RELIABILITY ANALYSIS IN BOLTED COMPOSITE JOINTS WITH SHIMMING MATERIAL

摘要

The aim of this paper is to discuss and define methodologies for reliability analysis of bolted joint elements in composite structures. The performance of a composite bolted joint is affected by uncertainties associated with loads, shimming material and its thickness, bolt hole clearance as well as laminate material and thickness. These uncertainties have traditionally been accounted by the use of safety factors. The safety factors in most designs have a probabilistic basis to ensure that various uncertainties are properly accounted for. However, in cases where they are not covered by the design principle, these safety factors may not be enough and a probabilistic design methodology is required. The development of numerical method based on probabilistic approach to tackle this kind of problem is a very difficult task. The objectives of this work are to demonstrate methods and codes that simulate the progressive damage in composite bolted joints with shimming material and probabilistically evaluate the effect of design variable uncertainties on structural failure. The methodologies and corresponding computer codes are used to determine the uncertainty in the damage load on bolt joints with shimming material. Finite element analysis (FEA) is used for the determination of contact stresses in the contact region around the bolt hole of a single lap joint. In particular, degradation of the structural behaviour will be quantified by using a FE method in which the damaged plies are identified. The present method is based on a point and average stress criteria for predicting failure stress and failure modes. Both of these criteria predict net-section, shear-out and bearing failures when the stress components at specific locations reach their corresponding unnotched strength level. The FEA is carried out using ABAQUS, a commercial available FE program. Furthermore, a probabilistic failure method is used to simulate progressive fracture and the statistical scatter response of the bolted composite joint. In addition probabilistic sensitivity factors are computed to identify parameters that have significant influence on a structural reliability. The design can therefore be improved by controlling distribution parameters associated with the scatter of various variables. This can be implemented during the manufacturing process to obtain maximum benefit with minimum modification.