Date of Award

2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Advisor

Sundaresan, Mannur J.

Abstract

Structural health monitoring (SHM) is a technology whose objective is to detect damage growth in metallic and composite structural elements long before they reach critical dimensions. Most structural health monitoring approaches that have been developed in the past have confined their attention to material degradation such as cracks in metals and delaminations in composite materials. Buckling instability is another cause of catastrophic failure commonly seen in engineering structures. The objective of this study is to develop a technique capable of detecting the onset of buckling instability in structural members and assessing the margin of safety from final collapse. The technique used is based on monitoring vibration characteristics of plate-like structures as they undergo different levels of buckling deformation. A square aluminum panel loaded under uniform shear stresses at the edges is considered for demonstrating the feasibility of this structural health monitoring technique. The buckling loads and the progressively increasing deformation in the post-buckled regime are first determined using finite element analysis. The results from finite element analysis indicate that the natural frequencies as well as mode shapes are highly sensitive to the level of deformation in the post-buckled condition. The vibration characteristics of the square panel under edge shear loading is also investigated through experiments. The plate is clamped in a “picture-frame” fixture loaded under diagonal compression to simulate edge shear loads, in an Materials Test Systems (MTS) machine. The transverse deformation pattern is measured at different load levels. The vibration characteristics are measured using a laser vibrometer. The experimental results in general agree with the results from numerical analysis, but there are differences in the mode shapes and frequencies between the experiments and finite element analysis. The differences may be attributable to initial imperfections in the plate, and the inability to apply completely clamped conditions in the experiments. However, the results demonstrate that vibration characteristics can serve as a sensitive indicator for predicting the incipient damage and final collapse of the structural element

Download

Share

COinS