Design & fabrication of a custom shear test fixture

Clients often approach us with the need to conduct tests that are not well defined. In this example, a client had a higher-than-expected field-failure rate for a particular part supplied by an overseas vendor. The vendor claimed that the parts were within specification, and to prove this, they provided our client with a brief and cryptic test report. The tests conducted by the vendor were not covered by any standards and were designed in-house for the vendor's use.

We used our experience in custom testing to reverse-engineer the vendor's test apparatus and designed our own fixture to reproduce the tests. As with all of our testing, we produce CAD drawings of each part and assembly before we fabricate items. When compared to ad-hoc test setups, this helps us prevent unnecessary modifications and re-designs later.

In order to have the most control over test conditions and to insure traceability to NIST standards, we fabricate almost all of out test apparatus in-house. Our engineers are also skilled fabricators and can make almost any part in our laboratory. In this case, the test apparatus was machined to exacting tolerances by hand in a few days. The finished apparatus is shown in the picture below.

We also do our own transducer calibration and in this case we used custom made signal conditioning to acquire the test data. The results of a shear test using this apparatus is shown below.