Fatigue Measurements on Composite Specimen Using VIC

Fatigue Measurements on
Composite Specimen
Using
VIC-3D, 3D
Digital Image Correlation System
System Installed At
Department of Aerospace Engineering
Indian Institute of Technology - Chennai
ILLUSTRATION OF DIGITAL IMAGE
CORRELATION - DIC
Raw video allows you to
QUALIFY
Digital Image Correlation
allows you to
QUANTIFY
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's
surface in digital images acquired during the loading.
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 and
application 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.
2D, DIC SYSTEM.
DIGITAL
IMAGE
CORRELATION
Firewire Camera interfaced to
the
Fire Wire Port of the PC.
Displacement and Strain Measurement
In-Plane Direction
( X and Y Direction).
Results Obtained from 2D Digital Image Correlation
Displacement:- u and v.
Strains:-
εxx, εyy , εxy , ε1 , ε2 ,Von Mises, Tresca
And Directions of Principal Strains
3D, DIC SYSTEM.
DIGITAL
IMAGE
CORRELATION
Two Fire Wire Cameras interfaced to
the Fire Wire Ports of the PC.
Displacement and Strain
Measurement In-Plane
Direction
( X and Y Direction)
And
Out of Plane Direction
(Z Direction)
Results Obtained from 3D Digital Image Correlation
Displacement:- u, v and w.
Strains:-
εxx , εyy , εxy , ε1 , ε2 , Von Mises, Tresca
and Directions of Principal Strains
Vibration Measurements with Vibration
Synchronisation module.
™ For sinusoidal excitation, no high-speed
cameras are required.
™ Precise triggering at known offsets to
excitation signal can be used.
™Images are taken in different cycles
depending on camera frame rate.
™ Complete vibration cycle can be
reconstructed.
‰Challenges
High Speed DIC
Measurements and
Modal Analysis
– Speckle adhesion during impact.
– High-speed cameras (frame rate, image quality,
price).
– Synchronization.
– Motion blur.
– Lighting.
– Camera motion during explosive/high energy
impact event.
Fatigue Measurements
on Composites.
A speckle Pattern was applied on the
Composite Specimen. Measurements are
made on the width of the specimen.
To study the failure measurements
were made both on the front and back
side of the specimen.
The failure mode is different in the front
and back of the specimen
Image of the Front of the Specimen
At No Load and After Failure.
Image of the Back of
the Specimen
At No Load and
After Failure.
System Set Up.
Two Prosilica GX Series were used for
Measurements.
These cameras are interfaced to the GigE Dual Port
of the PC.
Each camera can capture images at 63 fps
simultaneously.
The analog output of the Load cell from the UTM was
interfaced to the Daq.
So whenever an image was captured the analog
output was also recorded.
The specimen was subject to a cyclic load from
24 to 48KN. Frequency – 1 Hz
The specimen failed after 8558 cycles.
The VIC-SNAP software was programmed to capture
60 images in one second and a hold period of 100
seconds.
This cycle of image capture was looped until failure.
Duration of the Test:- 3 Hours.
Measurements were made on the Front and Back of the Specimen Simultaneously.
So the setup Included 2 Simultaneous Measurements in 2D DIC.
VIC-2D Software was used for Analysis.
Strain Plots – Front of the
Specimen - Strain - X
Failure Zone
Strain Plots – Back of the
Specimen – Strain X.
Failure Zone
From the plots its clear the failure mode and the strain
profile are different on the back and front of the
specimen.
List of End Users of
VIC-3D/2D Systems In India.
¾National Aerospace Laboratories – Bengaluru.
¾MRF Limited – Chennai.
¾Indian Institute of Technology – Chennai – Department of Aerospace Engineering.
¾General Motors Technical Centre – Bengaluru.
¾Indian Institute of Technology – New Delhi – Department of Applied Mechanics.
¾GEITC – John Welch Technology Centre – Bengaluru.
¾Central Glass and Ceramic Research Institute – Kolkatta.
¾Indian Institute of Technology – Chennai – Department of Engineering Design.
¾Indian Institute of Technology – Hyderabad – Department of Civil Engineering.
¾Vikram Sarabhai Space Centre – Thiruvananthapuram.
¾Central Glass and Ceramic Research Institute – Kolkatta.
¾Indian Institute of Science – Bengaluru – Department of Aerospace Engineering.
¾Indian Institute of Technology – Hyderabad – Department of Mechanical Engineering.
¾GEITC – John Welch Technology Centre – Bengaluru.
¾Indian Institute of Technology – Kharagpur - Department of Mechanical Engineering.
¾Indian Institute of Technology – Chennai – Department of Applied Mechanics.
¾Indian Institute of Science – Bengaluru – Department of Materials Engineering.
¾Indian Institute of Technology – Kharagpur – Tribology Laboratory.
¾Indian Institute of Technology – Kanpur – Department of Mechanical Engineering.
¾Indira Gandhi Centre For Atomic Research – Kalpakkam.
For More Detailed Information / Demonstration / Trial Test
Please contact us at
PYRODYNAMICS
No 632;22nd Main
4th “T” Block Jayanagar
Bengaluru – 560 041
TEL:- 011-91-80-2245 4993
FAX:- 011-91-80-2 66 55 333
E-Mail:- [email protected]
Web:- www.pyrodynamics-india.com