Cooling cyclic loading

After completion of DHC test specimen has been unloaded and cooled down in the furnace to the room temperature. Specimen then has been subjected to cyclic loading to outline the DHC crack and then fractured. After completion of DHC test actual crack length was measured from fractographs (Fig. 2). 

Figure 1.6 Cooling load and work of the cyclic process of liquefaction.

To a 15-mL sealed tube was added the vinylsulfone-bound resin 161 (0.078 mmol based on a loading of 0.52 mmol g, cyclic hydrazide (162) (5 equiv.), aldehyde (5 equiv.) and 1,2-dichloroethane (2.5 mb). The tube was capped, magnetically stirred, and treated at reflux for 48 h. The reaction mixture was cooled to room temperature the resin was filtered and washed as follows ... 

The experiments show that this loading causes first one crack to initiate at or near the center of the top layer. The location of this first crack somewhat depends on the location of the thermocouple which was placed at the surface to measure the temperature. Subsequently, the cyclic application of the thermal load results in the formation of a second crack followed by a third. This is schematically shown in Figure 6. The locations of these cracks is dependent on the stress distribution at the surface of the specimens. The distribution of the in-plane stresses on the surface during cooling is shown in Figure 7. In this figure, a typical location of the first crack is shown with the corresponding surface stress distribution. The location of the maximum stress indicates where the second crack is... 

The SME of the network nanocomposite with 42 wt% POSS content was investigated. Here POSS crystallites were used to fix the temporary shape. The cyclic thermomechanical test started with heating the composite to 110°C. At this temperature, the sample was deformed by applying a load of 0.23 N and then cooled under this load to 30 C (POSS crystallization occurred according to DSC measurements... 

Cyclic, thermomechanical tensile tests were performed for the nanocomposites with POSS/polyol ratio = 2.63 (see Fig. 15b). The sample was firstly heated to 80°C (T > Tg) and deformed (1) by ramping to a load of 0.3N. The sample was cooled under this load (2) to 10°C, to fix the temporary, elongated shape. After unloading (3) the sample was heated (4) to 80°C to recover the permanent shape. The first cycle showed about 5% creep occurring between the elongation and fixing step over... 

Using material which absorbed more of the neutron energy and without a divertor there would be an increase with up to 25% of P appearing as heat to be removed from the first wall. A factor of 8 will have a substantial effect upon the design of the wall - from the point of view of both the cyclic stress and heat transfer for cooling. When assessing the reactor potential of the various containment concepts it is clearly important to know not only the planned value of wall loading but the assumptions on the proportion which has to be removed as heat from the first wall. 

Figure 3-67. Examples of how fatigue loading in flexure affects thermoplastics, a) Temperature effects in PMMA acrylic with and without the cooling of specimens b) a comparison of strength regression in rigid PVC under cyclic and sustained loads of equal duration.

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