Utveckling av en stötprovningsanordning och testmetod för utvärdering av fästelement under snabba skjuvförlopp

Abstract

This thesis aimed to develop a testing method to analyze fast shear deformations and to design an impact testing device to assess the shear strength of screws and bolts. The project was carried out in collaboration with and at the request of Bulten Fasteners AB (BFAB). The request arose from the increasing issues of shear failure of bolts, particularly in collisions with electric vehicles with heavy battery packs installed. The work was done in three phases: mapping of existing methods, preliminary screening tests and final design of the test rig. The first phase began with mapping of existing testing methods and standards, where Charpy impact testing and drop weight tests were reviewed. A rough test rig was then constructed for screening of critical factors such as weight, relevant testing ranges, screw grade and how large an impact would need to be to cause shear failure in a bolt. Tests showed that a drop height of approximately 100 cm was sufficient to shear bolts and screws of interest with a 10 kg weight. The results from the prototype phase formed the basis for the final design of the test rig, which includes an improved screw holder, adjustable drop height, and increased stability. The developed test rig is compact, detachable, and adapted for laboratory environments. To ensure reliable results, a testing method was developed based on the ASTM D2444-21 standard, tailored for shear tests of bolts. By having a legitimate testing method that follows a standard, it will be much easier to gain customer approval for using the product and accepting the test results. The testing method is easy to use and enhances the reproducibility of the measurement values. The project has provided valuable insights into engineering product development and the practical application of testing methods for fasteners.