Bending Beam Fixtures

Dynamic mechanical properties of the irradiated wood was measured using a Pyris Diamond DMA, manufactured by PerkinElmer Life Sciences, Norwalk, CT equipped with a controlled hquid nitrogen cooling accessory. The materials were analyzed in bending mode with the dual cantilever beam fixture for the instrument. 

We use a variant of flexural testing to measure a sample s heat distortion temperature. In this test, we place the sample in a three point bending fixture, as shown in Fig. 8.6 b), and apply a load sufficient to generate a standard stress within it. We then ramp the temperature of the sample at a fixed rate and note the temperature at which the beam deflects by a specified amount. This test is very useful when selecting polymers for engineering applications that are used under severe conditions, such as under the hoods of automobiles or as gears in many small appliances or inside power tools where heat tends to accumulate. 

The transverse tensile strength (TTS) was measured with the 3-point bending fixture at l/h=5, but now with the fibres parallel to the rollers. Fracture initiates at the point of maximum tensile stress in the bottom face of the beam below the central roller. Samples with a length of 10 mm (this is the width in the test) were cut between perspex plates with a diamond saw in order to obtain smooth cuts. The transverse tensile strength was calculated as TTS = 3/2 F/(w h) (1/h). 

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