Material yield

Bromine addition to alkenes is an example of a stereospecific reaction A stereospecific reaction is one m which stereoisomeric starting materials yield products... 

An analogous sequence using terminal alkynes as starting materials yields alkynes of the type RC=CR ... 

Recall from Section 7 13 that a stereospecific reaction is one in which each stereoiso mer of a particular starting material yields a different stereoisomeric form of the reaction product In the ex amples shown the product from Diels-Alder cycloaddi tion of 1 3 butadiene to as cinnamic acid is a stereo isomer of the product from trans cinnamic acid Each product although chiral is formed as a racemic mixture... 

A comparison of the characteristics associated with propellant burning, explosive detonation, and the performance of conventional fuels (see Coal Gas, NATURAL Petroleum) is shown ia Table 1. The most notable difference is the rate at which energy is evolved. The energy Hberated by explosives and propellants depends on the thermochemical properties of the reactants. As a rough rule of thumb, these materials yield about 1000 cm of gas and 4.2 kj (1000 cal) of heat per gram of material. 

In moie ductile materials the assumptions of linear elastic fracture mechanics (LEFM) are not vahd because the material yields more at the crack tip, so that... 

The A, D, and C Rockwed scales used primarily for steel and hard materials yield hardness numbers from 20 to about 85. Hardness numbers lower than HRC 20 are invaUd the Rockwed B, G, or F scales should be used. Hardness conversions from one scale to another are available for some common... 

Partially Plastic Thick-Walled Cylinders. As the internal pressure is increased above the yield pressure, P, plastic deformation penetrates the wad of the cylinder so that the inner layers are stressed plasticady while the outer ones remain elastic. A rigorous analysis of the stresses and strains in a partiady plastic thick-waded cylinder made of a material which work hardens is very compHcated. However, if it is assumed that the material yields at a constant value of the yield shear stress (Fig. 4a), that the elastic—plastic boundary is cylindrical and concentric with the bore of the cylinder (Fig. 4b), and that the axial stress is the mean of the tangential and radial stresses, then it may be shown (10) that the internal pressure, needed to take the boundary to any radius r such that is given by... 

Code-allowable stresses are conservative with respect to stmctural failure that occurs when the limit load is reached, ie, the load that results when component deflections and distortions have destroyed its serviceabiUty. The limit load is generally reached when the stresses throughout a main portion of the component cross section exceed the material yield strength (29). 

The nitration step produces two isomers, 2,4-dinitrotoluene and 2,6-dinitrotoluene, the former predorninating. Mixtures of the two isomers are frequendy used, but if single isomers are desired, particulady the 2,4-dinitrotoluene, nitration is stopped at the mono stage and pure i ra-nitrotoluene is obtained by crysta11i2ation. Subsequent nitration of this material yields only 2,4-dinitrotoluene for conversion to the diisocyanate. 

Quinazoline alkaloids are found in at least six botanical families of which the Rutaceae are the most important in this respect. Thus, arborine was isolated from Glycosmis arborea in 1952 and in the following year appeared its structure (990) and synthesis by thermal cyclization of the phenylacetyl derivative (989) of (V-methylanthranilamide (53JCS3337>. The same plant material yields three related alkaloids, glycosmicine (991), glycorine (992) and glycosminine (993) (63T1011>. 

One Main Product Plus By-Products We shall let one unit of raw material yield %2, weights of products 1, 2, etc., respectively. The variable general expense per unit of raw material will be... 

In the case of mixtures of raw materials, the mrecd-material-usage variance can be further subdivided into (I) a direcd-material-mixture variance and (2) a direcd-material-yield variance. The former is due to the difference between the acdual and standard mixture compositions, and the latter to the difference between the actual and standard yields. Here, the standard yield is the output expected from the standard input of material. The yield variance denotes the extent of loss of material. The direc t-material-mixture variance can be illustrated by Example 22. 

The direct-material-yield variance is illustrated as follows. Let us assume that the standard mixture (cost 9.20 for 100 units) has a standard loss of 20 percent, making the cost 9.20 for 80 units, or 0,115 per unit of output. Now let us consider the actual loss to be 30 percent, leaving 70 units of output for each 100 units of input. The direct-material-yield variance is 0.115(80 — 70) = 1.15 and is unfavorable. 

Example Approximate calculation of the hardness of solids. This concept of shear yielding - where we ignore the details of the grains in our polycrystal and treat the material as a continuum - is useful in many respects. For example, we can use it to calculate the loads that would make our material yield for all sorts of quite complicated geometries. 

There is also growing interest in multi-phase systems in which hard phase materials are dispersed in softer polyether diols. Such hard phase materials include polyureas, rigid polyurethanes and urea melamine formaldehyde condensates. Some of these materials yield high-resilience foams with load deflection characteristics claimed to be more satisfactory for cushioning as well as in some cases improving heat resistance and flame retardancy. 

The total alkaloidal eontent of Ephedra varies widely, being influeneed by the speeies eolleeted and the seasonal and environmental eonditions, as has been shown by Read and by Chopra and their eolleagues. For speeially eolleeted material yields as high as 2- 56 per cent., of which 1- 8 per cent, is ephedrine, have been recorded, but about 1 per cent, of total alkaloids is not usually exceeded in the commercial product. 

Preparation—Cholestane-3(i,5a,6P-triol 3-Cathylate A solution of choles-tane-3/ ,5a,6j5-triol (1 g) in dioxane (10 ml) and pyridine (1.6 ml) is cooled to 25° and treated dropwise and with cooling with 2 ml of ethyl chlorocarbonate. After 1 hr, 25 ml of water and 1 ml of 36 % hydrochloric acid are added and the mixture is heated for 30 min on the steam bath and cooled. The product, a granular white solid, is filtered to yield 1.19 g mp 180-182°. Crystallization from methanol (75 ml) gives 0.62 g or prisms, mp 184.5-185°, and a second crop, 0.38 g, mp 183-184° (total yield 83%). Two recrystallizations of the 1st crop material yield prisms mp 184-185° [ ] —16° (CHCI3). 

In order to obtain exact results wb cansed a certain quantity ol the material to be aerted into leaves and stalks. One hundred kilos material yielded —... 

Material Yield stress (MPa) Failure time (h) (MPa Vm) Iscc (MPa Vm) Plateau velocity (m/s)... 

Decomposition following thermal treatment of the separated material yielding solid oxides and gaseous components (solid-gas interaction). 

To a solution of 3.5 uiL (25 mmol) of trimethylsilylacetylcne in 40 mL of THF are added dropwise, at — 78 °C, 10.4 mL of 2.5 M BuLi (26 mmol) in hexane. After stirring for 15 min at —78 X, 25 mL of 1 M 9-methoxy-9-borabicyclo[3.3, l]nonane in hexane are added. The mixture is stirred at —78 "C for a further 1.5 h. Then, 4 mL (33 mmol) of BF3 OEt2 are added and the mixture is stirred for an additional 15 min at — 78 °C before being allowed to warm to r.t. The volatiles are evaporated under reduced pressure to afford a white solid. After the addition of 25 mL of pentane, the suspension is stirred for a few minutes and allowed to settle. The supernatant liquid is decanted into a second flask via a double-ended needle. This procedure is repeated twice, each time with 10 mL of pentane. The combined pentane solution is cooled to — 78 X to precipitate the product. The mother liquor is removed and the crystals are dried under vacuum to afford an extremely hygroscopic, white crystalline material yield 6.52 g (90%). 

The first point of zero slope on the curve (point C) is identified with material yielding and so its coordinates are called the yield strain and stress (strength) of the material. The yield strain and stress usually decrease as temperature increases or as strain rate decreases. The final point on the curve (point D) corresponds to specimen fracture. This represents the maximum elongation of the material specimen its coordinates are called the ultimate, or failure strain and stress. Ultimate elongation usually decreases as temperature decreases or as strain rate increases. 

Brittleness Brittle materials exhibit tensile stress-strain behavior different from that illustrated in Fig. 2-13. Specimens of such materials fracture without appreciable material yielding. Thus, the tensile stress-strain curves of brittle materials often show relatively little deviation from the initial linearity, relatively low strain at failure, and no point of zero slope. Different materials may exhibit significantly different tensile stress-strain behavior when exposed to different factors such as the same temperature and strain rate or at different temperatures. Tensile stress-strain data obtained per ASTM for several plastics at room temperature are shown in Table 2-3. 

As an example eonsider a thin walled tube, free to pivot at both ends, where we want it to yield (exeeed its elastie limit) just as it buckles. Assume it is a high strength material (yield stress O.OIE ). We then obtain L/r = 31 or L/a = 22. 

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