Tensile Testing of Plastics using Microtensile Specimens ASTM D1708.
Tensile tests measure the force required to break a specimen and the extent to which the specimen stretches or elongates to that breaking point. The data is often used to specify a material, to design parts to withstand application force and as a quality control check of materials. ASTM D1708 is typically used to compare to historical data. ASTM D638 offers a type V specimen for use when material is limited and offers modulus information. Since the physical properties of many materials (especially thermoplastics) can vary depending on ambient temperature, it is sometimes appropriate to test materials at temperatures that simulate the intended end use environment.
Specimens are placed in the grips of the Universal Test Machine at a specified grip separation and pulled until failure. For ASTM D1708 the test speed is approximately 1/4 of the test speed that would be used for ASTM D638. No extensometer is used, and tensile modulus is not measured.
Elevated or Reduced Temperature Test Procedure:
A thermal chamber is installed on the universal test machine. The chamber is designed to allow the test mounts from the base and crosshead of the universal tester to pass through the top and bottom of the chamber. Standard test fixtures are installed inside the chamber, and testing is conducted inside the controlled thermal environment the same as it would be at ambient temperature. The chamber has internal electric heaters for elevated temperatures and uses external carbon dioxide gas as a coolant for reduced temperatures. The size of the chamber places a limitation on the maximum elongation that can be reached.
Specimens can be die cut, machined, or molded. The specimens are dog bone in shape, 38mm x 15mm overall in size, 5mm x 22mm in the gauge area.
The following calculations can be made from tensile test results:
- tensile strength (at yield and at break)
- elongation and percent elongation at yield
- elongation and percent elongation at break
**Please note that this test description is intentionally generic in nature and aimed at providing a descriptive summary to enhance test understanding. Standards can be obtained from appropriate standard authorities.