Voids, the most studied type of manufacturing defects, form very often in processing of fiber-reinforced composites. Due to their considerable influence on physical and thermomechanical properties ...

https://journals.sagepub.com/doi/pdf/10.1177/0021998318772152

Voids in fiber-reinforced polymer composites: A review on their formation, characteristics, and effects on mechanical performance:

3D printed continuous CF/PA6 composites: Effect of microscopic voids on mechanical performance

Several consolidation cycles were performed to study the impact of processing parameters on void content, ultrasonic NDT and mechanical performance of CF/PEEK composites. A series of [+45/−45]4S laminates were manufactured by out-of-autoclave technologies including vacuum bag only, hot-press, and automatic lay-up with in-situ consolidation. A range of porosity between 0 and 19% of void content was assessed by varying the processing temperature from 340 to 500 °C and pressure from 0.25 to 1.5 MPa. Void content, shape and location were characterized by using C-scan, matrix digestion and 2D microscopy. Mechanical characterization including in-plane shear and interlaminar shear testing was performed. The results show a critical void content where properties start to decrease at a given drop-off rate. The results suggest that each processing technology should have its own quality control criteria. The proposed methodology is useful for engineering applications of thermoplastic composites and the creation of NDT acceptance criteria.

Effect of processing parameters and void content on mechanical properties and NDI of thermoplastic composites

The ability of a modern near infra-red laser tape placement system to produce high-quality laminates is investigated by performing short beam strength tests on samples manufactured at different process temperatures from 400 °C to 600 °C at placement rates of 100 mm/s and 400 mm/s. The temperature history in tape placement is highly dynamic and the correlation between the process control temperature, laser power and the consolidation temperature is not well understood. The complete temperature history was therefore estimated with a previously developed optical-thermal model and validated using long wave infra-red imaging. Short beam strengths equivalent to conventional manufacturing methods were found for placement rates of 400 mm/s. Failure modes of the samples were elucidated by scanning electron microscopy of the fracture surfaces. Signs of degradation were observed on samples prepared with a 600 °C process temperature at 100 mm/s, however none was evidenced at 400 mm/s for the same process temperature.

The effect of processing temperature and placement rate on the short beam strength of carbon fibre-PEEK manufactured using a laser tape placement process

Fiber-reinforced composite materials are replacing metallic components due to their higher specific strength and stiffness. Automation and thermoplastics emerged to overcome the time and labor inte...

Processing of thermoplastic matrix composites through automated fiber placement and tape laying methods: A review

Obtaining autoclave-level mechanical properties using in-situ consolidation of thermoplastic composites by Automated Tape Placement (ATP) is challenging. However, relatively recent availability of high quality ATP grade pre-preg material and tape heads equipped with more efficient heat sources (e.g. lasers) offers an opportunity to achieve improved mechanical properties and deposition rates. In the present study, carbon fibre–PEEK laminates, manufactured by laser-assisted ATP (LATP) and autoclave, are compared. Analysis of the through-thickness temperature distribution during LATP processing using thermocouples indicates that LATP cooling rates are extremely rapid and suggests full through-thickness melting of the pre-preg tape may not occur. Inadequate crystallinity, in conjunction with voids, compromised mechanical properties compared to autoclaved laminates but was beneficial in terms of the toughness of LATP laminates. Optimisation of pre-preg properties and processing parameters is required to realise the full potential of the LATP process in terms of mechanical properties, energy requirements, cost and deposition rates.

Mechanical characterisation of carbon fibre–PEEK manufactured by laser-assisted automated-tape-placement and autoclave

Mechanical characterisation of carbon fibre–PEEK manufactured by laser-assisted automated-tape-placement and autoclave Part A Applied science and manufacturing

I. Rosca

Papers

Mechanical characterisation of carbon fibre–PEEK manufactured by laser-assisted automated-tape-placement and autoclave

Mechanical characterisation of carbon fibre–PEEK manufactured by laser-assisted automated-tape-placement and autoclave Part A Applied science and manufacturing

Hydrothermal in-plane-shear strength of carbon fibre/benzoxazine laminates manufactured out-of-autoclave by liquid-resin-infusion