About calculations of composite plate tensile failure in cross-section with bolt hole of single-shear bolted joint

Abstract

Background. Bolted joints (BJ) are the main type of detachable connection. When designing the BJ with plates of layered composite material, there is a problem of calculating the BJ strength, in particular, the cross-sections weakened by the bolt hole. It is due to the complex nature of the interaction of the layers of the composite plate with each other and also with bolts, as well as the presence of a number of structural and technological parameters of the connection.Objective. The main task of this research is to find the functions of influence of the magnitude of the bolt / hole gap, also structure and secondary bending of the bolt and plate on the value of the generalized stress concentration coefficient (SCC) in the cross-sections with bolt hole of the layered carbon fiber reinforced plastic (CFRP) plate using the results of BJ numerical simulation.Methods. It was used a method of finite-elements and the 3D contact model as much as possible approached to real geometry and conditions of load application. Earlier, the authors created 24 3D models of samples of single-shear two-row bolted joint with CFRP (contact task), in which the structures of CFRP (6 variants) varied, as well as the bolt / hole gap (4 values). The magnitudes of bolt tightening force and the force that stretched the sample were unchanged. Based on the results of calculations, stress distributions were determined and values of SCC in CFRP plates in the bolt holes (tables, graphs) were obtained.Results. Based on these results and additional calculations, the following conclusions were reached:in the static calculation of composite plate tensile failure in cross-section with hole of single-shear bolted joint the upper value estimate of the theoretical SCC in the pin-loaded hole in the plate of orthotropic material can be obtained in accordance with the formula arising from the solution of EHS (Echavarrı’a, C., Haller, P. and Salenikovich, A).in order to obtain a generalized SCC , which additionally takes into account a number of factors of BJ with CFRP, the upper value estimate of the theoretical SCC must be multiplied by next factors:function of influence of the bolt / hole gap, structure and the secondary bending of the CFRP plate; - taking into account the interplay of CFRP layers. For the considered BJ with CFRP an evaluation was obtained ;Conclusions. There is an easy-to-use formula for the upper estimation of SCC in a pin-loaded bolt-hole in an orthotropic material plate. The functions of influence of the bolt / hole gap, structure, and bending of the CFRP plate at first approximation are linear. The refined value of the correction factor, which takes into account the interplay of the layers of the CFRP, should be obtained in additional experiments (physical or numerical).