Utveckling av en stötprovningsanordning och testmetod för utvärdering av fästelement under snabba skjuvförlopp
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Examensarbete på grundnivå
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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.
Beskrivning
Ämne/nyckelord
shear strength, design, impact testing, test method, bolts, screws, material durability