Variability in the Failure of Composite Tubes Subjected to Combined Axial and Torsional Loadings Due to Manufacturing Defects and Nondeterministic Material Properties

Abstract

Tubes made with polymer-matrix fiber-reinforced composite materials are widely used in automobile, mechanical and aerospace engineering applications. Composite tubes are increasingly manufactured using the modern Automated Fiber Placement (AFP) technique. The ply manufacturing parameters and the tube manufacturing parameters have considerable influence on the quality of the manufactured composite tubes. Manufacturing defects and variations in the material properties are inevitable in composite tubes due to the inherent unavoidable variations in these parameters. The commonly identified manufacturing defects include voids, fiber waviness, variation in volume fraction, and fiber misalignment. These have considerable influence on the mechanical behavior and failure of the composite tube. In the present work, the effects of the fiber misalignment and the variations in the material properties on the failure behavior of uniform-diameter composite tubes subjected to combined axial and torsional loadings are determined considering the First-Ply Failure (FPF) characteristics. The first-ply failure envelopes of the composite tube are developed based on the Classical Laminate Theory and Finite Element Modeling and Analysis. Existing works in the literature are used to validate the three-dimensional finite element model of the uniform-diameter composite tube developed using the commercial software ANSYS®. The variations in the first-ply failure loading limits of the uniform-diameter composite tube made of a Carbon Fiber Reinforced Polymer (CFRP) composite material are investigated using the Monte Carlo Simulation (MCS) method, considering the random variability in the material properties and the fiber misalignment. The random variables corresponding to the material properties and the fiber misalignment are generated. For the composite tube with a sample set of simulated random variables the corresponding first-ply failure envelope is determined. The ensemble of such failure envelopes is developed based on an adequate number of simulations from which the probabilistic distributions of the first-ply failure loadings are determined. Design aspects are brought out.