The infrared thermography was applied for the analysis of different materials subjected to different loading conditions. The main attention of the researches was focused on the investigation of the temperature evolution of steels during the tests in low cycle, high cycle and very high cycle fatigue regimes. The traditional methods of fatigue assessment of materials are extremely time consuming, so an innovative approach, based on thermographic analyses of the temperature evolution during the fatigue tests, has been proposed for a rapid prediction of the fatigue limit and the S-N curve, using a very limited number of tests: the Thermographic Method (TM). There are many studies in literature on the thermal response of composites during static tests for a prediction of the fatigue limit, but only few studies about the thermal response of steels during static tests, and nothing about the application to welded joints, as far as the authors are aware. The aim of this study is the application of the Thermographic Method during static tensile tests for the fatigue assessment of steel material and also steel welded joints. The predictions of the fatigue limit, obtained by the analysis of the temperature evolution during the static tests, were compared with the predictions obtained applying the TM during fatigue tests.

1. UNIVERSITÀ DEGLI STUDI DI MESSINA
Dipartimento di Ingegneria
Gruppo di Lavoro AIAS Tecniche di Giunzione
«Giornate di studio Progressi della Ricerca Italiana sui Sistemi di Giunzione»
5 - 6 Aprile 2018
Dipartimento di Ingegneria, Università degli Studi di Messina, Messina
Application of Full-field Research
Techniques on Welded Joints
P. Corigliano, V. Crupi, G. Epasto, E. Guglielmino, G. Risitano

2. Reference Papers
6 Aprile 2018 Giacomo Risitano et Al. 2
Corigliano P, Crupi V, Epasto G, Guglielmino E and Risitano G.
Fatigue assessment by thermal analysis during tensile tests on
steel. 23° Convegno Nazionale IGF, First International Edition,
Favignana (Italy), June 22-24, 2015. Procedia Engineering (2015)
109: 210-218.
Corigliano P, Crupi V, Epasto G, Guglielmino E and
Risitano G. Fatigue life prediction of high strength steel
welded joints by Energy Approach. 21° European
Conference on Fracture (ECF 21), Catania (Italy), June 20-
24, 2016. Procedia Structural Integrity (2016) 2: 2156 –
2163.
Corigliano P, Epasto G, Guglielmino E and Risitano G.
Fatigue analysis of marine welded joints by means of DIC
and IR images during static and fatigue tests. Engineering
Fracture Mechanics (2017); 183: 26-38.

3. Aim of the Work
There are many studies in literature on the thermal response of composites during static tests for a
prediction of the fatigue limit, but only few studies about the thermal response of steels during
static tests.
In this work, tensile tests were carried out on base material and welded specimens, made of
S690QL steel.
The Digital Image Correlation and thermographic techniques have been used during all tests.
The aim of this study is the application of the Thermographic Method during static tensile tests for
the fatigue assessment of steel material and also steel welded joints.
The predictions of the fatigue limit, obtained by the analysis of the temperature evolution during
the static tests, were compared with the predictions obtained applying the TM during fatigue
tests.
6 Aprile 2018 Giacomo Risitano et Al. 3

4. Introduction
The infrared thermography was applied for the analysis of different materials
subjected to different loading conditions:
• notched steel specimens under tensile static tests [1];
• laminated composites under tensile static loading [2];
• short glass fiber-reinforced polyamide composites under static and fatigue
loading [3];
• shape memory alloys under fatigue loading [4];
• sandwiches under impact loading [5];
6 Aprile 2018 Giacomo Risitano et Al. 4
[1] A. Risitano, G. Risitano. Determining Fatigue Limits with Thermal Analysis of Static Traction Tests, Fatigue Fract. Engng. Mater. Struct. 36 (2013) 631-639.
[2] L. Vergani, C. Colombo, F. Libonati. A review of thermographic techniques for damage investigation in composites, Frat Integ Strut. 27 (2014) 1-12.
[3] V. Crupi, E. Guglielmino, G. Risitano, F. Tavilla. Experimental analyses of SFRP material under static and fatigue loading by means of thermographic and DIC techniques, Composites Part B:
Engineering. 77 (2015) 268-277.
[4] C. Maletta, L. Bruno, P. Corigliano, V. Crupi, E. Guglielmino. Crack-tip thermal and mechanical hysteresis in Shape Memory Alloys under fatigue loading. Mater Sci Eng A: Struct. 616 (2014)
281–287.
[5] V. Crupi, G. Epasto, E. Guglielmino. Low-velocity impact strength of sandwich materials, J. Sandw. Struct. Mater. 13 (2011) 409 - 426.

5. Introduction
The main attention of the researches was focused on the investigation of the temperature evolution of steels
during the tests in low cycle, high cycle and very high cycle fatigue regimes.
The traditional methods of fatigue assessment of materials are extremely time consuming, so an innovative
approach, based on thermographic analyses of the temperature evolution during the fatigue tests, has been
proposed for a rapid prediction of the fatigue limit and the S-N curve, using a very limited number of tests: the
Thermographic Method (TM).
As reported in [1], there are many studies in literature on the thermal response of composites during static
tests for a prediction of the fatigue limit, but only few studies [2] about the thermal response of steels during
static tests, and nothing about the application to welded joints, as far as the authors are aware.
6 Aprile 2018 Giacomo Risitano et Al. 5
[1] L. Vergani, C. Colombo, F. Libonati. A review of thermographic techniques for damage investigation in composites, Frat Integ Strut. 27 (2014) 1-12.
[2] A. Risitano, G. Risitano. Determining Fatigue Limits with Thermal Analysis of Static Traction Tests, Fatigue Fract. Engng. Mater. Struct. 36 (2013) 631-639.

6. Thermographic Method
6 Aprile 2018 Giacomo Risitano et Al. 6
G. Curti, G. La Rosa, M. Orlando, A. Risitano. Analisi tramite infrarosso termico della temperatura limite in prove di fatica, Conf.
Proceedings: 14th AIAS Italian National Conference, Catania, Italy, (1986).
Camera IR
Limite di fatica

7. Static Thermographic Method
• During static tests of common engineering metals, the
temperature evolution on the specimen surface, detected by
means of an infrared camera, is characterized by three phases:
1. an initial approximately linear decrease due to the
thermoelastic effect (phase 1),
2. then the temperature deviates from linearity until a minimum
(phase 2)
3. and a very high further temperature increment until the failure
(phase 3).
• The first deviation from linearity, which corresponds to the end of
the phase 1, was correlated to the fatigue limit [1-3].
6 Aprile 2018 Giacomo Risitano et Al. 7
[1] A. Risitano, G. Risitano, C. Clienti. Fatigue limit by thermal analysis of specimen surface in
mono axial traction test. ICEM 14 Conference, Poitiers, France, 4-9 July (2010). Conference Proceeding:
EPJ volume 6 – 2010.
[2] A. Risitano, G. Risitano, C. Clienti. Determination of fatigue limit by mono-axial tensile
specimens using thermal analysis. 9th International Conference on Fracture and Damage Mechanics,
Nagasaki, Japan, 20-22 September (2010). Conference Proceeding: Key Engineering Materials; 452-
453: 361-364.
[3] A. Risitano, G. Risitano. Determining Fatigue Limits with Thermal Analysis of Static Traction
Tests, Fatigue Fract. Engng. Mater. Struct. 36 (2013) 631-639.
s [MPa] DT [°C]
s0
t [s]
Phase
1
Phase
2
Phase
3

8. Static Test
The material used in this study is a
S690QL steel.
The static tensile tests were carried
out on base material specimens
and butt-welded specimens with
welds overfill removed, using a
servo-hydraulic load machine
(INSTRON 8854) at a crosshead
rate equal to 3 mm/min on base
material and welded specimens.
The DIC (ARAMIS 3D 12M ) and IR
Camera (FLIR Systems SC 8400)
have been used during all tests.
6 Aprile 2018 Giacomo Risitano et Al. 8
A commercial high strength structural steel (HSSS),
with a thickness of 5 mm is tested in quenched
and tempered condition (Q + T) corresponding
to European Standard Steel EN 10137-2
S690QL.

9. Static Tests
6 Aprile 2018 Giacomo Risitano et Al. 9
0
200
400
600
800
1000
0 10 20
Stress[MPa]
y -strain %

10. Static Tests
Figure shows the pattern of the applied stress and the experimental temperature increment DTs,
detected by means of the IR camera, during static tensile tests carried out on base material.
6 Aprile 2018 Giacomo Risitano et Al. 10
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
-800
-700
-600
-500
-400
-300
-200
-100
0
100
200
300
400
500
600
700
800
0 5 10 15 20
DT[°C]
Stress[MPa]
time[s]
Stress [MPa] DT Real [°C] DT theoretical [°C]
Base Material
smax= 390 MPa

11. Static Tests
Figure shows the pattern of the applied stress and the experimental temperature increment DTs,
detected by means of the IR camera, during static tensile tests carried out on welded joints.
6 Aprile 2018 Giacomo Risitano et Al. 11
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
-800
-700
-600
-500
-400
-300
-200
-100
0
100
200
300
400
500
600
700
800
0 5 10 15 20
DT[°C]
Stress[MPa]
time[s]
Stress [MPa] DT Real [°C] DT theoretical [°C]
22/06/2015
Welded Joint
smax= 280 MPa

12. Fatigue Test
The specimens, investigated under fatigue loading, have the same geometry of those used for the static tests and are made from the
same steel and the same servo-hydraulic load machine (INSTRON 8854) was used.
Fatigue tests were carried out at R= 0.1 and f= 10 Hz, applying increasing loads by a stepwise succession (applied to the same
specimen), starting from Ds= 480 MPa (Ds= 340 MPa for welded joint) with steps of 50 MPa every 20.000 cycles.
In order to apply the TM, the surface temperature of the specimen was monitored during the whole fatigue test with IR Camera (model
FLIR Systems A40M).
6 Aprile 2018 Giacomo Risitano et Al. 12
0
1
1
2
2
3
0E+00 1E+05 2E+05 3E+05 4E+05 5E+05 6E+05 7E+05 8E+05
DTAS[°C]
smax
2 [MPa2]
base material
test 1
base material
test 2
base material
test 3
welded joint
smaxeTM
= 408 MPa
smaxeTM
= 393 MPa
smaxeTM
= 255 MPa
smaxeTM
= 347 MPa
The Thermographic
Method allows to
assess the fatigue limit
using theoretically only
one specimen.
The values of the
asymptotic
temperature increment
DTas, reached at every
loading step, were
plotted versus the
corresponding values
of maximum stress
squared smax
2 and a
linear regression was
performed.
The fatigue limit smax_eTM
can be assessed by the
intersection of the
regression straight line
with the abscissa axis: this
intersection corresponds
to the highest maximum
stress for which there is no
temperature variation.

13. Results and Conclusions
6 Aprile 2018 Giacomo Risitano et Al. 13
BASE MATERIAL STM TM
Average Value s0
[MPa]
390 383
WELDED JOINT STM TM
Average Value s0
[MPa]
280 255
The value of fatigue limit predicted for base material was confirmed by a fatigue test carried out at smax= 420 MPa, which did not produce the
specimen failure after 2E+06 cycles.
200
300
400
500
600
700
800
900
1.00E+04 1.00E+05 1.00E+06 1.00E+07
smax[MPa]
N
Base Material (R= 0,1)
TRM 1 TRM 2 TRM 3 TRM 4 SINGLE STEP
Run Out
200
300
400
500
600
700
800
900
1.00E+04 1.00E+05 1.00E+06 1.00E+07
smax[MPa]
N
Welded Material (R= 0,1)
TRM 1 TRM 2 TRM 3 SINGLE STEP
1.00E+00
1.00E+01
1.00E+02
1.00E+03
1.00E+04
1.00E+05
1.00E+06
F
INTEGRO SALDATO