Thermomechanical spectrum

Thermomechanical spectrum n. A plot of a mechanical property such as tensile modulus or strength vresus temperature. 

Those PASs that ranged from 35 to 53 wt% in PDMS content clearly show the upper and lower two transitions corresponding to hard aramid segments and soft PDMS segments, respectively. Between the two transitions there are rubbery plateaus that have somewhat constant E values. The thermomechanical spectrum showed that the nature and extent of rubbery plateaus were affected by varying the amount of PDMS. It can be seen that as the soft-segment content is increased, the value of the modulus corresponding to the rubbery plateau decreased and the PAS with 75 wt% of PDMS showed a very sharp drop in modulus. This drop in modulus at... 

FIGURE 2.13 Thermomechanical spectra fundamentals, (a) Regions of thermomechanical spectrum, (b) viscoelastic parameters of the thermomechanical spectrum. 

The phase diagram shows the state of the adhesive at the end of the cure cycle at a given cure temperature. For example, for a cure time of and a cure temperature of the adhesive is in the rubbery state at the intersection point labeled A. However, if this material is cooled to an operating temperature below T, then this material would be in a glassy state. Do not confuse this glassy state with the glassy state from the thermomechanical spectrum, where the material is glassy or often brittle. 

Until recently, the mechanism of the inhibition of light-induced yellowing was subject to speculation. However, solid state ESR and CIDEP have provided insight into the mode of inhibition by thiols (Wan, J.K.S., et al, J. Wood Chem. Technol., in press). Near-uv irradiation of unbleached and peroxide bleached thermomechanical pulp impregnated with thiols caused a rapid increase of the thiol radicals. The time resolved CIDEP spectrum, however, shows a symmetric broad band characteristic of the polarized phenoxy radical. This result suggests that thiols quench triplet generated phenoxy radicals in a secondary thermal process. 

Ti-6A1-4V is an alpha-beta alloy that can be modified extensively by both thermal and thermomechanical processing to produce a large variety of microstructures and hence a wide spectrum of mechanical properties. The beta-transus temperature is approximately 1000 °C (1830 °F) and is a function of interstitial content (Ref 1). Samples of Ti-6A1-4V cooled at relatively slow rates from elevated temperatures contain mainly the alpha and beta phases as a result of diffusional transformations, while those cooled rapidly may also contain martensitic phases such as the cc (hep structure) or the a" (orthorhombic structure) phases. 

The thermomechanical analysis (TMA) spectrum was obtained for these polyurethane-ureas to observe the transitions associated with the hard and soft segments. Figure 7 compares the TMA measurements of three representative copolymers with different hard segment contents. The... 

Thermomechanical properties were determined for a vast array of 10-40 wt% SGFR composites, which encompass a wide spectrum of chemical coupling. The observed data coalesced into a single master plot shown in... 

The large variability in the chemical constitution and architecture of macromolecules opens a broad route to the preparation of materials with a wide spectrum of different properties. Chemistry, however, is not the only factor responsible for the actual behavior. It is a specific feature of polymers that one finds a particularly strong impact of the thermomechanical processes experienced during manufacture since these control the final formation of structures. An understanding of these processes is a necessary prerequisite for a successful utilization of polymers, and the promotion of knowledge to levels as high as possible therefore constitutes one of the main aims of polymer physics. 

In vibration and acoustic analysis the viscoelastic spectrum are often represented as a master curve known as the reduced frequency nomograph. Figure 14.3 is an example of a nomograph constructed with simulated data. In addition to the thermomechanical information that is usually presented, both absolute temperature and frequency axes are included in the nomograph. The information presented by the inclusion of the temperature and frequency axes is already contained in the master curve of the viscoelastic data. However, it is convoluted within the master curve. In order to obtain frequency data at other tanperatures, a new master curve must be created from the raw data or transformed from the original master curve. 

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