2

I've been trying to compare popular materials for bicycle frames in terms of their mechanical properties. One thing I noticed is that it's hardly possible to find a data sheet specifying the impact toughness of a material. I've only found it for some carbon-fibre composites and nothing else.

Why is impact toughness not a commonly listed material specification? Is it considered unimportant? Are the measurement and testing standards unclear? Are there any other reasons?

I'm specifically referring for aluminium 6061 and 7005, steel 4140 and 4130, Titanium 3Al-2.5V and some carbon fibre composites. I could find the data for carbon fibre, but none for any of the metal alloys.

Air
  • 3,211
  • 4
  • 26
  • 47
Slovakov
  • 171
  • 1
  • 1
  • 7

1 Answers1

1

The problem is that there is no absolute material property which generally describes material toughness in the same way that, for example, yield stress describes strength.

As mentioned in the comments charpy testing allows meaningful comparison between bulk materials but is less useful in terms of actual calculations of real world performance without so fairly thorough modelling based on the specific application.

A crucial issue is that toughness may be very dependant on specific geometries and indeed surface finish and is significantly affected by local stress raisers and strain rate. There is also a very big difference in whether the loading is distributed or acts at a point.

This inherent ambiguity in toughness as a general property is one of the reasons why cars are required to pass physical impact testing for safety certification but not for things like the strength of suspension parts.

Chris Johns
  • 15,326
  • 3
  • 24
  • 42