Abstract
Using the closed-form solution of obround shell, the stress and displacement of obround shells were theoretically analyzed. With the straight segment introduced, the maximum stresses and displacement of obround shells increase significantly. The length of the straight segment is a key factor in determining the maximum stress and location. For obround shells, the maximum stress is the function of two dimensionless geometrical parameters. Parameter study results show that for most engineering applications, the maximum stress occurs in the middle section of the curved segment. The maximum displacement appears in the middle of the straight segment. The stress increment caused by the out-of-roundness of cylindrical shells was studied. A cylindrical shell with out-of-roundness is treated as an elliptical shell. Two methods are proposed to estimate the maximum stress in the out-of-roundness shells. The ovalized cylindrical method simplifies the numerical analysis model. Complex out-of-roundness details are replaced by ellipse. The virtual obround method provides a theoretical analysis tool. The analysis results show that the stress increase of out-of-roundness shell depends not only on the amount of distortion, but also on the type of distortion. The equivalent out-of-roundness is defined to normalize the distortion according to stress concentration level for each distortion type. Based on existing design codes, simply limiting the measured diameter differences does not appear to be sufficient. The analysis results show that even within the range of out-of-roundness value accepted by the codes, the stress increment caused by out-of-roundness may exceed expectations. In some situations, especially for thin- to medium-walled shells, the minimum required wall thickness estimated by the existing codes may be underestimated.
