Softening Behavior

Model polyamicdialkylamides were prepared by the reaction of the secondary amines (XX) and (XXI) with the polyisoimide (XVII) in DMAC at room temperature. Unfortunately, the resultant polyamicdialkylamides only exhibited limited softening behavior for processing into bulk specimens. The inability to provide molded specimens prevented the validation of the In Situ Molecular Composite concept. Research is currently being carried out at a number of academic and industrial institutions on new thermoset chemistry, polyamices-ters, and extended chain polyimides. 

In all the scans, there is evidence of temporary softening of the TICA samples at around 200 C to 300 C. The softening behavior is the same between the two resins, but the behavior exhibited in air is distinctly different from that in nitrogen. 

Softening behavior of ceramic materials is compared using the Seger cone test... 

A characteristic property of highly refractory materials is their softening behavior under pressure (pressure softening, pressure flow)... 

Li, V.C., Wang, Y., and Backer, S. (1991) A statistical-micromechanical model of tension-softening behavior of short fiber reinforced brittle matrix composites , Journal of Mechanics and Physics of Solids, Vol. 39, No. 5, 1991, 607-625. 

Softening Behavior. The softening behavior of the PS control, a sodium C-PS, and a sodium S-PS are illustrated in Figure 4. These softening curves were obtained on materials that were compression molded. Both ionomers contained about 5 mol % ionic functionality and at that level are extremely difficult to melt process. Compression molding can be effected at temperatures of 250°C for the S-PS and 200°C for C-PS, provided that the molding is effected over a sufficiently long time to permit the viscous flow processes to occur. A Du Pont Thermo Mechanical Analyzer was used (10°C/min) under the same conditions for all three materials. 

Figure 2 shows the relationship between axial displacement and differential stress. Temperatures were in the range of 25 to 600°C and confining pressure and pore pressure were lOOMPa and 25MPa, respectively. The tests were performed at a constant ram displacement rate of 0.02 mm/min. It is seen that nonlinear deformation and softening behavior were observed and peak strength was reducing with increasing temperature. The fractured specimen was shown in Fig. 3. Thus, the brittle shear fracture was occurred in any case of temperature conditions. Using the fracture angle...

The design engineer often requires to know the maximum temperature for which a polymer can be used in a given application. This depends largely on two independent factors (1) the thermal stability of the polymer, particularly in air and (2) the softening behavior of the polymer. 

There are physical interactions between the individual macromolecules that constitute a plastic material, just as there are between the molecules of a low molecular weight compound. These physical interactions are responsible for cohesion and related properties such as strength, hardness, and softening behavior. Plastics that consist of linear threadlike molecules (several hundred nanometers (nm) long and a few tenths of a nanometer in diameter) (1 nm = 10 m = 10 A = 10 mm), i.e., of macromolecules, that are not strongly crosslinked can usually be softened on heating. In many cases they melt. Thus, when a polymeric material is heated above a certain... 

The softening behavior has also been observed with Cytec EM 1000-Al single lap joints exposed to 100% relative humidity at 50°C for 1000 hours [91]. As shown in Fig. 8, wet and dry joints exhibited similar strength-temperature relationships, but with the former being shifted to a lower temperature by 30-50°C, a quantity close to the water-induced depression of the Tg. Hence, in this case, the Tg depression acts as a shift factor that defines the strength-temperature relationship between the dry and wet adhesive so that at a given temperature, a wet joint exhibits lower strength than a dry one. 

It is well known in concrete engineering that the fracture process zone is created ahead of a notch (crack) in concrete, without revealing the notch sensitivity. Nucleation of micro-cracks in the fracture process zone is clarified as shown in Fig. 10.25 (Nomura, Mihashi et al. 1991). The fracture process zone was ideally introduced in order to explain the tension-softening behavior. Then, as shown in the figure, the presence of the zone is physically confirmed. 

As seen in Fig. 3.20, these elastic properties decrease rapidly at doses less than 0.1 MD-dpa and the decrease becomes smaller at high dose levels. Due to the dose dependence of the formation and coalescence of point defects and small clusters, it was concluded [18] that point defects and small clusters contribute much more than topological disorder to the degradation of the elastic properties of a-SiC. The elastic constants and elastic modulus showed the expected softening behavior under irradiation for the dose range of interest. 

The sheet is softened to an extent such that to stretch, enable, or ease without tearing. The softening behavior purely depends on the thermomechanical behavior in the form of orientation, stress, and crystallinity of the polymeric material. Therefore, the sheet memory is partially removed because of comparatively low temperatures over short periods of time. Polymer with amorphous nature is thermoformed above its glass transition temperature. The forming temperature is slightly above the melting temperature of their crystalline domains. The polymeric sheet is heated by contact, convection, or radiant heater. Then, the heated sheet... 

Fig. 3.1-60 Effect of Al—Mg alloy composition on the softening behavior the material was 90% cold-worked and annealed for 1 h at temperature shown [1.36]...

Some of the conclusions drawn are that, for our specific finite element models (non-symmetric, using penalty method for some connections, possible softening behavior), direct solvers outperform the iterative solver significantly. As expected direct solver were not as scalable as iterative solvers, however, specifics of our finite element models (dealing with soil-structure interaction) resulted in poor initial performance of iterative solvers, that, even with excellent performance scaling, could not catch up with the efficiency of direct solvers. IT is also important to note that parallel direct solvers, such as MUMPS and SPOOLES provided the best performance and would be recommended for use with finite element models that, as ours did, feature non-symmetry, are poorly conditioned (they are ill-posed due to use of penalty method) and can be negative definite (for softening materials). 

Since the very notion of the glass-rubber transition stems from a softening behavior, the mechanical methods provide the most direct determination... 

The overlapping of curves for final stages of the separation event validates the existence of a universal strain-softening behavior (exponent), independent of the initial condition of the specimen. This observation can be corroborated by a loading-reloading static PFT test on the same specimen. 

The softening behavior of hemicelluloses in a humidity scan of 0.1%RH/min is exemplified in Figure 2 for the birch xylan at 60°C at a load frequency of 1 Hz. With increasing moisture content in the material the mobility of the polymer chains increased, evident as a drop in the storage modulus. 

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