Impact of hole generation techniques on the mechanical strength of carbon/Onyx 3D printed composites

Additive manufacturing (AM), particularly in composite materials, has revolutionized the industries, offering design flexibility and enabling the creation of lightweight, high-strength components. In structural applications, joining composite parts often requires holes, which can be generated through various methods. This study investigates the effects of two hole generation techniques: conventional drilling and direct printing on the mechanical performance of additively manufactured Carbon fiber-reinforced polymer (CFRP) composites. Experimental tests, including tensile and three-point bending (3PB), were conducted and instrumented with Digital Image Correlation (DIC) and Acoustic Emission (AE). DIC was used to monitor strain localization, whereas AE was employed as a damage characterization tool to identify and compare the different failure mechanisms throughout the loading process. Finite Element Models (FEM) were developed to validate the experimental findings. Results showed slightly higher tensile stiffness and strength for the drilled-hole specimens. This difference was associated with variations in hole geometry, edge condition and local fiber architecture. Conversely, printed specimens showed higher displacement at failure, attributed to concentric rings around the holes. On the other hand, 3PB tests highlighted brittle failure in drilled specimens and progressive post-peak response with greater deformation before final failure in printed ones. FEM models showed good agreement with experimental data, validating their accuracy in predicting mechanical behavior and damage localization. This study highlights the critical influence of hole generation methods on the mechanical performance of AM composites and underscores the need for further optimization to enhance mechanical performance. Future research should focus on microstructural analysis, environmental testing, and sustainability assessments to advance AM applications in industry.