Explore the vast range of titles available.

Cracks in oil and gas pipelines cause leakage which results in property damage, environmental pollution, and even personal injury or loss of lives. In this paper, an active-sensing approach was conducted to identify the crack damage in pipeline structure using a stress wave propagation approach with piezoceramic transducers. A pipeline segment instrumented with five distributed piezoceramic transducers was used as the testing specimen in this research. Four cracks were artificially cut on the specimen, and each crack had six damage cases corresponding to different crack depths. In this way, cracks at different locations with different damage degrees were simulated. In each damage case, one piezoceramic transducer was used as an actuator to generate a stress wave to propagate along the pipeline specimen, and the other piezoceramic transducers were used as sensors to detect the wave responses. To quantitatively evaluate the crack damage status, a wavelet packet-based damage index matrix was developed. Experimental results show that the proposed method can evaluate the crack severity and estimate the crack location in the pipeline structure based on the proposed damage index matrix. The sensitivity of the proposed method decreases with increasing distance between the crack and the mounted piezoceramic transducers.

Rock is generally regarded as a heterogeneous and anisotropic material containing massive initial defects, such as cracks, joints, and porosities. In the present work, based on the maximum tensile stress and Mohr–Coulomb criteria, the fracturing modeling algorithm implemented into the numerical manifold method (NMM) is perfected and applied to a comprehensive simulation study of the fracturing of rock specimens. Disc and semi-disc specimens containing a single pre-existing crack, along with rectangular specimens containing two parallel pre-existing cracks, are simulated, respectively, to verify the fracturing modeling algorithm in terms of crack initiation, propagation, interaction, and coalescence. On this basis, four rectangular specimens containing multiple randomly distributing cracks are also simulated and the effective mechanical response of the specimen is investigated. The simulation of disc and semi-disc indicates that the crack initiation, propagation, and final crack path are all in great agreement with the experimental results. The simulation of rectangular specimens with two parallel pre-existing cracks shows the crack interaction and coalescence of the crack pairs. The results are also in good agreement with the experimental and theoretical results. For the simulation of complicated model with multiple cracks, results indicate that the increase in the crack density leads to a dramatic decrease in the effective elastic modulus and compressive strength as the evolution of pre-existing cracks. The NMM enriched with the fracturing modeling algorithm can be applied to solve more rock fracturing problems with diverse type and large number of initial defects.

This paper presents the lattice element models, as a class of discrete models, in which the structural solid is represented as an assembly of one-dimensional elements. This idea allows one to provide robust models for propagation of discontinuities, multiple cracks interaction or cracks coalescence. Many procedures for computation of lattice element parameters for representing linear elastic continuum have been developed, with the most often used ones discussed herein. Special attention is dedicated to presenting the ability of this kind of models to consider material disorder, heterogeneities and multi-phase materials, which makes lattice models attractive for meso- or micro-scale simulations of failure phenomena in quasi-brittle materials, such as concrete or rocks. Common difficulties encountered in material failure and a way of dealing with them in the lattice models framework are explained in detail. Namely, the size of the localized fracture process zone around the propagating crack plays a key role in failure mechanism, which is observed in various models of linear elastic fracture mechanics, multi-scale theories, homogenization techniques, finite element models, molecular dynamics. An efficient way of dealing with this kind of phenomena is by introducing the embedded strong discontinuity into lattice elements, resulting with mesh-independent computations of failure response. Moreover, mechanical lattice can be coupled with mass transfer problems, such as moisture, heat or chloride ions transfer which affect the material durability. Any close interaction with a fluid can lead to additional time dependent degradation. For illustration, the lattice approach to porous media coupling is given here as well. Thus, the lattice element models can serve for efficient simulations of material failure mechanisms, even when considering multi-physics coupling. The main peculiarities of such an approach have been presented and discussed in this work.

The phase field method (PFM) has been proposed and incorporated into the finite element method (FEM) for complex crack evolution problems. However, explicit cracks cannot be obtained in the phase field FEM (PFFEM). In the field of rock engineering, explicit cracks are indispensable for hydraulic fracturing problem in which crack opening displacement should be known, and compression-shear crack problems in which contact region should be determined. In this paper, the recently proposed phase field numerical manifold method (PFNMM) is developed to model rock fracturing processes. In PFNMM, PFM is regarded as a fracturing criterion, which deals with crack initiation, propagation, bifurcation and coalescence in a unified form; then crack paths are reconstructed and reproduced from smearing cracks; finally, the physical patches and manifold elements are cut with the reconstructed paths to obtain explicit cracks. The numerical results for several typical examples indicate that rock fracturing processes, including crack initiation without any preset cracks, crack propagation and crack merging, can be explicitly predicted. Besides, the results are in good agreement with the literature. Compared with PFFEM, explicit cracks and jump displacement fields across rock crack faces can be easily obtained by PFNMM.HighlightsThe combination of PFM and NMM can reproduce the explicit fracture process in rock.The proposed method is capable of simulating the free opening and closing of cracks.The PFNMM can predict the evolution mechanism of multi-cracks and merging crack.

The composite materials are widely used across industries however, these materials are prone to damages like cracking and delamination due to its complexity. The Electromechanical Impedance (EMI) technique offers a reliable non-destructive solution for detecting such damage using piezoelectric sensors and enabling effective structural health monitoring and enhancing safety and durability. This study explores the application of the EMI technique for monitoring damages in composite fibre concrete specimens. The specimens were prepared using Ordinary Portland Cement (OPC), fly ash, and polypropylene, glass fiber mixture, water, fine and coarse aggregates. The Piezoelectric sensors were employed to record conductance and susceptance signatures, enabling early detection and quantification of damages. The severity of damages were assessed using statistical indices such as Root Mean Square Deviation (RMSD), Mean Absolute Percentage Deviation (MAPD), and Correlation Coefficient (CC) revealing higher sensitivity. A notable leftward shift in EMI signatures with increasing damage was confirmed progressive structural degradation. Additionally, structural parameters equivalent stiffness and equivalent damping were evaluated, demonstrating a decrease in stiffness and an increase in damping with greater damage depth. Temperature effects on EMI responses were also investigated, necessitating compensation for reliable analysis. An Artificial Neural Network (ANN) model was trained using Levenberg-Marquardt (LM) algorithm and implemented to predict conductance values and damage depth. The developed ANN showed high accuracy, with strong agreement between experimental and predicted results. Overall, the findings confirm the EMI technique’s potential for SHM of composite fiber concrete and integration with machine learning for improved predictive its durability assessment.

Vibrothermography often employs a high-power actuator to generate heat on a specimen to reveal damage, however, the high-power actuator brings inconvenience to the application and possibly introduces additional damage to the inspected objects. This study uses a low-power piezoceramic transducer as the actuator of vibrothermography and explores its ability to detect multiple surface cracks in a metal part. Experiments were conducted on a thin aluminum beam with three cracks in different orientations. Detailed analyses of both thermograms and temperature data are presented to validate the proposed vibrothermography method. To further investigate the performance of the proposed vibrothermography method, we experimentally studied the effects of several critical factors, including the amplitude of excitation signal, specimen constraints, relative position between the transducer and cracks (the transducer is mounted on the same or the opposite side with the cracks). The results demonstrate that all cracks can be detected conveniently and simultaneously by using the proposed low-power vibrothermography. We also found that the magnitude of excitation signal and the specimen constraints have a great influence on detection results. Combined with effective data processing methods, such as Fourier transformation employed in this study, the proposed method provides a promising potential to detect multiple cracks on a metal surface in a safe and effective manner.

In this paper, the interaction between the fluid-driven fracture and frictional natural fault is modeled using an enriched-FEM technique based on the partition of unity method. The intersection between two discontinuities is modeled by introducing a junction enrichment function. In order to model the fluid effect within the fracture, the fluid pressure is assumed to be constant throughout the propagation process. The frictional contact behavior along the fault faces is modeled using an X-FEM penalty method within the context of the plasticity theory of friction. Finally, several numerical examples are solved to illustrate the accuracy and robustness of proposed computational algorithm as well as to investigate the mechanism of interaction between the fluid-driven fracture and the natural fault.

Improving the strength–ductility combination is a critical challenge in metallic materials. Cu–Pb bronze alloys, commonly used in bearing materials, require superior mechanical properties and service safety. However, they face a significant reduction in ductility due to concentrated plastic deformation within the low-strength Pb phase. To address this issue, the solid–liquid continuous casting (SLC) method was used to overlay Cu–Pb alloy onto a mild steel substrate, forming a bi-layered structure that significantly enhances overall ductility. An in situ tensile test in conjunction with digital image correlation (DIC) and electron back-scattered diffraction (EBSD) methods revealed that localized strain within the bronze layer concentrates at Pb phases and transitions into dispersive strain bands. This transformation is attributed to the constraint from the layered structure. The well-bonded interface, demonstrated by the interface-affected zone (IAZ), ensures coordinated deformation of the bi-layered sheet. Moreover, the layered structure effectively constrains individual crack propagation and encourages a multiple-crack behavior. Graphical abstract

This study investigates the stationary interacting of multiple cracks within both the interface and the embedded layer of a homogeneous half-plane coated with a functionally graded material (FGM) under elastodynamic in-plane loading. Leveraging the distributed dislocation technique, this research provides a novel framework for exploring the intricate fracture mechanics of this specific material configuration. To accurately quantify dynamic stress intensity factors (DSIFs) within this complex medium, the study employs the method of integral transformations. This approach involves strategically positioning Volterra-type climb and glide edge dislocations at the critical interface between the half-plane and the FG coating. To characterize the traction vector along the surfaces of multiple cracks, we construct systems of Cauchy singular integral equations using dislocation solutions. By numerically solving these equations, we precisely determine the dislocation density along the crack surfaces. This critical information then enables exceptionally accurate computation of DSIFs at the crack tips. This study's numerical findings reveal how material gradient characteristics, Poisson's ratio, excitation frequency, coating thickness, crack length and crack interactions collectively govern the DSIFs of graded coatings. These results clarify the complex mechanics of these materials under elastodynamic loading.

This paper discussed the fracture analysis of two collinear cracks under a thermo-magnetic-electric-elastic field. Taking advantage of the permeable crack models and the singular integral equation, the analytical solutions of important parameters around two collinear cracks are obtained. An example is used to demonstrate the method provided in this paper. The effects of the dimensionless quantities between the upper and lower crack surfaces, such as heat flux on the crack surface, electric displacement, magnetic induction per unit thickness, and the corresponding intensity factors near the inner and outer crack tips, are shown in the case analysis. It should be emphasized that because the theoretical solution obtained in this paper has an explicit form, it is convenient to solve the stress intensity factor. In particular, it is very convenient to solve the influence of various physical quantities on the stress intensity factor of the crack tip.