TWI is involved in two broad monitoring fields. Structural Health Monitoring and Condition Monitoring. For ease of distinction and for TWI purposes, Structural Health Monitoring is concerned, as its name implies, with the structure, whilst Condition Monitoring deals with machinery, mainly moving components (gears, bearings and the like), but including boilers and heat exchangers.
Structural Health Monitoring (SHM) is the process of implementing a damage detection and characterization strategy for engineering structures. Damage is defined as changes to the material and/or geometric properties of a structural system which adversely affect its performance. The SHM process involves the observation of a system over time using periodically sampled response measurements from an array of sensors, the extraction of damage-sensitive features from these measurements, and the statistical analysis of these features to determine the current state of system health. For long term SHM, the output of this process is periodically updated information regarding the ability of the structure to perform its intended function in light of the inevitable aging and degradation resulting from operational environments. After extreme events, such as earthquakes or blast loading, SHM is used for rapid condition screening and aims to provide, in near real time, reliable information regarding the integrity of the structure.
The elements of an SHM system are:
- The structure
- Sensors
- Data acquisition system
- Data transfer and storage mechanism
- Data management
- Data interpretation and analysis
Benefits
- Improved safety and reliability
- Reduced inspection and maintenance costs
- Continuous monitoring process
TWI's SHM Programmes
The background to TWI’s involvement with SHM is its long term research into the three ingredients that lead to the failure of a metallic structure namely a defect, an imposed stress and a susceptible microstructure. TWI has been deeply involved in research into the two principal degradation mechanisms that lead to defect growth, namely fatigue and corrosion. For many years, TWI has also studied the major final failure mechanisms of brittle or ductile fracture. Finally, for over 40 years, TWI has studied the non-destructive testing techniques that enable the sensors and data acquisition systems to be designed so that flaw growth can be detected.
One such technique, in which TWI is heavily involved, is Long Range Ultrasonic Testing. A recent development in this technology is Teletest Permamount™, in which the LRU sensor array is permanently mounted on the pipe. The flaw detector is connected to the array and the pipe is surveyed to a pre-planned schedule, so that flaw growth can be detected.
TWI is also studying the application of acoustic emission (AE) techniques to structural health monitoring. In some cases, the same piezoelectric sensors can be used for both AE and LRU.
TWI projects are concerned with developing SHM systems for a range of structural types.
For more information, please contact us.
