A stress-strain testing apparatus imposes a stress-strain on a specimen while disposed in a controlled environment. Each end of the specimen is fastened to an end cap and a strain gage is attached to the specimen. An adjusting mechanism and a compression element are disposed between the end caps forming a frame for applying forces to the end caps and thereby stress-straining the specimen. The adjusting mechanism may be extended or retracted to increase or decrease the imposed stress-strain on the specimen, and the stress-strain is measured by the strain gage on the specimen while the apparatus is exposed to an environment such as high pressure hydrogen. Strain gages may be placed on the frame to measure stress-strains in the frame that may be caused by the environment.