An apparatus is
required for measuring the coefficient of thermal expansion for low-temperature
fiber- reinforced polymer-matrix composite materials.
The purpose of this project was to design an apparatus for measuring the coefficient of thermal expansion (CTE) of polymer matrix composite (PMC) materials at low temperatures (32-300°F). This testing is required because polymers are being used extensively in applications with varying temperatures. The apparatus was to operate with an accuracy of three microns, accommodate two-inch long specimens, and cost under $3,000. Four basic methods of measurement were proposed as solutions to this problem: linear voltage displacement transducers (LVDTs), water displacement, sand displacement, and a mechanical rocker arm. Each design idea was evaluated by considering the accuracy, ease of operation, ease of construction, and cost. Three of the designs were dismissed due to impracticality and poor user-interface.
After the most efficient method of
measurement was selected, a design was made to construct the measuring device.
After several iterations, it was determined that the design required an
oven to heat the composite specimen and two LVDTs to measure the changes in
axial distance. The oven was to
be controlled by a proportional-integral-derivative (PID) controller and the
LVDTs were to be connected to a two-channel display box.
A quartz rod was implemented as a means of extending the contact
surfaces of the LVDTs. Theoretical
calculations were performed to verify oven power requirements and precision
constraints.
A
Pro/Engineer CAD model and technical drawings extracted from the model were
created as a means for communicating the design intent of the apparatus. The
drawing package was used to machine parts that could not be ordered.
With all the parts machined and/or ordered, the apparatus was assembled
and tests were run to validate the design.
