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