Interfacial Fracture Research Articles

Review on interpretations, applications, and developments of numerical methods in studying interface fracture

Review on interpretations, applications, and developments of numerical methods in studying interface fracture

A critical note on the role of the contact stiffness in fracture of the multi-punch contact interface

A critical note on the role of the contact stiffness in fracture of the multi-punch contact interface

The Influence of Reinforcement Size and Shape on the Mechanical Properties of Composites

Abstract: In the present work the effects of size and shape of reinforcements on the mechanical properties of composite material is discussed in detail Since reinforcements have a dominant control on mechanical properties such as, tensile strength, stiffness, toughness and fracture resistance. This work comprehensively assesses how the size and the shape of reinforcements, which can be nano, micro and macroscopic, and can be fibers, particles, or platelets, affect the behaviour of the resulting composites. Both numerical and experimental approaches were used to investigate the interface adhesion, stress profile and fracture characteristics as influenced by the kind of reinforcements. Specific outcomes suggest that the use of nano-sized reinforcements results in enhanced values of toughness and thermal stability, when compared with the use of micro- and macro-sized reinforcements of glass fibers in epoxy composites, which in turn results in improved tensile strength and bulk mechanical stability. Reinforcement shape was also identified as playing a significant part; continuous fibers provided the best load-carrying capability, spherical particles uniform stress distribution, while platelet strengthened impact strength of the composite. In addition, the study on the hybrid reinforcement systems revealed the interaction and cooperation of different reinforcement types to design composite properties for certain industries. The findings of the current study offer corollary guidelines on the development high-performance composites with enhanced mechanical features and fathom the innovative research solutions for the existing flaws such as testing methodologies and bio- spheres reinforcements.

Investigating the bonding performance of metal‐CFRP hybrid composites: A study on aircraft components

AbstractThe increasing reliance of the aerospace industry on lightweight yet robust materials, notably carbon fiber‐reinforced polymers (CFRPs), has emphasized the need for efficient joining methods for composite structures. This study investigates the influence of various bonding techniques on the strength of two distinct joint configurations: CFRP/CFRP and CFRP/301 steel interfaces. The CFRP/CFRP joints were configured as single lap joints, where two CFRP laminates and/or prepregs were overlapped and bonded using co‐curing, secondary bonding, or co‐bonding. The configuration ensured adhesion between the cured or uncured CFRP layers, depending on the bonding technique applied. For CFRP/301 steel, CFRP laminates and/or prepregs were similarly bonded to 301 steel substrates in an overlapping region. Both configurations were subjected to single lap shear tests following ASTM D3165 standards to assess the mechanical performance of each bonding method. The post‐test interface damage and fracture mechanisms were analyzed using optical microscopy, providing insights into the failure modes for each joint type. This study offers comprehensive experimental data on various joining techniques that can be useful during the initial design phase of aerospace systems, ultimately resulting in cost savings. The findings of this study, when analyzed from an industrial standpoint, indicate that co‐curing offers a promising solution due to its affordability and simplicity, making it especially advantageous for CFRP/301 steel overlap joining when combined with adhesive films.Highlights Co‐curing, co‐bonding, and secondary bonding techniques were applied to CFRP/steel joints in real aircraft components. The CFRP/CFRP joints obtained via co‐curing exhibited improved thermal stability and strength. Peel ply surface preparation enhanced adhesion the strength of the CFRP/CFRP bonded samples. Cohesion failure was observed in adhesive joints, with no failure at the bond lines.

A Study on the Accurate Equation Inversion Method for Uncoupled Interface Parameters of OA Media Considering Initial Stress

Underground media are generally affected by the initial stress of the overlying strata. At the same time, the uncoupled interface is an important influencing factor of seismic response, as well as an essential reservoir environment, reservoir space, and migration channel. It is significant to explore the parameters of the uncoupled interface under stress for identifying oil and gas reservoirs. As an effective means of predicting reservoir physical parameters, pre-stack seismic inversion uses information on uncoupled interface fractures under stress to improve the accuracy of reservoir parameter prediction, overcome the problem of insufficient interface parameter prediction methods, and promote oil and gas reservoir exploration and development. Based on the precise equations for directly characterizing uncoupled interface fracture weakness parameters, this paper uses the ANNI inversion method to realize the nonlinear inversion method of uncoupled interface fracture parameters. The feasibility and practicability of predicting underground medium parameters from seismic response characteristics have been verified through model testing and actual work area application.

Interfacial fracture in soft solids — How geometry and viscoplasticity make crack fronts unstable

Interfacial fracture in soft solids — How geometry and viscoplasticity make crack fronts unstable

Zn interlayer-induced modifications in interfacial structure and fracture behavior of Cyclic Hot-Pressed Mg/Al laminated composites

In this study, a new type of cyclic hot pressing technology was used to prepare magnesium-aluminum composites. In order to further simplify the process, the active zinc interlayer was introduced, and the interfacial bonding strength of Mg/Al LMCs was increased by 43.25%. The traditional Mg/Al LMCs interface is mainly composed of Mg-Al IMCs (β-Mg2Al3 and γ-Mg17Al12), in which the highly regular HCP-β phase leads to brittle fracture of the material. After adding zinc layer, the interface of the composites mainly presents Al-SS, η (MgZn2) and Mg-SS phases. During the preparation process, the solid solution treatment and aging treatment occurred at the composite interface, and a chain GPII zone was formed at the interface between Al-SS and η phase. This region is mainly composed of structurally unstable η′(Al-Mg-Zn), resulting in the GP II band becoming a region rich in lattice defects and a fracture source of the composite.

Experimental study of propellant/liner interface fracture characteristics

Abstract The propellant/liner interface debonding is one of the main failure modes affecting the structural integrity of solid rocket motors. In order to study the mechanical properties of the propellant/liner interface, the Double-Cantilever Beam (DCB) specimen of the propellant/liner interface was improved. Based on the propellant/liner interface DCB specimens, tensile tests at different temperatures and loading rates were carried out. Based on the digital image correlation(DIC) method, the strain field of the whole DCB specimen and the propellant part was analyzed respectively. Meanwhile, the fracture morphology of DCB specimen was analysed. The results show that the improved specimen can effectively characterize the properties of the propellant/liner interface. The propellant/liner interface shows obvious temperature and strain rate dependence, and the effect of temperature on the propellant/liner interface performance is more significant than that of loading rate. The deformation at the propellant/liner interface of the DCB specimen can reach about 50%, and the interface fracture mode of propellant/liner is cohesive fracture.

Microscopic deformation mechanism of inelasticity in graphene foams under quasi-static tension and compression

The unique porous structure and exceptional elasticity of graphene foams (GrFs) qualify them as prime candidates for various applications. However, the claim of their super-elasticity under compressive strains up to 90% is ambiguous, as the super-elastic behavior is accompanied by inelastic phenomena such as plasticity and microscale damage. This study systematically investigated the microscopic deformation mechanisms underlying the inelasticity of GrFs under both tension and compression using numerical experiments based on the coarse-grained molecular dynamics method. The “non-uniformity of deformation” parameter is proposed, and it revealed a two-stage deformation process characterized by nonlocalized and localized inelasticity. When the GrFs were subjected to tensile strains below a critical threshold, irreversible microstructural deformation resulted in nonlocalized inelasticity. Beyond this threshold, inelasticity was predominantly driven by localized plastic deformation and damage caused by bond breakages at the fracture interface. In contrast, only nonlocalized inelasticity occurred during the compression process. Furthermore, the results indicated that when nonlocalized inelasticity occurred, a negative correlation between the crosslink densities and the number of graphene layers existed. These results can deepen our understanding of the deformation properties of GrFs, which is crucial for their design and application.

A molecular dynamics study on the mechanical and tribological behaviors of nitrile butadiene rubber composites reinforced by boron nitride nanotubes

To study the enhancing effect of carbon nanotubes (CNTs) and boron nitride nanotubes (BNNTs) on the mechanical, tribological, and interfacial performances of nitrile butadiene rubber (NBR) matrices, two NBR composite models strengthened by the same weight percentage of CNTs and BNNTs are constructed. The uniaxial tensile test and pull-out simulation are respectively employed to determine the mechanical capacities and interfacial characteristics of the composites. Results indicate that the inclusion of BNNTs can endow the NBR composites with more excellent mechanical properties and better thermal aging resistance compared to that of CNTs. Moreover, about 40.78% higher in the interfacial friction force, 120.7% higher in the interfacial shear strength, and 81.25% higher in the interfacial fracture toughness are achieved for the composites by the addition of BNNTs than those by the addition of CNTs. It is found that BNNTs play a better role in retarding crack propagation. Furthermore, about 23.53% lower in the friction coefficient and 2.36% lower in the abrasion rate can be obtained by the incorporation of BNNTs than by the incorporation of CNTs. To unveil the reinforcing mechanisms on the strengthened mechanical and tribological performances, the interfacial interaction energy, mean coordination number, and radial distribution function of the NBR composites are calculated accordingly. These findings have significant value for the structural design and product development of high-performance rubber composites under extreme working conditions.

Fracture Dynamics in Silicon Anode Solid-State Batteries.

Solid-state batteries (SSBs) with silicon anodes could enable improved safety and energy density compared to lithium-ion batteries. However, degradation arising from the massive volumetric changes of silicon anodes during cycling is not well understood in solid-state systems. Here, we use operando X-ray computed microtomography to reveal micro- to macro-scale chemo-mechanical degradation processes of silicon anodes in SSBs. Mud-type channel cracks driven by biaxial tensile stress form across the electrode during delithiation. We also find detrimental cracks at the silicon/solid electrolyte interface that form due to local reaction competition between neighboring domains of different sizes. Continuum phase-field damage modeling quantifies stress-driven channel cracking and shows that the lithiated silicon stress state is critical for determining the extent of interfacial fracture. This work reveals the mechanisms that govern SSBs compared to conventional lithium-ion batteries and provides guidelines for engineering chemo-mechanically resilient electrodes for high-energy batteries.

Investigation of two sandwich-structured nanohybrid coating derived from graphene oxide/carbon nanotube on interfacial adhesion and fracture toughness of carbon fiber composites

Designing stronger interphase towards solving the long-standing dilemma of interfacial delamination is critical for stable application of carbon fiber composites. Herein, nano-scale sandwich-structured coatings, where carbon nanotubes (CNTs) were uniformly anchored on both sides of graphene oxide (GO) layer (abbreviated as C/GO/C) and its reverse, that is double GO layers encapsulated CNT network (G/CNT/G in short), were reported around fiber periphery via vacuum filtration method. The effects of surface structure differences on interfacial shear strength (IFSS) and fracture toughness were compared in epoxy matrix. Impressively, composite incorporating G/CNT/G modified fiber delivered prominent IFSS and interfacial fracture toughness of 114.6 MPa and 137.0 J/m2, 105.7 % and 279.5 % increases over control fiber composite. This strategy was also superior to C/GO/C and other reported GO and CNT related works. The main factors for maximal IFSS offered by G/CNT/G are that two GO panels enrich active sites to tightly bridge fiber and epoxy, as well as its layered feature and large surface area provide a stable “skeleton” at interphase for stress transfer. Additionally, the G/CNT/G “skeleton” is closer to sandwich structure of iris leaf, in which the porous CNT intermediate network creates larger deformation and adsorb more energy, leading to peak interfacial fracture toughness.

Synchrotron X-Ray Micro Computed Tomography Investigation of in-Situ Deformation of PFSA Membranes for Water Electrolyzers

Proton exchange membrane water electrolysis (PEMWE) is an electrochemical energy conversion technology that splits water molecules to produce hydrogen gas. PEMWE, when powered by renewable electricity sources, offers a promising solution to generate clean hydrogen fuel as well as for storing energy [1]. One barrier to the wide-scale commercialization of PEMWEs is their durability, which is compromised in part by mechanical damage to the membrane. It has been hypothesized that the rough surface of the PTL causes damage to the surface of the membrane in the form of pinholes and interfacial fractures under PEMWE operating conditions, which lead to increased degradation of the membrane and reduced performance and longevity of the PEMWE cell [3]. Furthermore, the extent of damage and deformation to the membrane can be related to the morphology (i.e. the feature and pore size/distribution) of the PTL. Thus, characterizing the interfacial contact between the PEM-PTL and the stresses induced in the membrane during operation is of great importance for understanding and mitigating the mechanical aspects of failure in PEM electrolyzers.To investigate this phenomenon, we conducted X-ray micro computed tomography (MCT) at the advanced light source (ALS) at Lawrence Berkeley National Laboratory (LBNL) on a PTL/membrane stack being pressed together at 2.2, 4.4, 8.9, and 22.2 MPa using a custom compression stage. We tested the effect of two different standard PTL morphologies: a sintered Ti from Mott® and a fibrous Ti from Bekeart® on both wet and dry membrane specimens (Nafion 115). By carefully segmenting the X-ray MCT images, we were able to construct 3D strain mappings across the membrane to highlight areas of concentrated stress due to prominent features of the PTL protruding into the membrane and portions of membrane extruding into the pores of the PTL. Based on these results, we find that prominent features on the PTL surfaces lead to increased membrane surface roughness and strain, and indeed can pierce the hydrated membrane surface at elevated pressures. In summary, our study offers a unique insight into the deformation mechanisms that occur at the membrane surface as it interfaces with the PTL under standard PEMWE operating conditions of high compressive stress and hydrated states. This work will guide researchers within the PEMWE community to develop material and integration strategies that mitigate mechanical degradation and improve the system lifetime.

Hydrogen bombardment-induced nano blisters in multilayered Mo/Si coatings

Nanometer-thick multilayered Mo/Si coatings, employed as artificial Bragg structures, are essential for reflecting specific wavelengths of light in synchrotrons, space telescopes, and extreme ultraviolet optical systems. However, these coatings are prone to blistering failures when exposed to energetic fluxes, such as hydrogen bombardment and solar wind particles. The blistering mechanism is investigated through systematic analysis of experimental data and the development of a multilayered mechanical model based on pockets of energy concentration theory. Energy release rates for pure mode fracture at blister tips, the evolution of blister morphologies, and interface fracture toughness are assessed through theoretical derivations. The relationship between blister radii and heights is elucidated and quantitatively validated against experimental data. Variations in fracture toughness are correlated to hydrogen characteristics, and the influence of hydrogen species, exposure temperature, dose, energy, and strained layer thickness on blister formation is evaluated using the developed model. These findings provide crucial insights for optimizing exposure parameters to mitigate blistering and enhance the performance and reliability of multilayered Mo/Si coatings.

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.

Effect of temperature variation on bonding properties of magnesium potassium phosphate cement: A multiscale analysis

In magnesium potassium phosphate cement (MKPC) repair work, varying ambient temperatures significantly affect the repair outcomes. To quantitatively characterize the effect of temperature variation on the bonding properties of MKPC, this paper comprehensively explores the issue at multiple levels, evaluating the bonding properties of the combined specimens using double-shear tests, scanning electron microscope tests, and nuclear magnetic resonance tests, followed by quantitatively characterizing the form of interfacial damage using digital image processing of interfaces. Finally, the Pearson correlation coefficient method was employed to analyze the correlation between different scales. The results indicate that, for the MKPC combined specimens, the interface shear bearing capacity slightly decreased at low temperatures and improved back to normal temperature, with a retention coefficient (K) of 0.977. The internal structure was dominated by small holes, whereas at high temperatures, the capacity severely decreased, with K only 0.4, and a large number of large holes and cracks were present internally. The DIP results reveal that the interface damage forms of the combined specimens at low temperatures were dominated by the MKPC-NC interface, which accounted for 76.38 %. At high temperatures, the damage was mostly within the MKPC, with the MKPC interface accounting for 52.06 % of the fracture interface of the specimen. Pearson correlation analysis demonstrates that temperature has a strong relationship with the scale indicators, with an |R| value greater than 0.7. The |R| value between macroscopic performance and microstructure is 0.95, providing strong evidence that macroscopic performance can be characterized by the microstructure.

On the investigation of microstructure and mechanical properties of the AlCoCrFeNi2.1/316 L dissimilar spot-welded joint

This study receives a free-defect spot-welded joint, using the base metal of AlCoCrFeNi2.1/316 L, for the first time, by a resistance spot welding technique. Electron backscatter diffraction, X-ray diffraction, and scanning electron microscopy were used to analyze the microstructure of the nugget and heat-affected zone of the spot-welded joint. Mechanical experiments were conducted to gain mechanical properties such as micro-hardness and shear tensile strength. The nugget on the side of 316 L and AlCoCrFeNi2.1 is not fully symmetrical, and the nugget offset is observed on the AlCoCrFeNi2.1 side owing to dissimilar thermo-physical properties. Thermodynamic calculation and XRD diffraction analysis confirm that both austenite and (Fe, Ni) phases are existent in the nugget zone. Eventually, under a shear load, an interface fracture of the spot-welded joint was observed and the fracture morphology was examined. This work could serve as an initial basis for further research on high entropy alloy resistance spot welding.

Flexural behaviours and heterogeneous interface fracture in overmoulded multi-material thermoplastic composites

The development of lightweight multi-material composites is imperative to meet the demands of the aerospace and automotive industries. Thermoplastic-based multi-material composites represent a novel approach, wherein two or more distinct composite materials are combined to create a hybrid material with enhanced performance characteristics. However, varying failure modes across multi-scale interfaces in the composites affect their mechanical performance in a complex manner. In this study, multi-material composites were manufactured through overmoulding of virgin polycarbonate (VP) and short-fibre reinforced polycarbonate (SFP) on continuous fibre-reinforced thermoplastic polycarbonate (CFRTP) laminate to assess behaviours of heterogeneous interfaces and structural performance under flexural loading. In the compression overmoulding process, the consolidation of thermoplastics creates interdiffusion of polymer chains across the multi-material interfaces. The multi-material composites successfully demonstrated enhanced flexural properties compared to single material constituent such as VP, SFP, and CFRTP. Benchmarking with CFRTP composite laminates, results revealed that overmoulding SFP on CFRTP results in 319 % higher flexural strength and 36 % higher of flexural modulus. VP/CFRTP composite offered 103 % more flexural strain and 175 % more specific energy absorption during fracture. Strategic optimization of the neutral axis (NA) and integration of high modulus materials in multi-material systems contributed to such performance enhancements. Failure analysis conducted using optical microscope and scanning electron microscopy (SEM) revealed progressive heterogeneous interface fracture and crack propagation in the CFRTP laminate layer. Results indicated that control of interface failure modes need to be considered in multi-material structure design to achieve desired flexural strength.

A cohesive fracture-enhanced phase-field approach for modeling the damage behavior of steel fiber-reinforced concrete

This study introduces a novel computational framework based on the phase-field fracture/damage model (PFM), providing rapid and accurate predictions of the damage behavior of Steel Fiber Reinforced Concrete (SFRC) material. The framework integrates the interfacial cohesive fracture model with the PFM to depict the interaction between the cementitious matrix and fibers, marking the first demonstration that this model adequately captures both local fracture phenomena between fibers and concrete (such as fiber bridging and interfacial debonding) and mesoscopic stress–strain behavior. Additionally, an enhanced geometric approximation is established based on the spatial distribution density function of fibers and particles, allowing for the transformation of the three-dimensions (3-D) fiber-reinforced material structure into an equivalent two-dimensions (2-D) material. This approach enables the reduction of computational time, a significant limitation of the phase-field method, thereby allowing an in-house code to perform various computations with complex material structures such as SFRC. The effectiveness of the approach is demonstrated through four examples involving variations in the microgeometry and material properties of SFRC structures, ranging from the simplest configurations to real experimental material structures. Extensive Monte Carlo simulations of the model are also employed to provide results closer to reality, which are then compared with recent experimental data and numerical models, demonstrating the efficacy of the proposed computational model.

Combined hybrid machining of laser ablation-drilling small holes in Cf/SiC composites

Carbon fiber-reinforced silicon carbide composite material (Cf/SiC) serves as a typical advanced material for fabricating hot-end components of aircraft engines. Its unique properties, including high hardness and anisotropy, pose significant challenges in processing. Nevertheless, a crucial structural element of hot-end components, specifically the cooling and heat dissipation holes, necessitates hole machining within the Cf/SiC composites. The intricate nature of machining this material often leads to compromised surface quality and severe wear on cutting tools during the hole machining process. This study delves into the feasibility of combined hybrid machining of laser ablation-drilling(L-DCM) for fabricating small holes in woven Cf/SiC composites, along with elucidating the underlying material removal mechanisms. The findings reveal approach significantly enhances the cutting performance of hard alloys tools when dealing with ceramic matrix composites. Notably, the wear mechanisms of the cutting tools primarily involve abrasive wear and adhesive wear. The primary processing defects observed in the small holes include fiber pullout at the entrance and exit, as well as material delamination at the exit, which are primarily attributed to debonding at the layer interface and brittle fracture of the matrix. The subsequent drilling process, conducted based on laser drilling, effectively eliminates thermal defects such as the heat-affected zone and recast layer, as well as morphological defects like taper. Additionally, this approach mitigates the tool wear process, minimizes the impact of compression effects on material removal, and enhances the shear action of the tool. Consequently, the layer interface remains securely bonded and intact after processing, thereby preserving the material's strength.