In addition to tensile and flexural testing, another common form of determining the material properties of plastic (both unreinforced and reinforced) is compression testing. This test is useful for determining the
modulus of elasticity, yield stress,
compressive strength, and the deformation beyond yield point. The method by which the compression test shall be conducted is defined in ASTM D695.
Based on testing we have conducted in our lab, we recommend the following equipment for compression testing to ASTM D695: two 50mm (2in) diameter hardened-steel
compression platens mounted on a
tensile testing machine, our compression fixture 2505-022 and a strain measuring device such as a 25mm (1in) GL extensometer attached directly to the specimen. A strain measurement device is often required for stiff specimens where system compliance can affect test results. Our Bluehill® 3 material testing software allows you to set the desired test control, automatically calculate the desired results and statistics, and produce a test report.
The standard requires that the specimen is compressively loaded at a rate of 1.3 mm/min until fracture. Prior to testing, you should make sure all specimens are made to the sizes specified in the standard and are free of visible surface flaws. When performing compression testing, we have found that specimen alignment plays an important role in achieving even load distribution, which contributes to the consistency of the results.