# What is the effect of lateral friction on the specimen shape

During compression test lateral friction occurs on the lower and upper surfaces of the specimen how does this affect the final shape of it and how do we reduce this effect?

## 1 Answer

The effect should be minimal in most "engineering" materials (high stiffness). It will be more significant when the ratio $$\frac{E}{\mu}$$ becomes smaller.

The effect in itself will be that you will have a specimen with a smaller radius of curvature closer to the grips.

Normally you don't need to do anything about it (I've never had to or heard someone needed to). Having said that, on way you can minimise it, is that you could use a low friction surface (a teflon sheet between the specimen and the fixture). The problem is that you'd probably need to redesign the fixture, and also there might be limitation if the aspect ratio of the specimen is high (the shorter and wider the specimens the better)