Narrow Results

For China Railway Track System (CRTS) I twin-block slab tracks, the interface between the sleeper and track slab is susceptible to damage under the coupled effect of long-term train load and external environment factors. In order to analyze the damage behavior and identify the type of debonding at the interface, this paper established a three-dimensional finite element model and introduced the cohesion zone model and concrete damaged plasticity model to simulate the interface damage and the inner-layer damage of the track slab, respectively. The interface debonding induced by the temperature effect was analyzed, and the debonding types were identified based on the obtained vertical vibration responses of the sleeper surface under the train load. The results reveal that the damage mainly occurs on the bottom and lateral sides at the interface under the temperature load. The track model can be refined further to obtain higher analysis accuracy with acceptable calculation time using the sequential loading method. The 26 damage features derived from the time domain, frequency domain, and time–frequency domain are in good representativeness in reflecting the damage information hidden in the vibration signals. Among them, the peak values (maximum vertical acceleration of the sleeper) are 55.0, 56.7, 60.3, and 61.6m/s² for no debonding, debonding on the lateral side, debonding at the bottom, and debonding on the longitudinal side of the interface under train load, respectively. Moreover, the identification accuracy of the debonding type can reach 93.75% combining the particle swarm algorithm and support vector machine. It indicates that the proposed identification method is effective and reliable to provide theoretical guidance for developing scientific maintenance and repair strategies for twin-block slab tracks.

Fracture research of natural gas pipelines with cracks is an important part of pipeline integrity evaluation. Based on the cohesive zone model (CZM), a numerical analysis is conducted of the dynamic fracture of X80 steel pipelines under explosion load. The factors considered include the crack propagation length, crack propagation velocity, dynamic crack tip opening angle (CTOA) and gas pressure. The results show that the whole cracking process can be divided into three stages: rapid cracking, stable propagation, and deceleration and stop cracking. When in the rapid cracking stage, the axial cracking of the pipeline is dominant. However, in the stable propagation stage, lateral expansion plays a more significant role. Besides, there exist upper limits on the length and velocity of crack propagation. In addition, it is also found that the time for the inflection point of rapid cracking and stable propagation is later than that to reach the velocity peak. The dynamic CTOA decreases with axial crack propagation, and the steady-state value of the CTOA is positively correlated with the load. The high-pressure gas escapes from the pipeline along the crack, resulting in the increase of air pressure outside the pipeline. Moreover, the peak pressure outside the pipeline is approximately linear its the initial crack length. The present research on the dynamic fracture mechanics behavior of the pipeline provides a necessary supplement for the test.

This paper describes the development of the Voronoi cell finite element model (VCFEM) with interfacial decohesion for simulating debonding induced microstructural damage in fiber reinforced composites. Normal and tangential cohesive zone models at the matrix-fiber interface are used to describe the onset and growth of damage along the inclusion-matrix interface. It is shown that the initiation and especially the propagation of debonding depends not only on the total cohesive energy, but also on the shape of the traction-displacement curve. The model is used to study the influence of various local morphological parameters on damage evolution by interfacial debonding. A special function of various geometric parameters is developed to predict the location of debonding in microstructures with varying morphology. Various numerical examples are solved to establish the effectiveness of the model.

Realizing the importance of widely used technique of plating for flexural retrofitting of reinforced concrete (RC) beams and its drawbacks due to premature failure(s), present work concentrates in developing a finite element tool model capable of successfully capturing multiple premature failure modes and their corresponding behaviors. The model is simple but focused; the capability and accuracy of the results have been validated through test literature, particularly focusing on the load capacities of beams at progressive stages of failure modes; which is from crack initiation through to complete failure, such as the load of crack initiation, first crack and complete failure. Acceptable accuracy is shown in terms of crack type(s), crack patterns, sequence, location and direction of propagation through the innovative use of cohesive zone model (CZM). The model clearly explains that debonding and peeling, although originating from a same location for most cases, are extensions of different types of cracks.

Macroscale mesh sensitivity and RVE size dependence are the two major issues that make the conventional homogenization techniques incapable of modeling the softening behavior of quasi-brittle materials. In this paper, a new continuous–discontinuous multiscale modeling approach to failure is presented. Inspired by the classical crack band model of Bazant and Oh (1983), this approach is built upon an extended computational homogenization (CH) scheme for representing the macroscale crack behavior. During the multiscale computation, once a macroscale material point loses its stability with the XFEM, a new crack segment represented is inserted for which cohesive RVE models using the extended CH and with copied initial states are coupled to crack integration points. In the extended CH, the macroscale strain applied to the boundary of the cohesive RVE model is enriched with a macroscale discontinuity related term regularized with the effective length of the microscale localization band. This helps alleviate the RVE size dependency of the homogenized cohesive response. The weakly periodic BCs that are aligned with the localization direction are employed to minimize spurious boundary effects. Several numerical examples are provided to demonstrate the effectiveness of this framework, with a comparison against direct numerical simulations.

In the framework of the extended finite element method, a two-dimensional four-node quadrilateral element enriched with only the Heaviside step function is formulated for stationary and propagating crack analyses. In the proposed method, two types of signed distance functions are used to implicitly express crack geometry, and finite elements, which interact with the crack, are appropriately partitioned according to the level set values and are then integrated numerically for derivation of the stiffness matrix and internal force vectors. The proposed method was verified by evaluating stress intensity factors, performing crack propagation analyses and comparing the obtained results with reference solutions.

Multiscale analyses considering the stretching problem in plates composed of metal matrix composites (MMC) have been performed using a coupled BEM/FEM model, where the boundary element method (BEM) and the finite element method (FEM) models, respectively, the macrocontinuum and the material microstructure, denoted as representative volume element (RVE). The RVE matrix zone behavior is governed by the von Mises elasto-plastic model while elastic inclusions have been incorporated to the matrix to improve the material mechanical properties. To simulate the microcracks evolution at the interface zone surrounding the inclusions, a modified cohesive fracture model has been adopted, where the interface zone is modeled by means of cohesive contact finite elements to capture the effects of phase debonding. Thus, this paper investigates how this phase debonding affects the microstructure mechanical behavior and consequently affects the macrostructure response in a multiscale analysis. For that, initially, only RVEs subjected to a generic strain are analyzed. Then, multiscale analyses of plates have been performed being each macro point represented by a RVE where the macro-strain must be imposed to solve its equilibrium problem and obtain the macroscopic constitutive response given by the homogenized values of stress and constitutive tensor fields over the RVE.

The peeling behavior of a thin film bonded to a substrate is investigated by using the cohesive interface model. We compare the peeling processes of film/substrate interfaces with three different geometric shapes, including a flat interface, a curved interface of sinusoidal shape, and a wavy interface with two-level sinusoidal hierarchy. The effect of the peeling angle on the maximal peeling strength is also examined. It is demonstrated that the peeling strength can be significantly improved by introducing a hierarchical wavy morphology at the film/substrate interface. This study may be helpful for the design of film/substrate systems with enhanced mechanical properties.

The transformation toughening behavior of a finite edge through crack in zirconia ceramics is studied with a three-dimensional finite element model. The continuum-based constitutive law of zirconia ceramics is implemented into a user-defined subroutine in ABAQUS to simulate the loading and unloading mechanical response of zirconia ceramics. We have given up the small-scale transformation assumption. The propagation behavior of a finite edge through crack in a zirconia plate is simulated at the structural level with the cohesive zone model and compared with the case in which the material is purely elastic. The influences of the stress state, the cohesive strength, the shear transformation strain and the activation energy threshold on the size of the transformation zone and the crack propagation behavior are systematically discussed. The numerical method and results presented in this work may be helpful for the design of engineering components made of zirconia ceramics.

Soft adhesives are widely used in soft robotics, biomedicine, flexible electronics and other fields. In practical applications, soft adhesives are frequently subjected to monotonic loading, static loading and cyclic loading. It is extremely important but challenging to analyze the failure behavior of soft adhesives due to their complicated mechanical properties and failure mechanisms, as well as the effect of different loading conditions. In this paper, the methodology of developing the cohesive zone model (CZM) for understanding the failure behavior of soft adhesives is systematically reviewed. First, for the one-time failure of soft adhesives, the establishment of the CZM considering the effect of loading rate, fibrillation, and mixed-mode loading is summarized. Second, the delayed failure of soft adhesives is studied. The development of the corresponding CZM considering the creep behavior under constant force and various potential mechanisms to explain the delayed failure under displacement holding is discussed. Then, for the fatigue failure of soft adhesives, remarks for CZM that are capable of expressing the loading-unloading process under the high cycle fatigue process and addressing the effect of viscoelasticity on fatigue damage have been provided. Finally, based on the application of soft adhesives in the frontier areas, the challenges and prospects faced for future research are presented.

A numerical aspect of the implementation cohesive zone model for delamination analysis is presented in this work by employing interface elements and higher-order B-spline functions. The stress oscillation is addressed, and Newton–Cotes integration scheme is considered as a good candidate to overcome this phenomenon. In order to track the nonlinear equilibrium path, a general arc-length constraint named dissipation-based arc-length method is applied. A numerical example is presented to perform the ability of the formulation in predicting the delamination behavior of studied structures.

The purpose of this paper is to investigate the influence of cohesive zone model (CZM) on the mechanical properties of CNTs-composites with debonding interface, and the finite element computation is carried out by the ANSYS software with CZM. The CZM model represents the interface separation and traction using three parameters derived from a surface potential function, and the effective plastic strain and stress concentration factor are calculated for the models with and without cohesive zone. It is obviously found that the effective plastic strain increases and the stress concentration factor decreases with the application of CZM, and it is reasonable to improve the mechanical properties of CNT-composites with debonding interface by applying the CZM.