ASTM E8 Tensile Testing of Thin Aluminum Foil Specimens Using Video Extensometry

Sheet metal tensile testing applications require the use of an extensometer to comply with relevant ASTM and ISO testing standards accuracy requirements. In some cases, the thickness of the specimens may be too thin for use with a traditional clip-on extensometer. This is especially true when testing metal foils (< 0.020"), where the knife-edges place high stress concentrations on the specimen, as well as the mass of the extensometer hanging on the specimen, causing premature failure.

We have found that video extensometry is not frequently used in these applications, as most customers in the metals industry use traditional contacting extensometers and trust the reliability of the results. Developments in the technology of extensometry offer metals testing customers other options, such as our Advanced Video Extensometer 2 (AVE 2). Not only does this solution prevent premature specimen failure and reduce the maintenance required for wear and tear on knife-edges, it may also increase productivity and simplify testing. The purpose of this test is to demonstrate the accuracy and reliability of the Instron AVE for testing thin aluminum specimens.

For this test, we used our 5982 universal testing system with an AVE 2 with 200 mm Field of View (FOV) lens, a 10 kN load cell, and 5 kN pneumatic grips with serrated faces. We used a test speed of 3 mm/min until the 0.2% yield offset was reached and then changed the speed to 25 mm/min through the break. We captured the test results with our Bluehill® 3 materials testing software.

With this test configuration, we were able to successfully test all of the specimens in the sample, with failure occurring consistently in the gauge area. This test showed the repeatability and reliability of the AVE 2 for measuring strain. We would recommend it for future applications.