fatigue in composites

8/2/2019 Fatigue in Composites

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t _ f .

Fatigue in compositesScience and technology of thefatigue response of fibre-reinforced plastics

Edited byBryanH~s

CRC PressBoca Raton Boston New York Washington, DC

WOODHEAD PUBLISHING LIMITEDCambridge England


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Contents

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. X111Acknowledgements xviContributor contact details xviiPart I Introduction to fatigue in composites .1 A historical review o f the fatigue behaviour o f fibre-reinforced plastics ..... ' 3B. Harris, Materials Research Centre, Universityof Bath, UK1.1 Introduction ' 31.2 Fatigue phenomena in fibre composites ' 41.3 Concluding COmments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 301.4 Bibliography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 311.5 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ] 1

2 Fatigue test methods, problems and standards 36G . D. Sims, National Physical Laboratory. London, UK2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 362.2 Fatigue data requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 362.3 Fatigue testing requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 382.4 Fatigue test equipment " 392.5 Artefacts in fatigue testing 422.6 Standardized test methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 522.7 Precision data 562.8 Data presentation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 582.9 Concluding comments ' 592.10 Future trends 6J2.11 Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 612.12 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 62

3 Fatigue under rnultiaxial stress systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 63M.M Shokrieh, Iran University of Science and Technology, Tehran, fran,and L. B. Lessard, McGill University, Montreal, Canada3.1 Introduction 63


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3.2 Fatigue failure criteria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 633.3 Material properties degradation 683.4 Progressive fatigue damage modelling. . . . . . . . . . . . . . . . . . . . . . . . . . .. 783.5 Material characterization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 803.6 Experimental evaluation of [he model. '. 933.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. L083.8 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 109

Part n Micromechanical aspects of fatigue in composites . . . . . . . . . . . . . . . .. 1154 The effects of aggressive environments on long-term behaviour. . . . . . . . .. 117

FR. Jones, University o/Sheffield. UK4.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. J J 74.2 Aqueous environments ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1174.3 Moisture sensitivity of resins 1204.4 Thermal spiking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1234.5 Thermomechanical response of matrix resins. . . . . . . . . . . . . . . . . . . . .. 1234.6 Effect of moisture on composite performance. . . . . . . . . . . . . . . . . . . .. 1264.7 Fibre-dominated properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1294.8 Role of the matrix and interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1354.9 Environmental stress-corrosion cracking (ESCC) of GRP . . . . . . . . . . .. J 374.10 Designing for stress-corrosion resistance ' 1424.11 Non-aqueous environments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1434.12 Conclusions................................................ 1454.13 References 145

5 The effect of the interface on the fatigue performance of fibrecomposites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 147C. Galiotis and C Koimtzoglou. Institute of Chemical Engineering and HighTemperature Processes, Foundation for Research and Technology. Greeceand Materials Department, University of Parras, Greece5 .1 Introduction ' 1475.2 Effect of interface parameters on .fatigue performance. . . . . . . . . . . . . .. 1475.3 Effect of other parameters that indirectly affect the interface on fatigue

performance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. IS S5A Effect of fatigue loading on interface. . . . . . . . . . . . . . . . . . . . . . . . . . .. 1635.5 Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1685.6 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. J 70

6 Delamination fatigue. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 173R. Martin, Materials Engineering Research. Laboratory, UK6.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. J 736.2 The interlarninar fracture mechanics approach for fatigue. . . . . . . . . . .. 1756.3 Characterizing delamination in fatigue ' 1776 0 4 Modelling a delamination. , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1836 .S Using fracture mechanics analysis as a design tool .,............... 1846.6 Structural integrity prediction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. i876.7 References , 187


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Contents VII

7 The fatigue of hybrid composites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 189G. F. Fernando. Cranfield University, UK and FA. A. Al-Khodairi, SaudiBasic Industries Corporation, Saudi Arabia7.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1897.2 Comparison of fatigue data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1957.3 Materials and experimental procedures. . . . . . . . . . . . . . . . . . . . . . . . . .. 1987.4 Results and discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2027.5 Fractography 2337.6 Conclusions 2367.7 Acknowledgements 2377.8 References 238

8 Non-destructive evaluation of damage accumulation. . . . . . . . . . . . . . . . . .. 242A.P. Mouritz, RMIT University, Australia8. t Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2428.2 Acoustic NDE techniques. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2438.3 Acoustic emission. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2548.4 Radiography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2568.5 Thermographic NDE methods 2598.6 Eddy currents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 259

Part III

8.78.88.98 . J O8.11

Moire interferometry ". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 259Summary and concluding remarks 26]Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 262Information sources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 262References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 262

Fatigue in different types of composites . . . . . . . . . . . . . . . . . . . . . . . .. 2679 Short-fibre thermoset composites .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 269

G. Caprino, University of Naples "Federico ll", italy9.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2699.2 Structure and composition of short-fibre thermoset composites. . . . . . .. 2709.3 Static behaviour. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2709.4 Fatigue behaviour. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2789.5 Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 2929.6 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 292

10 Woven-fibre thermoset composites .N. K. Naik, Indian Institute of Technology, Bombay, india10.1 Introduction .

296

10.210.310.410.510.610.7to.810.9

29629829930330430831031031 J

Fatigue performance of laminated composites .Woven-fabric laminated composites .Fatigue testing .Fatigue damage in woven-fabric composites .Fatigue loading: stiffness, strength and life .Recent studies of the fatigue behaviour of WF composites .Future trends .Nomenclature

10.10 References................................................. 311


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11 Fatigue of thermoplastic composites, , , , , .. 314E.K. Gamstedt and L.A. Berglund. KTH, Sweden11.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 3141 1 . 2 ThermopJ astics 316!J.3 Continuous-fibre composites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 321I J.4 Short-fibre composites 33111.5 Future of thermoplastic composites 33411.6 References.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 335

12 Fatigue of wood and wood panel products. . . . . . . . . . . . . . . . . . . . . . . . . . .. 339M.P. Ansell, University of Bath, UK12.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 33912.2 The structure and properties of wood and timber. . . . . . .. . . . . . . . . . .. 33912.3 Fatigue life of wood and panel products. . . . . . . . . . . . . . . . . . . . . . . . .. 34312.4 Dynamic property changes in fatigue of wood and panel products . . . .. 34912.5 Fatigue damage development in wood and panel products 35612.6 Fatigue in timber joints 357\2.7 Fatigue o f n atu ral fibre composites ' 35812.8 Conclusions...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 35812.9 Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 35812.10 References................................................. 359

Part IV Life-prediction methods for constant stress and variable stress. . . . .. 36313 Physical modelling of damage development in structural composite

materials under stress. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 365P.WR. Beaumont, Cambridge University, UK13.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 365132 A framework for understanding damage development. . . . . . . . . . . . . .. 36513.3 A question of design route 36713.4 A question of physical modelling " 36913.5 A question of fatigue " 37213.6 Physical modelling of fatigue damage development. " 37613.7 Physical modelling of fatigue damage development at stress

concentrators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 39613.8 Computer implementation 40813.9 Summary and final remarks ,....................... 40913.10 Acknowledgements ,.41013. t I References................................................. 410

14 Micromechanical models 413K Reifsnider and S. Case, Virginia Tech, USA14.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 41314.2 Damage accum ulation in composite materials ' 41414.3 Changes in stiffness 41614.4 Changes in local material strength 41714.5 Strength: an internal state variable and damage metric '. 41914.6 Strength of a composite material: 'Critical element' concepts " 419


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14.7 Non-uniform stress states: characteristic material dimensions. . . . . . . .. 42114.8 Strength evolution 42114.9 Applications '" , 42614.10 Conclusions 429]4.11 Acknowledgements.......................................... 43014.12 References _ 430

15 A computational meso-damage model for life prediction for laminates. . .. 432P. Ladeve:e and G. Lubineau, LMT Cachan, France15.1 Introduction _. 43215.2 The damage scenarios on the micro structural scale (Fig. 15.1) . . . . . . .. 43215.3 The 3D damage model for laminates according to scenarios 3 and 4 43315.4 The 'micro' modelling oflaminate composite for scenarios I and 2 43415.5 Mesomodel of the laminated composite (Fig. 15.4) . . . . . . . . . . . . . . . .. 43615.6 Comparison with experiments for [0/90,,), 43715.7 Perspectives.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 44015.8 References _ 441

16 A statistical study of the fatigue performance of fibre-reinforcedcomposite laminates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 442X. Diao, PreciCad Inc., Canada. L Ye and Y-W. Mai, University of Sydney,Australia16.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . .. 44216.2 Fatigue and methodology , , , . .. 44316.3 Statistical model .. " .. ,', .. , , , 44716.4 Stress redistribution function , ,...... 44916.5 Evaluation of fatigue performance of composite laminates , . . . . .. 45316.6 Concluding remarks , __. .. 46316.7 Acknowledgements _ , __ . , , _.. , .. , .. ' _ 46816.8 References , __ . , , .. , ,_ 468

17 Analysis of matrix crack-induced delamination in composite laminatesunder static and fatigue loading , , , _.. , .. , _. 470M Kashtalyan, University of Aberdeen and C. Souris, University ofSheffield, UK17.1 Introduction. __ ..... ' ... , ... , . __ . _..... , _, ..... , , . _ , 47017.2 Stiffness properties of cracked laminates with delaminations , "'" 47117.3 Delamination onset and growth prediction, .. _. _, .. , . _. _ , .... , 48617.4 Conclusions, __ , , _, _' , .. _.. _ _' . __ ' . . .. 49617.5 Acknowledgements, , , , , , , , __ . , , . __ .. 49817.6 References __ , .. ' , .. __ , _, , . _. . . .. 49917.7 Appendices __, _.. .. , , , __. , , _. _ . ' .. ,. 500

18 Fatigue strength of composites under variable plane stress ' . . .. 504TP. Philippidis and kP. Yassilopoulos, University of Patras, Greece18.1 Introduction ,............. 50418.2 Life prediction under combined stress: theoretical considerations. . . . .. 50S18.3 Experimental and property evaluation .. __ _ , ' . . .. 509


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18.4 Verification oflife prediction methodology. . . . . . . . . . . . . . . . . . . . . .. 5!618.5 Structural application example: Inboard part of a rotor blade 52018.6 Concluding remarks 521IS.7 References... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 523

19 Life prediction under service loading spectra 526L.J. Lee and K.E. Fu, National Cheng Kung University, Taiwan19.1 introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 52619.2 Stiffness degradation under block-type loading spectrum. . . . . . . . . . .. 52819.3 Statistical distribution of fatigue life. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 53119.4 Experimental program. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 53219.5 Experimental verification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 53319.6 Conclusions.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 54419.7 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 545

20 A parametric constant-life model for prediction of the fatigue livesof fibre-reinforced plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 546B. Harris, University of Bath. UK20.1 Introduction.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 54620.2 The nature of fatigue processes in composites . . . . . . . . . . . . . . . . . . . .. 54620.3 Cracks in composites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 54720.4 Life prediction: the alternatives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 54820.5 A parametric constant-life model for life prediction , .. 55020.6 Conclusions....... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 56520.7 Acknowledgements 56720.8 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 567

21 A neural-network approach to fatigue-life prediction , . . . . . .. 569J.A. Lee and D.P. Almond, University of Bath. UK21.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 56921.221.321.421.521.621.7

2L821.921.102Ul21.1221.I321.1421.1521.1621.17

Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 570Biological neural networks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 570Multi-variate non-linear mappings. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 570Artificial neural network models. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 573The use of artificial neural networks in practice. . . . . . . . . . . . . . . . . . .. 577Application of artificial neural networks to the analysis of fatiguelife data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 579Optimum artificial neural network architecture , . . . . . . . . . . . .. 580Selection of inputs for training the artificial neural network ..... . . . .. 580Constant stress amplitude fatigue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 580New material application. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 581Block-loading data analysis .... ,.............................. 582Suggested procedure for applying neural networks to fatigue life data.. 583Comparison with other methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 585Future trends . , , . . . . . . . . . . . . . . . . . . . . . . . .. 588Acknowledgements 588References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 588


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Contents xi

Part V Fatigue in practical situations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 59l22 The fatigue performance of composite structural components 593

M.D. Gilchrist, University College Dublin, Ireland22.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 59322.2 General approach. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 59322.3 Damage growth and life prediction. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 59522.4 An approach to full-scale testing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 59822.5 Reliability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 59922.6 Applications... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 59922.722.822.922.10

Conclusions .References .Appendix .Nomenclature .

616616619620

23 Fatigue of joints in composite structures 621J. Schon and R. Starikov, Swedish Defence Research Agency, Sweden23.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 62123.2 Composite joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 62123.3 Fatigue in adhesive joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 62523.4 Fatigue in bolted joints ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 63323.5 Outlook.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 63923.6 Summary... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 64023.7 References 641

24 Fatigue in filament-wound structures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 644D. Perreux and F. Thiebaud, Laboratoire de Mecanique Appliquee RC,France24.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 64424.2 Brief overview of literature on pipe behaviour. . . . . . . . . . . . . . . . . . . .. 64524.3 Breadboard fixtures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 64624.4 Fatigue behaviour of bi-directional [+55/-55] glass-fibre/epoxy-matrix

filament-wound pipes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 64824.5 Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 65524.6 References................................................. 655

25 Fatigue of FRP composites in civil engineering applications .J.MC. Cadei, FaberMaunsell Ltd, UK25.1 Introduction .

658658

25.2 Composite material applications in civil engineering. . . . . . . . . . . . . . .. 65825.3 Typical fatigue loadings in civil engineering structures. . . . . . . . . . . . .. 66725.4 Fatigue behaviour of composite structures and components 67125.5 Design and analysis of structures for fatigue .... . . . . . . . . . . . . . . . . .. 67725.6 Case study: FRP road deck fatigue performance (TRL test programme on

ACCS Roadway Panel) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 67925.7 Operational aspects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 68425.8 Concluding remarks 685


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26 Fatigue in aerospace applications 686AJ Davies, QinetiQ, UK and P.T Curtis, osa. UK26.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 686

688692695698

25.9 References........ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 685

26.2 Overview of fatigue performance of aerospace materials .Fatigue life prediction .Damage mechanisms , .Airframe structural elements , , , .

26.326.426.526.626.826.9

Conclusions , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 706Acknowledgements , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 707References , . . . . . . . . . . . . .. 1m

27 Fatigue and durability of marine composites. , " 709P. Davies and D. Choqueuse, JFREMER, Centre de Brest. France and A Roy,CRITT Materiaux, Rochefort, France27.1 Introduction , " 10927.2 Specific nature of the marine environment , " 11127.3 Marine composites , ,............................ 71527,4 Durability of marine laminates , '. 71727.5 Durability of sandwich materials , ,.......... 71927.6 Assemblies ' 72027.7 Slamming impact response , '. 72227.8 Cylinders for underwater applications ' " 72427.9 Future directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 72727.10 References , ,................... 727Index 730


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Sample Illustration

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mIIII298 Fatigue in composites

2 3 4

t1. Matrix cracking, fibre breaking2. Crack coupling. interfacial debonding. fibre breaking3.Delamination, fibre breaking4. Delamination growth, localized fibre breaking5. Fracture

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Fig. 10.1 Schematic representation of damage development in laminated composites made oflayers during fatigue life.

This chapter deals with the fatigue behaviour of 2D woven composites. Fortypical results for laminated composites made of UD layers arc also presented.

10.2 Fatigue performance of laminated compositesDamage initiation and growth in laminated composites made of UD layers underloading has been studied for the last three decades and is well documentcd-i" Arepresentation of damage initiation and growth process is shown in Fig. 1O.1.1?edevelopment is multi-staged. The main damage mechanisms observed dunngloading are: matrix cracking, crack coupling, fibre/matrix interfacial debonding,fibre breaking and finally fracture. Figure 10.2 shows damage accumulation as apercentage of life behaviour for a typical laminated composite made of UD

Matrix micro-cracks are initiated early in the fatigue process. Matrix cra~ksfirst along fibres in the layers inclined to the principal tensile loading directIOn.of parallel cracks appear in a layer during fatigue loading. As the laminate iscracking occurs in the other layers also. The crack density increases as theThis process depends upon the layer stresses and adjacent layers.

As the crack density increases, cracks grow into each other. leading toThe cracking process continues until cracks in each layer have attained anhsaturation spacing and size. At this stage, stress redistribution would limtt t e

fatigue in composites

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