Search Results (97)

This study presents a combined numerical–statistical framework based on the Extended Finite Element Method (XFEM) and the Taguchi optimization method to assess the fracture behavior of pressurized pipelines containing external longitudinal cracks. XFEM is employed to evaluate the local fracture response without remeshing, while the Taguchi method is used to quantify the influence of key parameters and identify an optimal configuration with a limited number of simulations. The control parameters considered are internal pressure, initial crack length, and wall thickness, and the evaluated mechanical responses include circumferential stress, the J-integral, and the stress intensity factor. The optimization follows the “smaller-the-better” criterion to minimize stress concentration, fracture-driving forces, and the risk of structural failure. Results indicate that internal pressure predominantly affects circumferential stress and the stress intensity factor, whereas wall thickness has the greatest influence on the J-integral. The optimal parameter combination is determined through signal-to-noise ratio analysis and validated using the delta method, confirming the robustness of the selected configuration. A confirmation simulation performed with XFEM demonstrates a consistent reduction in all fracture-related mechanical responses, highlighting the effectiveness of the proposed approach. It should be noted that the present study is limited to the static fracture assessment of external cracks and does not address fatigue crack growth or fatigue life prediction. Overall, the proposed methodology provides a decision-support tool for pipeline integrity management by integrating numerical fracture mechanics analysis with robust design optimization, thereby contributing to safer operation and improved structural reliability. Full article

The scientific literature increasingly supports the use of computational models to predict fracture across a wide range of applications, which, when calibrated with experimental data, can yield highly consistent results. Although the extended finite element method (XFEM) is widely used in commercial packages, phase field (PF) methods have emerged as a robust alternative. In this study, a cohesive zone model (CZM) was implemented using both approaches (a PF model with an implicit damage initiation criterion and a standard commercial XFEM solver with an explicit damage initiation criterion) to analyze their robustness and computational efficiency. First, a standardized fracture test of a compact tension (CT) specimen was simulated and compared with experimental data to validate both methods, achieving accurate predictions under plane strain conditions with a dominant mode I fracture behavior. Subsequently, the application of both fracture models was extended to flexible thoracic prostheses across two distinct chest wall reconstruction scenarios: a single-rib unilateral model and a multi-rib bilateral configuration. An extreme-case compressive displacement was assessed to identify critical regions susceptible to fracture initiation and to evaluate the structural limits of the proposed designs. The results showed that the PF approach required a higher computational time, but exhibited more stable convergence. In contrast, the XFEM-based solver required careful mesh calibration to ensure convergence under complex conditions. These results highlight the potential of the PF approach as a practical tool for identifying and improving critical regions of implants, overcoming the limitations of commercial XFEM implementations. Full article

Fatigue failure in scaffolding components poses significant risks to worker safety, particularly in high-altitude construction environments. This study investigates the fatigue behavior of scaffolding stirrups, a critical structural element prone to premature failure. The objective is to analyze the fatigue damage mechanisms in stirrups through a combined experimental and numerical approach. Mechanical characterization and micro-hardness testing were conducted to assess the material properties of the stirrup, while finite element modeling (FEM) was employed to simulate its performance under cyclic loading. The Johnson–Cook material model was utilized to compare experimental hysteresis curves with FEM results, validating the numerical approach. Additionally, the Extended Finite Element Method (XFEM) was applied to model crack initiation and propagation. Results reveal that material hardening and fatigue crack growth are the primary causes of stirrup failure, with distinct fatigue zones and crack paths identified. The study quantifies the relationship between crack growth stages and stirrup bending, providing insights into the failure process. These findings contribute to improving the safety and lifespan of scaffolding systems by identifying key factors influencing stirrup durability. Full article

Concrete structures often develop penetrating cracks due to the initiation and propagation of local cracks during service, which may lead to the fracture and failure of the entire structure. The propagation modes and laws of cracks in structural members are closely related to the safety of the overall structure. Conducting research on crack propagation and predicting crack propagation paths for cracked structures can provide technical support for the safety design and reinforcement of structures. Based on the basic framework of the extended finite element method (XFEM), this paper develops a user-defined element (UEL) for ABAQUS using the level set method, and simulates in a two-dimensional space the crack propagation in concrete beam bending tests with the self-developed UEL and the built-in XFEM module of the software. The solution results of the self-developed UEL are consistent in trend with those of the XFEM module, yet the cracks simulated by the XFEM module can only propagate along element boundaries and cannot cross elements, and the accuracy of its results is highly dependent on mesh size. The crack tip simulated by the self-developed UEL can stay inside the element, and the simulated crack propagation paths show a higher degree of agreement with the experimental results. The correctness of the UEL is verified through comparative analysis with the results of the four-point bending tests of concrete beams and the XFEM module of the software. The UEL developed in this paper can effectively predict the crack propagation paths of concrete beams and reveal the multi-crack propagation laws of concrete beams. Full article

Cantilevered unstable rock masses constitute a prevalent geological hazard, with their stability intrinsically governed by the depth of trailing edge cracks. Traditional stability assessment methods, which largely rely on static calculations or displacement monitoring, often suffer from poor timeliness and insufficient early warning capabilities. To address these limitations, this study employs the Extended Finite Element Method (XFEM) to simulate the natural crack propagation trajectory and investigate the associated dynamic response characteristics under loading. The simulation results demonstrate that XFEM effectively captures the natural “vertical-to-oblique” fracture morphology, overcoming the limitations of pre-defined crack models. A critical correlation is established between crack evolution and natural frequency: the first-order natural frequency exhibits a staged decline, characterized by a precipitous drop of approximately 7 Hz during the late stage of fracture development (80–97% depth). Consequently, a “crack evolution–frequency response” model is proposed. This model confirms that natural frequency is a significantly more sensitive indicator of internal damage than displacement, providing a novel theoretical foundation and technical pathway for the early identification and dynamic evaluation of rock mass stability. Full article

As the core load-transfer medium in bonded structures, the adhesive layer critically governs overall reliability, with Mode I fracture representing its dominant failure mechanism under tensile loading. This study systematically compares the eXtended Finite Element Method (XFEM) and its two coupled variants—the XFEM-Cohesive Zone Model (CZM) and XFEM-Virtual Crack Closure Technique (VCCT)—in simulating Mode I fractures of adhesive joints. Key comparisons include predictions of stress distribution, load-transfer evolution, and crack propagation paths, all validated through Double Cantilever Beam (DCB) simulations and experiments. Results show that standard XFEM accurately predicts initial stiffness (error < 8%) but overestimates peak load by 10.7%. XFEM-CZM maintains errors below 8% for both stiffness and peak load, while XFEM-VCCT achieves exceptional peak-load accuracy (error < 1%) but overestimates stiffness. In crack evolution, standard XFEM yields an idealized propagation path, whereas the coupled methods reveal a distinct three-stage process. Stress/strain fields in standard XFEM remain stable during propagation, while the coupled approaches exhibit interfacial irregularities before crack arrival, followed by tip concentration and band-like transfer during stable growth. Each method offers distinct advantages, underscoring that selection should align with specific research objectives and modeling requirements. Full article

Under long-term dynamic water pressure, weld zones in vertical shaft pressure-bearing steel pipes are prone to cracking induced by welding residual stresses (WRSs), which may further propagate and threaten structural safety. This study investigates the effects of initial crack angle and position on crack tip stress and propagation path under the influence of WRSs. Using the XFEM combined with a DFLUX-based thermomechanical simulation, a numerical model of crack growth in vertical shaft steel pipes is developed. Results indicate that increasing the initial crack angle raises the stress intensity factor, while crack-tip residual stress initially increases and then decreases, reaching a maximum value of 457.9 MPa when the initial crack angle is 30°. When WRSs are considered, localized stress concentration at the crack tip intensifies, leading to higher stress, stress amplitude, and stress intensity factor, with the amplitude peaking at 365.49 MPa. Moreover, cracks located outside the weld exhibit higher stress intensity factors than those inside. Overall, WRS, crack angle, and crack location all contribute to crack propagation, with crack angle being the dominant factor. Cracks within welds and oriented between 15° and 45° exhibit a significantly higher likelihood of propagation. These findings aid in identifying hazardous crack scenarios and provide guidance for the operation and monitoring of pressure pipelines. Full article

This study proposes a hybrid computational framework that integrates the Extended Finite Element Method (XFEM), Artificial Neural Network (ANN), and Monte Carlo simulation to evaluate the fatigue crack propagation and reliability of reinforced concrete (RC) bridge decks. First, XFEM was employed to simulate crack initiation and propagation under cyclic loading based on the statistical distributions of the Paris law parameters C and m. The fatigue life data generated from these simulations were used to train a multilayer feedforward ANN optimized with the Adam algorithm and the ReLU activation function. The trained network achieved a high prediction accuracy (R² = 0.99, MAPE = 0.977%) and demonstrated strong generalization capability for predicting the XFEM-derived fatigue life. Subsequently, 10,000 Monte Carlo samples of C and m were analyzed using the trained ANN to perform probabilistic fatigue life assessment. The results revealed a nonlinear degradation pattern in reliability: the structural reliability remained high at low fatigue cycles but decreased sharply once a critical threshold of approximately 1.45 × 10⁹ cycles was reached. When actual bridge traffic was considered, the deck maintained a reliability of 0.99 after 23 years and 0.95 after 67 years of service. Compared with the XFEM, the ANN-based prediction improved computational efficiency by more than 10⁴ times while maintaining satisfactory accuracy. The proposed hybrid framework effectively combines deterministic simulation, probabilistic analysis, and data-driven modeling, providing a rapid and reliable approach for predicting fatigue life and evaluating the reliability of concrete bridge structures. Full article

Cracking in asphalt layers of rigid–flexible composite pavements under coupled ambient temperature fields and traffic loading represents a critical failure mode. Traditional models based on uniform temperature assumptions inadequately capture the crack propagation mechanisms. This study developed a thermo-mechanical coupling model that incorporates realistic temperature-modulus gradients to analyze the compressive-shear behavior and simulate crack propagation using the extended finite element method (XFEM) coupled with a modified Paris’ law. Key findings reveal that the asphalt layer exhibits a predominant compressive-shear stress state; increasing the base modulus from 10,000 MPa to 30,000 MPa reduces the maximum shear stress by 22.8% at the tire centerline and 8.6% at the edge; thermal stress predominantly drives crack initiation, whereas vehicle loading governs the propagation path; field validation via cored samples confirms inclined top-down cracking under thermo-mechanical coupling; and the fracture energy release rate (G_f) reaches a minimum of 155 J·m⁻² at 14:00, corresponding to a maximum fatigue life of 32,625 cycles, and peaks at 350 J·m⁻² at 01:00, resulting in a reduced life of 29,933 cycles—reflecting a 9.0% temperature-induced fatigue life variation. The proposed model, which integrates non-uniform temperature gradients, offers enhanced accuracy in capturing complex boundary conditions and stress states, providing a more reliable tool for durability design and assessment of composite pavements. Full article

Natural cracks are prone to form in toppling deformed rock masses during the toppling process, and these cracks are likely to undergo hydraulic fracturing failure under the action of high water head. This paper leverages the advantage of the extended finite element method (XFEM) in simulating crack propagation, considers the effect of water pressure on the crack surface, conducts numerical simulation and analysis on the hydraulic fracturing of cracks in toppling deformed rock masses, and studies the influences of different crack lengths, rock formation dip angles and crack surface water pressures on crack propagation. The main conclusions are as follows: (1) After hydraulic fracturing occurs in the rock mass, with the continuous rise in the water level, the crack propagation rate is slow first and then fast. When the water pressure is low, microcracks extend slowly; when the water pressure reaches a certain level, the rock formation cracks expand rapidly and eventually fracture. (2) Under the same water pressure, rock formations with longer initial crack lengths are more prone to hydraulic fracturing, and their cracks expand faster; rock formations with a dip angle of 45° are more likely to undergo hydraulic fracturing than those with other dip angles, while rock formations with a dip angle close to 90° are hardly susceptible to hydraulic fracturing. (3) The instability failure mechanism of hydraulic fracturing in toppling deformed rock masses is tension shear action. As the fissure water pressure rises, the tensile stress at the crack tip will increase sharply. Once new microcracks appear in the initial crack, it will be in an unstable expansion state. Full article

Voids behind tunnel linings are common hidden defects in underground engineering, leading to reduced structural capacity and potential safety hazards. To address the deficiencies in the understanding of the mechanism and the optimization of design of the existing steel plate reinforcement methods, this study systematically investigates the reinforcement mechanisms and proposes refined design strategies through numerical simulations and experimental validation. First, a comparative analysis of the Concrete Damage Plasticity (CDP) model and the Extended Finite Element Method (XFEM) revealed that the CDP model exhibits superior accuracy and computational efficiency in simulating large-scale void linings. Second, the effectiveness of different reinforcement schemes (chemical anchor bolts alone, structural adhesive alone, and combined systems) was evaluated, demonstrating that structural adhesive dominates stress transfer, while chemical anchor bolts primarily prevent plate detachment. Through further optimization simulations of the steel plate spacing, it was found that a spacing of 0.25 m can balance the reinforcement effect and cost. This spacing restricts the maximum principal stress (1.83 MPa) below the tensile strength of concrete while essentially eliminating damage to the lower surface of the lining. An optimized steel plate reinforcement structure was ultimately proposed. By reducing the number of chemical anchor bolts and decreasing their size (with only M12 chemical anchor bolts arranged at the edges), local damage is minimized while maintaining reinforcement efficiency. The research results provide theoretical support and engineering guidance for the safe repair of tunnel void areas. Full article

This article is devoted to the prediction of the service life of selected structural materials under simulated operating conditions. Special attention is paid to the so-called representative volume element, which characterizes the damage behaviour, since it includes a critical number of microdefects. The overall damage prediction is based on the energy approach, and the development of damage comes from the traction separation laws; the shape of the damage varies for different materials. The calculations were performed using the extended finite element method (XFEM), where several minor modifications were made. This method has been successfully used in many areas of engineering sciences for research, simulation, and prediction of the behaviour of structures. XFEM reformulates the continuous boundary and initial value problems into similar variational forms instead of using the classical forms of differential equations. The simulation of fracture and damage phenomena is presented for two different materials: austenitic steel with a pronounced grain structure under creep (viscous) loading conditions and cement pasta reinforced with metal fibres under conditions of predominantly static loading. Full article

This study investigates a novel anchor-based method for controlled rock fragmentation, designed as an alternative to conventional excavation or explosive techniques. The proposed solution utilizes a specially modified undercut anchor that induces localized failure within the rock mass through radial expansion rather than traditional pull-out forces. Finite Element Method simulations, performed in ABAQUS with an extended fracture mechanics approach, were used to model the initiation and propagation of failure zones in sandstone. The results revealed a two-phase cracking process starting beneath the anchor’s driving element and progressing toward the rock’s free surface, forming a breakout cone. This behavior significantly deviates from conventional prediction models, such as the 45° cone or Concrete Capacity Design methods (cone 35°). The simulations were supported by field tests, confirming both the feasibility and practical advantages of the proposed anchor system, especially in confined or safety-critical environments. The findings offer valuable insights for the development of compact and efficient rock fragmentation technologies suitable for mining, rescue operations, and civil engineering applications. Full article

Residual particles embedded at the bond coat/substrate (BC/SUB) interface after grit blasting can affect the failure behavior of thermal barrier coatings (TBCs) under thermal cycling. This study employed a 2D finite element model combining the cohesive zone method (CZM) and extended finite element method (XFEM) to analyze the effect of interfacial grit particles. Specifically, the CZM was used to simulate crack propagation at the BC/thermally grown oxide (TGO) interface, while XFEM was applied to model the arbitrary crack propagation within the BC layer. Three models were analyzed: no grit inclusion, 20 μm grit particles, and 50 μm grit particles at the BC/SUB interface. This systematic variation allowed isolating the influence of particle size on the location of crack propagation onset, stress distribution, and crack growth behavior. The results showed that grit particles at the SUB/BC interface had negligible influence on the crack propagation location and rate at the BC/TGO interface, due to their spatial separation. However, their presence significantly altered the radial tensile stress distribution within the BC layer. Larger grit particles induced more intense stress concentrations and promoted earlier and more extensive vertical crack propagation within the BC. However, due to plastic deformation and stress redistribution in the BC, the crack propagation was progressively suppressed in the later stages of thermal cycling. Overall, grit particles primarily promoted vertical crack propagation within the BC layer. Optimizing grit blasting to control grit particle size is crucial for improving the durability of TBCs. Full article

The simulation of damage in composite materials is an important research area that impacts different engineering applications from aerospace structures to renewable energy systems. This review provides a comprehensive analysis of current damage modeling approaches, including intra-layer and inter-layer failures. Various numerical strategies, such as continuum damage mechanics (CDM), cohesive zone models (CZM), extended finite element methods (XFEM), phase-field models (PFM), and peridynamics (PD), are examined to assess their efficiency in predicting crack initiation, propagation, and interaction. Additionally, the role of data-assisted (driven) techniques, such as machine learning, in enhancing predictive capabilities is explored. This review highlights the strengths and limitations of each approach, underscoring the need for further advancements in computational efficiency, multiscale modeling, and integration with experimental data. The findings serve as a foundation for future research into optimizing damage prediction techniques to improve the reliability and durability of composite structures. Full article