Design buckling-critical

A polypropylene rod, 150 mm long is to be designed so that it will buckle at a critical strain of 0.5%. C culate a suitable diameter for the rod and the compressive load which it could transmit for at least one year. 

For AS ME Code vessels the allowable compressive stress is Factor B. The ASME Code, factor B. considers radius and length but does not consider length unless external pressure is involved. This procedure illustrates other methods of defining critical stress and the allowable buckling stress for vessels during transport and erection as well as equipment not designed to the ASME Code. For example, shell compressive stresses are developed in tall silos and bins due to the side wall friction of the contents on the bin wall. 

The fact that the cellular core provides resistance against shear and buckling stresses implies an ideal density for given foam wall thickness (Figure 7.50). This optimum thickness is critically important in designing complex stressed parts. 

Now critical buckling flexural stress > design material strength... 

Creep-buckling is an issue when the cylindrical component operates in the creep range. The protection against buckling is determined by calculating a critical stress or failure point and applying a safety factor. This safety factor is a variable in the design of such components. 

Since Fermi s early work on exponential experiments the design of reactors has depended heavily on the experimental determination of nuclear properties of multiplying assemblies in subcritical Or critical experiments. In thermal assemblies the nuclear properties studied have included macroscopic flux traverses, from which the material buckling can be obtained, and ratios related to quantities which enter into the four-factor formula for k. One ratio measured in uranium fueled assemblies is ... 

The measurements mentioned have been used for two purposes to develop semiempirical calculatlonal schemes, recipes , for the design of real reactor and to provide experimental information with which theory can be compared, ip the hope of arriving, eventually, at a real understanding bf the physics of thermal reactors. A serious problem that arises is that of the possible difference between results of measurements of a particular quantity when made in a critical assembhf and in a subcritical assembly. For example, recent work at the Savannah River liaboratory has indicated significant differences between values of the material buckling obtained from exponential and critical assemblies moderated by heavy water. A similar effect does not seem to have been observed in assemblies moderated by graphite or ordinary water. 

To meet the designed deflection of no more dian 5% the pipe wall structure could be either a straight wall pipe with a thickness of about 1.3 cm (0.50 in.) or a rib wall pipe that provides the same stiffness. It has to be determined if the wall structure selected is of sufficient stiffness to resist the buckling pressures of burial or superimposed longitudinal loads. The ASME Standard of a four-to-one safety factor on critical buckling is used based on many years of field experience. To calculate the stiffness or wall thickness capable of meeting that design criterion one must know what anticipated external loads will occur (Fig. 4.26). 

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