John Kihiu

Geometric Constants in Plain Cross-Bored Cylinders

A three-dimensional FEM computer program was developed to establish the stress distributions and SCFs in thick walled cylinders with flush and nonprotruding plain cross bores under internal pressure. The displacement formulation and eight-noded brick isoparametric elements were used. The Frontal solution technique was used due to the limited computing facilities. In the far field, the FEM stresses and displacements were in good agreement with the through thickness analytical values. The variation of SCF with d was established for various thickness ratios. For k> 1.25, the maximum hoop stress occurred away from the crotch corner when d≤0.2. For k=1.25, the maximum hoop stress occurred away from the crotch corner when d≤0.15. For k≥1.75, d was found to be a geometrical constant equal to 0.2 where the k values have a SCF of 2.734. For k <I.75, d was found to be a geometrical constant equal to 0.11 where the k values have a SCF of 2.67. A new categorization of cylinders has been proposed: thin shells, thick shells, and thick cylinders.

Time and Space Management in Structural Analysis Problems

In this work, a static linear elastic stress analysis has been performed on a thick-walled cylinder with closed ends under internal pressure. The displacement formulation of the finite element method of structural analysis has been used. Three programs using different solution schemes in Fortran code have been developed. Each of the solution schemes was tested on the different operating systems of DOS and Windows. The thick-walled cylinder was discretized in the radial, hoop and axial directions. The time taken to evaluate the primary and secondary variables during each of the possible discretization modes and the accuracy achieved were determined. The effect of the discretization mode on the time and accuracy of the solution has been presented and highlighted. The results obtained by using the two different operating systems have been compared and the advantages of each system are discussed. The results of using any of the solution schemes have been presented and discussed. The advantages, disadvantages and limitations of all the solution schemes are also discussed and highlighted. The importance and applications of the results obtained are emphasized.

Overstraining of flush plain cross-bored cylinders

Abstract A three-dimensional finite element method computer program was developed to establish the elastic-plastic, residual and service stress distributions in thick-walled cylinders with flush and non-protruding plain cross bores under internal pressure. The displacement formulation and eight-noded brick isoparametric elements were used. The incremental theory of plasticity with a 5 per cent yield condition (an element is assumed to have yielded when the effective stress is within 5 per cent of the material yield stress) and von Mises yield criterion were assumed. The frontal solution technique was used. The incipient yield pressure and the pressure resulting in a 0.3 per cent overstrain ratio were established for various cylinder thickness ratios and cross bore-main bore radius ratios. For a thickness ratio of 2.25 and a cross bore-main bore radius ratio of 0.1, the stresses were determined for varying overstrain and an optimum overstrain ratio of 37 per cent was established. To find the accuracy of the results, the more stringent yield condition of 0.5 per cent was also considered. The benefits of autofrettage were presented and alternative autofrettage and yield condition procedures proposed.

Overstrain in flush optimal-chamfered cross-bored cylinders

Abstract A three-dimensional finite-element method computer program was developed to establish the elastic—plastic, residual, and service stress distributions in cylinders with flush and non-protruding optimal-chamfered cross-bores under internal pressure. Eight-noded brick and four-noded tetrahedral isoparametric elements and the displacement formulation were used. The incremental theory of plasticity with a 5 per cent yield condition and von Mises yield criterion were assumed. The incipient and 5 per cent overstrain (ov) pressures were established for various thickness ratios and cross-bore to main bore radius ratios. For the optimum chamfer angle geometrical configuration, the stresses were determined for varying ov. The maximum and minimum effective stresses were located 7.5° from the meridional and transverse planes, respectively. Meridional plane through thickness yielding occurred at an ov of 41 per cent. The service stress gradients at the cross-bore chamfer end increased with ov for ovs >30 per cent. Stress reversals were eliminated for overstrain >27 per cent. Alternative autofrettage and yield condition procedures were proposed.