Pulsating stress

The specimen (R = 0, R = -1) demonstrate clear effects of corrosion fatigue (Fig. 6 and 7). There evidently is a good correlation of the fatigue strength reduction between the pulsating stress (R = 0, uniaxial) and the pulsating pressure loaded pipe specimen (Fig. 8). The reversed bending probes (R = -1, uniaxial) exhibit some deviations. 

The corrosion fatigue data from uniaxial tests can be transmitted to the notched pulsating pressure loaded components quantitatively or with additional safety. The uniaxial pulsating stress yields to be the stricter criterion. 

The weight of the trunk on the anterior edge of the upper portion of the sacrum causes increased contact pressure between the two bony surfaces, leading to absorption of bone, which permits further kyphosis to occur. The disc, which is not protected by a competent posterior facet mechanism, is subjected to pulsating stresses that are in excess of its experimental maximums, and its starts to degenerate and fail, compounding the deformity. 

Springs were made of steel 60C2A (C - 0.57-0.65%, Si - 1.5-2.0%). Testing loading was at pulsating stress. The picture caption states the outer fibers strain amount, which is the elongation of the outer fiber under spring... 

The pulsations can cause the use of excess horsepower when compared to the ideal or a system design that reduces pulsations and thereby improves cylinder performance and efficiency. The pulsation shaking forces in the suction and discharge dampeners (bottles) can be evaluated by computer analysis, and the magnitude and frequency in hertz can be reduced to an acceptable level by adjusting the dimensions (size) of the dampeners. The magnitude of the internal forces directly affects the mechanical stress on the nozzles of the cylinder and of the dampeners. Compressor... 

As von Nimitz points out, only cyclic stresses are directly related to failure probability. These stresses are often produced by pulsations in the fluid system, by mechanical vibrations produced by the mechanical movement of certain equipment components, and as a result of the fluid pulsations. Figure 13-8 lists the sequence of events that leads to most failures of equipment and piping. 

Figure 13-8. Relationship of pulsations to vibrations to cycle stresses. (Used by permission von Nimitz, W. W. Lecture of Reference 13, Part 1, Table 1, proceedings of the 1974 Purdue Compressor Technology Conference.)...

Although the titanium oxide layer at the surface of the nitinol is highly biocompatible and protects the underlying substrate from electrochemical corrosion, the titanium oxide layer itself is mechanically very brittle. Under mechanical stress, such as the shear of blood flow in the aorta or under the bending moments of aortic pulsations, the titanium oxide surface layer can fracture, exposing the underlying metal to corrosion. Not only is corrosion undesirable in terms of biocompatibility (i.e., leaching of nickel and its... 

The so-called hypercompressors for the production of LDPE represent a special case. The ethylene is compressed in a primary piston compressor, with several stages up to around 200 to 300 bar the hypercompressor (or secondary compressor) brings the gas up from there to 3000 bar. The hypercompressors show pairwise-opposite-cylinders, and are built with up to fourteen cylinders in a multiplex arrangement. The components loaded by an internally pulsating pressure are either shrunk and/or autofrettage-treated in order to implement protective compressive residual stresses (Fig. 4.1-34). 

It should be remembered [39], that when evaluating data about fatigue limits in the pulsating or alternating mode which have been determined with inert fluid environments, that the corrosion fatigue may not only effect remarkably the reduction of the admissible stresses but also depends on the number of cycles (a continuous small slope of the Wohler-curve). 

When the wall of a cylindrical pressure vessel is subjected to a temperature gradient, every part expands depending on the coefficient of linear thermal expansion of the steel. The parts at lower temperature impede the expansion of those parts with higher temperature, and induce additional thermal stresses. To estimate the transient thermal stresses which regularly appear e.g. during start-up or shut-down of process components or as well as a result of process interruptions and in the case of pulsating temperature conditions during operation. Informations about the temperature distribution across the vessel wall as a function of radius and time [12]... 

The design of thickwalled components for pulsating pressure is based on the stress calculation with analytical or numerical methods and the determination of the maximum equivalent stress in relation to the admissible stresses at uniaxial conditions. The latter have to be extracted from Woehler-tests with specimen. If the stresses yield too large at load conditions including a safety factor, the design must be optimized by avoiding the major stress concentrations at bore intersections. The avoidance of T-intersections is reducing stresses by factor 2-3 (Fig. Id). 

The proportionality constant typically is close to unity [Seibert and Fair, Ind. Eng. Chem. Res., 27(3), pp. 470-481 (1988)]. Note that Eq. (15-42) indicates the maximum stable drop diameter and not the Sauter mean diameter (although the two are proportionally related and may be close in value). Smaller drops may be formed at the distributor due to jetting of the inlet liquid through the distributor holes or by mechanical pulsation of the liquid inside the distributor [Koch and Vogelpohl, Chem. Eng. Technol., 24(12), pp. 1245-1248 (2001)]. In static extractors, hydrodynamic stresses within the main body of the... 

Figure 3.5 Velocity (A) and shear stress profiles (B) for consequent time moments 5 - t = 4At = AT/20, 6 -1 = 5At, etc. for a half-period of the pressure pulsations with the amplitude a = 2.5 and the high frequency a> = 50. Bottoms - duct without EPR, tops - with EPR 6 = 0.5 and A = 50.

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