Composites are widely used in the building sector for high-rise building load-bearing components, bridge decks, prefabricated structural panels, and seismic-resistant members, where excellent mechanical performance and structural durability are critical. As specialized advanced composites, variable stiffness composites (VSCs) have gained increasing engineering applications due to their excellent overall performance. Nevertheless, exploring the fracture characteristics of composite materials, especially VSCs, remains a significant challenge. In particular, cracks in composite components can adversely affect structural integrity and durability. In this study, a dynamic fracture phase-field model for VSCs is developed within the framework of elastic dynamics to investigate crack propagation behavior of VSCs under dynamic loads. The proposed model is first validated by experimental results of fracture behavior of single-edge cracked FRC laminae. Then, the proposed model is employed to systematically study the effects of three fiber orientation design variables and internal defects on the fracture behavior of VSCs. Additionally, fiber trajectories are optimized for different pore distribution configurations. The results demonstrate that the model effectively captures the fracture behavior of VSCs and that optimizing these three design parameters enables the fabrication of high-performance VSCs with enhanced crack propagation resistance. This work provides fundamental insights for the design of curvilinearly fiber-reinforced composites and lays a solid theoretical foundation for the practical application of VSCs in building engineering.
Understanding dynamic fracture in both brittle and ductile materials has attracted considerable attention from engineers and researchers due to its practical importance. In ductile materials, crack initiation and growth are strongly influenced by plastic deformation and the associated microstructural damage, which gradually reduces the material's resistance to crack propagation. Capturing this evolving fracture resistance remains a key challenge for predictive phase-field models. In this study, a phase-field framework is presented in which the effect of plastic deformation on fracture evolution is introduced through a history-dependent fracture resistance. The critical energy release rate is allowed to degrade as a function of accumulated plastic strain, providing a phenomenological description of plasticity-induced weakening without treating plastic dissipation as a direct crack driving force. The formulation is developed within a small-strain elasto-plastic setting based on classical von Mises plasticity with isotropic hardening and is extended to dynamic fracture by accounting for inertia effects in the phase-field evolution. The model is implemented in a commercial finite element environment and examined through a set of representative quasi-static and dynamic numerical examples. The results illustrate the ability of the framework to capture key trends in ductile crack initiation and propagation, as well as the influence of plastic deformation on fracture behavior. The capabilities and limitations of the proposed approach are discussed in the context of existing phase-field models for ductile fracture.
Unknown authors· International Journal of Str...· 0 citations
To mitigate the violent movement of overlying strata in goaf areas, rock–concrete composite support systems are widely utilized. However, the mechanical behavior of such systems under the influence of complex pre-existing defects, such as arc-shaped fractures, remains insufficiently understood. This study aims to clarify the failure mechanisms and the evolution of stability in these composites by evaluating the influence of fracture inclination angles. A synergistic methodology was adopted, combining laboratory uniaxial compression tests with discrete-element method simulations. Based on energy dissipation theory and the strain equivalence hypothesis, a statistical damage constitutive model was established to bridge the gap between microscopic damage and macroscopic mechanical response. The results demonstrate that fracture inclination significantly dictates the energy partitioning and crack propagation patterns within the composite. The established constitutive model, validated by numerical results (
R
2
> 0.999), effectively quantifies how increasing inclination angles enhance energy absorption efficiency and retard structural damage progression. Due to the high toughness of the concrete component, the composite maintains substantial residual bearing capacity, preventing instantaneous failure. These findings provide a robust theoretical framework and practical guidance for optimizing support designs in deep underground excavations with intricate geological defects.
Shubing Zhang, Hongkai Zhao, B. Hong et al.· International Journal of Geo...· 0 citations
This study examines the fracture and mechanical performance of hybrid fiber-reinforced high-strength concrete (HFRHSC) with different water-to-binder (W/B) ratios. Six mixtures incorporating hybrid combinations of steel, polymer, glass, and basalt fibers were investigated at W/B ratios of 0.42, 0.31, and 0.25. The synergistic effects of the fiber systems were evaluated in terms of compressive strength, splitting tensile strength, flexural behavior, fracture energy, residual strength, and toughness indices. Fracture properties were assessed using three-point bending tests on notched beams, where load-crack mouth opening displacement (CMOD) and load–deflection curves were used to characterize post-cracking behavior. In addition, bilinear softening and multi-exponential models were applied to reproduce the experimental load–CMOD response and estimate fracture energy. The multi-exponential model provided a more accurate representation of the nonlinear post-peak response, with coefficients of determination generally exceeding 0.95, whereas the bilinear model remained simpler and more suitable for practical engineering interpretation. The results show that hybridization substantially improved fracture resistance, particularly at lower W/B ratios. The steel–glass fiber system achieved approximately 54% higher fracture energy, a 40% improvement in toughness index, and 35% higher peak load-carrying capacity compared to the control mixture. The steel-polymer system at W/B = 0.31 exhibited the highest energy absorption capacity, with a 124% increase in total energy absorbed up to 10 mm deflection. These findings demonstrate that properly selected hybrid fiber systems can significantly improve crack resistance and post-cracking energy dissipation in HFRHSC, while analytical modeling provides a useful tool for interpreting load-CMOD behavior and fracture energy.
P. Smarzewski, T. A. Tawfik, Mohamed Abdellatief· International Journal of Civ...· 0 citations
The quasi-brittle nature of the concrete materials causes progressive propagation of crack under mechanical load in concrete beams. In this paper, a mathematical model based on fracture mechanics is presented, which is suitable to analyze the behavior of crack initiation, the stress distribution and the crack growth in concrete beams. The proposed scheme combines the Linear Elastic Fracture Mechanics (LEFM) with the cohesive nonlinear model of fracture, to investigate stress intensity factors, strain energy release rates, and fracture stability conditions when the load increases. The mathematical formulation of governing elasticity equations, crack-tip stress fields and fracture propagation criteria allow the prediction of structural degradation. Experimental fracture parameters show that with applied loading, the length of the crack and the energy released increases with fracture. The results show that the proposed model could accurately predict the crack propagation behavior and structural instability, which could be used to improve the failure assessment accuracy of concrete structural systems.
Amena Ansari, M. Darade, Devdatta Mokashi et al.· Journal of Intelligent Decis...· 0 citations
Predicting compressive–shear fracture in rock masses containing complex flaw distributions remains a major challenge in rock engineering. We propose an improved non-ordinary state-based peridynamics (NOSB-PD) model to simulate rock fracture behavior in this work. A stabilized NOSB-PD formulation is developed by incorporating a bond-level deformation gradient strategy to effectively suppress the zero-energy mode inherent in conventional NOSB-PD formulations, thereby ensuring deformation compatibility and numerical robustness. More importantly, the triple-shear energy criterion is introduced into the PD framework for the first time, enabling a more accurate characterization of shear fracture in rocks under complex stress states. The proposed NOSB-PD model is validated using two examples, demonstrating its excellent capability in suppressing the zero-energy mode and capturing fracture behavior in rock under compressive–shear conditions. Subsequently, the proposed model is used to systematically investigate the influence of flaw distribution on crack propagation and failure modes in rocks. The results indicate that variations in flaw distribution alter the local stress field, leading to a change in the rock fracture mode. Consequently, the rock bridge failure mode transitions from shear-dominated direct coalescence to mixed tensile-shear failure, and finally to tension-dominated indirect failure. The overall rock specimen is more prone to tensile–shear-mixed failure under conditions of shorter rock bridges with larger inclinations, or longer rock bridges with smaller inclinations. These findings provide new insights into the role of flaw distribution on rock fracture behavior.
Concrete readily develops cracks under service loads, which poses severe risks to the overall safety of engineering structures. In this work, the discrete element method (DEM) integrated with PFC2D 5.0 numerical software is adopted to construct a mesoscale concrete numerical model containing pre-existing internal fractures, and uniaxial compressive loading simulations are subsequently carried out. Unlike previous studies that predominantly examined isolated fracture parameters, this work systematically investigates the coupled effects of fracture inclination angle, length, and quantity on crack propagation mechanisms at the mesoscale, and for the first time establishes a quantitative relationship between microcrack spatial distribution patterns and macroscopic mechanical degradation. Parametric analyses are performed to quantify the influences of fracture geometric characteristics, including fracture inclination angle (30°, 45°, 60°), fracture length (short, long and extra-long), fracture quantity (4, 8 and 16), as well as the comparison between intact and fractured concrete specimens. The fracture quantities of 4, 8, and 16 are selected to represent low, medium, and high levels of initial defect density within the concrete matrix, corresponding to approximately 1%, 2%, and 4% of the total specimen area, respectively, thereby enabling a systematic investigation into the progressive deterioration of mechanical performance with increasing internal damage severity. The whole evolution process of crack initiation, crack propagation and ultimate failure patterns of concrete is systematically explored. Numerical results reveal that specimens with larger fracture angles exhibit higher compressive strength yet generate abundant newly formed microcracks, whereas low-angle prefabricated fractures are prone to triggering abrupt brittle failure. Specimens embedded with shorter fractures achieve superior mechanical strength and develop denser, more intensive microcrack distributions; in contrast, long pre-existing fractures drastically degrade compressive strength while limiting the generation of secondary cracks. Reducing the number of internal defects simultaneously improves compressive strength and expands the coverage range of the induced fracture network. Specimens with 16 prefabricated fractures deliver the weakest mechanical performance, owing to the excessively high initial defect density inside the matrix. In comparison with fractured samples, intact concrete without pre-set fractures achieves better comprehensive performance in terms of compressive strength, deformation compatibility and uniform microcrack development. A core conclusion drawn from this study is that the total quantity of microcracks cannot serve as a direct indicator to evaluate the damage degradation degree of concrete; instead, the spatial distribution pattern of microcracks dominates the deterioration level. Evenly scattered microcrack populations maintain relatively high residual strength, whereas the concentrated coalescence of microcracks into continuous penetrating macrocracks leads to an abrupt decline in structural load-carrying capacity. The findings of this research can provide theoretical references for stability evaluation and safety diagnosis of defective concrete structures in practical engineering.
Haiying Mao, Jun Zhen, Zuodong Zhou et al.· Materials· 0 citations