Article citation information:
Szymczak,
T., Herman, P. Anisotropy of mechanical parameters of weld for high-strength
steel in tensile test for towing and coupling components in
recovery vehicles. Scientific Journal of
Silesian University of Technology. Series Transport. 2025, 126, 255-266. ISSN: 0209-3324. DOI: https://doi.org/10.20858/sjsutst.2025.126.16.
Tadeusz SZYMCZAK[1],
Patryk HERMAN[2]
ANISOTROPY OF MECHANICAL PARAMETERS OF WELD FOR HIGH-STRENGTH STEEL IN
TENSILE TEST FOR TOWING AND COUPLING COMPONENTS IN RECOVERY VEHICLES
Summary. The paper
presents results for S700MC high-strength steel and
its weld at longitudinal and transverse orientations of specimens. The
determination of anisotropy features is proposed for the parent material and
welding joint due to the often usage of this steel for manufacturing of towing
and coupling components in recovery vehicles. This means that the most
important mechanical parameters of the regions questioned should be determined
for numerical and analytical analysis with the target to get their type
approval and to keep the road safety. The mini-specimens were used to reflect
the joint behaviour subjected to monotonic tension. The weld behaviour was
assessed using the longitudinal specimen that was manufactured from the joint.
The results enabled to indicate differences in the section tested depending on
the loading orientations considered.
Keywords: high-strength
steel, weld, anisotropy, mechanical parameters, testing
1. INTRODUCTION
High-strength steel (HSS) is regarded as a
modern structural material for various engineering applications because it
reflects attractive mechanical parameters such as yield stress (min. 600 MPa),
ultimate tensile strength (min. 1300 MPa) and ductility (min. 15%) if compared
to other structural materials [1], [2], [3]. HSS can also be characterised by a
lower mass in comparison to the conventional structural materials [4], [5]. As
a consequence, this steel is recommended to various branches of industry [1],
[4], [5], [6]. Among them, one can indicate:
a) machine industry
(components of machines for building: excavator bucket, scoops, grabs),
b) automotive (container trailers, flatbed
trailers, box trailers, bulk and tank trailers, car carriage trailers, buses
and light trucks, concrete pump cranes, mobile cranes, cargo handlers),
c) forest and
agricultural (timber trailers, harvesters, forwarders, tippers and trailers),
d) ocean energy (wave
energy, tidal and stream energy converters, offshore wind farms),
e) marine mining (jack-u
legs and pylons),
f) recovery marine (boom
parts, joints and knees, winch equipment).
Fig. 1. The coupling zone made of the
S700MC high-strength steel
Typical applications of the S700MC steel for the coupling regions (Fig. 1) and supports
for the towing booms used in recovery vehicles are presented in Fig.1 and Fig. 2, respectively.
A wide
range of the S700MC steel applications is strongly
dependent on the mechanical resistance of a weld on the loading type used, [7],
[8], [9]. Therefore, the basic mechanical parameters
such as yield point (YP) and ultimate tensile
strength (UTS) should be determined as the first step
of the experimental procedure. The steel manufacturers indicate many important
aspects and parameters of welding, that play an important
role, taking into account the joint quality [7], [8].
They should
be determined within the temperature range from 500 oC
to 800 oC
executed in a period from 5 to 25 seconds. A value of the period depends on the
steel grade. In the case of the S1300MC steel, for
example, it is equal to 15. Applying optimal cooling time intervals, higher
values of mechanical properties can be obtained. Such procedure is strongly
recommended for different welding processes, i.e.: MAG (Metal Active Gas), MMA (Manual Metal Arc), TIG
(Tungsten Inner Gas) as well as SAW (Submerged Arc Welding) (SSAB), [7], [8].
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Fig. 2. Support of a towing boom body
made of the S700MC high-strength steel for the
recovery vehicle |
Fig. 3. The S700MC
high strength steel plate with a weld |
Among many
important issues related to mechanical parameters, the determination one can
indicate a quality of the welding joint materials reflecting their anisotropic
character of either the parent material or weld sections. Many aspects of the
majority of the research works in such context have not been thoroughly studied
yet. Therefore, in order to fill this gap, the S700MC
steel was selected as the object of tests, Figs. 3 and 4.
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(a) |
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(b) |
Fig. 4. The S700MC
high-strength weld: face (a) and root (b) of the weld, respectively
2. DETAILS OF EXPERIMENT
The S700MC
steel with a weld in the form of a plate of 10 mm thickness was tested,
Fig. 3.
Fig. 5. Mini-specimen used
for the parent material and its weld testing
under monotonic tensile conditions
Fig. 6.
The specimens’ arrangements in the S700MC plate with
a weld
The joint was manufactured, Figs. 3,
4, under the following welding parameters (MAG): 175 A and 20 V for remelting, 178 A and 24 V for joint filling under current
pulsation within the range of 5.6 – 8.2 m/min.
A flat mini-specimen was designed
for testing the parent material and weld, Fig. 5. The specimens were arranged
taking a major axis of the weld as the reference axis to produce specimens
along longitudinal (L) and transverse (T) directions, Fig. 6.
Therefore, the specimen for
examining the weld was manufactured from the region entirely composed of it.
The testing of the Heat Affected Zone (HAZ) was
carried out on specimens situated in parallel to this area, Fig. 6.
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(b) |
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Fig. 7. Mini-specimen in grips of
the 8874 Instron servo-hydraulic testing machine
before a tensile test: (a) general view, (b) specimen and 2620-601 Instron uniaxial extensometer |
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All specimens containing the weld
were mechanically processed by removing the face and root. The specimens were
directly mounted in the grips of the 8874 Instron
servo-hydraulic testing machine, Figs. 7, 8. The values of axial strain were
captured using a 2620-601 Instron uniaxial
extensometer of gauge length equal to 12.5 mm and measuring capacity of
± 5 mm, Figs. 7a, b. All tests were carried out at
room temperature for a displacement velocity equal to 1 mm/min up to the
specimens’ fracture, Fig. 8.
Fig. 8. Mini-specimen made of parent
material (the S700MC steel) from transversal
direction to the weld’s major axis before the final stage of tensile test
3. RESULTS
Data collected during the tensile tests of the parent material were
carried out on the specimens taken from either the transverse or lateral
directions, Fig. 6.
It has to be emphasized that quite good similarity can be easily observed
of both tensile characteristics, Fig. 9. One can conclude that the material
exhibited almost isotropic behaviour, and therefore, the manufacturing process
applied to the material production can be treated as good enough in terms of
ensuring uniform mechanical parameters of the manufactured semi-finished
product.
Fig. 9. Tensile characteristics of the parent
material selected from both directions, i.e. longitudinal (L) and transverse
(T), E – Young’s modulus, PL – proportional limit,
EL – elastic limit, YP – yield point, UTS – ultimate tensile strength
An opposite effect was for the parent material and weld, Figs. 10, 11.
Both tensile characteristics differ significantly. In the case of weld
material, the physical yield point disappeared. For the transverse direction
(Fig. 11) due to the weld position, besides the clear mechanical parameters’
reduction, the tensile curve is located much lower than that for the parent
material of the same orientation. Also, a 50% reduction of elongation can be
observed, Fig. 11.
The results for the HAZ and weld are presented
in Fig. 12. One can easily notice that the behaviour of the weld material
depends strongly on the specimen orientation. For the same specimen
orientation, the tensile curves were very similar for both the HAZ and weld material (the longitudinal direction).
If directions of the specimens representing HAZ
and weld materials are perpendicular
(Fig. 12), then the tensile curves take a completely different shape, thus
identifying the anisotropic character of the mechanical properties of the
welding joint material. This is reflected by the lower values of mechanical
parameters and ductility at 13% and 50%, respectively. As a consequence, a
high-strength component behaviour with weld should be numerically modelled
using lower values of mechanical parameters than the parent material.
Fig. 10. Tensile
characteristics of the parent material and its weld determined
using specimens selected from the longitudinal direction
Fig. 11. Tensile characteristics of the parent
material and its weld determined by
means of specimens selected from the transverse direction
Fig. 12. Tensile
characteristics of the weld and HAZ
The anisotropy features were also analysed in the form of power law
equations, Tab. 1. This approach has enabled indicating the same values of
strain hardening exponent for the parent material, HAZ
and weld material. This means the hardening of the material regions examined
under tension is represented by very similar deformation mechanisms. It can be
easily noticed as the advance of the joining process concerning the steel
examined. The second coefficient of power of law, representing stress,
indicates that the lowest mechanical resistance is observed for the weld
material in the transverse direction.
Tab. 1
Power law equations: PM-parent material
|
PM-L |
PM-T |
HAZ |
Weld-L |
Weld-T |
|
1096.69 |
1074.34 |
1109.54 |
1113.71 |
974.46 |
From a practical point of view, it is worth noticing that this kind of
data supports designing components such as platform, working frame and towing
booms with coupling functions, for the requirements of UN Regulation 55 (UNR55) [10], which reflects the mechanical resistance of
coupling components under cyclic loading. This means the fatigue limit of a
weld should be known because this region is very often indicated as the weakest
one, and it is inspected after 2×106 cycles using dye-penetrant and
macrophotography techniques for the regimes of UNR55.
The experimental program was supplemented by analysis of the fracture
regions. Differences were represented by fracture regions’ orientation, Fig.
13. In the case of the parent material (Figs. 13a,
b), despite the high similarity of the tension curves (Fig. 9), there was a
difference in the share of stress components involved in the material decohesion. For a longitudinal direction (Fig. 13a), axial stress was dominant for fracturing while in the
case of perpendicular one (Fig. 13b) axial and shear
components occurred significantly.
The weld and HAZ degradations were very
similar concerning the fracture region inclination, i.e. axial stress has
followed the process, Fig. 13c, d. Certain
differences in the fracture regions of the weld (Figs. 13c,
d) and HAZ (Fig. 14) were observed on the direct
observation of the fracturing details on the decohesion
plane. In the case of the weld, the fracture zones were represented by
horizontal and tangential fracture planes, Figs. 14c1,
d1 without any cracks – oppositely to the HAZ degradation, Fig. 15.
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(a) |
(b) |
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(c) |
(d) |
Fig. 13. Specimens after decohesion
in tensile test: (a) and (b) parent material and weld in L direction -
respectively, (c) weld in T direction, (d) HAZ
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(a1) |
(b1) |
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(a2) |
(b2) |
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(d1) |
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Fig. 14. Fracture zones of
the parent material and weld; the parent material in (a1,
a2) longitudinal and (b1,
b2) transverse directions; the weld in (c1) longitudinal and (d1, 2)
transverse direction |
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(a) |
(b) |
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Fig. 15.
Fracture zones of the HAZ |
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Moreover, it is worth noticing that in the case of weld, instead of
cracks, small dimples and bi-planar cracking regions were discovered, Figs. 14c1, d2. The HAZ
fracture (Fig. 15b) was very similar to that obtained
for the parent material, Figs. 14a2, b2. They indicate a small influence of the MAG on the HAZ zone.
In comparison to the SSAB welding requirements
of the S700MC, the HAZ
should represent the soft zone [11].
The results captured in this research enable formulating a general
conclusion that the MAG process used for the welding process of the S700MC steel led to the elimination of the physical yield point
for all regions of the joint examined, and as a consequence, enforced necessity
for introduction of the proof yield.
4. CONCLUSIONS
The quality of the welding joint should be determined using
specimens selected from longitudinal and transverse directions concerning the
weld, as well as its heat-affected zone and welded material.
Anisotropy features of a welded region enable indicating
the weakest zone of the joint. Hence, the real values of mechanical parameters
can be applied for calculations, modelling and designing components for the
automotive industry.
Acknowledgments
The authors would like to express their gratitude to
Professor Zbigniew L. Kowalewski
(IPPT PAN, Warsaw, Poland) for his comments and
suggestions.
The authors’ gratitude is also addressed to the TEVOR Sp. z o.o. company (ul. Moscickiego 27-29,
26-111 Skarzysko-Kamienna, Poland) for the support of
the tests.
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Scientific Journal of Silesian University of Technology. Series
Transport is licensed under a Creative Commons Attribution 4.0
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[1] Department of Vehicle Type-Approval
& Testing, Motor Transport Institute, Jagiellonska
80 Street, 03-301 Warsaw, Poland. Email: tadeusz.szymczak@its.waw.pl.
ORCID: https://orcid.org/ 0000-0003-2533-7200
[2] TEVOR Sp. z o.o., Ignacego Moscickiego 27-29 Street, 26-110 Skarzysko-Kamienna, Poland. Email: patryk.herman@tevor.pl. ORCID: https://orcid.org/0009-0003-9304-9064