Comparison of fatigue performance of polyethylene pipe grades in the form of extruded and compression molded specimens
Abstract
Due to the very long operational lifetimes (up to 100 years) of polyethylene pipes, there is a strong demand for accelerated testing of pipe materials to experimentally prove the ability of a certain material to achieve such lifetime. Among the accelerated tests of performance, the cracked round bar (CRB) test is the most convenient. The CRB test takes advantage of cyclic loading that is applied on cylindrical specimens with a circumferential notch in the middle. The specimens are usually manufactured from plates produced by compression molding from the investigated material. However, for polyethylene pipe producers, the possibility of making the specimens by extrusion would save time and lower the costs. This study is dealing with the comparison of CRB test, and a new test carried out on notched pipe samples produced by extrusion. The goal is to investigate the possibility of measuring the performance directly on extruded pipe specimens. The comparison is illustrated on experimental results of several polyethylene pipe grades of PE80, PE100 and PE100RC often used for pipe manufacture.
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P ocedia S uc u al In eg i y 43 (2023) 148–153
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©
2023 The Au ho s. Published by ELSEVIER B.V.
This is an open access a icle unde he CC BY-NC-ND license (h ps://c ea i ecommons.o g/licenses/by-nc-nd/4.0)
Pee - e iew unde he esponsibili y o MSMF10 o ganize s.
10.1016/j.p os .2022.12.250
10.1016/j.p os .2022.12.250 2452-3216
© 2023 The Au ho s. Published by Else ie B.V.
This is an open access a icle unde he CC BY-NC-ND license (
h ps://c ea i ecommons.o g/licenses/by-nc-nd/4.0
)
Pee - e iew unde he esponsibili y o MSMF10 o ganize s.
A ailable online a www.sciencedi ec .com
ScienceDi ec
S uc u al In eg i y P ocedia 00 (2022) 000–000
www.else ie .com/loca e/p ocedia
2452-3216 © 2023 The Au ho s. Published by Else ie B.V.
This is an open access a icle unde he CC BY-NC-ND license (h ps://c ea i ecommons.o g/licenses/by-nc-nd/4.0)
Pee - e iew unde he esponsibili y o MSMF10 o ganize s.
10 h In e na ional Con e ence on Ma e ials S uc u e and Mic omechanics o F ac u e
Compa ison o a igue pe o mance o polye hylene pipe g ades in
he o m o ex uded and comp ession molded specimens
Lukáš T á níčeka,b*, Jan Poduškab, Ja osla Kuče ac, Luboš Náhlíkb and Pa el Hu ařb
aCEITEC BUT, Pu kyňo a 123, 621 00 B no, Czech Republic
bIns i u e o Physics o Ma e ials AS CR, Žižko a 22, 616 00 B no, Czech Republic
cPolyme Ins i u e B no, Tkalco ská 36/2, 602 00 B no, Czech Republic
Abs ac
Due o he e y long ope a ional li e imes (up o 100 yea s) o polye hylene pipes, he e is a s ong demand o accele a ed es ing
o pipe ma e ials o expe imen ally p o e he abili y o a ce ain ma e ial o achie e such li e ime. Among he accele a ed es s o
pe o mance, he c acked ound ba (CRB) es is he mos con enien . The CRB es akes ad an age o cyclic loading ha is
applied on cylind ical specimens wi h a ci cum e en ial no ch in he middle. The specimens a e usually manu ac u ed om pla es
p oduced by comp ession molding om he in es iga ed ma e ial. Howe e , o polye hylene pipe p oduce s, he possibili y o
making he specimens by ex usion would sa e ime and lowe he cos s. This s udy is dealing wi h he compa ison o CRB es ,
and a new es ca ied ou on no ched pipe samples p oduced by ex usion. The goal is o in es iga e he possibili y o measu ing
he pe o mance di ec ly on ex uded pipe specimens. The compa ison is illus a ed on expe imen al esul s o se e al polye hylene
pipe g ades o PE80, PE100 and PE100RC o en used o pipe manu ac u e.
© 2023 The Au ho s. Published by Else ie B.V.
This is an open access a icle unde he CC BY-NC-ND license (h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/)
Pee - e iew unde he esponsibili y o MSMF10 o ganize s.
Keywo ds: ex uded pipe specimens; SCG esis ance; polye hylene pipe li e ime; accele a ed es ing
1. In oduc ion
Polyme pipes ha e been used o mo e han 70 yea s o wa e and gas anspo a ion as well as o sewage sys ems.
Fo high-quali y pipes made o mode n ma e ials, such as high-densi y polye hylene (HDPE), li e imes be ween 50 o
* Co esponding au ho . Tel.: +420 532 290 347.
E-mail add ess: a [email protected]
A ailable online a www.sciencedi ec .com
ScienceDi ec
S uc u al In eg i y P ocedia 00 (2022) 000–000
www.else ie .com/loca e/p ocedia
2452-3216 © 2023 The Au ho s. Published by Else ie B.V.
This is an open access a icle unde he CC BY-NC-ND license (h ps://c ea i ecommons.o g/licenses/by-nc-nd/4.0)
Pee - e iew unde he esponsibili y o MSMF10 o ganize s.
10 h In e na ional Con e ence on Ma e ials S uc u e and Mic omechanics o F ac u e
Compa ison o a igue pe o mance o polye hylene pipe g ades in
he o m o ex uded and comp ession molded specimens
Lukáš T á níčeka,b*, Jan Poduškab, Ja osla Kuče ac, Luboš Náhlíkb and Pa el Hu ařb
aCEITEC BUT, Pu kyňo a 123, 621 00 B no, Czech Republic
bIns i u e o Physics o Ma e ials AS CR, Žižko a 22, 616 00 B no, Czech Republic
cPolyme Ins i u e B no, Tkalco ská 36/2, 602 00 B no, Czech Republic
Abs ac
Due o he e y long ope a ional li e imes (up o 100 yea s) o polye hylene pipes, he e is a s ong demand o accele a ed es ing
o pipe ma e ials o expe imen ally p o e he abili y o a ce ain ma e ial o achie e such li e ime. Among he accele a ed es s o
pe o mance, he c acked ound ba (CRB) es is he mos con enien . The CRB es akes ad an age o cyclic loading ha is
applied on cylind ical specimens wi h a ci cum e en ial no ch in he middle. The specimens a e usually manu ac u ed om pla es
p oduced by comp ession molding om he in es iga ed ma e ial. Howe e , o polye hylene pipe p oduce s, he possibili y o
making he specimens by ex usion would sa e ime and lowe he cos s. This s udy is dealing wi h he compa ison o CRB es ,
and a new es ca ied ou on no ched pipe samples p oduced by ex usion. The goal is o in es iga e he possibili y o measu ing
he pe o mance di ec ly on ex uded pipe specimens. The compa ison is illus a ed on expe imen al esul s o se e al polye hylene
pipe g ades o PE80, PE100 and PE100RC o en used o pipe manu ac u e.
© 2023 The Au ho s. Published by Else ie B.V.
This is an open access a icle unde he CC BY-NC-ND license (h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/)
Pee - e iew unde he esponsibili y o MSMF10 o ganize s.
Keywo ds: ex uded pipe specimens; SCG esis ance; polye hylene pipe li e ime; accele a ed es ing
1. In oduc ion
Polyme pipes ha e been used o mo e han 70 yea s o wa e and gas anspo a ion as well as o sewage sys ems.
Fo high-quali y pipes made o mode n ma e ials, such as high-densi y polye hylene (HDPE), li e imes be ween 50 o
* Co esponding au ho . Tel.: +420 532 290 347.
E-mail add ess: a [email protected]
2 Au ho name / S uc u al In eg i y P ocedia 00 (2022) 000–000
Nomencla u e
aini ini ial c ack leng h
CRB c acked ound ba
D diame e o a CRB specimen
Din inne diame e o a pipe specimen
Dou ou e diame e o a pipe specimen
ΔF o ce loading ange
Δσ s ess loading ange
ΔKI s ess in ensi y ac o ange
Fmin minimum applied o ce
Fmax maximum applied o ce
FNCT ull no ched c eep es
HDPE high densi y polye hylene
l leng h o a CRB specimen
N numbe o cycles o ailu e
NPT no ched pipe es
PENT pennsyl ania edge no ch es
R loading a io in a cyclic es
SCG slow c ack g ow h
hickness o he pipe wall
100 yea s a e gene ally expec ed oday. Du ing hei se ice li e, he s uc u al eliabili y o piping sys ems is essen ial
as p ema u e ailu es may cause se e e ma e ial loss (Nayya 2000).
Fo he long- e m applica ions o polye hylene pipes, he li e ime is connec ed o he esis ance agains c ack
ini ia ion and slow c ack g ow h (SCG). The adi ional expe imen al es ing me hod is based on in e nal p essu e es
s anda dized in ISO 9080 (ISO 2012). Howe e , wi h he de elopmen o polye hylene pipe g ades comes highe SCG
esis ance o he ma e ials, o which he in e nal p essu e es mee s i s ime limi s. This ac led he pipe communi y
o de elop accele a ed es ing me hods o ob ain he ma e ial anking o he SCG esis ance in sho e imes. Among
he mos common me hods a e No ched Pipe Tes (NPT) (Beech 2013), Pennsyl ania Edge No ch Tes (PENT) (Lu
1992) and Full No ch C eep Tes (FNCT) (Fleissne 1998). All hese accele a ed es s a e ca ied ou a ele a ed
empe a u es o T = 80°C and/o unde he in luence o agg essi e chemical en i onmen o accele a e he c ack
ini ia ion and SCG. These es s p o ide a signi ican educ ion in es ing imes in compa ison wi h he hyd os a ic
p essu e es , bu o mode n polye hylene pipe g ades (such as PE100RC) hey s ill equi e imes o se e al mon hs.
The e o e, C acked Round Ba (CRB) es , ha was ecen ly s anda dized as a anking me hod o polye hylene pipes
(ISO 2015), was de eloped (Pin e 2007, F ank 2014, A bei e 2015). The CRB es is ca ied ou on cylind ical
specimens wi h a azo -sha p ci cum e en ial no ch in he middle. The accele a ion o c ack ini ia ion and SCG is
done by cyclic loading ha is much mo e e ec i e han he special agg essi e en i onmen o high empe a u e. The
impo an ac is ha he cyclic loading does no change he mechanism o ailu e (Pin e 2013) and he e o e, i is
sui able o he accele a ion o he SCG (F ank 2019). Mo eo e , he esul s a e ob ained wi hin a ew days e en o
he mos du able ma e ials. I ollows om he abo e ha he CRB es is a quick, obus , and e ec i e ool o quan i y
he esis ance agains SCG o polyme ma e ials.
The specimens o all accele a ed es s a e ypically manu ac u ed om pla es p oduced by comp ession molding,
which is a di e en p ocess ha he one used o polyme pipes p oduc ion – ex usion. Fo polyme pipes p oduce s,
he di ec ex usion o he specimens o accele a ed es ing would lowe he cos and sa e ime. In his espec , he
main aim o he p esen ed wo k is o classi y di e en ypes o polye hylene pipe g ades o PE80, PE100 and PE100RC
using new ex uded pipe specimens in he es s and compa e he esul s wi h classic CRB es s. The expe imen s o
new pipe specimens we e ca ied ou unde he same condi ions as CRB es s, so he accele a ion o he c ack ini ia ion
and SCG was achie ed by cyclic loading. The compa ison as well as he usabili y o he new pipes specimens is
discussed he e, based on he ob ained esul s.
Lukáš T á níček e al. / P ocedia S uc u al In eg i y 43 (2023) 148–153 149
A ailable online a www.sciencedi ec .com
ScienceDi ec
S uc u al In eg i y P ocedia 00 (2022) 000–000
www.else ie .com/loca e/p ocedia
2452-3216 © 2023 The Au ho s. Published by Else ie B.V.
This is an open access a icle unde he CC BY-NC-ND license (h ps://c ea i ecommons.o g/licenses/by-nc-nd/4.0)
Pee - e iew unde he esponsibili y o MSMF10 o ganize s.
10 h In e na ional Con e ence on Ma e ials S uc u e and Mic omechanics o F ac u e
Compa ison o a igue pe o mance o polye hylene pipe g ades in
he o m o ex uded and comp ession molded specimens
Lukáš T á níčeka,b*, Jan Poduškab, Ja osla Kuče ac, Luboš Náhlíkb and Pa el Hu ařb
aCEITEC BUT, Pu kyňo a 123, 621 00 B no, Czech Republic
bIns i u e o Physics o Ma e ials AS CR, Žižko a 22, 616 00 B no, Czech Republic
cPolyme Ins i u e B no, Tkalco ská 36/2, 602 00 B no, Czech Republic
Abs ac
Due o he e y long ope a ional li e imes (up o 100 yea s) o polye hylene pipes, he e is a s ong demand o accele a ed es ing
o pipe ma e ials o expe imen ally p o e he abili y o a ce ain ma e ial o achie e such li e ime. Among he accele a ed es s o
pe o mance, he c acked ound ba (CRB) es is he mos con enien . The CRB es akes ad an age o cyclic loading ha is
applied on cylind ical specimens wi h a ci cum e en ial no ch in he middle. The specimens a e usually manu ac u ed om pla es
p oduced by comp ession molding om he in es iga ed ma e ial. Howe e , o polye hylene pipe p oduce s, he possibili y o
making he specimens by ex usion would sa e ime and lowe he cos s. This s udy is dealing wi h he compa ison o CRB es ,
and a new es ca ied ou on no ched pipe samples p oduced by ex usion. The goal is o in es iga e he possibili y o measu ing
he pe o mance di ec ly on ex uded pipe specimens. The compa ison is illus a ed on expe imen al esul s o se e al polye hylene
pipe g ades o PE80, PE100 and PE100RC o en used o pipe manu ac u e.
© 2023 The Au ho s. Published by Else ie B.V.
This is an open access a icle unde he CC BY-NC-ND license (h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/)
Pee - e iew unde he esponsibili y o MSMF10 o ganize s.
Keywo ds: ex uded pipe specimens; SCG esis ance; polye hylene pipe li e ime; accele a ed es ing
1. In oduc ion
Polyme pipes ha e been used o mo e han 70 yea s o wa e and gas anspo a ion as well as o sewage sys ems.
Fo high-quali y pipes made o mode n ma e ials, such as high-densi y polye hylene (HDPE), li e imes be ween 50 o
* Co esponding au ho . Tel.: +420 532 290 347.
E-mail add ess: a [email protected]
A ailable online a www.sciencedi ec .com
ScienceDi ec
S uc u al In eg i y P ocedia 00 (2022) 000–000
www.else ie .com/loca e/p ocedia
2452-3216 © 2023 The Au ho s. Published by Else ie B.V.
This is an open access a icle unde he CC BY-NC-ND license (h ps://c ea i ecommons.o g/licenses/by-nc-nd/4.0)
Pee - e iew unde he esponsibili y o MSMF10 o ganize s.
10 h In e na ional Con e ence on Ma e ials S uc u e and Mic omechanics o F ac u e
Compa ison o a igue pe o mance o polye hylene pipe g ades in
he o m o ex uded and comp ession molded specimens
Lukáš T á níčeka,b*, Jan Poduškab, Ja osla Kuče ac, Luboš Náhlíkb and Pa el Hu ařb
aCEITEC BUT, Pu kyňo a 123, 621 00 B no, Czech Republic
bIns i u e o Physics o Ma e ials AS CR, Žižko a 22, 616 00 B no, Czech Republic
cPolyme Ins i u e B no, Tkalco ská 36/2, 602 00 B no, Czech Republic
Abs ac
Due o he e y long ope a ional li e imes (up o 100 yea s) o polye hylene pipes, he e is a s ong demand o accele a ed es ing
o pipe ma e ials o expe imen ally p o e he abili y o a ce ain ma e ial o achie e such li e ime. Among he accele a ed es s o
pe o mance, he c acked ound ba (CRB) es is he mos con enien . The CRB es akes ad an age o cyclic loading ha is
applied on cylind ical specimens wi h a ci cum e en ial no ch in he middle. The specimens a e usually manu ac u ed om pla es
p oduced by comp ession molding om he in es iga ed ma e ial. Howe e , o polye hylene pipe p oduce s, he possibili y o
making he specimens by ex usion would sa e ime and lowe he cos s. This s udy is dealing wi h he compa ison o CRB es ,
and a new es ca ied ou on no ched pipe samples p oduced by ex usion. The goal is o in es iga e he possibili y o measu ing
he pe o mance di ec ly on ex uded pipe specimens. The compa ison is illus a ed on expe imen al esul s o se e al polye hylene
pipe g ades o PE80, PE100 and PE100RC o en used o pipe manu ac u e.
© 2023 The Au ho s. Published by Else ie B.V.
This is an open access a icle unde he CC BY-NC-ND license (h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/)
Pee - e iew unde he esponsibili y o MSMF10 o ganize s.
Keywo ds: ex uded pipe specimens; SCG esis ance; polye hylene pipe li e ime; accele a ed es ing
1. In oduc ion
Polyme pipes ha e been used o mo e han 70 yea s o wa e and gas anspo a ion as well as o sewage sys ems.
Fo high-quali y pipes made o mode n ma e ials, such as high-densi y polye hylene (HDPE), li e imes be ween 50 o
* Co esponding au ho . Tel.: +420 532 290 347.
E-mail add ess: a [email protected]
2 Au ho name / S uc u al In eg i y P ocedia 00 (2022) 000–000
Nomencla u e
aini ini ial c ack leng h
CRB c acked ound ba
D diame e o a CRB specimen
Din inne diame e o a pipe specimen
Dou ou e diame e o a pipe specimen
ΔF o ce loading ange
Δσ s ess loading ange
ΔKI s ess in ensi y ac o ange
Fmin minimum applied o ce
Fmax maximum applied o ce
FNCT ull no ched c eep es
HDPE high densi y polye hylene
l leng h o a CRB specimen
N numbe o cycles o ailu e
NPT no ched pipe es
PENT pennsyl ania edge no ch es
R loading a io in a cyclic es
SCG slow c ack g ow h
hickness o he pipe wall
100 yea s a e gene ally expec ed oday. Du ing hei se ice li e, he s uc u al eliabili y o piping sys ems is essen ial
as p ema u e ailu es may cause se e e ma e ial loss (Nayya 2000).
Fo he long- e m applica ions o polye hylene pipes, he li e ime is connec ed o he esis ance agains c ack
ini ia ion and slow c ack g ow h (SCG). The adi ional expe imen al es ing me hod is based on in e nal p essu e es
s anda dized in ISO 9080 (ISO 2012). Howe e , wi h he de elopmen o polye hylene pipe g ades comes highe SCG
esis ance o he ma e ials, o which he in e nal p essu e es mee s i s ime limi s. This ac led he pipe communi y
o de elop accele a ed es ing me hods o ob ain he ma e ial anking o he SCG esis ance in sho e imes. Among
he mos common me hods a e No ched Pipe Tes (NPT) (Beech 2013), Pennsyl ania Edge No ch Tes (PENT) (Lu
1992) and Full No ch C eep Tes (FNCT) (Fleissne 1998). All hese accele a ed es s a e ca ied ou a ele a ed
empe a u es o T = 80°C and/o unde he in luence o agg essi e chemical en i onmen o accele a e he c ack
ini ia ion and SCG. These es s p o ide a signi ican educ ion in es ing imes in compa ison wi h he hyd os a ic
p essu e es , bu o mode n polye hylene pipe g ades (such as PE100RC) hey s ill equi e imes o se e al mon hs.
The e o e, C acked Round Ba (CRB) es , ha was ecen ly s anda dized as a anking me hod o polye hylene pipes
(ISO 2015), was de eloped (Pin e 2007, F ank 2014, A bei e 2015). The CRB es is ca ied ou on cylind ical
specimens wi h a azo -sha p ci cum e en ial no ch in he middle. The accele a ion o c ack ini ia ion and SCG is
done by cyclic loading ha is much mo e e ec i e han he special agg essi e en i onmen o high empe a u e. The
impo an ac is ha he cyclic loading does no change he mechanism o ailu e (Pin e 2013) and he e o e, i is
sui able o he accele a ion o he SCG (F ank 2019). Mo eo e , he esul s a e ob ained wi hin a ew days e en o
he mos du able ma e ials. I ollows om he abo e ha he CRB es is a quick, obus , and e ec i e ool o quan i y
he esis ance agains SCG o polyme ma e ials.
The specimens o all accele a ed es s a e ypically manu ac u ed om pla es p oduced by comp ession molding,
which is a di e en p ocess ha he one used o polyme pipes p oduc ion – ex usion. Fo polyme pipes p oduce s,
he di ec ex usion o he specimens o accele a ed es ing would lowe he cos and sa e ime. In his espec , he
main aim o he p esen ed wo k is o classi y di e en ypes o polye hylene pipe g ades o PE80, PE100 and PE100RC
using new ex uded pipe specimens in he es s and compa e he esul s wi h classic CRB es s. The expe imen s o
new pipe specimens we e ca ied ou unde he same condi ions as CRB es s, so he accele a ion o he c ack ini ia ion
and SCG was achie ed by cyclic loading. The compa ison as well as he usabili y o he new pipes specimens is
discussed he e, based on he ob ained esul s.
150 Lukáš T á níček e al. / P ocedia S uc u al In eg i y 43 (2023) 148–153
Au ho name / S uc u al In eg i y P ocedia 00 (2022) 000–000 3
2. Expe imen al de ails
CRB specimens wi h he dimensions acco ding o he s anda d (ISO 2015): ou e diame e D = 14 mm, leng h
l = 100 mm and ci cum e en ial azo -sha p no ch aini = 1.5 mm; we e machined om comp ession molded shee s.
Polye hylene pipes wi h ou e diame e Dou = 20 mm and inne diame e Din = 14 mm we e p oduced by ex usion.
The pipe wall hickness = 3 mm was chosen – i was a maximum ha he ex usion die allowed. The pipes we e cu
in o 100 mm long specimens wi h 1 mm deep azo -sha p ci cum e en ial no ch in he middle. Bo h ypes o specimens
we e p epa ed a he Polyme Ins i u e B no.
To ally, 9 di e en polye hylene ma e ials o he pipe g ades PE80, PE100 and PE100RC we e es ed wi h he pipe
specimens and o 5 ou o hese ma e ials CRB es s we e also ca ied ou – see summa y in Table 1.
Table 1. O e iew o es ed polye hylene pipe g ades.
Ma e ial numbe
1
2
3
4
5
6
7
8
9
Pipe g ade
PE80
PE100
PE100RC
Pipe specimen
✓
✓
✓
✓
✓
✓
✓
✓
✓
CRB specimen
✓
✓
✓
✓
✓
The uniaxial a igue es s we e pe o med using he compu e -con olled es ing machine INSTRON E10000. The
specimens we e loaded cyclically wi h equency 10 Hz. The cyclic loading was con olled by o ce, and i had he
sine o m de ined by he maximum o ce Fmax and cyclic load a io R = 0.1 (R = Fmin/Fmax). Acco ding o he ISO
18489, he load ange Δσ is ela ed o he ligamen a ea, hus he o ces Fmin, Fmax and he ange ΔF mus be calcula ed
acco dingly om he chosen Δσ. The le els o Δσ = 11, 12 and 13 MPa we e chosen o PE100 and PE100RC ma e ials,
and 10.5, 11.5, and 12.5 MPa o PE80 ma e ial we e applied. On he o he hand, he pipe specimens we e es ed only
on he le el o Δσ = 10 MPa. The es s we e s opped when he specimens b oke, o he numbe o cycles eached
1×107.
Fig. 1. (a) geome y o he CRB specimen; (b) geome y o he new pipe specimen.
3. Resul s
3.1. F ac u e su ace obse a ion
In he case o CRB es s, i is common o obse e asymme ic ma ks on he ac u e su ace ha esul om he
discon inuous p opaga ion o he c ack, which consis s o epea ed phases o de elopmen and subsequen b eakage
o a p ocess zone (c aze) in on o he c ack ip – see Fig. 2. This is a ypical phenomenon o SCG in polye hylene.
The s anda d o CRB specimens speci ies ha a signi ican pa o he ac u e su ace mus show he SCG
mechanism, o he wise he esul om he specimen is no ep esen a i e because he dominan ailu e mechanism was
duc ile ailu e, which means he load was oo high. The same mechanism o SCG was obse ed on he ac u e su ace
o pipe specimens depic ed in Fig. 3. Howe e , he asymme y was much s onge and he a ea o SCG was much
smalle , which caused a la ge sca e in he da a.
I was e y di icul o ind he op imal load ange o he pipe specimen so ha accep able ep esen a i e esul s
a e ob ained wi h su icien amoun o SCG. This is di ec ly linked o he geome y o he pipe specimens, and i
u ned ou o be he bigges limi a ion o hem. Fo he load ange Δσ = 10 MPa, accep able ep esen a i e esul s can
be ob ained wi h bo h specimens (e en hough he es ing imes end o be e y long o he PE100 and PE100RC
4 Au ho name / S uc u al In eg i y P ocedia 00 (2022) 000–000
g ades). Howe e , going highe wi h he load ange causes he pipe specimens o b eak wi h a duc ile ailu e, which
is illus a ed by he ac u e su ace in he Fig. 4, whe e a pipe specimen made o ma e ial 1 (PE 80) loaded by Δσ =
12 MPa ailed a e N =13694 cycles by duc ile ailu e – no SCG occu ed. This happens, e en hough he s ess
in ensi y ac o ange (ΔKI = 0.59 MPa·m1/2, ob ained by FEM) a his load le el is lowe han o CRB specimens
( o Δσ = 10 MPa i is ΔKI = 0.65 MPa·m1/2), which s ill pe o m well and p oduce ep esen a i e esul s a his le el
e en o less SCG- esis an ma e ials. This is caused by he ela i ely hin wall o he pipe – he hin wall makes
cons ain in he icini y o he c ack la ge , which p e en s SCG ini ia ion a a lowe ΔKI, bu when he p opaga ion
s a s, he amoun o SCG is low because i ans e s in o he duc ile ailu e mode e y ea ly o almos ins an ly as he
ligamen becomes hinne , making he esul s no ep esen a i e.
To be able o so he ma e ials acco ding o SCG esis ance, he loading ange o Δσ = 10 MPa was chosen o all
he pipe specimens. The esul s o a igue es ing a e p esen ed in he nex sec ion.
Fig. 2. Pho o o ac u e su ace o a CRB specimen made o PE100RC – ma e ial 8 aken by op ical mic oscope. The a eas o SCG and inal
duc ile ailu e a e depic ed.
Fig. 3. Pho o o ac u e su ace o an ex uded pipe specimen made o PE100RC – ma e ial 8 aken by op ical mic oscope. The a eas o SCG and
inal duc ile ailu e a e shown in he de ail.
3.2. Fa igue pe o mance
Fig. 5 summa izes he ma e ial anking based on he numbe o cycles o ailu e N o ex uded pipe specimens and
CRB specimens, espec i ely. Fo he pipe specimens, he mean alue o N o e e y ma e ial is depic ed by black
do s. Resul s om bo h ypes o specimens di ide he ma e ials in o he polye hylene pipe g ades g oups co ec ly.
Howe e , he esul s o pipe specimens su e by high sca e wi hin e e y es ed pipe g ade, which is caused by he
lack o cons ain and lack o space o he c ack o p opaga e. This makes he c ack p opaga ion mo e suscep ible o
any de ec s and i egula i ies in he geome y as opposed o he CRB specimens, whe e he esul s a e no ably less
Lukáš T á níček e al. / P ocedia S uc u al In eg i y 43 (2023) 148–153 151
Au ho name / S uc u al In eg i y P ocedia 00 (2022) 000–000 3
2. Expe imen al de ails
CRB specimens wi h he dimensions acco ding o he s anda d (ISO 2015): ou e diame e D = 14 mm, leng h
l = 100 mm and ci cum e en ial azo -sha p no ch aini = 1.5 mm; we e machined om comp ession molded shee s.
Polye hylene pipes wi h ou e diame e Dou = 20 mm and inne diame e Din = 14 mm we e p oduced by ex usion.
The pipe wall hickness = 3 mm was chosen – i was a maximum ha he ex usion die allowed. The pipes we e cu
in o 100 mm long specimens wi h 1 mm deep azo -sha p ci cum e en ial no ch in he middle. Bo h ypes o specimens
we e p epa ed a he Polyme Ins i u e B no.
To ally, 9 di e en polye hylene ma e ials o he pipe g ades PE80, PE100 and PE100RC we e es ed wi h he pipe
specimens and o 5 ou o hese ma e ials CRB es s we e also ca ied ou – see summa y in Table 1.
Table 1. O e iew o es ed polye hylene pipe g ades.
Ma e ial numbe
1
2
3
4
5
6
7
8
9
Pipe g ade
PE80
PE100
PE100RC
Pipe specimen
✓
✓
✓
✓
✓
✓
✓
✓
✓
CRB specimen
✓
✓
✓
✓
✓
The uniaxial a igue es s we e pe o med using he compu e -con olled es ing machine INSTRON E10000. The
specimens we e loaded cyclically wi h equency 10 Hz. The cyclic loading was con olled by o ce, and i had he
sine o m de ined by he maximum o ce Fmax and cyclic load a io R = 0.1 (R = Fmin/Fmax). Acco ding o he ISO
18489, he load ange Δσ is ela ed o he ligamen a ea, hus he o ces Fmin, Fmax and he ange ΔF mus be calcula ed
acco dingly om he chosen Δσ. The le els o Δσ = 11, 12 and 13 MPa we e chosen o PE100 and PE100RC ma e ials,
and 10.5, 11.5, and 12.5 MPa o PE80 ma e ial we e applied. On he o he hand, he pipe specimens we e es ed only
on he le el o Δσ = 10 MPa. The es s we e s opped when he specimens b oke, o he numbe o cycles eached
1×107.
Fig. 1. (a) geome y o he CRB specimen; (b) geome y o he new pipe specimen.
3. Resul s
3.1. F ac u e su ace obse a ion
In he case o CRB es s, i is common o obse e asymme ic ma ks on he ac u e su ace ha esul om he
discon inuous p opaga ion o he c ack, which consis s o epea ed phases o de elopmen and subsequen b eakage
o a p ocess zone (c aze) in on o he c ack ip – see Fig. 2. This is a ypical phenomenon o SCG in polye hylene.
The s anda d o CRB specimens speci ies ha a signi ican pa o he ac u e su ace mus show he SCG
mechanism, o he wise he esul om he specimen is no ep esen a i e because he dominan ailu e mechanism was
duc ile ailu e, which means he load was oo high. The same mechanism o SCG was obse ed on he ac u e su ace
o pipe specimens depic ed in Fig. 3. Howe e , he asymme y was much s onge and he a ea o SCG was much
smalle , which caused a la ge sca e in he da a.
I was e y di icul o ind he op imal load ange o he pipe specimen so ha accep able ep esen a i e esul s
a e ob ained wi h su icien amoun o SCG. This is di ec ly linked o he geome y o he pipe specimens, and i
u ned ou o be he bigges limi a ion o hem. Fo he load ange Δσ = 10 MPa, accep able ep esen a i e esul s can
be ob ained wi h bo h specimens (e en hough he es ing imes end o be e y long o he PE100 and PE100RC
4 Au ho name / S uc u al In eg i y P ocedia 00 (2022) 000–000
g ades). Howe e , going highe wi h he load ange causes he pipe specimens o b eak wi h a duc ile ailu e, which
is illus a ed by he ac u e su ace in he Fig. 4, whe e a pipe specimen made o ma e ial 1 (PE 80) loaded by Δσ =
12 MPa ailed a e N =13694 cycles by duc ile ailu e – no SCG occu ed. This happens, e en hough he s ess
in ensi y ac o ange (ΔKI = 0.59 MPa·m1/2, ob ained by FEM) a his load le el is lowe han o CRB specimens
( o Δσ = 10 MPa i is ΔKI = 0.65 MPa·m1/2), which s ill pe o m well and p oduce ep esen a i e esul s a his le el
e en o less SCG- esis an ma e ials. This is caused by he ela i ely hin wall o he pipe – he hin wall makes
cons ain in he icini y o he c ack la ge , which p e en s SCG ini ia ion a a lowe ΔKI, bu when he p opaga ion
s a s, he amoun o SCG is low because i ans e s in o he duc ile ailu e mode e y ea ly o almos ins an ly as he
ligamen becomes hinne , making he esul s no ep esen a i e.
To be able o so he ma e ials acco ding o SCG esis ance, he loading ange o Δσ = 10 MPa was chosen o all
he pipe specimens. The esul s o a igue es ing a e p esen ed in he nex sec ion.
Fig. 2. Pho o o ac u e su ace o a CRB specimen made o PE100RC – ma e ial 8 aken by op ical mic oscope. The a eas o SCG and inal
duc ile ailu e a e depic ed.
Fig. 3. Pho o o ac u e su ace o an ex uded pipe specimen made o PE100RC – ma e ial 8 aken by op ical mic oscope. The a eas o SCG and
inal duc ile ailu e a e shown in he de ail.
3.2. Fa igue pe o mance
Fig. 5 summa izes he ma e ial anking based on he numbe o cycles o ailu e N o ex uded pipe specimens and
CRB specimens, espec i ely. Fo he pipe specimens, he mean alue o N o e e y ma e ial is depic ed by black
do s. Resul s om bo h ypes o specimens di ide he ma e ials in o he polye hylene pipe g ades g oups co ec ly.
Howe e , he esul s o pipe specimens su e by high sca e wi hin e e y es ed pipe g ade, which is caused by he
lack o cons ain and lack o space o he c ack o p opaga e. This makes he c ack p opaga ion mo e suscep ible o
any de ec s and i egula i ies in he geome y as opposed o he CRB specimens, whe e he esul s a e no ably less
152 Lukáš T á níček e al. / P ocedia S uc u al In eg i y 43 (2023) 148–153
Au ho name / S uc u al In eg i y P ocedia 00 (2022) 000–000 5
sca e ed. The e o e, es ing o mo e pipe specimens would be needed o ob ain mo e accu a e esul s. I mus be also
no ed he e ha he es ing imes o he ex uded pipe specimens we e app oxima ely 2 imes longe , which is caused
by he gene ally lowe s ess in ensi y ac o ange a which hese specimens mus be es ed o ob ain ep esen a i e
esul s. Tha is ano he g ea d awback o he pipe specimens.
The compa ison o bo h es s is depic ed in Fig. 6, whe e no malized numbe o cycles is plo ed o i e ma e ials,
o which bo h ypes o specimens we e es ed. The esul s o ma e ial 1 a e aken as he e e ence alues, i.e., he
esul s o N o ma e ials 2, 6, 7 and 8 a e di ided by he N o ma e ial 1. The compa ison shows ha he esis ance
agains SCG o he ma e ials 1 and 2 is he same acco ding o bo h ypes o es s. Howe e , he di e ence in SCG
pe o mance o ma e ials 6, 7 and 8 is no able only in he case o CRB es s. This demons a es he highe sensi i i y
o he CRB es as he new pipe es shows simila pe o mance o hese h ee ma e ials.
Fig. 4. Pho o o ac u e su ace o an ex uded pipe specimen made o PE80 – ma e ial 1 aken by op ical mic oscope. The a ea o duc ile ailu e
is shown in he de ail. No SCG occu ed.
Fig. 5. Expe imen al esul s o SCG esis ance measu ed on (a) ex uded pipe specimens and (b) CRB specimens.
4. Conclusions
This pape p esen s esea ch o SCG esis ance on nine di e en PE ma e ials om he pipe g ades PE80, PE100
and PE100RC. The SCG esis ance was measu ed using wo ypes o specimens: he s anda dized CRB specimens
manu ac u ed om comp ession molded pla es and new ex uded pipe specimens p oposed in his pape .
I can be concluded om he p esen ed esul s ha he new pipe specimens so ed he ma e ials in o pipe g ade
g oups (PE80, PE100 and PE100RC) co ec ly. Howe e , he esul s o all he es ed ma e ials su e by high sca e
and he e o e, mo e specimens would be needed o es ing o ob ain a leas sligh ly mo e accu a e esul s. The eason
o he high sca e o he esul s is gene ally he hin wall o he pipe specimens. I causes ha he slow c ack g ow h
6 Au ho name / S uc u al In eg i y P ocedia 00 (2022) 000–000
is subs i u ed by he duc ile ac u e e y ea ly in he c ack g ow h p ocess, o he slow c ack g ow h does no occu
a all. The highe cons ain in he CRB specimens, which is caused by hei shape o a ull cylinde , allows o an
ea ly ini ia ion o he SCG p ocess and p o ides a su icien space o he c ack p opaga ion, which esul s in he
abili y o hese specimens o ca ch ine di e ences be ween he ma e ials. The compa ison o he pipe specimens
wi h he CRB es s con i ms his conclusion.
Fig. 6. Compa ison o esis ance agains SCG o CRB and pipe specimens.
The o iginal mo i a ion o expe imen ing wi h he ex uded pipe specimens was o sa e ime. Howe e , i u ned
ou ha he ime sa ed by he e y as specimen p epa a ion is consumed by he much longe es ing imes o he pipe
specimens. Some modi ica ions o he specimens a e possible o y educing he es ing imes and ob ain mo e
accu a e esul s – inc easing he pipe wall hickness o he specimens and p ecisely de e mining he op imal es ing
load, especially o he mo e SCG- esis an PE g ades. These modi ica ions a e planned o he upcoming wo k in his
ield.
Acknowledgemen s
This esea ch was suppo ed by he p ojec TN01000071 o Na ional Compe ence Cen e o Mecha onics and
Sma Technologies o Mechanical Enginee ing co ounded by he Technology Agency o he Czech Republic.
Re e ences
A bei e , F., Sch i esse , B., F ank, A., Be e , M., Pin e , G., 2015. Cyclic es s on c acked ound ba s as a quick ool o assess he long- e m
beha iou o he moplas ics and elas ome s. Polyme Tes ing 45, 83–92.
Beech, S., Clu on, E., 2013. In e p e a ion o esul s o ull no ch c eep es and compa ison wi h no ched pipe es . Plas ics, Rubbe and Composi es
34(7), 294-300.
Fleissne , M., 1998. Expe ience wi h a ull no ch c eep es in de e mining he s ess c ack pe o mance o polye hylene. Polyme Enginee ing and
Science (2), 330-341.
F ank, A., A bei e , A., Be ge , I., Hu ař, P., Náhlík, L., Pin e , G., 2019. F ac u e Mechanics Li e ime P edic ion o Polye hylene Pipes. Jou nal
o Pipeline Sys ems Enginee ing and P ac ice 10(1).
F ank, A., Pin e , G., 2014. E alua ion o he applicabili y o he c acked ound ba es as s anda dized PE-pipe anking ool. Polyme Tes ing 33,
161-171.
ISO. 2015. Polye hylene (PE) ma e ials o piping sys ems – De e mina ion o esis ance o slow c ack g ow h unde cyclic loading – C acked
Round Ba es me hod. ISO 18489.
ISO. 2012. Plas ics piping and duc ing sys ems: De e mina ion o he long- e m hyd os a ic s eng h o he moplas ics ma e ials in pipe o m
by ex apola ion. ISO 9080.
Lu, X., B own, N., 1992. A es o slow c ack g ow h ailu e in polye hylene unde a cons an load. Polyme Tes ing 11(4), 309-319.
Nayya , M., King, S., 2000. Piping handbook. 7 h edi ion. New Yo k: McG awHill. ISBN 0-07-047106-1.
Pin e , G., Haage , M., Balika, W., Lang, R. W., 2013. Fa igue c ack g ow h in PE-HD pipe g ades. Plas ics, Rubbe and Composi es 34(1), 25-33.
Pin e , G., Haage , M., Balika, W., Lang, R. W., 2007. Cyclic c ack g ow h es s wi h CRB specimens o he e alua ion o he long- e m
pe o mance o PE pipe g ades. Polyme Tes ing 26(2), 180–188.
Lukáš T á níček e al. / P ocedia S uc u al In eg i y 43 (2023) 148–153 153
Au ho name / S uc u al In eg i y P ocedia 00 (2022) 000–000 5
sca e ed. The e o e, es ing o mo e pipe specimens would be needed o ob ain mo e accu a e esul s. I mus be also
no ed he e ha he es ing imes o he ex uded pipe specimens we e app oxima ely 2 imes longe , which is caused
by he gene ally lowe s ess in ensi y ac o ange a which hese specimens mus be es ed o ob ain ep esen a i e
esul s. Tha is ano he g ea d awback o he pipe specimens.
The compa ison o bo h es s is depic ed in Fig. 6, whe e no malized numbe o cycles is plo ed o i e ma e ials,
o which bo h ypes o specimens we e es ed. The esul s o ma e ial 1 a e aken as he e e ence alues, i.e., he
esul s o N o ma e ials 2, 6, 7 and 8 a e di ided by he N o ma e ial 1. The compa ison shows ha he esis ance
agains SCG o he ma e ials 1 and 2 is he same acco ding o bo h ypes o es s. Howe e , he di e ence in SCG
pe o mance o ma e ials 6, 7 and 8 is no able only in he case o CRB es s. This demons a es he highe sensi i i y
o he CRB es as he new pipe es shows simila pe o mance o hese h ee ma e ials.
Fig. 4. Pho o o ac u e su ace o an ex uded pipe specimen made o PE80 – ma e ial 1 aken by op ical mic oscope. The a ea o duc ile ailu e
is shown in he de ail. No SCG occu ed.
Fig. 5. Expe imen al esul s o SCG esis ance measu ed on (a) ex uded pipe specimens and (b) CRB specimens.
4. Conclusions
This pape p esen s esea ch o SCG esis ance on nine di e en PE ma e ials om he pipe g ades PE80, PE100
and PE100RC. The SCG esis ance was measu ed using wo ypes o specimens: he s anda dized CRB specimens
manu ac u ed om comp ession molded pla es and new ex uded pipe specimens p oposed in his pape .
I can be concluded om he p esen ed esul s ha he new pipe specimens so ed he ma e ials in o pipe g ade
g oups (PE80, PE100 and PE100RC) co ec ly. Howe e , he esul s o all he es ed ma e ials su e by high sca e
and he e o e, mo e specimens would be needed o es ing o ob ain a leas sligh ly mo e accu a e esul s. The eason
o he high sca e o he esul s is gene ally he hin wall o he pipe specimens. I causes ha he slow c ack g ow h
6 Au ho name / S uc u al In eg i y P ocedia 00 (2022) 000–000
is subs i u ed by he duc ile ac u e e y ea ly in he c ack g ow h p ocess, o he slow c ack g ow h does no occu
a all. The highe cons ain in he CRB specimens, which is caused by hei shape o a ull cylinde , allows o an
ea ly ini ia ion o he SCG p ocess and p o ides a su icien space o he c ack p opaga ion, which esul s in he
abili y o hese specimens o ca ch ine di e ences be ween he ma e ials. The compa ison o he pipe specimens
wi h he CRB es s con i ms his conclusion.
Fig. 6. Compa ison o esis ance agains SCG o CRB and pipe specimens.
The o iginal mo i a ion o expe imen ing wi h he ex uded pipe specimens was o sa e ime. Howe e , i u ned
ou ha he ime sa ed by he e y as specimen p epa a ion is consumed by he much longe es ing imes o he pipe
specimens. Some modi ica ions o he specimens a e possible o y educing he es ing imes and ob ain mo e
accu a e esul s – inc easing he pipe wall hickness o he specimens and p ecisely de e mining he op imal es ing
load, especially o he mo e SCG- esis an PE g ades. These modi ica ions a e planned o he upcoming wo k in his
ield.
Acknowledgemen s
This esea ch was suppo ed by he p ojec TN01000071 o Na ional Compe ence Cen e o Mecha onics and
Sma Technologies o Mechanical Enginee ing co ounded by he Technology Agency o he Czech Republic.
Re e ences
A bei e , F., Sch i esse , B., F ank, A., Be e , M., Pin e , G., 2015. Cyclic es s on c acked ound ba s as a quick ool o assess he long- e m
beha iou o he moplas ics and elas ome s. Polyme Tes ing 45, 83–92.
Beech, S., Clu on, E., 2013. In e p e a ion o esul s o ull no ch c eep es and compa ison wi h no ched pipe es . Plas ics, Rubbe and Composi es
34(7), 294-300.
Fleissne , M., 1998. Expe ience wi h a ull no ch c eep es in de e mining he s ess c ack pe o mance o polye hylene. Polyme Enginee ing and
Science (2), 330-341.
F ank, A., A bei e , A., Be ge , I., Hu ař, P., Náhlík, L., Pin e , G., 2019. F ac u e Mechanics Li e ime P edic ion o Polye hylene Pipes. Jou nal
o Pipeline Sys ems Enginee ing and P ac ice 10(1).
F ank, A., Pin e , G., 2014. E alua ion o he applicabili y o he c acked ound ba es as s anda dized PE-pipe anking ool. Polyme Tes ing 33,
161-171.
ISO. 2015. Polye hylene (PE) ma e ials o piping sys ems – De e mina ion o esis ance o slow c ack g ow h unde cyclic loading – C acked
Round Ba es me hod. ISO 18489.
ISO. 2012. Plas ics piping and duc ing sys ems: De e mina ion o he long- e m hyd os a ic s eng h o he moplas ics ma e ials in pipe o m
by ex apola ion. ISO 9080.
Lu, X., B own, N., 1992. A es o slow c ack g ow h ailu e in polye hylene unde a cons an load. Polyme Tes ing 11(4), 309-319.
Nayya , M., King, S., 2000. Piping handbook. 7 h edi ion. New Yo k: McG awHill. ISBN 0-07-047106-1.
Pin e , G., Haage , M., Balika, W., Lang, R. W., 2013. Fa igue c ack g ow h in PE-HD pipe g ades. Plas ics, Rubbe and Composi es 34(1), 25-33.
Pin e , G., Haage , M., Balika, W., Lang, R. W., 2007. Cyclic c ack g ow h es s wi h CRB specimens o he e alua ion o he long- e m
pe o mance o PE pipe g ades. Polyme Tes ing 26(2), 180–188.