Gilardoni, in collaboration with the company Dantec Dynamics, has decided to offer its customers another non destructive method: Shearography, also called Laser Shearography.
The control with sherography turns out to be complementary in some cases, and in other cases a substitute for the controls with X-rays or ultrasounds that Gilardoni has been offering with experience for 75 years: x-rays and ultrasounds.
The Shearography, Laser Shearography (LS) method is a non-destructive testing (NDT) that is used to detect sub-surface defects predominantly in composite components.
The sherography is an optical method and is based on the surface deformation of the component under investigation, deformation obtained by applying a stress.
The system compares the unsolicited image with the stressed one, the result of comparing the deformed and reference state is presented as a phase map, which shows the out-of-plane displacement gradient of the surface as a series of fringes.
The sensor, the heart of the system, is sensitive to changes in interference in laser light, and can detect changes in the order of sub-micrometers (<1 microns).
The stress methods used to induce deformation may be:
utilizzati per indurre la deformazione possono essere:
- Thermal stressing that usually only heats up the sample up to 15°C with respect to ambient temperature
- (Partial) vacuum excitation works from 50 mbar (5 kPa) to 150 mbar (15 kPa)
- Glove box depression
- (Ambient) vacuum excitation works also within this range from 50 mbar (5 kPa) to 150 mbar (15 kPa)- this uses a vacuum chamber
- Vibration, acoustic and mechanical.
The shearographic system consists of:
– A sensor that incluces:
- A Laser source which is used to create a diffracted speckle pattern over the specimen surface
- Internal shearing optics which are used to create a 2nd offset, sheared image
- A camera which is used for imaging the change in the fringe intensity between the reference and sheared image
– A PC & SW for data processing, storage and control
– A excitation system, such as: thermal (heat) excitation or vacuum excitation
Shearography is a versatile solution and can be used as a manual, semi-or fully automated system for NDT applications, as part of production quality control or in-service inspection, on field.
It is currently used for a wide range of applications in various industries, including Aerospace, Aviation & MRO, Automotive, Oil & Gas, Wind Power and Marine.
Examples of detectable defects:
- Porosity (Air Bubbles)
- Delaminations and Matrix Cracking
- Cracked Cores.
- Fluid Ingresses i
- Foreign Bodies (Inserts)
- Crushed Cores
- Dry Spots
- Kissing Bonds
- Node Bond Splits
- Ply Wrinkling
- Corrosion (Aluminium)
- Cracking & Abrasions
- Impact Damage (BVID)
Maximum thicknesses that can be inspected:
̴15 mm ( ̴0,6 inch) for CFRP laminates
̴100 mm ( ̴4 inch) for honeycomb sandwich
̴30 mm ( ̴1,2 inch) for GFRP
̴ 8 mm (0,3 inch) for aluminium laminates
The ultimate goal of any NDT system is deliver reliable measurement results as economically as possible.
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
- No need for coupling means
- Possibility to inspect components with complex geometries
- Possibility of automation
- Easy comparison and repeatability of results over time
- ASTM E2581 – 07 Standard Practice for Shearography of Polymer Matrix Composites, Sandwich Core Materials and Filament-Wound Pressure Vessels in Aerospace Applications
- ASTM E2581 – 14 Standard Practice for Shearography of Polymer Matrix Composites and Sandwich Core Materials in Aerospace Applications EU
- Operators Certification according to EN, ASNT Standards for levels II and III