Title page for ETD etd-02232001-114006

Type of Document

Dissertation

Author

Ionita, Axinte

Author's Email Address

ionita@vt.edu

URN

etd-02232001-114006

Title

Finite Element Analysis of the Deformation of a Rubber Diaphragm

Degree

PhD

Department

Engineering Science and Mechanics

Advisory Committee

Advisor Name	Title
David Y. Gao	Committee Chair
Edmund G. Henneke	Committee Member
Ken Reifsnider	Committee Member
Liviu Librescu	Committee Member
Saad A. Ragab	Committee Member

Keywords

Diaphragm
Rubber
Eversion
Buckling
Finite Element

Date of Defense

2001-02-05

Availability

unrestricted

Abstract

Several rubber diaphragms, of the same type used inside an hydraulic accumulator, failed
a short time after they were mounted. While there is nothing special with these failures
the cost, in some cases can be high. A closer look, at the damaged diaphragms reveal an
interesting nonsymmetric radial deformation accompanied in some cases by cracks. Most
of the analyses regarding the failures of rubber diaphragms oer explanations only from a
chemical or material science point of view. We propose in this thesis a new perspective from a
mechanical-structural engineering view. Therefore the main goal of the thesis is to investigate
the deformation of a diaphragm and based on this analysis to propose an explanation for
formation of the cracks. It is shown that the analysis of the diaphragm problem leads to
a pseudo-nonconservative system and involves a buckling, a post buckling (dynamic snap-
through), an eversion, and a load response analysis. The problem is approached numerically
using the nite element method. The character of pseudo-nonconservativeness of the system
requires, in this case, an update of the tangent stiness matrix with a certain stiness
correction. This new correction is proposed also. The result is valid not only for this
particular problem but for the entire class of problems to which the diaphragm belongs.
This correction is implemented in an existing nite element program (NIKE3D) and used
to analyze the diaphragm deformation. The results indicate that under the typical load
condition for a diaphragm a certain deformation pattern occurs, and this can lead to the
formation of cracks. This deformation matches extremely well with the actual deformed
shape of a typical failed diaphragm. It is shown that the deformation pattern depends on
the structural properties of the diaphragm rather than on the magnitude of the applied load.
The nonsymmetry in the diaphragm deformation and the dierence in the crack development
is explained also.

Files

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