It's depend upon the material as well as as system. Strength can be measured by using the either the formation or breaking. For the breaking, there are two methods available one is mechanical breaking including dilution second thermal breaking. Please, use the UV and fluorescence instrumental techniques.

@mr dubey: could you please explain better those methods or post bibliography  i could check ? we are interested in measuring the strength differences in quite complex powder mixtures before and after application of mechanical energy. how could we measure with the"mechanical breaking including dilution or thermal breaking" you cite ? thanks

Please, read my publication in RSC or can search about Rheology.

i only have access to public site of rsc http://pubs.rsc.org/ and the search of your name gives no results back. could you please provide more infos? (tilel, abstract or upload the paper(s)?) thanks a lot