Dynamic mechanical response

As these problems were encountered in the past, it became evident that we did not have at hand the physical or mathematical description of the behavior of materials necessary to produce realistic solutions. Thus, during the past half century, there has been considerable effort expended toward the generation of both experimental data on the static and dynamic mechanical response of materials (steel, plastic, etc.) as well as the formulation of realistic constitutive theories (Appendix A PLASTICS DESIGN TOOLBOX). 

For this work, the epoxy/amine ratio was varied and the dynamic mechanical response was determined for ... 

An investigation is reported of the dynamic mechanical response of aluminium silicate filled closed cell microcellular ethylene-octene copolymer (Engage) vulcanisates. The effect of blowing agent, frequency and temperature on dynamic mechanical properties is studied, and the strain-dependent dynamic mechanical properties of microcellular Engage are also investigated. 25 refs. INDIA... 

AFMs have also been used to eshmate the cohesive energy of ionic materials with face-centred-cubic structure (Fraxedas et al., 2002a). In these experiments an ultrasharp AFM hp (hp radius / < 10 nm) indents a hat surface of a single crystal and the dynamical mechanical response of the surface during indentahon is transformed into a force plot (applied force vs. penetrahon). It turns out that the... 

By combining the results of several methods (dynamic mechanical, dielectric, NMR, etc.), it is usually possible to determine quite reliably the structural units whose motions give rise to secondary relaxations. If dynamic mechanical measurements alone are employed, the usual procedure is that the chemical constitution is systematically altered and correlated with the dynamic mechanical response spectra, i.e. with the temperature-dependence of the G" and G moduli. If the presence of a certain group in polymers is marked by the formation of a loss peak characterized by a certain temperature position, size and shape etc., then the conclusion may be drawn that the motional units responsible for the secondary relaxation are identical or related with that group. Naturally, the relations obtained in this way are empirical and qualitative. 

Dynamic mechanical response spectra of elastin145 (insoluble protein of vessels and ligaments), poly(ethylene terephthalate)141 and polycarbonate based on Bisphenol A (4,4 -dihydroxydiphenylmethane)141 show that incorporated water brings about enlargement of the existing secondary loss peak and its displacement toward lower temperatures. In conformity with the latter result, the activation energy of the relaxation process of elastin decreases. So far, no detailed data on this type of relaxation have been collected so that the copartidpation of water in the molecular motion cannot be specified more accurately. 

Most conspicuous modifications of the dynamic mechanical response spectra of PHEMA and related polymers are brought about by incorporation of low-molecular weight compounds (Fig. 13). Along with alterations of parameters (temperature, height, shape) of the peaks characteristic of a dry polymer, usually a new diluent peak appears. (The relaxation patterns of various polymethacrylates are not modified by diluents in a unique way but several modes can be distinguished as mentioned before.) A remarkable feature... 

With the exception of local main-chain motions, the above-mentioned types of molecular motions have been investigated on a series of hydrophilic polymethacrylates and polyacrylates by means of dynamic mechanical measurements carried out with a torsional pendulum. For this purpose, the constitution of polymethacrylates was systematically altered and correlated with the dynamic mechanical response spectra. It was established for a series of copolymers of poly(2-hydroxyethyl methacrylate) that the temperature of the y relaxation (140 K 1 Hz), assigned to the motion of 2-hydroxyethyl... 

Once the molecular motions occurring in the glassy state have been characterised and assigned through dielectric relaxation, 13C and 2H NMR, it is interesting to investigate their effect on the dynamic mechanical response of Ar-Al-PA [60,61],... 

At higher temperatures, a broad transition, present in all epoxy resins independently of the reacting species (amines or anhydrides), is much more complex than the y transition. Its position and shape vary strongly with the chemical structure of the epoxy resin. The dynamic mechanical response and the solid-state 13C NMR of the various model networks referred to in Table 9 focus precisely on the analysis of this /3 transition [62,63]. 

The dynamic mechanical response of a material can be characterised through the loss modulus, the loss tangent, tan S, or the loss compliance, However, as already mentioned for Ar-Al-PA (Sect. 6), the loss compliance can be considered the most relevant parameter for quantitatively comparing different materials, at least for additive purposes. For this reason, the semi-quantitative analysis and the comparison of viscoelastic data determined for different systems have been performed [63] in terms of /", whereas the determination of activation energies and entropies are based on loss modulus data. 

The investigation of the ft transition of PMMA ([1], Sect. 8.1.3) has revealed that physical ageing has an influence on the dynamic mechanical response in the ft-a crossover temperature region. As a consequence, it is worth checking whether it leads to some changes in the plastic deformation behaviour [32]. 

Figure 7 shows the dynamic mechanical response obtained with the latex prepared with a constant monomer feed composition. 

The dynamic mechanical responses of the two power feed latexes are quite different from either of those discussed above. 

The dynamic mechanical response of three 2,4-T-2P samples at 11 Hz is shown in Figure 7 for three hard-segment concentrations. A low temperature relaxation maximum, s, in the region of — 68° to — 54°C,... 

Figure 4. Low-temperature dynamic mechanical response of a typical block copolymer, interfacially prepared bis-A-poly-sulfone/bis-A-polycarbonate (10,000/10,000)...

Typically, these instruments measure dynamic mechanical responses to sinusoidal input. To characterize the viscoelastic properties of a material, these tests must be repeated over a range of temperatures and frequencies. This is sometimes done at a fixed frequency while the polymer specimen is heated or cooled and... 

Dynamic Mechanical Response of In Situ Polyurethane—Poly (methyl methacrylate) Interpenetrating Polymer Networks... 

An alternative set of terms is best introduced by noting that a complex number can be represented as in Fig. 11-15 by a point P (with coordinates x and y) or by a vector OP in a plane. Since dynamic mechanical behavior can be represented by a rotating vector in Fig. 11-13, this vector and hence the dynamic mechanical response is equivalent to a single complex quantity such as G (complex modulus)... 

The dynamic mechanical response of liquid crystalline polymers has received a great deal of attention in the recent literature. Yoon and Jaffe (18) examined the response in tension of annealed, highly oriented strands of various composition liquid crystalline polymers. More recently, Hard, et al (19.201 studied the dynamic mechanical response in both tension and torsion of these same polymers. The following brief summary takes into account the results of both of those works. 

Figure 8 depicts the dynamic mechanical response of the two component materials as well as a blend which contains 75 weight percent of the copolymer component. 

Of the microphase-structure dependent physical properties of ionomers, perhaps the most widely studied are glass transition temperatures, (Tg), and dynamic mechanical response. The contribution of the Coulombic forces acting at the ionic sites to the cohesive forces of a number of ionomeric materials has been treated by Eisenberg and coworkers (7). In cases in which the interionic cohesive force must be overcome in order for the cooperative relaxation to occur at Tg, this temperature varies with the magnitude of the force. For materials in which other relaxations are forced to occur at Tg, the correlation is less direct. 

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