Interlaminar fracture toughness of carbon fiber reinforced thermoplastic in-situ joints

Abstract

Abstract. Due to their ability to form fusion bonds, composites with thermoplastic matrix offer new opportunities to assemble complex structures with a multitude of single components. By combining the laser-assisted Thermoplastic Automated Fiber Placement process (TP-AFP) with the thermoforming technology, a time-efficient process chain for producing hollow skin-stiffener structures was developed. Removable core systems are inserted into the cavity of thermoformed omega profiles for subsequent TP-AFP processing of skin layers to the top of the flanges. This enables in-situ joining between the flanges of the thermoformed profile and the skin layers without the need for other joining technologies or supplementary bonding materials. Mode I interlaminar fracture toughness tests were conducted to evaluate the performance of this joining strategy. Partially fiber-placed and thermoformed test specimen were produced by the combined TP-AFP/thermoforming process transferring the developed joining strategy to coupon level. In addition, fiber-placed specimens were manufactured with and without additional processing in a press to act as a reference. The effects of different cooling rates during production of the test panels on the crystallinity were determined by Differential Scanning Calorimetry (DSC). The mode I interlaminar fracture toughness test results show that partially fiber-placed and thermoformed test specimen have a comparable level of resistance against delamination as entirely fiber-placed or thermoformed test specimen. The similar amount of crystallinity of these test panels, determined by an introduced crystallinity ratio (CR), correlates with the mode I interlaminar fracture toughness test results and indicates a low influence of the developed joining strategy on the crystallinity amount at the joint zone.

On the Dynamic Tensile Behaviour of Thermoplastic Composite Carbon/Polyamide 6.6 Using Split Hopkinson Pressure Bar

“…The mechanical characterization process of a material is critical in determining its reliability and mechanical performance, particularly under real-world applications under impact conditions, e.g., vehicle collision [ 3 , 4 ], bird strike [ 5 , 6 ], and sports impact [ 7 ]. Traditional standardized test procedures are typically performed under quasi-static conditions [ 8 , 9 , 10 , 11 , 12 , 13 ]. However, if a test specimen is ten millimeters long and is deformed at a loading rate of 1–100 m/s, the strain rate in the specimen is 10 2 –10 4 /s and conventional universal testing machines or load frames are not usually capable of achieving such loading rates.…”