Assessment of failure and cohesive zone length in co-consolidated hybrid C/PEKK butt joint

Abstract

The failure mechanisms and the cohesive zone length (CZL) during fracture of recently developed butt jointed thermoplastic composite are evaluated in this paper. The laminated skin and the web were made of AS4/PEKK. The butt joint (filler) was injection molded from 20 % short AS4 filled PEKK. The skin and web were co-consolidated together with the filler to form a hybrid butt joint structure. The crack initiation and propagation in the filler and the delamination at the skin-filler interface were captured using a high-speed camera. It was found from the experimental observations that the crack initiated in the filler and then propagated towards the skin-filler interface in less than 33 µs under three-point bending. A numerical model was developed using the finite element method in ABAQUS to predict the failure and CZL. The crack initiation and progression in the filler was predicted using the Virtual Crack Closure Techniques (VCCT) and the delamination at the skin-filler interface was modelled using the cohesive surfaces. The predicted stiffness of the specimen, the location of crack initiation and propagation as well as the force drop during delamination were in good agreement with experiments. The development of CZL was critically assessed and it was found that the CZL increases during delamination. The effect of interface strength and critical energy release rate on the CZL was investigated in the parameter analysis.

Estimation of cohesive zone model parameters for glass/Elium composites with different processing temperature

“…Tables 2 and 3 display three pairs of cohesive parameters (interface stiffness and strength) that correlate to a tested fracture energy release rate. The estimated interface stiffness and strength of RT, 50°C, and 80°C laminates were in the range of 10 5 -10 6 MPa/mm and 30-100 MPa, 8,[14][15][16][17][22][23][24][25][26] respectively.…”

“…These values are typically obtained through trial and error method. 8,[14][15][16][17][22][23][24][25][26] It was discovered that all research appeared to concur on interface stiffness between about 10 4 and 10 6 N/mm 3 . Therefore, a trial and error approach was also used in the current work to get adequate values of the interface stiffness and interface strength.…”

Experimental Investigation of the Interlaminar Failure of Glass/Elium® Thermoplastic Composites Manufactured With Different Processing Temperatures

“…Although there have been several studies carried out to quantify the mechanical properties and performance, a critical assessment of the effect of processing temperature on the interlaminar failure behavior of FRECs needs to be addressed to develop future's high damage tolerant FRECs. The manufacturing process has a direct influence on the material properties of the final product such as fracture toughness, degree of cure, degree of crystallinity, elastic modulus and strength [28][29][30]. The mechanical properties of Elium ® resins are also directly influenced by the processing temperature and initiator percentage, which affect the final degree of the polymerization as studied in [31,32].…”

Enhanced Interfacial Properties of High-Modulus Carbon Fiber Reinforced PEKK Composites by a Two-Step Surface Treatment: Electrochemical Oxidation Followed by Thermoplastic Sizing

“…Previous published works on CF/PEKK composites also mainly focus on reinforcing CFs with standard tensile modulus around 230 GPa, such as Hexcel AS4 CFs [35][36][37][38]. In the present work, high strength and high modulus CFs (HSHM-CFs) with the tensile strength and the tensile modulus around 5.0 GPa and 310 GPa, respectively, were prepared through a continuous production line and taken as the reinforcing fibers of PEKK matrix composites.…”