Numerical prediction of the stress state in CFRP induced by installing a blind rivet nut

Abstract

The present paper offers a FE modeling strategy to predict the stress state in carbon fiber reinforced plastic (CFRP) plate material after installing a Blind Rivet Nut (BRN). In industry, a BRN is a permanent mechanical fastener used to equip plate material with a threaded part. Analogue to the installing process of the more common blind rivet, the BRN deforms plastically in such a way a counter head is formed on the underside of the plate. Simultaneously, the upper side of the deformation chamber expands in the radial direction creating an interference fit. The interference fit together with the counter head units the nut to the plate. However, the high contact forces between the BRN and the plate often cause damage in the CFRP material compromising the integrity of the joint. The latter observation implies that while setting a BRN in CFRP, the detrimental contact forces must be controlled to guarantee a qualitative joint. The necessary understanding of the stress distribution in the plate material is numerically investigated in two steps. In the first step, a computational efficient axisymmetric model is used to reveal the contract pressure between the BRN and the plate during the setting process. In the second step, the contact pressures are transferred to a 3D model of the plate. In this stage, the orthotropic properties of the composite are assigned to the plate material and an adequate failure criterion is adopted. The result is compared to a full 3D model using the Tsai – Wu failure criterion.