Mechanical response of carbon fiber/polyphenylene sulfide commingled fiber & polymethacrylimide foam core sandwich composites

Composite materials are desired for aerospace and other high-tech applications due to their impressive physical properties and resilience. Carbon fiber is used extensively in the aerospace industry in the form of prepreg materials for structural applications such as wing bodies, storage compartments, seats, and other areas. In order to aid in the light-weighting of aircraft, sandwich structures can be utilized. These sandwich structures often have a stiff face material surrounding a dense and light weight core material. The sandwich construction used in aerospace typically uses carbon or glass composite facing (skin) and foam, Nomex, or aluminum honeycomb core. The aim of this research is to combine two high performance constituents to create a sandwich composite capable of meeting performance criteria for aerospace conditions – high strength and high impact toughness under elevated temperatures. To create the sandwich structures, a face material was chosen to be a carbon fiber/polyphenylene sulfide (CF/PPS) commingled fiber composite panel with a closed cell polymethacrylimide (PMI) foam as the core material. The design of the sandwich structure of a ½ inch foam core with a 1.0-1.5 mm thick face of CF/PPS was chosen for this study. The CF/PPS panels were created through a filament winding process of the commingled fibers followed by a hot compression molding process to consolidate the fibers into a composite panel. The panels were then bonded to the PMI foam through the usage of an epoxy resin system from Huntsman through hot compression. Non-destructive testing was performed on a representative panel prior to testing to examine the bonding between the face and core materials. The sandwich was tested for Core Shear at room temperature (RT) and Static Indentation testing was performed at RT and an elevated temperature to examine the impact energy response. It was found that the sandwich absorbs twice the energy (11.3 vs 5.6 J) at room temperature when compared to testing at 100 °C.