Effect of drilling induced defects on the mechanical properties of carbon fiber-reinforced thermoplastic polyamide
The files represent the result for the flexural and tensile tests. The initial state as well as two different drill hole qualities were examined. The quasi-static experiments of the undrilled / drilled specimens were carried out on an universal testing machine. The 5.9 mm diameter holes were made in the center of gravity. Ultimate tensile (UTS), open-hole tensile (OHT) and ultimate flexural (UFS), open-hole flexural (OHF) strengths and the load progression were determined for at least five individual test specimens. The test set-up for the 4-point flexural tests were adapted from ISO 14125. The corresponding set-up for the tensile tests was in accordance to ISO 527-4. Both test set-ups are describe in detail in the manuscript. A first key finding is that the drill hole quality has neither a critical influence onto the fiber dominated strength under tensile load nor onto the matrix dominated flexural strength. Both drill hole qualities led to about the same decrease of the particular strength value in comparison with the undrilled specimens. Therefore one can say, that the borehole itself is by far the most strength limiting factor, whereas the machining quality seems to be minor relevant for the strength behavior in drilled thermoplastic CFRP laminates under static loading. A second key finding is that the detected strength degradation induced by a 5.9 mm borehole was significantly higher under 4-point flexural loading (14%) compared to the 8 % under tensile loading. This shows, that tests under 4-point flexural load have a greater influence on the mechanical properties of drilled CFRTP than under tensile load.