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

Theoretical Formulation and Measurement 0f Infrared Imaging of Green-State PM Compacts Souheil Benzerrouk Prof. Reinhold Ludwig Worcester Polytechnic Institute October 22-23, 2003 M orris B oorky P owder M etallurgy R esearch C enter

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 Technique Capabilities Limitations Eddy Current n Ideal for surface and near surface n Depth of penetration defects in sintered parts limits the usability in green state Ultrasonic n Can detect deeply embedded defects n Inefficient in green state due to their porous n Cost effective nature n Requires a matching layer usually a gel X-Ray n Can detect defects in both green n Not suitable for high state and sintered volume applications (slow) n High resolution, deep penetration. n High ownership cost n Established technology for high n Not effective in quality samples (aerospace, military) detecting near corner defects Resistivity n Demonstrated performance with n Requires very high green state parts sensitivity in sintered parts

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 Heat source SUT

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 IR detection and Power prediction Signal and image processing

Governing Equations Current Density J n ( V ) n J .( V ) 0 Electrostatic ⋅ s — = - ⋅ — s — = V,E 2 Q V Heating Power = s — T ∂ ( r , T ) Heat transfer s n ( k T ) q h ( T T ) c .( k T ) Q ⋅ — = + ext - r - — — = t ∂ Heat equation T ( r , z ) IR imaging 2 2 hc 0 W ( , T ) l = Emitted energy 5 [ ] ( ) exp hc KT 1 l l -

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: ( hR ) cosh( z R ) g g n n 1 - È ˘ Ê ˆ 3 tan( L R ) ( hR ) cosh L R g + g Á g ˜ • Í ˙ 2 QhR n n n Á ˜ Í ˙ Á ˜ Ê ˆ T ( r , z ) J r R = Î ˚ Ë ¯ g  Á ˜ 0 n Á ˜ 2 k È ˘ 4 Ë ¯ n 1 Ê ˆ = 1 hR J ( ) Í ˙ + g g g Á ˜ n n 0 n Á ˜ Í ˙ Ë ¯ Í ˙ Î ˚

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) 20 m m x 100 m m 1mm x 1mm Defects Defect

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) T (Kelvin) 305 304 303 302 301 0.02 0.03 0.04 0.05 L (m) 0.06 0.01 0 300

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 Power Supply Image Processing laptop IR Camera Sample under test

Experimental Results n Green state parts n Static imaging Parts courtesy of GKN Worcester n Surface flows, with various shapes, sizes and orientations n Apply simple thresholding algorithm n Create temperature profiles

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 Developed the theoretical foundation of heating with direct n current (electrostatics and heat transfer) Built a suitable model for predicting the thermal profile on n the surface of a part ( close to what the IR camera will capture) Conducted a simple test bed for static testing n Proof-of-concept appears successful!

Future Milestones Complete the theoretical modeling effort to include effects n of external radiation behavior Conduct experimentation to determine the thermo-physical n properties of green-state and sintered parts for further simulations and measurements Test controlled samples n n Simple geometries of different powders/densities compositions n Green state and sintered state Explore dynamic evaluation with improved image processing n

Interesting observation n Subtle density variations produce measurable temperature differences