Title: Knit Line Tensile Strength in Sheet Molding Compound

Authors: Courtney A. Morgan

DOI: 10.33599/nasampe/c.25.8

Abstract: Sheet molding compound (SMC) has been used in the thermoset composites industry since the 1960’s. The SMC molding process is highly regarded within the industry for its advantages in complex molding applications. However, localized areas with lower mechanical properties due to inherent material flow remain the predominant challenge for certain products with complex geometries and higher structural requirements. The flow of material during the molding process can contribute to high fiber alignment through charge placement, tool geometry, close rate, SMC viscosity, material gel and cure time, molding temperature and/or other factors. These areas of high fiber alignment, commonly referred to as knit lines, can create resin rich areas where minimal to no cross-fiber reinforcement is present. The lack of interlaced reinforcement can significantly reduce SMC laminate strength in these localized areas. Preliminary data suggests that the knit line tensile strength of SMC laminate is on average 75 % weaker than its isotropic counterpart. In this paper, we will investigate how SMC laminate knit line tensile strength is affected by three commonly used thermoset resin chemistries: PG maleate, polyethylene terephthalic, and neopentyl glycol. In addition, we will explore how the fiber volume of glass reinforcement in the three resin chemistries impacts knit line tensile strength.

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Conference: CAMX 2025

Publication Date: 2025/09/08

SKU: 8

Pages: 13

Price: $26.00