Determination of influence factores and stress concentration factor for express strength calculations of single-cut bolted connections of layered composite plates. Message 2

When designing bolted joints (BJ), it is necessary, in particular, to carry out their verification calculations for strength. In this case, it is desirable to use express analysis: calculations using simple formulas of sufficient accuracy. For BJ plates made of layered polymer composite materials (PCM), the problem has not yet been solved. In particular, a formula for determining the maximum stress near the hole for reinforcement schemes of the type [0/φ/-φ/90]s and [φ/-φ]s has not been found, at 0<φ<90 (for all other schemes there are already five formulas, as discussed in Message 1). The aim of the work was to obtain information on the distribution of maximum stresses for reinforcement schemes of the type [0/φ/-φ/90]s and [φ/-φ]s at variable values ​​of the reinforcement angle 0<φ<90, based on the results of calculations using the finite element method (FEM). Model numerical calculations were performed using the FEM (contact problem) for the interaction of a layered PCM plate with a rigid "bolt" (pin). 3D orthotropy of each layer, linear elasticity, absence of friction and lateral clearance "bolt"/hole were assumed. The results are summarized in the tables, illustrations are given. The results were analyzed. It is proposed to introduce two more factors of influence on the value of the maximum tensile stress near the hole in the layered PCM plate. An analytical formula for calculating the stress concentration coefficient for a plate section weakened by a hole with a reinforcement scheme of the type [φ/-φ]s , 0<φ<90 could not be found. Additional research is required.