Stretch Forming of Thermoplastic Aligned Discontinuous Fiber Composites: Effects of Environmental Conditions on Forming Optimization


  • Owen Ferrone, Mechanical Engineering, University of Delaware

Faculty Mentor(s)

  • Tom Cender, Center for Composite Materials, University of Delaware


A thermoplastic matrix aligned discontinuous fiber (ADF) composite material is a specialized material form which becomes stretchable at high temperatures and solidifies upon cooling. ties of highly-aligned carbon fibers, the composite is able to stretch to form complex parts while maintaining properties equal to those of aerospace-use composites. The objective of this research is to show the relationship between the forming process conditions and the material properties (e.g. mechanical strength). In particular, this analysis seeks to determine the optimal temperature conditions for the stretch forming process.

To stretch samples under controlled conditions, an Instron Tensile Testing Machine was equipped with a 2 kN load cell and environmental chamber. All samples were single ply thick (0.12mm) and were cut to dimensions of 8in x 1in. Before testing, sandblasted aluminum end tabs were attached to each sample, which allow the grips to secure each sample. Tension was applied to each sample with a constant strain rate of 0.001 s-1 until each sample was strained to 100%, at temperatures between 280ºC and 350ºC. Once all tests were complete, the collected force and displacement data was converted to engineering stress and strain as well as true stress and strain.

To determine the best temperature for forming, the data was examined to determine the strain at which failure occurred. Four samples (280 ºC ,300ºC, 340ºC, and 350ºC), both high and low temperature, failed before the test was complete. One sample stretched at310ºC reached the target strain while exhibiting no observable failure. This result demonstrates that material formability is highly sensitive to temperature and that measuring the effect of process conditions on formed material performance (e.g. strength) is critical.