Experimental study on the effects of temperature on mechanical properties of 3D printed continuous carbon fiber reinforced polymer (C-CFRP) composites

Design for safety of 3D printed continuous carbon fiber reinforced polymer (CCFRP) composites remains challenging for accommodating harsh service environments with a wide range of temperatures. To investigate thermal effects on mechanical properties and failure mechanism of CCFRP materials, this study carried out a series of experimental tests on the laminates with layups of [0](n), [90](n) and [0/90](n) for tension, as well as [+/- 45](n) for in-plane shearing. The application of classical laminate theory and rule of mixtures to the 3D printed CCFRP composites under varying temperatures is then evaluated. The results indicate that the transverse elastic modulus/strength and in-plane shear modulus/strength increase at a low temperature, but all the mechanical properties decrease at a high temperature. Notably, an unexpected decrease in strength of [0/90](n) laminates is observed when the temperature drops from -10 degrees C to -40 degrees C. Significant strain concentrations are visualized during tensile experiments at high temperature through the digital image correlation (DIC) technique. With increasing temperature, the [0](n) laminates undergo a transition from an explosive to a jagged failure mode, while the [90](n) laminates shift from brittle to ductile failure. The alteration is attributed to decrease in the mechanical properties of both the matrix and the matrix fiber interface, as revealed by scanning electron microscopy (SEM) analysis. It is found that although the classical laminate theory exhibits an acceptable prediction accuracy for the 3D printed CCFRP composites under varying temperature conditions, the rule of mixtures is not applicable. For this reason, the new formulations for the rule of mixtures are then proposed to enable accurate predictions for 3D printed CCFRP composites under different temperatures. This study is anticipated to provide insightful understanding on mechanical properties and failure mechanisms for 3D printed CCFRP composites at different temperatures.