Investigation of Tensile Strength of Long-Fiber Thermoplastic Composites Based on Evaluation of Fiber-Reinforced Structure

Abstract

Thermoplastic composites reinforced by discontinuous and long fibers are suitable for continuous production processes because of their high fluidity during compression molding. In addition, the molded structural part possesses high strength and rigidity as well as a light weight. However, the fibers flowing during the molding process disperse changing their orientation and density, and consequently, the consolidated molded part exhibits local variations in the mechanical properties depending on the state of the fibers inside. When the molded part is segmented into sections of a certain size, the strength characteristics fluctuate during each section. This makes it difficult to design and manage the strength of the molded part. In this study, we used three-dimensional X-ray CT to visualize the state of the fiber reinforcement in long-fiber reinforced thermoplastic composites and quantitatively evaluated fiber volume fraction and orientation degree through image analysis of each segmented compartment. A predictive method was proposed to theoretically calculate the strength of molded parts, including the strength of each compartment, and statistically analyze a series of the strength values. The method was validated by comparing the predicted strength values with the experimental results.