In the past, this was usually done by carrying out tests on mock-ups of the component in the laboratory. However, more recently, numerical modelling of the interaction of ultrasound with the component has found an increasing role.
Modelling reduces the time required for on-site testing and increases the reliability of the tests.
Modelling can be used for:
- Prediction and visualisation of ultrasonic fields
- Calculation of focal points
- Design of phased array transducers
- Design of focusing in long-range ultrasonic testing (LRUT)
- Prediction of the interaction of ultrasound with flaws of various types
- Verification of the behaviour of ultrasound in components of complex geometry (e.g. pressure vessel nozzles)
TWI uses three modelling systems:
- Finite element modelling (FEM)
- Acoustic Ideas' Continuum Ultrasonic Modeler™
- CIVA (CEA) – another specialised ultrasonic modeller
Finite element modelling
TWI uses the Abaqus finite element package to conduct stress analysis, predict heat flow and, in particular, to model ultrasound. Examples are:
- Guided wave applications
- Straight pipes
- Pipes with branches
- Pipes with bends and elbows
- Phased array focusing in LRUT
- Rods (square, round, L-shaped)
- Conventional UT of turbine blades
Finite element analysis has the advantage that it is the most accurate method against which other methods can be calibrated. Its principal drawback is that it is extremely demanding in terms of computer time.
Acoustic Ideas' Continuum Ultrasonic Modeler™ is a general-purpose ultrasonic modelling package which provides:
- Calculation of focal laws
- Accurate modelling of ultrasonic fields, including diffraction
- Visualisation of ray paths in multilayer components
- Accurate calculation of scattered echoes from defects Interpretation of experimental or field data
- Development and verification of transducer designs
CIVA is also a general-purpose package developed by CEA (France). It is able to model real life inspection scenarios to improve the design of inspection procedures. A wide variety of geometries can be used including CAD representation, making it a very versatile tool. CIVA is also able to model a wide variety of engineering materials including those with anisotropy. Furthermore the user can investigate a wide variety of flaw shapes and sizes.
PZFLex (which stands for 'piezo-electric fast large and explicit') is another finite element software package used by TWI. The software has the capability to predict wave propagation based on an explicit time domain solver to resolve wave propagation problem. It can resolve 1-, 2- and 3-dimensional problems and can be used in transient analysis, that is, it allows a time-limited pulse to be input (as opposed to a continuous wave).
Another modelling package used by the NDT group is COMSOL Multiphysics, an implicit solver, which can be used to evaluate the global system of equations at each node for each element at every time step.
Advanced Engineering and Materials Research Institute
In 2016 TWI announced plans to construct a state-of-the-art engineering inspection and validation facility at its Wales base. The Advanced Engineering and Materials Research Institute (AEMRI) will combine expertise, equipment and resources for bespoke structural testing and evaluation services designed to determine, test and validate the limits of performance of advanced materials and to find ways of saving time, minimising production costs and reducing the risk of structural failure.
For more information visit www.aemri.co.uk.
For more information about TWI's NDT and asset reliability services, please email firstname.lastname@example.org.