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Numerical study of specimen with steel inclusion: Influence of interfacial transition zone

Abstract

In this paper, the influence of the interfacial transition zone (ITZ) between steel inclusion and fine-grained cement-based composite on fracture behaviour is investigated. Specimens of the nominal dimensions 40 × 40 × 160 mm with the steel inclusion of the prismatic shape with nominal dimensions 8 × 8 × 40 mm were provided with an initial central edge notch with a depth 12 mm. The aim of this paper is to analyse the behaviour of such specimen by means of numerical modelling by finite element method (Ansys software). A simplified 2D model (plane strain) based on the fracture test configuration was created. The crack propagation assessment was based on the criterion of the average value of tangential stress calculated over certain distance d in dependence on the polar coordinate. It is assumed that the crack is initiated when the average stress reaches its critical value, which depends on the fracture toughness of the material and on the distance d. From the detailed numerical analysis of the described fracture test, we concluded that the crack propagation path depends strongly on the fracture properties of ITZ. The central inclusion works as an obstacle to crack propagation only in the initial stage of failure. The mechanical fracture parameters of the ITZ strongly influence the overall fracture behavior of test specimens

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Numerical study of specimen with steel inclusion: Influence of interfacial transition zone

Author: Vyhlídal, Michal; Klusák, Jan
Publisher: Elsevier
Year: 2023
DOI: 10.1016/j.prostr.2022.12.126
Source: https://dspace.vut.cz/bitstreams/5089df5b-7fd4-42f5-a164-5ff15ae9d2bd/download
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Pee - e iew unde esponsibili y o he scien i ic commi ee o he 23 Eu opean Con e ence on F ac u e – ECF23
10.1016/j.p os .2022.12.126
10.1016/j.p os .2022.12.126 2452-3216
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2452-3216 © 2020 The Au ho s. Published by Else ie B.V.
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Pee - e iew unde esponsibili y o 23 Eu opean Con e ence on F ac u e - ECF23
23 Eu opean Con e ence on F ac u e - ECF23
Nume ical s udy o specimen wi h s eel inclusion:
In luence o in e acial ansi ion zone
Michal Vyhlídala,*, Jan Klusákb
aB no Uni e si y o Technology, Facul y o Ci il Enginee ing, Ve eří 331/95, 602 00 B no, Czech Republic
bCzech Academy o Sciences, Ins i u e o Physics o Ma e ials, Žižko a 22, 616 00 B no, Czech Republic
Abs ac
In his pape , he in luence o he in e acial ansi ion zone (ITZ) be ween s eel inclusion and ine-g ained cemen -based composi e
on ac u e beha iou is in es iga ed. Specimens o he nominal dimensions 40 × 40 × 160 mm wi h he s eel inclusion o he
p isma ic shape wi h nominal dimensions 8 × 8 × 40 mm we e p o ided wi h an ini ial cen al edge no ch wi h a dep h 12 mm.
The aim o his pape is o analyse he beha iou o such specimen by means o nume ical modelling by ini e elemen me hod
(Ansys so wa e). A simpli ied 2D model (plane s ain) based on he ac u e es con igu a ion was c ea ed. The c ack p opaga ion
assessmen was based on he c i e ion o he a e age alue o angen ial s ess 𝜎𝜎θθ calcula ed o e ce ain dis ance d in dependence
on he pola coo dina e θ. I is assumed ha he c ack is ini ia ed when he a e age s ess 𝜎𝜎θθ(𝜃𝜃0) eaches i s c i ical alue
𝜎𝜎θθ,c(𝜃𝜃0), which depends on he ac u e oughness 𝐾𝐾Ic o he ma e ial and on he dis ance d.
F om he de ailed nume ical analysis o he desc ibed ac u e es , we concluded ha he c ack p opaga ion pa h depends s ongly
on he ac u e p ope ies o ITZ. The cen al inclusion wo ks as an obs acle o c ack p opaga ion only in he ini ial s age o ailu e.
The mechanical ac u e pa ame e s o he ITZ s ongly in luence he o e all ac u e beha io o es specimens.
© 2020 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 esponsibili y o 23 Eu opean Con e ence on F ac u e - ECF23
Keywo ds: : S eel inclusion, ac u e es , nume ical simula ion, c ack p opaga ion pa h, he c i e ion o a e age angen ial s ess.
* Co esponding au ho .
E-mail add ess: Michal.Vyhlidal@ u b .cz
A ailable online a www.sciencedi ec .com
^ĐŝĞŶĐĞŝƌĞĐƚ
S uc u al In eg i y P ocedia 00 (2019) 000–000
www.else ie .com/loca e/p ocedia
2452-3216 © 2020 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 esponsibili y o 23 Eu opean Con e ence on F ac u e - ECF23
23 Eu opean Con e ence on F ac u e - ECF23
Nume ical s udy o specimen wi h s eel inclusion:
In luence o in e acial ansi ion zone
Michal Vyhlídala,*, Jan Klusákb
aB no Uni e si y o Technology, Facul y o Ci il Enginee ing, Ve eří 331/95, 602 00 B no, Czech Republic
bCzech Academy o Sciences, Ins i u e o Physics o Ma e ials, Žižko a 22, 616 00 B no, Czech Republic
Abs ac
In his pape , he in luence o he in e acial ansi ion zone (ITZ) be ween s eel inclusion and ine-g ained cemen -based composi e
on ac u e beha iou is in es iga ed. Specimens o he nominal dimensions 40 × 40 × 160 mm wi h he s eel inclusion o he
p isma ic shape wi h nominal dimensions 8 × 8 × 40 mm we e p o ided wi h an ini ial cen al edge no ch wi h a dep h 12 mm.
The aim o his pape is o analyse he beha iou o such specimen by means o nume ical modelling by ini e elemen me hod
(Ansys so wa e). A simpli ied 2D model (plane s ain) based on he ac u e es con igu a ion was c ea ed. The c ack p opaga ion
assessmen was based on he c i e ion o he a e age alue o angen ial s ess 𝜎𝜎θθ calcula ed o e ce ain dis ance d in dependence
on he pola coo dina e θ. I is assumed ha he c ack is ini ia ed when he a e age s ess 𝜎𝜎θθ(𝜃𝜃0) eaches i s c i ical alue
𝜎𝜎θθ,c(𝜃𝜃0), which depends on he ac u e oughness 𝐾𝐾Ic o he ma e ial and on he dis ance d.
F om he de ailed nume ical analysis o he desc ibed ac u e es , we concluded ha he c ack p opaga ion pa h depends s ongly
on he ac u e p ope ies o ITZ. The cen al inclusion wo ks as an obs acle o c ack p opaga ion only in he ini ial s age o ailu e.
The mechanical ac u e pa ame e s o he ITZ s ongly in luence he o e all ac u e beha io o es specimens.
© 2020 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 esponsibili y o 23 Eu opean Con e ence on F ac u e - ECF23
Keywo ds: : S eel inclusion, ac u e es , nume ical simula ion, c ack p opaga ion pa h, he c i e ion o a e age angen ial s ess.
* Co esponding au ho .
E-mail add ess: Michal.Vyhlidal@ u b .cz
Michal Vyhlídal e al. / P ocedia S uc u al In eg i y 42 (2022) 1000–1007 1001
A ailable online a www.sciencedi ec .com
^ĐŝĞŶĐĞŝƌĞĐƚ
S uc u al In eg i y P ocedia 00 (2019) 000–000
www.else ie .com/loca e/p ocedia
2452-3216 © 2020 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 esponsibili y o 23 Eu opean Con e ence on F ac u e - ECF23
23 Eu opean Con e ence on F ac u e - ECF23
Nume ical s udy o specimen wi h s eel inclusion:
In luence o in e acial ansi ion zone
Michal Vyhlídala,*, Jan Klusákb
aB no Uni e si y o Technology, Facul y o Ci il Enginee ing, Ve eří 331/95, 602 00 B no, Czech Republic
bCzech Academy o Sciences, Ins i u e o Physics o Ma e ials, Žižko a 22, 616 00 B no, Czech Republic
Abs ac
In his pape , he in luence o he in e acial ansi ion zone (ITZ) be ween s eel inclusion and ine-g ained cemen -based composi e
on ac u e beha iou is in es iga ed. Specimens o he nominal dimensions 40 × 40 × 160 mm wi h he s eel inclusion o he
p isma ic shape wi h nominal dimensions 8 × 8 × 40 mm we e p o ided wi h an ini ial cen al edge no ch wi h a dep h 12 mm.
The aim o his pape is o analyse he beha iou o such specimen by means o nume ical modelling by ini e elemen me hod
(Ansys so wa e). A simpli ied 2D model (plane s ain) based on he ac u e es con igu a ion was c ea ed. The c ack p opaga ion
assessmen was based on he c i e ion o he a e age alue o angen ial s ess 𝜎𝜎θθ calcula ed o e ce ain dis ance d in dependence
on he pola coo dina e θ. I is assumed ha he c ack is ini ia ed when he a e age s ess 𝜎𝜎θθ(𝜃𝜃0) eaches i s c i ical alue
𝜎𝜎θθ,c(𝜃𝜃0), which depends on he ac u e oughness 𝐾𝐾Ic o he ma e ial and on he dis ance d.
F om he de ailed nume ical analysis o he desc ibed ac u e es , we concluded ha he c ack p opaga ion pa h depends s ongly
on he ac u e p ope ies o ITZ. The cen al inclusion wo ks as an obs acle o c ack p opaga ion only in he ini ial s age o ailu e.
The mechanical ac u e pa ame e s o he ITZ s ongly in luence he o e all ac u e beha io o es specimens.
© 2020 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 esponsibili y o 23 Eu opean Con e ence on F ac u e - ECF23
Keywo ds: : S eel inclusion, ac u e es , nume ical simula ion, c ack p opaga ion pa h, he c i e ion o a e age angen ial s ess.
* Co esponding au ho .
E-mail add ess: Michal.Vyhlidal@ u b .cz
A ailable online a www.sciencedi ec .com
^ĐŝĞŶĐĞŝƌĞĐƚ
S uc u al In eg i y P ocedia 00 (2019) 000–000
www.else ie .com/loca e/p ocedia
2452-3216 © 2020 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 esponsibili y o 23 Eu opean Con e ence on F ac u e - ECF23
23 Eu opean Con e ence on F ac u e - ECF23
Nume ical s udy o specimen wi h s eel inclusion:
In luence o in e acial ansi ion zone
Michal Vyhlídala,*, Jan Klusákb
aB no Uni e si y o Technology, Facul y o Ci il Enginee ing, Ve eří 331/95, 602 00 B no, Czech Republic
bCzech Academy o Sciences, Ins i u e o Physics o Ma e ials, Žižko a 22, 616 00 B no, Czech Republic
Abs ac
In his pape , he in luence o he in e acial ansi ion zone (ITZ) be ween s eel inclusion and ine-g ained cemen -based composi e
on ac u e beha iou is in es iga ed. Specimens o he nominal dimensions 40 × 40 × 160 mm wi h he s eel inclusion o he
p isma ic shape wi h nominal dimensions 8 × 8 × 40 mm we e p o ided wi h an ini ial cen al edge no ch wi h a dep h 12 mm.
The aim o his pape is o analyse he beha iou o such specimen by means o nume ical modelling by ini e elemen me hod
(Ansys so wa e). A simpli ied 2D model (plane s ain) based on he ac u e es con igu a ion was c ea ed. The c ack p opaga ion
assessmen was based on he c i e ion o he a e age alue o angen ial s ess 𝜎𝜎θθ calcula ed o e ce ain dis ance d in dependence
on he pola coo dina e θ. I is assumed ha he c ack is ini ia ed when he a e age s ess 𝜎𝜎θθ(𝜃𝜃0) eaches i s c i ical alue
𝜎𝜎θθ,c(𝜃𝜃0), which depends on he ac u e oughness 𝐾𝐾Ic o he ma e ial and on he dis ance d.
F om he de ailed nume ical analysis o he desc ibed ac u e es , we concluded ha he c ack p opaga ion pa h depends s ongly
on he ac u e p ope ies o ITZ. The cen al inclusion wo ks as an obs acle o c ack p opaga ion only in he ini ial s age o ailu e.
The mechanical ac u e pa ame e s o he ITZ s ongly in luence he o e all ac u e beha io o es specimens.
© 2020 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 esponsibili y o 23 Eu opean Con e ence on F ac u e - ECF23
Keywo ds: : S eel inclusion, ac u e es , nume ical simula ion, c ack p opaga ion pa h, he c i e ion o a e age angen ial s ess.
* Co esponding au ho .
E-mail add ess: Michal.Vyhlidal@ u b .cz
2 Au ho name / S uc u al In eg i y P ocedia 00 (2019) 000–000
1. In oduc ion
Conc e e is a composi e, which is o med, in a esh s a e, om coa se agg ega e, ine agg ega e, binde (mos ly
Po land cemen ) and wa e , e en ually admix u es. Due o he hyd a ion p ocess conc e e ob ain i s aluable
p ope ies – high s eng h (mainly comp essi e), du abili y, i e esis ance e c. Du ing he hyd a ion and ha dening,
he sh inkage and o he p ocesses occu and lead o he o ma ion o mic o and mac o-de ec s (c acks, po es, e c.).
Ne e heless, conc e e s uc u es a e designed using p ocedu es men ioned in s anda ds – e. g. EN 1992-1-1 (2011)
o ecommenda ions which do no conside he exis ence o de ec s, such as c acks, po es, inclusions, ansi ion zones,
e c. Howe e , hese discon inui ies can ac as po en ial weak elemen s, which in luences he ac u e beha io
o conc e e s uc u es. In he mo e complex design o hese s uc u es (e. g. complex geome y), i is ad isable o apply
he p inciples o ac u e mechanics.
In his pape , ma e ial discon inui y is o med by special s eel inclusion placed in he middle o he es specimen.
Such a specimen made o ine-g ained cemen -based composi e was es ed in h ee-poin bending con igu a ion.
The aim o his pape is o iden i y he in luence o he in e ace be ween s eel inclusion and ma ix which is o med
by he in e acial ansi ion zone (ITZ). In he pape , esul s o nume ical assessmen o c ack p opaga ion s ages a e
p esen ed.
Nomencla u e
d a e aging dis ance
E Young’s modulus
EITZ Young’s modulus o he in e acial ansi ion zone
Fappl applied loading o ce
Fc i c i ical alue he applied o ce
𝐹𝐹𝑖𝑖𝑖𝑖(𝑛𝑛,𝜃𝜃) shape unc ions
GMTS gene alized maximum angen ial s ess
H1 gene alized s ess in ensi y ac o
ITZ in e acial ansi ion zone
KI s ess in ensi y ac o in loading mode I
KIc ac u e oughness (unde pu e mode I)
KIc, ITZ ac u e oughness (unde pu e mode I) o he in e acial ansi ion zone
KIc, MTX ac u e oughness (unde pu e mode I) o he ma ix
MTX ma ix – ine-g ained cemen -based composi e
p1 s ess singula i y exponen
𝑟𝑟,𝜃𝜃 pola coo dina es
ν Poisson’s a io
𝜎𝜎
ij
s ess enso componen
𝜎𝜎𝜃𝜃𝜃𝜃(𝑟𝑟,𝜃𝜃) angen ial s ess
𝜎𝜎𝜃𝜃𝜃𝜃(𝜃𝜃) a e age angen ial s ess
𝜎𝜎𝜃𝜃𝜃𝜃,c c i ical alue o he a e age angen ial s ess
2. Theo e ical backg ound
2.1. The In e acial T ansi ion Zone
The exis ence o he ITZ be ween agg ega e and cemen pas e was i s desc ibed in he 1950s by Fa an (1956).
The p ope ies o he ITZ and i s impac on he beha io o cemen -based composi es ha e been s udied om many
poin s o iew since ha . The ITZ is a egion o abou 50 µm in size, and i s mic os uc u e is o med mainly
by e ingi e needles and po landi e pla es (Diamond and Huang, 1998). The signi ican ea u e o he ITZ is mainly
1002 Michal Vyhlídal e al. / P ocedia S uc u al In eg i y 42 (2022) 1000–1007
Au ho name / S uc u al In eg i y P ocedia 00 (2019) 000–000 3
i s highe po osi y compa ed o he bulk ma ix which is ela ed o he highe local wa e o cemen a io
(Sc i ene e al., 2004). The local inc ease in po osi y leads o poo e bonds be ween he componen s, and hus
o lowe alues o he mechanical ac u e pa ame e s o he ITZ, see e. g. Zacha da e al. (2018)
o Vyhlídal and Klusák (2020). The p ope ies o ITZ in luence he o e all ac u e beha io o conc e e.
2.2. Linea elas ic ac u e mechanics and i s gene alized o m
F ac u e mechanics is a widely used ool o an assessmen o c ack beha io in ma e ials. Linea elas ic ac u e
mechanics supposes c acks in homogenous, iso opic, and linea ly elas ic ma e ial, see Ande son (2005). Williams
(1957) p esen ed a uni e sal solu ion o he s ess componen s a ound a c ack ip in he o m o in ini e se ies. Nea
c ack ip (𝑟𝑟 → 0), only he i s (singula ) e m is used o desc ibe he s ess ield, while he highe o de e ms
o he in ini e se ies can some imes be neglec ed. Componen s o he s ess enso a e gi en by he supe posi ion
o h ee basic ailu e modes de ined by I win (1957), whe e he opening mode I is p edominan ailu e mode.
Gene alized linea elas ic ac u e mechanics deals wi h an assessmen o gene al singula s ess concen a o s,
such as sha p no ches, bi-ma e ial no ches, bi-ma e ial inclusions, in e ace c acks e c. – see Klusák e al. (2013),
De Co e e al. (2017), o Klusák e al. (2016). In mos cases, he loading modes canno be assigned o he se ies e ms,
so he e ms a e labeled by A abic subsc ip s. The dependence o s ess on pola coo dina e is exp essed by a gene al
s ess singula i y exponen p1:
𝜎𝜎
ij
=𝐻𝐻1
√2𝜋𝜋 𝑟𝑟−𝑝𝑝1𝐹𝐹𝑖𝑖𝑖𝑖
1(

)
  
ሺͳሻ
whe e σij a e he s ess enso componen s o i, j = ,

. Gene alized s ess in ensi y ac o H1 ha e he uni s
[MPa𝑚𝑚𝑝𝑝1], and Fij a e he shape unc ions. Fo c acks in homogeneous media, he s ess in ensi y ac o s can be
de e mined di ec ly in he FEM so wa e, e.g. Ansys Inc. so wa e (2021), while o he gene al singula s ess
concen a o s, a ious di ec o in eg a ion me hods a e used, see Ping e al. (2008), Klusák e al. (2008)
o P o an e al. (2008). The alues H1 a e asce ained om a nume ical solu ion o he s udied geome y, ma e ials,
and bounda y condi ions.
2.3. C i e ion o s abili y based on a e age s ess ahead o he c ack ip
In he pape , he c ack p opaga ion condi ion is de e mined om he gene alized maximum angen ial s ess
(GMTS) c i e ion. This s abili y condi ion is based on wo well-known ac u e mechanics s abili y condi ions – (a)
c ack ini ia ion occu s i he s ess in ensi y ac o KI eaches i s c i ical alue KIc (also known as ac u e oughness),
see e.g. Ande son (2005), and (b) c ack will p opaga e in he di ec ion whe e he angen ial s ess σθθ is maximal, see
E dogan and Sih (1963). The GMTS s abili y c i e ion employs he a e age s ess σθθ(𝜃𝜃) calcula ed ac oss a dis ance
d ahead o he c ack ip. The dis ance d is usually chosen in dependence on he mechanism o a up u e (dimension
o a plas ic zone o me als, dimension o p ocess zone o quasi-b i le ma e ials, ma e ial g ain size, o ini e supposed
c ack ini ia ion/p opaga ion inc emen ). The a e age s ess σθθ(𝜃𝜃) ahead o he c ack ip is gi en by he ollowing
equa ion.
𝜎𝜎𝜃𝜃𝜃𝜃 =1
𝑑𝑑∫𝜎𝜎𝜃𝜃𝜃𝜃(𝑟𝑟,𝜃𝜃)𝑑𝑑𝑟𝑟
𝑑𝑑
0 (2)
The c ack p opaga ion di ec ion is supposed in he di ec ion o maximum o he a e age angen ial s ess esul ing
om nume ical analysis. The c i ical alue o angen ial s ess σθθ(𝜃𝜃) co esponding o he c ack ini ia ion is
de e mined om he knowledge o c ack p opaga ion condi ions o a c ack in homogeneous ma e ial unde mode I,
whe e ac u e oughness KIc is employed:
𝜎𝜎𝜃𝜃𝜃𝜃,𝑐𝑐 =2𝐾𝐾𝐼𝐼𝐼𝐼
√2𝜋𝜋𝑑𝑑 (3)
Michal Vyhlídal e al. / P ocedia S uc u al In eg i y 42 (2022) 1000–1007 1003
Au ho name / S uc u al In eg i y P ocedia 00 (2019) 000–000 3
i s highe po osi y compa ed o he bulk ma ix which is ela ed o he highe local wa e o cemen a io
(Sc i ene e al., 2004). The local inc ease in po osi y leads o poo e bonds be ween he componen s, and hus
o lowe alues o he mechanical ac u e pa ame e s o he ITZ, see e. g. Zacha da e al. (2018)
o Vyhlídal and Klusák (2020). The p ope ies o ITZ in luence he o e all ac u e beha io o conc e e.
2.2. Linea elas ic ac u e mechanics and i s gene alized o m
F ac u e mechanics is a widely used ool o an assessmen o c ack beha io in ma e ials. Linea elas ic ac u e
mechanics supposes c acks in homogenous, iso opic, and linea ly elas ic ma e ial, see Ande son (2005). Williams
(1957) p esen ed a uni e sal solu ion o he s ess componen s a ound a c ack ip in he o m o in ini e se ies. Nea
c ack ip (𝑟𝑟 → 0), only he i s (singula ) e m is used o desc ibe he s ess ield, while he highe o de e ms
o he in ini e se ies can some imes be neglec ed. Componen s o he s ess enso a e gi en by he supe posi ion
o h ee basic ailu e modes de ined by I win (1957), whe e he opening mode I is p edominan ailu e mode.
Gene alized linea elas ic ac u e mechanics deals wi h an assessmen o gene al singula s ess concen a o s,
such as sha p no ches, bi-ma e ial no ches, bi-ma e ial inclusions, in e ace c acks e c. – see Klusák e al. (2013),
De Co e e al. (2017), o Klusák e al. (2016). In mos cases, he loading modes canno be assigned o he se ies e ms,
so he e ms a e labeled by A abic subsc ip s. The dependence o s ess on pola coo dina e is exp essed by a gene al
s ess singula i y exponen p1:
𝜎𝜎
ij
=𝐻𝐻1
√2𝜋𝜋 𝑟𝑟−𝑝𝑝1𝐹𝐹𝑖𝑖𝑖𝑖
1(

)
  
ሺͳሻ
whe e σij a e he s ess enso componen s o i, j = ,

. Gene alized s ess in ensi y ac o H1 ha e he uni s
[MPa𝑚𝑚𝑝𝑝1], and Fij a e he shape unc ions. Fo c acks in homogeneous media, he s ess in ensi y ac o s can be
de e mined di ec ly in he FEM so wa e, e.g. Ansys Inc. so wa e (2021), while o he gene al singula s ess
concen a o s, a ious di ec o in eg a ion me hods a e used, see Ping e al. (2008), Klusák e al. (2008)
o P o an e al. (2008). The alues H1 a e asce ained om a nume ical solu ion o he s udied geome y, ma e ials,
and bounda y condi ions.
2.3. C i e ion o s abili y based on a e age s ess ahead o he c ack ip
In he pape , he c ack p opaga ion condi ion is de e mined om he gene alized maximum angen ial s ess
(GMTS) c i e ion. This s abili y condi ion is based on wo well-known ac u e mechanics s abili y condi ions – (a)
c ack ini ia ion occu s i he s ess in ensi y ac o KI eaches i s c i ical alue KIc (also known as ac u e oughness),
see e.g. Ande son (2005), and (b) c ack will p opaga e in he di ec ion whe e he angen ial s ess σθθ is maximal, see
E dogan and Sih (1963). The GMTS s abili y c i e ion employs he a e age s ess σθθ(𝜃𝜃) calcula ed ac oss a dis ance
d ahead o he c ack ip. The dis ance d is usually chosen in dependence on he mechanism o a up u e (dimension
o a plas ic zone o me als, dimension o p ocess zone o quasi-b i le ma e ials, ma e ial g ain size, o ini e supposed
c ack ini ia ion/p opaga ion inc emen ). The a e age s ess σθθ(𝜃𝜃) ahead o he c ack ip is gi en by he ollowing
equa ion.
𝜎𝜎𝜃𝜃𝜃𝜃 =1
𝑑𝑑∫𝜎𝜎𝜃𝜃𝜃𝜃(𝑟𝑟,𝜃𝜃)𝑑𝑑𝑟𝑟
𝑑𝑑
0 (2)
The c ack p opaga ion di ec ion is supposed in he di ec ion o maximum o he a e age angen ial s ess esul ing
om nume ical analysis. The c i ical alue o angen ial s ess σθθ(𝜃𝜃) co esponding o he c ack ini ia ion is
de e mined om he knowledge o c ack p opaga ion condi ions o a c ack in homogeneous ma e ial unde mode I,
whe e ac u e oughness KIc is employed:
𝜎𝜎𝜃𝜃𝜃𝜃,𝑐𝑐 =2𝐾𝐾𝐼𝐼𝐼𝐼
√2𝜋𝜋𝑑𝑑 (3)
4 Au ho name / S uc u al In eg i y P ocedia 00 (2019) 000–000
The c ack p opaga es when he mean alue o angen ial s ess
σθθ(𝜃𝜃0)
exceeds i s c i ical alue
𝜎𝜎𝜃𝜃𝜃𝜃,c
.
𝜎𝜎𝜃𝜃𝜃𝜃(𝜃𝜃0)≥ 𝜎𝜎𝜃𝜃𝜃𝜃,𝑐𝑐 (4)
In he case o bi-ma e ial combina ions, he c ack p opaga es in o di ec ion θ0 and ma e ial m co esponding
o he lowes alue o c i ical applied o ce Fc i ,m. The c i ical applied o ce Fc i ,m depends on ac u e oughness
o pa icula ma e ial KIc,m and on he a io o he c i ical alue 𝜎𝜎𝜃𝜃𝜃𝜃,𝑐𝑐 and he a e age angen ial s ess co esponding
o he applied o ce Fappl.
𝐹𝐹c i ,𝑚𝑚 = 𝐹𝐹appl 𝜎𝜎
𝜃𝜃𝜃𝜃,c(𝐾𝐾Ic,𝑚𝑚)
𝜎𝜎𝜃𝜃𝜃𝜃(𝜃𝜃0,𝑚𝑚) (5)
3. Nume ical s udy
3.1. Nume ical model
A simpli ied 2D model o he specimen was c ea ed in Ansys Inc. so wa e (2021). The dimensions o he specimen
a e in Fig. 1. The specimen con ains a s eel inclusion wi h dimensions 8×8×40 mm placed in he middle o he span.
The specimens include an ini ial no ch wi h a dep h o 12 mm.
Fig. 1. Designed specimen geome y (dimensions in mm).
Ma e ials we e modelled as linea , elas ic, and iso opic and hey we e ep esen ed by he elas ic cons an s,
i.e. Young’s modulus E, and Poisson’s a io ν. F ac u e p ope ies we e de ined by he ac u e oughness KIc (Table 1).
Table 1. O e iew o he ma e ial’s pa ame e s used in he nume ical model.
Ma e ial
E
[GPa]
ν
[–]
K
Ic
[MPa∙m1/2]
Ma ix (MTX) – ine-g ained cemen -based composi e
39.3
0.20
0.58
ITZ
14.7
0.20
0.7K
Ic, MTX
Inclusion – s eel S235
210
0.30
i ele an
Young’s modulus o elas ici y o he ITZ EITZ was es ima ed acco ding o app oaches in Zacha da e al. (2018).
F ac u e oughness o he ITZ was chosen as 0.7KIc, MTX.
The c ack was modelled as ideally sha p. Because o high s ess g adien s su ounding c ack ips and edges, highly
e ined meshes we e equi ed nea he c ack ip, bo om, le and uppe co ne o s eel inclusion, see Fig. 2.
In he ollowing s udy o c ack p opaga ion, he esul ing c i ical o ces will be compa ed o a e e ence specimen.
The e e ence specimen has he same geome y bu is made o homogeneous ma e ial wi h he p ope ies o ma ix.
In he g aphs o esul s, he c i ical o ces co esponding o he specimens wi h s eel inclusion a e labeled as STE,
while Fc i o he e e ence specimens a e labeled as REF.
1004 Michal Vyhlídal e al. / P ocedia S uc u al In eg i y 42 (2022) 1000–1007
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Fig. 2. Radial mesh a ound – c ack ip (le ); le co ne o s eel inclusion (middle); op co ne o s eel inclusion ( igh ).
3.2. C ack ini ia ion om he no ch
Dis ance d was conside ed as he leng h be ween he c ack ip and bo om co ne o he inclusion, which a e bo h
po en ial s ess concen a o s. Acco ding o he heo ies o ini e ac u e mechanics, see Taylo e al. (2005),
Co ne i e al. (2006), Taylo (2017), we suppose, ha his dis ance d co esponds o cu en c ack inc emen o inal
leng h. We suppose ha he b idge be ween he ini ial c ack (edge no ch) and he inclusion b eaks a once. The s ess
concen a ion ahead o he c ack ip and he inclusion is shown in Fig. 3.
Fig. 3. Isosu aces o he i s p incipal s ess o he specimen wi h he s eel inclusion (le ) and he homogeneous e e ence specimen ( igh ).
Va ious no ch dep hs would lead o di e en s ess dis ibu ions as shown in Vyhlídal and Klusák (2019), whe e i
was ound ha he diamond blade o he saw can damage he specimen mo e han expec ed. He e in he s udy
o he no ch wi h he dep h 12 mm, he c i ical applied o ce was de e mined as c ack p opaga ion in he ma ix:
Fc i (STE) = 1.36 kN. Simila ly, he c i ical o ces we e calcula ed o he e e ence specimens: Fc i (REF) = 1.14 kN.
3.3. C ack p opaga ion om he bo om co ne o he inclusion
In his s age, we analyzed he c ack p opaga ion in he bo om co ne o he inclusion. The dis ibu ion o he i s
p incipal s ess can be seen in Fig. 4 (le ), while a g aph desc ibing he de elopmen o he c i ical o ce Fc i
in dependence on he dis ance d is shown in Fig. 4 ( igh ). I should be no ed ha he c i ical o ce Fc i was de e mined
o he c ack p opaga ion along he in e ace, whose ac u e oughness was equal o 70 % o he ac u e oughness
o he ma ix in he nume ical model. The c i ical o ces o e e ence specimen a e also shown in Fig. 4 ( igh ).
Al hough he c ack p opaga ion along he in e ace is no na u al, in con as o he e ical c ack p opaga ion
in he case o e e ence specimens, he Fc i (STE) eaches lowe alues in compa ison o he Fc i (REF). I is caused
by he lowe ac u e oughness o he in e ace KIc, ITZ compa ed o he KIc, MTX.

Michal Vyhlídal e al. / P ocedia S uc u al In eg i y 42 (2022) 1000–1007 1005
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Fig. 2. Radial mesh a ound – c ack ip (le ); le co ne o s eel inclusion (middle); op co ne o s eel inclusion ( igh ).
3.2. C ack ini ia ion om he no ch
Dis ance d was conside ed as he leng h be ween he c ack ip and bo om co ne o he inclusion, which a e bo h
po en ial s ess concen a o s. Acco ding o he heo ies o ini e ac u e mechanics, see Taylo e al. (2005),
Co ne i e al. (2006), Taylo (2017), we suppose, ha his dis ance d co esponds o cu en c ack inc emen o inal
leng h. We suppose ha he b idge be ween he ini ial c ack (edge no ch) and he inclusion b eaks a once. The s ess
concen a ion ahead o he c ack ip and he inclusion is shown in Fig. 3.
Fig. 3. Isosu aces o he i s p incipal s ess o he specimen wi h he s eel inclusion (le ) and he homogeneous e e ence specimen ( igh ).
Va ious no ch dep hs would lead o di e en s ess dis ibu ions as shown in Vyhlídal and Klusák (2019), whe e i
was ound ha he diamond blade o he saw can damage he specimen mo e han expec ed. He e in he s udy
o he no ch wi h he dep h 12 mm, he c i ical applied o ce was de e mined as c ack p opaga ion in he ma ix:
Fc i (STE) = 1.36 kN. Simila ly, he c i ical o ces we e calcula ed o he e e ence specimens: Fc i (REF) = 1.14 kN.
3.3. C ack p opaga ion om he bo om co ne o he inclusion
In his s age, we analyzed he c ack p opaga ion in he bo om co ne o he inclusion. The dis ibu ion o he i s
p incipal s ess can be seen in Fig. 4 (le ), while a g aph desc ibing he de elopmen o he c i ical o ce Fc i
in dependence on he dis ance d is shown in Fig. 4 ( igh ). I should be no ed ha he c i ical o ce Fc i was de e mined
o he c ack p opaga ion along he in e ace, whose ac u e oughness was equal o 70 % o he ac u e oughness
o he ma ix in he nume ical model. The c i ical o ces o e e ence specimen a e also shown in Fig. 4 ( igh ).
Al hough he c ack p opaga ion along he in e ace is no na u al, in con as o he e ical c ack p opaga ion
in he case o e e ence specimens, he Fc i (STE) eaches lowe alues in compa ison o he Fc i (REF). I is caused
by he lowe ac u e oughness o he in e ace KIc, ITZ compa ed o he KIc, MTX.
6 Au ho name / S uc u al In eg i y P ocedia 00 (2019) 000–000
Fig. 4. Isosu aces o he i s p incipal s ess (le ), and a g aph desc ibing he dependence o he Fc i on he alue o d ( igh ).
3.4. C ack p opaga ion in he le co ne o he inclusion
The dis ibu ion o a e age angen ial s ess 𝜎𝜎𝜃𝜃𝜃𝜃 in dependence on he pola coo dina e

and he dis ance d,
o he c ack wi h i s ip a he le co ne o s eel inclusion can be seen in Fig. 5 ( igh ). The pola coo dina e

be ween
0 ° and 90 ° ep esen s he a ea o he s eel inclusion which means, ha he di ec ion

= 0° is o ien ed in he edge
o he inclusion (c ack ace) and posi i e alues a e coun ed coun e clockwise. The g aph clea ly desc ibes
he maximum 𝜎𝜎𝜃𝜃𝜃𝜃 in he di ec ion abou 135°, which goes o he ma ix (almos e ically). This is also
in he ag eemen wi h he dis ibu ion o he i s p incipal s ess (Fig. 5, le ).
Fig. 5. Isosu aces o he i s p incipal s ess (le ), A e age opening s ess 𝜎𝜎𝜃𝜃𝜃𝜃 ( igh ).
Ne e heless, o de e mine he c ack p opaga ion di ec ion, c i ical applied o ces mus be de e mined sepa a ely
o each ma e ial egion. O cou se, p opaga ion o he s eel inclusion is no possible, and only he ma ix o he ITZ
can be conside ed as po en ial c ack p opaga ion egions. These wo egions a e cha ac e ized by he alues o ac u e
oughness KIc,MTX, and KIc, ITZ. The g aph o Fc i is shown in Fig. 6 in dependence on he ma e ial egions
and on he dis ance d. We can see ha he minimum alue o c i ical o ce is in he ITZ, because we ha e chosen
he ac u e oughness o ITZ as 0.7 × KIc,MTX. I ac u e oughness o ITZ is g ea e , c ack p opaga es e ically
o he ma ix, i i is less han o equal o 0.7  KIc,MTX, c ack p opaga es along he in e ace be ween s eel inclusion
and he ma ix. No e ha also he dis ance d plays a ole in he compe i ion be ween he c ack p opaga ion di ec ion
in o MTX o ITZ.
The compa ison o c i ical o ces o specimen wi h he inclusion and he e e ence specimen is no easy he e,
because he c ack p opaga es in a s aigh line in homogeneous ma e ial. Fo his eason, he alues o Fc i (REF) a e
calcula ed o he c ack ip in he cen e o he specimen. Due o he lowe alues o he ac u e oughness o he ITZ
KIc, ITZ, he Fc i (STE) also eaches lowe alues in compa ison o he Fc i (REF).
1006 Michal Vyhlídal e al. / P ocedia S uc u al In eg i y 42 (2022) 1000–1007
Au ho name / S uc u al In eg i y P ocedia 00 (2019) 000–000 7
Fig. 6. Dis ibu ion o c i ical o ce Fc i in dependence on he pola coo dina e

, and in dependence on he dis ance d (on he le );
minimum alue o c i ical o ce Fc i in dependence on he dis ance d (on he igh ).
3.5. C ack p opaga ion om he op co ne o he inclusion
The g aph in Fig. 7 shows he dis ibu ion o a e age angen ial s ess o he c ack wi h i s ip a he op co ne
o s eel inclusion in dependence on he pola coo dina e and dis ance d. C ack p opaga ion in he almos e ical
di ec ion (abou 215°) is expec ed. Fu he , he c ack will u n in e ical di ec ion. The dependences o c i ical o ces
Fc i on he dis ance d a e shown in Fig. 7 ( igh ) o he specimens bo h wi h and wi hou he inclusion. Simila ly
o he sec ion 3.4, he alues o Fc i (REF) a e calcula ed o he c ack ip in he posi ion which co esponds o he op
co ne o he inclusion. The di e ences be ween Fc i (REF) and Fc i (STE) a e due o he di e en di ec ions o c ack
p opaga ion o bo h specimens (STE and REF) bu a e negligible in his case.
Fig. 7. Dis ibu ion o a e age alues o angen ial s ess 𝜎𝜎𝜃𝜃𝜃𝜃 in dependence on pola angle (po en ial c ack p opaga ion di ec ion), c i ical o ce
Fc i in dependence on he dis ance d, espec i ely.
4. Conclusions
The nume ical s udy in he p e ious pa ag aphs es ima ed po en ial c ack p opaga ion pa hs and he c i ical applied
o ces du ing c ack p opaga ion s ages: c ack ini ia ion in he cen al edge no ch, and p opaga ion in he bo om, le ,
and uppe co ne s o he inclusion. The Fig. 8 shows he e olu ion o he c i ical o ce Fc i in he c ack s ages.
The esul s o c i ical o ces o c ack p opaga ion a ound he inclusion a e compa ed o he c ack p opaga ion
in homogeneous ma e ial ( he e e ence specimen).
Al hough he dependence on he dis ance d is o en discussed, i is appa en , ha i is e y weak. C ack p opaga ion
pa h depends mainly on he ac u e p ope ies o ITZ, see he sec ion 3.4. The compa ison o he specimens
wi h and wi hou he inclusion shows ha he cen al inclusion wo ks as an obs acle o c ack p opaga ion only
in he beginning s age – he c ack ini ia ion in he no ch ip, whe e Fc i (STE) is highe han Fc i (REF).
The mechanical ac u e pa ame e s o he ITZ s ongly in luence he o e all ac u e beha io o es specimens,
as we epo ed in p e ious pape s, see e.g. Vyhlídal e al. (2022), Vyhlídal and Klusák (2020) o Zacha da e al. (2018).
8 Au ho name / S uc u al In eg i y P ocedia 00 (2019) 000–000
Fig. 8. E olu ion o he c i ical applied o ce Fc i o he c ack p opaga ion s ages in dependence on he dis ance d.
Acknowledgemen s
This ou come has been achie ed wi h he inancial suppo o he B no Uni e si y o Technology unde p ojec
No. FAST-J-22-8038. Au ho s a e g a e ul o suppo om he Czech Science Founda ions, p ojec No. 21-08772S.
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Fig. 6. Dis ibu ion o c i ical o ce Fc i in dependence on he pola coo dina e

, and in dependence on he dis ance d (on he le );
minimum alue o c i ical o ce Fc i in dependence on he dis ance d (on he igh ).
3.5. C ack p opaga ion om he op co ne o he inclusion
The g aph in Fig. 7 shows he dis ibu ion o a e age angen ial s ess o he c ack wi h i s ip a he op co ne
o s eel inclusion in dependence on he pola coo dina e and dis ance d. C ack p opaga ion in he almos e ical
di ec ion (abou 215°) is expec ed. Fu he , he c ack will u n in e ical di ec ion. The dependences o c i ical o ces
Fc i on he dis ance d a e shown in Fig. 7 ( igh ) o he specimens bo h wi h and wi hou he inclusion. Simila ly
o he sec ion 3.4, he alues o Fc i (REF) a e calcula ed o he c ack ip in he posi ion which co esponds o he op
co ne o he inclusion. The di e ences be ween Fc i (REF) and Fc i (STE) a e due o he di e en di ec ions o c ack
p opaga ion o bo h specimens (STE and REF) bu a e negligible in his case.
Fig. 7. Dis ibu ion o a e age alues o angen ial s ess 𝜎𝜎𝜃𝜃𝜃𝜃 in dependence on pola angle (po en ial c ack p opaga ion di ec ion), c i ical o ce
Fc i in dependence on he dis ance d, espec i ely.
4. Conclusions
The nume ical s udy in he p e ious pa ag aphs es ima ed po en ial c ack p opaga ion pa hs and he c i ical applied
o ces du ing c ack p opaga ion s ages: c ack ini ia ion in he cen al edge no ch, and p opaga ion in he bo om, le ,
and uppe co ne s o he inclusion. The Fig. 8 shows he e olu ion o he c i ical o ce Fc i in he c ack s ages.
The esul s o c i ical o ces o c ack p opaga ion a ound he inclusion a e compa ed o he c ack p opaga ion
in homogeneous ma e ial ( he e e ence specimen).
Al hough he dependence on he dis ance d is o en discussed, i is appa en , ha i is e y weak. C ack p opaga ion
pa h depends mainly on he ac u e p ope ies o ITZ, see he sec ion 3.4. The compa ison o he specimens
wi h and wi hou he inclusion shows ha he cen al inclusion wo ks as an obs acle o c ack p opaga ion only
in he beginning s age – he c ack ini ia ion in he no ch ip, whe e Fc i (STE) is highe han Fc i (REF).
The mechanical ac u e pa ame e s o he ITZ s ongly in luence he o e all ac u e beha io o es specimens,
as we epo ed in p e ious pape s, see e.g. Vyhlídal e al. (2022), Vyhlídal and Klusák (2020) o Zacha da e al. (2018).
8 Au ho name / S uc u al In eg i y P ocedia 00 (2019) 000–000
Fig. 8. E olu ion o he c i ical applied o ce Fc i o he c ack p opaga ion s ages in dependence on he dis ance d.
Acknowledgemen s
This ou come has been achie ed wi h he inancial suppo o he B no Uni e si y o Technology unde p ojec
No. FAST-J-22-8038. Au ho s a e g a e ul o suppo om he Czech Science Founda ions, p ojec No. 21-08772S.
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