33 research outputs found
Signal processing for guided wave structural health monitoring
The importance of Structural Health Monitoring (SHM) in several industrial fields
has been continuously growing in the last few years with the increasing need for
the development of systems able to monitor continuously the integrity of complex
structures. In order to be competitive with conventional non destructive evaluation
techniques, SHM must be able to effectively detect the occurrence of damage in
the structure, giving information regarding the damage location. Ultrasonic guided
waves offer the possibility of inspecting large areas of structures from a small number
of sensor positions. However, inspection of complex structures is difficult as the
reflections from different features overlap. Therefore damage detection becomes an
extremely challenging problem and robust signal processing is required in order to
resolve strongly overlapping echoes.
In our work we have considered at first the possibility of employing a deconvolution
approach for enhancing the resolution of ultrasonic time traces and the potential
and the limitations of this approach for reliable SHM applications have been shown.
The effects of noise on the bandwidth of the typical signals in SHM and the effects
of frequency dependent phase shifts are the main detrimental issues that strongly
reduce the performance of deconvolution in SHM applications.
The second part of this thesis is concerned with the evaluation of a subtraction approach
for SHM when changes of environmental conditions are taken into account.
Temperature changes result in imperfect subtraction even for an undamaged structure,
since temperature changes modify the mechanical properties of the material
and therefore the velocity of propagation of ultrasonic guided waves. Compensation
techniques have previously been used effectively to overcome temperature effects, in
order to reduce the residual in the subtraction. In this work the performance of temperature
compensation techniques has been evaluated also in the presence of other
detrimental effects, such as liquid loading and different temperature responses of
materials in adhesive joints. Numerical simulations and experiments have been conducted
and it has been shown that temperature compensation techniques can cope in principle with non temperature effects. It is concluded that subtraction approach
represents a promising method for reliable Structural Health Monitoring. Nonetheless
the feasibility of a subtraction approach for SHM depends on environmental
conditions