Exponential Cohesive Model Research Articles

Finite element analysis of competitive damage mechanisms of composite scarf adhesive joints by considering thickness effect

Cohesive zone models are demonstrated to fail to predict damage mechanisms of adhesive layer with the increase of thickness, although the load response and ultimate failure strength of adhesive joints are evaluated well to some extent. This paper attempts to explore damage mechanisms of composite scarf adhesive joints with brittle adhesive material under quasi-static loading, where the competitive relationships between the damage behaviors of adhesive layer and the interface debonding between the adhesive layer and composite laminates are investigated. For the epoxy adhesive layer, the damage initiation criteria are developed by considering the hydrostatic pressure, the tension/compression asymmetry and frictional effects, and the damage evolution law is derived using continuum damage mechanics. The bilinear cohesive model and the modified Xu and Needleman’s exponential cohesive model are used to predict the interface debonding between the epoxy adhesive layer and glassy fiber/epoxy composite laminates, respectively. FEA is performed to study two competitive damage mechanisms of composite scarf adhesive joints by discussing the effects of the scarf angle, the thickness of adhesive layer and the shape of cohesive models. Results show that 1. two approaches with/without considering damage mechanisms of adhesive layer can be chosen alternatively within the thickness of adhesive layer 0.5–1.0 mm, by weighing calculation efficiency and precision appropriately; 2. damage features of adhesive layer deserve more attention as the thickness increases beyond 1.0 mm.

Ultra-High-Performance Concrete Crack Propagation Based on Fiber Random Distribution Model

The tensile strength, crack behavior, and strain-hardening properties of ultra-high-performance concrete (UHPC) are mainly affected by the steel fibers distributed in the matrix. In this study, a mesoscopic model of UHPC was established using a numerical simulation method to study the effects of steel fibers on the crack propagation and tensile properties of UHPC. First, the exponential cohesive model was used to simulate the pull-out of a fiber embedded in a UHPC matrix. Then, the distribution and variation of the interfacial shear stress during the fiber pull-out process were obtained, and the UHPC fiber-pull-out load–displacement curve was obtained. Using the Monte Carlo method, a meso-scale finite element model of UHPC was established by modeling randomly distributed steel fibers in the UHPC matrix. After verification, the model was used to study the effects of fiber characteristics, interface strength, and matrix strength on the crack propagation path and tensile properties of UHPC. The results showed that the exponential cohesive constitutive model with a softening coefficient of –1 can effectively characterize the mechanical behavior of the interface between the steel fibers and matrix in UHPC. Affected by the random distribution of fibers, the main propagation mode of cracks in UHPC was that the cracks bypassed the fiber-dense area and extended to the fiber-sparse area, and the crack propagation path was mainly affected by the fiber distribution. The distribution of fibers significantly affected the tensile strength and peak strain of UHPC. When the fiber inclination angle was in the range of 15°–30°, the comprehensive tensile properties of UHPC were the best. With increasing fiber volume fraction and fiber length, UHPC gradually began to exhibit multi-cracking and strain hardening (when the fiber volume fraction was more than 2.5% or fiber length was more than 15.5 mm). The interface strength and matrix strength had little effect on the crack propagation path, but had significant effects on the tensile strength and toughness of the UHPC. The higher the strength of the UHPC matrix, the more fully the anti-cracking effect of the steel fiber that can be achieved.

Experimental and numerical analysis on concrete interface damage of ballastless track using different cohesive models

The Interface damage has become one of the most critical issues for ballastless tracks, which is a severe challenge to the rapid development of high speed railway. This paper presents experimental and numerical analyses on the concrete interface damage of ballastless track using different cohesive constitutive models and their implementation methods. The interface damage evolution characteristics of the ballastless track are investigated by combining damage mechanics method with finite element model, in particularly, the potential-based cohesive models are firstly used into the interface damage analysis of ballastless track by secondary development in software ABAQUS. Primarily, three types of cohesive constitutive model including a concise bilinear constitutive model and two potential-based cohesive constitutive models are implemented in ABAQUS through user-defined material subroutine, and then the interface damage simulation is completed by a DCB finite element model to verify the effectiveness of programmed cohesive constitutive subroutines. Subsequently, the experiment of concrete interface specimens is conducted by combining the concrete tensile test and the DIC full-field stress–strain test to obtain the mechanical properties and the constitutive relationship of the concrete interface. Finally, the interface damage evolution of a ballastless track with different cohesive constitutive models under temperature gradient load are investigated. The experimental results show that the exponential constitutive has the best agreement with the tested interface mechanical properties than other two types of cohesive law and the polynomial constitutive shows the worst match with test results. Moreover, the simulation results indicate that the interface failure of the track structure is a mix-mode damage process under temperature gradient load, and exponential cohesive model is recommended for the mix-mode damage analysis of track interface under quasi-static condition, whereas the polynomial cohesive model predicts asymmetrical damage distribution at the track interface due to its insufficient definition of the constitutive model.

Impact of damage on the effective properties of network materials and on bulk and surface wave propagation characteristics

We analyze in this contribution the propagation of bulk and Rayleigh surface waves in periodic architectured materials undergoing internal damage. An elastic damageable continuum-based model is developed in the framework of the thermodynamics of irreversible processes, whereby the displacement experiences a jump across the faces of the propagating crack. The crack propagation involves an enhancement of the displacement field associated with embedded discontinuities, which remain localized within each (triangular type) finite element. The displacement discontinuity is regulated by the traction separation behavior described by an exponential cohesive model with damage hardening followed by softening. The effective mechanical properties of the overall network are evaluated versus the increasing damage. The phase velocities for the longitudinal and transverse modes are then computed continuously versus the amount of damage, considering successively the situations of symmetrically and unsymmetrically distributed damage occurrence and propagation. Simulation results show that although the crack pattern is different in these two situations, it has no impact on the evolution of the effective moduli versus global damage. The phase velocities computed based on the effective moduli decrease as damage propagates within the network; thus, it is an indicator of the amount of global damage.

Finite Element Analysis of Micromechanical Progressive Failure Properties of Glass Fiber/Phenolic Resin Composites by Monte Carlo Simulation

This paper studies the micromechanical progressive failure properties of glass fiber/phenolic resin composites by finite element analysis and experiments. First, a set of theoretical methods on the failure criteria and damage evolution of fiber, matrix, and interface are introduced, which include Monte Carlo simulation on random fiber fracture, damage evolution and stiffness degradation of matrix based on thermodynamic theory, an exponential cohesive model for interface debonding, and a strain localization-based Mori–Tanaka homogenization method. Second, the proposed model is implemented using ANSYS PARAMETRIC DESIGN LANGUAGE (ANSYS-APDL) that uses the restart numerical technique. In order to predict the tensile strength of the composites, the numerical convergence issue is solved by introducing viscous effect into the stiffness equations. Finally, numerical results in terms of the damage evolution behaviors and tensile strengths of composite microstructures are validated by tensile experiments and acoustic emission tests on unidirectional glass fiber/phenolic composites.

A nonlinear cohesive/friction coupled model for shear induced delamination of adhesive composite joint

This paper originally proposes a nonlinear cohesive/frictional contact coupled model for the mode-II shear delamination of adhesive composite joint based on a modified Xu and Needleman’s exponential cohesive model. First, the friction is assumed to increase nonlinearly at the delamination interface when the tangential cohesive softening appears. Second, a non-associative plasticity model based on the Mohr–Coulomb frictional contact law is proposed, which includes a frictional slip criterion and a slip potential function. Third, a return mapping algorithm based on the non-associative plasticity theory is proposed to solve the updated normal and tangential tractions and stiffnesses. It is shown the tangential cohesive traction and stiffness depend on the friction and dilatancy of the delamination interface. Finally, the proposed theoretical model is implemented using three-dimensional finite element analysis by ABAQUS-UEL (user element subroutine) and demonstrated by comparing the finite element results with the analytical results for the $$[0^{\circ }]_{6}$$ , $$[\pm 30^{\circ }]_{5}$$ , $$[\pm 45^{\circ }]_{5}$$ end-notched flexure adhesive composite joints with the mode-II shear delamination. The effects of the friction coefficient, cohesive strength, normal contact stiffness and mesh size on the load–displacement curves and delamination mechanisms of composites are studied. Numerical results show the shear delamination growth is governed by the transition from the decreased tangential cohesive traction to the increased tangential friction, and the frictional effect becomes distinct after unstable delamination for angle-ply laminates.