinning was studied to process Cu/Al laminated composite into thin-walled composite tube. The multi-scale interfacial structure, element diffusion, microscopic evolution, mechanical properties and fracture mechanism of the tubes with different thickness reduction (TR) were studied by different material characterization methods. The results show that with the increase of TR, the interface experienced brittle layer fracture, fresh metal extrusion, new diffusion layer and the formation of the interface, and always maintained a good combination. Under the shearing force of the outer rotating wheel, the grain sizes of both sides of Cu and Al with 80%TR are reduced to 0.75 μm and 1.15 μm by 82% and 80% refinement, respectively. The deformation of Cu is induced by work hardening and dynamic recrystallization (DRX), and the strain inhomogeneity caused by 〈111〉 fiber is transferred from grain boundary to interior with the increase of TR. The Al side is mainly dominated by dynamic recovery (DRV), and the grain presents random and uneven strain, and finally changes to the internal grain strain mutation dominated by 〈001〉 fiber. The Cu grains near the rotating wheel are elongated at an inclination of 45°, but others at the interface are fine and equiaxed, suggesting good deformation coordination at the interface. The deformation coordination and strain transfer are stimulated by the change of micro-nano mechanical properties of Cu, interface and Al. Compared with the initial state (IS), the YS (124.52 MPa) and UTS (145.26 MPa) of Cu/Al composite tube with 80%TR are improved by 58% and 10%, respectively. Cu and Al show ductile fracture and brittle fracture respectively, and more metastable critical cracks are excited at the interface to avoid debonding and delamination.

Inter-fibre failure under biaxial loads in glass–epoxy composite materials: Effect of the presence of a nearby fibre

Fibre-reinforced composite materials are especially prone to transverse failure. It appears at the lamina level following the mechanism known as matrix/inter-fibre failure. This mechanism of damage is associated with the appearance of fibre–matrix debonds (interface cracks), as shown in previous numerical micromechanical studies. After the nucleation, growth and kinking into the matrix, these interface cracks give rise to the final macro-failure.When compared to uniaxial loading, the growth stages of this mechanism of damage (analysed in light of Interfacial Fracture Mechanics) show some alterations under different combinations of biaxial loads. This work gives a step forward and focuses on the micromechanical BEM study of the evolution of an interface crack in the presence of a neighbouring fibre.Thus, after considering a transverse tensile load (nominally responsible for the failure) a secondary transverse load is also applied (tensile or compressive, perpendicular to the primary load). When considering the two-fibre BEM model, the results obtained lead to identifying the neighbouring fibre locations that act as accelerative agents on failure progression and establishing the effect of the biaxial load on them. Specifically, when a secondary tensile load is applied, the presence of the nearby fibre (for most of its positions) confirms the slight inhibition of the mechanism of failure for biaxial tensile loads already referred to in previous single-fibre studies by the authors. As the secondary tensile load increases, it tends to mitigate the effect of the presence of the neighbouring fibre that was previously observed for uniaxial tensile load. The opposite effects are found when a secondary compressive load is considered, which intensifies the alterations of the presence of the neighbouring fibre on the interface crack growth. Experimental evidence on some aspects is provided confirming the associated conclusions derived from the numerical models.

Interfacial fracture characteristics of Mg/Al composite plates with different thickness ratios by asymmetrical rolling with differential temperature rolls

In this work, Mg/Al laminated metal composites with different thickness ratios were prepared by a two-pass rolling process combining asymmetrical rolling with differential temperature rolls and isothermal symmetrical rolling. The effects of different matrix thickness on the interfacial microstructure, texture evolution, mechanical properties and interfacial fracture mechanisms of Mg/Al composite plates were systematically investigated. Results showed that the thickness ratios can induce different recrystallization degrees and deformation amounts of Mg and Al layers. This results in a strong positive correlation between the thickness of diffusion layer and the thickness ratio of plate. For thickness ratios (TR) of AZ31B/Al6061 at 2, 3 and 5, the TR5 sample had the relatively largest thickness of intermetallic compounds (IMCs) and the relatively smallest bonding strength. The thickness of diffusion layer has different effects on crack initiation and propagation, which leads to first increase and then decrease in the strength and plasticity of composite plates with increasing thickness ratios. Cracking occurs at the bond between the β (Al3Mg2) in IMCs and Al layers, which is due to the aggregation of the Mg2Si phase at this location. The distribution state of the Mg2Si phase at the interface is closely related to the thickness ratio. The Mg2Si phase at the interface of the TR3 sample is better refined and uniformly distributed, which gives it the relatively best mechanical properties.

The influence of substrate stiffness on interfacial stresses for adhesive microfibrils

Bioinspired microfibrillar surfaces adhere by exploiting the presence of intermolecular forces at the contact interface. Experimental work has shown that compliant mushroom shaped fibrils can facilitate optimal adhesion across a range of substrates. This work evaluates numerically how fibril contact tip shape and the degree of elastic mismatch at the fibril-substrate interface influence adhesion. In a finite element simulation of fibrils subject to a remote stress, the interfacial stress distributions that define the detachment behaviour are computed for a range of fibril cap diameters, thicknesses, and substrate stiffnesses. Depending on the substrate stiffness, there is a singular stress field present at the edge of contact for smaller mushroom cap and straight punch fibrils while the stress at the corner for larger mushroom fibrils tends to zero. This variation in fibril-substrate interfacial stress has implications for the most probable defect type to initiate detachment and the stability of this crack growth. For fibrils within this corner singularity regime, the adhesion strength of a patch of fibrils is determined using interfacial fracture mechanics. The simulations are compared with experimental data of pull-off strengths and the biomedical applications of adhesive microfibrillar patches are considered.

A Facile Way to Modify Polyester Fabric to Enhance the Adhesion Behavior to Rubber

Due to the extremely inert surface of polyester (PET) fabric, a toxic and traditional resorcinol-formaldehyde-latex (RFL) dipping solution is always necessary in the rubber composite industry. Unfortunately, other effective methods for fabric surface treatment are in urgent need to improve the poor bonding interface between the fabric and the rubber matrix. In our study, a facile way to modify PET fabric was developed. Specifically, the fabric was treated by an alkaline solution and a coupling agent with magnetic agitation. Afterwards, the treated fabric/rubber composites were prepared through a co-vulcanization process. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and thermogravimetric analysis (TGA) were used to characterize the surface chemical composition of the modified fabrics. The adhesion behavior was analyzed by the peel test. The results showed that the fabric surface was successfully grafted with a coupling agent, and the peel strength reached 9.8 N/mm after KH550 treatment, which was an increase if 32% compared with that of the original fabric/rubber composite. In addition, the vulcanization rate and interfacial fracture mechanism are also researched.

Study on Interfacial Crack Initiation of Jointed Rock Mass Based on Interface Fracture Mechanics

The fracture of interfacial crack is the main failure type of jointed rock mass. Therefore, it is very important to study the interfacial fracture of jointed rock mass. For the similarity of jointed rock mass and composites (all are composed by two parts, intact materials and their contact interfaces), the interface fracture mechanics widely used for analysis the interface crack of the composites (bimaterials) can be applied to study the interfacial fracture of jointed rock mass. Therefore, based on the basic theories of interface fracture mechanics, the interfacial fracture of jointed rock mass was analyzed, and one new criterion of interfacial crack initiation for jointed rock mass is proposed. Moreover, based on the proposed interfacial crack initiation criterion, the effect of main influence factors on the interfacial crack initiation of jointed rock mass was analyzed comprehensively. At last, by using the triaxial compression numerical tests on a jointed rock mass specimen with interfacial crack, the theoretical studies were verified.

Effect of clamping pressure on interfacial fusion morphology and fracture mechanism of CFRTP/Ti6Al4V laser bonding joint featuring blind hole surface microtextures

Carbon fiber reinforced thermoplastic composites (CFRTP) and titanium (Ti) alloy are both important lightweight materials in aircraft and aerospace applications, whose heterogeneous hybrid structure manufactured by laser joining technology is propitious to leverage the performance advantages of each component. The clamping pressure during the laser joining procedure is one of the most critical process parameters affecting the joint performance. Laser joining of CFRTP to Ti alloy (Ti6Al4V) under various clamping pressure is carried out, aimed to investigate the effect of clamping pressure on interfacial fusion morphology, mechanical property and fracture mechanism of bonding joint featuring blind hole surface microtextures. The fusion morphology and element distribution at joining interface are observed by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). Moreover, the fracture morphology and fracture mechanism are analyzed after tensile-shear test. The results show that an appropriate increase of clamping pressure improves the filling effect of melted resin to microtextures on Ti alloy surface, while too high pressure is inclined to induce the generation of pores and cracks at the joining interface. The fracture load of the joints increases and then decreases as the pressure rises, and it reaches a peak value of 3821.4 N corresponding to the optimal interfacial fusion effect when the pressure is 0.8 MPa. Significant distinctions exist in the main fracture mechanisms under different clamping pressure conditions, which lead to different fracture surface morphologies and mechanical performance of laser bonding joints.

Experimental and Statistical Study of the Fracture Mechanism of Sn96.5Ag3Cu0.5 Solder Joints via Ball Shear Test.

Ball shear testing is an efficient approach to investigate the mechanical reliability of solder joints at the structural level. In the present study, a series of low-speed ball shear tests were conducted to study the deformation and fracture characteristics of Sn96.5Ag3Cu0.5 solder joints at continuous speeds from 10 μm/s to 200 μm/s. In order to account for randomness, the quantity of tests was repeated for each shear rate. The relationship between mechanical properties and shear speeds was calculated in detail via effective statistical analysis. In addition, by utilizing SEM imaging and ingredient analysis the interfacial effect and fracture mechanism of solder balls were obtained and their fracture mode classified into two types, viz., bulk fracture and interface fracture. Furthermore, by means of statistical analysis and approximate calculation it was proven that bulk fracture balls have greater adhesive powers and reliability compared with interface fracture balls.