Laser Shearography NDT

Laser Shearography NDT system with the FlawExplorer Sensor and Short-Wave Thermal Excitation
Figure 1 – Laser Shearography NDT system with the FlawExplorer Sensor and Short-Wave Thermal Excitation

Laser Shearography is an optical, Non-Destructive Testing (NDT) technique used to reveal sub-surface defects in structures. Through the application of a load using either thermal, vacuum-partial, vacuum-ambient or vibration-mechanical excitation to a structure, a laser shearography sensor (such as our FlawExplorer or FlawScout) can observe (minimal) surface bending in the form of an out-of-plane strain field and image the measurement as a phase map. Since the sensor is sensitive to changes in the interference in laser light, the capability of the sensor to detect bending is within the sub-micrometer range.

A Laser Shearogaphy NDT system (example) consisting of the FlawScout Sensor and Medium-Wave Thermal Excitation
Figure 2 – A Laser Shearogaphy NDT system (example) consisting of the FlawScout Sensor and Medium-Wave Thermal Excitation
Advantages of using Laser Shearography
Figure 3 – Advantages of using Laser Shearography

The ultimate goal of any NDT system is deliver reliable measurement results as economically as possible. Laser Shearography can detect defects which other NDT methods cannot, including; kissing bonds, node bond splits and ply wrinkling. In many cases the reliability of the technique, as quantified through the small defect size detection at 90% Probability of Detection (PoD) and low False Call Rates, is unmatched. The economic advantages of using Laser Shearography include; high inspection rates (i.e. m2/sec), low sample preparation times, simple automatability and formal NDT technique approval & recognition.

Laser Shearography is a versatile solution and can be used as a manual, semi- or fully-automated system for NDT applications within production quality control or in-service inspection. Currently the technique is used for a large array of testing applications in various industries including; Aeropace, Aviation & MRO, Automotive, Wind Power and Marine.

Depending on the surface material strength, the technique can detect most discontinuities that occur within 30 mm (and in some cases up to 40 mm) below the surface. Examples of applications include, but are not limited to;

  • honeycombs & sandwiches for disbonds, cracked cores, crushed cores, node bond spits and (aluminim) corrosion.
  • laminates & overwraps for delaminations, fluid ingresses, dry spots and ply wrinkling.
  • bondings & coatings for disbonds, dry spots and kissing bonds.
  • compounds & ceramics for voids, cracking and abrasions.
  • spray foams & sealants for porosity and voids.

Additional structural information can also be detected using shearography including; ply drops, bulkheads, overlaps, splices, stringers and ribs.

Overview of Laser Shearography applications
Figure 4 – Overview of Laser Shearography applications
A 7 second measurement using vacuum-ambient excitation of an aluminium honeycomb component
Figure 5 – A 7 second measurement using vacuum-ambient excitation of an aluminium honeycomb component
A 15 second measurement using thermal excitation of a COPV (Fibreglass)
Figure 6 – A 15 second measurement using thermal excitation of a COPV (Fibreglass)