Impac Pe o mance o Composi e Sandwich
Shells wi h Co k Co e
L.M. Fe ei a1,2[0000−0002−5223−5309], C.A.C.P. Coelho3[0000−0002−4433−2002],
and P.N.B Reis4[0000−0001−5203−3670]
1G upo de Elas icidad y Resis encia de Ma e iales, Escuela Técnica Supe io de
Ingenie ía, Uni e sidad de Se illa, Camino Descub imien os S/N, 41092 Se illa, Spain
2Escuela Poli écnica Supe io , Uni e sidad de Se illa, C/ Vi gen de Á ica 7, 41011
Se illa, Spain
[email p o ec ed]
3Unidade Depa amen al de Engenha ias, Escola Supe io de Tecnologia de
Ab an es, Ins i u o Poli écnico de Toma , Rua 17 de Agos o de 1808 S/N, 2200-370
Ab an es Po ugal
[email p o ec ed]
4Depa men o Mechanical Enginee ing, Uni e si y o Coimb a, CEMMPRE,
ARISE, 3030-194 Coimb a, Po ugal
[email p o ec ed]
Abs ac . Composi e sandwich s uc u es ha e gained signi ican a -
en ion in enginee ing applica ions due o hei excep ional s eng h- o-
weigh a io, s i ness, and ene gy abso p ion capabili ies. One p omis-
ing co e ma e ial is co k, which possesses desi able cha ac e is ics such
as low densi y, high comp essi e s eng h, and good ene gy abso p ion
capaci y. This s udy aimed o compa e he impac pe o mance o com-
posi e shells wi h composi e sandwich shells ea u ing an agglome a ed
co k co e, while in es iga ing he in luence o semicylind ical shell diam-
e e s. The esul s unde sco e he signi ican impac o specimen diame e
on he pe o mance o hese s uc u es. La ge diame e specimens (106
mm) exhibi ed no ably highe maximum o ce, albei wi h lowe max-
imum displacemen , ene gy abso p ion, and con ac ime compa ed o
hose wi h smalle diame e (82 mm). Simila ends we e obse ed in
composi e sandwich shells. Fu he mo e, he inclusion o co k in com-
posi e sandwich shells ma ginally educed s eng h o he specimens. Fo
iden ical diame e s, bo h con igu a ions exhibi ed compa able maximum
o ce and displacemen . Howe e , composi e sandwich shells wi h a co k
co e abso bed less ene gy han hose wi hou a co k co e. This beha iou
pe sis ed ac oss bo h shell geome ies, wi h sligh ly highe pe cen age
di e ences obse ed in he la ge diame e specimens.
Keywo ds: Composi e sandwich shell ·Low- eloci y impac ·Mechan-
ical es ing.
1 In oduc ion
Composi e sandwich s uc u es ha e gained signi ican a en ion in enginee ing
applica ions due o hei excep ional s eng h- o-weigh a io, s i ness, and en-
e gy abso p ion capabili ies. These s uc u es consis o wo ou e composi e ace
shee s sepa a ed by a ligh weigh co e ma e ial, p o iding enhanced mechanical
p ope ies and s uc u al in eg i y. One p omising co e ma e ial is co k, which
possesses desi able cha ac e is ics such as low densi y, high comp essi e s eng h,
and good ene gy abso p ion capaci y [13, 15, 10].
In ecen yea s, se e al s udies ha e explo ed he impac beha iou o com-
posi e shells [7, 12, 9, 8, 6] and composi e sandwich shells [11, 4]. Speci ically o
composi e sandwich shells, esea che s ha e in es iga ed a ious co e ma e ials,
such as oams, honeycombs, and balsa wood, o enhance he impac esis ance
and ene gy abso p ion capabili ies. Howe e , he u ilisa ion o co k as a co e
ma e ial in composi e sandwich shells o impac applica ions emains ela i ely
unexplo ed, despi e i s p omising p ope ies. This s udy builds upon he exis -
ing s a e o he a by examining he impac pe o mance o composi e sandwich
shells wi h a co k co e wi h di e en diame e s and compa ing he esul s wi h
composi e shells (wi hou a co k co e). The objec i e is o e alua e hei e-
sponse o impac loading, including ac o s such as maximum o ce, maximum
displacemen , ene gy abso p ion, and con ac ime.
The indings o his s udy con ibu e o expand he knowledge on he impac
beha iou o composi e sandwich shells wi h a co k co e, while in es iga ing he
e ec s o a ying hei diame e . This in o ma ion can be used in op imising
he design and ma e ial selec ion o applica ions whe e impac esis ance is
c i ical, such as ae ospace, au omo i e, and ma ine indus ies. Addi ionally, he
s udy p o ides insigh s in o he po en ial ad an ages and limi a ions o using
co k as a co e ma e ial, helping o guide u u e de elopmen and imp o emen
o composi e sandwich s uc u es.
2 Ma e ials and expe imen al p ocedu e
Composi e semicylind ical shells and composi e sandwich semicylind ical shells
wi h an agglome a ed co k co e, we e manu ac u ed wi h wo di e en diame e s
using he hand lay-up me hod. The ma e ials employed o manu ac u e he shells
we e he ollowing: (i) plain wea e T300 ca bon ib e 3k ab ic wi h a mass o
160 g/m2and a densi y o 1.76 g/cm3, supplied by To ay (as ein o cemen );
(ii) epoxy esin SR1500 wi h ha dene SD2503, supplied by Sicomin (as ma ix);
(iii) agglome a ed co k NL 20 CORECORK wi h 2 mm and a densi y o 0.25
g/cm3, supplied by Amo im Co k Composi es (as sandwich co e).
The s acking sequences and he geome ic pa ame e s o he specimens em-
ployed in his s udy a e lis ed in Table 1 and depic ed in Fig. 1. No ice ha all
he composi e laye s we e aligned in he same di ec ion.
Following he assembly o he laye s, hey we e placed inside a acuum bag
o 24 hou s. Subsequen ly, a maximum acuum p essu e o 0.5 ba was applied
o 9 hou s o ensu e a consis en ib e olume ac ion, uni o m hickness, and
emo al o any ai bubbles p esen wi hin he lamina e. In acco dance wi h he
supplie ’s da a-shee , he pos -cu ing p ocess was conduc ed in an o en a 60°C
o 16 hou s.
Table 1. S acking sequence and geome ic pa ame e s o he specimens.
Layup Sequence Label Thickness (mm) Diame e (mm) Leng h (mm)
[0]8C1 2.1 82 100
[0]8C2 2.6 106 100
[04, Co k, 04]C//C1 4.0 82 100
[04, Co k, 04]C//C2 4.3 106 100
Fig. 1. Tes ed specimens: (a) Geome ic pa ame e s o he semicylind ical shells and
impac loca ion; (b) Lay-up sequence o he composi e shell and o he composi e
sandwich shell.
Fig. 2. Schema ic ep esen a ion o he expe imen al se up.
The low- eloci y impac es s we e conduc ed using an IMATEK-IM10 d op
weigh es ing machine. De ailed in o ma ion abou his impac machine can be
ound in [5]. A 10 mm diame e impac o , weighing 2.826 kg, was u ilised, and
he impac was di ec ed a he cen e o he samples. The cu ed edges o he
specimens we e ee, while he s aigh edges we e simply suppo ed (Fig. 2). An
impac ene gy o 5 J was employed, which had been p e iously de e mined o
induce isible damage wi hou causing pe o a ion o he specimens. The impac
es s we e pe o med in acco dance wi h he guidelines ou lined in [2]. All es s
we e conduc ed a oom empe a u e, and a o al o i e specimens we e es ed
o each con igu a ion.
3 Resul s and discussion
To e alua e he impac pe o mance o bo h he composi e shells and he com-
posi e sandwich shells wi h co k co e wi h wo di e en diame e s, an exami-
na ion o he ep esen a i e impac cu es was conduc ed. These impac cu es
encompassed he o ce- ime, o ce-displacemen , and ene gy- ime esul s o he
a ious specimen con igu a ions. In addi ion o he impac cu es, pa ame e s
such as he maximum o ce and displacemen alues, as well as he abso bed
ene gy quan i ies, we e de e mined. These pa ame e s play an impo an ole in
unde s anding and compa ing he pe o mance o he di e en specimen con igu-
a ions. Fu he mo e, he con ac ime, which p o ides insigh s in o he du a ion
o impac and ene gy ans e , was also calcula ed and conside ed in he e alu-
a ion p ocess.
Rep esen a i e esul s ob ained speci ically o he C1 and C2 specimens,
which co espond o he composi e shells wi h diame e s o 82 mm and 106
mm, espec i ely, a e shown in Fig. 3. Fu he mo e, in Fig. 4, he co esponding
impac cu es o he composi e sandwich shells, speci ically he C//C1 and
C//C2 con igu a ions a e p esen ed. I is e iden om he expe imen al da a
ha all esponse cu es exhibi dis inc i e oscilla ions, which a ise due o he
p opaga ion o elas ic wa es esul ing om he ib a ions o he specimens [14].
These oscilla ions a e di ec ly in luenced by he s i ness and mass cha ac e is ics
o bo h he es specimen and he impac o [3].
To acili a e he analysis and compa ison among he a ious specimen con ig-
u a ions, he o ce and ene gy his o ies a e p esen ed in Fig. 5. These g aphical
ep esen a ions p o ide a isual depic ion o he o ce and ene gy a ia ions
h oughou he impac e en , enabling a be e unde s anding o he impac
pe o mance o he conside ed con igu a ions/geome ies. Addi ionally, a sum-
ma y o he mos signi ican esul s ex ac ed om he impac cu es is compiled
in Table 2. I encompasses pa ame e s such as maximum o ce, maximum dis-
placemen , abso bed (dissipa ed) ene gy, and con ac ime.
The expe imen al p ocedu es inco po a ed he u ilisa ion o a high-speed
came a, enabling he eco ding and subsequen isualisa ion o he specimen’s
de o ma ion du ing he impac e en . In Figu e 6, a se ies o sample pho os cap-
u ing he de o ma ion o he specimens a he poin o maximum displacemen
Fig. 3. Rep esen a i e o ce- ime, o ce-displacemen and ene gy- ime cu es o he
C1 and C2 composi e shell specimens.

Fig. 4. Rep esen a i e o ce- ime, o ce-displacemen and ene gy- ime cu es o he
C//C1 and C//C2 composi e sandwich shell specimens.
Table 2. Summa y o he a e aged impac esul s (maximum o ce, maximum dis-
placemen , abso bed ene gy and con ac ime) wi h s anda d de ia ions o he es ed
specimens.
Specimen Max. Fo ce (kN) Max. Displac. (mm) Abs. Ene gy (J) Con ac ime (ms)
C1 1.36±0.08 5.76±0.10 4.74±0.25 12.6±0.12
C2 1.96±0.05 4.20±0.02 3.82±0.38 7.30±0.18
C//C1 1.31±0.22 5.51±0.18 4.38±0.22 9.98±0.34
C//C2 1.76±0.09 4.70±0.05 3.40±0.01 8.47±0.17
Fig. 5. Rep esen a i e o ce- ime, o ce-displacemen and ene gy- ime cu es o all
he es ed specimens.
a e p esen ed. These images p o ide a isual ep esen a ion o he beha iou
exhibi ed by he a ious con igu a ions/geome ies es ed. I is wo h no ing
ha he quali y o he pho os depic ing he C//C1 specimens was a ec ed by
poo ligh ing condi ions du ing he es ing p ocess. As a esul , he cla i y and
isibili y o his pa icula image was comp omised.
Fig. 6. Tes ed specimens a he momen o maximum displacemen .
F om he analysis o he ene gy his o ies in Fig. 5 o all he es ed con ig-
u a ions, i is clea ha he impac o makes con ac wi h he specimens and
subsequen ly ebounds, clea ly indica ing ha he applied impac ene gy was
insu icien o punc u e he specimens. I is no ewo hy ha he ini ia ion o he
pla eau phase signi ies he momen when con ac be ween he impac o and he
specimen is los , indica ing he ene gy abso bed by he specimen [1].
The esul s highligh he signi ican impac o specimen diame e on he pe -
o mance o composi e shells and composi e sandwich shells. Speci ically, la ge
diame e specimens (C2) expe ienced a conside ably highe maximum o ce com-
pa ed o smalle diame e specimens (C1), wi h a di e ence o app oxima ely
44.1%. In con as , C1 exhibi ed highe maximum displacemen (a ound 27.1%),
abso bed mo e ene gy (abou 19.4%), and had a longe con ac ime compa ed
o C2 (app oxima ely 19.8%). A simila end can be obse ed when compa ing
he esul s o composi e sandwich shells wi h di e en diame e s. The pe cen age
di e ences o he conside ed pa ame e s we e no subs an ially a ec ed, excep
o maximum displacemen . Fo example, C//C2 had a 34.9% highe maximum
o ce compa ed o C//C1, while o he maximum displacemen , abso bed ene gy
and impac ime, C//C1 expe ienced highe alues han C//C2, wi h pe cen age
di e ences o app oxima ely 9%, 20.2% and 16% espec i ely.
Fu he mo e, when compa ing composi e shells (C1 and C2) wi h composi e
sandwich shells wi h co k co e (C//C1 and C//C2) o he same diame e , i
becomes e iden ha he inclusion o co k educes esis ance and he amoun
o ene gy abso bed as damage, albei o a minimal ex en . Fo ins ance, C1
and C//C1 exhibi compa able maximum o ce and displacemen alues wi h
pe cen age di e ences o less han 4.5%. Howe e , C//C1 abso bs less ene gy
and has a sho e con ac ime compa ed o C1, wi h pe cen age di e ences
o app oxima ely 7.6% and 21.1%, espec i ely. A simila pa e n is obse ed
when compa ing C2 wi h C//C2. In his case, he pe cen age di e ences o
maximum o ce, displacemen , and abso bed ene gy a e sligh ly highe , wi h
alues o 10.2%, 7.4%, and 11%, espec i ely. Addi ionally, C//C2 has a sligh ly
sho e con ac ime compa ed o C2, wi h a pe cen age di e ence o abou
14.1%.
O e all, hese esul s indica e ha la ge diame e s lead o inc eased s eng h,
while esul ing in dec eased abso bed ene gy, con ac ime and displacemen .
Fu he mo e, he composi e shells composed solely o ca bon ib e exhibi a
highe deg ee o damage and g ea e s eng h compa ed o he composi e sand-
wich shells wi h a co k co e.
4 Conclusions
This s udy compa es he impac pe o mance o wo ypes o s uc u es: com-
posi e shells and composi e sandwich shells inco po a ing an agglome a ed co k
co e. Mo eo e , i aims o in es iga e how a ying semicylind ical shell diame e s
a ec he pe o mance o hese s uc u es. The indings emphasise he signi ican
in luence o specimen diame e on hei beha iou .
Speci ically, when compa ing composi e shells, hose wi h a 106 mm diame-
e displayed highe maximum o ce bu lowe maximum displacemen , ene gy
abso p ion, and con ac ime alues in con as o hei 82 mm diame e coun-
e pa s. A simila pa e n was obse ed in he composi e sandwich shells.
Addi ionally, he in oduc ion o co k in o composi e sandwich shells led o
a ma ginal educ ion in impac s eng h. In cases wi h iden ical geome ies,
bo h con igu a ions exhibi ed simila maximum o ce and displacemen . How-
e e , composi e sandwich shells wi h a co k co e abso bed less ene gy. This end
was consis en ac oss a ious shell geome ies, wi h sligh ly mo e p onounced
pe cen age di e ences obse ed in he la ge diame e specimens.
Acknowledgmen s. This esea ch was sponso ed by na ional unds h ough FCT
— Fundação pa a a Ciência e a Tecnologia, unde he p ojec UIDB/00285/2020 and
LA/P/0112/2020.