Fracture behaviour of polymeric composites

Fracture behaviour of polymer and polymeric

composites.

Harish.L

AM13D025ME7190 Term paper presentation

16th April, 2014

Harish L (AM13D025) 16thApril, 2014 1 / 39

Outline

1 Introduction

2 Spiral Notch Torsion Test

3 Mixed mode

4 Finite element analysis of epoxy material

5 Testing and analysis of composite materials

6 SNTT testing and fracture surface characterisation

7 FEA of composite materials

8 Suggestions for future work

9 References


Introduction

Contents

1 Introduction


3 Mixed mode






9 References


Introduction

Introduction

Wind turbine blades are usually fabricated from fiber reinforcespolymeric composites.

Spiral Notch Torsion Test (SNTT)

The current standard fracture toughness test are not efficientunder mixed mode loading conditions, especially ModeI+ModeIII

Figure : Schematic diagram of SNTT


Introduction

Introduction






Introduction

Introduction






Introduction

Introduction






Spiral Notch Torsion Test

Contents

1 Introduction


3 Mixed mode






9 References



SNTT

Only shallow surface notch is required for testing brittlematerials thus it significantly reducing specimen size.

Mode1 fracture toughness is obtained when cylindrical specimenhaving pitch angle 45o .

The SNTT test methods has advantages relative to bend-beamtesting, because

The size effect is minimisesNo free surface(normal to the specimen axis) exists in theSNTT specimen geometry under pure torsionMixed mode fracture toughness values can be easily obtained bychanging the pitch angle of the spiral line.



SNTT







SNTT







SNTT Testing

A servo hydraulic axial/torsional testing machine was used toperform SNTT.

Figure : (a) machined epoxy samples and (b) SNTT testing setup



SNTT Testing

A servo hydraulic axial/torsional testing machine was used toperform SNTT.

Figure : (a) machined epoxy samples and (b) SNTT testing setup



Contd.

Samples were either fractured as machined or after cyclingfatigue with a fixed loading rate 4.52Nm/s.

The in situ fracture process of epoxy samples was examinedusing an infrared camera.

After SNTT testing, the fracture surface were examined byoptical microscopy, scannig electron microscopy, and white lightinferometer.



Contd.






Contd.






SNTT Testing and Fractographic charecterisation

All epoxies samples exhibited linear elastic behaviour duringSNTT, it is expected for brittle materials such as epoxies.

Figure : Example loading curves during final fracture tests performed on epoxy samples in this study.

Different materials and different geometry exhibit differentbehaviour during SNTT testing.



SNTT Testing and Fractographic charecterisation

All epoxies samples exhibited linear elastic behaviour duringSNTT, it is expected for brittle materials such as epoxies.

Figure : Example loading curves during final fracture tests performed on epoxy samples in this study.

Different materials and different geometry exhibit differentbehaviour during SNTT testing.



Contd

Figure : IR Images of an epoxy sample during SNTT testing

The primary IR resultsverified that the notchgroove was subjected totensile states underSNTT pure torsionloading.



Mode1 Fracture

Figure : Optical microscope images showing:(a) the crack plane and (b) the fracture surface of aMode1 sample fractured without fatigue pre-crack

Figure : Fracture surface of a mode1 sample fractured after cycling fatigue: (a) an optical microscopyimage and (b) a white light inferometry 3D


Mixed mode

Contents

1 Introduction


3 Mixed mode






9 References


Mixed mode

Mixed mode fracture

This type of failure is difficult to simulate from the conventionalapproaches or testing methods.

But in SNTT it can be easily simulated by varying pitch anglesof spiral notch.

Figure : Samples with out fatigue showing fracture along (a) the 45o spiral plane(GB2-1) and (b) the36o spiral plane GB4-7

Crack deviated from notch root and propagated along 45o spiralplane.


Mixed mode

Mixed mode fracture






Mixed mode

Mixed mode fracture






Mixed mode

Mixed mode fracture

Figure : Fracture surface of mixed mode of samples to fatigue loading (a) and (b) optical image and(c) a white light interferometry 3D


Finite element analysis of epoxy material

Contents

1 Introduction


3 Mixed mode






9 References



Finite element analysis

1/8th of the SNTT sample were used in modeling due rotationalsymmetry in ABAQUS

crack tip area(A1) was meshed with wedge element C3D15. restareas (A2,A3 ) was meshed with C3020R elements.



Finite element analysis

1/8th of the SNTT sample were used in modeling due rotationalsymmetry in ABAQUS

crack tip area(A1) was meshed with wedge element C3D15. restareas (A2,A3 ) was meshed with C3020R elements.



Figure : Displacement countours of epoxy SNTT sample GB3-1 (a) the cylindrical coordinatedefinition (b) radial displacement vector (c) axial displacement vector



Figure : von Mises contour of epoxy SNTT sample GB3-1: (a) the deformed cylinder and (b) vonMises stress contour around the deformed spiral notch tip

The Stress concentration could be observed around spiral notch

The butter fly plastic zone was also captured with in the wedgemesh area.



Figure : von Mises contour of epoxy SNTT sample GB3-1: (a) the deformed cylinder and (b) vonMises stress contour around the deformed spiral notch tip

The Stress concentration could be observed around spiral notch

The butter fly plastic zone was also captured with in the wedgemesh area.


Testing and analysis of composite materials

Contents

1 Introduction


3 Mixed mode






9 References



materials and samples

SNTT samples were obtained from composite plates fabricatedusing the vaccume assisted infusion technique.

Figure : (a) Vacuume assisted infusion process for composite fabrication and (b) a finished compositeplate

The infused plates were cured at 70oC for 8hrs



materials and samples

SNTT samples were obtained from composite plates fabricatedusing the vaccume assisted infusion technique.

Figure : (a) Vacuume assisted infusion process for composite fabrication and (b) a finished compositeplate

The infused plates were cured at 70oC for 8hrs



Depending on the relative orientations between the samples andthe fibers, three types of samples were fabricated

Figure : (a) The schematic showing the orientations of three types of SNTT samples; and picture of(b) typeA,(c)typeB and (d)typeC samples


SNTT testing and fracture surface characterisation

Contents

1 Introduction


3 Mixed mode






9 References



A-type samples

Figure : Infrared images obtained during the testing of an A-type sample (A-13). The images weretaken: (a) at the start of the testing, (b) at the crack initiation, (c) during the crack propagation, and(d) after the complete separation of the sample.

Bright spot was observed along the spiral notch during tesing

Crack propagated along the notch and large amount of surfaceenergy was released.



Loading curve

Figure : Typical loading curve A,B and C-type samples

linear elastic behaviour was observed until failure occured.

All A and C samples were completely separated into halves afterSNTT testing.

Due to fiber strengthening B samples were not separated andshowed consistent resistence.



Figure : Images showing: (a) a failed A-type sample (A-1) and (b) its fracture surface. Note: thelength unit of the ruler is inch.

Figure : SEM images of the fracture surface of a failed A-type sample (A-1) taken at: (a) lowmagnification and (b) high magnification.

Fracture occured along the spiral notch

Crack propagation direction was parallel to the fiber orientation.



The fiber surfaces were very smooth and interfacial debondingoccurs.

River lines were observed in the resin region which were evidenceof crack propagation through the matrix.

Fiber/resin interfacial debond and resin matrix cracking aredominant failure mechanisms



B-Type samples

Figure : IR images showing the loading of a B-type sample (B-12): (a) when a crack initiated and (b)further propagated.

The primary cracks in B type sample could not propagatethrough the center of the sample.

Cracks runnig parallel to the sample axis.



Figure : Pictures of a failed B-type sample (B-2) showing: (a) the front view, (b) the back view, and(c) the cross-section view. Note: the length unit of the ruler is inch.

Multiple delaminations occured internally and interfacial regionsseemed to be the most vulnerable in this sample geometry.



C-Type samples

Figure : IR images showing the loading of a C-type sample (C-10): (a) when a crack initiated and (b)further propagated.

Figure : Pictures of a failed C-type sample (C-2) showing: (a) the separated two halves and (b) thecurved fracture surface. Note: the length unit of the ruler is inch.

curvature was observed on the fracture surface but in A typesample are flat.



Effect of loading rates

Figure : Failure loads of composite SNTT samples

There is no significant difference in failure torques among thesame type of samples tested with range of loading rates.


FEA of composite materials

Contents

1 Introduction


3 Mixed mode






9 References



Figure : Composite materials in SNTT model with different fiber orientations: (a) a schematic ofcomposite fiber orientations, (b) A-type sample, (c) B-type sample, and (d) C-type sample.

Concentrated torque was applied in one side and x,y translationson the other end were fixed.

Displacement contours of all composite samples are similar tothose obtained from epoxy samples.



von Mises stress contours

Figure : von Mises stress contour of A, B and C-type samples with a scale deformed factor of 20: (a)sample A6, (b) sample B4, (c) sample C6, (d) sample A6 crack tip, (e) sample B4 crack tip, and (f)sample C6 crack tip (unit: Pa).



Figure : Energy replease rate of composite SNTT samples.

Time dependent effect was not significant in energy release rateof composite SNTT samples.


Suggestions for future work

Contents

1 Introduction


3 Mixed mode






9 References




Extend the SNTT Method to investigate the fracture behaviourfor the brittle materials and composite plys


References

Contents

1 Introduction


3 Mixed mode






9 References


References

References

1 Araki W, Nemoto K, Adachi T, Yamaji A. Fracture toughness for

mixed Mode of epoxy resin. Acta Mater 2005;53:86975.2 Selby K, Miller LE. Fracture toughness and mechanical behaviour of

an epoxy resin. J Mater Sci 1975;10:1224.3 Plangsangmas L, Mecholsky JJ, Brennan AB. Determination of

fracture toughness of epoxy using fractography. J Appl Polym Sci

1999;72:25768.4 Wang JA, Liu KC, McCabe DE, David SA. Using torsional bar testing

to determine fracture toughness. Engng Mater Struct 2000;23:4556.5 Ting Tan , Fei Ren , John JyAn Wang , Edgar Lara Curzio ,

Pancasatya Agastra, John Mandell, Williams D. Bertelsen , Carl M.

LaFrance Investigating fracture behavior of polymer and polymeric

composite materials using spiral notch torsion test,Volume

101,March 2013, Pages 109-128.


Thank You


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Fracture behaviour of polymeric composites