Abstract

In this work the different failure mechanisms have been studied on 5HS woven composite laminates subjected to low velocity impacts. A large range of energies (5-75J) has been used to induce different failures: delamination, fiber failure, out-plane shear and perforation. In addition, different configurations of AGP 280-5HS woven coupons have been manufactured to analyze the influence of thickness ((0/90)4S, (0/90)6S and (0/90)8S) and ply sequence ((0/90)8S, (±45)8S, [(±45)/(0/90)]4S, [(±45)2/(0/90)2]2S, and [(±45)4/(0/90)4]S)). Laminates have been subjected to low velocity impact using an INSTRON-CEAST Fractovis 6875 drop weight tower according to ASTM standards (D7136). Each test has been recorded with two high speed video-cameras (Photron SA-Z 2100K) in order to analyze the plate behavior during the impact. In addition, a three dimensional high velocity digital image correlation (HV-DIC) analysis has been performed to measure the out of plane displacement. Once impacted, the damaged area of the composite laminates was evaluated by ultrasonic inspections. The analysis of the influence of the plate thickness and ply sequence have been made according to the Composite Structure Impact Performance Assessment Program (CSIPAP) proposed by Feraboli and Kedward using the peak force and the absorbed energy.

Abstract

Nowadays carbon fibre reinforced epoxy laminates represent the standard material in the designing and manufacturing of aeronautical composite structures. However, advantages related to metals manufacturing could represent an important menace for the role of composite materials in this industry. Therefore, new improvements in composite structures have to be seek in order to improve their competitiveness.

Graphene is a nanomaterial that possess the higher stiffness and strength ever measured. Therefore, the use of Graphene Related Material (GRM) for enhancing composite laminate materials could represent an important advance in order to reduce their impact vulnerability and to improve the performance of Resin Transfer Molding (RTM) composites.

  In this work epoxy resin doped with GRM were used to manufacture carbon fiber aeronautical composites by RTM. Low velocity impacts and Compression After Impact (CAI) tests were performed. Regarding experimental methodology, ASTM standard was followed, also new measuring techniques were used as 3D High Speed Digital Image Correlations. All tests were performed on GRM enhanced material and reference material to compare their results. Under impact loads, elastic behavior, peak force or damage results do not depend on the addition of graphenic particles. Whereas, a minor improvement enhanced with GRM in compression preserving the visible damage for an impact equivalent to the tool drop (30 J). Is important to keep this effect in order to detect damages in the composites structures.

Abstract

One of the mayor threats for FRP is the out-of-plane loading conditions such as impacts, which produce interlaminar failures, among others, decreasing drastically the material's strengths in plane. Drop weight and compression after impacts tests have been selected as the standard methodology to evaluate laminate performance under impact loadings. The present work aims to reveal the influence of the material structure in woven laminate response under impact. To this end a complete set of experiments was designed using the actual ASTM standards (D7136/D7137), including the actual monitoring capabilities to address this problem. Composite coupons, made of AGP 280-5H carbon/Epoxy satin, were manufactured using three laminate configurations to analyze the effect of ply clustering [(+-45)/(0/90)]4S, [(+-45)2/(0/90)2]2S, and [(+-45)4/(0/90)4]S).

Laminates have been subjected to low velocity impact using an INSTRON-CEAST Fractovis 6875 drop weight tower while compression test has been performed using a INSTRON 250 kN. Impact tests have been recorded with two high speed video-cameras (Photron SA-Z 2100K) configured at 20000 fps in order to analyze the plate behavior during the impact. In addition, a three dimensional high velocity digital image correlation (3D-HV-DIC) analysis has been done with the VIC-3D 7 system to measure the out of plane displacement and strains evolution. Also 3D-DIC analysis has been carried out for the CAI test to check the validity of the failure modes. It has been observed that the most clustered laminates increase the perforation threshold, while it decrease the residual strength of the material, due to damage spreading effect.