Optical techniques, including digital image correlation (DIC), projectometry, and moiré or speckle interferometry, have the advantages of whole-field, non-contact or remote measurement of surface displacement and/or deformation of a structural component. By capturing images of a specimen during its deformation process, quantitative information about its mechanical behaviour can be obtained. This information is valuable for characterising material properties and evaluating the structural integrity of components. Following rapid advances in opto-electronics and computer hardware, the accuracy and capability of digital image techniques have been significantly improved, making optical and digital image techniques a powerful quantitative measurement or monitoring technique in a wide range of industrial applications.
The demand for more energy efficient structures and products has led to a trend that more engineering components are expected to operate under harsher working conditions such as high temperature. To ensure the structural integrity of these systems, it is crucial to measure or monitor the mechanical behaviour (eg creep) of structural components at elevated temperature. Digital image techniques have great potential in this aspect.
Another area in which optical techniques can play a major role is the measurement and monitoring of mechanical behaviour of a component during a rapid process such as impact. High speed cameras can capture images of the component during a dynamic process, and quantitative whole-field deformation measurement can be carried out using DIC.
In addition to conventional DIC techniques for measuring 2D and 3D displacement and strain fields, TWI has proposed an innovative method, deformation pattern based digital image correlation (DPDIC), for specific measurement tasks such as measuring residual stress. Measurement accuracy and reliability have been improved using this new technique.
TWI is leading two collaborative projects to develop innovative optical techniques for industrial applications.
The CreepImage project will develop a creep deformation monitoring technique for power plant components. TWI is providing new DPDIC algorithms for creep measurement.
The DashWin project will develop an advanced shearography system to inspect wind turbine blades on-site. TWI is developing a novel spatially phase shifted shearography technique.
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