Sharp comers

Whilst the aliphatic nylons are generally classified as being impact resistant, they are affected by stress concentrators like sharp comers which may lead to brittle failures. Incorporation of mbbers which are not soluble in the nylons and hence form dispersions of rubber droplets in the polyamide matrix but which nevertheless can have some interaction between mbber and polyamide can be most effective. Materials described in the literature include the ethylene-propylene rubbers, ionomers (q.v.), polyurethanes, acrylates and methacrylates, ABS polymers and polyamides from dimer acid. 

C. E. Inglis, Stresses in a Plate Due to the Presence of Cracks and Sharp Comers, Trans. Inst. Naval Architects, 1913, 55, 219 241. 

The presence of stress raisers, including sharp comers and imperfect welds, produces locally high stress levels. These should be avoided where possible or taken into account when designing the materials for use in environments in which they are susceptible to stress corrosion cracking or corrosion fatigue. 

After a material type and grade that will fulfill performance requirements has been decided upon, steps should be taken to ensure that degrading features such as inside sharp comers, nonuniform wall thicknesses, etc., are... 

Basically, in the vicinity of a sharp comer all fringes converge toward the apex. Having a high density of lines at this point indicates the presence of high stress level. At a rounded corner there will be considerably less concentration. Besides the molding problems, sharp corners often cause premature failure because of the stress concentration. To avoid these problems, inside comer radii should be equal to one-half the nominal wall... 

Sharp corner As reviewed, and never to many times, when a drawing does not show a radius, the tendency is for the toolmaker while manufacturing a mold to leave the intersecting machined or ground surfaces as they are generated by the machine tool. The result is a sharp comer on the molded product. Such sharp comers on the insides of products are the most frequent property detractors. 

Products in this process can have deep sections and relatively sharp comers. However RM flat, particularly large relatively uniform wall thickness surfaces are difficult if not impossible to produce. This process can be used to mold complex products that may require three or four split molds. Also, different finished surfaces are obtained. For example, the products surface finish is dictated by the inside surface of the mold. This makes it easy to obtain smooth as well as textured surfaces on the product. Raised or depressed letters, fluting, and other decorative inscriptions may also be molded. 

Since, for obvious reasons, the series of Poincar6 cannot be applied here, attempts were made to use the so-called asymptotic expansions (this approach is to a great extent also due to Poincar6) which are not analytic and, for that reason, seem to be adequate when a trajectory has to turn around a sharp comer, as was explained in Section 6.28. 

TPEs in comparison to thermoset are also suited for thermoforming, which is a fast, low-cost production. The maximum draw ratio decreases with decrease in hardness. Draw ratio up to 0.1 can be attained with TPEs in the hardness range of 40-50 Shore D. The major limitations are to avoid undercut sharp comers, and adequate taper angle for rapid ejection of parts. 

Retreating blade turbine Yes No limitation 0.33 (Nre)0-67 (Np,-)0 33 (Pb/P.)0 14 Glassed-steel impeller. Three retreating blades. The lower constant (0.33) for the glassed-steel impeller is attributed to greater slippage around its curved surfaces than around the sharp comers of the alloy-steel impeller. 

Stainless steels exhibit the best resistance to corrosion when the surface is oxidized to a passive state. This condition can be obtained, at least temporarily, by a so-called passivation operation in which the surface is treated with nitric acid and then rinsed with water. Localized corrosion can occur at places where foreign material collects, such as in scratches, crevices, or comers. Consequently, mars or scratches should be avoided, and the equipment design should specify a minimum of sharp comers, seams, and joints. Stainless steels show great susceptibility to stress corrosion cracking. As one example, stress plus contact with small concentrations of halides can result in failure of the metal wall. 

Y. Turbulent flow, noncircular ducts Use correlations with j 4 cross-sectional area wetted perimeter Can be suspect for systems with sharp comers. Parallel plates , 2 htv dgn = 4 - 2to + 2 h [141] p. 289... 

Abrasiveness. This property is closely related to hardness in homogenous materials, but can be affected by particle shape, eg, the presence of sharp comers. In many cases a small proportion, as low as 0.5%, of a hard impurity is enough to cause severe wear to many high speed machines. 

Air bubbles, mould marks and total lack of sharp comers from cutting indicate a moulded simulant (Figs 10.18-10.20). 

Figure 11.57 SEM images of four different stages of galvanic replacement reaction with Ag nanocubes serving as the sacrificial template. (A to D) Ag nanocubes with sharp comers titrated with 0.1 mM HAUCI4,0,0.6,1.6, and 3.0 mL, respectively. (E to H) Ag nanocubes with truncated comers reacted with the same volumes of 0.1 mM HAuCld as for the sharp cubes. (Inset) TEM image of each respective sample. Reprinted with permission from reference [134]. (2006) American Chemical Society.

Xia and coworkers have demonstrated that the polarization of light plays an important role for nanoparticles with anisotropic shapes, especially with tmncated comers [77]. Optical dark-field mode imaging was employed to identify individual silver nanocubes deposited on silicon substrate as shown in Fig. 15.10a. Raman spectra were collected from the nanocubes, which were oriented in different directions with respect to the laser polarization. Subsequent SEM imaging of the same cubes enabled the authors to directly correlate the orientation of the nanocubes with respect to the light polarization and the SERS enhancement factor. They observed dramatic variation in SERS intensity when the nanocubes were oriented at different angles relative to the polarization of excitation laser as shown in Fig. 15.10b. SERS spectra of 1,4-benzenedithiol adsorbed on Ag nanocubes oriented in different directions showed different intensities with respect to the light polarization direction. The individual nanocubes with sharp comers were the most... 

The studies were carried out in air-conditioned areas from which hazards of accidental injury had been eliminated as thoroughly as possible (e.g., glass panels in doors were replaced with wood, electric outlets and cables shielded, and sharp comers padded). Beds and collet, messing and recreational facilities were provided within the research areas. The research was conducted under surveillance of qualified physicians, who administered all injections or oral doses of the test substances. When volunteers were exposed to inhalation of vapors or aerosols, the concentrations of these substances in the air to be breached by the subjects were established by appropriate personnel. Breaching of the contaminated air by the volunteers was observed and supervised by physicians. After an exposure to an agent, the volunteers were observed continuously for 8-24 h, and then Intermlctently for up CO 14 d. In a few cases, followup studies were made 6 mo or more after the exposure. 

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