Acta Polytechnica CTU Proceedings


doi:10.14311/APP.2018.18.0066
Acta Polytechnica CTU Proceedings 18:66–71, 2018 © Czech Technical University in Prague, 2018

available online at http://ojs.cvut.cz/ojs/index.php/app

EXPERIMENTAL INVESTIGATION OF THE FAILURE
BEHAVIOUR OF POLYPROPYLENE COMPOUNDS FOR

INSTRUMENTED PUNCTURE TESTS

Florian Kiehasa, ∗, Anna Kalteisa, Michael Jerabekb, Zoltán Majora

a Institute for Polymer Product Engineering, Altenberger Straße 69, 4040 Linz, Austria
b Borealis Polyolefine GmbH, Sankt-Peter-Straße 25, 4020 Linz, Austria
∗ corresponding author: florian.kiehas@jku.at

Abstract. Instrumented puncture tests according to ISO 6603-2 and ASTM D3763 were executed for
five different Polypropylene compounds (talcum-, glass fibre- and elastomer modified) with specimen
thicknesses ranging from 1 mm to 4 mm. Over 1500 puncture tests were executed at the Impact &
Long-term Behaviour laboratory of the company Borealisr in Linz. This serves as strong foundation
for statistical evaluations of the ductile/brittle transition temperature. For different materials and
ductile/brittle transition determination methods, similar trends have been observed, which were
characterized by introducing shift factors.

Keywords: polypropylene, compound, puncture, mechanical testing, ductile/brittle transition.

1. Introduction
For polymers, the energy absorption capacity strongly
depends on the morphology of the plastic and the
experimental environment. In the case of impact or
puncture tests, temperature and strain rate variations
have a significant influence on the failure behaviour:
Almost all unoriented plastics exhibit brittle behaviour
at low temperatures as well as at high strain rates [1].

Mechanical measurements of different puncture test
standards result in distinct force-deflection curves,
which in turn give different transitions from ductile to
brittle. Furthermore, there is no concise method for
the calculation of an exact transition temperature. It
is assumed to be somewhere in the transition regime,
a temperature range where sudden drops in energy
absorption capacity indicate a change of impact be-
haviour from ductile to brittle. First, a precise method
for the calculation has to be introduced. Then, the
difference of the transition as a function of specimen
thickness, temperature, test standard and other pa-
rameters can be determined.

2. Experimental Investigation
2.1. Test Parameters
The test setup and parameters of ISO 6603-2 and
ASTM D3763 vary greatly. The main difference is the
striker- and support ring geometry. For this refer-
ence analysis, tests for both standards were executed
clamped, lubricated and at a speed of 4400 mm/s to
allow for comparison. Therefore, the ASTM D3763
was slightly modified. A summary of all parameters
can be looked up in Table 1 and Figure 1 shows the
different geometries of each test standard. A more de-
tailed description of each test standard can be looked
up in literature [2, 3].

ISO modified* ASTM

Specimen dimensions 60×60 mm ∅102 mm
Specimen thickness 1,2,3 mm 1,2,3,4 mm*
Striker diameter 20.0 mm 12.7 mm
Support ring diameter 40.0 mm 76.0 mm
Test speed 4400 mm/s 4400 mm/s*
Clamped yes yes
Lubricated yes yes*

Table 1. Selected test conditions and parameters.

Figure 1. Striker and support ring geometries ISO
(left) and ASTM (right).

2.2. Materials and test schedule
An extensive test program with a total number
of 1586 specimens was carried out. The work-
load was divided between two machines: a servohy-
draulic ROELL/AMSLER High Speed and a gravi-
tative (spring driven) CEAST Fractovis Plus. The
comparability of measurement data obtained by both
machines is documented by [4].
Five different polypropylene grades developed and

produced by the company Borealisr were selected for
this analysis. Three materials are in-reactor made het-
erophasic copolymers, which are different in rubber-
and matrix design (elastomer modified polypropylene
M1 to M3). M5 is also an in-reactor made heteropha-
sic copolymer filled with talc. M4 is a glass filled
polypropylene.

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vol. 18/2018 Investigation of PP-compounds for Instrumented Puncture Tests

Four specimen thicknesses from 1 mm to 4 mm were
tested with the exception of 4 mm ISO 6603-2 speci-
mens, for which no injection moulding tool was avail-
able for manufacturing. 1 mm thick glass-fibre rein-
forced ISO plaques were also not available. Examined
conditioning temperatures range from -70 ◦C to 23 ◦C.
Eight temperature levels with five repetitions respec-
tively were executed for each material, test standard
and specimen thickness. In certain cases, additional
measurements with three repetitions were carried out
in the transition regime. Altogether, there are 34 test
series with descriptions following Table 2:

Polypropylene compound Test standard Thickness
M1(Elastomer modified PP) ISO(ISO 6603-2) t1(1mm)

M2(Elastomer modified PP) ASTM(ASTMD3763) t2(2mm)

M3(Elastomer modified PP) t3(3mm)

M4(Glass fibre reinforced PP) t4(4mm)

M5(Talcum reinforced PP)

Table 2. Nomenclature of test series.

For example, M4ASTMt3 represents a test series of
material M4 with 3 mm thick specimens tested under
the modified ASTM D3763 standard conditions.

2.3. Data evaluation
For both test standards, the failure criterion is 50 %
force drop after peak load Fm. The corresponding
puncture energy Ep is obtained by integrating the
force up to the deflection at puncture sp.
The transition from elastic to elastic-plastic mate-

rial behaviour was described with the introduction
of a yield equivalent point (sy/Fy)[5, 6]. The initial
slope klin (corresponding to the relative stiffness [3])
of the curve can be approximated through the specifi-
cation of another characteristic data point (sy0/Fy0),
which is necessary to avoid deviations caused by dis-
continuities at the start of impact. These points are
defined as having the largest orthogonal distance from
the direct connection line between origin (0/0) and
peak load (sm/Fm).

Thus, the energy Em expended up to the maximum
load can be split into an elastic part Eel and a plastic
part Epl. The graphical determination of the starting
and end point of the initial slope, as well as the geo-
metric interpretation of the plastic and elastic energy
contributions are illustrated in Figure 2. Following
characteristic values are examined:

• Maximum force/deflection/energy Fm/sm/Em
• Puncture force/deflection/energy Fp/sp/Ep
• Initial force/deflection Fy0/sy0
• Yield equivalent force/deflection Fy/sy
• Elastic/inelastic energy portions Eel/Epl
• Relative stiffness klin
• Width of plastic plateau ∆sw

klin =
Fy − Fy0
sy − sy0

(1)

Eel =
F 2m

2klin
(2)

Epl = Em − Eel (3)

Figure 2. Evaluation of force-deflection data.

Two characteristic energy ratios have been introduced
to describe the elastic properties as well as the failure
behaviour of force-deflection data: the elastic energy
ratio Rel and the ductility index [7] Rduc are specified
in the following equations:

Rel =
Epl + Eel

Eel
(4)

Rduc =
Ep − Em

Ep
(5)

2.3.1. Curve characterization
The ISO 6603-2 curve type evaluation is a common
method to characterize the force/deflection data ob-
tained by puncture test ecperiments. It provides four
typical types of curve progression that can usually be
observed during data evaluation. In general, these
range from ductile to brittle and focus on information
like yielding, crack initiation and crack propagation
[2]. Obtained data has been divided into these four
categories, which are compiled in Figure 3.

The determination of the ductile/brittle transition
by means of curve type characterization is described
in section 2.4.5.

2.3.2. Optical characterization
The different types of fracture appearance are taken
from a company-internal standard developed by Gen-
eral Motors Corporation. It grades fracture appear-
ances from 1 to 11 and covers almost all kinds of break
that may occur during impact testing. A subdivision
ranging from ductile, to semi-ductile, up to brittle can
be made. Illustrations of the individual fracture types
are depicted in Figure 4.
The optical characterization was utilized to deter-

mine the ductile/brittle transition as well, which is
described in section 2.4.6.

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F. Kiehas, A. Kalteis, M. Jerabek, Z. Major Acta Polytechnica CTU Proceedings

Figure 3. Curve types: YD Yielding with deep draw-
ing (top left), YS Yielding with stable crack (top right),
YU Yielding with unstable crack (bottom left), NY No
yielding (bottom right) [2].

1 2 3 4

5 6 7 8

9 10 11

Figure 4. Fracture appearances: from ductile (1 - 5),
to ductile-fragile (6 - 7), to fragile-ductile (8 - 9), up to
fragile (10 - 11).

2.4. Ductile/brittle transition
temperature

Various methods for the determination of the duc-
tile/brittle transition temperature have been proposed
in literature. For impact tests with steep inclines in
the transition regime, not only the tangent formation
of the upper- and lower shelf impact strengths [8, 9]
but also optical investigations of the fracture appear-
ance was investigated [10]. In [11] the inflection point
of the temperature-dependent course was determined.
Likewise, the penetration energy was proposed for
exploration.

For this reference analysis, six different methods for
the determination of the ductile/brittle transition tem-
perature have been introduced and will be listed in the
following subsections. It should be pointed out, that
values are interpolated between data points. Figure 5
depicts graphic representations for the determination
of each transition temperature.

2.4.1. Puncture energy
The arithmetic mean of the local minimum and maxi-
mum puncture energy Ep is calculated and the transi-
tion is assumed at the corresponding condition tem-

Figure 5. Determination of transition temperatures.

perature T E.

2.4.2. Elastic energy ratio
The peak load energy Em is compared to the elas-
tic energy Eel. It should be pointed out that the
minimum value for this energy ratio is 1 when the
plastic portion disappears. This case corresponds to
absolutely no yielding before peak load with the cor-
responding curve type NY No yielding. Threshold
values of 1.4, 1.2 and 1.0 were examined, with T Rat1.2
giving the most consistent results.

2.4.3. Ductility index
In contrast to the elastic energy ratio Rel, the ductil-
ity index Rduc is only obtained from information of
the force deflection data after peak load. Therefore,
yielding before peak load can not be detected with
this method and is neglected. A ductility index of
0 implies, that the peak load is directly followed by
an unstable crack, and consequently brittle fracture.
Threshold values of 40 %, 30 % and 5 % were examined,
with T Duc30 giving the most consistent results.

2.4.4. Deflection
For completely brittle fractures, all characteristic
events of a puncture test happen in a narrow time
frame. The deflection difference between sm, sp and
stotal (as well as sy when there is no plastic plateau)
becomes very small. T s is the temperature where sm
and sp converge.

2.4.5. Curve characterization
This method for the ductile/brittle transition tem-
perature determination takes advantage of the elabo-
rate ISO6603-2 curve characterization introduced in
section 2.3.1. The curve types usually occur in the
sequence of YD, YS, YU and NY from high to low

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vol. 18/2018 Investigation of PP-compounds for Instrumented Puncture Tests

temperatures. An attempt was made to describe the
ductile/brittle behaviour by looking out for the tran-
sitions from YU Yielding with unstable crack (bottom
left) to NY No yielding. This leads to two specific
temperatures TY U and TN Y , which are triggered at
the first appearance of their respective curve type.

2.4.6. Optical characterization
TGM corresponds to the test temperature, where a
fragile fracture type occurs for the first time.

2.5. Overview transition temperatures
A compilation of all calculated transition tempera-
tures is given in Table 3. With the exception of the
glass fibre reinforced material M4, all materials follow
similar trends between test standards and specimen
thicknesses. Reproducibility, consistency and compa-
rability are the main factors that need to be considered
when evaluating the transition temperatures. At the
same time, the calculations involved should be as
simple as possible.
T Duc30 shows the most inconsistent results because it

is sensitive to noise of the force-deflection data after
crack initiation.

Despite occasional outliers, the ISO characterization
has proven itself to be an adequate representation of
the transition regime with most of the other transition
temperatures lying between the boundary values of
TY U and TN Y . For thin specimens, TN Y and TY U
stretch over a wide temperature range, which gets
more narrow for thicker specimens.
In comparison to all the other categories, the frac-

ture appearance usually gives much higher transition
temperatures TGM , because fractures are classified as
brittle as soon as crack initiation is observed disre-
garding any plasticity that might be present before.

2.6. Transition shift factors
Since the trends of all categories are strikingly sim-
ilar as can be seen in Table 3, the shift factors are
contemplated to be universally applicable for all tran-
sition temperatures. However, the impact behaviour
of glass fibre- and talcum reinforced PP-compounds is
vastly different from the other tested materials. Con-
sequently, only elastomer modified PP-grades (M1,
M2, M3) as well as the most consistent transition
temperatures (T E, T Rat1.2 , T s) are used to determine
the shift factors. For data extrapolation, 1 mm ISO
test series are chosen as initial reference values, since
1 mm test series show the least standard deviations
and ISO is generally more consistent than ASTM.
This procedure is illustrated in Table 4. Finally, these
shift factors are summarized in average values α, β,
γ, δ, � and ζ, which are listed in Table 5.
It should be pointed out, that the transition from

ductile to brittle was not fully covered for the material
M2, even at -70 ◦C, which is the reason why T s values
for M2ISOt2 and M2ISOt3 are assumed to be -70 ◦C.

T E T Rat1.2 T
s T Duc30 TN Y TY U TGM

M1ISOt1 -47 -50 -49 -35 -52 -30 -30
M1ISOt1 -57 -59 -57 -53 -58 -52 -50
M1ISOt3 -56 -56 -58 -55 -60 -56 -56
M1ASTMt1 -40 -29 -30 18 -40 -23 -30
M1ASTMt2 -47 -45 -50 -41 -50 -40 50
M1ASTMt3 -43 -43 -50 -36 -50 -50 -40
M1ASTMt4 -45 -45 -50 -41 -50 -50 -50

M2ISOt1 -50 -55 -50 -40 - 0 -20
M2ISOt2 -63 -66 -70 -56 - -30 -30
M2ISOt3 -64 -65 -70 - - -40 -30
M2ASTMt1 -40 -36 -37 7 - 23 -20
M2ASTMt2 -55 -55 -60 -41 - -40 -20
M2ASTMt3 -52 -50 -60 -43 - -50
M2ASTMt4 -54 - -60 -22 - -30 -30

M3ISOt1 -19 -20 -17 6 -30 -10 -20
M3ISOt2 -28 -29 -30 -8 -40 -10 -30
M3ISOt3 -26 -27 -25 -17 -34 -20 -30
M3ASTMt1 -23 -3 -10 16 -20 23 -10
M3ASTMt2 -26 -14 -19 5 -20 0 -10
M3ASTMt3 -26 -13 -19 7 -20 -10 -10
M3ASTMt4 -24 - -28 -6 -30 -10 -20

M4ISOt2 -18 - - - - - -
M4ISOt3 -7 - - -7 - - -
M4ASTMt1 -17 - -17 -11 - - -
M4ASTMt2 -7 -27 -52 -27 - - -
M4ASTMt3 -6 -14 -5 -1 - - -
M4ASTMt4 5 -59 -22 6 - - -

M5ISOt1 -35 -35 -27 -4 -36 -10 -30
M5ISOt2 -36 -36 -36 -23 -38 -30 -40
M5ISOt3 -39 - -36 -21 -50 -20 -40
M5ASTMt1 -35 -25 -21 11 -30 23 -30
M5ASTMt2 -35 -34 -30 -17 -40 -20 -30
M5ASTMt3 -34 -30 -39 -14 -40 -20 -30
M5ASTMt4 -27 - -39 -12 -40 -20 -20

Table 3. Overview of all transition temperatures
(all values in Celsius); nomenclature e.g. M3ISOt1:
material M3, ISO test standard and 1 mm thick speci-
mens.

T E T Rat1.2 T
s

M1ISOt1 226 = x 223 = x 224 = x
M1ISOt1 216 = x · 0.955 214 = x · 0.959 216 = x · 0.964
M1ISOt3 217 = x · 0.960 217 = x · 0.973 215 = x · 0.959
M1ASTMt1 233 = x · 1.030 244 = x · 1.094 243 = x · 1.084
M1ASTMt2 226 = x · 1.000 228 = x · 1.022 223 = x · 0.995
M1ASTMt3 230 = x · 1.017 230 = x · 1.031 223 = x · 0.995
M1ASTMt4 228 = x · 1.008 228 = x · 1.022 223 = x · 0.995

M2ISOt1 223 = x 218 = x 223 = x
M2ISOt2 210 = x · 0.941 207 = x · 0.949 208 = x · 0.932
M2ISOt3 209 = x · 0.937 207 = x · 0.954 208 = x · 0.932
M2ASTMt1 233 = x · 1.044 237 = x · 1.087 236 = x · 1.058
M2ASTMt2 218 = x · 0.977 218 = x · 1.000 213 = x · 0.955
M2ASTMt3 221 = x · 0.991 223 = x · 1.022 213 = x · 0.955
M2ASTMt4 219 = x · 0.982 213 = x · 0.955

M3ISOt1 254 = x 253 = x 256 = x
M3ISOt2 245 = x · 0.964 244 = x · 0.964 243 = x · 0.949
M3ISOt3 247 = x · 0.972 246 = x · 0.972 248 = x · 0.968
M3ASTMt1 250 = x · 0.984 270 = x · 1.067 263 = x · 1.027
M3ASTMt2 247 = x · 0.972 259 = x · 1.023 254 = x · 0.992
M3ASTMt3 247 = x · 0.972 260 = x · 1.027 254 = x · 0.992
M3ASTMt4 249 = x · 0.980 245 = x · 0.957

Table 4. Determination of individual shift factors
(all values in Kelvin).

avg. std.
α 0.953 0.011 ISO1mm to ISO2mm
β 0.958 0.015 ISO1mm to ISO3mm
γ 1.053 0.035 ISO1mm to ASTM1mm
δ 0.993 0.022 ISO1mm to ASTM2mm
� 1.000 0.026 ISO1mm to ASTM3mm
ζ 1.005 0.038 ISO1mm to ASTM4mm

Table 5. Average Kelvin temperature shift factors α,
β, γ, δ, � and ζ and their standard deviations.

The standard deviation of the shift factors listed
in Table 5 become greater for thicker specimens. The
predictions from 1 mm ISO to thicker ISO series shows
accurate predictions, while extrapolations from ISO
to ASTM generally hold higher deviations.
Figure 6 compares the predictions of the average

shift factors with the results of the measured data.

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F. Kiehas, A. Kalteis, M. Jerabek, Z. Major Acta Polytechnica CTU Proceedings

(a) M1

(b) M2

(c) M3

Figure 6. Shift factor predictions versus reality: The
trend between ISO 1 mm (black) and thicker specimens
(purple) can be predicted (blue) with temperature shift
factors α, β, γ, δ, � and ζ.

3. Conclusions
The experimental investigations show that transition
temperatures for elastomer modified materials hold
similar trends between test standards and specimen
thicknesses. Temperature shift factors can be estab-
lished to allow for the prediction of transition tem-
peratures for elastomer filled PP at different testing
conditions. While the data extrapolation is more con-
sistent for ISO 6603-2 than ASTM D3763, satisfying
values for all tested materials and conditions can be
achieved. This may drastically reduce testing time,
effort and costs and allow for comparison of data
obtained by different test standards.

List of symbols
Fm Peak load [kN]
sm Deflection at peak load [mm]
Em Energy up to peak load [J]
Fp Puncture force [kN]
sp Puncture deflection [mm]
Ep Puncture energy [J]
Fy0 Initial force [kN]
sy0 Initial deflection [mm]
Fy Yield equivalent force [kN]
sy Yield equivalent deflection [mm]
Eel Elastic energy portion [J]
Epl Plastic energy portion [J]
klin Relative stiffness [N/mm]
∆sw Width of plastic plateau [mm]

Rel Elastic energy ratio [–]
Rduc Ductility index [–]
stotal Total deflection [mm]
Y D Yielding with deep drawing
Y S Yielding with stable crack growth
Y U Yielding with unstable crack growth
NY No yielding
T Temperature [◦C]
T E Transition temperature; puncture energy [◦C]
T Rat1.2 Transition temperature; elastic energy ratio [◦C]
T Duc30 Transition temperature; ductility index [◦C]
TGM Transition temperature; optical [◦C]
TN Y Transition temperature; curve type NY [◦C]
TY U Transition temperature; curve type YU [◦C]
α,β,γ,δ,�,ζ Average shift factors [–]

Acknowledgements
This research was supported by Borealis Polyolefine GmbH
(Linz, A.)

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	Acta Polytechnica CTU Proceedings 18:66–71, 2018
	1 Introduction
	2 Experimental Investigation
	2.1 Test Parameters
	2.2 Materials and test schedule
	2.3 Data evaluation
	2.3.1 Curve characterization
	2.3.2 Optical characterization

	2.4 Ductile/brittle transition temperature
	2.4.1 Puncture energy
	2.4.2 Elastic energy ratio
	2.4.3 Ductility index
	2.4.4 Deflection
	2.4.5 Curve characterization
	2.4.6 Optical characterization

	2.5 Overview transition temperatures
	2.6 Transition shift factors

	3 Conclusions
	List of symbols
	Acknowledgements
	References