High strain rate characterization of unidirectional
carbon-epoxy IM7-8552 in transverse compression
and in-plane shear via digital image correlation
Pedro P. Camanho
DEMec, University of Porto, Portugal
Hannes Körber
DEMec, University of Porto, Portugal
Technische Universität München, Lehrstuhl für Carbon Composites, Germany
José Xavier
UTAD, Vila Real, Portugal
1.1.Introduction
Introduction 2. Longitudinal compression 3. Off-axis compression 4. Analysis model 5. Conclusions
Contents
1. Introduction.
2. Longitudinal compression tests.
3. Off-axis compression tests.
4. Analysis model.
5. Conclusions.
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1.1.Introduction
Introduction 2. Longitudinal compression 3. Off-axis compression 4. Analysis model 5. Conclusions
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 reached
in previous studies; further
investigations are required
3 /19
1.1.Introduction
Introduction 2. Longitudinal compression 3. Off-axis compression 4. Analysis model 5. Conclusions
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.
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1. Introduction 2. Longitudinal compression 3. Off-axis compression 4. Analysis model 5. Conclusions
SHPB Experiment Simulation
IM7-8552 longitudinal compressive stress
[0]12 UD laminate; nominal dimensions: 23x7x1.5mm3
(Koerber and Camanho, Composites – Part A, in press, 2011).
5 /19
1. Introduction 2.
2. Longitudinal
Longitudinal compression
compression 3. Off-axis compression 4. Analysis model 5. Conclusions
Longitudinal stress-strain diagram
Longitudinal modulus is not rate-dependent.
Longitudinal compressive strength increases
by 40% under dynamic loading.
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3.Off-axis
1. Introduction 2. Longitudinal compression 3.
Off-axiscompression
compression 4. Analysis model 5. Conclusions
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).
7 /19
3.Off-axis
1. Introduction 2. Longitudinal compression 3.
Off-axiscompression
compression 4. Analysis model 5. Conclusions
High strain rate failure modes
In-plane shear dominated
failure modes
15° off-axis compression (front view)
30° off-axis compression (front view)
Transverse compression
dominated failure modes
45° off-axis compression (side view)
60° off-axis compression (side view)
75° off-axis compression (side view)
90° transverse compression (side view)
8 /19
3.Off-axis
1. Introduction 2. Longitudinal compression 3.
Off-axiscompression
compression 4. Analysis model 5. Conclusions
15° off-axis compression
30° off-axis compression
45° off-axis compression
60° off-axis compression
75° off-axis compression
90° transverse compression
9 /19
3.Off-axis
1. Introduction 2. Longitudinal compression 3.
Off-axiscompression
compression 4. Analysis model 5. Conclusions
45°
In-plane shear stress-strain response
Extrapolation of in-plane shear strength
30°
15°
10 /19
3.Off-axis
1. Introduction 2. Longitudinal compression 3.
Off-axiscompression
compression 4. Analysis model 5. Conclusions
Failure domain, dynamic.
Failure domain, quasi-static.
Elastic domain, dynamic.
Elastic domain, quasi-static.
11 /19
3.Off-axis
1. Introduction 2. Longitudinal compression 3.
Off-axiscompression
compression 4. Analysis model 5. Conclusions
Transverse compressive modulus
Transverse compressive strength
Shear modulus
In-plane shear strength
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4. Analysis
Analysis model
model 5. Conclusions
1. Introduction 2. Longitudinal compression 3. Off-axis compression 4.
Failure criterion:
𝜀 ≈ 250 𝑠 −1
𝜀 = 4 × 10−4 𝑠 −1
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4. Analysis
Analysis model
model 5. Conclusions
1. Introduction 2. Longitudinal compression 3. Off-axis compression 4.
Two-parameter plasticity 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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4. Analysis
Analysis model
model 5. Conclusions
1. Introduction 2. Longitudinal compression 3. Off-axis compression 4.
Identification of model parameters
selected so that all curves collapse into one master curve
master
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4. Analysis
Analysis model
model 5. Conclusions
1. Introduction 2. Longitudinal compression 3. Off-axis compression 4.
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
Analysis model
model 5. Conclusions
1. Introduction 2. Longitudinal compression 3. Off-axis compression 4.
15⁰
30⁰
45⁰
60⁰
75⁰
90⁰
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1. Introduction 2. Longitudinal compression 3. Off-axis compression 4. Analysis model 5. Conclusions
Conclusions
 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.
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1. Introduction 2. Longitudinal compression 3. Off-axis compression 4. Analysis model 5. Conclusions
Future work
 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.
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