Plastic
Testing Methods
- Tensile
Testing of Plastics using Microtensile Specimens
Scope:
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. 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.
Test Procedure:
Specimens are placed in the grips of the Instron 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 Instron
universal test machine. The chamber is designed to allow the test
mounts from the base and crosshead of the Instron 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.
Specimen Size:
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.
Data:
The following calculations can be made from tensile
test results:
1. tensile strength (at yield and at break)
2. elongation and percent elongation at yield
3. elongation and percent elongation at break
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