题目：Damage development in composites due to machining processes and their impact on structural integrity
Machinability of composites remains an open problem due to the existing heterogeneity and anisotropy resulting in poor machining quality. In particular, trimming or drilling defects make machined surface characterization complex which in turn makes attainment of dimensional tolerance requirements difficult. In industry, the parameter used for qualifying the machined surface is the arithmetic average roughness (Ra) or equivalent. It is important to note that Ra was initially proposed to qualify the machined surfaces of metallic materials. However, the use of Ra for composite machined surface qualification is rife with controversy.
The main focus of this presentation is to investigate the defects generated by trimming and drilling using both traditional (cutting tool) and non-traditional (abrasive water jet machining ‘AWJM’, abrasive diamond cutter ‘ADS’) techniques. In addition, the impact of these machining defects on the mechanical behavior of CFRPs in quasi-static (compression and inter-laminar shear) and tensile-tensile fatigue tests have been investigated and correlated to the surface quality measurements (i.e., Ra). Both contact and non-contact surface characterization techniques have been used to qualify the machined surface. In addition, SEM observations have also been conducted.
The results show that the defects generated during trimming and drilling processes with a cutting tool are fiber pull-out and resin degradation. These defects are mainly located in the layers with the fibers oriented at -45 ° and 90°. However, when using AWJM and ADS, the defects generated have the form of streaks (and craters) and are not dependent on the fiber orientation. Furthermore, the results of quasi-static tests performed on all machined specimens (with the same Ra) show that AWJM specimens offer a better resistance in compression and the ADS machined specimens offer higher inter-laminar shear strengths. Moreover, the results of fatigue tests show that specimens machined with a cutting tool offer higher endurance limit as compared to the ADS process. Finally, it is concluded that for the characterization of the machined surface it is important to take into account the mode of machining process as well as the nature of loading that the structure is subjected to.