A&T 2016, Torino Lingotto Fiere Sessione specialistica del 20 aprile 2016, ore 14:45 - 17:20 Relatori: Lucia Rosso, Vito Fernicola, Shahin Tabandeh (INRIM)

1. A&T International exhibition - APRIL 20th-21st 2016 1
Un sensore a fibra ottica per misure di
temperatura in situ in prove tribologiche
Lucia Rosso1, Vito Fernicola1, Shahin Tabandeh1
1 INRIM- ISTITUTO NAZIONALE DI RICERCA METROLOGICA

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Scope of the project
An EMRP joint research project “Metrology to assess the durability and function of engineered
surfaces” (JRP IND 11 MADES) was trying to address fundamental aspects of metrology for tribology
in order to improve the long-term performance of tribological surfaces in industrial applications.
Durability and performance of many products and engineering devices depend critically on
tribological properties of the surfaces, such as wear and friction.
The temperature at wear interface - contact point between the surfaces - has a major influence on
the tribological performance of the materials.

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Pin-on-Disk wear testing
(ASTM G99-04)
• Pin-on-Disk testing consists of a flat rotating disk in contact with a fixed perpendicular pin
with a radius tip. The pin is pressed against the disk at a defined load.
• Both the normal and friction forces are measured by transducers. Performance is generally
characterized by friction coefficient and wear rates determined by mass or volume loss.
Load
Pin
Wear track
Disk

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Optical fibre
Blind hole
Ruby hemisphere
Modified Pin-on-Disk probe
• The original sapphire pin tip is replaced by a
machined ruby half-sphere.
• Ruby (Cr-doped sapphire) is a well-known
temperature sensitive material.
• The pin becomes, at the same time, the
wear test probe and the temperature sensor
at the contact point!

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Ruby-based fibre optic probe
for in situ temperature measurements
ST-connector
Ruby pin
Optical fibre
& silica tubing
Cap
blind hole
O.D.= 20 mm

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Temperature response curve of the sensor probe
calibrated by immersion
Caveat: sensor calibration was carried out in a thermostatic medium, but sensor operation is far
from thermal equilibrium!
Ave. temperature
sensitivity is 10 µs/°C
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Std. dev. = 0.1 °C
Temperature
[°C]
Life time
[ms]
Std.dev.
[µs]
25.92 3.1065 1
49.99 2.8693 0.9
100.70 2.2813 1.2
149.69 1.6213 0.5
200.33 1.0364 0.3
T/ K
τ/ms
τ/ms

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Sensor response to 200°C step input
TS
Tpin
TS
heatflux
Time/ S
Temperature/°C

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Finite element modeling
TS
convection
insolationinsolation
T=TsThermal contact
resistance is
unknown

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Surface temperature calibration:
experimental results & model validation
Reference
PRTs
Pin-on-disk
temperature
probe
0
5
10
15
20
25
0 25 50 75 100 125 150 175 200
Temperatureerror/°C
Surface temperature / °C
model
Experiment

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CFD modelling of the probe-surface contact
Glass-
ceramic
Low TC
polyamide
Ruby
hemisphere

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0
50
100
150
200
250
Third partial error 3b
Third partial error 3a
Second partial error
Tpin
Partial temperature errors
(Ts=200°C)
20.54 °c14.34 °C
2.84 °c

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Model-based compensation Idea
Tே்஼
TRuby
Ttip
?
Tே்஼
TRuby
Ttip
Model
Tே்஼
TRuby
Ttip
model

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Tpin - Tthermistor / °C
NTC
Temperatureerror/°C
0 20 2515105
20
0
40
60
120
80
100
140
160
180
30
Temperature error at the probe-surface contact:
heat flux and transient studies

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Temperature error at the probe-surface contact:
modelling the transient
Tthermistor/°C
Tpin / °C
Blue lines are
transient measured
temperature and red
line is the model
steady state output
The red line turns to be unique for
different possible experimental layouts
and thus used for A.N.N. training
Tsurface = 200 °C
Set of arbitrary values
?

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Tthermistor
Tpin
Input
layer
Hidden
layer
Hidden
layer
output
layer
Artificial neural network training
Surface temperature / °C
Temperatureerror/°C
Ttip

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“ANN” vs “surface calibrator”
temperature error compensation
The temperature estimation at 98 % of
the final value is >3 times faster
Time / s
Advantages of ANN compensation:
o More than 3 times faster
o Applicable for live error
compensation in tribometers

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Operation of the probe in tribometers
P=20N
TRuby Tthermistor Tcompensated
Tmin [°C] 22.01 22.63 21.69
Tmax[°C] 29.76 25.78 31.83
T[°C] 7.75 3.15 10.14
Truby Tthermistor Tcompensated
Tmin [°C] 22.41 23.28 21.98
Tmax[°C] 29.90 26.24 31.81
T[°C] 7.48 2.96 9.83
Time/ S Time/ S
Temperature/°C
Temperature/°C

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Operation of the probe in tribometers
Temperature/°C
P=40N P=60N P=80N
T=19.74°C
T=30.78°C T=40.11°C
Time/ S

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Operation of the probe in tribometers
Normal load/ N
∆T/°C
T=0.5051*P+0.318

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Conclusions
A fibre-optic point sensor for in situ temperature measurements was developed.
The sensor - based on the fluorescence thermometry method - was integrated
into a modified pin-on-disk wear test facility, together with a portable
fluorescence excitation/detection module.
The temperature probe was studied over the range 20 °C to 200 °C.
Finite element modelling identified the main limitations of the method and
helped to compensate for large intrinsic temperature errors.
An ANN model was developed for live passive compensation of the temperature
error and yeilded to a faster time responce.
Operation of the probe was succesfully chechecked in a tribometer.
An expectated linear trend was evident in the ΔT vs P diagram.

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Thank you!
s.tabandeh@inrim.it