D. J. Lekou Centre for Renewable Energy Sources (CRES) T. T. Assimakopoulou, T. P. Philippidis

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Estimation of the Uncertainty in Measurement of Composite Material Mechanical Properties during Static Testing. D. J. Lekou Centre for Renewable Energy Sources (CRES) T. T. Assimakopoulou, T. P. Philippidis University of Patras. Blade Structural Design. Lamina Characterization. - PowerPoint PPT Presentation

Transcript of D. J. Lekou Centre for Renewable Energy Sources (CRES) T. T. Assimakopoulou, T. P. Philippidis

  • Estimation of the Uncertainty in Measurement of Composite Material Mechanical Properties during Static TestingD. J. LekouCentre for Renewable Energy Sources (CRES)T. T. Assimakopoulou, T. P. PhilippidisUniversity of Patras

  • Blade Structural Design

  • Lamina Characterization

    y

    x

    1

    2

  • The uncertaintyParameter associated with the result of a measurementCharacterizing the dispersion of values, reasonable attributed to the measurande.g. standard deviationDescribes the level of knowledge of the measurandIncreases confidence in the validity of a measurement result

  • The Tests

  • The Measurands

  • Uncertainty analysis Test instruments Load Cell, Strain gauges, MicrometerSpecimen Dimensions, Shape & TolerancesTest procedure Zeroing, Sampling, AlignmentTest environment Temperature, Humidity

  • Uncertainty of Coupon StrengthCross-sectional areaInstrument, Coupon shapeLoadLoad cellSpecimen alignmentManufacturing & Test procedureRecording of Ultimate StressSample rate & Equipment

  • Uncertainty of Coupon Elastic Property Stress (measurand)Strain (measured)k-factor, etc.MisalignmentCalculation procedureRangeLinear regressionAveragingTest procedureZeroing

  • Uncertainty of Reported PropertiesArithmetic mean

    Standard deviation

    Correlated measurementsSame equipmentCoupons from same batch

  • Properties of UD on-axisUnc. in Cross-SectionuA = 0.84%Unc. in Strengthu = 1.10%Unc. in Ult. Strainu = 0.90%Unc. in E-modulusuE = 1.65%

  • Misalignment effects on properties

  • E-modulus

  • Mean value of E1 Experiments: 29 tests, Mean= 39.04 GPa, COV= 2.64% Usual approach (95% conf. level):E1 = 39.04 0.63 GPa (1.6%)Current analysis: E1 = 39.04 1.28 GPa (3.3%)2% lower Stiffness (95% Conf.)

  • Mean value of XT Experiments:29 tests, Mean= 776.50 MPa, COV= 4.65%Usual approach:Rk,XT = 695.55 MPa (89.6% of mean value)Current analysis:Rk,XT = 646.92 MPa (83.3% of mean value)7% lower characteristic strength value

  • Conclusions RecommendationsUncertainty in MeasurementsDistinguish between uncertainty in measurement and inherent property variabilityReport Uncertainty of measurementsAs input for designers & certification bodiesFor improvement on test proceduresUse Analysis on UncertaintyFor estimation of number of tests Extension of presented analysis Fatigue results

  • Thank you for your attention