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Materials Engineering Research Laboratory Ltd Tamworth Road Hertford SG13 7DG

BS EN ISO 9001. Mode I and Mode II Delamination Characterisation of UD and Woven Glass Fibre Vinyl Ester Composites. Materials Engineering Research Laboratory Ltd Tamworth Road Hertford SG13 7DG Tel. +44 (0)1992 500120 Fax +44 (0)1992 586439 enquiries@merl-ltd.co.uk www.merl-ltd.co.uk.

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Materials Engineering Research Laboratory Ltd Tamworth Road Hertford SG13 7DG

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  1. BS EN ISO 9001 Mode I and Mode II Delamination Characterisation of UD and Woven Glass Fibre Vinyl Ester Composites Materials Engineering Research Laboratory Ltd Tamworth Road Hertford SG13 7DG Tel. +44 (0)1992 500120 Fax +44 (0)1992 586439 enquiries@merl-ltd.co.uk www.merl-ltd.co.uk

  2. FRACTURE MECHANICS FOR COMPOSITE STRUCTURES • Delaminations may be present in composite structures • Stress based failure criteria do not account for stress singularities from geometric and material discontinuities STRESS-BASED CRITERION Predicts translaminar failures where no singularities are present FRACTURE-BASED CRITERION Predicts onset and growth of delaminations (cracks) from singularities SUITABLE FAILURE CRITERION Predicts final failure e.g. tensile fibre failure, buckling, etc.

  3. NO DAMAGE GROWTH DESIGN • In the life of a component under normal operating conditions, a crack in a composite laminate should not initiate. • If such damage is already present, be it from a manufacturing flaw or other acceptable damage event, then the damage will not grow any further during normal service. Composite Crack length Metal Crack detected Inspection intervals Fatigue cycles

  4. INTERLAMINAR FRACTURE TEST SPECIMENS DCB ELS (end loaded split ) ISO 15024:2000(E) European Structural Integrity Society draft protocol • No rollers for ELS • Translucent specimen

  5. Material Static Fatigue Mode I (DCB) Mode II (ELS) Mode I (DCB) Mode II (ELS) UD 5 5 5 15 Woven 5 5 5 15 MERL MMS 13 TEST PROGRAMME • VT/Halmatic Test Panels • UD glass fibre vinyl ester composite (stitched unidirectional blanket) • Woven glass fibre vinyl ester composite

  6. DCB STATIC LOAD-DISPLACEMENT Typical UD DCB Typical woven DCB ratchetting

  7. DCB STATIC TEST RESULTS Compliance vs. Crack Length UD Woven • Linear but some scatter

  8. DCB STATIC TEST RESULTS R-Curve UD Woven • Both materials show an increase in delamination growth resistance that demonstrates the presence of fibre bridging - more in UD than Woven • Models fitted to R-Curves for use in fatigue analysis

  9. DCB STATIC TEST RESULTS UD INITIATION DATA FROM THE INSERT WOVEN INITIATION DATA FROM THE INSERT • Similar data from the precrack • VIS data preferred

  10. ELS STATIC LOAD-DISPLACEMENT Woven UD Offset after initial loading

  11. ELS COMPLIANCE vs. DELAMINATION LENGTH UD Woven • Linear but some scatter

  12. ELS R-CURVE UD Woven • Both materials show an increase in delamination growth resistance that demonstrates the presence of fibre bridging • Models fitted to R-Curves for use in fatigue analysis

  13. ELS STATIC TEST RESULTS UD INITIATION DATA FROM THE INSERT WOVEN INITIATION DATA FROM THE INSERT • Similar data from the precrack • VIS data preferred

  14. SUMMARY OF MODE I AND MODE II FRACTURE SURFACES MODE I UD MODE II WOVEN MODE II UD MODE I WOVEN

  15. 3P 2B(a + ) 3P2ma2 2B OVERVIEW OF FATIGUE DATA ANALYSIS • Measure Compliance vs. Cycles • All testing carried out under displacement control loading with an R ratio 0.1 and frequency 5Hz. • Determine Crack Length vs. Cycles From Compliance Data • Compliance and crack length measured at the start and end of each fatigue • test are used to convert the compliance data to crack length data. • Mode I C1/3 vs. a • Mode II C vs. a3 • Determine Peak Cyclic G vs. Cycles • Mode I CBT GI = • Mode II ECM GII = • Obtain Peak Cyclic G vs. Crack Growth Rate Relationship • Note, these data where provided require factoring for the influence of fibre bridging effects

  16. MULTI-STATION TESTING Fatigue testing under displacement control with constant amplitude

  17. CRACK GROWTH DURABILITY TESTING

  18. Delamination (mm) Compliance (mm/N) Cycles Cycles Peak Cyclic G Cycles MODE I UD FATIGUE DATA

  19. MODE I UD FATIGUE DATA CORRECTED da/dN vs. peak cyclic G da/dN (mm/cycle) da/dN (mm/cycle) GIMAX x (GIc(VIS) / GIR) (J/m2) Peak Cyclic GI (J/m2) To account for fibre bridging multiply the fatigue G data by GIc/GIR for the Mode I data

  20. MODE I WOVEN CORRECTED FATIGUE DATA

  21. MODE II UD CORRECTED FATIGUE DATA

  22. MODE II WOVEN CORRECTED FATIGUE DATA

  23. R-CURVE SPREAD MODE I UD FATIGUE DATA

  24. CONCLUSIONS • UD and woven both display fibre bridging in Mode I and Mode II • Fibre bridging must be accounted for in fatigue tests • Normalisation by the R-Curve can provide fatigue relationships free from fibre bridging • Upper and lower bounds can account for scatter in data

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