Acoustic emission analysis for failure identification in composite materials Markus G. R. Sause Experimental Physics II Institute of Physics University of Augsburg 1. Motivation 2. Methods of AE analysis 3. Validation of classification procedure 4. Applications 5. Summary 1
1. Motivation failure of materials x After x DV y Before t all microscopic failure mechanisms in composites generate acoustic emission Freund et al. J. Appl. Mech-T. ASME 39 601-602 (1972) Scruby J. Phys. E: Sci. Instrum. 20 946-955 (1987) Sause et al. J. Nondest. Eval. 29:2 123-142 (2010) 2
1 6.2 m m 1. Motivation failure of fiber reinforced composites fib e r b re a k a g e S p e c im e n 2 S p e c im e n 1 0 in te r-p ly d e la m in a tio n cross-ply stacking Challenges: complex modes of failure scatter of material properties Possibilities: improved failure theories improved testing methods acoustic emission for material research 3
1. Motivation failure of fiber reinforced composites Manhattan Bridge Space Shuttle Discovery CFRP structural part monitoring of structure in the field detection of abnormal behaviour indication of imminent failure acoustic emission for monitoring of structural integrity 4
2. Methods of AE analysis Amplitude [V] 0.1 AE signal 0.0-0.1 200 300 400 500 Zeit [µs] Signal prediction Counting Localization Classification Amount Position Type of damage Material analysis 5
2. Methods of AE analysis AE source localization A E -s o u rc e t 0 d iffe re n c e in p ro p a g a tio n le n g th t 2 Dt-based localization: uses sensor array attached to specimen calculation of arrival time differences inverse calculation of source position visualization as function of load r S o u rc e r 2 grip region (0,0,0 ) r 1 t 1 force specimen Source density: low medium high 6
Intensität Intensity Intensity Intensität Intensity Intensität 2. Methods of AE analysis Identification of failure mechanisms Feature based pattern recognition and numerical validation: 0.10 0.05 feature 1 feature 2 feature 1 0.00 0 500 1000 Frequenz [khz] 0.10 0.05 0.00 0 500 1000 Frequenz [khz] 0.10 Frequency [khz] Frequency [khz] Feature Extraction 0.05 0.00 0 500 1000 Frequenz [khz] Frequency [khz] feature 2 Definition of features Sause et al. J. Nondest. Eval. 29:2 123-142 (2010) Sause et al. Comp. Sci. Technol. 72 167-174 (2012) Sause et al. Pat. Rec.Letters 33:1 17-23 (2012) 7
Intensität Intensity Intensity Intensität Intensity Intensität 2. Methods of AE analysis Identification of failure mechanisms Feature based pattern recognition and numerical validation: 0.10 0.05 feature 1 feature 2 feature 1 0.00 0 500 1000 Frequenz [khz] 0.10 0.05 0.00 0 500 1000 Frequenz [khz] 0.10 Frequency [khz] Frequency [khz] Feature Extraction 0.05 0.00 0 500 1000 Frequenz [khz] Frequency [khz] feature 2 Definition of features Application of pattern recognition algorithm Sause et al. J. Nondest. Eval. 29:2 123-142 (2010) Sause et al. Comp. Sci. Technol. 72 167-174 (2012) Sause et al. Pat. Rec.Letters 33:1 17-23 (2012) 8
Intensität Intensity Intensity Intensität Intensity Intensität 2. Methods of AE analysis Identification of failure mechanisms Feature based pattern recognition and numerical validation: 0.10 0.05 feature 1 feature 2 feature 1 0.00 0 500 1000 Frequenz [khz] 0.10 0.05 0.00 0 500 1000 Frequenz [khz] 0.10 Frequency [khz] Frequency [khz] Feature Extraction 0.05 0.00 0 500 1000 Frequenz [khz] Frequency [khz] feature 2 Definition of features Application of pattern recognition algorithm Numerical validation Sause et al. J. Nondest. Eval. 29:2 123-142 (2010) Sause et al. Comp. Sci. Technol. 72 167-174 (2012) Sause et al. Pat. Rec.Letters 33:1 17-23 (2012) 9
3. Validation of classification procedure Which secondary knowledge can link AE signals and their source? in-situ methods Thermography Digital Image Correlation model predictions single source experiments model composites in-situ CT electromagnetic emission analytical calculations numerical modeling micromechanical experiments online microscopy 10
3. Validation of classification procedure FEM modeling of acoustic emission AE source modeling (simple example): force F 2D-plane von Mises stress coordinate system origin 5.2 mm 2 mm a crack growth y z x fixed constraint y x signal detection point explicit modeling of crack growth in material by cohesive zone type approach simultaneous modeling of acoustic signal propagation 11
3. Validation of classification procedure FEM modeling of acoustic emission AE source modeling (simple example): radiation radiation crack growth accumulated stress velocity field (near field) velocity field (far field) 12
3. Validation of classification procedure FEM modeling of acoustic emission AE source modeling (composite): AE sensors AE source: Matrix cracking t < 5x10-5 s Fiber-PML RVE Composite-PML crack model Fiber breakage t < 5x10-5 s Details of FEM modeling procedure: Sause et al. 19th ICCM, Montreal (2013) Sause et al. J. Nondest. Eval. 29:2 123-142 (2010) Sause et al. J. Acoustic Emission 28 109-121 (2010) Sause et al. Composites Part B 53 249-257 (2013) Sause J. Acoustic Emission 29 (2012) Sause J. Acoustic Emission 31:1 (2013) Sause et al. Sens. Act. A 184 64-71 (2012) Sause et al. 29th EWGAE, Vienna (2010) source modeling signal propagation signal detection 13
Partial Power 2 [%] 3. Validation of classification procedure Partial Power 2 [%] Result of forward modeling procedure Comparison between simulation and experiment: Simulation Experiment Matrix crack, all angles (IFF) 60 Matrixcrack (IFF) Interfacial failure (DEF) Fiber breakage (FF) 60 Out-of-plane delamination (DEF) Fiber-Matrix debonding (DEF) Fiber bundle breakage (FF) Single Fiber breakage (FF) 40 40 source-sensor distance 20 20 0 0 200 400 600 800 1000 1200 Weighted Peak-Frequency [khz] 0 0 200 400 600 800 1000 1200 Weighted Peak-Frequency [khz] similar cluster structures observed for experiment and simulation possibility to correlate experimental signal clusters to respective source mechanisms Model based validation of cluster origins 14
force Kraft [N] Akkumulierte number Anzahl of signals AE-Signale 4. Applications short beam shear test force 1600 500 450 specimen WD sensor 1400 1200 F visible 400 350 1 1000 800 F AE AE onset 300 250 600 400 200 150 100 200 50 0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Traversenweg [mm] cross-head displacement [mm] Mechanical parameters: velocity1 mm/min loading till first load drop Acoustic emission: detection using one WD sensor 40dB preamplification 10 MSPs acquisition rate 20 khz 1 MHz bandpass filter 15
2.2 m m 1 8 0 m m 7 4 m m 4. Applications tensile testing 0 4 5 0 0 9 0 0 9 0 1 3 5 0 4.2 m m [0 /0 /9 0 /0 /0 ] s y m [0 /0 /9 0 /9 0 /0 ] s y m 0 9 0 9 0 0 0 [0 /9 0 /9 0 /9 0 /0 ] s y m 1 6 m m 1 W D -S e n s o r Specimens: Sigratex CE 1250-230-39 prepreg Cross-ply stacking with additional reinforcements in non-tapered regions 0 2.0 m m 2 markers for strain measurement M a rk e r fü r D e h n u n g s m e s s u n g Mechanical parameters: velocity1 mm/min loading till load drop to 40% F max non-contact optical strain measurement K ra ft gripping region S p a n n - b e re ic h Acoustic emission: detection using two WD sensors 40dB preamplification 10 MSPs acquisition rate 20 khz 1 MHz bandpass filter 16
stress [MPa] 4. Applications accumulated number of signals acoustic emission recorded during tensile test 1600 Evolution of failure mechanisms: time [s] 0 400 800 1200 1600 2000 2400 220 matrix cracks in off-axis plies 1400 1200 1000 800 600 Laminate [0/0/90/0/0] sym Matrix Cracking Interfacial failure Fiber breakage Stress-strain curve 200 180 160 140 120 100 80 onset of delamination 400 200 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 strain [%] 60 40 20 0 onset of single filament failure 17
Stress [MPa] Strain [%] 4. Applications comparison to Puck s failure criteria Comparison to acoustic emission results: 1400 1200 1000 800 600 Calculated First ply failure Last ply failure Measured Onset Matrix cracking Onset Interfacial failure Onset Fiber breakage Maximum stress 1.6 1.5 1.4 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 Calculated First ply failure Last ply failure Measured Onset Matrix cracking Onset Interfacial failure Onset Fiber breakage Maximum strain 400 0.5 0.4 200 0.3 0.2 0.1 0 0.0 [0/0/90/0/0] sym [0/0/90/90/0] sym [0/90/90/90/0] sym [0/0/90/0/0] sym [0/0/90/90/0] sym [0/90/90/90/0] sym onset of first ply failure in good coincidence with onset of matrix cracking and interfacial failure onset of first filament failure preceeds last ply failure systematically 18
3-4 m m 4. Applications W D -S e n s o re n H ilfs s e n s o r DCB Double Cantilever Beam 1 C F K -P ro b e 2 3 Source density: R is s s p itz e 2 5 0 m m x t 100 s x 60 mm crack progress vs. time pseudo-3d view unequal density of acoustic emission sources during experiment indicates changes in crack growth microscopic origin? 19
Akkumulierte number Anzahl of der signals SE-Signale [#] force Kraft [N] relative Relative accumulated akkumulierte signal Signalamplitude amplitudes [%] Hexcel RTM6= 168 [J/m²] HexPly914= 103[J/m²] 4. Applications DCB Double Cantilever Beam cross-head Traversenweg displacement [mm] [mm] 0 2 4 6 8 10 12 14 2500 matrix Matrixrisse cracking interfacial Interfaceversagen failure 2000 fiber Faserbruch breakage force-disp. Kraft-Weg Kurve curve 1500 SE-Ersteinsatz AE onset 1000 100 70 90 60 80 70 50 60 40 50 30 40 Matrixriss matrix cracking Lineare linear regression Regression Interfaceversagen interfacial failure Lineare linear regression Regression Faserbruch fiber breakage 500 20 10 30 20 10 0 0 10 20 30 40 50 60 70 80 90 time Zeit [s] [s] systematic relationship between contributions of different failure mechanisms and the resulting fracture toughness values confirmed by microscopy investigations of fracture surface 0 0 0 50 100 150 200 250 300 350 400 450 500 550 G G Ic - Wert [J/m²] Ic -value [J/m²] 20
5. Summary Summary: acoustic emission allows for 1. localization of active damage in composite materials 2. distinction of different failure types in composite materials acoustic emission allows for a variety of possibilities to diagnose and understand damage progression in fiber reinforced composites and hybrids other applications adressed in the past comprise bondings, ENF, NOLrings, CT-specimens, SENB-specimens, DENT-specimens, TDCBspecimens, peel-tests, fiber fragmentation, single filament testing, coating integrity, sandwich structures, burst pressure tests, windmill blades, 21
Acknowledgments: Dr. G. Obermeier Dr.-Ing. A.-M. Zelenyak M. Sc. T. Guglhör M. Sc. S. Kalafat M. Sc. A. Monden M. Sc. S. Richler M. Sc. E. Laukmanis Dipl. Phys. S. Gade B. Sc. F. Staab B. Sc. U. Buchner B. Sc. N. Anderle B. Sc. N. Schorer Thank you for your attention! S. Bessel Dipl.Ing. (FH) S. Schmitt 22