A micromechanical framework for predicting interfacial fracture in electronic boards using strain energy release rate concept

A photothermal antibacterial hydrogel based on a "nano-bridge" strategy with high toughness and self-healing capacity.

Physical characterization and bond performance of a non-methacrylate dental adhesive in long-term biochemical and thermal aging models.

Purpose The purpose of this study is to explore the size effect on shear mechanical behavior of microscale ball grid array (BGA) structure Cu/SAC305/Cu solder joints with different heights under current stressing, and to reveal the influence mechanism of current and solder joint’s height on shear performance and fracture behavior. Design/methodology/approach A dynamic mechanical analyzer was used in conjunction with a constant current power supply to conduct shear mechanical testing of solder joints under current stressing with current densities from 6.0 × 103 to 1.1 × 104 A/cm2. Meanwhile, temperature, current density, stress and strain distribution in solder joint are analyzed in combination with finite element simulation to further reveal the evolution mechanism of mechanical behavior of solder joint. Findings This study reveals that the shear size effect in solder joints originates from the weakened constraint effect of the intermetallic compound (IMC)/substrate interface on the solder matrix with increase of joint height. Furthermore, incorporating in situ current stressing demonstrates that greater joint height leads to greater heat accumulation at identical current densities, resulting in monotonic degradation of shear strength with greater joint height. Simultaneously, greater joint height intensifies current crowding and strain mismatch at the solder/IMC interface, promoting interfacial fracture. These findings are rigorously supported by decline-rate trends and a finite element (FE)-validated simulation mechanism chain (including stress triaxiality, temperature, current density and stress/strain fields), establishing quantitative thresholds for interfacial fracture initiation. Originality/value This study extends previous research on shear size effect of solder joints by incorporating in situ current stressing. The coupling influence of joint height and current stressing was revealed by a FE-validated mechanism chain, and relevant quantitative thresholds was established, providing critical data and theoretical support for evaluating the reliability of microscale BGA-structured solder joints under current stressing.

Comment on “A critical note on the role of the contact stiffness in fracture of the multi-punch contact interface” by I. Argatov

Interfacial Bonding and Fracture Mechanism of Tempered Glass and Aluminium Alloy Direct Welding by Top-hat Nanosecond Laser

Cutting soft materials is a complex process governed by the interplay of bulk large deformation, interfacial soft fracture, and contact forces with the cutting tool. Existing experimental characterizations and numerical models often fail to capture the variety of observed cutting behaviors, especially the transition from indentation to cutting and the roles of dissipative mechanisms. Here, we combine novel experimental cutting tests on three representative materials—a soft hydrogel, an elastomer, and food materials—with a coupled computational model that integrates soft fracture, adhesion, and frictional interactions. Our experiments reveal material-dependent cutting behaviors, with abrupt or smooth transitions from indentation to crack initiation, followed by distinct steady cutting regimes. The computational model captures these behaviors and shows that adhesion and damping contributions in the cohesive forces dominate tangential stresses, while Coulomb friction plays a negligible role due to low contact pressures. Together, these results provide new mechanistic insights into the physics of soft cutting and offer a unified framework for soft cutting mechanics to guide the design of soft materials, cutting tools, and cutting protocols, with direct relevance to surgical dissection and the engineering of food textures optimized for mastication.

The mechanical performance of additively manufactured composites is strongly governed by fibre–matrix interfacial adhesion, which can be compromised by process-induced imperfections. This study examines how fibre embedded length controls interfacial adhesion behaviour and failure mechanisms in 3D-printed continuous carbon fibre-reinforced polyethylene terephthalate glycol (PETG) composites, using single-fibre pull-out testing combined with scanning electron microscopy (SEM). Specimens with embedded lengths ranging from 1 mm to 50 mm were tested to capture the transition between fibre slippage and fibre fracture. A critical embedded length ( L c ) of 4.88 ± 0.54 mm was determined, beyond which fibre fracture dominates. The apparent interfacial shear strength (IFSS) was measured as 18.6 ± 1.2 MPa, while the interfacial fracture energy ( G c ) was calculated as 27.3 J/m 2 . A linear traction–separation cohesive law was fitted based on these experimental parameters. SEM imaging reveals distinct microstructural features associated with the two failure modes. These findings establish practical benchmarks for optimising fibre placement, orientation strategies, and load transfer efficiency in 3D-printed composites. The outcomes contribute to the advancement of lightweight composite structures for aerospace and automotive applications.

Alloys with low thermal expansion, high strength, and superior plasticity are crucial for critical applications in industries such as aerospace. Although the in-situ formation of low or negative thermal expansion particles presents a promising strategy, these materials generally suffer from limited ductility. Here, we demonstrate that the construction of nanoscale gradient ordered architectures can effectively addresses this limitation. By facilitating the diffusion and reaction of aluminum (Al) atoms into boronized manganese (Mn-B), we induce a gradient ordering architecture between rare-earthed magnesium (Mg) alloys and MnB phase, achieving a near-zero thermal expansion coefficient of 0.8 × 10-6·°C-1 within the temperature range of 280–320 °C. As fully transitioning from Mn-B to a multi-gradient ordered Mn-Al-B configuration results in a stabilized thermal expansion coefficient of 23 ×10-6·°C-1 across a broad temperature range (25–400 °C). This nanoscale architecture not only mitigates brittle interfacial fractures by maintaining the mechanical integrity but also enables the Mg alloy to reach an ultrahigh compressive strength of 507 MPa, with a 23.8% compressive strain. Our findings highlight the potential of designing gradient ordered architectures as a strategic approach to enhance the mechanical properties of lightweight alloys.

Abstract The study aims to investigate the fracture properties of dam‐heel interfaces, which are often weak points in hydraulic structures such as arch dams. The research examines how high‐pressure water exposure influences crack evolution, damage mechanisms, and fracture behavior at concrete‐rock composite interfaces. Specimens were innovatively tested for three‐point bending and four‐point shear after water pressures ranging from 0 to 4 MPa, imitating high dam conditions. Digital image correlation and acoustic emission techniques caught the FPZ evolution process across scales, revealing crack propagation from micro‐crack accumulation to macro‐crack penetration. The study found that initial material degradation from high‐pressure water altered the fracture mode and energy release mechanism. It prevented micro‐crack activity and shear crack formation and shifted the major fracture mechanism from shear to tensile, modifying the crack propagation path and reducing interface fracture toughness. Computational models incorporating the characteristic length and width of the nonlinear fracture process zone revealed a substantial reduction in fracture properties, which increased proportionally with the modal mixing ratio. The findings highlight that high‐pressure water exposure deteriorates the fracture properties at the concrete‐rock interface and corrected the water's impact on FPZ. These insights provide a novel theoretical basis and essential criteria for the safety evaluation of hydraulic engineering while advancing crack resistance design strategies for high dam structures in light of high‐pressure water damage during the design phase.

A novel method to assess the interfacial fracture toughness of two universal resin cements to dentin.

ABSTRACT The failure of the SiO2/Y2Si2O7 interface in environmental barrier coatings (EBCs) significantly limits service life, yet the atomic-scale mechanism by which termination-dependent bonding chemistry governs interfacial fracture remains unclear. Using density functional theory, we compared four terminations (Si-Si, Si-Y, O-Si, and O-Y) and found the O-Si-terminated interface exhibits the highest stability. Its work of adhesion (5.72 J/m2) and tensile strength (852 MPa) are 20% and 25% higher, respectively, than those of the Si-Y termination. Electronic structure analysis reveals that this superiority arises from strong Si-p and O-p orbital hybridization, forming covalent Si-O bonds (bond population = 0.57) and continuous electron cloud accumulation across the interface. In contrast, the Si-Y termination features weak bonds (bond population = 0.19–0.34), causing electron localization and reduced cohesion. Interfacial fracture toughness ( K I c i n t = 2.04–2.48 MPa·m1/2) correlates positively with adhesion work, confirming the bonding-performance relationship. Based on these findings, an interface design guideline is proposed: preferential formation of oxygen-terminated interfaces via optimized deposition conditions can enhance the toughness of EBC interfaces. Nonetheless, discrepancies between theoretical predictions and experimental measurements of toughness require further investigation through multiscale simulations, including grain boundary effects.

This paper investigates the interfacial bonding mechanism between basalt fiber-reinforced polymer-modified magnesium phosphate cement (BFPMPC) and conventional cement concrete. An asymmetric semicircular bending specimen with a preset crack was designed to evaluate the fracture resistance of the repair interface. Interface fracture behavior was further analyzed using fracture parameter evaluation. In addition, the interfacial hydration morphology was characterized by scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS) and backscattered electron imaging. The results showed that the compressive and flexural strengths of the BFPMPC mortar reached 46.1 and 11.2 MPa, respectively. Among the tested configurations, the interface subjected to Mode II fracture exhibited the highest flexural strength, and the minimum fracture toughness (1.711 MPa·m 1/2 ) occurred under Mixed mode I/II at M e = 0.346, indicating the lowest resistance to crack propagation. Fracture behavior was influenced by a cubic fit interaction between the fracture parameters K IC and K IIC , which probably resulted from microstructural heterogeneity and nonlinear stress redistribution. The SEM/EDS observations revealed that the hydration products at the interface were porous and loosely structured. Among the sub-interfacial transition zones (ITZs) in the repair interface, ITZ-4 exhibited the smallest pore gradient variation, and ITZ-3 showed the loosest structure, contributing to its reduced mechanical properties.

Living conductive hydrogels that unite biological activity with robust electrogenic performance are emerging as transformative platforms for adaptive bioelectronics, yet most lose electrical functionality after mechanical damage or extended use. Here, we introduce an electrogenic living hydrogel embedding Bacillus subtilis spores─metabolically dormant, environmentally resilient, and capable of germinating into electrogenic bacteria─within a dual self-healing framework. The primary mechanism exploits hydrogen-bonded poly(3,4-ethylenedioxythiophene):polystyrenesulfonate-poly(vinyl alcohol) (PEDOT:PSS-PVA) networks to restore mechanical integrity, while a secondary, conductivity-specific mechanism is activated by rupture of carbon nanotube (CNT)-loaded cellulose acetate microcapsules at the fracture interface, re-establishing percolation pathways. Germination triggers extracellular electron transfer (EET) by B. subtilis, synergistically boosting conductivity beyond the undamaged state and reducing internal resistances. As a proof-of-concept, the hydrogel served as the anode in a paper-based microbial fuel cell (MFC), achieving a maximum power density of 1.5 μW cm-2 and an open-circuit voltage of 0.38 V─comparable to state-of-the-art paper MFCs. By integrating mechanically resilient matrices, microcapsule-mediated conductivity restoration, and biologically triggered electroactivity, this platform establishes a paradigm for self-repairing, high-performance living electronics with broad potential in biosensing, energy harvesting, and soft bioelectronic systems.

ABSTRACT Understanding the role of surface defects in nanoparticles is crucial for optimizing the interfacial design of polymer composites. In this study, molecular dynamics (MD) simulations were employed to investigate the influence of geometrical defects in boron nitride nanotubes (BNNTs) on the mechanical, interfacial, and tribological properties of nitrile butadiene rubber (NBR) matrices. Results reveal that defect‐free BNNTs provide the most effective reinforcement of the tensile properties of NBR, followed by Stone–Thrower–Wales (STW)‐defective BNNTs, whereas di‐vacancy (DV)‐defective BNNTs only have an obvious enhancement effect on the elastic modulus of NBR. Pull‐out simulations further demonstrate that, compared to DV‐ and STW‐defective BNNTs, defect‐free BNNTs enhance the interfacial shear strength and interfacial fracture toughness of NBR composites by 21.2% and 5.96%, and 22.5% and 5.14%, respectively. Additionally, compared with neat NBR, the incorporation of defect‐free, DV‐defective, and STW‐defective BNNTs reduces the friction coefficient and abrasion rate by 1.92% and 18.36%, 3.69% and 17.24%, and 3.97% and 17.84%, respectively. To elucidate the underlying mechanisms of BNNT surface defects, detailed analyses of the structural evolution of the composite networks and interfacial states were conducted. Overall, these findings provide new insights into the defect‐mediated reinforcement behavior of BNNTs and offer guidance for the rational design of defect‐engineered nanofillers to improve the performance of polymer composites.

Resistance spot welding (RSW) was carried out on a 3 mm thick 7075 aluminium alloy. A 50 μm thick Zn interlayer was added to improve the weld quality and mechanical properties of the joint. The macroscopic morphology, microstructure, precipitated phase, microhardness, and mechanical properties of the RSW joint before and after the addition of the Zn interlayer were comparatively analyzed. After adding the Zn interlayer, the microstructure and mechanical properties of the welding joints were considerably improved, and the effective range of the welding current was expanded. The grain size of the welding joint was clearly refined, the columnar crystal zone narrowed, and the equiaxed crystal zone widened. The precipitated phase changed from a reticular or long-strip-like to point- or short-strip-like and decreased in size. The number of precipitated phases increased, and the phase distribution became more uniform. The number of defects in the welding joint clearly decreased, and the joint microhardness increased. The maximum tensile shear force sustained by the Zn-RSW joint was 14.29 kN, which was 51.5 % greater than that without the Zn interlayer. The addition of the Zn interlayer changed the fracture mode from interfacial fracture to button fracture, and obvious plastic deformation occurred before the fracture. The Zn-RSW joint could absorb 245 % more energy than the RSW joint.

Natural fractures are critical for hydrocarbon extraction in unconventional reservoirs, but they are often cemented by minerals. Hydraulic fracturing can open these cemented fractures, creating a bounded empty-porous system with an empty region and a cement pack. However, no studies have yet characterized fluid flow in this scenario, leading to inaccurate predictions of the delivery capacity of opening cemented natural fractures (OCNFs). This study presents a novel analytical model to evaluate the equivalent permeability of OCNFs, incorporating viscous shear from fracture walls and the coupled empty-porous system. Unlike traditional Darcy's law, fluid flow in the cement pack is described using the Brinkman equation to account for effects from the porous medium, fracture walls, and viscous drag at the empty-porous interface. The model is validated through commercial software (e.g., COMSOL Multiphysics). The equivalent permeability and flow velocity profiles of OCNFs are analyzed with various impact factors. Results show that fracture wall and empty-porous interface effects become more significant as cement pack permeability increases, while their influence on fluid flow decreases with greater cement pack width. If the fracture width is large enough, these effects become negligible. Integrating the permeability predicted by both models into reservoir simulations reveals that neglecting fracture wall and interface effects leads to significant errors in well performance evaluation.

Identification of the interfacial fracture energy at high temperature of an environmental barrier coating on a ceramic matrix composite

Overview of interfacial fracture toughness testing of ceramic coatings at room and elevated temperatures

A surrogate-based machine learning model for prediction of interfacial fracture energy of externally bonded FRP–concrete with a user-friendly tool