Method and apparatus for measuring linear thermal expansion of polymeric material

The method of measuring the linear thermal expansion of a sample of a polymeric material for determining the coefficient of linear expansion of the material, comprising:

• preparing a wedge shaped sample of polymeric material having a sharp tip;
• positioning the wedge shaped sample on a graphite block within a temperature controlled chamber;
• securing the base of the wedge shaped sample to the graphite block with the tip of the wedge lying in the plane of the junction of the sample base and a surface of the graphite block;
• recording the temperature of the sample;
• directing a collimated coherent laser object beam toward said sample;
• positioning a holographic plate in the path of reflected light from said sample with the central beam path of the incident beam on the sample to the holographic plate lying in a plane perpendicular to the plane of the junction of the sample base and the surface of the graphite block;
• and being at equal angles with respect to a line perpendicular to the plane of the junction of the sample base and the surface of the graphite block;
• directing a collimated reference beam toward said holographic plate;
• blocking and object beam and said reference beam after a predetermined exposure time interval;
• removing the holographic plate;
• developing the holographic plate;
• restoring the holographic plate in its former position;
• heating the sample at small temperature increments to a predetermined temperature above the original measured temperature;
• allowing the sample to remain at said predetermined temperature for between 30 and 45 minutes;
• recording the sample temperature after expansion of the sample;
• illuminating said holographic plate with said reference beam and the sample with the object beam to reconstruct the sample image on the sample with a resulting fringe pattern thereon which provide an indication of the thermal expansion of the polymeric sample.

An apparatus for measuring the linear thermal expansion of a polymeric material;

• comprising;
• a temperature controlled chamber;
• a graphite block within said chamber;
• a notch on said block for holding a sample of said polymeric material;
• a sample of said polymeric material positioned in said notch;
• said sample having a wedge surface;
• means for securing the base of the sample to the surface of the graphite block with the tip of the wedge lying in the plane of the junction of the sample base and the surface of the graphite block;
• a window in said chamber for passing laser light to said sample;
• means for directing an object beam of collimated coherent light toward said sample;
• a holographic plate positioned in the path of reflected light from said sample with the central beam of the light incident on said sample and the central beam of the light reflected from said sample being in a plane perpendicular to the plane of the junction of the sample base and the surface of the graphite block and making equal angles with respect to a line perpendicular to the plane of the junction of the sample base and the surface of the graphite block;
• means, for directing a collimated reference beam toward said holographic plate;
• means for selectively blocking the light in said object beam and said reference beam;
• means for adjusting the temperature within said chamber and means for indicating the temperature of the sample within the chamber.