And plastic yielding

Although resistance to deflection and plastic yielding are obviously of first importance in choosing alternative materials, other properties enter into the selection. Let us look at these briefly. Table 27.4 lists the conditions imposed by the service environment. 

Finally we note that the data which are compiled in Tables II-V are mostly based on simple laboratory tests with single specimen of typical fuel types. The applicability of these data to mass fires is debatable (Powell et al., 1979). In fact, according to Rasbash and Drysdale (1982), the effect of the environments into which the fire volatiles are released is probably more important than the nature of the combustibles. Lack of ventilation enhances smoke production, as can clearly be seen from the data of Rasbash and Pratt (1979), listed in Table II. As shown in Tables II-IV, burning of unoxidized fossil fuels and plastics yields much more... 

Figure 18. Effect of interparticle distance, A, on plastic deformation of matrix strands between particles (a) definitions of the size parameters D = particle diameter, vP = particle volume content, aQ = applied stress, and aK = stress concentration (b) with a small interparticle distance, a uniaxial stress state is dominant between the particles and microvoids after cracking of the particles, and plastic yielding can be obtained and (c) with a large interparticle distance, thick matrix strands favor a triaxial stress state between the particles and microvoids, and plastic yielding is hindered.

The significance of the theory of elastic deformation and plastic yielding for contact models is illustrated by a simplified version of a treatment published by Archard [4]. If we think of a deformable surface... 

In a realistic situation the adhesive filament will not act as a perfect elastic body uniformly stressed up to fracture. Uneven stress distributions and plastic yielding would be expected to increase the energy dissipation observed beyond that calculated for the ideal elastic model. It will be very interesting to see whether in the future auxetic materials can be developed to an extent that they can be used as coatings for such porous substrates. Even greater increases in fracture energy can then be anticipated. 

Typically, the yardstick for qualitatively measuring the internal resistance of an adhesive bond to an external load has been the determination of the strain distribution in the adhesive and adherends. This is a difficult task. Even in simple lap joints, the actual stress-strain distributions under load are extremely complex combinations of shear and tensile stresses, and are very prone to disturbance by non-uniform material characteristics, stress concentrations or locaUzed partial failures, creep and plastic yielding, etc. It is extremely difficult to accurately measure the strains in adhesive joints with such small glue Une thicknesses and such relatively inaccessible adhesive. Extensometers, strain gauges, and photoelasticity are being used with limited success." ... 

Almost all current methods of design analysis are based on models of material behavior that are relevant to traditional metallic materials, as for example elasticity and plastic yield (see Chapter 3). These principles are embodied in design formulas design sheets or charts and in more modem techniques, such as computer-aided design (CAD) using finite element analysis. The design analyst is merely required to supply appropriate elastic or plastic constants for the material. Thus, traditional analysts can be expected to have little experience with plastics, a situation that is changing. 

The extensibility and plastic yield strength of a solid over the whole range of sizes can be formulated based on the T-BOLS correlation and LBA mechanism, which has enabled the reproduction of the observed HPR and IHPR effect and identification of factors dominating the strongest sizes. Matching predictions to observations reveals the following ... 

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