Cold-compression programming

Figure 3.13 Schematic of cold-compression programming (steps 1 to 3), free shape recovery (step 4), and fully constrained stress recovery (step 5)...

The 3-D strcss-strain-time behaviors for the entire themomechanical cycle, which include the three-step cold-compression programming process and the one-step heating recovery, are shown in Figure 3.35, for both the 10% and 30% pre-strain levels. An extremely nonlinear, and time and temperature dependent constitutive behavior is revealed. In-depth understanding of... 

Cold-Compression Programming of Thermosetting SMP Based Syntactic Foam... 

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 3.37 SEM observation of (a) a pristine specimen and (b) a specimen after 30% cold-compression programming. Source [45] Reproduced with permission from ASME...

Because Figure 3.44 is a stress-strain-temperature plot, step 2 (30 minutes of holding or relaxation) during cold-compression programming cannot be visualized. To have a better understanding of the stress-strain evolution with time, a typical thermomechanical cycle in terms of stress-strain-time for the four groups of specimens is shown in Figure 3.45 (a) to (d), respectively. In order to have both tension and compression direction in the same quadrant, the compression stress and compression strain are also treated as positive. 

The veloeity gradient is essential in analyzing path dependent materials such as plastic deformation of cold-compression programmed SMP. It is also useful in determining the energetically conjugate stress and strain, as will be demonstrated in the section on stress definition. 

Constitutive Modeling of Cold-Compression Programmed Thermosetting SMP... 

In continuum mechanics, constitutive modeling of materials follows certain steps, including deformation response, stress response, as well as other particular steps based on materials studied, such as structural relaxation for polymers and a plastic flow mle, and a hardening rule for materials with plastic deformation. In the following, we will present the deformation response, structural relaxation, stress response, and flow rule for the thermosetting SMP programmed by cold-compression programming. 

Other parameters such as the glass transition temperature, programming temperamre, relaxation time during cold-compression programming, and glassy shear modulus can be found from the test results presented in Chapter 3. The determined model parameters for the polystyrene based thermosetting SMP arc summarized in Table 4.2. 

Once the model is validated by test results, it is used for predictions. First, we consider the effect of the volume fraction of the SMP matrix 0p on the thermomechanical cycle. As shown in Figure 4.25, two SMP volume ffaetions ( = 0.5 and = 0.6), which experienced a 40 minute relaxing period during cold-compression programming and had a recovery heating rate of 0.4 °C/min, were conducted. It was found that less SMP appears to slightly increase the... 

Stress Definition in Solid Mechanics Multiplicative Decomposition of Deformation Gradient Constitutive Modeling of Cold-Compression Programmed Thermosetting SMP... 

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