Small Punch Testing

When we determine mechanical properties by doing testing, we need to make and test a lot of samples.  This means we need quite a bit of material to make samples from.  This can be a problem in certain situations such as when the material is difficult to produce, when the material is expensive, or, in a forensic investigation where material is limited.  Here at the ISM over the last couple of years we have been collaborating and developing the Small Punch Test.  This test takes a very small disc of material about the size of the end of a pen, and uses an indenter.  The rate at which it deforms tells us about the mechanical properties.

In a Small Punch Test we apply a force and a temperature to a very small amount of material.  Using less material is an advantage, but this test method introduces complexities.  When the indenter pushes through sample, unlike the other test types, we have both compressive and tensile forces in the material.  You can see this in the following animation.

This makes Small Punch Testing different to other methods as it measures a different stress state.  All being said, we can still get a lot of information about mechanical properties from Small Punch Testing.  One of those is how a material fails.  In a Small Punch Test the indenter pushes through the disc, and the shape of the hole made gives us insight into how the material failed.  Check out the animations below to see the shape of these holes.