Shape memory mechanism

Fig. 5.2 Schematic figures of the shape memory mechanism of LLDPE/PP/LLDPE-PP blends [12]...

Schematic figures of the shape memory mechanism of the styrene-butadiene-styrene (SBS) triblock copolymer/poly(e-caprolactone) (PCL) blend in (a)-(d). (Adapted from Zhang, H., Wang, H., Zhong, W, and Du, Q. 2009. A novel type of shape memory polymer blend and the shape memory mechanism. Polymer 50 1596-1601. Copyright Elsevier Ltd. Reproduced with permission.)...

Zhang, H., Wang, H., Zhong, W., and Du, Q. 2009. A novel type of shape memory polymer blend and the shape memory mechanism. Polymer 50 1596-1601. 

Fig. 26 Left Shape-memory response curve of an elastomer containing 2 mol% of UPy pendant side groups. Right Proposed shape-memory mechanism (states 1—5) involving thennoieveisible H-bonding. Colored side groups represent H-bonding groups in the hot (red) and cold (blue) states darker lines represent the lightly cross-linked covalent netwoik. Adopted with pennissirai liom [144]. Copyright 2(X)7, John Wiley Sons, Inc.

Figure 3.49 Schematic showing the shape memory mechanism involved in the two-stage biaxial programming and recovery. Note the contribution of the compression programming to the further segmental alignment along the tension direction. Source [59] Reproduced with permission from the American Society of Civil Engineers...

Like other polymeric materials, rheological modeling was first attempted to predict the constitutive behavior of SMPs. Although earher efforts [5-8] using rheological models were able to describe the characteristic thermomechanical behavior of SMPs, loss of the strain storage and release mechanisms usually led to limited prediction accuracy. Also, the models were 1-D and could only predict the behavior under a uniaxial stress condition, such as 1-D tension. Furthermore, these models can oidy work for a small strain. They cannot predict the thermomechanical behavior of SMPs with finite strain, which is the case for most SMPs. Later, meso-scale models [9,10] were developed to predict the constitutive behavior of SMPs. However, one limitation is that a meso-scale model cannot understand the shape memory mechanisms in detail because the mechanisms controlling the shape memory are in a molecular... 

In Section 5.2, we treated the SMPF as a microphase segregated structure and, based on their chemical composition and shape memory mechanisms, these phases are classified as soft phase and hard domain, and both may be semicrystalline. From the point of view of micromechanics modeling, however, this is not convenient because the RVE, which is made of a semicrystalline soft phase and a semicrystalline hard domain, will be difficult to analyze. Therefore, in the following, we will treat the SMPF as a two-phase composite with a crystalline phase and an amorphous phase that is, the RVE will be a two-phase element. Clearly, both the soft phase and hard domain contribute to the amorphous phase and crystalline phase. Selection of the RVE in such way makes it easier to utilize existing constitutive relations for both amorphous polymer and crystalline polymer. 

In fact, not only alloys have shape memory properties, some polymers, ceramics and even biological systems also possess such properties. For example, bacteriophages can use the shape memory mechanism to enter into host cells. However, to date, only SMAs are widely used in microvalve fabrication. We will focus on the introduction of SMA microvalves. 

Shape memory ceramics (SMCs) have also been studied. The principal drawback of the SMC materials is their small recovery strain, much smaller than those of metal alloys, due to the intrinsic fragile behaviour and the microfractures that ceramics tend to produce in their structure. However, it is possible to classify these materials in terms of their shape memory mechanisms (Wei et al, 1998) ... 

Directly light-activated shape memory mechanism. 

Abrahamson, E. R., Lake, M. S., GaU, K. (2003), Shape memory mechanics of an elastic memory composite resin. Journal of Intelligent Material System and Structures, 14, 623-32. 

Key words supramolecular shape memory polyurethane, pyridine, thermal-responsive shape memory effect, shape memory mechanism, N,N-bis(2-hydroxyl ethyl) isonicotinamide. 

Model of thermally-induced shape memory mechanism of BIN-SMPUs... 

Shape memory mechanism of thermally-induced SME of BIN-SMPUs. 

The shape memory mechanism of the SMF can be illustrated as follows during melt spinning, at a temperature which is higher than T (222°C in the given ejqieriment), the fiber is extruded from a spinneret. Upon cooling to an ambient temperature, which is below T, the fiber is wound up and the permanent fiber shape is cast. 

The main-chain type pyridine containing SMPU has so far not been fully investigated. In future studies, the pyridine ring will be attached to the polymer backbone as a pendant. Based on the hydrogen-bonded supramolecular stmcture, the BIN-SMPUs will have maity unique advantages due to their shape memory, mechanical and damping properties. 

Relaxations and Shape Memories Mechanical deformations of synthetic materials... 

The intermetallic Ni-Ti system has the imusual property of after being distorted, returning to its original shape when heated. This was the first of the shape memory alloys (SMAs) and was discovered by accident at the Naval Ordnance Laboratory, hence its name Nitinol. Other SMAs include Cu-Al-Ni, Cu-Zn-Al, and Fe-Mn-Si alloys. The shape memory mechanism depends on a martensitic solid-state phase transition that takes place at a modest temperature (50°C—150°C), depending on the alloy. The high temperature phase is referred to as austenite and the low temperature phase is called martensite (following the terminology of the Fe-FeCa system). 

---