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CAMERA
Centre for Advanced Measurements in Engineering Research Applications
   
   
  

Electronic Speckle Pattern Interferometry

Electronic Speckle Pattern Interferometry
Dantec Q300 3D ESPI system 

Summary of system

Electronic speckle pattern interferometry (ESPI) is an optical method for measuring very small displacements and strains. It relies on interference between diffusely-reflected light from two beams, or from diffusely-reflected light from one beam and from a reference beam. In the form which our system implements, it can measure 3D displacements on a specimen (though the out-of-plane displacements can o nly be measured relative to other points on the specimen). It is extremely sensitive and can detect displacements in the order of 50 nm in-plane and 20 nm out-of-plane, but the disadvantage of this sensitivity is that the system is also extremely sensitive to vibration, so is normally used in a vibration-isolated environment. The displacements are presented as maps of displacement components and can be differentiated with respect to spatial coordinates to give maps of in-plane strain. It is suitable for measuring small strains (in the order of 50-100 microstrain upwards) making it appropriate for work in the elastic region. Large strains can be measured by applying the load in a number of small steps.

Apparatus

CAMERA has purchased a Dantec Q300 3D ESPI system for mounting on a dedicated Instron 5966 10kN testing machine. These are both mounted on a vibration isolation table. Our system is supplied with long arms to enhance the in-plane sensitivity of the system. It incorporates a 1.4 MP monochrome camera, and is equipped with a 6-15 mm zoom lens to cover a range of fields of view from around 40mm x 40mm (TBC) up to around 200mm x 200mm (limited by laser intensity).

Restrictions

Because of the vibration sensitivity, the system is recommended for use only in L4-144 which is equipped with a large vibration isolation table and a dedicated tensile testing machine. Experience indicates that reasonable results are unobtainable unless the table is “inflated”. Specimens will need to be prepared with a diffuse surface such as that obtained by spraying with matt white paint.

Training

System includes two 70 mW borderline IR/visible class 3B lasers. In order to become an authorised user of this equipment, the researcher must have a current designated laser user and must also have either completed the ESPI training course in the last year, or have been a previous user of the system less than a year ago. The system will change with time as it adapts and new protocols might be introduced as usage develops.

Contact

To discuss use of the system contact Arthur Jones

 

Faculty of Engineering

The University of Nottingham
University Park
Nottingham, NG7 2RD

Contact:
Nick Eyley
email: nick.eyley@nottingham.ac.uk