Experimental assessment of delamination extension on carbon / epoxy drilled plates

Abstract

In the last decades, composite materials have been getting predominance, due to their peculiar characteristics, making their application attractive in the most diverse areas. One of the most used machining processes is drilling. This process allows for the use of mechanical connections to join parts in non-permanent connections, unlike the adhesive joints which are permanent connections.Thus, there is a need for a broad assessment of the damage caused by the drilling to the material. This work presents a study on how the machining parameters affect the delamination extension by drilling a set of carbon fiber reinforced polymer plates. Enhanced radiography and image analysis techniques are utilized and, in the end, a correlation between these results and the mechanical characteristics of the machined plates is obtained. Different drilling parameters are used, namely two feed rates while keeping the spindle speed constant, and three different drill geometries (Step, Brad and Helical). The thrust force is monitored during drilling and after drilling, parts are non-destructively and destructively (bearing, pin-bearing) tested. The results show that, although the thrust force varies and the delamination extension is affected by machining parameters, the mechanical resistance obtained in the tests did not evidence significant variations. The results show that, although the thrust force, varying around 50% in average, and the delamination extension, with a variation of 8%, are affected by machining parameters, the mechanical resistance obtained in the tests did not evidence significant variations, with an average difference of 2%. The main outcome of this work is to demonstrate that existing bearing tests may not the most suitable ones to assess mechanical consequences of drilling damage extension.