Fracture Behavior Research Articles

Impact of surface preparation method on the fracture toughness of adhesive joints subjected to diverse loading modes

While research has explored surface treatment effects on fracture energies in pure modes (I or II), there is a lack of research under mixed-mode loading. The aim of this paper is to investigate the influence of surface treatment approaches on the fracture behaviour and fracture energy of adhesive joints at different loading modes. To achieve this, double cantilever beam (DCB) adhesive joints were manufactured considering two different surface treatment methods namely grit blasting and mechanical bristle blasting. The joints were subjected to five different mode mixities. Fracture energy for each tested condition was calculated based on a compliance-based approach. The fracture energies in mode I reached an increase of 55 % when grit blasting surface treatment was applied, while for mode II the fracture energy reached a value three times higher for mechanical bristle blasting surface treatment, both energies from the mixed mode tests. The failure mechanisms were also evaluated for joints with different surface treatments as a function of loading mode. In all tested conditions, a cohesive failure mode was observed; however, the results underscore the substantial influence of the surface treatment method on the fracture energy of adhesive joints. This is attributed to the distinct failure mechanisms observed under varying surface treatment conditions.

Shear-induced permeability evolution of natural fractures in granite: Implications for stimulation of EGS reservoirs

Permeability evolution of natural fractures during shearing is one of the critical issues in enhanced geothermal system (EGS). In this study, we conducted a series of numerical simulations of shear-flow tests under different normal stresses to investigate the permeability evolution and shear behavior of natural fractures during shearing. All numerical simulations in this study are executed based on a coupled hydro-mechanical pore network model (PNM) for fluid flow within the discrete element method (DEM). The numerical model uses a 33 mm × 25 mm fracture surface profile extracted from X-ray computed tomography scanning data of joints in a rock core retrieved from a 4.2-km-deep well at the Pohang EGS site. The results demonstrate a positive correlation between fracture permeability and shear displacement when the normal stress is relatively high. The central aspect of permeability evolution lies in the variation of local aperture distribution along the pathway: an increase in the variance of fracture aperture distribution leads to an increase in fracture permeability. Permeability evolution of fractures is significantly affected by normal stress, fracture roughness, and relative flow direction. Larger fracture roughness facilitates the formation of high-permeability pathways. Higher local normal stress often corresponds to lower local permeability. Moreover, high normal stress amplifies the effect of fracture roughness on permeability evolution. These findings enhance our comprehensive understanding of hydraulic-mechanical coupling effects during EGS stimulation.

Discrete Element Method Simulation of Particulate Material Fracture Behavior on a Stretchable Single Filter Fiber with Additional Gas Flow

This study presents a comprehensive discrete element method (DEM) simulation approach for the stretching of a filter fiber with a separated polydisperse particle structure on top. For a realistic interaction between the fiber surface and the particles, the original surface of the polymer fiber was projected onto the surface of the fiber cylinder using surface imaging technologies (atomic force microscopy (AFM) and white-light interferometry). In addition, the adhesive forces between particle–fiber and particle–particle contacts were calibrated in the DEM domain using values from self-conducted AFM measurements. Fiber stretching was implemented by the linear motion of small periodic fiber elements. Discretization problems were resolved through studying the stretching of a fiber segment at the size of 8 mm. A critical fiber element length was discovered to be ≈100 μm for minimizing discretization dependencies during the cracking of the particle structure. The number and density of particle–particle contacts within the particle loading on the fiber were obtained at two different elongation rates. Effects such as densification of the particulate structure and increased detachment due to additional air flow were demonstrated.

Fracture behaviour of reaction-bonded silicon carbide-boron carbide using digital image correlation

The current research uses the Digital Image Correlation (DIC) approach to study the fracture behaviour of Reaction-Bonded Silicon Carbide-Boron Carbide (SiC–B4C) ceramic (RBSBC). A Photron camera with 137,500 fps was used to capture the crack propagation at an interframe time frame of 2.6 ms before final fracture. The purpose was to capture the rapid brittle behaviour of the ceramic during the onset of crack propagation. The RBSBC failed in a transgranular manner like most monolithic SiC-based materials as Hexoloy-SA. The presence of randomly dispersed coarse B4C grains helps in deflecting the crack path which increases the overall crack length. The material’s resistance to crack propagation (R-curve) was measured using the crack tip opening displacement, the stress intensity at the crack tip KI, and the J-integral against crack extension. Two methods were used to determine the KI: experimentally based on the displacement values at the crack tip as obtained from the DIC images, and quasistatic based on the fracture load and the geometrical dimension of the crack. The experimentally-determined KI and J resulted in higher values compared to the quasistatic ones. However, they reflect the actual conditions at the crack tip, while the quasistatic conditions underestimate the resistance-plot. The RBSBC has higher R-curve compared to commercially available SiC-only materials as Hexoloy-SA and ABC-SiC. To improve the crack-resistance of RBSBC, the Si amount should decrease to a nm level, while the percentage of B4C grains should increase and be evenly dispersed across the material.

Mechanical properties and fracture behavior of seawater-mixed sea sand recycled aggregate concrete

Despite their undeniable potential for promoting sustainability in construction materials, the characteristics of recycled aggregates (RCA), seawater, and sea sand may vary significantly, thereby affecting their use in structural concrete. This study exploits these materials to investigate their performance in producing sustainable concrete and establishing its mechanical and fracture behavior. The so produced material, referred to as seawater sea sand recycled aggregate concrete (SSRAC) could lend a hand in widening the usage of RCA and sea sand in a variety of applications where the use of ever-depleting natural materials as concrete constituents becomes an issue. Consequently, the variables of the study include the type of water (fresh versus seawater), type of coarse aggregate (RCA versus natural coarse aggregate, NCA), and the type of fine aggregate (dune sand versus sea sand). For each water type, three concrete mixtures are produced using NCA-dune sand, RCA-dune sand, and RCA-sea sand combinations. Analyses of the mechanical characteristics of the concrete, including compressive strength, flexural strength, modulus of elasticity, and fracture toughness, were conducted based on experimental tests. X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) analyses were also conducted on the designed specimens to investigate their microstructure. In terms of fracture characteristics, the use of seawater resulted in improvement in the fracture toughness. The use of recycled aggregate along with seawater resulted in improved compressive strength. However, natural aggregate concrete (NAC) showed higher flexural strengths than recycled aggregate concrete (RAC). The results also revealed that the addition of sea sand had a detrimental impact on all mechanical characteristics. Thus, optimizing the concrete composition in which the investigated materials partially replace the conventional concrete constituents is required in order to consider alternative constituents to generate sustainable concrete for practical applications.

Investigation of mode I fracture behavior of copper slag-SFRSCC

This study has examined how coarse CS (copper slag) aggregates (20–60 %) and HESFs (hooked-end steel fibers) (0.1–0.5 %) affect the performance, microstructure, and fracture/mechanical features of SCCs (self-compacting concretes) under pure loading mode I. To estimate the SCC ductility, fracture toughness and fracture energy behavior, use has been made of common specimens such as ENDB, ENDC and SCB and the Work Fracture Method. According to the results, adding CS (up to 30 %) improves the efficiency and strengthens the microstructure and mechanical properties. While 0.3–0.5 % SFs affect the fresh concrete properties negatively, they affect those of the hardened concrete positively and increase the mechanical properties. At high CS and SF values, fracture parameters weaken slightly due to improper fiber distribution and bad SF-CS locking and interaction effects. The WFM yielded close fracture features for ENDB specimens, but those of ENDC specimens were more than the actual values. SCB specimens were more suitable than others because they were prepared easily, consumed less material and were modeled better under pure mode I. According to the results, ALK (Active Learning Kriging) models estimated the fracture characteristics with high accuracy and yielded a correlation coefficient in the 0.87–0.95 range.

Comparison of SEM and TPM methods for evaluating the effect of nano-silica and silica fume on the fracture behavior of SCLC

ABSTRACT This study compares the fracture parameters of self-compacting lightweight concrete (SCLC) obtained from two-parameter model (TPM) and size effect method (SEM). Moreover, the influence of using silica fume and nano-silica on the fracture parameters and mechanical properties of SCLC was evaluated. For this purpose, eight mix designs were made by replacing 0, 1, 3, and 5% of the cement weight with nano-silica and using 0 and 10% of the cement weight with silica fume. The SCLC incorporating 3% nano-silica and 10% silica fume was the best mix design. This mix enhanced the compressive strength, tensile strength, and elasticity modulus of SCLC by about 36, 17, and 18%, respectively. Based on SEM, this mix increased the fracture energy and fracture toughness by about 32% and 25%, respectively. According to TPM, this mix improved the mentioned parameters by approximately 33 and 25%, respectively. The average value of differences in the fracture energy and fracture toughness attained from SEM and TPM were about 2% and 1%, respectively. The average difference in the critical crack tip opening displacement (CTODc) results was about 6%.

Bio-based connections and hybrid planar truss: A parallel genetic algorithm approach for model updating

Bolted steel to laminated bio-based material connections experience significant performance challenges due to the nonlinear response and high stress concentrations at their joints. This paper introduces an innovative 3D plasticity-fracture continuum Finite Element (FE) model that significantly advances the simulation of such truss joints by integrating Hill's yielding criteria with an element removal methodology for fracture simulation. This novel approach captures both plastic and fracture behaviors simultaneously, a capability not sufficiently addressed in existing models. We detail the theoretical framework for these models, including the derivation of constitutive equations and the algorithms necessary for their implementation in ABAQUS. Additionally, it is provided a low-fidelity modeling of truss joints, offering a comprehensive analysis of connector elements, joint models, and parametric modeling via Python scripting. The model's efficacy is demonstrated through identification of connection and of hybrid planar trusses under cyclic loading, which validates the practical applicability of the method. To optimize computational efficiency, we developed a Parallel Genetic Algorithm (PGA) that integrates seamlessly with ABAQUS and Python to facilitate parameter calibration. This integration not only enhances the model's accuracy but also reduces computational load, making it feasible for complex engineering applications. Our findings illustrate a significant improvement in modeling accuracy and efficiency, establishing a robust methodology for analyzing truss joints in bio-based construction materials.

An experimental-analytical investigation of particle size effect on the mode I fracture behavior of polymer/graphene nanocomposites

Due to their outstanding specific mechanical and functional properties, the engineering use of polymer nanocomposites and their carbon composites is becoming increasingly pervasive. Current and potential applications include micro- and flexible electronics, energy storage devices, and the use as reinforcement for advanced carbon fiber composites for light-weighting of aerospace and mechanical structures, thereby reducing their fuel consumption and carbon footprint. While a large amount of data and models regarding the effect of the weight fraction of nanoplatelets on the mechanical properties of nanocomposites is currently available in the literature, an aspect often overlooked is the scaling of the fracture behavior and the related particle size effects. Not only is the lack of understanding of size effects in nanomaterials hindering the full exploitation of their properties, it is also a serious issue since the design of large nanocomposite structures or small-scale electronic components requires capturing the scaling of their mechanical properties and developing predictive capabilities. This paper aims at filling this knowledge gap by proposing a novel analytical and experimental approach to investigate particle size effects in nanocomposites at and leveraging the acquired knowledge to improve their fracture properties, from the nanoscale all the way to the macroscale. To this end, crack initiation fracture toughness data for graphene/epoxy nanocomposite are presented as a function of nanoparticle size and weight fraction and compared with model predictions using a novel analytical model based on enhanced crack-tip shielding effect due to the reduced nanoparticle size. Extensive fracture test data are presented for model calibration and model verification.

Conventionally and digitally fabricated removable complete dentures: manufacturing accuracy, fracture resistance and repairability

ObjectivesConventionally and digitally manufactured removable complete dentures with different dentition forms were examined for manufacturing accuracy (trueness, precision), fracture forces under torsional loading and subsequent repairability. MethodsA total of 90 mandibular prostheses were manufactured. Ten were made using the injection molding technique and finished with prefabricated teeth. 40 bases each, were manufactured subtractively and additively. Digitally the prosthesis’ dental arch was divided either into two quadrants or three sextants, or kept as full arch. Afterwards, ten additive and subtractive bases were finished with prefabricated teeth and ten of each with milled quadrants, sextants and full arches. After manufacturing, all specimens were rescanned for accuracy comparisons using the Root Mean Square (RMS). Lastly, all specimens were tested to failure under torsional loading. ResultsConventionally manufactured dentures showed the greatest deviation in accuracy. The type of base manufacturing did not determine the fracture resistance of the prostheses. The dentition form had a significant influence. While prefabricated teeth (86.01 ± 19.76 N) and quadrants (77.89 ± 9.58 N) showed a low fracture resistance, sextants (139.12 ± 21.41 N) and full arches (141.05 ± 17.14 N) achieved the highest fracture forces. Subtractive bases with prefabricated teeth or quadrants were assessed to be repairable, digital dentures with full arch were assessed as not repairable. SignificanceThe presented testing set-up is suitable to determine the fracture behavior of dentures rather than of standards. With the possibility of digital design and individual manufacturing, dentures’ mechanical stability can be significantly increased, especially with suitable dentition forms.

Failure analysis of CFRP-aluminum electromagnetic self-pierce riveting-bonded joints subjected to highspeed loading

The mechanical performance of dissimilar material riveted joints is important for passenger safety during a crash situation. Hence, in this paper, the mechanical properties of CFRP-aluminum electromagnetic self-pierce riveting-bonded (E-SPR-bonded) joints under quasi-static and dynamic loading was investigated. First, the hybrid joints were manufactured under five discharge energies to explore the best process parameter, then, the effect of shearing speed on the mechanical properties were studied. Digital image correlation (DIC) method was carried out to further understand the surface strain distribution. Results indicated that the evolution of shear tests could be divided into two stages, including two peak loads, named peak A and peak B, respectively. The hybrid joint at 7.7 kJ had the best peak load during static load. Under the dynamic loading condition, the peak load increased with ascending load speed, especially the peak B, under 4, 8 and 12 m/s, were 189.0 %, 205.5 %, and 215 % higher than that of 2 mm/min, respectively. The hardening effect of sheets was increased under high shear speeds, which dominated the fracture behaviors of the bonding layer. The hybrid joints failure behavior was the CFRP fracture, and the rivet remained in the aluminum sheets. The results could provide theoretical guidance for the structural design of automobiles and promote its engineering application.

Effect of Fiber-Reinforced Composite Placement Site on Fracture Resistance of Premolar Teeth: An in vitro Study.

This study aimed to investigate the fracture behavior of upper premolars with deep MOD cavities that were restored with Ribbond resin-reinforced fibers (FRCs) placed in different orientations. A total of 54 extracted maxillary premolars were randomly divided into nine groups. The experimental groups underwent MOD cavity preparation with or without root canal treatment, followed by FRCs placed in the pulpal floor, proximal walls, or both. Fracture resistance was tested using an Instron Machine. The samples were visually inspected to analyze the fracture mode. The highest fracture resistance was observed in intact teeth (1299.98 ± 284.66 MPa). Placing Ribbond fibers in the pulpal floor (1155.86 ± 244.21 MPa) or the proximal walls (1077.56 ± 260.60 MPa) significantly improved fracture resistance (p= <0.05), compared to cavities restored with only resin composite (804.58 ± 93.34 MPa). However, placing Ribbond fibers in both the pulpal and proximal walls did not enhance fracture resistance. In the MOD-RCT groups, fracture resistance was improved only when Ribbond fibers were placed in the pulpal floor and the proximal walls. Fracture mode analysis revealed a combined fracture in most of the groups. This study concluded that using FRCs significantly improved the fracture resistance of MOD cavities in premolars and revealed that the placement site could be a determinant factor.

Tensile fracture of blunt V-notches in rectangular plates additively manufactured from Acrylonitrile Butadiene Styrene with different raster angles

In this research, the tensile fracture behavior of rectangular specimens made of Acrylonitrile Butadiene Styrene (ABS) containing double-edge blunt V-notches is evaluated. The specimens are printed using the fused deposition modeling (FDM) technique with five different raster angles and three different notch tip radii. To simplify the complex calculations related to the anisotropic behavior of these specimens, the Virtual Isotropic Material Concept (VIMC) is used in conjunction with three well-known linear elastic notch fracture mechanics (LENFM) criteria, i.e., the mean stress (MS), point stress (PS), and averaged strain energy density (ASED) criteria as well as the extended finite element method (XFEM). It is shown that all these fracture models can predict the load-bearing capacity of the 3D-printed notched specimens by acceptable accuracies, where the best predictions belong to the MS criterion with the critical distance obtained directly from the finite element method, and the least accurate predictions belong to the XFEM method.

Statistical model and fracture behavior of manufactured sand concrete with varying replacement rates and stone powder contents

Manufactured sand (MS) is considered a reliable alternative to natural sand (NS) in concrete due to its wide availability and cost-effectiveness. In this study, the influences of water-cement ratio (0.41, 0.44, 0.47), replacement rate of MS (20 %, 60 %, 100 %) and stone powder content (0 %, 5 %, 10 %) on the mechanical and fracture characteristics of manufactured sand concrete (MSC) were investigated. Statistical model of mechanical properties (compressive strength, flexural strength and flexural toughness) of MSC was constructed based on response surface methodology (RSM). Acoustic emission (AE) technology was used to monitor the MSC fracture process in real time. The correlation between the cumulative AE parameters and the strength of MSC was analyzed. The results showed that the compressive strength, flexural strength and flexural toughness of MSC were negatively correlated with water-cement ratio while positively correlated with the replacement rate of MS. The optimum stone powder content can be determined for MSC to reach its maximum compressive strength. The coupling effects of water-cement ratio and replacement rate of MS was the most significant. This was followed by the coupling effect of water-cement ratio and stone powder content. The coupling effect of stone powder content and replacement rate of MS was the weakest. Moreover, AE analysis on the fracture process of MSC indicated that the AE parameters were more active when the water-cement ratio increased. As the replacement rate of MS increased, the AE parameters were smoother and the specimens were less damaged. The stone powder content played greater role in affecting the AE parameters in compression, while the effect of stone powder content on the four-point bending test was not significant. The cumulative AE parameters were linearly related to the strength of MSC. The cumulative AE parameters can reflect the strength of MSC.

How crack twisting in bouligand structures lead to damage delocalization and toughening

Fiber-reinforced composites with Bouligand structure exhibit remarkable mechanical properties due to the intricate arrangement of fibers. In this study, we propose a coarse-graining (CG) model specifically developed to capture the behavior of Bouligand structures. The model incorporates bonded interactions to represent the fibers and employs a double-well potential to describe the non-bonded interactions within the matrix. Using this model, we investigate the fracture mechanics properties of Bouligand structures, with a particular focus on the emergence of helicoidal cracks. Our primary objective is to validate the hypothesis that these twisting cracks, which align with the fiber orientation, contribute to local hardening mechanisms. By hindering the growth of individual cracks, these hardening mechanisms facilitate the nucleation and growth of multiple cracks, thereby promoting a delocalization effect within the material. Through extensive simulations and analysis, we confirm the validity of our hypothesis. The presence of twisting cracks indeed induces local hardening mechanisms, making it more challenging for individual cracks to propagate. This phenomenon effectively spreads the damage, dissipating energy across larger volumes of the material. Consequently, the toughness of these Bouligand structures is enhanced, as this delocalization effect effectively mitigates the concentration of damage. These findings provide valuable insights into the fracture behavior of Bouligand structures and shed light into the underlying mechanisms responsible for their exceptional mechanical performance. Moreover, our CG model offers a practical and efficient approach to studying and understanding the fracture mechanics properties of complex fiber-reinforced composites. The ability to simulate and analyze the behavior of helicoidal cracks within Bouligand structures opens up new avenues for designing and optimizing advanced materials with enhanced toughness and damage resistance.

The effect of surface roughness, stiffness, and size on ice adhesion

The combined effect of parameters like surface stiffness, topography, and interface size on ice adhesion and its interfacial fracture behavior was studied. Ice adhesion on aluminum and polyurethane with three different surface roughness and two different surface sizes was evaluated experimentally through mode II interfacial fracture tests on a previously formed block of ice. Results showed that, for stiff surfaces the surface roughness increases the adhesion significantly, due to the transition from adhesive to cohesive fracture. Compliant surfaces do not show this transition, in the same roughness scale due to its susceptibility to deformation. The force required to fracture an ice block from stiff surfaces stabilize after a certain length, while compliant surfaces do not show this transition at the length scales studied. The article elucidates the relevance of different parameters and the consideration of size scales for designing low ice adhesion surfaces.

Diffusion-induced stress amplification in phase-transition materials for electrodes of lithium-ion batteries

This work sheds the light on the stress amplification in active material particles of electrodes caused by the localized lithium concentration inhomogeneity due to phase transitions. This is a significant issue usually neglected in the literature, as generally the ideal Fickian diffusion model is used to describe the lithium diffusion, which particularly fails when dealing with phase change materials, resulting in the underestimation of the stress. In turn, this results in the underestimation of the fracture behavior of the electrode and the battery degradation, ultimately.To overcome these limitations, this work proposes a mechanical-transport model where the lithium transport is modeled according to the non-ideal solution theory with an equivalent diffusion coefficient depending on the potential of the host material vs Li/Li+. The results show that the proposed model correctly describes the concentration distribution within the particle of phase-change materials (graphite is chosen as a case study), in agreement with the existent experimental measurements. The differences with respect to the traditional Fickian diffusion model is substantial as the stress is up to 85% higher with the proposed model and the concentration distribution can capture the inhomogeneity caused by phase transitions.

Microstructural characterization and equibiaxial flexural strength of CeO2 and Ti-doped CeO2

In this study, the synthesis of CeO2 and titanium dioxide (TiO2) doped CeO2 (TDC) monoliths are investigated, and their fracture strength is assessed using an equibiaxial flexure testing technique at room temperature. Pellets were synthesized using conventional powder processing and sintering methods to produce the desired characteristics. The TiO2 dopant concentration was optimized at 0.1 wt % TiO2 to obtain dense, solid-solution pellets with an enhanced grain microstructure. A ball-on-ring fixture was used to obtain the TRS and Weibull parameters of over 30 pellets for CeO2 and 0.1 wt % TDC to compare fracture behavior. The TRS of CeO2 pellets ranged from 88 to 160 MPa and the TRS of 0.1 wt % TDC pellets ranged from 102 to 171 MPa, both being consistent with published values. Weibull parameters, such as characteristic strength and Weibull modulus, were extracted as 129 MPa and 8.5 for CeO2 and 150 MPa and 9.3 for 0.1 wt % TDC, respectively. Although Hertzian contact damage was observed on compressive surfaces, failure initiation occurred on the tensile surfaces of both types of samples. Fracture surface analysis for CeO2 indicated a predominantly intergranular fracture while 0.1 wt % TDC had a predominantly transgranular fracture mode. The TRS of 0.1 wt % TDC resulted in increased Weibull parameters when compared to CeO2, indicating sample chemistry and microstructure impact mechanical behavior for these samples.

Interlaminar fracture behaviour of emerging laminated-pultruded CFRP plates for wind turbine blades

Laminated pultruded composite plates are gaining interest for use in wind turbine blades due to their excellent structural performance with affordable cost. However, there is limited understanding of their fracture properties. The present work explores the interlaminar fracture behaviour of pultruded composite plates, bonded through resin infusion, to form thick CFRP structures. Mode-I, −II, and mixed-mode (I/II) tests were performed to obtain fracture properties at different mixed-mode ratios. Mode I crack propagation exhibits stick–slip behaviour, resulting in brittle failure in a few steps, while mode II provides more stable crack propagation along with cohesive failure. The mixed-mode fracture patterns follow the trend of the mode-mix ratios, in which higher mode-mix ratios (more mode II) induce more stable crack propagation. Benzeggagh-Kenane and power law criteria were compared regarding their prediction of crack initiation toughness given a mode mix ratio, and a linear relation between the mixed mode I/II fracture toughness components could exist at interfaces of laminated pultruded plates. Meanwhile, applicability of testing standards and the effect of manufacturing-induced defects on fracture properties are thoroughly discussed. The results show that existing standards provide sufficient support for characterising fracture properties of bonded pultruded plates; and that manufacturing-induced defects can be detrimental to crack propagation and cause more brittle behaviour in mode I dominant cases, while beneficial effect of defects by toughening the interface was exhibited in mode II dominant cases.

The analysis and simulation of fracture behavior of fused quartz under dynamic loading

The analysis and simulation of fracture behavior of fused quartz under dynamic loading