多層ベローズの応力解析

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Expansion bellows are widely to absorb thermal expansion of tubes in pipeline system. Considering narrow piping space and small number of special positions where pipes are strongly fixed, the designing of pipelines for ship service requests the expansion bellow to have shorter effective length and smaller spring rate. The accurate stress-strain analysis concerning the deformation of bellows is necessary in order to assure the safety of the pipeline system. However, the mechanical behaviour of multilayer bellows has not been sufficiently analysed. Stress and strain applied to a monolayer bellow and a multilayer bellow during loading of axial deflection and internal pressure were experimentally measured with strain gage, and also calculated with the aid of elastic finite element method. The measurement and calculation were conducted with a 200 A-diameter bellow made of type 304 stainless steel. In the course of the finite element analysis, the gap/friction elements were developed to model the inter-surface between each layer of the mutilayer bellow. The friction coefficient was assumed to be 0 or 10000. When axial deflection was applied to a monolayer bellow, it was found that the calculated results from the finite element method were in good accordance with the experimental results from actual measurement. In case of a multilayer bellow, the calculated results coincided well with the observed results when the friction coeffecient was 0. It was noted that strain and stress generated in a multilayer bellow were much smaller than those in a monolayer bellow. In case of internal pressure, the finite element results of a monolayer bellow fitted to the measured results. The measaured values of stress and strain in a multilayer bellow were nearly equal to those in a monolayer bellow. Whereas the calculated values of stress and strain in a multilayer bellow with the friction coeffcient of 0 were a little larger than the observed values. However, it was confirmed that the finite element method was more suitable for the stress analysis of multilayer bellows than the EJMA equation. Multilayer bellows have an advantage over monolayer bellows with respect to endurance because smaller amount of stress is generated through loading, in the former than the latter.
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多層ベローズの応力解析

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