High-Cycle Fatigue Properties and Damage Mechanism of Q345B Structural Steel
The high-cycle fatigue behavior of Q345B structural steel was investigated experimentally. Highfrequency vibration fatigue testing machine and scanning electron microscopy were used to study the high-cycle fatigue S—N curve characteristics and crack initiation mechanism at ambient temperature. The...
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| citation_txt | High-Cycle Fatigue Properties and Damage Mechanism of Q345B Structural Steel / X.L. Hu, Y.J. Liu, M.K. Khan, Q.Y. Wang // Проблемы прочности. — 2017. — № 1. — С. 79-86. — Бібліогр.: 16 назв. — англ. |
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| description | The high-cycle fatigue behavior of Q345B structural steel was investigated experimentally. Highfrequency vibration fatigue testing machine and scanning electron microscopy were used to study the high-cycle fatigue S—N curve characteristics and crack initiation mechanism at ambient temperature. The surface temperature of the specimens was monitored. The relation between the fatigue limit and the amount of heat dissipation was also investigated. It was found that the fatigue life changed inversely with the stress amplitude in the high-cycle range. The fatigue limit in high cycle range was obtained from heat dissipation in the specimen and found to have good agreement with the S—N curve. The crack initiation was attributed to the surface defects and the persistent slip bands due to the cycle slip in fatigue loading.
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UDC 539.4
High-Cycle Fatigue Properties and Damage Mechanism of Q345B Structural
Steel
X. L . H u ,a Y. J . L iu ,a1 M . K . K h an ,b an d Q. Y. W an g a c 2
a Key Laboratory of Energy Engineering Safety and Disaster Mechanics, Ministry of Education,
College of Architecture & Environment, Sichuan University, Chengdu, China
b Faculty of Engineerint and Computing, Coventry University, Coventry, UK
c School of Urban and Rural Construction, Chengdu University, Chengdu, China
1 liuyongjie@scu.edu.cn
2 wangqy@scu.edu.cn
The high-cycle fatigue behavior o f Q345B structural steel was investigated experimentally. High-
frequency vibration fatigue testing machine and scanning electron microscopy were used to study the
high-cycle fatigue S—N curve characteristics and crack initiation mechanism at ambient temperature.
The surface temperature o f the specimens was monitored. The relation between the fatigue limit and
the amount o f heat dissipation was also investigated. It was found that the fatigue life changed
inversely with the stress amplitude in the high-cycle range. The fatigue limit in high cycle range was
obtained from heat dissipation in the specimen and found to have good agreement with the S—N
curve. The crack initiation was attributed to the surface defects and the persistent slip bands due to
the cycle slip in fatigue loading.
K eyw ords: Q345B structural steel, high-cycle fatigue, heat dissipation, fatigue strength,
fatigue crack initiation mechanism.
In tro d u c tio n . Q345B is a low -alloy steel o f Chinese brand, w hich exhibits excellent
perform ance in low-tem perature, cold stamping, cutting, welding applications. It is w idely
used in bridge construction, automotive com ponents, pressure vessels etc. In bridge civil
engineering bridge applications, the m aterial experiences static and dynam ic loading due to
vehicles and wind. The dynam ic loads are o f low level but act for large am ount o f cycles. If
the structural com ponents in this application are not designed appropriately, the cum ulative
dam age due to all these loadings result in the fatigue fracture, w hich m ay be o f serious
consequences.
In structural com ponents, the com m only used h igh strength steel [1, 2], low carbon
steel [3, 4] and stainless steel [5, 6] alloys, the eariler studies m ainly focused on low-cycle
fatigue w here the fatigue cycles m ainly rem ain less than 105 cycles. Recent studies have
shown that for m any engineering alloys the concept o f traditional fatigue lim it is not very
accurate. The fatigue failure occur after h igh-cycle periodic loads beyond 10 cycles. Under
these conditions, the stresses are found low er than the y ield strength. O ther param eters have
been studied to investigate the high-cycle fatigue behavior o f structural steels [7-12] such
as S - N curves, fatigue strength, fatigue life prediction, structure evolution law, fatigue
crack initiation and propagation mechanism. The effect o f microstructure, prestrain, average
stress, m aterial defects (inclusions), gaps and surface treatm ents, on the cracking behaviour
o f the m aterial have also been studied. However, the research on the high cycle fatigue
behavior o f Q345B structural steel is still scarce at present. This study used high-frequency
tension and com pression load to study the high-cycle fatigue perform ance o f Q345B
structural steel beyond 10 cycles. The fatigue fracture o f specim ens was observed by
electron m icroscope and the fatigue cracks initiation m echanism w as investigated. The
surface tem perature o f the specim ens during the high-frequency tension and com pression
© X. L. HU, Y. J. LIU, M. K. KHAN, Q. Y. WANG, 2017
ISSN 0556-Î7ÎX. Проблемы прочности, 2017, № 1 79
mailto:liuyongjie@scu.edu.cn
mailto:wangqy@scu.edu.cn
X. L. Hu, Y. J. Liu, M. K. Khan, Q. Y. Wang
progress was m onitored and analyzed by infrared imager. The relationship betw een the heat
dissipation am ount and fatigue lim its was discussed to acquire the fatigue lim it of the
material.
1. Test M a te ria ls an d Specim ens. The com m ercial hot-rolled Q345B low alloy steel
o f thickness o f 20 m m was used in this study. The m ain chem ical com positions and
m echanical properties of the m aterial are shown in Tables 1 and 2, respectively. The
m icrostructure o f the m aterial is show n in Fig. 1. The m aterial is a rolled ferrite pearlite
dual phase low carbon steel, and the two phases are in zonal distribution. The microstructure
content o f lam ellar hard pearlite is about 30%, and the ferrite content is about 70%. Due to
the low carbon content in the m aterial com position, the ferrite phase w as abundant while
pearlite w as scarce in the m icrostructure. The strength and hardness o f ferrite was not high
however, the m aterial showed good ductility and toughness.
T a b l e 1
Chemical Composition of Q345B Steel (wt.%)
C Si Mn S P
0.16 0.35 1.34 0.11 0.22
T a b l e 2
Mechanical Properties of Q345B Steel
E , GPa o s , MPa a b, MPa p , g/cm3 A
201 395 550 7.85 0.27
Fig. 1. Microstructure of Q345B steel.
The fatigue specim en w as designed based on the resonance principle. Its size is shown
in Fig. 2. The natural vibration frequency is 155 Hz.
2. M ethods.
2.1. Test M ethods. The fatigue tests w ere carried out on the high-frequency
electrom agnetic vibration fatigue test m achine (Changchun Q ian Bang QBG-100). The test
m achine utilized the electrom agnetic resonance principle. The loading stress ratio R was
set as —1. The test frequency w as determ ined by the aforem entioned frequency of
specim en and set as 155 Hz. Cyclic loaded stresses w ere set from 250 to 300 M Pa at 6
levels.
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High-Cyde Fatigue Properties and Damage Mechanism
Fig. 2. Schematic diagram of the specimen dimensions (in mm).
2.2. H ea t D issipation Test. As a non-contact, real-tim e, nondestructive m easurem ent
technology, infrared im aging can precisely measure, display and analyze the temperature
distribution on the surface o f the specimen. As a result, it can be applied to the heat
dissipation analysis. The heat dissipation in the fatigue progress w as analyzed through the
tem perature changes on the surface o f the specimen. The m easurem ent system is show n in
Fig. 3. The tem perature distribution o f the specim en was m onitored by an infrared imager
(NEC NS9500) w ith an accuracy o f ± 0.1°. The infrared im ager was calibrated by
therm ocouples and m ercury therm om eters before the test. To avoid the errors caused by the
fluctuation o f am bient tem perature, a test piece w as placed next to the sample as a
reference. So the change o f the surface tem perature o f the test p iece can be expressed as
M a = A T t - A T r , (1)
where A T t and A T r are the changes o f the surface tem perature o f the test and referenced
pieces, respectively.
Fig. 3. Measurement of thermal dissipation.
2.3. M icroscopic A na lysis o f F atigue Fracture. Scanning electron m icroscopy (SEM)
w as used for m icroscopic observation o f the fatigue fracture o f the specimens. The
m echanism o f initiation and propagation o f fatigue cracks w as investigated.
2.4. Statistics o f F atigue Data. The S - N curve is usually described by exponential
function, pow er function, Basquin equation [13, 14] or three-param eter m odel [15]. The
Basquin equation w as used in this study and it is expressed as
a a = a f ( 2 N f )b , (2)
where a a is the load am plitude, M Pa, N f is the fatigue life, a f is the coefficient o f
fatigue strength, M Pa, and b is the exponent o f fatigue strength, nam ely the Basquin
exponent. The constants a f and b are obtained by the least squares method.
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X. L. Hu, Y. J. Liu, M. K. Khan, Q. Y. Wang
3. R esu lts an d D iscussion.
3.1. S - N Curve. The tested S - N data o f high-frequency tension and com pression
fatigue for Q345B in the high-cycle range are shown in Fig. 4. As it can be seen from the
figure, the fatigue life varied inversely w ith stress amplitude. The specimen below 240 MPa
stress did not show fracture. So the fatigue lim it o f Q345B in the high-cycle range was
concluded as 240 MPa.
2 N f , cycles
Fig. 4. S -N curve for high-frequency tension and compression fatigue with high cycles of Q345 steel.
The tested S - N data are fitted by Basquin equation and the result is
a a = 444.95(2N f )_0'041, R 2 = 0.962. (3)
The fitted curve w as plotted in F ig. 4 as solid line. It can be seen that the test data
distribute around the Basquin equation, w ith the fitted R close to 1. So Basquin equation
can quantitatively describe the features o f sym m etrical tension and com pression fatigue
S - N curve in the high-cycle range for Q345B.
3.2. The M echan ism o f F atigue C rack Initia tion . Fatigue fracture w as observed
m icroscopically by scanning electron microscopy. The cross-sections o f fatigue specim ens
w ere all flat fractures norm al to the axial stress. A ll the fatigue cracks initiate on the surface
o f specimen. M ore crack initiations occur under the conditions of high stress and short life.
The fracture m orphologies are shown in Fig. 5 for a equal to 260 M Pa and N f
equal to 7.55-10 . The fatigue initiation zone, crack propagation zone and fracture zone can
be clearly seen from the full view o f fracture m orphologies in Fig. 5a. The fracture surface
show ed a feature o f radial river pattern in the crack propagation zone. The radial center was
located at the fatigue crack initiation position on the surface o f the specim en, w hich can be
seen from the crack initiation zone in Fig. 5b. The fatigue crack initiation position was
observed under high magnification, as shown in Fig. 5c. Strips on the surface o f specimen
can be seen clearly. For low-cycle and high-cycle fatigue fractures, large alternating loads
result in the plastic deform ation on the surface of specim en, especially in the areas w ith
defects like m achining m arks, scraping scratches, inclusions or geom etric discontinuity.
U nder the alternating loads, the m aterial “ squeezes” and “extrudes.” As a consequence, slip
lines or slip bands form on the surface. W ith the further effect o f alternating loads, these
slip lines or slip bands gradually extended to the interior o f the m aterial and formed
persistent slip bands. A lternating slip results in the form ation o f slip steps, penetrated ditch
82 ISSN 0556-171X. npoôëeubi 2017, № 1
High-Cyde Fatigue Properties and Damage Mechanism
and extruded strips on the surface o f material, leading to the uneven surface and m icrocrack
initiation. W hen the m icrocracks reached to a certain size, the fatigue cracks started to
propagate and left traces in the crack propagation zone, nam ely fatigue striations as shown
in Fig. 5d. Each step o f fatigue cracks represents a forward extended “pace” under cyclic
load. The crack propagation can be quantitatively analyzed according to the w idth of
fatigue striations [16].
Fig. 5. Fatigue fracture for a = 260 MPa and N f = 7.55-104 cycles: (a) full view of fracture
morphologies; (b) fatigue initiation zone; (c) high magnification of the fatigue initiation position;
(d) fatigue striations.
The fatigue cracks usually initiate at m ultiple positions instead o f a single one on the
m aterial surface. The propagation o f cracks under alternating loads leads to m ore crack
initiation and propagation, especially under high stress. Figure 6 shows that two fatigue
cracks initiate and propagate on the surface w ith o = 280 MPa. As shown in Fig. 6b, all the
fatigue cracks initiate on the m aterial surface. The cracks expand into the interior o f the
m aterial under cyclic loads. The two cracks intersect w ith each other at the position o f the
white stair. Then the stress concentration is strengthened and a large factor o f stress
intensity is produced at the tip o f the cracks. The two cracks merge to each other to form a
m ain crack and further accelerate the propagation.
3.3. A na lysis o f H ea t D issipation to D eterm ine the F atigue L im it. The temperature
raising curves o f Q345B steel in the fatigue progress are shown in Fig. 7. The specim en is
under five different loads betw een 260 and 300 MPa. It can be seen that the fatigue
progress has three typical stages, nam ely the initial stage o f tem perature rise, tem perature
stabilization stage and rapid tem perature rising stage. The tem perature changes m easured
by infrared im ager before and after the specim ens fracture are shown in Fig. 8. The
ISSN 0556-171X. npoôaeMbi 2017, № 1 83
X. L. Hu, Y. J. Liu, M. K. Khan, Q. Y. Wang
Fig. 6. Fatigue fracture for a = 280 MPa and N f = 3.45-104 cycles: (a) fracture morphologies;
(b) fatigue initiation zone.
j i i i i i i i i i________
0 1000 2000 3000 4000 5000
Time (s)
Fig. 7. Temperature rising curves of Q345B steel rate and the amplitude of load.
625 627 629 631 633 635
Fig. 8. Temperature change before and after the specimen fractures.
tem perature rises rapidly after the cracks propagate, leading to higher tem perature in the
propagating zone than that in other areas. This progress corresponds to the inflection point
of phase II and phase III in the tem perature raising curves. The specim en fractures soon
after the cracks begin to propagate. Therefore, the fatigue crack initiation is verified to be
the m ain part of the fatigue life fo r high-cycle fatigue.
84 ISSN 0556-171X. npoôxeMbi nponnocmu, 2017, № 1
High-Cycle Fatigue Properties and Damage Mechanism
Figure 8 shows that the initial and rapid tem perature-rising stages take up a small part
of the fatigue progress. As the am plitude of the load increases, the tem perature curve at the
initial tem perature rising stage turned steeper. The rate of initial tem perature rising
increased linearly w ith the am plitude o f load, as shown in Fig. 9. In addition, the difference
betw een the stable tem perature and initial tem perature increased w ith the am plitude o f load.
The relations are plotted in Fig. 10, w hich shows that the tem perature changes also
increased linearly w ith the load amplitude.
Stress amplitude (MPa) Stress amplitude (MPa)
Fig. 9 Fig. 10
Fig. 9. Relation between the temperature rising rate and the amplitude of load.
Fig. 10. Relation between the stable temperature changes and the amplitude of stress.
W hen the am plitude o f load was sm aller than the fatigue limit, the tem perature change
was not very evident. Therefore, the relationship betw een the stable tem perature change
and the load am plitude was obtained by linear regression according to the curve in F ig. 10.
The am plitude at 0 tem perature change is acquired as the fatigue limit. The relationship
betw een the stable tem perature change and the load am plitude for Q345B w as linear. The
intersection o f the line and the x-axis was the fatigue limit. For Q345B steel the fatigue
limit was obtained as 253 MPa, w hich was similar to the high-cycle fatigue limit o f 240 MPa
as obtained by the S - N curve.
C onclusions. The present w ork investigated the fatigue behavior o f Q345B steel in
high-cycle range by the high frequency vibration fatigue in tension and compression,
m easurem ents o f infrared heat dissipation and m icroscopic observation. The conclusions
are given below.
1. The fatigue life varied inversely w ith the loading stress in the range o f 104 ~ 107
cycles. The m aterial under 107 cycles show ed no fracture below 240 MPa. The fatigue lim it
o f Q345B in the high-cycle range w as obtained as 240 MPa. The test data was analyzed
w ith Basquin equation and S - N curve characteristics o f structural steel Q345B was acquired.
2. The fatigue cracks under high cycle initially occurred on the surface o f specimens.
The stress concentration on the surface, caused by the surface defects and persistent slip
bands, resulted in the cycle slip leading to the crack initiation.
3. The initial tem perature rise and the stable tem perature change increased linearly
w ith the stress amplitude. A sim ilar fatigue lim it was obtained by heat dissipation analysis
and S - N curve.
A cknow ledgm ents. The authors gratefully acknow ledged the financial supports from
the N ational Science Foundation o f China (NSFC-11172188, 11302142) and the Program
for Changjiang Scholars and Innovative Research Team (IRT14R37).
ISSN 0556-171X. Проблемы прочности, 2017, № 1 85
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Received 30. 08. 2016
X. L. Hu, Y. J. Liu, M. K. Khan, Q. Y. Wang
86 ISSN 0556-171X. npo6n.eubi 2017, N2 1
|
| id | nasplib_isofts_kiev_ua-123456789-173585 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 0556-171X |
| language | English |
| last_indexed | 2025-12-07T13:39:52Z |
| publishDate | 2017 |
| publisher | Інститут проблем міцності ім. Г.С. Писаренко НАН України |
| record_format | dspace |
| spelling | Hu, X.L. Liu, Y.J. Khan, M.K Wang, Q.Y. 2020-12-12T14:02:16Z 2020-12-12T14:02:16Z 2017 High-Cycle Fatigue Properties and Damage Mechanism of Q345B Structural Steel / X.L. Hu, Y.J. Liu, M.K. Khan, Q.Y. Wang // Проблемы прочности. — 2017. — № 1. — С. 79-86. — Бібліогр.: 16 назв. — англ. 0556-171X https://nasplib.isofts.kiev.ua/handle/123456789/173585 539.4 The high-cycle fatigue behavior of Q345B structural steel was investigated experimentally. Highfrequency vibration fatigue testing machine and scanning electron microscopy were used to study the high-cycle fatigue S—N curve characteristics and crack initiation mechanism at ambient temperature. The surface temperature of the specimens was monitored. The relation between the fatigue limit and the amount of heat dissipation was also investigated. It was found that the fatigue life changed inversely with the stress amplitude in the high-cycle range. The fatigue limit in high cycle range was obtained from heat dissipation in the specimen and found to have good agreement with the S—N curve. The crack initiation was attributed to the surface defects and the persistent slip bands due to the cycle slip in fatigue loading. The authors gratefully acknowledged the financial supports from the National Science Foundation of China (NSFC-11172188, 11302142) and the Program for Changjiang Scholars and Innovative Research Team (IRT14R37). en Інститут проблем міцності ім. Г.С. Писаренко НАН України Проблемы прочности Научно-технический раздел High-Cycle Fatigue Properties and Damage Mechanism of Q345B Structural Steel Характеристики многоцикловой усталости и механизм повреждения конструкционной стали Q345B Article published earlier |
| spellingShingle | High-Cycle Fatigue Properties and Damage Mechanism of Q345B Structural Steel Hu, X.L. Liu, Y.J. Khan, M.K Wang, Q.Y. Научно-технический раздел |
| title | High-Cycle Fatigue Properties and Damage Mechanism of Q345B Structural Steel |
| title_alt | Характеристики многоцикловой усталости и механизм повреждения конструкционной стали Q345B |
| title_full | High-Cycle Fatigue Properties and Damage Mechanism of Q345B Structural Steel |
| title_fullStr | High-Cycle Fatigue Properties and Damage Mechanism of Q345B Structural Steel |
| title_full_unstemmed | High-Cycle Fatigue Properties and Damage Mechanism of Q345B Structural Steel |
| title_short | High-Cycle Fatigue Properties and Damage Mechanism of Q345B Structural Steel |
| title_sort | high-cycle fatigue properties and damage mechanism of q345b structural steel |
| topic | Научно-технический раздел |
| topic_facet | Научно-технический раздел |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/173585 |
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