Thermal deformations, marking

The subsequent thermal processes201 give rise to diffusion of the polycarbonate substrate into the dye layer, decomposition of the dye, and mechanical deformation of the film due to thermal contraction. Each of these processes can contribute to a reduction in the optical path length of the low-intensity readout beam. The optics within the detector are designed such that phase differences due to the optical path length differences cause the light intensity falling on the detector to be reduced when the beam passes over a recorded mark .196... 

At elevated temperatures, the thermal recovery processes described in Section 5.1.2.3 can occur concurrently with deformation, and both strength and strain hardening are consequently reduced. The latter effect results in decreasing the difference between yield and tensile strengths until at sufficiently high temperatures, they are essentially equal. At lower temperatures, temperature has a marked influence on deformation in crystalline materials. Temperature can affect the number of active slip systems in some... 

In contrast to the rubbery state, the properties of glassy networks (mechanical, thermal) at temperatures markedly below T p do not practically depend on chemical composition and cure conversion at the latest stages of the cure process. The sensitivity of the properties to the chemical structure of the network is very weak. The shortness of intercrosslinked chains is displayed only in small values of eb, e and in the absence of deformation hardening for the glassy state of the considered polymers. 

For test temperatures Tflow stress increases markedly. Borderlines between elastic/anelastic strain (cta) and microstrain/macrostrain deformation ranges can be deduced, subdivided into athermal ([Pg.316]

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.

Fig. 7.19. Experimentally determined stress versus temperature hysteresis data for a 1 jjLm. thick A1 film deposited on a relatively thick elastic substrate. The specimen was first heated from room temperature to 300 °C (the data point set marked 1 ), held at that temperature for 30 min., and then subsequently cooled to a minimum temperature before being heated again to 300 °C. This minimum temperature was chosen to be 110, 50, 20 and —10 °C for the four thermal cycles, the heating portions of which are denoted by the numbers 2, 3, 4 and 5, respectively. The specimen was held at 300 °C for 30 min. during each thermal cycle. The as a function of temperature. The solid curves in Figure 7.19 show the response for elastic and plastic deformation implied by (7.75) and (7.76). To denotes the stress-free reference temperature. Experimental data provided by Y. J. Choi, Massachusetts Institute of Technology (2002).

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