Hi Xinfu, 

What materials are you talking about here?  Sometimes subscript "m" stands for "material", sometimes "maximum", or even "matrix" in case of composite materials. R can be resistance. I personally do not think these symbols are commonly used. Normally Ys, UTS, σY, σf are used to show stresses.

Cheers,

Ahmad 

Dear Ahmad :

    These symbols are used in the international standard of tensile test. In China, our standard of tensile test has been modified to be consistent with the international standard. I just wonder why use the letter R, Z etc. in the standards. Thank you.

Best regards,

Xinfu

Hi Xinfu, 

I do not know about Z, but I'm pretty sure that R stands for resistance and "m" maximum. A very misleading symbol though. First thing crossed my mind when I saw R, was the stress ratio in fatigue. 

Cheers, 

Ahmad