Formability Characterization of Fiber Reinforced Polymer Composites Using a Novel Test Method

Abstract

Fiber reinforced polymer composites are often used as a replacement for metal alloys because of the superior strength to weight ratio. However, a major drawback of these materials is the lack of formability caused by the low strain to failure ratio that does not allow the material to follow tooling contours into deep drawn shapes or tight radii. Composite materials have a multiscale hierarchical structure where micro and meso scale effects (fiber and tow scales) contribute to the macro structural response (laminate scale). In particular, during forming, different deformation occurs simultaneously at every scale. Currently, the amount of quantifiable and comparable forming data for both continuous and discontinuous fiber reinforced polymer composites, including a multi-scale understanding of the deformation response, is limited because of the lack of a testing system. This article proposes a novel test method and an apparatus called “the forming fixture” for testing the tow formability of fiber reinforced polymer composites by determining the required load to form an uncured resin impregnated fiber tow sample into a stretch drawn profile. Test results from forming of Hexcel (Stamford, CT) IM7-G continuous carbon fiber impregnated with Huntsman (The Woodlands, TX) RDM 2019-053 resin system, in the temperature range of 21°C–121°C, are discussed to demonstrate the use of the proposed apparatus including representative data. Results showed consistency and repeatability, validating the reliability of the novel method. The test aided in defining the forming behavior of the material in real time both visually (e.g. sample failure location) and as forming load versus displacement curves. A novel forming metrics, relating the maximum drawing depth with no failure and the maximum forming load, is defined to compare and select different fiber and resin formulations. Widespread adoption of the forming fixture will reduce reliance on a “trial and error” approach during the the forming process.