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In the design of structures involving quasi-brittle materials such as concrete, it is essential to consider the scale dependence of the mechanical properties of the material. Among the theories used to describe the phenomenon of size effect, the fractal theory proposed by Carpinteri and colleagues has attracted attention for its results in the last three decades of research. The present study employs the fractal perspective to examine the scale effect in three-point bending tests conducted on expanded polyethylene (EPS) beam specimens. The influence of size on flexural strength, fracture energy, and critical angle of rotation is investigated. Additionally, numerical simulations based on peridynamic (PD) theory are performed based on the experimental tests. The global behavior, brittleness, failure configuration, and fractal scale effect obtained numerically are evaluated. The numerical results show a good correlation with the experimental ones and, moreover, both the experimental and numerical results are in agreement with the fractal theory of scale effect. More precisely, the error of the sum of the fractal exponents, computed with respect to the theoretical one, is equal to −1.20% and −2.10% for the experimental and numerical results, respectively. Moreover, the classical dimensional analysis has been employed to demonstrate that the scale effect can be naturally described by the PD model parameters, allowing to extend the results for scales beyond those analyzed experimentally. [ABSTRACT FROM AUTHOR]

This paper proposes a new precursor for monitoring coal–rock dynamic disasters based on a fiber bundle model (FBM), which has been validated in the study of material fracture and critical phenomena. First, the FBM was simulated using the Monte Carlo method to analyze the variations of force and energy. The derivative of energy was identified as a precursor characteristic for model failure. The acoustic emission (AE) features of coal–rock under uniaxial compression were also analyzed, and a constitutive model for coal–rock damage evolution under uniaxial compression was established using AE ringing count. Furthermore, the energy derivative was calculated using the constitutive model to verify the simulation results and propose a new precursor indicator for coal–rock collapse. The research results provide useful guidance for preventing coal mine dynamic disasters. Practical Applications: This study presents a novel methodology for predicting engineering geological hazards, focusing specifically on monitoring and preventing rockburst disasters in coal mines. The crucial precursor characteristics of coal and rock damage are unveiled by research findings, offering valuable insights for the accurate forecasting of potential disaster risks. This approach holds substantial promise not only within the coal mining sector but also across various engineering domains, including geotechnical engineering and other fields necessitating meticulous risk assessment. Implementation of this methodology empowers practitioners to refine disaster prediction, proactively ensuring the sustainability and safety of engineering ventures. It is recommended that project teams consider the integration of this innovative indicator alongside widely adopted microseismic monitoring techniques, thus mitigating the limitations of existing geophysical monitoring methods. This innovative approach is poised to have a profound and transformative impact on the enhancement of geological hazard monitoring and engineering risk management, providing invaluable support for upcoming engineering projects. [ABSTRACT FROM AUTHOR]

In engineering applications, it is crucial to consider the size dependence of a material's mechanical properties and its overall behavior. One of the theories that quantifies this phenomenon in quasi-brittle materials is the cohesive fractal theory (CFT) introduced by Carpinteri and his collaborators. This theory describes the behavior of materials using fractal dimensions. To investigate whether the scale effect can be analyzed using the CFT, a version of the Lattice Discrete Element Method (LDEM) is employed. The accuracy of the LDEM in capturing the scale effect is evaluated through simulations of three primary tests. Specifically, rock specimens are subjected to tensile, compressive, and bending loads to determine their mechanical properties. The influence of material heterogeneity and boundary conditions is also examined. In scenarios involving tensile and bending loads, the localization of a significant crack leads to failure. According to the CFT, the sum of the fractal exponents is close to unity, with values of 1.0 (mean value) for tensile loading and 0.97 for bending loading. However, the compressive loading results do not exhibit this characteristic, as no single prominent crack leads to failure. Overall, the LDEM results are consistent with the CFT, effectively quantifying the scale effect without modifying the elementary constitutive law. [ABSTRACT FROM AUTHOR]

The mechanical description of the failure of quasi-brittle materials is a challenging task. Rocks, concrete, ceramics, and natural or artificial composites could be considered for this material classification. Several characteristic phenomena appear as emergent global behaviors based on the interaction of many simple elements, such as the effect of size and the interactions between micro-cracks. These are essential features of a complex system. These topics were investigated using acoustic emission techniques and a numerical approach that used a continuum media hypothesis called peridynamics. In this context, a pre-notched concrete specimen was manufactured. A mechanical test was performed to acquire acoustic emission signals. The problem was also simulated using the peridynamic model. The evolution of the damage process, which is presented in terms that go beyond only the global reaction vs. displacement and the evolution of the acoustical emission global parameter, is presented. Finally, the synergy between the experiments and simulations is discussed. [ABSTRACT FROM AUTHOR]