Analytical and Numerical Study of The Plate Twist Test in Composite Laminates and Sandwich Panels

Abstract

An analytical and numerical research work related to the plate twist test of specially orthotropic plates is developed in this thesis. Two finite element models and two analytical closed-form solutions are developed for deflections and rotations of thick specially orthotropic materials under twisting loads by using the first-order shear deformation theory. These solutions show good agreement in the compliance predictions with respect to previously reported measurements and finite element estimations. The first solution considers the effect solely of the stiffness D66 and A44, A55 in the compliance, assuming shear correction factors of 2/3 and a twisting moment Mxy = P/4 The second solution not only considers the influence of D66 and A44, A55 on the compliance but alsothat by D11, D12, D22 stiffnesses, varying the shear correction factors and Mxy according to the material system and geometry. The results of the parametrical analys is show that both solutions are able to adequately predict the deflections of specially orthotropic plates from low to moderately high side-length to thickness ratios (1 ≤ side-lengths/thickness ≤ 20and(1 ≤ side-lengths/thickness ≤ 61), respectively; also both solutions can be used for rectangular plates with ratios between sides-length (1 ≤side-length in X axis/side-length in Y axis ≤ 10).Examination of the in-plane shear modulus ratio between face sheets and core (G12f / G12c) points out that the first solutions lightly underpredicts the compliance with respect to finite element method (FEM), specially for G12f / G12c ratios larger than 100,whilstthe second solution match very well for those ratios. Examination of the Mxy by finite element method showed that Mxy has a parabolic behavior for sandwich panels with compliant cores, reaching a maximum value at the center of the plate different to P/4 and being dependent of the material properties.