Simulation of Delamination Evolution of Slab Ballastless Track under Vertical Impact

During the running of a high-speed train, the wheel may bounce on the rail due to the track irregularity. The wheel bounce could generate a vertical impact, leading to the initiation and expansion of delamination between layers of the track structure. In this paper, the evolution of the interfacial damage and delamination subjected to the vertical impact is simulated using finite element analysis (FEA). In the FEA, a bilinear cohesive zone model (CZM) is adopted to simulate the interface between the track slab and the CA mortar layer. For different levels of impact energy, the contact force, vertical deformation, absorbed energy, area of interfacial damage, and area of delamination are calculated and compared. The effects of the tangential and normal stiffness of the interface on the distribution of interfacial damage and delamination are investigated. The results show that the contact force, vertical deformation, absorbed energy, area of interfacial damage, and area of delamination increase with the increase of the impact energy. The area of interfacial damage in the compression stage is closely related to the tangential stiffness, whereas the area of delamination depends on the normal stiffness. The normal stiffness that gives the largest area of delamination is recommended to be taken as the lower bound of the normal stiffness for both controlling the delamination and preventing an exceedance of the track irregularity limit.

Determination of fracture toughness of an adhesive in civil engineering and interfacial damage analysis of carbon fiber reinforced polymer–steel structure bonded joints

Carbon fiber reinforced polymer–steel structural bonded joints are often subject to mixed-mode loading i.e. coupling action of normal and shear stress occurs in the joints. In this paper, an experimental approach based on fracture mechanics was adopted to obtain the fracture toughness (GΙC and GΙΙC) of an adhesive currently employed in civil engineering applications, with the corresponding pure cohesive models verified by numerical results. Furthermore, feasibility of the mixed-mode cohesive model for the current adhesive was validated through comparison of numerical and experimental results of carbon fiber reinforced polymer–steel single-lap joints. Finally, based on the validated mixed-mode cohesive model, the interfacial damage of carbon fiber reinforced polymer–steel beam joints was analyzed using the finite element method, accounting for the long-term degradation that can occur in the joint materials i.e. carbon fiber reinforced polymer and adhesive. The work in this paper can provide some useful data such as the fracture properties of the adhesive and shed some light on the design optimization of carbon fiber reinforced polymer–steel structure joints as well as the estimation of its long-term interfacial behavior when in service in civil engineering applications.

Adaptive Affine Homogenization Method for Visco-hyperelastic Composites with Interfacial Damage

Despite intense research on the homogenization methods, it still is a challenging task to predict the nonlinear mechanical responses of visco-hyperelastic particulate-reinforced composites. In this work, we propose the adaptive affine method, a novel mean-field homogenization method designed to ensure the consistency of the accumulated strain state and the concentration tensor, and apply the method to predict the mechanical response of the composite in the large strain regime under uniaxial, cyclic, and bi-axial loadings. Our method is also extended to predict the mechanical response in the presence of interfacial imperfections described by linear cohesive traction-separation laws. The analytic predictions are validated against finite element analyses of representative volume elements. We believe that our adaptive affine method can be extended to model various nonlinear responses of load-bearing composites including the effects of (visco)plasticity and finite deformation.

Effective anti-plane moduli of couple stress composites containing elliptic multi-coated nano-fibers with interfacial damage and variational bounds

Prediction of the anti-plane moduli of solids consisting of a given distribution of unidirectionally aligned elliptic multi-coated fibers with interfacial damage is the focus of this paper. The fibers and their coating layers may be in the order of nano or micro scales. All the constituent phases of the composite are supposed to be described in terms of couple stress elasticity. Accordingly, the bounds for the overall shear moduli of the aforementioned composites are provided by employing the principles of minimum potential and complementary energies. Certain subtleties associated with the elliptic multi-coated fibers for three cases of pure sliding (completely damaged), imperfect (partially damaged), and perfect (undamaged) interface conditions will be discussed. The inherent anisotropy introduced due to the ellipse geometry of the fibers’ cross-sections is addressed. The effects of the ellipse aspect ratio as well as its size, interfacial damage, and rigidity on the effective anti-plane moduli of such composites will be examined.