Scope of ASTM D638 Test Method:

ASTM D638 and ISO 527 are technically equivalent test methods. Poisson’s Ratio is a measure of transverse strain against axial strain when uniaxial stress is applied. The uniaxial force is used to deform the sample in both axial and lateral directions. A high tensile modulus means that the test material is rigid and more amount of stress is required to produce a given strain. The tensile properties of plastic materials are determined by ASTM D638 test process, which can be used to test components up to 14 mm thick (0.55 inches). 

Test Procedure of ASTM D638 Test Method:

For the ASTM D638 test, a universal tester is used.  The sample is clamped into the grips of the tester. Next, the sample is attached with two strain measuring instruments, one axially and the other laterally.Finally,a uniaxial force is applied at a fixed speed.

Sample size:

Usually, a standard tensile bar is used in ASTM D638 test method.

Data:

In ASTM D638 test method, a stress-strain graph is produced and Poisson’s ratio is calculated. 

Conclusion

ASTM D638 test method requires a universal testing machine (tensile testing machine). The most common sized universal or tensile testing machine for moulded plastics is 5 or 10 kN (1,125 or 2,250 lbf). As reinforced polymers and composites get stronger, a greater capacity 50 kN (11,250 lbf) unit may be required.