Challenges in Composite Materials Research for Lightweight Structures

Ramesh Talreja Tenneco Professor

Department of Aerospace Engineering Department of Materials Science and

Engineering Texas A&M University

Content

• Lightweighting with composite materials

• Current status and roadblocks

• Remedies for way forward

• Challenges and opportunities

• Conclusions

What is lightweighting?

Lightweighting is the engineering process of reducing the weight of products, components, and systems for the purpose of enhancing

(1) performance, (2) operational supportability, and (3) survivability.

It entails

Design, development, and implementation of lightweight materials and technologies.

Engineered Lightweighting with Composites

• Creative fiber architecture (coupled response, multifunctionality)

• Cost-effective manufacturing (effects of defects)

• Physics based failure analysis (beyond “strength” criteria)

• Integrated computational materials engineering (ICME)

Integrated Computational Materials Engineering

Materials information

The “Big Picture” of Cost-effective Composite Design

Traditional design 6

Traditional design process

Defect-Damage Mechanics

• Fiber Defects

Misalignment,

waviness

Breakage

• Matrix Defects

Incomplete curing

Voids

• Interface Defects

Fiber/matrix disbonds

Delamination

• Fiber volume

fraction

• Fiber

Distribution

Length

Orientation

Idealized models:

Heterogeneities,

no defects

Real composites:

Defects

8

Cost-performance trade-off

Voids – RTM process

10

Hamedi-Atlan (2003) E-Glass/Epoxy composite

Fiber Void Matrix

Voids in GFRP [0/45/-45]3s cured with vacuum, no pressure CT-scan

Lambert, et al., CST, 2010

11

Spatial distribution of voids

GFRP [0/45/-45]3s

Lambert, et al., CST, 2010

Voids induced by irregular manufacturing

Voids caused by dissolved moisure In resin (Grunenfelder & Nutt, CST, 2010)

Voids caused by not applying vacuum (Huang, et al., 2011)

13

Voids initiating cracks

Cracks initiating from weak planes Cracks initiating from voids

Delamination from Fiber waviness

Cairns, et al., 2009 15

Defect-damage mechanics Case studies

• Effect of voids on elastic properties (H. Huang, R. Talreja)

• Effect of fiber clusters on crack initiation in short fiber composites (H. Huang, R. Talreja)

• Effect of voids on crack growth in woven fabric composites (M. Ricotta, M. Quaresimin, R. Talreja

• Effect of defects on damage progression in laminates (Y. Huang, P. Carraro, M. Quaresimin, J. Varna, R. Talreja)

Defect-damage mechanics Case studies

• Effect of voids on delamination growth under compression (L. Zhuang, R. Talreja)

• Effects of voids and interfacial disbonds on failure of joints (C. Chen, R. Talreja)

• …..

Failure in Multi-axial Fatigue

Global loading is MULTIAXIAL However, Local failure is in BIAXIAL stress state

Gravity forces

Aerodynamic forces

Combined forces

Laminated composite

Current state of multi-axial fatigue

• Most current approaches are essentially modified “metal fatigue”, lacking THINK COMPOSITES content.

• Schemes, formulas, ad-hoc ideas with poor, uncertain predictive capability.

References: • Fatigue behaviour and life assessment of composite laminates under

multiaxial loadings, M. Quaresimin, L.Susmel, R. Talreja International Journal of Fatigue, 32 (2010) 2–16

• M. Quaresimin, R. Talreja “Fatigue of fiber reinforced composites under multiaxial loading” in Fatigue life prediction of composites and composite structures, A.Vassilopoulos Ed. , 2010 Woodhead Publishing Ltd,, 2010, p. 334-389.

Failure criteria adopted from metals

• Tsai-Hill criterion (metal plasticity)

• Smith-Pascoe crierion (metal crack growth)

• Fewaz-Ellyin criterion (S-N curve based)

Prediction by Tsai-Hill criterion

Nf (cycles) actual

Prediction by Smith-Pascoe criterion

Prediction by Fewaz-Ellyin criterion

10

100

1000

10000

100000

1000000

10000000

10 100 1000 10000 100000 1000000 10000000

Nf,e [Cycles]

Nf [C

ycle

s]

G, R=0.1H, R=0H, R=0.5H, R=-1I, R=0.1K, R=0.1 (W)L, R=0.1L, R=0.3-0.5L, R=-1M, R=0.1

Non-Conservative

Conservative

Roadblocks

• Current failure analyses are empirical, semi-empirical, or phenomenological

• Manufacturing and performance assessment processes are disconnected

• Cost considerations are mostly limited to acquisition cost

Remedies, directions for future research

Remedy #1: Multi-scale approach. Need to go to levels below the homogenized composite. That’s where the action is.

Remedy #2: Constraint analysis. Need to look at lamina (UD composite) failure within the constrained environment of a laminate.

Remedy #3: Defect mechanics. Need to consider defects. They are the initiators of failure.

Way forward: Remedy #1 multi-scale analysis

Tensile stress

Shear stress

2

3

1

fiber

matrix

Investigate the failure process at the fiber/matrix scale under imposed (homogeneous) ply level stresses. Model that failure process in terms of the ply stresses. Competing failure processes occur depending on the local stress state.

Way forward: Remedy #1 multi-scale analysis

5 55

𝜎

Load

ing

dir

ecti

on

Near the 0° ply at the free edge ((y, z)=(W, h))

Central plane of the free edge ((y, z)=(W, 0))

Internal section ((y, z)=(0, 0))

Cracking positions

W

1/8

model

h

(y, z)=(0, 0)

L

Lxx

0°pl

y

90°ply

Resin

x y

z

Macro

Micro

Way forward: Remedy #2: Analyze constrained ply cracking und

Fiber/matrix debonding Single crack formation

Multiple Cracking

Lamina within a laminate

Fiber bundle within a woven fabric composite

PROGRESSIVE FAILURE CAUSED BY CONSTRAINT

Integrated overall strategy (including Remedy #3)

Matrix dominated

failure

Fiber dominated

failure

Damage Threshold Behavior

Effects of Manufacturing Defects

Lamination constraints

Interlaminar failure

Failure criteria

Structural analysis

and design

Looking further out in the future

The Big Picture

Materials Characterization

Stiffness, Strength, Toughness

Life Cycle Cost Analysis Cost/Performance Trade-offs

Performance Evaluation

Durability, Damage Tolerance

Manufacturing

Process Modeling & Simulation

Tooling, Machining, Assembly

The sustainability dimension

The design of materials, processes, products and systems should sustain good conditions for human health

and environment

PLANET

EARTH

Resources

Materials/Energy

Products/

Processes

Reuse/

Recycle

Waste

PLANET

EARTH

Resources

Materials/Energy

Products/

Processes

Reuse/

Recycle

Waste

Conclusions – challenges and opportunities Lightweight engineering with composite materials can

produce high performance, cost-effective structures

Current failure models must be improved by multi-scale

laminate based analyses incorporating manufacturing

defects

Looking further in the future, cost analysis should be

expanded to life-cycle cost

Sustainable composite design will require more advanced

design concepts such as design for disassembly,

reuse/recycling and life cycle assessment.