No abstract

Design Rules in the ASME Code, Section VIII, Division 1, cover the design of unreinforced and reinforced rectangular pressure vessels. These rules are based on “infinitely long” vessels of non-circular cross section and stresses calculated are based on a linearized “small deflection” theory of plate bending. In actual practice, many pressure vessels can be found which are of finite length, often operating successfully under pressures two to three times as high as those permitted under the Code rules cited. This paper investigates the effects of finite length on the design formulae given by the ASME Code, and also a design method based on “large deflection” theory coefficients for short rectangular pressure vessels. Results based on analysis are compared with values obtained from finite element computations, and with experimental data from strain gage measurements on a test pressure vessel.

In the present state of development of the polymer industry, all of the lower cost, widely used, plastics exhibit some susceptibility to environmental stress crazing. Past developments have improved some polymers' resistance to this phenomenon (e.g., the addition of rubber to polystyrene) and this paper , considers one such improved polymer, high-impact polystyrene, and examines its craze and creep resistance in the alcohols. This family of fluids does not affect the unstressed polymer but has a marked effect when the polymer is stressed. The results of creep tests at different stresses indicate the existence of a delay time after which the creep rate'accelerates rapidly. The requirement of a definitive time under stress before this acceleration occurs is supported by the results of cyclic stress tests. Plots of delay time against stress for the different alcohols show two distinct regions: (i) at high stresses, where the delay time increases from methanol to butanol and the mechanism would appear to be one of molecular volume controlling the mobility ofthe fluid to "penetrate" the polymer, and (ii) at low stresses, where the delay time decreases from methanol to butanol and the criterion would appear to be that of ability to "plasticize" the polymer as evidenced by the solubility parameters.

The effects of seventeen different fluids on polystyrene is investigated. The fluids are divided into three groups by their effect on the unstressed polymer, namely dissolving, softening, and non‐softening fluids. The accelerated rates of creep of the polymer when immersed in the dissolving fluids are shown to be due to the reduction in the load‐bearing area resulting from dissolution at the surface, The increase in creep strain rates (relative to that in air) when exposed to the softening fluids result from the combined effects of: (i) the accumulated deformation of numerous crazes; (ii) the reduction in stiffness of the surface layer due to the softening effect of the fluid; and (iii) the swelling of the softened layer. In the case of the non‐softening fluids, the creep rates “accelerated” after a specific delay time which is a function of the applied stress. For these fluids there exists a critical stress below which crazing does not occur. This critical stress is shown to increase with increasing difference between fluid and polymer solubility parameters.

A rectangular finite-element model has been developed for thermal-stress analysis of shallow shells. The elemental equations are obtained from a two-field variational principle which employs equilibriating stress fields within the elements and compatible displacement fields along inter-element boundaries. The extremization of the variational functional tends to satisfy the compatibility requirements within the elements and equilibrium conditions along inter-element boundaries. The element is employed for thermal-stress analysis of several examples and the numerical results obtained are compared with some analytical results.