Manufacturing controlled asymmetric wrinkles for experimental studies of the effect of defects

The strip placement method was used to manufacture nine carbon fibre reinforced epoxy laminates that were tested in bending to study the influence of asymmetric wrinkles on strength. Due to the accuracy of the process and material flow of the material during consolidation, the achieved wrinkles did not match the intended wrinkles in terms of maximum fibre angles or degree of asymmetry, highlighting the difficulty of creating controlled wrinkles in flat coupon specimens. Nevertheless, the experimental data showed decreasing ultimate bending strength with increasing maximum angle and increasing strength with increasing asymmetry. Therefore, for samples with the same maximum angle, the sample with higher wrinkle asymmetry had a higher ultimate bending failure strength, highlighting the importance of considering wrinkle asymmetry alongside the often-used maximum angle. Simulations of the as-designed coupons were also run to design the experiment. In terms of the relevance of asymmetry, both the numerical and experimental data are in line with previous numerical studies on asymmetric wrinkles under pure tension and compression. Contrasting the as-designed wrinkle morphologies to the manufactured wrinkles, it was found that overall, the study highlights the complexity and difficulty of creating controlled wrinkles within coupon specimens and provides evidence for the relevance of wrinkle shape asymmetry when characterising and simulating wrinkles across multiple load cases.