Implementation of Through the Thickness Compressive Stress on the Retardation of Delamination Initiation in Ply-Drop Off Regions F. Ergin1,∗, A. Kayran1,2, 1 Department of Aerospace Engineering, Middle East Technical University,Ankara 06800, Turkey 2 RUZGEM, METU Center of Wind Energy, Ankara 06800, Turkey ∗ firat.ergin@metu.edu.tr Keywords: Delamination, USDFLD, cohesive zone method Ply termination regions, ply drop-offs, are inevitable parts of laminated composite structures used in the aerospace industry, and they are responsible for the early initiation of damage due to material discontinuities in the structure. Therefore, it is necessary to numerically predict the failure initiation in ply drop-off region and design the structure accordingly. However, built-in cohesive elements, used for delamination prediction, provided by the commercial finite element software do not take into account the enhancement of the Mode II fracture toughness and shear strength under compression, which is important in the prediction of delamination in the thick section of a ply drop off [1]. Some studies successfully considered the effects of compressive stress by developing custom cohesive elements [2,3]. However, development of custom cohesive elements can be time-consuming and impractical for simple applications. In this study, a practical implementation of the enhancement of Mode II fracture toughness and shear strength of the layer interface, due to the presence of through the thickness compressive stress, on built-in cohesive elements is presented. ABAQUS commercial finite element software is used for the simulations and user defined field variables (USDFLD) is utilized to incorporate the effect of compressive stress on the behavior of the built-in cohesive elements. Verification studies showed that USDFLD can match the performance of the custom cohesive elements used in the literature. A parametric study of a drop-off model, in which the taper angle is considered as the only variable, showed that thick section delamination initiation load increases as the taper angle increases when the enhancement of the interface properties is considered. References [1] Zhang, B., Kawashita, L. F., Jones, M. I., Lander, J. K., and Hallett, S. R., 2020, “An Experimental and Numerical Investigation into Damage Mechanisms in Tapered Laminates under Tensile Loading,” Composites Part A: Applied Science and Manufacturing, 133, p. 105862. [2] Li, X., Hallett, S. R., and Wisnom, M. R., 2008, “Predicting the Effect of Through-Thickness Compressive Stress on Delamination Using Interface Elements,” Composites Part A: Applied Science and Manufacturing, 39(2), pp. 218–230. [3] Zou, Z., and Lee, H., 2017, “A Cohesive Zone Model Taking Account of the Effect of Through-Thickness Compression,” Composites Part A: Applied Science and Manufacturing, 98, pp. 90–98. 68
RkJQdWJsaXNoZXIy MjM0NDE=