ART is interested in developing a double diaphragm for operation in a pressure chamber. The chamber is a pressure vessel made by assembling two hemispherical dome shaped vessels. The double diaphragm is sandwiched between the dome shaped vessels. The double diaphragm physically divides the whole pressure chamber into two cavities; upper cavity and lower cavity. The double diaphragm shall have a leak adaptor at its periphery. The leak adaptor shall be inserted and sandwiched between the diaphragms of the bladder at the periphery. The fatigue life of the diaphragm shall exceed the duration of maintenance, so that it can be replaced at each maintenance interval.
The physics involved in the simulation are complex and can be summarized as follows:
- Contact between the diaphragms and between the diaphragms and cavities had to be included.
- Pressure loading conditions on the diaphragms make it deform to 300 % strain and higher.
- Large expansion deformation along with multi-step analysis procedure had to be carried out.
- The diaphragm material is non-linear and needs to be fully defined for the design to be properly validated.
Figure 1: FEA Model of the Diaphragm and the Deformed Shape
Results and Discussion:
The FEA model and the deformation plots are shown in the Figure 1. The diaphragm and the dome shaped cavities were modeled in Abaqus using 3-dimensional continuum elements. High stresses were noted along the curvatures in the design. An iterative design optimization procedure was carried out to lower stresses. The curvatures were represented so that the material deforms with as low strains as possible. The large deformation elastic analysis allowed the materials to be adequately defined. The stress-concentration locations were identified as ‘hot-spots’ and are fatigue-critical locations. The geometrical curvature in the diaphragm was used as an optimization variable to generate a better stress mitigating design.
- Dassault Systemes, Abaqus theory and reference manuals.
- Ionita, A. Finite Element Analysis of the Deformation of a Diaphragm, PhD Dissertation, Virginia Tech 2001.
- Ren, Finite Element Modeling for the Mechanical Behavior of Silicon Diaphragms Using Comsol Multiphysics, COMSOL Conference 2009.
- Migliavacca, et al. Mechanical behavior of coronary stents investigated through the finite element method, Journal of Biomechanics, June 2002.