Physics of Ultrasonic Testing Techniques

Modelling of wave propagation

The design of probes and inspection techniques for the ultrasonic nondestructive testing (NDT) requires a strong knowledge of wave propagation in solid-state materials and their interfaces. Future developments in this field are becoming more complicated, often requiring the inclusion of difficult boundary conditions in relation to component geometry or demands on the probe functionality, particularly in the case of phased array probes. This task requires the application of computer models for the sound-field and echo height calculation to determine an optimal solution for the probes and the whole inspection technique and also taking into consideration technical and financial constraints.
Based on this long term background, models are being developed for sound field calculation for probe optimisation and simulation of real inspection arrangements. This has led to successful transfer to practical applications.

• Development of computer-aided models for the sound propagation in acoustically isotropic and anisotropic materials for the characterisation, development and optimisation of ultrasonic probes. This problem is particularly suited to phased array probes.
  
  Examples
  • Inspecting of axles (axles with and without centre borehole) of rail vehicles (linear arrays and rotation scanner)
  • Wheel disc inspection on ICE wheels
  • Inspection of nuclear power plant components
  • Transmitter-receiver and tandem technique, longitudinal/longitudinal-transverse wave technique (LLT- technique)
  • Evaluation of the potential of matrix-array transducers

• Simulation of inspection arrangements considering geometry and material of the component, probe properties and configuration depending on the particular inspection technique. The aim is to estimate the resulting echo by varying the parameters and to integrate this information into planned tests and interpretation of testing results.
  
  Examples
  • Influence of defect position, orientation, size and shape
  • Superposition of different echo components (e.g. corner reflection, direct echo and redirected echo/indirect reflection)
  • Influence of curvature of cylindrical components (shafts with/without inner borehole)
  • Transmitter-receiver and tandem technique, longitudinal/longitudinal-transverse wave technique (LLT- technique)
  • Optimisation of transducer alignment on anistropic materials.
    Example: dissimilar weld testing

a) steering angle 0°

Two-dimensional directivity pattern
b) steering angle 30° lateral

c) steering angle 30° diagonal / steering angle 30° diagonal

Two-dimensional directivity pattern of a 4 x 4 element matrix array
distance, 100 mm, picture size ± 50° x ± 50°

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