Articles you may be interested inConstitutive modeling for moderate deformations of slightly compressible rubber J. Rheol. 53, 153 (2009); 10.1122/1.3037263 Relationship between loudness perception and peripheral compression in subjects with unilateral cochlear hearing loss One-dimensional compression measurements have been made on samples of natural rubber gum stock. The experimental stress-strain curve and the theoretical relation! = G(L-l/ L2) agreed quite well over the entire range (0%-32%) studied. No hysteresis loop was evident.The friction at the faces of the sample was eliminated by a new method of lubrication. The sample essentially floated between two thin films of a liquid which flowed under pressure between the sample and compressing plates allowing uniform lateral expansion of the sample.
Studies of nylon 6 of various relative lengths have been made by measuring the sonic modulus and length as functions of temperature from -50°C to 180°C. Conclusions based on these data indicate that the transition of dry nylon 6 yarn from a glass to rubberlike material takes place in two discrete steps, one centering about -50°C and the other starting at 70°C. Between these two steps, nylon 6 behaves like a ductile material, neither glassy nor rubberlike. The lower step in this transition is a result of attainment of sufficient thermal kinetic energy to permit rotational and translational motion of short-chain segments between completed hydrogen bonds in the amorphous regions. The upper step at 70°C is postulated to be the temperature at which the completed hydrogen bonds become sufficiently weak to allow motion of greater segmental lengths. Moisture in nylon 6 yarn is an effective plasticizer between 25°C and 100°C. However, it raises the temperature of the first step in the glass transition by interfering with segmental motion.
Although Columbus, on his second journey to America, found the natives playing with balls which bounced and were elastic, it was almost 300 years later before use was made in Europe of the gum used in these balls. Priestley found that it could be used for erasing lead pencil marks. However, when further applications of this material were attempted, it became recognized that rubbers from different parts of the country differed. These differences arose partly from the botanical origin of the plants from which the gum, or rubber, was collected and partly from the methods of collecting and preparing it. With the passage of time, fine Para rubber came to be recognized and used as the best rubber and it held this position until it was supplanted by plantation rubber from Hevea brasiliensis trees. These differences in rubbers from different sources made it necessary for the user to know more about the material. Even the distinguished physicist Faraday became involved in the problem and in 1826 he published an analysis of the latex and also the dry rubber. His results were as follows :
The dc conductivity and ac (1000 cps) properties of suspensions of R-40 carbon black in transformer, silicone, and linseed oils, and suspensions of Shawinigan black in linseed oil, were studied as functions of time, carbon black concentrations, and rotational speed of test cell. The dc conductivity was also studied as a function of voltage. Immediately after agitating the suspension, both ac and dc conductivities increase rapidly with time, then level off and approach a saturation value. For the dc conductivity, this value increases with increasing voltage in all suspensions studied except the highest concentrations (10 percent by weight), which obey Ohm's law. The rate of approach to saturation is independent of voltage but depends on carbon black concentration. Increasing the concentration increases the conductivity. Increasing the speed of rotation decreases the conductivity. Form factors for the carbon black particles are calculated from the dynamic values of the dielectric constant by Voet's method. Agglomeration factors are then determined. At low speeds the agglomeration factor decreases rapidly with increasing speed. At higher speeds it approaches unity asymptotically.
The theory of flatspotting in tires is reviewed and found to be in essential agreement with that given in earlier publications. The importance of cord moisture content (humidity), temperature, and dynamic response rate in affecting the flatspotting performance of tirecords is emphasized. Two methods are discussed for favorably altering the viscosity-temperature relationship of nylon tirecords: (a) incorporation of moleculea of bulky groups along the polymer chains (achieved through blending with other polymers), and (b) plasticization. A new, dynamic flatspot cord testing machine is described which permits close simulation of tirecord stress cycles that duplicate the flatspotting phenomena under various cord moisture contents (humidity test atmospheres) corresponding to both summer and winter driving conditions. Good correlation is obtained between the laboratory test results and tire results. Applications of the test machine in screening prospective low flatspotting tirecord materials is discussed. &dquo;
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