Post on 11-Jun-2021
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
Prüfen mit Verstand
Instrumented
Impact Testing
testXpo 2018
Helmut Fahrenholz
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
2
Agenda
Why impact testing ?
Typical DWT standards
Impact methods
Energy, speed and mass in DWT
Results evaluation acc. standards
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
3
Why impact testing ?
This is a way of testing football helmets back in 1912
We can offer better
solutions
more reliable
less painful
Picture source: https://rarehistoricalphotos.com/testing-
football-helmets-1912/
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
4
Why impact testing ?
There are many good reasons: for example in Automotive …
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
5
Why impact testing ?
… in the aircraft industry, ….
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
6
Why impact testing ?
… in the building industry, ….
Pipe systems
PMMA roofings
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
7
Why impact testing ?
.. as well as in many situations of our daily life.
Eye protection googles
Safety shoes
Body protection
Safety
screens
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
8
With increasing strain-rate:
Modulus increases
Max stress increases
Yield points disappear
Elongation decreases,
brittleness increases
With lower temperature:
Modulus increases
Max stress increases
Brittleness increases
Why impact testing ?
Polymers are viscoelastic. Therefore their mechanical behavior
changes strongly with the strain-rate applied.
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
9
Why impact testing ?
Zwick covers all relevant strain-rate ranges, from creep to
quasistatic …
Creep (Messphysik) Static - Zwick
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
10
Why impact testing ?
… up to high speed impact test methods.
Pendulum Impact (Zwick, US) Drop Weight (Zwick Taicang) Hydraulic High Speed (Zwick UP)
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
17
Agenda
Why impact testing ?
Typical DWT standards
Impact methods
Energy, speed and mass in DWT
Results evaluation acc. standards
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
Pendulum Impact
18
Zwick’s HIT pendulum impact series - a complete product
range for impact testing
Automation
5 Joule ISO
5.5 / 25 / 50 Joule universal, digital
Charpy Izod
tensile impact Dynstat
Instrumentation
Notch cutting machine
Manual notch cutter
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
Pendulum Impact – Basic principle
19
Instrumented pendulum impact is only standardized for the Charpy
method, but Izod and tensile-impact equipment is available.
Charpy
ISO 179, ASTM D 6110
IZOD
ISO 180, ASTM D 256
Tensile Impact
Here: ISO 8256 method A
Dynstat
DIN 53435
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
Pendulum Impact – Basic principle
20
Charpy is the recommended test method in the ISO standard.
Standards:
ISO 179 Part 1 and 2
ASTM D 6110
Notched or not notched
Evaluate type of break optically
ISO standard: always use the
biggest possible pendulum hammer
only use 10 to 80% of the pendulum
hammer‘s energy capability
impact strength normally is
measured in kJ/m²
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
E – energy
m – mass of the pendulum hammer
h – drop height
g – gravity acceleration (9,81 m/s²)
Pendulum Impact – Conventional method
21
In the conventional method, impact resilience is measured as
single-point data from the angle of raise of the pendulum.
h1
h2
𝐄𝟏 = 𝐦 ∗ 𝐠 ∗ 𝐡𝟏
𝐄𝟐 = 𝐦 ∗ 𝐠 ∗ 𝐡𝟐
𝐄 𝐒𝐩𝐞𝐜𝐢𝐦𝐞𝐧 = 𝐦 ∗ 𝐠 ∗ (𝐡𝟏 − 𝐡𝟐)
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
Instrumented Pendulum Impact Testing
23
Instrumented pendulum impact means force measurement
during impact. This offers supplementary characteristics.
used in R&D, TS and QA Charpy
Izod
tensile impact
Fracture mechanics
co
nve
ntio
na
l ha
mm
er
instr
um
ente
d h
am
mer
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
24
Use of standard load cells
Test setup remains unchanged
compared to standardized
tensile-impact
Same pendulum hammers,
same yokes.
Mass of the grip leads to lower
natural frequencies compared to
Charpy and thus limits the range
of application of this method.
Instrumented Pendulum Impact Testing
For tensile-impact, the force is measured at the level of the
grip, which is part of the vice.
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
Instrumented Impact Testing
25
The force-travel diagram provides supplementary materials
data obtained under high deformation rates.
E specimen
E specimen
𝐹
∆𝑠
E – energy
F – force
s – travel
EP = 𝐹 ∗ 𝑠 The conventional method may show
same results for completely different
stress-strain behavior.
Instrumented impact methods allow
to distinguish such situations, while
conventional impact can’t.
Break types can automatically be
detected
Information about fracture
mechanical characteristics can be
obtained.
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
Pendulum Impact - Tests and Curves
26
FI – First impact maximum
No contact between
pendulum hammer and
specimen
FM – maximum force
sM – deflection at
maximum force
Several points in a travel-deflection diagram are characteristic
for instrumented Charpy tests
The specimens natural
frequency has a square-
root function with the
materials tensile modulus
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
Pendulum Impact - Tests and Curves
27
This part of the curve shows the natural
frequency of the measurement system
The curve directly after break shows the resonance frequency of the
measurement system. No measurement beyond this frequency is possible.
Fo
rce
in N
Resonance ≥ 3 x natural frequency
of the specimen
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
Pendulum Impact - Tests and Curves
28
Zwick developed an automatic recognition of test curve types
according to ISO 179 part 2 in collaboration with Borealis.
tough break brittle break spall break
no break partial break
Complete break typesHinge break
Type of break can be
identified by instrumentation
Automatic classification of
the statistics by the type of
break
Safe and reliable test results
are obtained even with many
operators and in night shifts
Problems in test setup and
specimen handling become
visible and thus also
traceable.
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
Pendulum Impact - Tests and Curves
29
Fracture mechanic data can be obtained by using
instrumented impact and a stop-bloc.
Pre-cracked specimen
are submitted to impact
in Charpy configuration
The impact is stopped at
a given deflection
Under condition of stable
crack growth, the crack
can be stopped and its
length measured.
The result are R-curves.
Elastic materials behavior without and including crack propagation
energy
Fma
x
fma
x
f
[mm]
F [N
]
Ael
fgy
Fgy
Apl
RA
Fma
x
fma
x
f
[mm]
F [N
]
Ael
fgy
Fgy
Apl
f [mm]
f1
F [N
]
f2 fi
Apl
AelAel
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
Pendulum Impact - Tests and Curves
30
The resilience (energy) can still be obtained by the conventional
method – or by integration of the force deflection curve.
𝐹
∆𝑠
E specimen = 𝐹 𝑠 𝑑𝑠E specimen = 𝐹 ∗ 𝑠
E – energy
W – work (energy)
F – force
s – specimen deformation
Note:
The travel is obtained by double
integration of the acceleration (a)
which is obtained from the force
signal and the mass of the
pendulum hammer.
E specimen
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
31
Instrumented drop-weight and HTM
Impact characteristics can be obtained by drop-weight testers
or by hydraulic high-speed testing machines (HTM)
Drop weight tester Zwick HIT 230F High-speed Testing Machines (HTM 5020 and HTM 2512)
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
34
Agenda
Why impact testing ?
Typical DWT standards
Impact methods
Energy, speed and mass in DWT
Results evaluation acc. standards
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
35
Instrumented Drop-Weight Testers
The products range from single purpose instruments to universal drop
weight testers, covering materials characterization and parts testing.
HIT230F Multiaxial
H= 2600mm
Mass Min= 23.5kg
V1= 4.40m/s
E= 230J
HIT1100F
H= 3270mm
Mass Min= 9.27kg
Mass Max= 29.42kg
V1= 4.4m/s
V2= 14.1m/s @ 9.27kg
E= 1126J
HIT2000F
H= 3870mm
Mass Min= 9.27kg
Mass Max= 29.42kg
V1= 5.42m/s
V2= 19.4m/s @ 9.27kg
E= 2044J
Remark: H=Machine Height, V1= Max Velocity without acc, V2= Max Velocity with acc, E= Max Energy
HIT230F CAI
H= 2600mm
Mass Min= 2.02kg
Mass Max= 10.08kg
V1= 4.40m/s
E= 120J
HIT600F CAI
H= 3150mm
Mass Min= 2.04 kg
Mass Max= 10.03kg
V1= 5m/s
E= 125J
HIT600F Multiaxial
H= 3150mm
Mass Min= 4.43kg
Mass Max = 40.43kg
V1= 5m/s
V2= 8.15m/s @ 4.43kg
E= 647J
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
36
The basic principle is that of a free
falling mass, accelerated only by gravity.
The available energy is determined by
the mass and the drop height only.
Epot = Ekin
m g H = ½ m v²
The impact speed only depends on the
drop height.
v = √ (2gH)
Energy, speed and mass in DWT
The available potential energy is generated by the mass and
the drop height. The height determines the impact speed.
Epot = m g H
H
Ekin = ½m v²
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
37
calculates, that the available
potential energy must be at least
2,8 times the energy needed to
impact the test piece.
This means that at a drop height
of 1 m @ 23kg giving 230 J of
potential Energy, it is possible to
test specimen where the
consumed energy is up to 83 J.
Typical values for 2 mm plastics
are below 50 J.
Energy, speed and mass in DWT
Standards require that the speed drop during impact remains
less than 20% of the initial impact speed
Impacto
r
Specimen
4,4
m/s
> 0
.8 * 4
,4 m
/s
trave
l
speed
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
38
The drop weight tester needs to be
specified by
the impact speed = drop height
the available kinetic energy
The complete working range
including all available masses and
speeds, can be shown in a diagram
ENERGY / Impact SPEED
Energy, speed and mass in DWT
For a given specimen we need a defined minimum kinetic
energy at a fixed speed.
Speed, m/s
Energ
y in J
Both axes are logarithmic !
Min required
Energy
2,2
m/s
4,4
3 m
/s
10
m/s
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
40
Purpose: Multiaxial impact tests
Standards: ISO 6603-2, ASTM D 3763
Puncture test at a speed up to 4,4 m/s
Spherical impactor, diam. 20 mm or 10 mm
Design of clamps as fixed by the standards
Fast and easy operation for pre-cooled
specimen
Instrumented Drop-Weight Testers, HIT230F
The Amsler HIT230F are single purpose drop-weight testers.
Impactor and clamps Brittle and ductile specimen Amsler HIT230F in multiaxial impact configuration
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
43
Multiaxial impact tests to ISO and ASTM standards
at 1 m drop height (4.43 m/s)
Multiaxial impact to automotive specifications at low speed
of 2.2 m/s
Multiaxial impact to automotive specifications at higher
speed of 6.6 m/s
Multiaxial impact for research purposes at up to 8 m/s
Multiaxial impact testing with pre-cooled specimen
Multiaxial impact tests for plastic film, ISO 7765-2
Instrumented Charpy and Izod tests
CAI tests at variable and low impact work including second
impact prevention
Instrumented Drop-Weight Testers, HIT600F
The Amsler HIT600F is a universal drop-weight tester for
materials testing, covering many standards and methods.
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
44
HIT600F in multiaxial impact configuration
The working range covers the whole speed range
from 2.2 m/s to 8.1 m/s with a maximum available
potential energy of more than 600 J.
Instrumented Drop-Weight Testers, HIT600F
The HIT600F provides a large working range covering different
test methods and automotive specifications.
Working range
Working range, CAI
HIT600F in CAI configuration
The work range covers the needed low energy
range from less than 10J@2.2 m/s up to over
125J@5 m/s
Multiaxial impact,
Charpy, Izod
CAI configuration
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
45
Test methods:
Instrumented multiaxial impact tests
Instrument Charpy and Izod tests
Finished parts testing
Important features:
Very rigid guides to allowing for side
loads occurring during the tests
Impact speed of up to 19 m/s
Possible integration of a temperature
chamber
Instrumented Drop-Weight Testers
The Amsler HIT1100F and HIT2000F cover both, materials
testing and testing of components.
Amsler HIT1100F Amsler HIT2000F
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
47
Agenda
Why impact testing ?
Typical DWT standards
DWT versus other impact methods
Energy, speed and mass in DWT
Results evaluation acc. standards
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
48
Results evaluation acc. standards
Polymers designed for impact applications are typically quite
ductile. Examples are PC, PMMA, PP
Fo
rce in k
N
Indentation travel in mm
Ductile PC specimen of 2 mm thickness
tested in multiaxial impact
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
49
Travel is normally measured by
double integration of the load signal.
F = m * a
a = F/m
s = ∫∫ a dt dt
testXpert III integrates the
force/travel diagram to determine
consumed energy to any relevant
point:
Energy up to FM
Energy up to 50% FM
Results evaluation acc. standards
The surface below the stress strain curve represents the
energy being consumed by the specimen.
Fo
rce
Travel
Energy /
Work
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
50
FM – maximum force
lM – deflection at maximum force
EM – Energy at maximum force
½ FM – detection point for overall
deflection
lP – puncture deflection
EP – Energy at puncture deflection
Results evaluation acc. standards
Several characteristic points in the force-travel diagram are
defined as the result of this test.
Fo
rce
, F
Deflection, l
FM
½ FM
lM
lP
Sta
ble
cra
ckin
g
EM EP
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
51
These oscillations mainly result from the
natural frequency of the measurement
system.
FM – maximum force
is by half the amplitude too high
lM – deflection at maximum force
lP – puncture deflection
may strongly scatter
The influence is only little for
EM – Energy at maximum force
EP – Energy at puncture deflection
Results evaluation acc. standards
Oscillations of the signals may have some influence on the
test results, but in many cases they are not possible to avoid.
Fo
rce
, F
Deflection, l
FM
½ FM
lM
lP
EM EP
½ Amplitude
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
52
Results evaluation acc. standards
Brittle materials show low deformation and thus the test time
is often less than 1 millisecond. Sensor oscillations may
become visible and relevant.
Fo
rce
in
kN
Indentation in mm
Brittle PBT GF specimen tested in
multiaxial impact
Instrumented Impact Testing
testXpo 2018
03.08.2018
cb-fz
Instrumented Impact Testing
53
Thank you for your
attention !