Resistance and Deformation

As one might intuitively expect, the incorporation of rubber particles within the matrix of brittle plastics enormously improves their impact resistance. Indeed, the impact resistance imparted by the rubber is the principal reason for its incorporation (Rosen, 1967) in rubber-plastic blends and grafts. Toughening in such polymers is also observed under other loading conditions, such as simple low-rate stress-strain deformation and fatigue. It is believed that several deformation mechanisms are important in all such cases, though their relative importance may depend on the polymer and on the nature of the loading. 

In this section, stress-strain behavior of typical rubber-plastic systems at low and high (impact) rates of static testing and under low-frequency 

The importance of graft-type bonding and the finer, more complex morphology developed in graft copolymers should be emphasized. Table 3.2 

ASTM test D256 was followed, and the values reported have the units ft-lb/in. of notch. 

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Cheng, M.-Y., Parra-Montesinos, G. J. (2007) Punching shear resistance and deformation capacity of fiber reinforced concrete slab-column connections subjected to monotonic and reversed cyclic displacements, in International Workshop HPPRCC 5 in Mainz, RILEM, Proc. S3, W. H. Reinhardt and A. E. Naaman eds pp. 489-96. 

So for the purposes of flexural resistance and deformation capacity, one may concentrate the vertical reinforcement and provide concrete confinement only at the two edges of the section (Fig. 5). (If the cross section is not elongated, the vertical element is called upon to develop significant lateral-force resistance in both horizontal directions, then it is meaningless to distinguish between flanges on one hand, where vertical bars are concentrated and concrete is confined, and web on the other, where they are not). 

Composite constraction includes a wide range of structural systems, e.g., framed structures employing all steel-concrete composite (SCC) members and components (e.g., composite beam-to-columns and connections) and sub-assemblages of steel and/or reinforced concrete (RQ elements. Such components and elements are employed to optimize the resistance and deformation capacity (Uchida and Tohki 1997). SCC structures have been used... 

Prior to the corrosion test, to obtain the optimum compressive load, the relationship between compressive deformation of the conductive polymer in the sandwich configuration, deformation rate, and electrical resistance were measured as shown in Figure 3. From the resistance data as a function of deformation rate in this figure, the deformation rate was chosen as 20 % in view of stability of the resistance for the compression. Hysteresis in the relationship between resistance and deformation rate for repeated stress was not observed. 

VVuv (ffl). Within the series, one tenn dominates, for example, the n 2 term for ethylene. Ethylene strongly resists torsional deformation to any angle other than 0 and 7t (180") (Fig. 4-10). 

The resistance to plastic flow can be schematically illustrated by dashpots with characteristic viscosities. The resistance to deformations within the elastic regions can be characterized by elastic springs and spring force constants. In real fibers, in contrast to ideal fibers, the mechanical behavior is best characterized by simultaneous elastic and plastic deformations. Materials that undergo simultaneous elastic and plastic effects are said to be viscoelastic. Several models describing viscoelasticity in terms of springs and dashpots in various series and parallel combinations have been proposed. The concepts of elasticity, plasticity, and viscoelasticity have been the subjects of several excellent reviews (21,22). 

Hardness is a measure of a material s resistance to deformation. In this article hardness is taken to be the measure of a material s resistance to indentation by a tool or indenter harder than itself This seems a relatively simple concept until mathematical analysis is attempted the elastic, plastic, and elastic recovery properties of a material are involved, making the relationship quite complex. Further complications are introduced by variations in elastic modulus and frictional coefficients. 

A hardness indentation causes both elastic and plastic deformations which activate certain strengthening mechanisms in metals. Dislocations created by the deformation result in strain hardening of metals. Thus the indentation hardness test, which is a measure of resistance to deformation, is affected by the rate of strain hardening. 

Fillers. These are used to reduce cost in flexible PVC compounds. It is also possible to improve specific properties such as insulation resistance, yellowing in sunlight, scuff resistance, and heat deformation with the use of fillers (qv). Typical filler types used in PVC are calcium carbonate, clays, siHca, titanium dioxide, and carbon black. 

Refractory Materials. Extremely high melting metals and those that are more resistant to deformation when hot are considered refractory... 

In general, once the curtain of filaments has been produced, it is necessary to attenuate the filaments in order to provide strength and resistance to deformation. The most commonly practiced approach is to utilize a single slot, which is at least the width of the curtain, at a point below the spinning plate and above the laydown screen. There are two practical approaches taken. The first utilizes the injection of low pressure air at a point above the slot so that the fibers attain sufficient acceleration in the slot to provide adequate draw (22) (Fig. 7). The second utilizes a low pressure vacuum below a venturi to provide the pressure differential requited for sufficient acceleration and resulting attenuation (30). 

Lighting. An important appHcation of clear fused quartz is as envelop material for mercury vapor lamps (228). In addition to resistance to deformation at operating temperatures and pressures, fused quartz offers ultraviolet transmission to permit color correction. Color is corrected by coating the iaside of the outer envelope of the mercury vapor lamp with phosphor (see Luminescent materials). Ultraviolet light from the arc passes through the fused quartz envelope and excites the phosphor, produciag a color nearer the red end of the spectmm (229). A more recent improvement is the iacorporation of metal haHdes ia the lamp (230,231). 

Grease Retention, Wrinkle Resistance, and Durable Press. On bending or creasing of a textile material, the external portion of each filament in the yam is placed under tension, and the internal portion is placed in compression. Thus, the wrinMe-recovery properties must be governed in part by the inherent, tensional elastic deformation and recovery properties of the fibers. In addition to the inherent fiber properties, the yam and fabric geometry must be considered. 

Hardness (qv), which determines the resistance of a material to abrasion and deformation, is affected not only by composition but also by porosity and microstmcture. Higher cobalt content and larger carbide grain size reduce hardness and abrasion resistance but iacrease the toughness of cemented carbides. The trade-off of abrasion resistance and toughness enables the cemented carbide manufacturer to tailor these materials to a wide variety of metal-cutting and nonmetal-cutting appHcations. 

Elasticity is another manifestation of non-Newtonian behavior. Elastic Hquids resist stress and deform reversibly provided that the strain is not too large. The elastic modulus is the ratio of the stress to the strain. Elasticity can be characterized usiag transient measurements such as recoil when a spinning bob stops rotating, or by steady-state measurements such as normal stress ia rotating plates. 

Thermoplastic coatings based on vinyl plastisols and acryUc latexes resist severe deformation duting fabrication and exhibit good exterior durabdity. 

Most wrought alloys are provided in conditions that have been strengthened by various amounts of cold work or heat treatment. Cold worked tempers are the result of cold rolling or drawing by prescribed amounts of plastic deformation from the annealed condition. Alloys that respond to strengthening by heat treatment are referred to as precipitation or age hardenable. Cold worked conditions can also be thermally treated at relatively low temperatures to affect a slight decrease in strength (stress rehef annealed) to benefit other properties, such as corrosion resistance and formabiUty. 

Precipitation (Age) Hardening Alloys. Only a few copper alloys are capable of responding to precipitation or age hardening (7). Those that do have the constitutional characteristics of beiag siagle-phase (soHd solution) at elevated temperatures and are able to develop iato two or more phases at lower temperatures that are capable of resisting plastic deformation. The copper alloy systems of commercial importance are based on iadividual additions of Be, Cr, or Ni + X where X = Al, Sn, Si, and Zr. 

Precipitation Hardening Alloys. Copper alloys that can be precipitation hardened to high strength are limited in number. In addition to the metallurgical requirement that the solubiUty of the added element(s) decrease with temperature, the precipitated phase that forms during aging must be distributed finely and have characteristics that act to resist plastic deformation. 

An elastic impression material must be easily and quickly prepared set quickly to an elastic mass in the mouth not be harmful or cause discomfort to the oral tissues and flow to all areas without the need of excessive force. It also must copy detail accurately possess sufficient strength, toughness, and elasticity to resist permanent deformation when removed from the mouth not adversely affect the set properties of the cast material be capable of being... 

Because of increased production and the lower cost of raw material, thermoplastic elastomeric materials are a significant and growing part of the total polymers market. World consumption in 1995 is estimated to approach 1,000,000 metric tons (3). However, because the melt to soHd transition is reversible, some properties of thermoplastic elastomers, eg, compression set, solvent resistance, and resistance to deformation at high temperatures, are usually not as good as those of the conventional vulcanized mbbers. AppHcations of thermoplastic elastomers are, therefore, in areas where these properties are less important, eg, footwear, wine insulation, adhesives, polymer blending, and not in areas such as automobile tires. 

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