When selecting a material for a particular project one source of information on material suitability is the material datasheet.

You would think that this would provide all the information you require and make comparisons between different materials relatively simple and straightforward.  However, you would be wrong!  Firstly, the data against different performance criteria, such as impact strength, is fairly meaningless in itself.  This is because the test is carried out on a predefined piece of material which bears little resemblance to any part that may be moulded.  Secondly, the test itself may not represent the loads and stresses likely to be experienced by the part that is to be moulded.

So, the first point is that material datasheets are of only limited use on their own.  The main purpose is therefore to compare different materials and different grades in order to select the one that provides the best range of properties to suit the application.  At this point it is worth emphasising the need to be aware of relative costs and making selection on what is fit for purpose rather than over-engineering by selecting a material with outstanding properties that may then prove to be too costly.

Again, though, there are drawbacks with using datasheets for comparison purposes.  Some material suppliers provide more information than others on their datasheets and the particular performance criteria you are interested in may not be included.  The final problem is that there is not a uniform testing standard.  There are two main testing methods in use and they are not directly comparable.  Add in the further complication that the units of measure specified on the datasheet may also be different and it becomes a minefield.

For your information, the most common test standards are:

ASTM – American Society for Testing and Materials

ASTM logo

ISO – International Standard Organisation

ISO logo

DIN – Deutsche Institut fur Normung

DIN logo

BSI – British Standards Institute

BSI logo

UL – Underwriters’ Laboratory (American)

UL logo

The first two are the most common in use on material datasheets.  The Underwriters’ Laboratory (UL) appears on tests for flammability.  Why is there no universal standard now being employed?  Simply because material manufacturers are unable to agree which standard should be used and if one was selected there would be enormous cost for the manufacturers of materials that had used the test methods not selected.  This is because every grade of every material would have to retested under the chosen standard.

Future articles will deal with each of the main test criteria on the material datasheet, how the material is tested under each standard, and what the results are attempting to represent.