Analysis of fracture mechanisms and surface quality in drilling of composite materials
The aim of this work is to clarify the interaction mechanisms between the drilling tool and material. Drilling tests were carried out on glass/polyester and carbon/epoxy composites using different twist drills. The cutting tools and machined surfaces were examined by optical microscopy, scanning mic...
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Інститут проблем міцності ім. Г.С. Писаренко НАН України
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| Zitieren: | Analysis of fracture mechanisms and surface quality in drilling of composite materials / J. Sedlacek, A. Humar // Проблемы прочности. — 2008. — № 1. — С. 48-51. — Бібліогр.: 5 назв. — англ. |
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irk-123456789-484622013-08-19T23:00:53Z Analysis of fracture mechanisms and surface quality in drilling of composite materials Sedlacek, J. Humar, A. Научно-технический раздел The aim of this work is to clarify the interaction mechanisms between the drilling tool and material. Drilling tests were carried out on glass/polyester and carbon/epoxy composites using different twist drills. The cutting tools and machined surfaces were examined by optical microscopy, scanning microscopy and surface profilometry to study composite damage and tool wear. Among the defects caused by drilling, delamination appears to be the most critical and may occurs at both the entrance and exit planes. A prediction model of thrust force for drilling without delamination is proposed. Определены механизмы взаимодействия между сверлом и материалом. Испытания проводили на стеклонаполненном полиэфире и эпоксикарбопласте с использованием различных спиральных сверл. Режущий инструмент и обработанные поверхности изучали с помощью оптической микроскопии, сканирующей микроскопии и поверхностной профилометрии, чтобы выявить повреждение композиционного материала и износ инструмента. Среди дефектов, вызванных сверлением, наиболее серьезным является расслоение как на плоскостях входа, так и выхода. Предложена модель прогнозирования усилия подачи при сверлении без расслоения. 2008 Article Analysis of fracture mechanisms and surface quality in drilling of composite materials / J. Sedlacek, A. Humar // Проблемы прочности. — 2008. — № 1. — С. 48-51. — Бібліогр.: 5 назв. — англ. 0556-171X http://dspace.nbuv.gov.ua/handle/123456789/48462 539.4 en Проблемы прочности 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 Sedlacek, J. Humar, A. Analysis of fracture mechanisms and surface quality in drilling of composite materials Проблемы прочности |
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The aim of this work is to clarify the interaction mechanisms between the drilling tool and material. Drilling tests were carried out on glass/polyester and carbon/epoxy composites using different twist drills. The cutting tools and machined surfaces were examined by optical microscopy, scanning microscopy and surface profilometry to study composite damage and tool wear. Among the defects caused by drilling, delamination appears to be the most critical and may occurs at both the entrance and exit planes. A prediction model of thrust force for drilling without delamination is proposed. |
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Article |
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Sedlacek, J. Humar, A. |
| author_facet |
Sedlacek, J. Humar, A. |
| author_sort |
Sedlacek, J. |
| title |
Analysis of fracture mechanisms and surface quality in drilling of composite materials |
| title_short |
Analysis of fracture mechanisms and surface quality in drilling of composite materials |
| title_full |
Analysis of fracture mechanisms and surface quality in drilling of composite materials |
| title_fullStr |
Analysis of fracture mechanisms and surface quality in drilling of composite materials |
| title_full_unstemmed |
Analysis of fracture mechanisms and surface quality in drilling of composite materials |
| title_sort |
analysis of fracture mechanisms and surface quality in drilling of composite materials |
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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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http://dspace.nbuv.gov.ua/handle/123456789/48462 |
| citation_txt |
Analysis of fracture mechanisms and surface quality in drilling of composite materials / J. Sedlacek, A. Humar // Проблемы прочности. — 2008. — № 1. — С. 48-51. — Бібліогр.: 5 назв. — англ. |
| series |
Проблемы прочности |
| work_keys_str_mv |
AT sedlacekj analysisoffracturemechanismsandsurfacequalityindrillingofcompositematerials AT humara analysisoffracturemechanismsandsurfacequalityindrillingofcompositematerials |
| first_indexed |
2025-07-04T08:58:49Z |
| last_indexed |
2025-07-04T08:58:49Z |
| _version_ |
1836706199914938368 |
| fulltext |
UDC 539.4
A n a ly s i s o f F r a c t u r e M e c h a n is m s a n d S u r fa c e Q u a l i t y in D r i l l in g o f
C o m p o s i t e M a te r ia ls
J . S ed lacek 1,a and A . H u m a r1,b
1 Brno University o f Technology, Faculty of Mechanical Engineering, Institute o f Manufacturing
Technology, Brno, Czech Republic
a ysedla10@fme.vutbr.cz, b humar@fme.vutbr.cz
The aim o f this work is to clarify the interaction mechanisms between the drilling tool and material.
Drilling tests were carried out on glass/polyester and carbon/epoxy composites using different twist
drills. The cutting tools and machined surfaces were examined by optical microscopy, scanning
microscopy and surface profilometry to study composite damage and tool wear. Among the defects
caused by drilling, delamination appears to be the most critical and may occurs at both the entrance
and exit planes. A prediction model o f thrust force fo r drilling without delamination is proposed.
K eyw o rd s : com posite materials, delam ination, surface quality, drilling, tool wear.
In trod uction . M achining o f com posite materials is a rather com plex task ow ing to
its heterogeneity, heat sensitivity, and to the fact that reinforcem ents are extrem ely
abrasive. D rilling is a frequently practiced m achining process in industry ow ing to the
need for com ponent assem bly in m echanical p ieces and structures. On the other hand,
drilling o f lam inate com posite materials is significantly affected by the tendency o f these
materials to delam inate and the fibers to pull from the matrix under the action o f
m achining forces (thrust force and torque).
D elam in ation A n alysis. D elam ination occurs along the fiber direction and develops
in tw o phases: the ch isel edge action phase and the cutting edge action phase. The first
phase begins w hen the thrust force o f the ch isel edge into the exit surface reaches a critical
value and ends w hen the ch isel edge just penetrates the plate. B y exam ining the
photographs o f exit surfaces and finished w orkpieces, it w as found that the chisel edge has
a strong effect on the formation o f delam ination. First a sm all bulge em erges in the
vicin ity o f the drilling axis and then it develops along the fiber direction o f the exit
surface. W hen the bulge grow s to a certain degree, the surface layer splits open, the chisel
edge penetrates and the second (cutting edge action) phase starts. The delam ination
damage initiated in the first phase further develops due to the continuous pushing and
tw isting o f the cutting edge. The ch isel edge cuts the w orkpiece material w ith a large
negative rake angle and generates over 50% o f the thrust force. Thus the chisel edge plays
a key role [ 1].
D elam in ation M od el for P u sh -O u t at E xit. A sim ple m odel for predicting thrust
levels that w ill induce “push-out at exit” or “peel-up at entrance” delam inations has been
proposed [2 -4 ]. The delam inated area is assum ed to be circular, and uncut portion is
m odeled as an isotropic circular plate clam ped on its contour (Fig. 1). D rilling and fiber
directions are show n in Fig. 2 . The equation o f energy balance can by expressed as
fo llow s, using the linear elastic fracture m echanics (assum ing M ode I crack propagation)
GdA = F d X - d U , (1)
w here G is the energy release rate per unit area, dA is the increase in the area o f
delam ination crack, F is the thrust force, X is displacem ent o f the drill, measured from
position at w hich delam ination started, and U is the stored strain energy. N ote that
© J. SEDLACEK, A. HUMAR, 2008
48 ISSN 0556-171X. npo6n.eubi npounocmu, 2008, № 1
mailto:ysedla10@fme.vutbr.cz
mailto:humar@fme.vutbr.cz
Analysis o f Fracture Mechanisms and Surface Quality
X
Fig. 1 Fig. 2
Fig. 1. Delamination scheme: plate with clamped contour.
Fig. 2. Convention for drilling and fiber directions: arrow indicates the direction o f tool rotation.
dA = n ( a + da )( a + da ) —n a = Tmada, (2 )
w here a is the radius o f delam ination. For a circular plate w ith clam ped ends subjected to
a concentrated load, the stored strain energy U is
U =
8nM X 2
(3)
w here M is flexural rigidity o f plate under drill and is determ ined from thin plate theory
or also called K irchhoff plate theory as fo llow s
M =
E h 3
12(1—v 2 )
(4)
where E is the m odulus o f elasticity and v is the P o isson ’s ratio for isotropic materials.
The displacem ent X in Eqs. (1) and (3) is g iven by
X =
F a 2
16nM :
(5)
using a, F , and M according to [3]. A fter substitution o f above-m entioned equations
into Eq. (1), the energy balance o f system s can be written as
d F 2 a 2 2F ad X d U d F a 2
2G na = F -------------- = F ---------------------------------- = ---------- .
da da da 16rnM da 3 2 n M 16h M
(6 )
H ence, the critical thrust force for crack propagation (as function o f the uncut
thickness h) in case o f the unidirectional orthotropic fiber com posites is expressed as
fo llow s
F a (h ) = n ^ 3 T M G ~ = J G lcE 2 2h
V 3(1—v 21 )
(7)
N ote that E 2 is the m odulus o f elasticity across the fiber direction, v 21 is the minor
P oisson’s ratio, and GIc is the interlaminar critical energy release rate (crack driving
force) in M ode I loading.
2a
ISSN 0556-171X. npoôëeubi npounocmu, 2008, N9 1 49
J. Sedldcek and A. Humdr
Tool W ear and Its E ffect on D elam ination . A m ong the possib le wear m echanism s,
w hich include adhesion, diffusion, oxidation, plastic deform ation and brittle fracture, only
abrasion and som etim es adhesion are o f significance for cutting o f com posites [5]. Glass
fiber-reinforced plastic (GFRP) made by pultrusion, (polyester matrix, 70% glass volum e,
thickness 9.5 m m ) and drills m ade from different cutting materials were used for the wear
tests.
The wear intensity o f h igh-speed steel drills has been very h igh w hen drilling o f
GFRP, as it w as expected. The w idth o f facet at the drill major flank reached value
VB = 1.33 m m (vc = 31.7 m /m in, Fig. 3a) for non-coated drill and a value VB = 1.04 mm
(vc = 35.2 m /m in, Fig. 3b) for coated drill, after about tw o m inutes (102 s) o f work time.
It is o f interest that the wear o f high-speed steel drill is very h igh along all the length o f
the m ain cutting edge, even near o f the centre o f drill, w here the cutting speed is very low.
This fact confirm s the very h igh abrasive effect o f glass fibers in the wear process o f the
cutting tool w hen m achining o f GFRP. The values o f torque have increased approxim ately
2.5 tim es in accordance w ith an increase o f too l wear and the values o f thrust force have
increased alm ost 7 tim es for about tw o m inutes o f tool operation.
a b c
Fig. 3. Tool wear o f non-coated drill, vc = 31.7 m/min (a), coated drill, vc = 35.2 m/min (b), and
coated drill, vc = 56.5 m/min (c).
The wear o f the coated solid carbide drill w as stable at the value o f VB = 0 .12 mm
after the first stage o f grow ing for a relatively short time. It stayed w ithout any remarkable
changes for more than five m inutes (317 s) o f work, in spite o f the fact, that this drill had
operated at a higher cutting speed (vc = 56.5 m /m in, Fig. 3c) in com parison w ith
high-speed steel drills (vc = 3 1 .7 -3 5 .2 m /m in). It could be expected that the solid carbide
drill wear w ill not be increase considerably regardless o f the operation tim e over the next
few minutes. The values o f torque and thrust force especially are grow ing very slow ly due
to the tool wear for the solid carbide drill.
a b c d e
Fig. 4. Dependence o f delamination on tool wear for different: values of facet width at the drill
major flank VB: 0.12 (a), 0.26 (b), 0.39 (c), 0.60 (d), and 0.77 mm (e).
For any too l material type used, it is important to secure sharp cutting edge. W hen a
tool starts to lose its sharpness, it tends to pull and unw ind fibers from the drilled parts
instead o f cutting them. In addition, excessive tool wear causes increase o f thrust force
and consequent delam ination. H ence, the cutting too l m ust be changed before wear
occurs. The dependence o f delam ination on tool wear is show n in Fig. 4 a -e . The
50 ISSN 0556-171X. npo6n.eubi npounocmu, 2008, № 1
Analysis o f Fracture Mechanisms and Surface Quality
unidirectional reinforced carbon/epoxy lam inate, fabricated by hand lay-up technique
from prepreg w as used for test (total thickness 6 m m , thickness o f one layer 0.15 mm).
The holes o f 6 m m in diameter w ere drilled by h igh-speed steel drill (clearance angle
a f = 13°, point angle 2k r = 118°), cutting speed v c = 30.2 m /m in, feed per revolution
f = 0.1 mm.
Su rface Q uality. The typical appearance o f the drilled hole surfaces are show n in
Fig. 5a (along the fibers’ axes) and Fig. 5b (perpendicularly to the fibers axes) for the
GFRP drilling. The hole had been m achined w ith a coated solid carbide drill o f diameter
D = 10 m m at cutting speed v c = 56.5 m /m in and feed per revolution f = 0 .20 mm. The
hole axis is oriented horizontally in both o f these figures. It is evident, that reinforcing
fibers fail b y brittle fracture m echanism under tensile stress (Fig. 5a) and shear stress
(Fig. 5b). C lose-up v iew o f brittle fracture o f glass fiber is show n in Fig. 5c. The bond
betw een fibers and matrix is dam aged and a large amount o f m icro-particles is created
from fibers and matrix. Surface roughness is m axim um w hen the fibers are loaded
com pressively at 45° angle. W ith the convention o f Fig. 2, w here the arrow indicates the
direction o f tool rotation, surface roughness is m axim um at 135 and 315°, and in this
position the torque applied is m axim um . The sam e observation w as reported by other
investigators [2 ].
a b c
Fig. 5. Drilled hole surfaces: along (a) and perpendicularly (b) to the fibers’ axes and close-up view
of brittle fracture o f glass fiber (c).
C onclusions. A n analysis o f delam ination damage caused by thrust force (feed
force) o f tw ist drill at the exit plane has been provided. The critical thrust force for crack
propagation is a function o f uncut thickness h and material properties o f m achined
com posite materials. To avoid delam ination, the thrust force o f drill should not exceed this
value. H ence, the feed rate should be reduced and usage o f a drill w ith short ch isel edge
and sharp cutting edge is recom m ended. The ch isel edge generates over than 50% thrust
force, and w orn drills w ith VB = 1.33 m m can increase thrust force b y 7 tim es, as shown
experiment. The reinforcing fibers are the m ain reason o f tool wear in drilling o f
com posites, particularly in case o f h igh-speed steel drills. The surface roughness o f drilled
holes is m axim um w hen the fibers are loaded com pressively at 45° angle.
1. H. Zhang, W. Chen, D. Chen, and L. Zhang, Key Eng. Mater., 196, 43-52 (2001).
2. S. Abrate, in: P. K. Mallick (Ed.), Composites Engineering Handbook, Ch. 15, Marcel Dekker
Inc. (1997).
3. M. Ozaki, Supervisory Control o f Drilling o f Composite Materials, University of California,
Berkeley.
4. H. Hocheng and C. C. Tsao, J. Mater. Proc. Technol., 140, 335-339 (2003).
5. G. Spur and U. Lachmund, in: S. Jahanmir, M Ramulu, and P. Koshy (Eds.), Machining o f
Ceramics and Composites, Ch. 7, Marcel Dekker Inc. (1999).
Received 28. 06. 2007
ISSN 0556-171X. n poôëeu u npouuocmu, 2008, № 1 51
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