Finite element analysis of high pressure bolted flange connections

Two dimensional axisymmetric finite element models and three dimensional finite element models of high pressure bolted flange joints were generated to investigate the stresses in these joints. This investigation includes comparisons for axisymmetric loading in both 2-D and 3-D models, the effects of non-axisymmetric bolt pretensions in the 3-D models, and the differences between 2-D and 3-D models subjected to non-axisymmetric loading. The results of analyses including nonlinear material behavior for the 3-D models are presented. The methods used to model the bolt pretensions, applied bending moments and shear forces are discussed. In the 3-D models, the bolt pretensions are created by using temperature changes in the bolts. A one-step method for calculating the temperature changes required to produce the desired pretensions is developed and presented.;Analyses were performed to investigate the effects of unevenly distributed bolt pretensions on the distribution of von Mises stresses in the bolted flange joint. Comparisons were made between results from 3-D models with uniformly and unevenly distributed bolt pretensions. The comparisons indicated differences in von Mises stress at various points up to 15 percent. Comparisons were also made between 2-D models with uniformly distributed volt pretensions and 3-D models with unevenly distributed bolt pretensions. These comparisons indicated differences in von Mises stress at various points up to 26 percent.;Applied bending moments were converted to equivalent axial forces for use in the 2-D models. It was found that the largest von Mises stresses in 3-D models did not occur on the side of the connection where the bending stresses and applied axial stresses were additive. Hence, in 2-D models where the equivalent axial force (for bending moment) and applied axial forces were added, the 2-D models underestimated the maximum von Mises stresses obtained from the 3-D models.;The extension of the plastic region in nonlinear static analyses for the high pressure fuel duct was confined to the pipe section of the connection and dominated by the internal pressure. It was also found that changes in bolt stresses in the 3-D models were also dominated by the internal pressure. The internal pressure was found to cause the average axial bolt stress (and total clamping force) to decrease while the external applied loads caused the average axial bolt stress to increase.