Modeling and Interpretation of Fiber Orientation-Based Failure Mechanisms in Machining of Carbon Fiber-Reinforced Composites

Fiber-reinforced polymer composites have recently emerged as novel materials capable of playing a unique role in industrial applications. The advantage of these materials over traditional metals or polymers comes from the material property enhancements that can be achieved by combining appropriate fiber and matrix materials into the microstructure. While these materials have recently become popularized, many complications arise in the manufacturing process of the two-phase microstructures, specifically in the machining of FRP composites. Due to the complex nature of FRP two-phase microstructures, the fiber failure mechanisms occurring in the machining process are not fully understood. Many experimental and modeling techniques have been implemented to more fully explain the nature of the fiber failure mechanisms in the machining process, but these have fallen short of a complete understanding of the machining complexities. This research seeks to gain a fundamental understanding of the fiber orientation-based fiber failure mechanisms occurring in the micro-machining of FRP composites by employing two unique modeling techniques. In this research, both experimental and finite element-based modeling approaches are undertaken. Fibers oriented in 0, 45, 90, and 135 degrees with respect to the direction of tool motion are investigated and unique failure theories are developed for each of these orientations. The model based on experimental observations is focused on explaining the micro-scale failure mechanisms occurring in the machining process. The finite element machining model developed in this work uses a unique modeling approach, which is capable of explaining the fiber failure mechanisms occurring throughout the chip formation process. After development of the two machining models, the machining responses are compared to a set of machining experiments for validation purposes. ii Fibers orientated in the 45 and 90 degree orientations were found to fail in compressive crushing-dominated failure while fibers oriented in the 135 degree orientation were found to fail in bending below the surface of the cut. In the 0 degree orientation, the fibers were proposed to fail in buckling or bending-dominated failure, depending on the depth of cut, and tool geometry of the process. The micro-scale fiber failure mechanisms were observed to differ significantly from their macro-scale counterparts. The machining responses of the two models were found to agree well with the experimental validation analyses indicating that these models are an accurate representation of the chip formation process