Mechanical thermal response experiments

The origin of the deep localized states in the mobility gap that control the dark decay has been attributed to structural native thermodynamic defects [12]. Thermal cycling experiments show that the response of the depletion time to temperature steps is retarded, as would be expected when the structure relaxes toward its metastable liquid-like equilibrium state. As the structure relaxes toward the equilibrium state, t(j decreases further until the structure has reached equilibrium. The only possible inference is that must be controlled by structure-related thermodynamic defects. The generation of such defects is, therefore, thermally activated. We should note that because the depletion discharge mechanism involves the thermal emission of carriers... 

For both experiments extensive instrumentation allowed for monitoring of the hydraulic and mechanical performance of the system before, during and after the test. In the Buffer/Container experiment the thermal response of the system was also measured. 

Thus, with respect to the initiation of reaction, early work demonstrated the usefulness of a macroscopic, thermal model of the process and enabled the response of the more sensitive azides to be rationalized in a qualitative and sometimes semiquantitative way. The more difficult task of understanding the phenomena on an electronic or a molecular basis began to bear fruit, and gross, quantitative predictions of slow decomposition by heat or light became possible. However, unless their sensitivities had been first empirically established by statistical experiments, it remained impossible to predict the response of samples to different stimuli or to induce reaction with finesse or precision. Spontaneous initiation and explosion, such as encountered with crystals growing in solution, could not be explained by any mechanism, thermal, photochemical, or tribochemical. 

In this chapter, thermal response results were presented from full-scale experiments on cellular FRP beams and columns with and without liquid-cooling. The structural members were subjected to ISO fire curve and mechanical loading simultaneously until a stop criterion (water leakage or structural failure) or after the planned fire exposure duration. 

An internal liquid cooling system as an active fire protection was implemented in full-scale GFRP panels for beam and column applications, the resulting thermal responses have been introduced and modeled in Chapter 6 and the mechanical responses in Chapter 7. The fire endurance time of each scenario is summarized in Table 9.1 and more details can be found in the previous chapters. It can be concluded that combined mechanical loading and fire experiments on full-scale water-cooled cellular slabs and columns proved the feasibility of an effective fire protection. Fire endurance durations of up to 2 h could be reached at slow water... 

As noted in Subsection 24.1.2, viscoelasticity of polymers represents a combination of elastic and viscous flow material responses. Dynamic mechanical analysis (DMA, also called dynamic mechanical thermal analysis, DMTA) enables simultaneous study of both elastic (symbol ) and viscous flow (symbol ") types of behavior. One determines the response of a specimen to periodic deformations or stresses. Normally, the specimen is loaded in a sinusoidal fashion in shear, tension, flexion, or torsion. If, say, the experiment is performed in tension, one determines the elastic tensile modulus E called storage modulus and the corresponding viscous flow quantity E" called the loss modulus. 

However, such experiments are time-consuming and, therefore, expensive. Moreover, the derived predictions only hold for the used materials, geometries and investigated process parameters extrapolations of the results beyond these conditions are not possible. Consequently, it is desirable to have a general framework, which allows for the prediction of the thermal and mechanical material response following from an arbitrary choice of... 

The study of the dispersion of photoinjected charge-carrier packets in conventional TOP measurements can provide important information about the electronic and ionic charge transport mechanism in disordered semiconductors [5]. In several materials—among which polysilicon, a-Si H, and amorphous Se films are typical examples—it has been observed that following photoexcitation, the TOP photocurrent reaches the plateau region, within which the photocurrent is constant, and then exhibits considerable spread around the transit time. Because the photocurrent remains constant at times shorter than the transit time and, further, because the drift mobility determined from tt does not depend on the applied electric field, the sample thickness carrier thermalization effects cannot be responsible for the transit time dispersion observed in these experiments. 

The glass transition temperature can be measured in a variety of ways (DSC, dynamic mechanical analysis, thermal mechanical analysis), not all of which yield the same value [3,8,9,24,29], This results from the kinetic, rather than thermodynamic, nature of the transition [40,41], Tg depends on the heating rate of the experiment and the thermal history of the specimen [3,8,9], Also, any molecular parameter affecting chain mobility effects the T% [3,8], Table 16.2 provides a summary of molecular parameters that influence the T. From the point of view of DSC measurements, an increase in heat capacity occurs at Tg due to the onset of these additional molecular motions, which shows up as an endothermic response with a shift in the baseline [9,24]. 

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