Predicting Reinforced Plastic Material Performance

Finite Element Analysis (FEA) is a traditional technique used to predict the structural performance of fiber-reinforced plastics by design engineers. This technique works on the assumption that there is a uniform distribution of fiber throughout the molded part. It is a known fact that mold filling parameters and part geometry variations greatly affect the fiber distribution and orientation and, therefore, the resulting mechanical and thermal performance of parts. Thus, to prevent the failure of parts, designers apply safety factors to their assumptions of material strength. In some cases, though, the resulting designs can be too conservative – leading to added material cost – or simply marginal, requiring extra validation testing and development delays.

Effects on Part Performance

The mechanical properties such as part stiffness, tensile strength and resistance to heat distortion are affected by the orientation of reinforcing fibers resulting from the molding process. Fiber orientation within the molded part is non-uniform, resulting in varying material properties in different directions. This is known as anisotropy. Instead of the uniform, isotropic display of strength and properties in all directions previously assumed by FEA, more accurate FEA models should incorporate realistic non-uniform fiber orientation and the anisotropic, non-uniform properties directly related to variations in fiber orientation and concentration.

Typically, analysts use a safety factor to compensate for the gap in knowledge of how material properties vary in a fiber-reinforced plastic part. However, the safety factor neglects the part’s fiber orientation-induced anisotropy, accounting instead for its effect by degrading to some degree the strength and modulus values determined by tensile testing. Unfortunately, this approximation overestimates properties in some areas and underestimates them in others.

New “ULTRASIM™” software module links filling simulation and structural analysis of part

The ULTRASIM™ module factors fiber-orientation data into the structural analysis. Fiber orientations determined from the mold filling simulation transfer via the ULTRASIM™ software to the finite element mesh of the part’s structural model, thereby establishing a new set of local material parameters. Because the transfer is purely geometrical, the data can apply to a variety of meshes. User-defined functions allow inclusion of non-linearity and complex failure modes in the description of the material — something previously not possible. Efficient management of the vast quantity of input data required is fundamental to the whole process.

ULTRASIM™ thus forms a link between mold filling simulation, the resulting fiber orientation, and the structural analysis of the part. The results can be dramatic. In some cases, BASF’s ULTRASIM™ has already helped customers entirely eliminate, or reduce the time required for, a prototype stage or stages.

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