Experimental and Numerical Analysis of Hail Impact on Sheet Molding Compounds

Stochastic reconstruction and microstructure modeling of SMC chopped fiber composites

Micromechanical transverse tensile crack propagation of unidirectional fiber reinforced epoxy SMC slice imbedded in a TDCB specimen

An integrated computational materials engineering framework to analyze the failure behaviors of carbon fiber reinforced polymer composites for lightweight vehicle applications

Micromechanical FE analysis of UD fibre-reinforced composites with fibres distributed at random over the transverse cross-section

Predicting sizing dependent bending rigidity of glass fibre bundles in sheet moulding compounds

A damage threshold prediction model of CFRP panel by hail impact based on delamination mechanism

The dimensional stability of sample cylinders cured with sheet molding compound pastes was investigated. A significant amount of dimensional change was found for these samples when they were annealed. Furthermore, the amount of change varied with location from the center to the wall along the radial direction of the sample cylinder to form a strain gradient. A series of experiments were then carried out to determine property gradients along the same direction in search of the source of the dimensional instability. It was found that the sample also had a gradient in cure and a gradient in dynamic mechanical properties. But these gradients are not in full agreement. In particular, the gradient of cure appears to be opposite to the direction of the strain gradient, while the gradient of the dynamic mechanical properties coincides with it. These results, therefore, suggest that the dimensional stability may be predominantly governed by the viscoelastic behavior of the material.

Mechanics of the squeeze flow of planar fibre suspensions

Micro-mechanical failure analysis of a uni-directional fiber reinforced composite ply – Cohesive elements & a ductile fracture mechanics approach

A detailed micromechanical finite element analysis methodology is presented to predict the transverse tensile (fiber perpendicular) failure behavior of a unidirectional (UD) glass fiber-reinforced plastic composite ply. In order to understand the constituent-level stress–strain and damage behavior, finite element analysis is accomplished using representative volume element (RVE) that consists of random fiber distribution as observed in the microscopic image of an actual composite ply. For modeling the fiber/matrix interface failure behavior, cohesive zone module (cohesive surface/cohesive element) of Abaqus® is used. In order to capture the epoxy matrix stiffness and strength degradation, the following two different approaches are used: (i) initially, the linear Drucker–Prager plasticity model in combination with a ductile fracture criterion is used; (ii) later, a brittle failure approach such as the quadratic normal stress criterion within the framework of eXtended finite element method is used. From the detailed micromechanical analysis of the RVE, it is observed that the initial damage in the RVE occurs in the form of fiber/matrix interface decohesion. With increasing tensile load, interface crack propagates and creates a stress concentration region in the matrix material, adjacent to the crack tip. Further load application causes both interface crack tip and matrix stress concentration to move away from the load application direction. As soon as the interface crack tip reaches approximately 60° to 70° away from the load application direction, the conjunction of the matrix damage with the interface crack leads to the RVE final failure. The predicted average stress–strain curves from the above-mentioned two different epoxy matrix failure criterions (ductile and brittle) correlate very well with the experimental results, indicating that the brittle failure behavior of a UD fiber-reinforced plastic composite ply under transverse tensile load is mainly controlled by the fiber/matrix interface properties.

Homogenization of granular material modeled by a three-dimensional discrete element method

Investigation of electromechanical properties of piezoelectric structural fiber composites with micromechanics analysis and finite element modeling

Smoothed Particle Hydrodynamics (SPH) is not widely used in aerospace engineering applications that involve compressible flows despite compressible hydrodynamics being one of the focal points of SPH since its origins. A reason for this is the unavailability of boundary treatment methods for compressible flows within SPH, essential for simulating flows in and around bodies. Moreover, modulating the number of particles in a region becomes necessary in many scenarios involving compressible flows. The boundary treatment has been addressed in our recent work. In this work, we present our attempt at solving other critical issues that arise in compressible SPH simulations by combining our boundary treatment with an adaptive resolution procedure. We propose shock-based solution adaptivity and shock-aware particle shifting within the adaptivity procedure. A wide variety of test problems are employed to illustrate the effectiveness of boundary treatment and the adaptivity procedure in resolving existing issues, including errors due to interaction with differently spaced ghost particles, formation of spot-like structures due to particle clumping, and poorly resolved low-density regions. The boundary treatment method and adaptive resolution procedure would make SPH a more attractive choice for aerospace engineering applications involving compressible flows.

Numerical analysis on viscoelastic creep responses of aligned short fiber reinforced composites

Effective viscoelastic response of a unidirectional fiber composite with interfaces that may separate or slip according to uniform Needleman-type cohesive zones is analyzed. Previous work on the solitary elastic composite cylinder problem leads to a formulation for the mean response consisting of a stress-strain relation depending on the interface separation∕slip discontinuity together with an algebraic equation governing its evolution. Results for the fiber composite follow from the composite cylinders representation of a representative volume element (RVE) together with variational bounding. Here, the theory is extended to account for viscoelastic matrix response. For a solitary elastic fiber embedded in a cylindrical matrix which is an nth-order generalized Maxwell model in shear relaxation, a pair of nonlinear nth-order differential equations is obtained which governs the relaxation response through the time dependent stress and interface separation∕slip magnitude. When the matrix is an nth-order generalized Kelvin model in shear creep, a pair of nonlinear nth-order differential equations is obtained governing the creep response through the time dependent strain and interface separation∕slip magnitude. We appeal to the uniqueness of the Laplace transform and its inverse to show that these equations also apply to an RVE with the composite cylinders microstructure. For a matrix, which is a standard linear solid (n=2), the governing equations are analyzed in detail paying particular attention to issues of bifurcation of response. Results are obtained for transverse bulk response and antiplane shear response, while axial tension with related lateral Poisson contraction and transverse shear are discussed briefly. The paper concludes with an application of the theory to the analysis of stress relaxation in the pure torsion of a circular cylinder containing unidirectional fibers aligned parallel to the cylinder axis. For this problem, the redistribution of shear stress and interface slip throughout the cross section, and the movement of singular surfaces, are investigated for an interface model that allows for interface failure in shear mode.