Application of Failure Criteria to Short Fiber Reinforced Composites and Experimental Validation

The use of short fiber reinforced plastics has great extent in several industrial sedors in which a high rate and functionality manufacturing process (such as injection molding) applied to a high strength material is required. However the design with this type of material has the complication of a composite material in which, in addition, the structure is varying locally because of the local fiber orientation, which is affected by material characteristics, mould geometry and processing conditions. This provokes that the reliability of this components relies on wide and costly experimental programs, usually because of the misunderstanding of the relationship between the microstruture and the macroscopic properties.

In this paper, an attempt to relate analytically the fiber orientation with the anisotropic response of the material (elastic constants and stren.gth ) is presented. Then, first of all, an experimental program is presented in which the local fiber orientation distribution have been measured in an iniected plate bv means of imaee treatment software Atter. different tensile and flexural tests have been performed to obtain the elastic and strength response of the material.

In order to relate the microstructure with the mechanical properties, a numerical scheme has been implemented based on the use of minomechanical models and orientation averaging procedures.

This procedure includes the numerical simulation of the characterisation tests, by means of a finite element code. to obtain the stress fields on the material and the use of a locallv defined failure criteria in order to predid the strength.

This methodology can be used to extend the capabilities of the computational tools used in the design of this type of materials. Injection simulation software currently incorporates capabilities for predicting fiber orientation and the resulting elastic properties. These propelties can be transferred to a general purpose finite element code for structural calculation on the component. Via user subroutines, this anisotropic and non homogeneous failure criteria can be implemented in order to have an improved design tool that accounts for one of the most important minoestructural aspects. As an example, this procedure is applied to an industrial component and the results compared with a traditional method.