Fracture Mechanics Research Articles

Mixed-mode crack growth simulation in rock-like materials with the smoothing gradient-enhanced damage model associated with a novel equivalent strain

Accurately modeling mixed-mode crack propagation in rock-like materials remains challenging due to the complexity of the deformation states and mechanism of fracture throughout the loading history. The objective of this paper is to analyze the damage process in rock-like materials using an enhanced smeared damage model. The mixed-mode failure in rocks is captured using our recently developed smoothing gradient damage model in conjunction with a novel equivalent strain formulation, which is developed by combining both the bi-energy norm equivalent strain and the four-parameter equivalent strain. To validate the accuracy of the developed method, several commonly reported rock fracture examples are considered in which complex crack paths and responses are reproduced and compared with the available experimental data.

Effects of Temperature and Bimodal Microstructure on the Mechanical Properties and Fracture Mechanisms of High-Strength Al-Ni-Cu-Fe Alloy Fabricated through Laser Powder Bed Fusion

This study investigates the mechanical properties of an Al-Ni-Cu-Fe alloy fabricated using laser powder bed fusion (LPBF) technology, evaluated at temperatures ranging from room temperature to 300°C under various strain rates for potential aerospace and automotive applications. Aluminum alloys often face the challenges of maintaining high-temperature strength and stability, limiting their use in demanding environments. The results demonstrate that the LPBF Al-Ni-Cu-Fe alloy maintains strength above 300 MPa at standard strain rates and reaches up to 400 MPa at high strain rates at 300°C, indicating its suitability for lightweight, high-strength vehicles and thermal engineering systems. The high-temperature strengthening mechanisms are attributed to Al9FeNi submicron cellular eutectic walls that impede dislocation motion and precipitation strengthening from Al2Cu. Fracture analysis reveals that localized brittleness limits elongation to 3% at room temperature, with deformation distributed between coarse-grained (CG) and fine-grained (FG) regions. At elevated temperatures (300°C), partial homogenization of FG regions reduces melt pool constraints, promoting local deformation. Therefore, ductility increases significantly under high strain rates as the dispersed Al9FeNi phases become less effective in resisting instantaneous stresses, allowing deformation to overcome melt pool boundaries. At extreme strain rates during impact testing, twinning becomes the dominant deformation mechanism, contrasting with tensile testing. These findings confirm the potential of the LPBF Al-Ni-Cu-Fe alloy as a heat-resistant printed aluminum alloy for high-temperature applications and provide valuable insights into fracture mechanisms within the bimodal microstructure, guiding future alloy optimization.

The electrical discharge characteristics and ignition mechanism of coal mine roof fracture under stress

The electrical discharge characteristics and ignition mechanism of coal mine roof fracture under stress

Adaptive phase-field modeling of fracture propagation in layered media: Effects of mechanical property mismatches, layer thickness, and interface strength

Fracture propagation in layered media is investigated using an adaptive phase-field method. We focus on the interplay between cracks and interfaces, considering both perfectly and imperfectly bonded interfaces. For perfectly bonded interfaces, three-layer models are analyzed to study the effects of mechanical property mismatches, layer thickness, and confinement pressure on crack growth. Results reveal that critical energy release rate mismatch significantly influences the crack geometry, leading to single through-going fractures, middle layer fragmentation, or delamination. There is an inverse relationship between layer thickness and fragmentation, and between confinement pressure and delamination. For imperfectly bonded interfaces, a phase-field method incorporating an interface energy term is introduced and validated with benchmark examples. This model is used to study the combined effects of mechanical property mismatch and interface strength on crack growth. Our findings demonstrate that the interface strength strongly influences the dominant failure mechanism, with high strength favoring mechanical property mismatch-driven fracture and low strength leading to interfacial failure. Finally, the robustness of the proposed method is illustrated through a complex seven-layer model. This study provides valuable insights into the various factors influencing macroscopic failure mechanisms in layered materials.

Facies and mechanical stratigraphy control fracture intensity, topology and fractal dimension in folded turbidite sandstones, Northern Apennines, Italy

Fracture network intensity, topology and connectivity have been frequently analysed using circular scan windows, an efficient method for geometrical properties characterization, although affected by truncation and censoring. Many studies that use circular scans focus on the spatial variation of the geometrical properties in relation to tectonic structures such as faults and folds, and at the regional scale. A lower amount of information is available in the literature on the relations between depositional features, mechanical and petrophysical properties of facies, and the corresponding fracture network geometrical attributes. In this contribution, we focus on these relationships, which are fundamental controlling factors for predicting fracture geometry in the subsurface and for improving modelling in exploration, production and management of reservoirs for fluid exploitation and storage. We characterized these properties in 35 selected turbidite beds of the Marnoso-arenacea Fm., in the Northern Apennines of Italy, exposed along a 250 m-thick section. Moreover, we calculate the fractal dimensions of fracture networks through the box-counting method. Our data indicate that depositional facies control porosity and uniaxial compressive strength, as well as fracture intensity and fracture network topology. We show that fracture intensity is invariant and unrelated to the sandstone facies thickness in medium-grained turbidite beds. On the other hand, a strong control on fracture intensity in fine-grained turbidite beds is also exerted by the thickness of bounding claystone, which is higher when the bounding claystone is thicker. Moreover, we observe that the cross joint pattern and strike could be influenced by the depositional structures.

Application of equivalent distributed stress concept and modified cohesive zone model in elastic–plastic fracture mechanics analysis of surface cracks

Application of equivalent distributed stress concept and modified cohesive zone model in elastic–plastic fracture mechanics analysis of surface cracks

Experimental study on the dynamic direct tensile fracture mechanism of thermally damaged sandstone

Experimental study on the dynamic direct tensile fracture mechanism of thermally damaged sandstone

Research on the Fracture Mechanism of Bridge Piers Damaged by Jointed Rolling Stones

Research on the Fracture Mechanism of Bridge Piers Damaged by Jointed Rolling Stones

Extended physics-informed extreme learning machine for linear elastic fracture mechanics

Extended physics-informed extreme learning machine for linear elastic fracture mechanics

The study of mechanical properties and fracture evolution of coal-rock masses under hard roof-soft floor conditions

As the depth of coal mining in China continues to increase, the fracturing of coal rock masses has an increasingly complex impact on the surrounding rock roadways. The majority of the mine’s roadways run through coal rock masses with hard roofs and soft bottoms, which typically exhibit complex dynamic behaviour. To further research the mechanical behaviour and fracture evolution of coal rock masses under hard-roof and soft-floor conditions, the study is based on the majority of working faces in a mine, which have hard roofs and soft floors. Uniaxial compression tests were utilized to study the mechanical properties of coal rock masses under hard-roof and soft-floor circumstances, using acoustic emission monitoring, whole-process imaging technologies, and fractal dimension analysis. The experimental results are as follows: The uniaxial compressive strength of the coal rock mass is significantly higher than that of its weakest component. The results of the experiment are as follows: The uniaxial compressive strength of coal rock mass is significantly higher than that of its weakest component. Samples with different soft rock strengths exhibited dissipated energy greater than the accumulated energy before the stress maximum, accompanied by volume expansion and the formation of shear surfaces. Samples with higher soft rock strengths tend to exhibit brittle failure, while weaker samples show stress-softening behaviour. Internal fracture complexity varies amongst samples with varying soft rock strengths. A fractal study of the acoustic emission parameters was carried out utilizing MATLAB programming. The fractal analysis results show that acoustic emission ringing counts and energy time series of coal rock masses under hard-roof and soft-floor settings have good fractal properties. The fractal analysis results show that acoustic emission ringing counts and energy time series of coal rock masses under hard-roof and soft-floor settings have good fractal characteristics. Acoustic emission ringing counts tend to have a larger correlation dimension than acoustic emission energy. However, while the sample is fracturing on a vast scale, the ringing count correlation dimension fluctuates very little. The correlation dimension distribution of samples with lower strength is more concentrated after the stress maximum, implying that the deformation and fracturing of the floor rock in highways under hard-roof and soft-floor circumstances are more complex. Both the correlation dimension D of acoustic emission ringing counts and energy indicate a continuous fall before peak stress, which can be used to anticipate coal rock mass fracture. This study, based on the mechanical behaviour and fracture evolution of coal rock masses under hard-roof and soft-floor conditions, provides a foundation for disaster avoidance by controlling the stability and structural deformation of floor rock in hard-roof and soft-floor highways.

Energy consumption in refiner mechanical pulping

Abstract The efficiency of mechanical pulping has long been of interest due to the large energy consumed by the process. Previous estimates of theoretical efficiency have accounted for less than 20 % of the energy employed. In this study, we make new estimates based on fracture mechanics and abrasion as the mechanisms of new surface creation. We postulate that fracture mechanics comminutes wood into fibres and creates pores in fibre walls. This consumes around 100 kWh/t. Abrasion peels surface material from fibres in the form of morphologically different fines particles. Based on abrasion theory, we estimate this specific energy to be around 1,330 kWh/t. Together, fracture mechanics and abrasion, account for about 70 % of the specific energy (2,000 kWh/t) to produce TMP for printing paper grades. We postulate that the remaining energy is consumed as hysteresis losses from viscoelastic strains not linked to creation of new surface. The largest single source of energy consumption, abrasion, alone accounts for about 66 % of the energy of the process. Finally, we discuss how energy may be reduced by refining intensity and other means.

Analysis of Crack‐Tip Field in Orthotropic Compact Tension Shear Specimens: The Role of Elastic Mode Mixity and T‐Stress

ABSTRACTThe analysis of mixed‐mode crack propagation mechanisms in anisotropic materials remains a pivotal research focus. Although the compact tension shear (CTS) test is a recommended laboratory method, the lack of solutions for anisotropic crack‐tip field parameters hinders accurate assessment of stress states and deformations during crack propagation. To address this gap, this study conducted a systematic finite element analysis (FEA) to compute the elastic mode mixity and T‐stress results. It is found that by adjusting the loading angle along with the initial crack length, CTS tests on orthotropic specimens can similarly achieve a broad spectrum of Me at the crack‐tip. Statistical analysis indicates that applying isotropic solutions to estimate orthotropic T‐stress can lead to average errors of 234.1%. Subsequently, crack‐tip fields were analyzed, with crack initiation angles predicted using the maximum tangential stress (MTS) criterion and plastic zone profiles determined based on Hill's yield criterion. Larger fracture process zones enhance T‐stress correction effects on crack initiation angles, with positive T intensifying crack deflection, while negative T reduces it. Additionally, T also significantly affects the plastic zone's shape and size, with patterns varying according to material orthotropy. A detailed multiparameter characterization of crack‐tip fields will enhance the use of the CTS test for assessing multiaxial strength and mixed‐mode fracture mechanisms in anisotropic materials.

Failure analysis of LCF cracked medium-voltage switch bellows

Abstract Three cracked spring bellows used for medium voltage switches were subjected to materialographic examinations. They were installed in switches that were tested in the test facility performing simulated switching cycles and failed prematurely. The number of load cycles until crack initiation is not known. However, it was well under 10,000. The cause of the crack was low-cycle fatigue (LCF) induced by wall thinning wear resulting from a relative movement between the bellow and the inner polytetrafluoroethylene (PTFE) sleeve. Hot cracking characteristics or evidence of other fracture mechanisms were not found.

Analysis of Mechanisms of Mandible Fractures by Lateral Impact: A Biomechanical Approach Using Finite Element Models

Background/Aim: The purpose of this study was to reproduce a lateral fall using a computer simulation model and to clarify the circumstances of mandible fracture caused by a lateral impact. Material and methods: Fall scenarios were reconstructed using a computer simulation with finite element models. The fall condition was set as a fall from the head direction, which would cause facial injuries. In each simulation, the effective plastic strain of the mandible and its site were determined. Analysis of variance was performed to determine which factors had a significant effect on the maximum effective plastic strain of the mandible. Results: Significant differences with p-values less than 0.001 were found for the following factors: pitch angle, lateral bending angle, impact object, combination of pitch angle and lateral bending angle, and combination of pitch angle and impact object. In most cases with higher values of effective plastic strain, which can cause mandibular fractures, the site was found at the condylar process or mandibular angle of the attacked side. Conclusion: If the patient falls laterally and their face makes contact with a protruding object, medical professionals can predict fractures of the upper part of the mandibular angle and the condyle of the affected side.

Enhancing Fracture Performance of Non‐Conductive Composite Adhesively Bonded Joints With Magnetically Aligned MWCNT/Fe₃O₄ Hybrid Nanofillers

ABSTRACTThe Mode‐I fracture behavior of non‐conductive composite adhesively bonded joints (ABJs) reinforced with multi‐walled carbon nanotube/iron oxide (MWCNT/Fe₃O₄) hybrid nanofillers aligned in different directions was studied using double cantilever beam (DCB) tests. Fe₃O₄ nanoparticles were chemically coated onto MWCNTs to explore the practical potential of these produced magnetically controllable nanofillers in high‐tech industries that require precise nanofiller alignment in specific directions. Nanofillers were aligned within the ABJ adhesive layer using a low magnetic field at 0°, 45°, and 90° relative to the crack growth path, verified by Raman spectroscopy. ABJs with 90° alignment exhibited the highest fracture energy, surpassing unreinforced and randomly dispersed specimens by 136% and 41%, respectively. In contrast, 0°‐alignment showed the lowest fracture energy, while 45° alignment demonstrated intermediate performance. Cohesive zone modeling simulated the ABJ damage behavior, and the effects of nanofiller alignment on macro and microscale fracture mechanisms were assessed using optical and scanning electron microscopy.

Effect of Nb Alloying and Solution Treatment on the Mechanical Properties of Cold-Rolled Fe-Mn-Al-C Low-Density Steel

The automotive industry’s rapid expansion has made the development of lightweight, high-strength automotive steels essential for both energy efficiency and emission reduction. Among these materials, Fe-Mn-Al-C steel has drawn considerable interest due to its favorable combination of low density and high strength. This research examines the impact of Nb alloying (with Nb content of 0% and 0.5%) and solution treatment on the microstructure and mechanical properties of cold-rolled Fe-28Mn-10Al-C low-density steel. Various methods were employed, including Thermo-Calc thermodynamic simulations, the Olson–Cohen model, X-ray diffraction (XRD), metallographic microscopy, room-temperature tensile testing, and scanning electron microscopy (SEM). The findings demonstrate that Nb alloying significantly refines the austenite grain structure of the Fe-28Mn-10Al-C steel, improving both strength and ductility in comparison to the 0Nb steel. After solution treatment at 1050 °C for 30 min, the cold-rolling-induced defects are effectively removed, leading to a substantial increase in elongation at fracture (38.14–44.45%) and an ultimate tensile strength exceeding 900 MPa. As the solution treatment temperature increases, the austenite grains coarsen, and the number of twins increases, while yield strength and ultimate tensile strength decrease. However, there is a notable enhancement in ductility, with the material exhibiting a ductile fracture mechanism. These results offer valuable insights and a theoretical foundation for further improving the mechanical properties of Fe-Mn-Al-C low-density steels.

Evaluating Young Children With Fractures for Child Abuse: Clinical Report.

Fractures are common injuries in childhood and can be caused by unintentional injury, medical conditions, and child abuse. Although the consequences of failing to diagnose an abusive injury in a child can be grave, the consequences of incorrectly diagnosing child abuse in a child whose fractures have another etiology are also significant. This report aims to review recent advances in the understanding of fracture specificity, fracture mechanisms, and other medical conditions that predispose infants and children to fracture. This clinical report will aid pediatricians and pediatric care providers in developing an evidence-based differential diagnosis and performing appropriate evaluations when assessing a child with fractures.

Microstructure and High-Temperature Fracture Mechanism of Continuously Cast and Directly Rolled 2017 Al-Cu Alloy

Microstructure and High-Temperature Fracture Mechanism of Continuously Cast and Directly Rolled 2017 Al-Cu Alloy

Designing Bouligand‐inspired reinforcement for creating wood fiber‐reinforced composites with excellent bending properties

AbstractFiber‐reinforced composites with a bionic Bouligand structure are known for their excellent mechanical properties. Currently, most of the research in this field focuses on man‐made fibers, and research on natural unidirectional fiber materials is still limited. This paper designing Bouligand‐inspired reinforcement for creating wood fiber‐reinforced composites. We investigate the effects of the helix angle on the bending properties, impact resistance and extreme environments of the material through a combination of experimental methods, finite element analysis, and theoretical modeling. Morphological analysis using scanning electron microscopy (SEM) to further explore fracture mechanisms. The findings reveal that the load–displacement curves predicted by the finite element method closely align with the experimental results. The bionic composites demonstrate not only strong bending properties but also significant impact resistance. Notably, the highest bending strength, bending modulus, and impact strength were achieved at a small helix angle of 12.8°, reaching values of 184.66 MPa, 10.21 GPa and 28.03 kJ/m2. The bouligand structure is designed to withstand extreme environments. This research significantly expands the potential applications of the bionic Bouligand structure within the realm of wood fiber‐reinforced composites.Highlights Preparation of Bouloigand‐like composites utilizing wood. Helix stacking angle affects the performance of WFRCs. Finite element analysis was employed to predict the mechanical properties. “Green” composites exhibit exceptional mechanical properties. Expanding the application areas of wood fiber‐reinforced composites.

Investigating the Fracture Mechanisms Arising From the Inhomogeneous Shrinkage Behavior in the Anisotropic Structure of Natural Bamboo via Experimental and Numerical Methods

Investigating the Fracture Mechanisms Arising From the Inhomogeneous Shrinkage Behavior in the Anisotropic Structure of Natural Bamboo via Experimental and Numerical Methods