Towards best practice in numerical simulation of blind rivet nut installation

Abstract

The present paper derives best practices to accurately simulate the installation process of a Blind Rivet Nut (BRN) using FEA. A BRN is a mechanical fastener used to equip plate material with a threaded part. The installation of a BRN inherently induces a high contact force which can have detrimental consequences when applied to non-metals such as polymer composite materials. The effects of the localized stress in the plate on the mechanical performance of the BRN can be studied with the aid of finite element simulations. To this end, the joining by forming process itself is accurately simulated using a computational efficient axisymmetric 2D model. The 2D model enables to predict the metal flow and internal state of stress after setting with sufficient accuracy. The latter is validated using a full 3D model and a multitude of experimental observations. It is shown that the large strain flow curve of the BRN material needs to be adequately identified. An industrially relevant calibration procedure is presented mitigating the experimental effort. In addition, material test selection in case of highly anisotropic BRN materials is discussed based on a thorough stress state analysis. Finally, the sensitivity of the BRN geometry to a change in the most relevant geometrical parameters is demonstrated. The presented experimental methods and numerical models provide fundamental insights in the forming mechanism including process-induced ductile damage while installing the BRN. The latter will foster the development of new BRN applications in multi-material mechanical design.