Polymers compression clamp

We perform flexural testing on polymer rods or beams in the same basic apparatus that we use for tensile or compressive testing. Figure 8.6 illustrates two of the most common flexural testing configurations. In two-point bending, shown in Fig. 8,6 a), we clamp the sample by one end and apply a flexural load to the other. In three-point bending, shown in Fig. 8.6 b), we place the sample across two parallel supports and apply a flexural load to its center. 

Figure 9.32 Isothermal (173°C) variation of the storage modulus G with time. The blend contains 75% COP, obtained from solution by acetone precipitation and kept under compression at 210-220 C and 4.0 MPa for Imin. Dynamic-mechanical thermal analysis (DMTA) Polymer Labs MKII (8.0 mm X 8.0 cm x 1.5 mm samples) with cantilever clamps [125] and [128]. Reproduced with permission of Elsevier Science Ltd. For explanation see text.

In conventional injection moulding, a polymer melt is prepared in a heated barrel, using a compression-type extruder screw the melt is injected under high rates of shear into a cooled mould, which is clamped closed by a (high) force, sufficient to resist the hydraulic pressure of the injecting melt. 

Where moulds are split to enable the moulding to be removed, accurate matching is important. There should be no gaps which may allow molten polymer to leak out or air to enter the mould. Mould splitting should be made rapid and easy, using quick release clamps or compressed cylinders. Undercuts are only permissible if the product is flexible enough to be collapsed out of the mould or if the moulding will shrink out of the undercut. Moulds for the jacketed system are obviously more expensive to manufac-... 

Charpy test, 109,118 Clamping pressure, 118 Compliance measurements, 10 Composite materials, 206 Technical Committee on Polymers and Composites, 130 Compression creep compliance, 10... 

Figure 4.26 shows thermal expansion data for the same polymer (polycarbonate), tested as a 10 mm long bar sample mounted in the tension clamps, but this time with a compressive load of 1 N. The glassy expansion occurs as before, but when the sample softens at the Tg it is progressively squashed under the compressive load. The onset temperature for the 7 is the same, 145.9°C. Figure 4.27 shows the two curves together. 

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