Additive Manufacturing of Carbon Fiber Reinforced Plastic Composites: The Effect of Fiber Content on Compressive Properties

The additive manufacturing (AM) of carbon fiber reinforced plastic (CFRP) composites continue to grow due to the attractive strength-to-weight and modulus-to-weight ratios afforded by the composites combined with the ease of processibility achievable through the AM technique. Short fiber design factors such as fiber content effects have been shown to play determinant roles in the mechanical performance of AM fabricated CFRP composites. However, this has only been investigated for tensile and flexural properties, with no investigations to date on compressive properties effects of fiber content. This study examined the axial and transverse compressive properties of AM fabricated CFRP composites by testing CF-ABS with fiber contents from 0%, 10%, 20%, and 30% for samples printed in the axial and transverse build orientations, and for axial tensile in comparison to the axial compression properties. The results were that increasing carbon fiber content for the short-fiber thermoplastic CFRP composites slightly reduced compressive strength and modulus. However, it increased ductility and toughness. The 20% carbon fiber content provided the overall content with the most decent compressive properties for the 0–30% content studied. The AM fabricated composite demonstrates a generally higher compressive property than tensile property because of the higher plastic deformation ability which characterizes compression loaded parts, which were observed from the different failure modes.

Improvement of Heating Uniformity by Limiting the Absorption of Hot Areas in Microwave Processing of CFRP Composites

Carbon fiber reinforced polymer (CFRP) composites are integral to today’s industries. Curing or consolidation are vital processes for manufacturing CFRP components. Microwave processing has many advantages compared with conventional processing technologies using ovens or autoclaves; however, the uneven temperature distribution caused by the non-uniform microwave field has a significant influence on the quality of the cured products. In this study, we propose a new idea to solve this problem, i.e., limiting the absorption of hot areas. Under such circumstances, cold ones can catch up with them more easily. To adjust the absorbing capability of the CFRP laminate, periodically arranged metallic resonance structures supported by a dielectric spacer are introduced on its surface. The dielectric spacer, made of epoxy matrix and strontium titanate particles, is designed to possess a dielectric constant positively related to temperatures. In this situation, the microwave absorption (2.45 GHz) of the metal-dielectric-CFRP configuration is changed from 97.6% at room temperature to 55.9% at 150 °C continuously. As a result, a reduction of 43.1% in maximum temperature difference and 89% in standard deviation has been achieved.

Effect of Crack Orientation on Laminated CFRP Composites Using Vibration and Numerical Analysis

Crack orientation, a critical parameter, significantly affects the dynamic properties of composite structures. Experimental free vibration tests were conducted on carbon fiber–reinforced polymer (CFRP) composite plates at room temperature with different crack orientations. Dynamic properties such as damping ratio, natural frequency, and storage modulus were measured using a four-channel dynamic pulse analyzer. Multi-sensors were mounted on the test plate to pick up the vibration signals. Experimental modal analysis was performed to identify the first three mode shapes of the defective plates. A numerical model using ANSYS software was developed via parametric investigation to predict the correlation between crack orientation and resonant frequencies with corresponding mode shapes. The orientation of the introduced cracks had a significant effect on the dynamic properties of CFRP composites. Vertical cracks had the most significant influence on the eigenvalues of the mode shape frequencies. Furthermore, the damping ratio was an effective method to detect the cracks in CFRP composites.