The quantitative analysis of tensile strength of additively manufactured continuous carbon fiber reinforced polylactic acid (PLA)

Purpose: Continuous fiber-reinforced thermoplastic composites are being widely used in industry, but the fundamental understanding of their properties is still limited. The purpose of this paper is to quantitatively study the effects of carbon fiber content on the tensile strength of continuous carbon fiber-reinforced polylactic acid (CCFRPLA) fabricated through additive manufacturing using the fused deposition modeling (FDM) process. Design/methodology/approach: The strength of these materials is highly dependent on the interface that forms between the continuous fiber and the plastic. A cohesive zone model is proposed as a theoretical means to understand the effect of carbon fiber on the tensile strength properties of CCFRPLA. The interface formation mechanism is explored, and the single fiber pulling-out experiment is implemented to investigate the interface properties of CCFRPLA. The fracture mechanism is also explored by using the cohesive zone model. Findings: The interface between carbon fiber and PLA plays the main role in transferring external load to other fibers within CCFRPLA. The proposed model established in this paper quantitatively reveals the effects of continuous carbon fiber on the mechanical properties of CCFRPLA. The experimental results using additively manufacturing CCFRPLA provide validation and explanation of the observations based on the quantitative model that is established based on the micro-interface mechanics. Research limitations/implications: The predict model is established imagining that all the fibers and PLA form a perfect interface. While in a practical situation, only the peripheral carbon fibers of the carbon fiber bundle can fully infiltrate with PLA and form a transmission interface. These internal fibers that cannot contract with PLA fully, because of the limit space of the nozzle, will not form an effective interface. Originality/value: This paper theoretically reveals the fracture mechanism of CCFRPLA and provides a prediction model to estimate the tensile strength of CCFRPLA with different carbon fiber contents.