High strain rate characterization of unidirectional carbon-epoxy IM7-8552 in transverse compression

and in-plane shear via digital image correlation

Pedro P. CamanhoDEMec, University of Porto, Portugal

Hannes KörberDEMec, University of Porto, Portugal

Technische Universität München, Lehrstuhl für Carbon Composites, Germany

José XavierUTAD, Vila Real, Portugal

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1. Introduction 2. Longitudinal compression 3. Off-axis compression 4. Analysis model 5. Conclusions

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1. Introduction

Contents

1. Introduction.

2. Longitudinal compression tests.

3. Off-axis compression tests.

4. Analysis model.

5. Conclusions.

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Aircraft dynamic threats

• Crashworthiness.• Bird strike.• Tyre debris impact.• Hard debris impact.• Hail impact.

Bird strike Hail damage

[www.aviation-safety.net]

Longitudinal Compressive Modulus Longitudinal Compressive Strength

No consensus reachedin previous studies; further investigations are required

1. Introduction

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1. Introduction 2. Longitudinal compression 3. Off-axis compression 4. Analysis model 5. Conclusions

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Objectives

• To perform an experimental investigation of strain rate effects on the mechanical response of unidirectional carbon-epoxy composites:• elastic, plastic and strength properties.• uni-axial and multi-axial loading.

• To provide a sound scientific basis for the development of a strain rate dependent constitutive model.

Materials and methods

• Hexcel IM7-8552 CFRP used.• Unidirectional test specimens.• High-strain rate tests performed using a Split-Hopkinson Pressure Bar.• The same specimen configurations and load introduction systems used in-quasi static tests performed in an universal test machine.

1. Introduction

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1. Introduction 2. Longitudinal compression 3. Off-axis compression 4. Analysis model 5. Conclusions

/19(Koerber and Camanho, Composites – Part A, in press, 2011).

SHPB Experiment SimulationIM7-8552 longitudinal compressive stress

2. Longitudinal compression

[0]12 UD laminate; nominal dimensions: 23x7x1.5mm3

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1. Introduction 2. Longitudinal compression 3. Off-axis compression 4. Analysis model 5. Conclusions

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Longitudinal stress-strain diagram

Longitudinal modulus is not rate-dependent.

Longitudinal compressive strength increasesby 40% under dynamic loading.

2. Longitudinal compression

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3.Off-axis compression

Experimental Setup Dynamic test setup

Quasi-static test setup

[θ]32 UD laminate; θ=15˚, 30˚, 45˚, 60˚, 75˚, 90˚; nominal dimensions: 20x10x4mm3

(Koerber and Camanho, Mechanics of Materials, Vol. 42, 1004-1019, 2010).

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3.Off-axis compression

15° off-axis compression (front view) 30° off-axis compression (front view)

45° off-axis compression (side view) 60° off-axis compression (side view)

75° off-axis compression (side view) 90° transverse compression (side view)

High strain rate failure modes

In-plane shear dominated failure modes

Transverse compression dominated failure modes

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3.Off-axis compression

15° off-axis compression 30° off-axis compression 45° off-axis compression

60° off-axis compression 75° off-axis compression 90° transverse compression

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45°

Extrapolation of in-plane shear strength

30° 15°

In-plane shear stress-strain response

3.Off-axis compression

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3.Off-axis compression

Elastic domain, quasi-static.Elastic domain, dynamic.

Failure domain, quasi-static.

Failure domain, dynamic.

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3.Off-axis compression

Transverse compressive modulus Shear modulus

Transverse compressive strength In-plane shear strength

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4. Analysis model

�̇�≈250 𝑠− 1

�̇�=4×10−4 𝑠− 1

Failure criterion:

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1. Introduction 2. Longitudinal compression 3. Off-axis compression 4. Analysis model 5. Conclusions

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Two-parameter plasticity model

4. Analysis model

Plastic potential (plane stress, no plastic deformation in the fiber direction):

Associated flow:

Equivalent stress:

Effective plastic strain increment:

(Sun and Chen, J. Composite Materials, Vol. 23, 1009-1020, 1989).

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Identification of model parameters

4. Analysis model

selected so that all curves collapse into one master curve

master

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1. Introduction 2. Longitudinal compression 3. Off-axis compression 4. Analysis model 5. Conclusions

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4. Analysis model

Model implemented in ABAQUS explicit as a material model using a VUMAT user subroutine.

Forward-Euler integration scheme used for the stress update.

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4. Analysis model

15⁰ 30⁰

45⁰ 60⁰

75⁰ 90⁰

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The proposed modifications to the SHPB test methods enable a reliable measurement of the dynamic modulus and strengths of polymer composites.

The longitudinal compressive modulus of elasticity in not strain rate sensitive up to the strain rates considered in this work.

The longitudinal compressive strength increased 40% under dynamic loading.

Under dynamic loading the transverse compression modulus of elasticty, yield strength and failure strength increased by 12%, 83% and 45% respectively.

Under dynamic loading the in-plane shear modulus of elasticty, yield strength and failure strength increased by 25%, 88% and 42% respectively.

The failure angle and friction coefficients used in the failure criteria are not affected by the strain rate.

The experimental data obtained can be used to identify simple models that simulate the effect of strain rate on the plastic deformation and failure of composite materials.

5. Conclusions

Conclusions

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Tests at strain rates higher than 1000s-1.

Investigate the effect of strain rate on the fracture toughness of composites.

Enhancement of existing plastic-damage model by including strain rate effects.

5. Conclusions

Future work