Finite element analysis of composite tubes with integral ends subjected to bending loads

Abstract

An analytical investigation was performed to study the effect of applied bending loads on laminated composite tubes. Elasticity-based linear models were developed using finite element software to predict stresses within the individual plies of the tubes. The tubes under investigation were graphite/epoxy laminated composites with a stacking sequence of [0/-45/+45/90/90/+45/ -45/0] X 2 (Sixteen plies per tube). End pieces of isotropic titanium were integrally constructed with bonded interface joints. The material properties of the cylinder plies were orthotropic in the fiber direction.

The analytical models were developed to simulate two concentric laminated composite cylinders with a gap of 0.158 in between them. In the first part of the analysis, the gap was left void to simulate a completely debonded condition between the cylinders and material that is sandwiched between them. The second part of the analysis incorporated isotropic tungsten material filling the gap along two-thirds of the length of the cylinders in a perfectly bonded condition. The final part of the analysiS included a local model incorporating a bond joint at the titanium/composite interface.

Under applied bending loads, the analytical models predicted the highest stresses would occur in the 90° (axial) plies, the lowest stresses would occur in the 0° (hoop) plies, and median stresses would occur in the ±45° plies. The stresses in the cylinders when in a debonded condition were much higher than when the cylinders were perfectly bonded to the tungsten filler material. Stress concentrations occurred at the titanium/composite interfaces as well as at the tungsten/honeycomb interface. In the current investigation, the orthotropic plies showed no danger of failing under the applied bending load. The local model produced similar results as in the two global analyses. However, high shear stresses were apparent along the bond line.