Cooling stress-strain behavior

Figure 5.29 Stress-strain behavior of SMPFs during the entire thermomechanical cycle, (a) Sample 2 (hot-drawing programmed sample) step 1, stretch the fiber bundle to 100% strain at a rate of 200 mm/min at 100 °C step 2, hold the strain constant for 1 hour step 3, cool the fiber to room temperature slowly while holding the pre-strain constant step 4, release the fiber bundle from the fixture (unloading) step 5, relax the fiber in the stress free condition until the shape is fixed step 6, recover the fiber at 150 °C in a fully constrained condition (b) Sample 3 (cold-drawing programmed sample) step 1, stretch the fiber bundle to 100% strain at a rate of 200 mm/min at room temperature step 2, hold the strain constant for 1 hour step 3, release the fiber bundle from fixtures (unloading) step 4, relax the fiber in a stress free condition until the shape is fixed step 5, recover the fiber at 150 °C in a fully constrained condition. (Because the curves are black and white, please refer to Figure 5.12 to better differentiate each step).

Weil and Koeppel [15] reported a study in 2008 involving bonded comphant sealants. The thermally induced stress-strain behavior of the cell, sealant, and frame components was investigated using the 3D FEM. ANSYS was used for the calculations. The assembly was heated and cooled uniformly. A one-quarter section was modeled due to the fourfold symmetry of the component. The cell was treated computationally as a single material, considering the anode properties. 

Dynamic Mechanical Analysis and Stress Relaxation Behavior. Samples were compression molded into bars of the dimensions 38.xl2.5x0.78 0.007 mm and 65.x9.7xl.7 0.007 mm in a Carver laboratory hot press model C. A TA Instruments 983 DMA, which was operated in the fixed frequency mode, was used to characterize the storage and loss moduli as a function of temperature. Samples were scanned at fi-equencies from 0.05 to 10.0 Hz over a temperature range from -150 C to above the glass transition temperature. The displacement was 0.4 - 0.6 mm. Stress relaxation curves were determined for the same size samples at a constant strain. The sample was displaced for 10.0 minutes and then allowed to recover for 10.0 minutes. The stress data were taken in five degree increments. A microprocessor controlled Liquid Nitrogen Cooling Accessory (LNCA) was used for sub-ambient operations. 

Figure 3.29 Axial stress-time and temperature time behavior of the SMP foam with a nylon liner at a programming temperature of 79 °C and pre-strain level of 60%. The three steps (step 1 pre-stressing, step 2 cooling and unloading, and step 3 stress recovery) are shown by the three regions and the peak stress, programming stress, and peak recovered stress are indicated using black dots. Source [42] Reproduced...

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