Fracture toughness of multilayer pipes
Multilayer pipes composed of various materials improve partially the properties of a pipe system and are frequently used in service. To estimate the lifetime of these pipes the basic fracture parameters have to be measured. In the contribution a new approach to this estimation is presented. Special...
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Інститут проблем міцності ім. Г.С. Писаренко НАН України
2008
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nasplib_isofts_kiev_ua-123456789-484212025-02-09T14:10:39Z Fracture toughness of multilayer pipes Трещиностойкость многослойных труб Nezbedova, E. Fiedler, L. Majer, Z. Vlach, B. Knesl, Z. Научно-технический раздел Multilayer pipes composed of various materials improve partially the properties of a pipe system and are frequently used in service. To estimate the lifetime of these pipes the basic fracture parameters have to be measured. In the contribution a new approach to this estimation is presented. Special type of a C-shaped inhomogeneousfracture mechanics specimen machined directlyfrom a pipe has been proposed, numerically analyzed and tested. The corresponding K values are calculated by FEM and fracture toughness values of HDPE pipes material are obtained. Многослойные трубы, состоящие из различных материалов, позволяют частично повысить свойства систем трубопроводов и часто применяются на практике. Для оценки долго вечности таких труб необходимо определить их основные параметры разрушения. Представлен новый подход к выполнению такой оценки. Предлагается специальный тип не однородного С-образного образца, вырезаемого непосредственно из трубы, для исследования методами механики разрушения; выполнен численный анализ и проведены испытания. Расчет соответствующих значений К выполнен методом конечных элементов. Получены величины трещиностойкости материала труб из полиэтилена высокой плотности. The authors gratefully acknowledge the support provided by the Grant Agency of the Czech Republic (No. 101/05/0227) for this work. 2008 Article Fracture toughness of multilayer pipes / E. Nezbedova, L. Fiedler, Z. Majer, B. Vlach, Z. Knesl // Проблемы прочности. — 2008. — № 1. — С.146 -149. — Бібліогр.: 10 назв. — англ. 0556-171X https://nasplib.isofts.kiev.ua/handle/123456789/48421 539.4 en Проблемы прочности application/pdf Інститут проблем міцності ім. Г.С. Писаренко НАН України |
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Научно-технический раздел Научно-технический раздел |
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Научно-технический раздел Научно-технический раздел Nezbedova, E. Fiedler, L. Majer, Z. Vlach, B. Knesl, Z. Fracture toughness of multilayer pipes Проблемы прочности |
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Multilayer pipes composed of various materials improve partially the properties of a pipe system and are frequently used in service. To estimate the lifetime of these pipes the basic fracture parameters have to be measured. In the contribution a new approach to this estimation is presented. Special type of a C-shaped inhomogeneousfracture mechanics specimen machined directlyfrom a pipe has been proposed, numerically analyzed and tested. The corresponding K values are calculated by FEM and fracture toughness values of HDPE pipes material are obtained. |
| format |
Article |
| author |
Nezbedova, E. Fiedler, L. Majer, Z. Vlach, B. Knesl, Z. |
| author_facet |
Nezbedova, E. Fiedler, L. Majer, Z. Vlach, B. Knesl, Z. |
| author_sort |
Nezbedova, E. |
| title |
Fracture toughness of multilayer pipes |
| title_short |
Fracture toughness of multilayer pipes |
| title_full |
Fracture toughness of multilayer pipes |
| title_fullStr |
Fracture toughness of multilayer pipes |
| title_full_unstemmed |
Fracture toughness of multilayer pipes |
| title_sort |
fracture toughness of multilayer pipes |
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Інститут проблем міцності ім. Г.С. Писаренко НАН України |
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2008 |
| topic_facet |
Научно-технический раздел |
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https://nasplib.isofts.kiev.ua/handle/123456789/48421 |
| citation_txt |
Fracture toughness of multilayer pipes / E. Nezbedova, L. Fiedler, Z. Majer, B. Vlach, Z. Knesl // Проблемы прочности. — 2008. — № 1. — С.146 -149. — Бібліогр.: 10 назв. — англ. |
| series |
Проблемы прочности |
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| first_indexed |
2025-11-26T17:22:33Z |
| last_indexed |
2025-11-26T17:22:33Z |
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| fulltext |
UDC 539. 4
F r a c tu r e T o u g h n e s s o f M u lt i la y e r P ip e s
E . N ezb ed o v a ,1a L . F ied ler ,2 b Z . M a jer ,2,3c B . V lach ,2 d and Z . K n esl3,e
1 Faculty o f Chemistry, Institute o f Materials Science, Brno University o f Technology, Bmo, Czech
Republic
2 Faculty o f Mechanical Engineering, Brno Technical University, Brno, Czech Republic
3 Institute of Physics o f Materials, Academy of Science o f the Czech Republic, Brno, Czech Republic
a nezbedova@fch.vutbr.cz, b fidlub@post.cz, c majer@ipm.cz, d vlach@fme.vutbr.cz,
e knesl@ipm.cz
Multilayer pipes composed o f various materials improve partially the properties o f a pipe system
and are frequently used in service. To estimate the lifetime o f these pipes the basic fracture
parameters have to be measured. In the contribution a new approach to this estimation is presented.
Special type o f a C-shaped inhomogeneous fracture mechanics specimen machined directly from a
pipe has been proposed, numerically analyzed and tested. The corresponding K values are
calculated by FEM and fracture toughness values o f HDPE pipes material are obtained.
K eyw o rd s : polyethylene pipes, fracture toughness, K-calibration.
In troduction . P olyethylene (H DPE) and polypropylene (PP) materials can be
considered m odern and ecologic; they substitute for conventional pipe materials (steel,
cast-iron). This progress is fo llow ed by relevant legislation (international standards,
profession directives, national codes, etc.). A ccording to these standards the lifetim e o f the
new est bim odal type o f HDPE [1] is expected to be up to 100 years. This long lifetim e is
guaranteed on ly i f tubes are strained w ith just inner overpressure. Unfortunately, there are
other factors in service, w hich can reduce this lifetim e [2, 3]. These extraordinary
circum stances can evoke creation o f the stress raisers that can lead to form ing o f a crack
and then to brittle failure o f the w hole pipe system . U sing the fracture m echanics
approaches [4 -6 ] there have been developed m ethods and procedures w hich are able to
evaluate the resistance o f both native material and pipes from the v iew o f a slow [7] and
rapid crack growth [8].
The developm ent o f n ew materials has supported novel technologies, w hich could
not be used so far in laying o f n ew tubes and sanitation [9]. The so-called m ultilayer pipes
have received a w ider acceptance recently in the field o f p ipes system s. The purpose o f
the developm ent w as to im prove partially the properties profile o f p ipes from nonchained
polyethylene by com bining w ith other materials. This m ethod has essentially resulted in
tw o types o f pipes: (i) p ipes w ith dim ensional addition o f a protective surface and (ii)
pipes w ith a dim ensionally integrated protective surface.
In our contribution w e have focused on the second type o f m ultilayer pipes and its
lifetim e expectation. Specifically , the fracture toughness w as chosen as a relevant
parameter for evaluation o f a pipe material resistance to a so-called slow crack growth
(SCG). This type o f fracture occurs under long-term service conditions and lim its the
lifetim e. To estimate fracture toughness o f the pipe material a special inhom ogeneous
C-shaped specim en m achined directly from the pipe (Fig. 1a) w as proposed and numerically
analyzed. B ased on the num erical results the fracture m echanics parameters K g d were
estimated for tw o different temperatures.
E xp erim en ta l. The three-layer com m ercial plastic pipe W avin TS ( 0 1 1 0 SD R11)
w ith its outer and inner layers m ade o f an extrem ely durable PE material (X SC 50) and its
interlayer PE 100 w as chosen as experim ental material. The thickness o f both inner and
outer layers w as 2 .5 m m and that o f the interlayer w as 5 m m (Fig. 1b).
© E. N EZB ED O V A , L. FIEDLER, Z. MAJER, B. VLACH, Z. KNESL, 2008
146 ISSN 0556-171X. Проблемы прочности, 2008, № 1
mailto:nezbedova@fch.vutbr.cz
mailto:fidlub@post.cz
mailto:majer@ipm.cz
mailto:vlach@fme.vutbr.cz
mailto:knesl@ipm.cz
Fracture Toughness o f Multilayer Pipes
Fig. 1. C-shaped specimen and the experimental setup used for the fracture toughness measurements
(a); schematic o f the three-layer pipe (b).
The material m echanical characteristics (tensile m odulus E and y ield stress o y ) o f
individual layers w ere determ ined from standard tensile tests carried out according to
standard C SN E N ISO 527-1. Tensile test specim ens w ere directly cut from the pipe in the
longitudinal direction o f the pipe. Tests were carried out on the universal testing m achine
Z w ick Z 020. The load w as m easured using 2.5 kN dynam om eter and deform ation was
determ ined using an extensom eter w ith accuracy class 0.5. The testing conditions were as
fo llow s: in itial gauge length 20 m m , temperature 23°C and — 60oC, and crosshead speed
1 m m /m in. The obtained values o f tensile m odulus E and y ield stress o y are
sum marized in Table 1.
T a b l e 1
The Mechanical Characteristics o f the Pipe Layers
Temperature,
0 C
E, MPa a , MPa
Inner/outer layer Intermediate layer Inner outer layer Intermediate layer
x/ s x s x/ s xj s
23 827/34 1213/28 16 1 20 0
-6 0 2740/99 3399/91 45/0 48 0
Note. Here and in Table 2: x is the mean value and s is a corresponding standard deviation.
Fracture m echanics characteristics were determ ined using the tw o types o f
instrumented Charpy im pact testers. The first one w as a high-energy im pact tester PSW
300E/M FL w ith im pact energy 150 J. The second w as a low -energy im pact tester
Fraktoskop K4J w ith im pact energy 4 J (Fig. 1a). The notches were m ade b y pressing a
fresh razor blade into the specim ens.
The test conditions on the both types o f im pact testers were as follow s: test
temperature 23°C and — 60°C, im pact rate 1 m /s, and span distance 40 mm.
The specim en 10 m m thick w as tested on the high-energy im pact tester, w hile the
specim en o f 4 m m thickness w as tested on the low -energy im pact tester. N otches o f three
different depths (3.8, 4 .6 , and 5.6 m m ) were m ade on 4-m m -thick specim ens. In the case
o f 10-m m -thick specim ens the notches were o f the sam e depth - 4 .6 mm. In all cases the
crack tips w ere located in the interlayer PE 100 material. The resulting values o f dynamic
fracture toughness K Qd w ere calculated according to the equation
K Qd = a W )'
Here F max is the m axim um load, S is the span distance, B and W are the thickness
and width, respectively, a is the notch depth, and f ( a /W ) is a geom etric factor. The
ISSN 0556-171X. npoôëeubi npounocmu, 2008, N 1 147
E. Nezbedova, L. Fiedler, Z. Majer, et al.
geom etric factor is know n on ly for a hom ogeneous standard three-point bend specim en [9,
10]. The function f (a /W ) corresponding to the used C-shaped inhom ogeneous three
layers specim en has to be calculated numerically.
N u m erica l M odel. The num erical m odel corresponds to the experim ental setup. The
material data correspond to those g iven in Table 1. The num erical analyses were carried
out under plane strain conditions by using a finite elem ent m ethod as im plem ented in the
standard A N S Y S 10.0 system . To estim ate the corresponding values o f stress intensity
factor K i the standard K -CA LC procedure im plem ented in A N S Y S has been applied. A s
a result, the values o f K I w ere obtained and the corresponding function f (a /W ) was
estimated according to Eq. (1), see Fig. 2. The geom etric factor corresponding to the
standard three-point bend specim en is added for com parison. N ote that the f ( a / W )
values are practically independent o f P o isson ’s ratio. U sing Eq. (1) and the results
presented in Fig. 2, the values o f the dynam ic fracture toughness were estim ated (Table 2).
N ote that according to the A ST M standard the on ly valid value o f K ic is obtained for
temperature — 60oC and for the specim en thickness B 2 = 10 mm.
The values o f dynam ic fracture toughness for tw o different specim en thicknesses and
for temperatures 23°C and — 60°C, determ ined using tw o types o f instrumented Charpy
im pact testers, are g iven in Table 2.
T a b l e 2
Resulting Values of Dynamic Fracture Toughness for Two Different Specimen Thicknesses
Thickness, mm B1 = 4 2B =1 0
a , mm 3.8 4.6 5.6 4.6
Temperature,
0 C
K Qd , MPa • m1/2
x/s x/s X s x/s
23 3.0/0.4 2.0/0.3 1.2/0.1 2.4/0.2
— 60 2.4/0.2 1.8/0.3 1.1/0.6 3.5/0.1
0 --------------------1--------------------1--------------------1--------------------
0.3 Q.4 0.5 0.6 0.7
a/w
Fig. 2. Correction function f (ajW ) for a C-type specimen (middle layer): (!) homogeneous
specimen; (2) temperature T = —60°C; (5) temperature T = 23°C; (4) standard three-point bend
specimen [9, 10].
C onclusions. We have studied the lifetim e expectation o f the three-layer com m ercial
plastic pipe with dim ensionally integrated protective surfaces w as investigated. The
fracture toughness is chosen as a relevant parameter for evaluation o f the pipe material
148 ISSN 0556-171X. npo6n.eubi npounocmu, 2008, N 1
Fracture Toughness o f Multilayer Pipes
resistance to a slow crack growth. To evaluate fracture toughness values o f the interlayer
PE 100 pipe material the fo llow ing steps have been made:
• the material parameters (tensile m odulus E and y ield stress o y ) for both inner
and outer layers o f the three layers pipe w ere determ ined for temperatures 23°C and
- 6 0 oC;
• a new inhom ogeneous C-shaped fracture m echanics specim en m achined directly
from the pipe has been used and the corresponding values o f the stress intensity factor K
represented by the geom etric factor f (a /W ) have been calculated by FEM;
• the values o f dynam ic fracture toughness for tw o different specim en thicknesses
and for temperatures 23°C and — 60oC were determ ined using tw o types o f instrumented
Charpy im pact testers
Acknowledgments. The authors gratefully acknowledge the support provided by the Grant
Agency o f the Czech Republic (No. 101/05/0227) for this work.
1. E. Nezbedova, A. Zahradnlckova, and Z. Salajka, “Brittle failure versus structure o f HDPE
pipe grades,” J. Macromol. Sci. - Physics, B40 (384), 507-515 (2001).
2. J. Hessel, “Mindesbendsdauer von erdverlegten Rohen aus Polyethylen ohne Sandeinbettung,”
Sonderdruck aus 3R International; 40 Jahrgang, Heft 4 (2001), SS. 178-184.
3. A. L. Ward, X. Lu, Y. Huang, and N. Brown, Polymer Testing, 11, 309 (1992).
4. M. Fleipner, “Langsames Risswachstum und Zeitstandfestingkeit von Rohren aus Poly
ethylene,” Kunststoffe, 77, No. 1, 45-50 (1987).
5. S. J. Ritchie, P. Davis, and P. S. Leevers, “Brittle-tough transition of rapid crack propagation
in polyethylene,” Polymer, 39, 6657-6663 (1998).
6. ISO/CD 16770: Plastics. Determination o f Environmental Stress Cracking (ESC) o f
Polyethylene (PE), Full Notch Creep Test (FNCT) and ISO/CD 16 241: Notch Tensile Test to
Measure the Resistance to Slow Crack Growth o f Polyethylene Materials fo r Pipe and Fitting
Products (PENT).
7. ISO 13477:1997 Thermoplastics Pipes fo r the Conveyance o f Fluids. Determination o f
Resistance to Rapid Crack Propagation (RCP). Small-Scale Steady-State Test (S4 Test).
8. Y. Savidus, “Progresivni postupy pouzivane pri vystavbe potrubnich vedeni z plastu,” 10
rocnik mezinarodni konference Plasty v Rozvodech Plynu [in Czech], Sbornik referätü, Praha
(2003), str. 233.
9. ISO 13586: Determination o f Fracture Toughness (Gc and K c). Linear Elastic Fracture
Mechanics (LEFM) Approach.
10. W. Grellmann, S. Seidler, und W. Hesse, MPK-Prozedur: Prüfung von Kunststoffen -
Instrumentierter Kerbschlagbiegeversuch, Merseburg (2005).
Received 28. 06. 2007
ISSN 0556-171X. npoöxeMU npouHocmu, 2008, № 1 149
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