Mechanical behavior definitions

The basic nature of composite materials was introduced in Chapter 1. An overall classification scheme was presented, and the mechanical behavior aspects of composite materials that differ from those of conventional materials were described in a qualitative fashion. The book was then restricted to laminated fiber-reinforced composite mafeffals. The basic definitions and how such materials are made were then treated. Finally, the current and potential advantages of composite materials were discussed along with some case histories that clearly reveal how composite materials are used in structures. 

The discussion in the Introduction led to the convincing assumption that the strain-dependent behavior of filled rubbers is due to the break-down of filler networks within the rubber matrix. This conviction will be enhanced in the following sections. However, in contrast to this mechanism, sometimes alternative models have been proposed. Gui et al. theorized that the strain amplitude effect was due to deformation, flow and alignment of the rubber molecules attached to the filler particle [41 ]. Another concept has been developed by Smith [42]. He has indicated that a shell of hard rubber (bound rubber) of definite thickness surrounds the filler and the non-linearity in dynamic mechanical behavior is related to the desorption and reabsorption of the hard absorbed shell around the carbon black. In a similar way, recently Maier and Goritz suggested a Langmuir-type polymer chain adsorption on the filler surface to explain the Payne-effect [43]. 

Y Relaxation. Unlike the other dynamic mechanical relaxations observed in this study, the Y relaxation does not have an analog in the dynamic mechanical behavior of polyethylene, hydrogenated PP s, or other ionomer systems. In addition, it displays no definite trends in changing temperature or magnitude as the level of sulfonation and thermal history are altered. Coupled with the fact that these systems are known to contain water as well as nitrogen, it is not possible to assign this relaxation to any specific phase or mechanism. Additional studies are necessary before this task can be approached adequately. 

The most modern picture of membrane deformation recognizes that the membrane is a composite of two layers with distinct mechanical behavior. The membrane bilayer, composed of phospholipids and integral membrane proteins, exhibits a large elastic resistance to area dilation but is fluid in surface shear. The membrane skeleton, composed of a network of structural proteins at the cytoplasmic surface of the bilayer, is locally compressible and exhibits an elastic resistance to surface shear. The assumption that the membrane skeleton is locally incompressible is no longer applied. This assumption had been challenged over the years on the basis of theoretical considerations, but only very recently has experimental evidence emerged that shows definitively that the membrane skeleton is compressible. This has led to a new constitutive model for membrane behavior [Mohandas and Evans, 1994]. The principal stress resultants in the membrane skeleton are related to the membrane deformation by ... 

The most important terms for describing the mechanical behavior of soHd materials are listed in Table 1.1. The detailed definition of each property related to these behaviors, with equations, SI units, and orders of magnitude, will be discussed in the following paragraphs. 

A few definitions are in order. Depending on temperature and structure, amorphous polymers exhibit widely different physical and mechanical behavior patterns. At low temperatures, amorphous polymers are glassy, hard, and brittle. As the temperature is raised, they go through the glass-rubber transition. The glass transition temperature (Tg) is defined as the temperature at which the polymer softens because of the onset of long-range coordinated molecular motion. This is the subject of Chapter 8. 

The mechanical behavior of concrete should be viewed from the point of view of a composite material. A composite material is a three dimensional combination of at least two chemically and mechanically distinct materials with a definite interface separating the components. This multiphase material will have different properties from the original components. Concrete qualifies as such a multiphase material. Concrete is composed of hydrated cement paste (C-S-H, CH, aluminate, and ferrite-based compounds) and imhydrated cement, containing a network of a mixture of different materials. In dealing with cement paste behavior, basically it is considered that the paste consists of C-S-H and CH with a capillary system. The model of concrete is simplified by treating it as a matrix containing aggregate embedded in a matrix of cement paste. This model provides information on the mechanical properties of concrete. 

All these polymers exhibit a glass transition temperature higher than room temperature, and most of them are amorphous. Due to either the size of their substituent or their molecular symmetry, some of them are semicrystalline. They have a definite melting point, and according to its value they exhibit a mechanical behavior more complex than that of amorphous polyvinyls. Depending upon the nature of substituents A and B, the physicochemical properties of polymers of this family can be very different, thus enabling them to be used in many fields. Their overall economic importance is considerable but variable depending upon their stmcture it is not possible to make an exhaustive presentation of them. 

All CP results were obtained at 5°C. Correlation of SFC values at 5°C with CP data indicated that a small difference in SFC led to large variations in rheological behavior. Thus, the role of solid fat appeared to be secondary when it came to CP. The small changes in SFC were not solely responsible for the substantial differences in HI observed for the CIEbutterfat-canola oil blends with 70-100% butterfat. Other mechanisms were definitely at play. As stated by Mahklouf et al. (1987), fats with identical SFCs can have vastly different rheological properties. 

The electrode mechanical behavior during stress development was modeled under the following assumptions and definitions 1-11. The abbreviations and the physical constants that were used for the calculations are listed in Table 3.4. 

To fuUy understand the mechanics of flow, the following definitions explain the behavior of various types of fluids in both their static and flowing states. 

Another simple approach assumes temperature-dependent AH and AS and a nonlinear dependence of log k on T (123, 124, 130). When this dependence is assumed in a particular form, a linear relation between AH and AS can arise for a given temperature interval. This condition is met, for example, when ACp = aT" (124, 213). Further theoretical derivatives of general validity have also been attempted besides the early work (20, 29-32), particularly the treatment of Riietschi (96) in the framework of statistical mechanics and of Thorn (125) in thermodynamics are to be mentioned. All of the too general derivations in their utmost consequences predict isokinetic behavior for any reaction series, and this prediction is clearly at variance with the facts. Only Riietschi s theory makes allowance for nonisokinetic behavior (96), and Thorn first attempted to define the reaction series in terms of monotonicity of AS and AH (125, 209). It follows further from pure thermodynamics that a qualitative compensation effect (not exactly a linear dependence) is to be expected either for constant volume or for constant pressure parameters in all cases, when the free energy changes only slightly (214). The reaction series would thus be defined by small differences in reactivity. However, any more definite prediction, whether the isokinetic relationship will hold or not, seems not to be feasible at present. 

The behavioral effects of amphetamine, methamphetamine, MDMA, MDA, p-chloroamphetamine, and fenfluramine are not identical. Except for the last drug, all can cause some degree of behavioral stimulation, but exact behavioral effects differ markedly. More complete definition of their behavioral differences is a prerequisite to a better understanding of the mechanism(s) of these drugs. 

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