Shape thermally-induced effect

A massive amount of propane is instantaneously released in an open field. The cloud assumes a flat, circular shape as it spreads. When the internal fuel concentration in the cloud is about 10% by volume, the cloud s dimensions are approximately 1 m deep and 100 m in diameter. Then the cloud reaches an ignition source at its edge. Because turbulence-inducing effects are absent in this situation, blast effects are not anticipated. Therefore, thermal radiation and direct flame contact are the only hazardous effects encountered. Wind speed is 2 m/s. Relative humidity is 50%. Compute the incident heat flux as a function of time through a vertical surface at 100 m distance from the center of the cloud. 

Figure 1.2 Schematics of thermally induced shape memory polymer effect.

FIGURE 19.4 Molecular mechanism and macroscopic effect of a shape-memory polymer, (a) Schematic representation of the thermally induced shape-memory effect of a polymer network with (b) Shape recovery of a stent with T = 52° in water at 37°C. The stent gradually changed from its... 

It is noted that while the majority of constitutive modeling focuses on thermally induced dual-shape memory behavior, triple-shape and multishape SMPs have been developed recently and they call for constimtive modeling [1]. In addition, the effect of programming temperature and strain rate on the constimtive behavior also needs modeling [2]. Furthermore, some recent smdies have found that while the shape recovery ratio can be 100%, other mechanical properties such as recovery stress or modulus become smaller and smaller as the thermomechanical cycles increase, which has been explained by the shape memory effect in the microscopic scale [24]. Obviously, these new findings also call for constitutive modeling. 

Heuchel, M., Sauter, T., Kratz, K., and Lendlein, A. (2013) Thermally induced shape-memory effects in polymers quantification and related modeling approaches. Journal of Polymer Science Part B Polymer Physics, 51, 621-637. 

Since the homogeneous width y of the Lamb-dip profile increases with pressure p, the maximum allowed deflection angle e in (8.1) also increases with p. A comparison of pressure-induced effects on the kernel and on the background profile of the Lamb dips and on the Doppler profile therefore yields more detailed information on the collision processes. Velocity-selective optical pumping allows the measurement of the shape of velocity-changing coUisional line kernels over the full thermal range of velocity changes [979]. 

Conventional shape memory polymers are segmented polyfur-ethane) s and have hard segments that include aromatic moieties (70,71). But a series of other thermoplastic block copolymers with thermally induced shape memory effects have been summarized (69). 

If an increased temperature in the center of the column is induced through frictional heating in UHPLC, the analyte molecules will move faster in the column center, but the negative impact on the peak shape is similar. This is another reason, why UHPLC columns normally have reduced internal diameters, as this helps to minimize thermal mismatch effects. 

Indirect Actuation of Thermally-Induced Shape-Memory Effect... 

Pig. 1. Schematic demonstration of the thermally induced one-way shape-memory effect. By the programming process the permanent shape is transferred to the temporary shape. Heating up of the sample to a temperature above the switching transition Ttrans initiates the recovery of the permanent shape. From Ref 2. 

Fig. 3. Schematic demonstration of the molecular mechanism of the thermally induced shape-memory effect for a multiblock copolymer, Ttrans = Tm. If the rise in temperature is higher than Ttrans of the switching segments, these segments are flexible (marked red, here) and the polymer can be deformed elastically. The temporary shape is fixed by cooling down below Ttrans (marked blue, here). If the poljrmer is heated up again the permanent shape is recovered.

Table 1. Possible Combinations of Hard-Segment- and Switching-Segment-Determining Blocks in Linear, Thermoplastic Block Copolymers with Thermally Induced Shape-Memory Effect ...

Suppose that a thin film is bonded to one surface of a substrate of uniform thickness hs- It will be assumed that the substrate has the shape of a circular disk of radius R, although the principal results of this section are independent of the actual shape of the outer boundary of the substrate. A cylindrical r, 0, z—coordinate system is introduced with its origin at the center of the substrate midplane and with its z—axis perpendicular to the faces of the substrate the midplane is then at z = 0 and the film is bonded to the face at z = hs/2. The substrate is thin so that hs R, and the film is very thin in comparison to the substrate. The film has an incompatible elastic mismatch strain with respect to the substrate this strain might be due to thermal expansion effects, epitaxial mismatch, phase transformation, chemical reaction, moisture absorption or other physical effect. Whatever the origin of the strain, the goal here is to estimate the curvature of the substrate, within the range of elastic response, induced by the stress associated with this incompatible strain. For the time being, the mismatch strain is assumed to be an isotropic extension or compression in the plane of the interface, and the substrate is taken to be an isotropic elastic solid with elastic modulus Es and Poisson ratio Vs the subscript s is used to denote properties of the substrate material. The elastic shear modulus /Xg is related to the elastic modulus and Poisson ratio by /ig = Es/ 1 + t s). 

Shape memory materials are able to memorize a second, permanent shape besides their actual, temporary shape. After application of an external stimulus, e.g. an increase in temperature, such a material can be transferred into its memorized, permanent shape. The process of programming and restoring a shape can be repeated several times. This behaviour is called the thermally induced one-way shape memory effect. 

Shape memory effect in polymers is normally achieved by relaxation of the polymeric chains due to changes in temperature.When the programming and recovery stages in the shape memory effect are produced by changes in temperature, it is said that the effect is thermally induced. 

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