Full Field Deformation MeasurementUsing

VIC-3D, 3D Digital Image Correlation System

ILLUSTRATION OF DIGITAL IMAGE CORRELATION - DIC

Raw video allows you toQUALIFY

Digital Image Correlation allows you toQUANTIFY

VIC-3D, 3D Digital Image Correlation System

The 4 step process looks like this...

The method of 3-D DIGITAL IMAGE CORRELATION - DIC is based on principles similar to human depth perception: (Photogammetry) by viewing the same object or process from two different viewpoints, the precise shape of the object in three-dimensional space can be resolved. Position resolution in three-dimensions is accomplished by referencing a system-wide coordinate system that is established through a calibration process. The calibration process, conducted prior to the start of each test, establishes the intrinsic camera parameters (focal distance, lens distortion factor, and sensor aspect ratio) and geometric parameters (camera positions relative to each other and to the imaged object), that control the transformation between the system-wide coordinates and the coordinates on each camera’s image plane.

The idea behind the method is to infer the displacement of the material under test by tracking the deformation of a random speckle pattern applied to the component'ssurface in digital images acquired during the loading.

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Mathematically, this is accomplished by finding the region in a deformed image that maximizes the normalized cross-correlation score with regard to a small subset of the image taken while no load was applied. By repeating this process for a large number of subsets, full-field deformation data can be obtained.

The DIC method does not require the use of lasers and the specimen can be illuminated by means of a white-light source. However, the specimen surface must have a fairly uniform random pattern, which can either be naturally occurring or applied to the specimen before the test. Among the many methods for pattern application are self-adhesive, pre-printed patterns, stamps andapplication of paint speckles with air-brushes, spray cans or brushes.

Images of the Test Component in un deformed and Deformed State are captured using 2 CCD Cameras .

The two cameras are mounted on a rigid bar to avoid relative motion of the cameras.

STEREOSCOPIC CALIBRATION

Camera calibration is carried out in a very simple way by positioning of a calibration plate with a chess board pattern in front of the cameras and a series of exposures has been taken. The software detects the corners of the squares and the additional circular marks define the centre and orientation of the target. The algorithm calculates the parameters for each camera resulting from the deviation of the markings while the calibration target is at different spatial orientations. Camera Parameters:

Intrinsic Parameters: This includes focal length and principal point of the lenses and radial and tangential distortion of the lenses.

Extrinsic Parameters: This includes translation vector and rotation matrix.

DIGITALIMAGE

CORRELATION

2D, DIC SYSTEM.

Displacement and Strain Measurement In-Plane Direction

( X and Y Direction).Firewire Camera interfaced to the

Fire Wire Port of the PC.

Results Obtained from 2D Digital Image CorrelationDisplacement:- u and v.

Strains:- εxx, εyy , εxy , ε1 , ε2 ,Von Mises, Tresca

And Directions of Principal Strains

Two Fire Wire Cameras interfaced to the Fire Wire Ports of the PC.

DIGITALIMAGE

CORRELATION

Displacement and Strain Measurement In-Plane

Direction ( X and Y Direction)

And Out of Plane Direction

(Z Direction)

3D, DIC SYSTEM.

Results Obtained from 3D Digital Image CorrelationDisplacement:- u, v and w.

Strains:- εxx , εyy , εxy , ε1 , ε2 , Von Mises, Tresca

and Directions of Principal Strains

For sinusoidal excitation, no high-speedcameras are required.

Precise triggering at known offsets toexcitation signal can be used.

Images are taken in different cyclesdepending on camera frame rate.

Complete vibration cycle can be reconstructed.

Vibration Measurements with Vibration Synchronisation module.

The Fulcrum – Vibration Synchronization Module is An Add on Module to the 3D, 3D DIC System.

It comprises of:-

1) Fulcrum Software Module.

2) Data Acquisition Module.

3) Flash Lamp.

The Fulcrum requires a trigger signal. Typically this would Be the input signal to the shaker or a sensor (accelerometer or Displacement Sensor ) is mounted on the test object that is vibrating.

The trigger signal is converted into a Digital Signal using the D/A module of the Daq and is fed to the cameratrigger unit.

The same signal is fed to the flash lamp.

The flash lamp will flash light at the same frequency as the trigger signal.

The image of the vibrating test object is frozen and images are captured at various phase of the vibrating signal.

3D, DIC FULCRUM SYSTEM.

Test ObjectUnder Vibration

Two Fire Wire Cameras interfaced to the Fire Wire Ports of the PC.

DIGITALIMAGE

CORRELATION

Daq module interfaced to the PC

Trigger Signal FromShaker or Sensor+/- 10V Maximum

D/A Signal from the Daq to theCamera and Flash Lamp

3D, DIC FULCRUM SYSTEM.

Camera inter-frame time.

Original wave form can be reconstructed by sampling at appropriate phase offsets in different cycles.

3D, DIC FULCRUM SYSTEM.

STRAIN MEASUREMENT ON TENSILE SPECIMEN

A speckle pattern was applied on the Tensile Specimen.

The specimen had strain gage bonded at the back of the specimen.

The specimen was loaded upto failure of 10500 Newtons. The image was captured at every 500N.

The Strain Gage was connected to SCAD 500 Strain Measurement System and the strains were recorded at every load step.

STRAIN MEASUREMENT ON TENSILE SPECIMEN

Poisson’s Ration

Mean Value 0.908975

Strain Y ar 10500 N Strain X at 10500 N

Specimen at Failure

STRAIN MEASUREMENT ON AFT RIB

The Specimen was fixed at one end and load applied at the other end. Load was applied in steps of 100 Kgs upto 500 Kgs. 2 Dial Gages were mounted to record the displacements. Strain Gages were mounted at the back of the specimen and interfaced to SCAD 500 System. The location is marked X

V Displacement

Shear Strain

The Shear Strain Pattern Shows a Significant Strain Concentration.

VIC-3D,DIC System was successfully used for carrying out Full Field 3D Displacement &Strain Measurements.

Set up is easy and simple.

Surface Preparation takes very less time.

DIC Measurements can be made on any surface – Metal, Plastic, Composites…etc

VIC-3D, 3D DIC system measures In-Plane and Out of Plane Displacements, Strain X,Strain Y, Shear Strain,Principal Strains, von Mises and Tresca.

The FEM Data can be verified by DIC.

The DIC results matched very closely with the Strain Gage Results.

Real Time Monitoring displays the Strain Plots on Loading.

For More Detailed Information Please contact us at

PYRODYNAMICSNo 632;22nd Main

4th “T” Block JayanagarBengaluru – 560 041

TEL:- 011-91-80-2245 4993FAX:- 011-91-80-2 66 55 333

E-Mail:- pyrodynamics@bsnl.inWeb:- www.pyrodynamics-india.com