Normas ASTM Tribologia e Microdureza

Carlos V. Opelt, Geraldo M. Cândido and Mirabel C. Rezende

COMPRESSION FAILURE MODES OF CARBON FIBER FABRIC SCRAPS - EPOXY LAMINATES

Technological Institute of Aeronautics

São José dos Campos - Brazil

Federal University of São Paulo

São José dos Campos - Brazil

• Introduction

• Goals

• Failure modes

• Case studies

• Application to design of composites

• Conclusions

SUMMARY

• Introduction

• Goals

• Failure modes

• Case studies


• Conclusions

SUMMARY

• Few decades ago, the fiber reinforced polymer composites were considered the panacea of the materials for structural application.

• Over the years researchers have demonstrated that these materials are strongly affected by manufacturing defects and operation damages.

• The proper use of polymer composites requires the knowledge of their mechanical response under different loadings, as well as their failure mechanisms.

03 INTRODUCTION

• The compression behavior is a limiting in the design of structures made of carbon fiber reinforced polymers.

• The compressive strength of unidirectional carbon fiber/epoxy laminates is often less than 60% of their tensile strength.

• This relatively low compressive strength of polymer composites, compared to its tensile strength, is due to matrix properties governing the compressive failure.

04 INTRODUCTION

• The fiber-reinforced composites subjected to compressive loads can exhibit different failure modes with a different sequence of events to the fracture.

• There is a lack of consensus on the description and classification of the compressive failure modes that makes its assessment unfeasible.

• In some cases different authors end up describing the failure differently, despite the fracture aspects being very similar.

05 INTRODUCTION

• One example of classification is the one by ASTM standards (D3410M-03 e D6641-09).

06 INTRODUCTION

• Introduction

• Goals

• Failure modes

• Case studies


• Conclusions

SUMMARY

• Propose a classification that considers the failure modes already described in the literature and that can easily include new cases being reported.

• To present case studies that demonstrate how to apply this classification.

• Explore how the knowledge of the failure modes can help in the analysis and design of composite structures.

07 GOALS

• Introduction

• Goals

• Failure modes

• Case studies


• Conclusions

SUMMARY

• The proposed classification was based on the failure modes already reported in the literature, trying to cluster the ones with similar characteristics.

08 FAILURE MODES


08 FAILURE MODES

In-plane Shear Through-the-thickness

Shear Wedge Splitting

09 SHEAR FAILURES

In-plane Shear

09 SHEAR FAILURES

Propagation in the width direction

Angled propagation

Through-the-thickness Shear

09 SHEAR FAILURES

Propagation in the thickness direction

Angled propagation

Flexural damages due to the sliding

surfaces

Wedge Splitting

09 SHEAR FAILURES

Two cracks propagating in the thickness direction

Formation of a wedge

Propagation of a large delamination


08 FAILURE MODES

10 INTERLAMINAR FAILURES

Delamination Buckling Splitting


Delamination Buckling

Buckling of the layers

Multiple delaminations

Splaying of the layers


Splitting

Crushing of the layers



08 FAILURE MODES

11 INTERFACIAL FAILURES

Brooming Fiber Crushing


Brooming

Buckling of the fibers

Broom-like fracture

Extensive propagation of the interfacial cracks


Fiber Crushing

Restricted propagation of the interfacial cracks

Fibers are crushed against each other


08 FAILURE MODES

12 KINK-BAND FAILURES

In-plane Kink-band Through-the-thickness

Shear


In-plane Kink-band Propagation in the

width direction

Propagation of an angled band

The interfacial cracks are restricted to the band


Through-the-thickness Shear

Propagation in the thickness direction

Propagation of an angled band

The interfacial cracks are restricted to the band

13 IRREGULAR PROPAGATION

Multiple Failure Modes Mixed Failure Modes


Multiple Failure Modes

Irregular propagation in the width direction

Different failure modes in the two sides of the specimen


Mixed Failure Modes

Irregular propagation in the width direction

Different failure modes in the two sides of the specimen

14 GLOBAL AND LOCAL MODES

Global Failure Mode Local Failure Mode

14 GLOBAL AND LOCAL MODES

Global Failure Mode Local Failure Mode

Fiber Crushing Failure

Wedge Splitting Failure

• Introduction

• Goals

• Failure modes

• Case studies


• Conclusions

SUMMARY

• J.M.F. Paiva; S. Mayer; M.C. Rezende "Evaluation of mechanical properties of four different carbon/epoxy composites used in aeronautical field" Materials Research (2005, vol. 8, p. 91).

• Carbon fibers arranged as a plain weave fabric.

• Prepreg (epoxy matrix) - HexPly® F155, Hexcel Composites

15 FABRIC LAMINATE

16 FABRIC LAMINATE

16 FABRIC LAMINATE

Angled propagation

Shear Failure

16 FABRIC LAMINATE

Debris from the sliding of the fracture surfaces

Shear Failure

17 FABRIC LAMINATE

17 FABRIC LAMINATE

Irregular propagation in the thickness direction

Mixed Failure Mode Shear Failure

+ Delamination Buckling

17 FABRIC LAMINATE

Angled propagation



17 FABRIC LAMINATE




17 FABRIC LAMINATE

Splaying of the layers



18 FABRIC LAMINATE

18 FABRIC LAMINATE

Multiple Failure Modes Shear Failure Mode

+ Mixed Failure Modes

19 FABRIC LAMINATE

Local Failure Mode

19 FABRIC LAMINATE

Kink-band Failure

• C.V. Opelt; C.S.R. Souza; J.M.F. Marlet; G.M. Cândido; M.C. Rezende "Compression Failure Modes of Carbon Fiber Fabric Scraps/Epoxy Laminates" 20th International Conference on Composite Materials.

• Prepreg scraps plain weave fabric (HexPly® F155) were positioned side-by-side with a random orientatiom.

20 FABRIC SCRAPS LAMINATE



Delamination

Wedge

Wedge

Delamination


Flexural damages

Flexural damages










Irregular propagation

Irregular propagation








Delamination

Wedge

Wedge

Delamination


Flexural damages

Flexural damages

• Introduction

• Goals

• Failure modes

• Case studies


• Conclusions

SUMMARY

• The analysis of the compression failure modes is not straightforward and requires some time and effort to be made.

• This kind of information can aid the designers to control the compressive behavior of composite structures.

• The literature presents evidence that for each failure mode a compressive strength distribution can be found.

24 APLICATION TO DESIGN

• The paper of Odom and Adams (1990) shows some interesting findings:

• The through the thickness shear failures are related with the minimum possible compressive strength.

• The maximum possible compressive strength can be expected to be associated with the in plane shear failure.


• Among this two boundaries lay the other possible failure modes.

Narayanan and Schadler (1999)

Lankford (1995)


Compressive strength


Unidirectional composites (ISS)












Fabric composites (ILSS)




Fabric composites (ILSS)




• To improve the performance of composites in compression, the failure modes associated with low compressive strengths should be avoided.

• Tougher and stiffer matrices, would lead to the splitting/fiber crushing failures (depending on the fiber arrangement) or even to in plane shear failures


• Introduction

• Goals

• Failure modes

• Case studies


• Conclusions

SUMMARY

• It was possible to group the compression failure modes accordingly to the properties that govern the fracture phenomenon.

• Two case studies were presented to demonstrate how to apply the proposed classification.

• The compressive strength behavior was found for each failure mode.

29 CONCLUSIONS

Thanks for the attention!

Documents

Normas ASTM Tribologia e Microdureza