Incremental collapse

Excessive plastic deformation—The primary and secondary stress limits as outlined in ASME Section Vlll, Division 2, are intended to prevent excessive plastic deformation and incremental collapse. 

Plastic instability—Incremental collapse incremental collapse is cyclic strain accumulation or cumulative cyclic deformation. Cumulative damage leads to instability of vessel by plastic deformation. 

Thermal stress ratcheting is progressive incremental inelastic deformation or strain that occurs in a component that is subjected to variations of mechanical and thermal stress. Cyclic strain accumulation ultimately can lead to incremental collapse. Thermal stress ratcheting is the result of a sustained load and a cyclically applied temperature distribution. 

Ratcheting is produced by a combination of a sustained extensional load and either a strain-controlled cyclic load or a cyclic temperature distribution that is alternately applied and removed. This produces cycling straining of the material which in turn produces incremental growth (cyclic) leading to what is called an incremental collapse. This can also lead to low cycle fatigue. 

Potential failure modes and the various stress limits categories are related. Limits on primary stresses are set to prevent deformation and ductile burst. The primary plus secondary limits are set to prevent plastic deformation leading to incremental collapse and to validate using an elastic analysis to make a fatigue analysis. Finally, peak stress limits are set to prevent fatigue failure due to cyclic loadings. 

The first step in developing a resistance function is to determine the plastic section capacities, such as plastic moment, Mp, as shown in Figure 7.1. The next step is to determine the sequence of plastic hinge formation and the corresponding load and deformation values. This is done by incrementally applying loads until a collapse mechanism is formed as illustrated in Figure 7.2 for a fixed end beam with a uniform load. 

A finite element method is employed to study the nonlinear dynamic effect of a strong wind gust on a cooling tower. Geometric nonlinearities associated with finite deformations of the structure are considered but the material is assumed to remain elastic. Load is applied in small increments and the equation of motion is solved by a step-by-step integration technique. It has been found that the cooling tower will collapse under a wind gust of maximum pressure 1.2 psi. 13 refs, cited. 

The disordering of single-stranded poly(A) and poly(C) helices by Cu(II) is demonstrated by the collapse of the ORD curves characteristic of these helices when increments of Cu(II) are added (Figure 1). The... 

Support for this general picture comes from the electron diflFraction observations on the collapsed monolayer. If the sharp reflection at 5.36 A is a true meridional reflection (better orientation is necessary to be certain), it can be indexed as 005 and the 1.489 A meridional reflection as 00,18 for a hexagonal cell with c = 26.8 A. An 005 reflection would not be produced by a perfect helix, but it can probably be accounted for assuming a distorted a-helix, the distortions being caused by the unsatisfactory packing of the two forms. The reduced axial increment per residue, 1.489 A compared with 1.495 A in the enantiomorphic form, shows that the packing causes the helix to shorten slightly. 

If the cylindrical briquette of powder does not collapse under the weight of one disk, add another in (6 mm) Micarta disk, then the in (13 mm) disk, and if the briquette still stands after 30 seconds, add the weight of the plunger too. In 30-second intervals, add weights on top of the plunger in half-pound (227 g) increments until the briquette collapses and note the total load at failure. 

For further study, three samples which did not exhibit pressure decay after compression to 13 dynes/cm were selected. The stability limit for films of these materials was established by incremental compression, holding the monolayer at constant area for up to 15 min as surface pressure was progressively increased. In the second part of Table I, a typical experiment is detailed. By this procedure, these monolayers were each stable to a surface pressure of 16-18 dynes/cm. There was no hysteresis in compression-expansion cycles (at 2-10% of the total film area per minute) as long as this surface pressure was not exceeded. On the other hand, in a continuous compression experiment (at such rates), surface pressures of 27—32 dynes/cm could be developed before obvious evidence of film collapse (e.g., an increase in compressibility, or bending over of the 7r-A curve). Figure 1 shows the ir-A curves for these three samples, and characterization data are given in Table II. 

The stepladder (SL) model is simply a collapsed Gaussian, or delta function, distribution centered at the constant energy transfer increment value (Equations 19 and 20). Thus, in the spirit of quantized... 

Total-energy calculations (plane waves, pseudopotentials, GGA, VASP) allow the optimization of all lattice parameters and atomic positions. In addition, the energetically most favorable ordered arrangement of the N and O atoms over the three anionic sites is easily found. The calculated molar volume of a-TaON, however, turns out to be 20% smaller than the experimentally reported one, a real structural collapse This DFT finding might have also been derived, although much more cheaply, from the volume increments of Ta +,, and N, and the predicted 30 cm /mol is also 25% smaller than the reported volume for a-TaON (37.5 cm /mol). It is immediately clear that the... 

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