Description_of_the_Experiment5

3.4.2.1 Description of the Experiment

To study the fire resistance four types of wood-based materials were used:

• chipboard with dimensions of 40 x 40 x 15 mm
• laminated chipboard with dimensions of 40 x 40 x 8 mm
• plywood with dimensions of 40 x 40 x 18 mm
• retarded plywood with dimensions of 40 x 40 x 18 mm

To observe the fire resistance of wood-based test specimens the real-time method of holographic interferometry (see chapter 3.1.2) was applied.

The experimental equipment consisted of a holographic variant of the Mach-Zehnder interferometer adjusted to the infinite fringe width a part of which was also a fixture for location of the test specimen and a flame source located under the test specimen (Fig. 3–61).

The first condition for application of the holographic method was obtaining a hologram. We obtained the hologram by simultaneous illumination of the holographic plate by two light beams at homogeneous distribution of the refractive index in the measuring space, i.e. without insertion of the phase object.

After photochemical analysis of the holographic plate it is possible to reconstruct the original object beam that in the real time interferes with the real beam.

Test specimens were heated for 15 minutes by the flame from below and every minute of heating a record was made. With respect to the continual process of the experiment the CCD camera that works immediately and makes the record in the form of bmp files was used.

After finishing the experimental part it was necessary to analyse the interferograms. The temperature orders were counted at all test specimens above their centers, i.e. in the distance of 20 mm from their boundaries. At randomly selected test specimens we mapped the whole surface keeping the distance of 5 mm between the measured places. The numerical values obtained were statistically analysed and the dependencies of the measured data were graphically displayed.