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Necking-down mechanism

If the applied force exceeds a critical value for a filament, then a steady state will no longer exist and the filament will rupture. This rupture may occur by a necking-down mechanism. We may write, for the critical stress on the filament,... [Pg.55]

One gram of silver 0-alumina crystals is placed in a Vycor tube with a 1-cm id and 20 cm long and closed at one end. Three grams of gallium and 4 g of iodine are added, and the Vycor tube is necked down near the middle in preparation for sealing off. The tube is evacuated with a mechanical pump to <1 torr pressure and sealed. The sealed tube is placed in a cold furnace and then heated to... [Pg.56]

Machines that utilize rocker arms with a mechanical linkage between the upper and lower compression assemblies are normally instrumented by applying a strain gauge to the upper rocker arm or to the mechanical linkage connecting the assemblies. The point of strain gauge application is necked-down to increase the sensitivity of the member. These instrumented members should be calibrated in the machine to account for the effect of other machine members on the measured force. [Pg.3624]

In principle, the rupture of a fibril may occur by at least two or three mechanisms, which are not always clearly separable. One is the end point of the drawing (creep) mechanism at constant mass of polymer in the fibril. A condition of local necking down could develop, leading to failure (22). See Fig. 1. This would be more likely to exist with low than with high MW polymers. Alternatively, and particularly with high MW polymers, chain scission might occur. [Pg.41]

Figure 3, which is a replot of the data of Fig. 1, was included to focus attention on the deformational behavior of these steels as measured by elongation. At 70 F, these steels deform by localized necking and extensive reduction of area, followed by fracture in the necked area (see Fig. 10). At -320 and -423°F, these same steels deform by a much more uniform elongation and reduction of area over the entire reduced section (see Fig. 10). This condition is most pronounced in the 62 cold-worked samples. At low temperature, the increase in strength in the reduced section due to plastic strain and associated martensite formation more than offsets the increase in stress due to the reduction in cross-sectional area (i.e., necking down) hence, the sample elongates over the entire reduced section prior to failure. At -423 F this elongation frequently occurs in a discontinuous manner, accompanied by audible clicks, serrations in the stress—strain curve, and striations in the sample, whose appearance is not unlike Luder s bands. The cross section of such a striation is shown in Fig. 12. These striations have been observed in other alloys by other investigators, and have been variously attributed to catastrophic twinning, thermal instability, and the burst-type formation of dislocations [1]. In this material another possibility exists, namely, the formation of martensite. This transformation is known to occur by an instantaneous shear mechanism and yields a volume increase which could account for the serrated stress—strain curve [5]. These effects demonstrate again that the... Figure 3, which is a replot of the data of Fig. 1, was included to focus attention on the deformational behavior of these steels as measured by elongation. At 70 F, these steels deform by localized necking and extensive reduction of area, followed by fracture in the necked area (see Fig. 10). At -320 and -423°F, these same steels deform by a much more uniform elongation and reduction of area over the entire reduced section (see Fig. 10). This condition is most pronounced in the 62 cold-worked samples. At low temperature, the increase in strength in the reduced section due to plastic strain and associated martensite formation more than offsets the increase in stress due to the reduction in cross-sectional area (i.e., necking down) hence, the sample elongates over the entire reduced section prior to failure. At -423 F this elongation frequently occurs in a discontinuous manner, accompanied by audible clicks, serrations in the stress—strain curve, and striations in the sample, whose appearance is not unlike Luder s bands. The cross section of such a striation is shown in Fig. 12. These striations have been observed in other alloys by other investigators, and have been variously attributed to catastrophic twinning, thermal instability, and the burst-type formation of dislocations [1]. In this material another possibility exists, namely, the formation of martensite. This transformation is known to occur by an instantaneous shear mechanism and yields a volume increase which could account for the serrated stress—strain curve [5]. These effects demonstrate again that the...
Dimethyl octanedioate (dimethyl suberate), 71.2 g (0.352 mol), 1,4-butanediol (5% excess 0.370 mol, 33.3 g), and 0.02 g of tetraisopropoxytitanium (0.025% of final polyester mass) are placed in a three-necked round-bottomed flask fitted with a mechanical stirrer. The medium is slowly heated to 150°C within 4 h under nitrogen atmosphere while methanol is distilled off. Vacuum is then slowly applied and the reaction continued at 0.01 mbar and 150°C for 48 h. The resulting polyester is cooled down, dissolved in chloroform (50 g polyester/200 mL chloroform), and slowly added to a 10-fold volume of methanol under high-speed agitation (1000 rpm). The precipitated polyester is filtered off and dried at 30°C under vacuum (0.1 mbar). [Pg.98]

A 1-1. three-necked round-bottomed flask is fitted with a 50-ml. separatory funnel and a mechanical stirrer sealed with a well-lubricated rubber collar. A stopper in the third neck of the flask carries a glass tube that reaches to the bottom of the flask, enters the top of a 1-1. separatory funnel, and extends down to the stopcock. [Pg.29]

The shaking machme must also be mentioned here it is used to produce the finest possible mechanical division in heterogeneous systems. Narrow - necked bottles with well-fitting ground glass stoppers are almost exclusively used as containers. The stopper is held down by means of a piece of rubber tube drawn over it and fastened to the neck with thin wire. Unless appropriate safeguards... [Pg.39]

In a 5-L, three-necked, round-bottomed flask fitted with a 30-ml. dropping funnel, mechanical stirrer, and thermometer extending down into the liquid is placed a suspension of paraformaldehyde (trioxymethylene, 125 g., 4.16 moles) in freshly distilled (Note 1) nitromethane (2.5 1., 46.6 moles). The suspension is stirred vigorously, and 3N methanolic potassium hydroxide solution is added dropwise from the dropping funnel until, at an apparent pH of 6-8, but closer to pH 8 (pH paper), the paraformaldehyde begins to dissolve and the suspension assumes a clearer appearance. About 10 ml. of the alkaline solution is required, and the addition takes about 10 minutes. About 15-20 minutes after addition of the alkaline solution is complete, the paraformaldehyde dissolves completely. Shortly thereafter, the solution temperature reaches a maximum of 13-14 degrees above room temperature and then slowly drops. Stirring is continued 1 hour after addition of the alkaline solution is complete. [Pg.98]

Equipment. A three-neck distillation flask was used as a reactor. In a typical run, the flask was charged with waste oil and demetallizing reagents. The content was agitated and heated by a mechanical stirrer and heating mantle respectively. The reaction was carried out at atmospheric pressure, and water vapor and light ends were condensed and collected during the process. Oil was filtered immediately after the reaction by means of a vacuum filteration system, or allowed to settle down at constant temperature for a sedimentation study. [Pg.321]

Equip a 1-litre three-necked flask with an efficient double surface reflux condenser, a mechanical stirrer and a thermometer, the bulb of which is within 2 cm of the bottom of the flask. Place a warm solution of 80 g of sodium hydroxide in 80 ml of water in the flask, add a solution of 25 g (0.266mol) of phenol (CAUTION) in 25 ml of water and stir. Adjust the temperature inside the flask to 60-65 °C (by warming on a water bath or by cooling, as may be found necessary) do not allow the crystalline sodium phenoxide to separate out. Introduce 60 g (40.5 ml, 0.5 mol) of chloroform (CAUTION) in three portions at intervals of 15 minutes down the condenser. [Pg.997]


See other pages where Necking-down mechanism is mentioned: [Pg.257]    [Pg.154]    [Pg.195]    [Pg.155]    [Pg.100]    [Pg.101]    [Pg.107]    [Pg.41]    [Pg.446]    [Pg.396]    [Pg.161]    [Pg.155]    [Pg.32]    [Pg.138]    [Pg.463]    [Pg.220]    [Pg.96]    [Pg.112]    [Pg.879]    [Pg.296]    [Pg.72]    [Pg.879]    [Pg.6]    [Pg.248]    [Pg.879]    [Pg.576]    [Pg.296]    [Pg.37]    [Pg.775]    [Pg.1031]    [Pg.1186]    [Pg.109]    [Pg.9]    [Pg.208]    [Pg.775]    [Pg.1031]   
See also in sourсe #XX -- [ Pg.54 ]




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