Local thin area

Great care is taken that we design blow molds to avoid thin or weak regions that could result in premature failure. Molds are designed to avoid excessive draw into corners that would result in locally thin areas. For this reason, blow molded products invariably have rounded corners. Another potential source of weakness is the pinch-off line. To compensate for this fact, it is common to program the parison to produce a thickened base. 

Occasionally a vessel shell will sustain damage or be overground in a local area such that the thickness in the damaged area is below the minimum wall thickness. This is known as a Local Thin Area or LTA . ASME VIII-1 has allowance for such a case as long as certain proportions and guidelines are followed. These guidelines are taken from ASME Section VIII, Division 1, Mandatory Appendix 32 and are presented here. 

The proof pressure method is permitted where DOT or TC regulations do not require the determination of total and permanent volumetric expansion of the cylinder. It consists of visually examining the cylinder under specified test pressure for leaks or deformation of localized thinned areas. 

On the loaded side of a slab subjected to an intense reflected blast wave, a region of the slab will fail if the intensity of the compressive wave transmitted into the slab exceeds the dynamic compressive strength of the material. For an intense wave striking a thin concrete slab, the failure region can extend through the slab, and a sizeable area turned to rubble which can fall or be ejected from the slab. For a thicker slab or localized loaded area, spherical divergence of the stress wave can cause it to decay in amplitude within the slab so that only part of the loaded face side is crushed by direct compression. 

It is not only the can body that has to be kept free from corrosion the easy-open end must also be protected. This end is scored through to create a locally thinned line of metal - the tear line when the can is opened. If this area of the can is subject to stress corrosion, then rapid leakage can occur. 

In other words, we ignore the thin layer near the cathode surface where the lines of current are crowding toward those small electroactive sites on the surface. This is a fair assumption if the sizes of the lithographie features are much smaller than the scale of the problem. Since the active and superficial current densities are related directly by the local active-area density,... 

Auerbach (37) recorded with a diode laser in a thin film of a solvent-coated polymer-metal ion salt complex (e.g., poly-2-vinylpyridine-AgNO3). Using short-duration pulses (120 ns) of 820-nm light (10 mW), he showed that high reflectivity marks could be created that could be read with a lower power diode laser. The mechanism is believed to involve thermally induced electron transfer from the polymer to the metal ion forming localized metal areas (Ag + e — Ag°). The concept is not limited to silver salts of gold, copper, and tellurium can be used. Polymers other than vinylpyridine that can form charge-transfer complexes with metal ions should function as electron-transfer binders. 

Inliers or windows where salt is locally thin or absent from an area that is surrounded by salt usually indicate dissolution of salt, provided that the feature cannot be explained reasonably as a depositional feature. Examples of such inliers were shown by Jordan and Vosburg (1963) in the Flowerpot salt in Beaver County, Oklahoma, and evidence of such dissolution is found in the breccia chimneys and pipes [see (6) above]. 

In the case when a material is not uniform but has a recess, the danger of failure is increased. Under static conditions, the distribution of local stresses and strains is simply inversely proportional to the cross-sectional area, while under dynamic conditions, the stresses and energy are localized within thin areas, which increases the likelihood of sample failure. This is why the unthreaded part of the bolt is typically cut to the lowest diameter of the thread in this way the impact strength of the bolt can be enhanced. 

Elastohydrodynamic Lubrication (EHL). Lubrication needs in many machines ate minimized by carrying the load on concentrated contacts in ball and toUet beatings, gear teeth, cams, and some friction drives. With the load concentrated on a small elastically deformed area, these EHL contacts ate commonly characterized by a very thin separating hydrodynamic oil film which supports local stresses that tax the fatigue strength of the strongest steels. 

Similar to IFP s Dimersol process, the Alphabutol process uses a Ziegler-Natta type soluble catalyst based on a titanium complex, with triethyl aluminum as a co-catalyst. This soluble catalyst system avoids the isomerization of 1-butene to 2-butene and thus eliminates the need for removing the isomers from the 1-butene. The process is composed of four sections reaction, co-catalyst injection, catalyst removal, and distillation. Reaction takes place at 50—55°C and 2.4—2.8 MPa (350—400 psig) for 5—6 h. The catalyst is continuously fed to the reactor ethylene conversion is about 80—85% per pass with a selectivity to 1-butene of 93%. The catalyst is removed by vaporizing Hquid withdrawn from the reactor in two steps classical exchanger and thin-film evaporator. The purity of the butene produced with this technology is 99.90%. IFP has Hcensed this technology in areas where there is no local supply of 1-butene from other sources, such as Saudi Arabia and the Far East. 

Figure 4.4 Corrosion product mounds covering localized areas of metal loss on an aluminum heat exchanger tube. Attack initiated beneath a thin deposit layer.

Resistance to puncture is another type of loading. It is of particular interest in applications involving sheet and film as well as thin-walled tubing or molding and other membrane type loaded structures. Hie surface skins of sandwich panels are another area where it is important. A localized force is applied by a relatively sharp object perpendicular to the plane of the sheet of material being stressed. If the material is thick compared to the area of application of the stress, it is effectively a localized compression stress with some shear effects as the material is deformed below the surface of the sheet. 

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