Shape memory alloy (SMA) washers expand axially when heated, and the expansion for the one-way type SMA is
permanent even if the heat is removed. We investigated a method to repair bolted joint loosening defects using SMA
washers. We incorporated such a feature into our impedance-based structural health monitoring (SHM) system. An SMA
washer wrapped with a heater is installed between a bolt and the nut. Upon detection of a loosening defect, the heater is
turned on to expand the SMA washer, which in turn repairs the defect. Our experimental results show that (i) our
enhanced SHM system can detect bolted-joint loosening defects, and (ii) it can repair such defects effectively. Our
system suggests that self-repairing of some structural defects is feasible without human interventions.
An impedance-based structural health monitoring (SHM) system employs a piezoelectric patch to excite the structure
under test and capture its response. Impedance-based SHM offers several advantages over other methods such as good
performance for local damage detection and simple hardware. A major problem for impedance-based SHM is
temperature dependency. Specifically, baseline impedance profiles of structures vary as the ambient temperature changes.
In this paper, we propose a new method to compensate the effect of temperature on baseline profiles. Our method is to
select a small subset of baseline profiles for some critical temperatures and estimates the baseline profile for a given
ambient temperature through interpolation. We incorporated our method into our SHM system and investigated the
effectiveness of our method. Our experimental results show that (i) our method reduces the number of baseline profiles
to be stored, and (ii) estimates the baseline profile of a give temperature accurately.
Proc. SPIE. 7292, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2009
KEYWORDS: Ferroelectric materials, Digital signal processing, Sensors, Discrete wavelet transforms, Wave propagation, Signal processing, Structural health monitoring, Sensing systems, Signal generators, Phase measurement
We present an SHM system integrating both the impedance and the Lamb wave propagation method on a single board,
while sharing the same DSP (Digital Signal Processing) processor and the piezoelectric patches. Three functional blocks,
such as signal excitation/generation, signal sensing, and data processing, were implemented to incorporate the Lamb
wave method into our existing impedance-based SHM system. Both pitch-and-catch and pulse-and-echo schemes were
implemented for damage detection and location, respectively. Through synergetic integration of the two methods, our
SHM system can detect various types of simulated damages on aluminum plates.