Comparison of Analytical Methods Calculating the Stress Distribution in a Pin-loaded Composite Plate with subsequent Strength Analysis

Abstract

Lightweight composite structures are often joined via mechanical fasteners in order to satisfy the requirement for dismountability. A disadvantage of such joint designs, however, is the introduction of notches which lead to stress concentrations in the vicinity of fasteners and consequently affect the joints’ strength. Therefore, having access to accurate estimations of the stress distribution in each ply is essential for the design of efficient joints. In the present thesis, several published analytical methods are examined and evaluated regarding their ability to accurately predict stresses on ply level in pin-loaded composites. For this purpose, reference solutions are derived from three-dimensional finite element models which are validated against experimental measurements obtained from pin-bearing tests using the digital image correlation method. Two monolithic CFRP laminates and two FMLs with different degrees of anisotropy are investigated. A comparison of stresses on ply level shows that merely two of the five investigated methods, namely those of Waszczak & Cruse and de Jong, yield accurate predictions of the stress distribution whereas the remaining ones fail to capture significant physical phenomena. A subsequent strength analysis based on the characteristic curve method and failure criteria of Yamada & Sun, Cuntze and von Mises demonstrates the potential of the aforementioned methods to accurately predict failure loads, reaching relative errors of roughly 15% compared to the experiment. In addition, satisfactory estimations of underlying failure modes are achieved based on the locations where initial failure is predicted.