Continuous Fiber Reinforced Polymer Matrix Research Articles

Computational structural tailoring of continuous fibre reinforced polymer matrix composites by hybridisation of principal stress and thickness optimisation

Anisotropic composite material properties require special designing capabilities to fully exploit the remarkable properties in longitudinal fibre direction for stiffness and strength improvement. Therefore an optimisation scheme with hierarchical structuring of an optimality criterion based orientation optimisation and a gradient based technique for thickness optimisation is presented. The procedure is applied on two different space scales. Orientation optimisation based on principal stress directions is applied on a local laminate position. There fibre directions are affixed throughout the laminate until convergence is reached. On a local ply position thicknesses are determined in an iterative procedure. It is switched between both algorithms until global convergence is achieved. The application of algorithms on two different space scales leads to a robust engineering approach. The ability of the presented algorithm is tested with a numerical example and a structural optimisation of laminated composites is shown.

Thermally Activated Mechanical Composite Switches

A model describing the stiffness-temperature relationship of polymers was recently developed1,2. The present paper focuses on the integration of this model into classical lamination theory3. The computer simulations revealed that the stresses in off axis laminates are non-monotonic when temperature increases, i.e., continuous fibre reinforced polymer matrix composites seem to behave as thermally activated mechanical switches.

Modeling of injected pultrusion processes: A numerical approach

AbstractInjected pultrusion (IP) is an attractive process for high volume, high performance, and low cost manufacture of continuous fiber reinforced polymer matrix composites. In this work we focus our attention on development of a computer simulation model for the IP process. First, the governing equations for conservation of mass, momentum, and energy are developed using a local volume averaging approach. In turn, a computer simulation model of the IP process is developed using finite element/control volume (FE/CV) and finite difference techniques. Specifically, the equation of continuity and conservation of momentum are solved in 2‐D using a Galerkin FE/CV technique. The energy and chemical species balance equations are solved in 3‐D, where streamline upwind Petrov‐Galerkin (SUPG) or streamline upwind (SU) FE/CV are used to discretize the equations in two dimensions while finite differences have been used in the third dimension. The chemical species balance equation is solved in the Lagrangian frame of reference using finite differences. Different numerical formulations (Galerkin, Lagrangian, SU, and SUPG) are used to solve a number of benchmark problems to determine the best numerical formulation. It is shown that for coarse discretization, Streamline Upwind methods perform consistently better than the other methods. However, for refined meshes, the Lagrangian method produces the best solution for a given CPU time. Also, using the simulation model, the effect of fiber pull speed, reinforcement anistropy, and taper of the die on the quality of the product is studied. It is shown that the simulation model can be effectively used to design the die geometry as well as to optimize the operating conditions for a given product.

Micromechanics Analysis of Space Simulated Thermal Stresses in Composites. Part I: Theory and Unidirectional Laminates

A micromechanics approach was utilized to investigate the thermally in duced stress fields developed in the fiber and matrix of continuous fiber reinforced polymer matrix composites at cold temperatures typical of spacecraft operating tempera tures. Results from a finite element stress analysis of a periodic array of fibers were com pared to the closed-form solution of the composite cylinder model for several fiber/matrix materials. The influence of microstructural geometry, constituent properties, and fiber volume fraction were investigated. The results of this investigation showed that the as sumed microstructural geometry of the composite (i.e., composite cylinder, square or hex agonal array) did affect the distributions and magmtudes of thermally induced stresses. The matrix stresses were shown not to be strong functions of the fiber properties. Matrix stresses increased in absolute value with increasing fiber volume fraction, Vf. A global/ local analysis was used to approximate the stresses in localized regions of high Vf, con strained by a lower global Vf.