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3-Point Bending Impact Test of Carbon Fiber Reinforced Thermoplastic Composites
○ Fumiaki Yano (Shimadzu Corporation)
Yuki Kamei (Shimadzu Corporation)
Tsuyoshi Matsuo (The University of Tokyo)
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Background
superior specific strength and specific stiffness
high formability and productivity
Thermoplastic resin
Carbon fiber reinforced plastic (CFRP)
CFRP is used in a few kinds of transportation sectors(e.g. airplane, expensive car...)
Matrix is thermoplastic resin.
but low productivity and high cost
Carbon fiber reinforced thermoplastic (CFRTP)
CFRP
superior mechanical properties
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Background
High performance and high productivity
CFRTP is applied to mass produced automobile.
・Vehicle weight reduction・Improvement of fuel efficiency
Target
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Background
To apply CFRTP to mass produced automobiles
・static property・fatigue property・impact property・temperature property
Requirements
Important material properties
・Safety driving in desert and cold place・Collision safety
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Background
Development process for structural products by CAE
We need experimental data to evaluate the CAE model.
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National project
Car makers
Material makers
Testing machine maker
Project members
Collaborative research was conducted by 35 organizations including 3 material makers and 5 automobile makers.
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Objective
To clarify the influence of test speed and temperature dependence in 3-point bending test of CFRTP using static testing machine and high speed impact testing machine
Objective of this study
Static testing machine AG-Xplus(Shimadzu)
High speed impact testing machine (Shimadzu)
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Specimen
Chopped carbon fiber reinforced thermoplastic composite (CTT,by Toyobo)
Size :50 mm × 120 mm × 4.0 mmCF :TR50 Matrix :PolypropyleneVf :50%
Specimen
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Test equipment
Static testing machine
When a cage-type jig is used, loading is applied to the test piece in the compression direction (bending direction) when the crosshead is moved in the pulling direction, so it can be tested without buckling of the rod.
AG-Xplus (Shimadzu)
Capacity :100 kNTest speed :Temperature :
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Testing machine
High speed impact testing machine (Shimadzu)HITS-PX (Shimadzu)
Test speed : 0.0001 – 20 m/sTemperature : -40 – 150 ℃Capacity : 10 kN
An indenter and supports for 3 point bending test was developed and attached to a puncture impact testing machine with hydraulic control.
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Test equipment
Fixture for 3-point impact test
Specimen
Spring
support
Range of movement of the bar
Rotation around the support
Bar for holding specimen
In order to prevent the specimen from moving due to impact during the test, a mechanism for holding the specimen was provided.
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cv
Test equipment
Hydraulic control
Hydraulic power source
Extensometer
Displacement signal
Force signal
Testing machine is controlled by hydraulic actuation. Using hydraulic actuation, we can perform impact test without decreasing test speed.
Dis
pla
cem
ent
[mm
]
Time [ms]
Test
speed [
m/s
]Test speed
Displacement
Relationship between test speed and time
The test speed is kept almost constant after the test piece contact or after the test piece break.
Contact point
Maximum point
Break point
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Test equipment
Specimen : CTT (50 x 100 x 2 mm)Test speed : 0.023, 0.23, 2.3 m/sSpan : 80 mmIndenter : R 5 mmSupport : R 2 mm
Example of test results
Testing method for flexural properties of carbon fiber reinforced plastics
We set the test condition based on JIS standard.
JIS K7074
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Test equipment
Different in results depending on thickness of specimen
Since CTT randomly arranges tape materials, the variation of test results is large when the size of the specimen is small.
We determined the specimen thickness to be 4 mm. (Twice the standard)
CTT specimen
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Test condition
Test condition
Specimen : CTT Span : 80 mmNumber of test : n = 3Temperature [℃] : -30, 0, 25, 75, 100 [℃]Strain rate [/s] : 0.0002 (5 mm/min) / AG-Xplus
0.01, 0.1, 1, 10 (0.0025~2.5 m/s) / HITS-P10Indenter : R 5 mmSupport : R 2 mm
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Test results
Example of stress strain curves
Strain rate 1 /s Room temperature
・Differences in the curve shape were confirmed by the test temperature.・The flexural strength and inclination of curves change with temperature and
strain rate.
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Temperature dependence and strain dependence were confirmed in flexural strength.
Relationship between Flexural stress and strain rate
Relationship between Flexural stress and temperature
Test results
Flexural strength
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Relationship between elastic modulus and strain rate
Relationship between elastic modulus and temperature
Test results
The temperature dependence was confirmed in the elastic modulus but the strain rate dependence was small (in this strain rate).
Elastic modulus
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Shape of the curve
Difference in stress strain curve
Flexural stress gradually decreases from the maximum stress.
①
②
③
Stress strain curve can be classified into following 3 types.
Flexural stress decreases from the maximum stress, then gradually decrease.
Flexural stress decreases instantaneously from the maximum stress.
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Tendency of curves
Curve tendency at each temperature of CTT
Flexural stress decreases instantaneously from the maximum stress.
(Decrease amount is large.)
Low temperature Around room temperature High temperature
Repeat gradual decrease and instantaneous decrease of flexural stress.
(Decrease amount is small.)
Flexural stress gradually decreases.
A small peak appears.
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Side image of specimen after impact test
Failure in compression side
On the tensile side, there is a layer that is not destroyed.
Failure in the entire thickness range from the compression side to the tension side just under the indenter
Delamination occurs not only directly under the indenter but also in a wide area.
Large delamination with compression failure
Only compressive failureCompressive and tensile failure
Specimen after impact test
Low temperature Around room temperature High temperature
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Observation of fracture behavior
Fracture behavior of CTT10 /s (2.5 m/s) and room temperature
Recording rate:20kfps
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Observation of fracture behavior
Comparison of fracture images and stress strain curve
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■A small peak appears.
⇒The central part of specimen slightly rises.
■Flexural stress decreases instantaneously. (Decrease amount is small.)
⇒delamination on tensile side
■Flexural stress decreases stepwise.
⇒fracture on both compression and tensile
side under the indenter
■ Flexural stress decreases instantaneously.
(Decrease amount is large.)
⇒Large delamination
■Flexural stress gradually decreases.
⇒Specimen is bending.
Observation of fracture behavior
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Failure mode of CTT
Failure mode
Classification of three kinds of failure modes on the figure can be classified mainly by temperature.
Large delamination with compression failure
Only compressive failureCompressive and tensile failure
Failure mode can be classified into the following three from the tendency of curves and specimen after impact testing.
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Conclusion
・ There is temperature dependence and strain rate dependence on flexural strength
・ The flexural modulus has temperature dependence, but the strain rate dependence is small.
・ Fracture mode can be classified into 3 types.
・ The fracture behavior has temperature dependence, but the strain rate dependence is small.
・Three-point bending impact test can be performed at a constant speed by attaching a three-point bending fixture to a hydraulic control puncture testing machine
・By making the thickness twice as large as the existing test standards, it is possible to reduce variations.
Test method
Characteristics of CTT
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Thank you for your kind attention.This presentation is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization(NEDO). In particular, the authors are deeply grateful to Toyobo which offered materials.
Acknowledgement