Paint Coating Characterisation
for Thermoelastic Stress
Analysis
Andrew Robinson, Janice Dulieu-Barton, Simon Quinn, Richard Burguete
Contents
• Introduction to Thermoelastic Stress Analysis (TSA)
– Basics and Setup
• Surface Coatings for TSA
– Characteristics
– Paint Type
– Paint Thickness
– Theoretical vs. Experimental
– Conclusions
2
Thermoelastic stress analysis
T   KT0  kk
Bakis
C.E.
andDulieu-Barton,
Reifsnider K.L.J.M.
(1991)
thermoelastic
effect in
Wang,
W.J.,
andThe
Li,adiabatic
Q. “Assessment
of non-adiabatic
laminated
composites. stress
Journal
of Composite
, 25, pp 809behaviourfiber
in thermoelastic
analysis
of small Materials
scale components”,
830.
Experimental Mechanics, in press. DOI: 10.1007/s11340-009-9249-2.
Wong A.K. (1991) A non-adiabatic thermoelastic theory for composite
laminates. Journal of Physics and Chemistry of Solids, 52(3), pp 483-494.
Motivation
• Conventional thermoelastic stress analysis (TSA) is a well
established non-contact, full-field stress analysis
technique.
• Residual stress measuring second order nonlinear effects:
Temperature variations much smaller than those resolved
during normal TSA.
• Recent development in infra-red camera technology has
lead to renewed interest into residual stress analysis using
TSA.
• Signal attenuation from paint coating is more significant.
• This research is relevant to all practitioners of TSA where a
4
surface coating is applied.
Metallics: Surface Coatings for TSA
Why do we use a paint coating?
• Usually for metallic materials
• To enhance and standardise emissivity
• Avoid reflected radiation
What do we normally do?
• The standard used for previous TSA tests
– “two passes of RS matt black paint”
..what
does this
mean?
“two passes of RS matt black paint”
Coating Characteristics
• Paint type
..is RS still
applicable?
• Paint Thickness – Operator Dependent
• Loading Frequency effects
How do we approach this?
..what does
‘two passes’
mean?
T   KT0  kk
By comparing analytical and experimental thermoelastic constants
K   /  Cp
RESULTS…
6
Paint Type - Results
Aluminium strip specimens: Calculated thermoelastic constant: 9.54 x 10-12 Pa-1
Good results for
(Two passes applied for each paint)
Paint
Type
Thermoelastic
Constant, Pa-1
A
Hammerite – Smooth black
4.37 x 10-12
B
Plasti-kote – Radiator satin black
4.12 x 10-12
C
Plasti-kote – Matt super grey
3.60 x
D
Plasti-kote – Matt super black
9.33 x 10-12
E
Plasti-kote – Metal primer white
3.12 x 10-12
F
Hammerite – Satin black
4.61 x 10-12
G
Plasti-kote – BBQ black
6.55 x 10-12
H
Plasti-kote – Matt super white
3.55 x 10-12
I
RS Matt Black
9.61 x 10-12
Expected
10-12
9.54 x 10-12
RS Matt Black
and
Plasti-kote Matt
Super Black
Further testing
revealed RS Matt
Black was better
Paint thickness?
7
Paint Thickness
• How was it applied?
Successive passes of aerosol spray, from 1 – 6 passes.
Very Operator Dependent
• How was it quantified?
Confocal laser
microscopy
Typical thickness
measurement data
• Steel strip specimens
– Calculated thermoelastic constant - 3.02 x 10-12 Pa-1
8
Paint Thickness - Results
3.02 x 10-12 Pa-1
9
Paint Thickness - Results
What is 2 or 3 passes?
– 2 passes
ranged from 12 to 23µm
3.02 x 10-12 Pa-1
– 3 passes ranged from 17 to 29µm
– Analysis suggests suitable paint
thickness of between 15 to 25µm
– Frequency range 7.5 to 15Hz
What next?
10
Experimental vs Theory
Theoretical coating response modelled
as a complex wave problem:
F
T
e t  R a R s e  t




Ra
1

t (   )
t (    )
1

e

1

e

(   )
(   )


 R m   1 1  e t (    )  R a 1  e t (     )
 e 2 t  (   )
(   )

Q

1  e  t  Rm e 2d 1  e t
















Theory (1993) Welch and Zichel
What does this mean in reality?
11
Theory
How does
Updated
theory
parameters
compare to
– Our
experimental
theory results?
12
Theory
vs
Experimental
Ideal TSA test conditions:
Theory predicts a
Low thickness,
decrease
in response
with increasing
Low frequency
thickness or frequency
In reality we have a trade off:
Experimental work
Low
frequency
nonsuggests
thegives
variation
adiabatic
conditions
is minimal
if either
frequency or thickness
Low thickness and the
is sufficiently
small.
surface
is too reflective
Surface Coatings - Conclusions
• For thermoelastic stress analysis of metallic materials, RS matt black
paint is a suitable coating.
• A cyclic loading frequency of between 7.5 and 15 Hz should be employed
for future testing.
• Acceptable paint thickness for thermoelastic measurements range from
between 2 to 3 passes. This coating should correlate to a thickness of
between 15 and 25µm.
Paint coating characteristics are an important consideration for TSA
14
Thank you…