Plastic
Testing Methods
- Tensile
Testing of Thin Plastic Sheeting
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. Tensile tests produce a
stress-strain diagram, which is used to determine tensile
modulus. 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 and
pulled until failure. For ASTM D882 the test speed and grip
separation are based on the elongation to break of the material.
Elongation and tensile modulus can be calculated from crosshead
displacement, or with an extensometer.
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:
ASTM D882 uses 1" x 6" strips die cut from thin sheet
or film.
Data:
The following calculations can be made from tensile
test results:
1. tensile strength (at yield and at break)
2. tensile modulus
3. strain
4. elongation and percent elongation at yield
5. elongation and percent elongation at break
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