1 2
THE INFLUENCE OF THE FRACTURE SURFACE
ORIENTATION TO THE ROLLING DIRECTION ABOUT THE
FRACTURE TOUGHNESS OF A STEEL BELONGING TO A
PRESSURE VESSEL
Iosif HAJDU, Pavel TRIPA, Ovidiu BRÂNZAN
Universitatea “Politehnica” Timişoara, Facultatea de Mecanică
Universitatea “Politehnica” Timişoara, Facultatea de Mecanică
CIMVEST ARAD
Abstract
For a steel plate meant for pressure vessels we have determined the fracture
toughness on Chevron type specimens, with the longitudinal axes oriented on six
different directions, shifted with 30o.
The tests have been performed with constant loading speed of different values
at normal temperature. We had in view to determinate the direction, after which the
fracture toughness is maximum. But the primary results have not emphasized the
existence of such a direction.
Key words: fracture toughness, fracture mechanics, Chevron specimen,
normal temperature, steel for boilers, rolling direction
1. INTRODUCTION
The steel machine parts includes a lot of microscopic cracks which can not be
eliminated and diminish the strength capacity. The strength capacity is estimated be
the mechanical characteristics of the material which are influenced by a lot of factors.
In the case of steel plates, one of the factors may be the fracture surface orientation
to the rolling direction.
In the framework of the paper, as a mechanical characteristic, in order to
evaluate the strength capacity, the fracture toughness has been considered. As
influence elements, the fracture surface orientation to the rolling direction and the
loading rate have been taken into consideration.
The analysis has been performed for a pressure vessel steel STAS 2883/3-88,
brand R 360 , cutted from a thick rolling steel plate.
After a laboratory study, the following static and dynamic mechanical
characteristics have been obtained: Re = 256.2 MPa; Rm = 381.2 MPa, A10(δ10) =
26.6%; Z = 65.9%. KV = 13.3 [J]
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TOME II. Fascicole 1
2. SPECIMENS AND EXPERIMENTAL INSTALATION
In order to estimate the fracture toughness, the Chevron specimens have
been used. The option for these specimens is based on the fact that the thickness of
the rolling plate (22 mm) is too small to manufacture specimens according to the
standard STAS 9760-84. Moreover, for these range of specimens, it is not important
to respect the plane state of deformation.
In the same time, the tests performed on these range of specimens are easy
to be carried out, and these are not necessary special experimental installations. The
obtained results may be considered as acceptable for an experimental investigation.
The manufacturing process in order to obtain the Chevron specimens,
according to different directions reported to the rolling direction, is presented in Fig.1.
3/1
4/1
5/1
3/2
5/2
4/2
300
300
5/3
3/3
2/1
3/4
2/3
α
6/3
4/4
6/4
0
300
1/2
1/3
300
1/4
1/5
4/5
6/5
6/6
5/5
1/6
1/7
2/5
300
2/6
3/5
4/6
6/7
6/8
1/8
2/7
5/6
3/6
2/8
4/7
5/7
30
0
300
3/7
4/8
5/8
3/8
Fig. 1 The cutting plane inclined to the rolling direction in order to
manufacture the specimens
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Rolling direction
1/1
6/2
5/4
2/4
30
6/1
4/3
2/2
ANNALS OF THE FACULTY OF ENGINEERING HUNEDOARA – 2004
TOME II. Fascicole 1
The shape and the dimensions of the Chevron specimens, in order to estimate
the fracture toughness, is presented in Fig.2 [1,2].
10
A-A
F
A
R40
A
10
48
1
3
F
H2=38
B=20
10
10
F
h=19,3
L2 = 45
Fig.2 The test specimen
The Chevron specimens have to present a triangular shape of the fracture
surface. Because of the machanical manufacturing process, the real specimens not
present such a shape of the fracture surface, but a surface with curved lateral lines,
R = 40 mm (the continuous line in Fig.2). Taking into account the above mentioned
aspects, in order to calculate the fracture toughness, the both shape of the fracture
surface have been taken into account. The shape of the fracture surface, in direct
relationship with the fracture toughness has an influence about the maximum force
recorded during the test process.
The tests have been performed at the standard temperature and on an
experimental installation, proper conception and implementation [3], (Prof. dr. eng. I.
Hajdu). The installation is able to obtain different loading rates. The test may be
performed both at standard and high temperatures.
3. THE FRACTURE TOUGHNESS
As a result of the Chevron specimens analysis, the fracture toughness,
expressed by the stress intensity factor KIV, may be estimated according to the
relation [1,2]:
K IV = A ⋅
Fmax
B
3
2
(1)
where:
A – a coefficient in function of the sharpeed angle of the fracture surface. For
the used specimens, the coefficient value of A = 22 has been considered
Fmax – the maximum recorded force during the test
B – the specimen thickness (Fig.2).
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TOME II. Fascicole 1
The results, for different loading rates which are different to the rolling surrface
orientation, as well for the effective and corrected fracture surface, are presented in
Fig.3a,b,c,d,e,f.
a)
75
[MPa ⋅ m1/2]
65
KIV
70
50
60
For the primary results
For the corrected results
55
α = 00
45
40
5⋅10-3
5⋅10-1
50
Loading rate [MPa/s]
KIV
[MPa ⋅ m1/2]
b)
80
75
70
65
For the primary results
For the corrected results
60
55
50
α = 300
45
40
KIV
[MPa ⋅ m1/2]
c)
85
80
75
70
65
60
55
50
45
40
5⋅10-3
5⋅10-1
50
Loading rate [MPa/s]
For the primary results
For the corrected results
α = 600
5⋅10-3
5⋅10-1
50
Loading rate [MPa/s]
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ANNALS OF THE FACULTY OF ENGINEERING HUNEDOARA – 2004
d)
TOME II. Fascicole 1
80
[MPa ⋅ m1/2]
70
KIV
75
50
65
For the primary results
For the corrected results
60
55
α = 900
45
40
5⋅10-3
5⋅10-1
50
Loading rate [MPa/s]
e)
75
[MPa ⋅ m1/2]
65
KIV
70
50
60
For the primary results
For the corrected results
55
α = 1200
45
40
5⋅10-3
5⋅10-1
50
Loading rate [MPa/s]
KIV
[MPa ⋅ m1/2]
f)
85
80
75
70
65
60
55
50
45
40
For the primary results
For the corrected results
α = 1500
5⋅10-3
5⋅10-1
50
Loading rate [MPa/s]
Fig.3 The fracture toughness
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TOME II. Fascicole 1
4. CONCLUSIONS
As a consequance of the results in Fig.3, it may be concluded:
™ The fracture toughness KIV (except a single primary direction) with the
loading rate, afteh all the other directions of the longitudinal axys of the
tested specimens.
™ The fracture toughness estimated on Chevron specimens, considered as
primary specimens with the same shape of the fracture cross-section, has
high values (closely to the superior limit in comporison with the fracture
toughness re-calculeted for the corrected maximum fracture force value.
™ For the analysed steel, the fracture toughness is relatively less influenced
by the rolling direction orientation of the longitudinal axys of the tested
specimens.
™ As a relativ small influence, it may be obsrved an increasing of the KIV for
the specimens orientated in directions 2, 3 and 6 in comparison with the
direction a and 5 presented in Fig.1
™ It may be considered that the rolling process of the steel plate has no
influence about the promoting of a special direction for fracture
propagation.
5. REFERENCES
1. Brown, K. R., The Chevron Notched Fracture toughness test, ASTM
Standardization News, November 1988
2. Sherman, D. H., Fracture Toughness Testing Using Chevron Notched
Specimens, Metals Handbook, Nineth Sdition, Vol. 8, Mechanical Testing ASM,
Ohio, 1985
3. Hajdu, I., Contribuţii la studiul influenţei temperaturii şi vitezei de încărcare asupra
limitei de curgere al unui oţel moale, Teză de doctorat, Timişoara, 1964
4. Barsom, J. M., Rolfe, S. T., Fracture and fatigue Control in Structures. Application
of fracture Mechanics, Prentice Hall Inc. New Jersey, 1987
5. Tripa, P., Mecanica ruperii cu aplicaţii la conducte, REZMAT 4, Editura MIRTON,
Timişoara, 1998
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