Compression molding of long fiber-reinforced thermoplastics (LFTs) is a widely used process to produce semi-structural parts with advanced mechanical properties. LFTs have gained importance due to their exceptional lightweight properties. Furthermore, the direct processing of LFT (D-LFT) is a cost-efficient manufacturing processes used in the automotive industry. The anisotropy introduced into the part by discontinuous fibers must be considered for reliable structural analysis and part design. In particular, the prediction of fiber orientation is an important element for simulating the compression molding process of D-LFT to allow assessment of strength as well as warpage. Due to the plastification process in the extruder, a distinctive non-random fiber orientation distribution emerges within the D-LFT strand. Measurements and simulations show that intitial orientation affects the final fiber orientation and warpage predictions within the finished part. Preliminary experimental studies on fiber-matrix separation in LFT compression molding indicate that locally the fiber content and the fiber length distribution vary tremendously. Moreover, x-ray scans of molded plates show that the dispersion of the fibers within the matrix is not well understood. Fiber-matrix separation and fiber bundling cannot be modeled in commercially available software because the programs assume continuous fiber motion. A fundamental understanding of the physics behind fiber dispersion is necessary to achieve an accurate prediction of fiber dispersion and fiber bundling. A mechanistic model that represents each fiber as a chain of interconnected segments and aids in the understanding of fiber-fiber and fiber-matrix interactions will be introduced.
