Fig. 1. Setup for creep and recovery tests of automotive gaskets
Fig. 2. Recovery at different test durations Fig. 3. Recovery for 3 gaskets, 30-min tests
VISCOELASTIC PROPERTIES OF INDUSTRIAL POLYMERS
Proceedings of the 4th International Conference MECHANICS OF TIME-DEPENDENT MATERIALS
October 7-10, 2003, Lake Placid, New York, USA
Abstract
A novel experimental technology for studies of viscoelastic properties of polymers and composites has been developed, based on servo-control of either load or displacement and simultaneous real-time measurements of deformations and forces, as well as contact acoustical, electrical and temperature parameters. This technology has been effectively applied for parallel evaluation of elasticity, plasticity, creep, friction and wear of diverse industrial polymers, including gaskets, seals, and polishing pads.
A universal materials tester mod. UMT has been designed for highly precision comprehensive measurements of mechanical and physical properties of polymers and composites, including with hard and soft coatings. It has two main characteristics: closed-loop servo-control mechanism, which allows for ultra-accurate control of either load (with displacement, or deformation, being monitored) or displacement (with load being monitored), and multi-sensor capabilities, with a number of additional parameters measured in-situ, at a total sample rate of 20 kHz, including: forces and torques in all X, Y and Z directions, high-frequency acoustic emission, contact or surface electrical resistance (or impedance), temperature, as well as digital video (or still) images of the surfaces.
The servo-control allows for dramatically improved data repeatability and reproducibility, as well as for precision measurements of friction, wear, elastic modulus, micro-hardness at various programmable compression and tension levels. The multi-sensing allows for greater sensitivity in detection of various microscopic phenomena of materials behaviour, as well as in comparison and ranking of mechanical properties of seemingly similar materials. All the additional parameters are mutually complimentary. For example, high-frequency contact acoustic emission is very sensitive to the localized micro-cracks, while contact electrical resistance allows for better quantification of thickness and breakthrough thresholds of coatings during testing.
The test setup is shown in Fig. 1, some experimental results for 3 gaskets of different polymers are presented in Fig. 2 (same gasket 1, different recovery times) and Fig. 3 (different gaskets, same recovery time).
Fig. 1. Setup for creep and recovery tests of automotive gaskets
Fig. 2. Recovery at different test durations Fig. 3. Recovery for 3 gaskets, 30-min tests
Study of Pump Seals
A tester setup for elasticity, creep, friction and wear testing of pump seals is shown in Fig. 4, some experimental results are presented in Fig. 5.
Fig. 5. Data for lip seal at 6000 rpm, load of 1N
Study of Polishing Pads for Wafer Planarization
Within one test, we measured elasticity (at loading), creep (under the load of 50 N) and plasticity (after load removal). In Fig 6., one can see large differences between pad 2 (stiffness of 0.12 micron/N, practically no creep, post-test plastic deformation of 2.2 micron) and pad 1 (stiffness of 0.24 micron/N, creep of 1.7 micron, post-test plastic deformation of 6.6 micron).
Fig. 6. Pad load-unload tests
An important question is what indenter to choose for pad deformation tests, a 2” disc (which averages over many pad grooves) or a 0.25” ball (between the grooves), as they produce different results not only quantitatively, but even in pad ranking (Fig.7 ).
Fig. 7. Pad deformation summary