TY - THES

T1 - Design and development of a testing machine for compressive creep tests on polymers at elevated temperatures

AU - Brunbauer, Silvia

N1 - embargoed until null

PY - 2016

Y1 - 2016

N2 - In many long term applications, where polymers are used as engineering components, the creep behavior can be a dominating part of the observed material properties depending on the material and the load case. If creep tendencies are to be expected under load and temperature for a certain material, it is useful to have reliable creep measurement data available, that allow a more accurate component design. The development, validation and calibration of a compression creep test machine are presented in this thesis. Since the test setup should fit into a prescribed environment, a modular and compact test setup is developed. The design allows that a variable number of specimens can be applied with stress in parallel. Thus various reproductive creep measurements can be performed simultaneously at the same test conditions. The developed testing machine is able to characterize the compressive creep behavior of polymers at stress levels up to 2000 N and temperatures ranging from room temperature to 200°C. The displacement measurement range is up to 1 mm measurement distance with the currently implemented calibration. The stress in the specimen is applied by a moving piston, that is guided inside a cylinder and is loaded with pressurized air. The pressure on the piston is regulated by a proportional valve and a cylindrical specimen is positioned underneath the piston on a load cell. The time dependent displacement is detected by a sensor that is attached to the piston. For the development, three test rigs are combined to one test battery that is characterized in detail. To quantify the measuring certainty an extensive sensor calibration and uncertainty analysis is performed. It could be shown, that with careful calibration the displacement sensor performance can be increased significantly by one decimal power. Temperature influences on the displacement sensors could be estimated by a specially developed calibration method. After the sensor calibration, the test rig performance was investigated. The loading and unloading behavior of the system and the intrinsic system compliance are characterized at room temperature and elevated temperatures. It could be shown, that the chosen test setup allows controlled loading and unloading of the specimens with high reproducibility. With modified sealing elements on the piston and a nonlinear pressure regulation an overshooting of pressure during loading and an entire unloading is enabled. With all calibration procedures the displacement sensors allow an overall measuring certainty of 1% of the maximum measurement distance and the load cells a measuring certainty of 0.2%.

AB - In many long term applications, where polymers are used as engineering components, the creep behavior can be a dominating part of the observed material properties depending on the material and the load case. If creep tendencies are to be expected under load and temperature for a certain material, it is useful to have reliable creep measurement data available, that allow a more accurate component design. The development, validation and calibration of a compression creep test machine are presented in this thesis. Since the test setup should fit into a prescribed environment, a modular and compact test setup is developed. The design allows that a variable number of specimens can be applied with stress in parallel. Thus various reproductive creep measurements can be performed simultaneously at the same test conditions. The developed testing machine is able to characterize the compressive creep behavior of polymers at stress levels up to 2000 N and temperatures ranging from room temperature to 200°C. The displacement measurement range is up to 1 mm measurement distance with the currently implemented calibration. The stress in the specimen is applied by a moving piston, that is guided inside a cylinder and is loaded with pressurized air. The pressure on the piston is regulated by a proportional valve and a cylindrical specimen is positioned underneath the piston on a load cell. The time dependent displacement is detected by a sensor that is attached to the piston. For the development, three test rigs are combined to one test battery that is characterized in detail. To quantify the measuring certainty an extensive sensor calibration and uncertainty analysis is performed. It could be shown, that with careful calibration the displacement sensor performance can be increased significantly by one decimal power. Temperature influences on the displacement sensors could be estimated by a specially developed calibration method. After the sensor calibration, the test rig performance was investigated. The loading and unloading behavior of the system and the intrinsic system compliance are characterized at room temperature and elevated temperatures. It could be shown, that the chosen test setup allows controlled loading and unloading of the specimens with high reproducibility. With modified sealing elements on the piston and a nonlinear pressure regulation an overshooting of pressure during loading and an entire unloading is enabled. With all calibration procedures the displacement sensors allow an overall measuring certainty of 1% of the maximum measurement distance and the load cells a measuring certainty of 0.2%.

KW - testing

KW - compressive

KW - creep

KW - test machine

KW - polymers

KW - kriechen

KW - Druck

KW - Polymer

KW - Prüfstand

M3 - Master's Thesis

ER -