Theoretical Formulation and Measurement 0f Infrared Imaging of - - PowerPoint PPT Presentation

Theoretical Formulation and Measurement 0f Infrared Imaging

• f Green-State PM Compacts

Souheil Benzerrouk

• Prof. Reinhold Ludwig

Worcester Polytechnic Institute October 22-23, 2003

Morris Boorky Powder Metallurgy Research Center

Research Objectives

n Evaluate the applicability of IR imaging techniques

in the detection of surface and subsurface defects in P/M parts.

n Build on the previous research “ Electrostatic

density measurements in green state P/M parts” by Georg Leuenberger and Prof. Reinhold Ludwig

n Establish a full thermo-electric IR solution that

allows the testing of both green state and sintered parts.

Research Approach

n Establish a theoretical background in the fields of

electrostatics, heat transfer and IR imaging

n Estimate the sensitivity of the approach by

modeling a number of different conditions

n Study experimentally simple parts with two

techniques (static and pulsed thermography)

n Test complex parts (green state and sintered)

Presentation Outline

n Comparative study of NDT methods n Introduction to IR imaging n Governing equations

n Electrostatics n Heat transfer n IR imaging

n Modeling a simple part (cylinder) n Parametric Study and sensitivity estimation n Experimental results (static)

n Good, simple green state part n Flawed, simple green state part n Complex green state and sintered parts

Competitive Technologies

n Requires very high

sensitivity in sintered parts

n Demonstrated performance with

green state parts Resistivity

n Not suitable for high

volume applications (slow)

n High ownership cost nNot effective in

detecting near corner defects

n Can detect defects in both green

state and sintered

n High resolution, deep penetration. n Established technology for high

quality samples (aerospace, military) X-Ray

n Inefficient in green

state due to their porous nature

n Requires a matching

layer usually a gel

n Can detect deeply embedded defects n Cost effective

Ultrasonic

n Depth of penetration

limits the usability in green state

n Ideal for surface and near surface

defects in sintered parts Eddy Current

Limitations Capabilities Technique

IR Imaging

n Technology requires heat source n Special camera to record thermal signature n Elaborate signal acquisition and processing steps to

form image

n Additional image analysis post-processing

SUT

Heat source

IR Imaging- Pros and Cons

n Pros:

n Remote sensing capability n Non contacting n Fast response n High spatial resolution n High temperature range n Cameras have built-in image processing capability

n Cons:

n Need for straight viewing corridor with the target n Background calibration n Cost is primarily determined by camera

Generic testing approach

Current Input Electrostatic measurement and Power prediction IR detection Signal and image processing

Governing Equations

) .( = — — V s

Electrostatic

J n n ⋅

• =

— ⋅ ) ( V s

2

V Q — = s

V,E Heating Power

J Density Current

( )

[ ]

1 exp 2 ) , (

5 2

• =

KT hc hc T W l l l

Emitted energy

IR imaging

Q T k t T c = — —

• ∂

∂ ) .( r

) ( ) ( T T h q T k

ext -

+ = — ⋅ n

Heat transfer

) , ( z r T

Heat equation

( )

T r, s

Heat Transfer

The analytical approach is to study a homogenous solid cylinder of radius R: 0 £ r £ R and length 2L: -L £ z£ L. In the static case the heat equation is a second PDE which can be solved by using the separation of variables technique to give:

Â

• =

+ +

• =

˜ ˜ ¯ ˆ Á Á Ë Ê ˙ ˙ ˙ ˚ ˘ Í Í Í Î È ˜ ˜ ¯ ˆ Á Á Ë Ê

˜ ˜ ˜ ¯ ˆ Á Á Á Ë Ê ˙ ˙ ˚ ˘ Í Í Î È

1 ) ( 4 2 1 cosh ) ( ) tan( ) cosh( ) ( 1 3 2 ) , ( n R r n J n J n n hR R L n n hR R L n R z n n hR k QhR z r T g g g g g g g g g

Simulation (FEM)

n Static modeling in 3D

n Use simple geometry (cylinder) n Electrostatic - to show the voltage distribution n Heat transfer – local heating and major heat transfer

mechanisms

n Static modeling in 2D - Sensitivity study

n Surface and Subsurface defects n Combination of flaws (various sizes and orientations)

n Dynamic modeling in 2D - sensitivity study

n Extend the 2D model to include the dynamic effects

Static Modeling

n Surface current source n Uniform conductivity n Neglected temperature

dependency of conductivity

Static Modeling

n Coupled the results of the

electrostatic model.

n Included thermal effects

n Conduction n Convection

n Approximated material

properties

Static Modeling

n As expected, smooth and

symmetric temperature distribution with the hottest spot located in the center of the compact

Sensitivity Study (Static)

1mm x 1mm Defect 20mm x 100mm Defects

Sensitivity Study (Static)

n An obvious signature for surface defects

can be obtained. This signature varies in shape and amplitude with the input current (temperature) and the size of the flaw

n Subsurface flaws of smaller geometries

are not seen statically, requiring the use of dynamic (pulsed) thermography

Sensitivity Study (Dynamic)

Sensitivity Study (Dynamic)

Sensitivity Study (Dynamic)

305 304 303 302 301 300 0.01 0.02 0.03 0.04 0.05 0.06 T (Kelvin) L (m)

Sensitivity Study (Dynamic)

n Surface and subsurface defects are easily

detected

n Fast response, very efficient in a go/no go test n Highly sensitive, reduced post-processing

complexity

Test Arrangement

Image Processing laptop IR Camera Power Supply Sample under test

Experimental Results

n Green state parts n Static imaging n Surface flows, with various

shapes, sizes and orientations

n Apply simple thresholding

algorithm

n Create temperature profiles

Parts courtesy of GKN Worcester

Experimental Results

Results Analysis

Profile Line

Thresholding

Analysis after thresholding

Profile Line

Discussion

n Heating with direct current is easy to apply and

highly repeatable

n Static imaging can be successfully used in

detecting surface defects

n Dynamic imaging is highly promising for surface

and subsurface detection

n Today’s cameras can very easily accomplish the

task at hand (speed and resolution)

Accomplishments

n

Developed the theoretical foundation of heating with direct current (electrostatics and heat transfer)

n

Built a suitable model for predicting the thermal profile on the surface of a part ( close to what the IR camera will capture)

n

Conducted a simple test bed for static testing

Proof-of-concept appears successful!

Future Milestones

n

Complete the theoretical modeling effort to include effects

• f external radiation behavior

n

Conduct experimentation to determine the thermo-physical properties of green-state and sintered parts for further simulations and measurements

n

Test controlled samples

n Simple geometries of different powders/densities

compositions

n Green state and sintered state n

Explore dynamic evaluation with improved image processing

Interesting observation

n Subtle density variations

produce measurable temperature differences