Study of Behaviour of Bolted Joint in Sandwich Panels

Bolted joints are widely used in various kinds of aerospace and spacecraft structures. Accurate estimation of bolt forces is the prime requirement for the design and verification of joints when they are subjected to external loads. Usually, the bolts and joining components (flanges) are made of different materials having different mechanical properties like modulus, strength, surface finish qualities (friction coefficient), thermal co-efficient of expansions etc. Hence the integrity of the joint has to be maintained for thermal and external loads acting of the connecting elements and bolts. The change in the bolt force is a function of the stiffness of joining materials and type of the joint. In literature empirical equations are available for the analysis of bolted joints, but the methods are limited to the analysis of joints where flanges are clamped using a bolt and a nut. In case of spacecraft structure, the different sub-assemblies are connected to main structure using bolt and potted insert configuration. In this paper the behavior of such type of joints in the sandwich panels structures are studied.

Commonly used empirical formulae are used to analyze typical bolted joint in sandwich panels and finite element analysis were carried out to understand behaviour of the joint in detail. An Axisymmetric model using 2D solid elements is generated for bolted joints with different types of inserts to understand the bolt load variations due to temperature. The behavior of such joints due to external loads is also studied using the 3D finite element models. Variation in the bolt forces of different configurations are estimated using the formulae and FE analysis are discussed in this paper.