- Email: [email protected]
Acoustic emission in carbon fibre-reinforced plastic materials
0 Elsevier, Paris Carbon fibre-reinforced
Ann. Chim. Sci. Mat, 2000, 25, pp. 533-537
plastic materials
ACOUSTIC EMISSION IN CARBON FIBRE-REINFORCED PLASTIC MATERIALS 0livie.r National Institute of Materials l-l Higashi, Tsnkuba, 305-8565
SIRON*,
and Chemical Research Ibaraki, Japan.
Hiroshi TSUDA (NIMC),
AIST,
MITI,
Departmnt
of Composite
Materials,
Abstract - The mechanicalbehaviour of unidirectional (UD) and 2D-laminate Carbon FibreReinforced Plastic compositeswas investigated under 4-point bending and tensile loads at room temperature. The mechanicalbehaviour of UD compositeswas first studied. The mechanical behaviour of a quasi-isotropiclaminate was subsequentlyinvestigated under the sameloading conditions and correlatedto that of the UD plies. The damageand the failure mechanismswere identified by microscopeobservationson both UD and laminate composites.Two families of damage mode were identified, involving interfibre cracks and inter-layer delamination cracks homogeneouslydistributed within the composite. The fracture process is assignedto the propagation of the macrocrack in the failure envelope through a large intra and inter-layer delaminationprocessinterrupted by tibres/bundlesfracture. Acoustic emissionmeasurementwas performedduring the tests.An approachusinga combinationof acousticwaveform parametersas indicatorsof the physical damageis discussed. R&urn6 - Emission acoustique dans les math-iaux composites CFRP. Le comportement m&nique de mat&iaux compositesunidirectionnelet bidirectionnel stratifit de type CFKP a &tt &udiC sous chargement de flexion quatre points et de traction zi temphture ambiante. Le comportementmkanique du pli &nentaire a d’abord&& &udiC.Le comportementmkcaniqued’un stratifiCde type quasi-isotropiquea tt6 ensuiteanalysesouslesm&es conditionsexp&imentaleset corr& a celui du pli B&nentaire. Les modesd’endommagement ont &tBidentifies par desexamens en microscopic optique. Deux modes d’endommagementrkpartis de fqon homoghneont t%t6 identifiks, incluant desmicrofissuresintra-fil et desfissuresde dklaminageentreles plis. La rupture du mattiau a & attribde au dbveloppementd’une macrofissure,incluant de larges zones de d&rninage intra et inter-fil interrompuespar des rupturesde fibres / fils. L’&nission acoustique bmise sous chargement a &tB enregistrke. Une approche utilisant les paramhtresd’Cmission acoustiquecommeindicateursd’endommagement estdiscutte.
Remints:Hiroshi TSUDA, National Institute of Materials andChemicalResearch(NIMC), AET, MlTI, Departmentof CompositeMaterials, l-l Higashi,Tsukuba,3058565 Ibaraki, Japan. * , GERMA Member (httn:Ngerma.citeweb.net)
534
0. Siron,
H. Tsuda
1. INTRODUCTION Carbon Fibre-Reinforced Plastic (CFRP) composites display several advantageous properties for structural application in the aeronautics and space industry. In order to define an accurate design and life prediction of CFRP structures, it is important to identify and to predict the nature of the physical damage occuring within the structure under critical loads. The damage and failure process in CFRP composites is known to involve a sequential accumulation of matrix microcracks, delaminations and fibre/bundle failures. These features have been identified on unidirectional (UD) [l] and 2D-laminate CFRP composites [2-41 under several loading conditions at room temperature. An example of such CFRP composite (T800W3631) has been investigated in this study. In the first part of this work, the mechanical behaviour and the ultimate failure of the composites were investigated under quasi-static loading conditions at room temperature. The originality of this work is to study the mechanical behaviour of CFRP composites through multi-scale approach. The mechanical behaviour of UD composites under tensile and flexural loads was first studied. The mechanical behaviour of a quasi-isotropic laminate composite was subsequently investigated under the same loading conditions and correlated to that of the elementary plies. For both CFRP composites tested, the damage and the rupture processes were identified by optical microscopy. Non destructive evaluation (NDE) is useful to follow the integrity of structures during processing and industrial applications. Acoustic emission (AE) analysis was performed during the mechanical tests. AE waveform parameters were investigated as damage indicators and related to the physical damage of the composite. Numerous attemps have been done to correlate AE waveform parameters to the physical damage process. Major studies are reviewed in the references [5-91. In the present work, AE was recorded with a single sensor under several loading conditions generating localized (bending test) and diffuse (tepsile test) damage area. From a multi-scale experimental analysis of the composites, a double amplitude/duration analysis of the AE signals was performed. A correlation between the AE waveform parameters and the damage and fracture kinetics identified by optical microscopy was then proposed. 2. MATERIALS
AND EXPERIMENTS
The materials used are UD and quasi-isotropic ([+45/90/-45/0]2,) CFRP composites (manufactured by Toray Co. Ltd). All these materials were fabricated according to the same process. The prepreg used was TXOOH / 3631 (Epoxy matrix). The volume fraction of tibres (table I) was 60%. Prepregs were cured at 180 “C during two hours. An analysis by optical microscopy was performed on the as-received UD and 2D composites. No damage (including no porosity) was identified within the specimens. The apparent density of the specimens is 1.58kO.02 g/cm3. The length and width of the specimens tested were respectively 200 mm and 20 mm, except for the onaxis UD-composite of which the width has been reduced to 10 mm. The tensile tests were performed with a universal testing machine at a cross-head speed of 0.5 mmmin. The 4-point loading tests were performed according to ASTM standards [lo]. The specimens were loaded with a device whose lower and upper span were 150 mm and 50 mm respectively. The tests were performed with a universal testing machine with a Immmin cross-head speed. Al3 signals were recorded during the tests. A 3OOKHz resonance frequency AE sensor was attached to the specimen through a silicone grease coupling. The sensor output was connected to a 40 dB preamplifier and a 150-750 KHz bandwith plug-in filter. The threshold of the AE system was
Carbon fibre-reinforced
plastic materials
535
set to 30 dl3. The calibration of the recording system allowed the selection of the appropriate parametersand eliminationof the signalnoisef?omthe grip device.
3. RESULTS AND DISCUSSION 3.1. Mechanicalbehaviour andmicroscopeobservationsof damager8l The stress-strainrelationship of the UD and the laminate compositesare linear and interrupted by a brittle fracture processunder tensile and bending loading conditions (table 1). Optical microscopy inspectionsof the tested specimenswere usedto assess the damageand the failure processes of the composites.A few in&a-ply cracksand limited inter-ply delaminationcracks were identified, homogeneouslydistributedin the laminatecomposite.The 45” off-axis plies clearly fulfil their function delaying the propagationof the matrix cracksto the on-axis plies. For both of the compositestested,most of the damageis located in the failure envelope, including large intra and inter-layer delamination cracks as well as fibre/bundle failures. The damageand fracture processes aremainly due to local shearcomponents. Table
1. Mechanical properties of the CFRP composite materials (Notations : E : Young’s
modulus,v : Poissonratio, o : stress,E : strain, 1 : longitudinal, t : transverse,b : bending, r : failure, max : maximum) I C-fibreT800H(data 1 providedby Toray Co.)
Tensile Test ! Density: I or = 5.49 GPa q= 1.9% 90’ off-axis :
26oiSO MPa Er= 1.4WO.01%
On-axis:
90’ off-axis :
Eb=
Eb =
7.9OM.02 GPa
155.8k2.1 GPa
8.1kO.2 GPa
0,= 80MMPa Er= 1.05hO.l%
Omax= 1807*44MPa (E=
Omax= 11&2 MPa
1.3 1*0.03 %)
1.36aO.02 %)
Et’ m 10112p
4-ptBending Test
El = 61*1 GPa vlt = 0.32
(E =
omax= 7Oti12 MPa (E =
1.7*0.1%)
3.2. Damageand rupture urocesses in correlationwith AE waveform parametersr8l The multi-scale approachadoptedin this work allowed to clearly identify the damageand the failure modesinvolved during the loading of the CFRP composites.Basedon the variations in amplitude and duration of the AE events, several domainswere defined and correlated to the physical damageffigure 1). This multi-scaleapproachprovides evidencesof a correlation between the initiation and the propagationof matrix microcracking and the low duration and low/medium amplitudeevents. The initiation and the propagationof the intra and inter-ply delaminationcracks
536
0. Siron,
were associated to highest amplitude highest amplitude) large delamination
H. Tsuda
medium duration and mediumhigh amplitude AE events. Medium duration and events were assigned to fibre/bundle failure. Finally, high duration (and mainly events were associated to the sudden propagation of the macrocrack including cracks. Table 2 summarizes the classification of the AE signal parameters.
Time (s) Amplitude
(dB)
Figure 1. Typical stress-strain curve and AE (left) obtained during 4-point bend test performed a [+45/90/-45/0]2, AE events (right).
Table 2. Correlation
between
CFFW composite,
and a representation
of amplitude
the physical damage, the fracture mechanism
and duration
and the AE waveform
parameters. Amphtude Duration Low (< 1000 psec)
Medium (1000 << 10,000
ec)
Low (30 - 35/4odEq Domain I : onset of intraply matrix microcrack
Medium (35140 - 8OdB) Domain II : propagation of
High lOOdE%)
(80-
IlMtl-iX
microcrack Domain III : onset of delamination (initiation of transverse ply failure associated with inter-ply delamination crack)
@O-90/95 dB)
(90/95-1OOdB)
Domain IV(a) : i Domain IV(b) : I propagation of : tibre I bundie intra and inter- : failure Ply delamination / crack ;
~
High (> 10,000 flsec)
on of
DomainV: brutal i propagation of macrocrack I associated with large : delamination crack
Carbon fibre-reinforced
plastic materials
537
4. CONCLUSION
The mechanicalbehaviour of UD and quasi-isotropicCFRP compositeswas investigated under tensile and 4-point loads. These materials exhibits remarkably high elastic and failure properties.The damageand the failure mechanismswere identified by microscopeobservationson both UD and laminate composites.Two families of damagemode were identified, involving intertibre cracks and inter-layer delamination cracks homogeneouslydistributed within the composite.The fracture processis assignedto the propagation of the macrocrackin the failure envelope through a large intra and inter-layer delaminationprocessinterrupted by fibres/bundles fracture. The fracture processhas been attributed to local shear components.AE signalswere recordedduring the mechanicaltests. Baaedon the microscopy analysisof damage,an approach using AE waveform parametersas damageindicators is proposed.The next step will involve experiments with several AI? sensors(2 2). The AE waves attenuation could be studied in correlation with the location of the AE sources.These new results will be comparedto the classificationproposed. 5. REFERENCES
PI
N. Sate, T. Kurauchi and 0. Kamigaito, Fracture Mechanism of Unidirectional CFRP Composite,J. Mater. Sci., 21 (1986) 1005- 1010. PI J.E. Masters and K.L. Reifsnider,An Investigation of Cumulative DamageDevelopmentin Quasi-Isotropic Graphite/Epoxy Laminates,Damage in CompositeMaterials, ASTM STP 775, Ed. American Society for Testingand Materials (1982) 40 - 62. [31 P.W. Peters and T.W. Chou, On Cross-Ply Cracking in Glass and Carbon FibreReinforcedEpoxy Laminates,Composites,18 (1987) 40 - 46. [41 S. Ogihara, N. Takeda and A. Kobayashi, Experimental Characterization of Microscopic Failure ProcessUnder Quasi-Static Tension in Interleaved and Toughness-ImprovedCFRP Cross-PlyLaminates,Comp.Sci. & Tech., 57 (1997) 267 - 275. ES1 F. Meraghni, PhD Thesis,U.T. Compibgne(1994) 99 (in French). E61 0. Siron, G. Chollon, H. Tsuda,H. Yamauchi, K. Maedaand K. Kosaka, Microstructural and Mechanical Propertiesof Filler-Added Coal Tar Pitch-BasedC/C Composites: The damage and Fracture Processin Correlation With AE Waveform Parameters,to be published in Carbon. [71 0. Siron, H. Tsuda,Damageand Rupture Processof Filler-Added Coal-Tar Pitch-BasedC/C CompositeMaterials Under Quasi-StaticLoadingsat Room Temperature,Proceedingsof the 6th JapanInternationalSAMPE, Tokyo, October 26-29 (1999) 1135- 1138. PI 0. Siron, H. Tsuda, The Damage and Fracture Processesin CFRP in Correlation with AE Waveform Parameters,submittedto J. of Mater. Sci. [91 W.H. Prosser,K.E. Jackson,S. Kellas, B.T. Smith J. McKeon and A. Friedman, Advanced Waveform-BasedAcoustic EmissionDetection of Matrix Cracking in Composites,Materials Evaluation, 53 9 (1995) 1052- 1058. [lOI ASTM, D790-95a, Standard Test Methods for Flexural Properties of Unreinforced and ReinforcedPlasticsand Electrical InsulatingMaterials (1996) 155 - 163.
Ann. Chim. Sci. Mat, 2000, 25, pp. 533-537
plastic materials
ACOUSTIC EMISSION IN CARBON FIBRE-REINFORCED PLASTIC MATERIALS 0livie.r National Institute of Materials l-l Higashi, Tsnkuba, 305-8565
SIRON*,
and Chemical Research Ibaraki, Japan.
Hiroshi TSUDA (NIMC),
AIST,
MITI,
Departmnt
of Composite
Materials,
Abstract - The mechanicalbehaviour of unidirectional (UD) and 2D-laminate Carbon FibreReinforced Plastic compositeswas investigated under 4-point bending and tensile loads at room temperature. The mechanicalbehaviour of UD compositeswas first studied. The mechanical behaviour of a quasi-isotropiclaminate was subsequentlyinvestigated under the sameloading conditions and correlatedto that of the UD plies. The damageand the failure mechanismswere identified by microscopeobservationson both UD and laminate composites.Two families of damage mode were identified, involving interfibre cracks and inter-layer delamination cracks homogeneouslydistributed within the composite. The fracture process is assignedto the propagation of the macrocrack in the failure envelope through a large intra and inter-layer delaminationprocessinterrupted by tibres/bundlesfracture. Acoustic emissionmeasurementwas performedduring the tests.An approachusinga combinationof acousticwaveform parametersas indicatorsof the physical damageis discussed. R&urn6 - Emission acoustique dans les math-iaux composites CFRP. Le comportement m&nique de mat&iaux compositesunidirectionnelet bidirectionnel stratifit de type CFKP a &tt &udiC sous chargement de flexion quatre points et de traction zi temphture ambiante. Le comportementmkanique du pli &nentaire a d’abord&& &udiC.Le comportementmkcaniqued’un stratifiCde type quasi-isotropiquea tt6 ensuiteanalysesouslesm&es conditionsexp&imentaleset corr& a celui du pli B&nentaire. Les modesd’endommagement ont &tBidentifies par desexamens en microscopic optique. Deux modes d’endommagementrkpartis de fqon homoghneont t%t6 identifiks, incluant desmicrofissuresintra-fil et desfissuresde dklaminageentreles plis. La rupture du mattiau a & attribde au dbveloppementd’une macrofissure,incluant de larges zones de d&rninage intra et inter-fil interrompuespar des rupturesde fibres / fils. L’&nission acoustique bmise sous chargement a &tB enregistrke. Une approche utilisant les paramhtresd’Cmission acoustiquecommeindicateursd’endommagement estdiscutte.
Remints:Hiroshi TSUDA, National Institute of Materials andChemicalResearch(NIMC), AET, MlTI, Departmentof CompositeMaterials, l-l Higashi,Tsukuba,3058565 Ibaraki, Japan. * , GERMA Member (httn:Ngerma.citeweb.net)
534
0. Siron,
H. Tsuda
1. INTRODUCTION Carbon Fibre-Reinforced Plastic (CFRP) composites display several advantageous properties for structural application in the aeronautics and space industry. In order to define an accurate design and life prediction of CFRP structures, it is important to identify and to predict the nature of the physical damage occuring within the structure under critical loads. The damage and failure process in CFRP composites is known to involve a sequential accumulation of matrix microcracks, delaminations and fibre/bundle failures. These features have been identified on unidirectional (UD) [l] and 2D-laminate CFRP composites [2-41 under several loading conditions at room temperature. An example of such CFRP composite (T800W3631) has been investigated in this study. In the first part of this work, the mechanical behaviour and the ultimate failure of the composites were investigated under quasi-static loading conditions at room temperature. The originality of this work is to study the mechanical behaviour of CFRP composites through multi-scale approach. The mechanical behaviour of UD composites under tensile and flexural loads was first studied. The mechanical behaviour of a quasi-isotropic laminate composite was subsequently investigated under the same loading conditions and correlated to that of the elementary plies. For both CFRP composites tested, the damage and the rupture processes were identified by optical microscopy. Non destructive evaluation (NDE) is useful to follow the integrity of structures during processing and industrial applications. Acoustic emission (AE) analysis was performed during the mechanical tests. AE waveform parameters were investigated as damage indicators and related to the physical damage of the composite. Numerous attemps have been done to correlate AE waveform parameters to the physical damage process. Major studies are reviewed in the references [5-91. In the present work, AE was recorded with a single sensor under several loading conditions generating localized (bending test) and diffuse (tepsile test) damage area. From a multi-scale experimental analysis of the composites, a double amplitude/duration analysis of the AE signals was performed. A correlation between the AE waveform parameters and the damage and fracture kinetics identified by optical microscopy was then proposed. 2. MATERIALS
AND EXPERIMENTS
The materials used are UD and quasi-isotropic ([+45/90/-45/0]2,) CFRP composites (manufactured by Toray Co. Ltd). All these materials were fabricated according to the same process. The prepreg used was TXOOH / 3631 (Epoxy matrix). The volume fraction of tibres (table I) was 60%. Prepregs were cured at 180 “C during two hours. An analysis by optical microscopy was performed on the as-received UD and 2D composites. No damage (including no porosity) was identified within the specimens. The apparent density of the specimens is 1.58kO.02 g/cm3. The length and width of the specimens tested were respectively 200 mm and 20 mm, except for the onaxis UD-composite of which the width has been reduced to 10 mm. The tensile tests were performed with a universal testing machine at a cross-head speed of 0.5 mmmin. The 4-point loading tests were performed according to ASTM standards [lo]. The specimens were loaded with a device whose lower and upper span were 150 mm and 50 mm respectively. The tests were performed with a universal testing machine with a Immmin cross-head speed. Al3 signals were recorded during the tests. A 3OOKHz resonance frequency AE sensor was attached to the specimen through a silicone grease coupling. The sensor output was connected to a 40 dB preamplifier and a 150-750 KHz bandwith plug-in filter. The threshold of the AE system was
Carbon fibre-reinforced
plastic materials
535
set to 30 dl3. The calibration of the recording system allowed the selection of the appropriate parametersand eliminationof the signalnoisef?omthe grip device.
3. RESULTS AND DISCUSSION 3.1. Mechanicalbehaviour andmicroscopeobservationsof damager8l The stress-strainrelationship of the UD and the laminate compositesare linear and interrupted by a brittle fracture processunder tensile and bending loading conditions (table 1). Optical microscopy inspectionsof the tested specimenswere usedto assess the damageand the failure processes of the composites.A few in&a-ply cracksand limited inter-ply delaminationcracks were identified, homogeneouslydistributedin the laminatecomposite.The 45” off-axis plies clearly fulfil their function delaying the propagationof the matrix cracksto the on-axis plies. For both of the compositestested,most of the damageis located in the failure envelope, including large intra and inter-layer delamination cracks as well as fibre/bundle failures. The damageand fracture processes aremainly due to local shearcomponents. Table
1. Mechanical properties of the CFRP composite materials (Notations : E : Young’s
modulus,v : Poissonratio, o : stress,E : strain, 1 : longitudinal, t : transverse,b : bending, r : failure, max : maximum) I C-fibreT800H(data 1 providedby Toray Co.)
Tensile Test ! Density: I or = 5.49 GPa q= 1.9% 90’ off-axis :
26oiSO MPa Er= 1.4WO.01%
On-axis:
90’ off-axis :
Eb=
Eb =
7.9OM.02 GPa
155.8k2.1 GPa
8.1kO.2 GPa
0,= 80MMPa Er= 1.05hO.l%
Omax= 1807*44MPa (E=
Omax= 11&2 MPa
1.3 1*0.03 %)
1.36aO.02 %)
Et’ m 10112p
4-ptBending Test
El = 61*1 GPa vlt = 0.32
(E =
omax= 7Oti12 MPa (E =
1.7*0.1%)
3.2. Damageand rupture urocesses in correlationwith AE waveform parametersr8l The multi-scale approachadoptedin this work allowed to clearly identify the damageand the failure modesinvolved during the loading of the CFRP composites.Basedon the variations in amplitude and duration of the AE events, several domainswere defined and correlated to the physical damageffigure 1). This multi-scaleapproachprovides evidencesof a correlation between the initiation and the propagationof matrix microcracking and the low duration and low/medium amplitudeevents. The initiation and the propagationof the intra and inter-ply delaminationcracks
536
0. Siron,
were associated to highest amplitude highest amplitude) large delamination
H. Tsuda
medium duration and mediumhigh amplitude AE events. Medium duration and events were assigned to fibre/bundle failure. Finally, high duration (and mainly events were associated to the sudden propagation of the macrocrack including cracks. Table 2 summarizes the classification of the AE signal parameters.
Time (s) Amplitude
(dB)
Figure 1. Typical stress-strain curve and AE (left) obtained during 4-point bend test performed a [+45/90/-45/0]2, AE events (right).
Table 2. Correlation
between
CFFW composite,
and a representation
of amplitude
the physical damage, the fracture mechanism
and duration
and the AE waveform
parameters. Amphtude Duration Low (< 1000 psec)
Medium (1000 << 10,000
ec)
Low (30 - 35/4odEq Domain I : onset of intraply matrix microcrack
Medium (35140 - 8OdB) Domain II : propagation of
High lOOdE%)
(80-
IlMtl-iX
microcrack Domain III : onset of delamination (initiation of transverse ply failure associated with inter-ply delamination crack)
@O-90/95 dB)
(90/95-1OOdB)
Domain IV(a) : i Domain IV(b) : I propagation of : tibre I bundie intra and inter- : failure Ply delamination / crack ;
~
High (> 10,000 flsec)
on of
DomainV: brutal i propagation of macrocrack I associated with large : delamination crack
Carbon fibre-reinforced
plastic materials
537
4. CONCLUSION
The mechanicalbehaviour of UD and quasi-isotropicCFRP compositeswas investigated under tensile and 4-point loads. These materials exhibits remarkably high elastic and failure properties.The damageand the failure mechanismswere identified by microscopeobservationson both UD and laminate composites.Two families of damagemode were identified, involving intertibre cracks and inter-layer delamination cracks homogeneouslydistributed within the composite.The fracture processis assignedto the propagation of the macrocrackin the failure envelope through a large intra and inter-layer delaminationprocessinterrupted by fibres/bundles fracture. The fracture processhas been attributed to local shear components.AE signalswere recordedduring the mechanicaltests. Baaedon the microscopy analysisof damage,an approach using AE waveform parametersas damageindicators is proposed.The next step will involve experiments with several AI? sensors(2 2). The AE waves attenuation could be studied in correlation with the location of the AE sources.These new results will be comparedto the classificationproposed. 5. REFERENCES
PI
N. Sate, T. Kurauchi and 0. Kamigaito, Fracture Mechanism of Unidirectional CFRP Composite,J. Mater. Sci., 21 (1986) 1005- 1010. PI J.E. Masters and K.L. Reifsnider,An Investigation of Cumulative DamageDevelopmentin Quasi-Isotropic Graphite/Epoxy Laminates,Damage in CompositeMaterials, ASTM STP 775, Ed. American Society for Testingand Materials (1982) 40 - 62. [31 P.W. Peters and T.W. Chou, On Cross-Ply Cracking in Glass and Carbon FibreReinforcedEpoxy Laminates,Composites,18 (1987) 40 - 46. [41 S. Ogihara, N. Takeda and A. Kobayashi, Experimental Characterization of Microscopic Failure ProcessUnder Quasi-Static Tension in Interleaved and Toughness-ImprovedCFRP Cross-PlyLaminates,Comp.Sci. & Tech., 57 (1997) 267 - 275. ES1 F. Meraghni, PhD Thesis,U.T. Compibgne(1994) 99 (in French). E61 0. Siron, G. Chollon, H. Tsuda,H. Yamauchi, K. Maedaand K. Kosaka, Microstructural and Mechanical Propertiesof Filler-Added Coal Tar Pitch-BasedC/C Composites: The damage and Fracture Processin Correlation With AE Waveform Parameters,to be published in Carbon. [71 0. Siron, H. Tsuda,Damageand Rupture Processof Filler-Added Coal-Tar Pitch-BasedC/C CompositeMaterials Under Quasi-StaticLoadingsat Room Temperature,Proceedingsof the 6th JapanInternationalSAMPE, Tokyo, October 26-29 (1999) 1135- 1138. PI 0. Siron, H. Tsuda, The Damage and Fracture Processesin CFRP in Correlation with AE Waveform Parameters,submittedto J. of Mater. Sci. [91 W.H. Prosser,K.E. Jackson,S. Kellas, B.T. Smith J. McKeon and A. Friedman, Advanced Waveform-BasedAcoustic EmissionDetection of Matrix Cracking in Composites,Materials Evaluation, 53 9 (1995) 1052- 1058. [lOI ASTM, D790-95a, Standard Test Methods for Flexural Properties of Unreinforced and ReinforcedPlasticsand Electrical InsulatingMaterials (1996) 155 - 163.