Free shape recovery

Figure 3.12 Schematic of classical tension programnting (steps 1 to 3), free shape recovery (step 4), fuUy constrained stress recovery (step 5), and schematic of molecular mechanisms for shape fixing and shape recovery...

Figure 3.15 Four-step thermomechanical cycles (step 1 high temperature loading—> step 2 cooling step 3 room temperature unloading step 4 free shape recovery) for the pure SMP and syntactic foam programmed under a stress-controlled condition with a pre-stress of 263 kPa at 79 °C followed by free recovery. Source [41] Reproduced with permission from Elsevier...

Table 3.1 Shape fixity and recovery ratios for the pure SMP and SMP based syntactic foam under stress-controlled programming and free shape recovery at 79 °C...

Programming Using the 2-D Stress Condition and Free Shape Recovery... 

Figure 3.24 (a) Horizontal and (b) vertical strains of the cruciform sample under various stress levels during programming and recovery (steps 1 to 3 represent programming and step 4 represents free shape recovery) and (c) horizontal and vertical strains of the tenth thermo-mechanical cycle under the pre-stress level of 300.7 kPa (Note tensile stress is treated as negative and compressive stress is treated as positive in (c)). Source [57] Reproduced with permission from the American Society of Civil Engineers... 

Once the specimens were programmed, an unconstrained free shape recovery test was implemented, where the eompressed SMP specimen was heated to Thigh = 79 °C at an average heating rate of = 0.82 °C/min. The same LVDT system as given in Reference [41] was used to... 

The Hitachi S-3600N VP-Scanning Electron Microscope was used to examine the micro-stmcture change due to programming (see Figure 3.37). From Figure 3.37 (b), some of the microballoons have been cmshed after cold-compression programming by 30% pre-strain, which contributed to the irreversible strain after free shape recovery. 

Figure 3.39 Schematic of the entire thermomechanical cycle (two-stage programming and one-step free shape recovery). Source [59] Reproduced with permission from the American Society of Civil Engineers...

Figure 3.43 Thermomechanical cycle in the tension direction for a specimen of T25C25 (step 1 —> pretension to 25% strain at temperatures above Tg, step 2 —> cooling down to room temperature while holding the pre-strain constant, step 3 —> unloading, which completes the first stage of programming. The Poisson effect is due to the second programming in the transverse direction by compression. Step 4 —> free shape recovery). Source [59] Reproduced with permission from the American Society of Civil Engineers...

Figure 5.31 Schematic of the alignment change of amorphous molecules during free shape recovery and fiiUy constrained stress recovery.

Figure 6.34 Four-step thermomechanical cycle (steps 1 to 3 are programming and stq> 4 is free shape recovery). Source [46] Reproduced with permission from Elsevier...

In this beam model (length 2L), the two ends of the beam are elamped with a central crack of width IW. Now we want to narrow this crack using SM material. Let us insert an SM rod of length IW with the same cross-section as the beam, and tightly glue it to the fracmred two half beams. Assuming the SM material is pre-stretched so that it has a fully constrained recovery stress of Go (maximum recovery stress) and free shape recovery strain of (maximum... 

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