Two Sorts of Fiber Optic Sensor Monitoring the Cure Process of Composite Laminate

High Technology Letters , Vol.6 ,No.2 , April. 2000Two Sorts of Fiber Optic Sensor Monitoring the Cure Process ofComposite LaminateLi Chenshad李辰砂) , Zhang Boming , W ang Dianfu , Du Shanyi( Center for Composite M aterials , Harbin Institute of Technology , Harbin 150001 ,P . R. China )AbstractTwo new sorts of fiber optic sensor are designed. Firstly ，the variation of refractive index ofresin surrounding the embedded fiber optic w as mean to observed by measuring the speckle spatialspectrum at the end-face of the fiber optic. Secondly ，it is proposed to measuring the change ofthickness of the laminate by using fiber optic microbend attenuation. The ex periment results mea-sured by the fiber optic sensors are given. The first sort of sensor was found to be able to detectthe viscosity process of the resin matrix during cure process includeing the minimum point of vis-cosity，the gelation point and the end point of cure process ; the second sort of sensor could detectthe course of change of the thickness of composite laminate pressed by operation pressure. It isbenefit for us to optimize the operation technology and to establish the intelligent monitoring sys-tem about curing process of composites for the reason that the viscosity process and the changecourse of the thickness of laminate can be monitored.Key words : Composites , Cure , Fiber optic sensor , Speckle，M icrobending system of composite is shown in figure 1.0 IntroductionBleederAdvanced composite materials are beingDamincorporated in increasing amounts in combatand tactial vehicle systems , launch vehicles ,space platforms , composite wings and otherPrepregBaseprimary and secondary structures in aircraft ,the automotive industry ,and civil engineeringFig.1 The curing system of compositeapplications. parts and structures constructedfrom continuous fiber reinforced thermosettingThe cure cycle has a significant effect onresin composites are manufactured by arrang-ing the uncured fiber-resin mixture ( prepreg )the quality of the finished part. Some majorinto the desired shape and then curing the ma-considerations in selecting the proper cure for aterial inside the autoclave. The curing processgiven composite material include the uniformis accomplished by exposing the material to el-temperature distribution and the limited high-evated temperatures and pressures for a prede-est temperature during the curing process ,thetermined length of time . The elevated tempera-minized voids and residual stresses of the fin-tures applied during the curing provide theished product1. some other specificationsheat reqwired for initiating and maintaining theabout the operation approach are as follows :chemical reactions in the resin ; The appliedStarting curing process ，the autoclavepressure cause the force needed to compresstemperature is elevated at a predeterminatedthe laminate and squeeze excess resin out 0rate.中国煤化工e viscosity of resinthe materialo ，to consolidate the laminationgoes:[YTHC N M H Gth temperature ris-structure , and to compress voids 1. The cur-ing. The viscosity will go up after the nadir as* Supported by the Commission of National Defence Science and Industry of China.Received Nov.18 , 1999.-61--High Technology Letters , Vol.6 ,No.2 , April.2000the starting of chemical reactions which causecontrolled if every variables of the cure systemthe crosslinking changes in the molecularare monitored by sensors fixed in the cure sys-structure。the viscosity will significantly riseem. The general gauge of monitoring thenearby the gelatinization point at which thechange process of viscosity of resin matrix ismaterial becomes so viscous that resin cannotdielectric sensor-J , but this sort of sensor isflow under the applied pressure.undesirable for its high cost and inferior capa-During cure it must be ensured that albility with the monitored material. The devel-the plies are fully compacted before the gela-oped thickness gauges have shortingcomings oftinization . To assure proper volume ratio ostructural complication and more disturbing toresin and fiber as well as the uniform distribu-normal cure process 1.tion of the inner pressure , it is demanded toadd pressure nearby the nadir of viscosity for1 The Principles of Two Sort of Fiber Opticthe reason that the resin has a highly flow be-haviour to facilitate the compaction. To pre-Optical fiber sensors become the prefer-vent the rapid drop followed by a rapid rise inence of sensors used in smart technologies andviscosity so that there is plenty of time for thestructures for their superior sensing_ perfor-laminate to be completely compacted ,it ismance and compatibility with matrixIn thisneeded to keep the viscosity nearly constant atpaper ,we describe the development of a real-the lowest level by maintaining the autoclavetime monitoring technique based on two sortstemperature temporarily constant ( that isof special manufactured optical fiber sensorcalledintermediatetemperature :constantwhich are called the speckle spatial spectrumstage )from the start of the compression until( SSS )fiber optic sensor and the microbend at-compaction is completed. Once compaction istenuation fiber optic sensor. By measuring thecompleted , the temperature inside the auto-speckle spatial spectrum at the end of the fiberclave should be elevated again to the designedoptic ,the refractive index of the resin w hichhighest value which is named curing tempera-reflects the viscosity variation of the resin dur-ture to accelerate the chemical reactions anding cure process is obtained. On the otherraise the viscosity in the resin matrix in orderhand , the compression process of the compos-to avoid the resin being excessively lost. W henite laminate caused by the applied pressure isthe chemical reactions have been on the pointreflected by measuring the microbend attenua-of end ,the cure operation should be stopped sotion of the light transmitted through the fiberthat the cure time is shorten and the produc-optic embed the composite laminate. thesetion cost is saved.methods can indicate the w hole curing processBecause the processes of curing inside theincluding the nadir of the viscosity , the gela-autoclave can not be directly observed ，theion point ,the end point of the cure processvariables such as the viscosity and the cure de-and can indicate the process of thick ness .gree of resin matrix or the thickness of thechanging with time after the pressure is ap-laminate at every time etc are difficult to beplied. If these key points are determinated ,guessed. Therefore it is difficult for us to ad-the operation processes of autoclave tempera-just the autoclave temperature and the pressureture and pressure will be rightly executed.during the cure process. The traditional tech-M orwol lae foundation for apply-nologies based on empirical approach are unde-ing中国煤化工in itelligent onlinesirable in that they can not ensure the qualitiessysteTYHCN M H Ge monitor and con-of the products and the efficiency of produc-trol the curing process of composites , then thetion .aims of ensuring the qualities of products andThe operation condition can be effectivelyelevating the efficiency of the production will-62-High Technology Letters , Vol.6 , No.2 , April.2000be realized.amorphous form or crystalline form ，the gelationAfter the end of cure ,the fiber optic maintains thepointat which the resin transforms fromperformance of optical waveguide which can be used inamorphousness to crystalline during cure process cansensing vibration , stress and fatigue etc during servicebe observed as an abrupt change of the refractiveof composites.index of the resin for the reason that the densitychanges obviously near the gelation. With regard to1.1 FO Sensor Measuring Resin' s Refractive Indexthe polymer fluids ，the change of density alsoAs resin cure , the variations of viscosity ,densityindicates the free-volume expanding or lesseningand components of the resin matrix will change the re-among the molecular bonds ,which can reflectfractive index of the resin matrix. The index of refrac-lowering or increasing of viscosity of the materials.tion of majority thermosetting resin systems increases inTherefore , the viscosity of resin can also be reflectedthe range of 0.01 ~ 0.04 from initial uncured resin toby the refractive index.final cured products. Several authors have speculatedThe FO speckle spatial spectrum ( Sss ) sensorthat there is close correlation between the gain in re-is based on the special design of the optical fiber.fractive index and the cure degree of the resi[4-6].The fiber core is made of the glass whose refractiveThe refractive index of a given material dependsindex( n1)is a little higher than that of the resinon the types of molecular bonds it contains and its den-matix being monitored( np). A fiber optic with asity. If a material consists of several different types ofshort segment coat wiped off is embedded betweenmolecular bonds ,as is often the case of polymeric ma-any two bordered plies of the uncured compositeterials , the refractive index depends on the weighted( prepreg). Under the application of a coherentaverage of the molar refractivity of each bond type. Inlight，a singlemultimode fiber becomes aterms of Lorentz-Lorenz formula , the molar refractivityinterferometer which has many arms , all coexistingof one kind of molecular bond is written as :as propagation modes. When the output from thefiber optic is projected upon a screen , a circular .R =( Nm/N)n2+ 2(1)pattern consisting of a very large number ofWhere N is the number of molecules per unitspeckles" of varying intensities is observed. Thevolume，Nm is Avogadro' s number ，n is thedistribution of these speckles depends on the anglerefractive index. Let Nm/N = D ，n can be .of incidence , numerical aperture of the fiber and thedescribed as :perturbation of the fiber. Assuming that nonleaky.D+2Rmodes are equally excited , the speckle spatial power(2)D- Rspectrum can be described as 7]:The molar refractivity R depends on the .GIP(v)= A[ GIK ρ)]weighted average of each bond type for the materialswhich consist of several different types of molecular=2- pGK(ρ) do(3)bond. After the starting of cure reaction , the typesWhere A[ ] denote an Abel transform, GI( p)of molecular bond and their ratio in all types ofcaf中国煤化工so-called Chinese hatmolecular bond contained in the resin are changingCNMHGas the cure degree increases , it certainly make the:TYH八ρ=chakρ/ρo)refractive index of resin matrix changes. The densityD also influences the refractive index , as shown in二[cos-lp/po- p/po√1-(p/po}]，eq. (2). Many polymers can exist in either. ρ≤ρ0(4)一63-High Technology Letters , Vol.6 , No.2 , April.2000Where u is spatial frequency , ρ is integrationsome minor bends distributed on the fiber without mod-variable ,ρo=( sir(20m ))/入,0m= π/2-sin~( n?ifying the macro geometry of the fibef 9J0]. This loss- n2 ),λ is the wavelength of light.occurs most frequently when the highest-order mode inAs a segment of the embed fiber optic is wippedthe fiber core is coupled to the first cladding ( radia-off the coat , the naked core contacts the surroundingtion ) mode , then is rapidly attenuated. This couplingresin directly. the varying refractive index of thecan be induced by environmental effects , such as tem-resin matrix during cure process changes theperature , pressure , impact , or acoustic waves whichnumerical aperture of the fiber optic , and furthercreat structural strain. Mechanical coupling of struc-changes the speckle spatial power spectrums at thtural changes toward an embedded fiber optic modifiesoutput end of the fiber optic , thus the curing processthe micro geometry of the fiber optic and allows light tocan be monitored .be coupled between the modes ，thus modulates theIn this paper , the core refractive index n1 waslight intensity transmitting through the fiber optic. Thechosen to be 1.60 or 1. 62 , the normalized specklefibre bundle contained in the composite laminate has aspatial spectrums were calculated with the cladstationary spatial periodicity which can cause microbendrefractive index n2 = 1.54 ,1.56 and 1.58 , whichof the fiber optic and lead the attenuation of the lightare the variation range of the refractive index of resintransmitted through the fiber optic. This kind of intrin-matrix during cure process . The output results showsic microbend assembly may be employed in smartthat the normalized speckle spatial spectrums shouldstructures for its much compact intemal structure 9 ,10].change obviously with variation of the refractiveThe considerated sensors include two aspects :theindex of resin in cure process. The variation of thefiber microbending sensitivity , represented by △T/normalized speckle spatial spectrums will not be△X , and the mechanical design of the device , associ-obviously if the core refractive index n1 was chosenated with OX/OF.to be 1.65 or 1.67 which are excessively higher thanAT_ AT AX(6)OFOX△Fthat of the resin being monitored.where T is the fiber transmission ，F is the ap-The results of theoretic analysis have beenplied force ,and X is the deformation of fiber normal to .verified by the experiment carried out by theco-worker of substituting the resin by the matchingits axis. The ways of elevating the Sensitivity of mi-liquid with similar refractive index ，and thecrobending , or elevating the item of△T/OX , are de-relationship between cutoff frequency of specklecreaseing the value of numerical aperture , decreasingspatial spectrums and the refractive index is fittedthe number of microbend points and increaseing thdisturbing periodicitf9].nearly linear as follow58]:One example of the influences on the total sensi-n2 =- 0.0700ve + 1.6210(5)tivity of the microbend sensor is given by the length ofTherefore , the absulate value of the refractive in-dex of resin matrix can be calculated by processing thethe fiber optic. It has been found that the microbendsensitivity of the sensoroutput data from the fiber ptic.OT(7)中国煤化工1.2FO Microbend Sensor to Measure ThicknessMYHCNMH Gicrobend fiber ,and 0≤Change of the Laminateq≤1. A fiber with a perfectly absorbent jacket wouldIn optical fiber , the intensity of the transmittedhave q= 1 and a sensitiv-light is lost in response to the microbends which are一64一High Technology Letters , Vol.6 ,No.2 , April. 2000ity that depends linearly upon the sensingalso wipped off to strengthen the sensitivity .length 9].The fiber optic with asegment naked core isembed between two bordered plies near the2 The Experiment of Monitoring Cure Pro-middle of the composite laminate with twocess of Compositesends outside of the laminate. The light trans-mits through the optical fiber from one end toThe speckle spectrum fiber optic sensinganother end. The bare segment of the opticalsystems is shown in fig. 2. The diameter offiber surrounded by the resin matrix just likesoptical fiber is chosen to be 50~ 100 μm to en-black painted clad so as to have q≈1 ,whichsure enough modes , the refractive index of the .means highly microbending sensitivity tow ardscore is 1.62. A segment of the fiber ( aboutmonitoring the compression of laminate caused20mm ) whose coat is wipped off acts as sen-by external pressure.sor. The fiber optic including the sensor part isembed between any two bordered plies nearn三三>nthe middle plies with two ends outside of thecomposite laminate acting as the ports byw hich the light transmits through the fiber op-tic.Laser Dideomposite ,CCD Arayn三二>n2IpdFig.3 Intrinsic fiber optic microbend sensor→PCThe polymer coats of two sorts of fiber .Laser Diodecompositeoptic have high capabilities with the materialsand are easy wiped off by chemistry method.Single mode He-Ne laser with high coherenceis used as light source , a CCD camera is usedFig.2 System of FO Speckle Spectrum( SS ) col-to gather speckle distribution and a silicon pho-lection experimenttodiode is used to detect microbend at tenua-The microbend fiber optic sensing systemtion. The datum gathered at any time are au-is shown in fig.3. It has been found that thetomatically imported to the computer and im-microbend sensitivity of telecommunication op-mediately processed by codes , thus the refrac-tical fibers is low for the reason that the anti-tive indexs of the resin and the attenuations ofdamping quality of general fiber optics is em-the transmitted light can be derived in realphasized in order to transmit signals withouttime. The composite laminate containing thelosting. Contrary ,it is demanded that the mi-fiber optic sensor are cured on a hotpress.crobend fiber optic applied in monitoring theThe SSS signal recorded during curing ofcompression process of the laminate should haspure bismaleimide( BMI ) resin and carbonthe performance of making the transmittedfiber reinforced/BMI resin matrix prepreg arelight attenuated in a certain extent. In our ex-show“中国煤化respectly; Tempera-periment，specially manufactured PCS glassture:TYHCNMHGure cycles are alsofiber optic is employed. In order to ensure therature is fluctuateddefinite sensitivity , the selected core radius is .about 59C due to temperature controlled sys-100μm and clad radius is 150μm. The coat oftem .a short segment optical fiber( about 20mm ) is一65一High Technology Letters , Vol.6 ,No.2 , April.2000200of this point and a few neighboring points.| 1.584180M个1.582Then one order derivative is calculated ，asshown in fig. 6. When one order derivative1.578) 1401.576reaches the maximum value , resin has gela-g 121.5741.572”tinized. Cure process is indicated complete1000.568when one order derivative keep fluctuating60|156.566near zero in the post period of cure process.|156220406080100120140160180181.582.ne/min160, 1.58Fig.4 SsS signal monitoring the mould curing withpure BMI- I resin1201.5720上1.568The results of the experiments are dis-30 /1.566cussed as follow. As the reactions have notI0 E/1.5641.582started in the early stage of cure process , theviscosity of resin goes down to the minimumTime/minpoint with temperature rising , thus the refrac-tive index of the resin goes down to the mini-Fig.5 Sss signal monitoring the mould curing withmum point a. After then the refractive indexBMI- I /T300 prepregrising with the rising of the viscosity due to the .0.0018 Estarting of reactions of cross-link in the resin .0.005 tMww| 1.58The gel point b can be determinated in the0.0012curve because the refractive index should rise0.00061.574_sharply near the gelation point. After the gel茗0.0003point the refractive index remains in rising be-0.0003- 1.57cause the types of molecular bonds continuous--0.00060.0000ly change with the developing of cure reac--0.0012tions. The cure rate declines up to 0 when the0.0015 t00120140160180process of cure reaction attains the termina-tion ,thus the varing rate of refractive indexdeclines and the curves of refractive indexFig.6 The processed results of monitored data ofdrive to being constant near the end point ofcure reaction C ,then the end time of cure reac-tion can also be determinated. Fig.4 is theIn order to verify the relability of our ex-monitored results of pure BMI resin and fig.5periment，the experiment results of SSS areis that of carbon fiber reinforced/ BMI resincompared with the results monitored by dielec-matrix composite，but they are much coinci-tric sensor w hose principle is based on the factdent. This situation makes out that the fiberthat the ionic conductivity of resin matrixoptic sensors have the right capabilities withchanges with the viscosity of resin as the pro-the composites in our experiment that can ex-cess of cure reaction and can also monitor theactly measure the parameters of resin matrixmini中国煤化工of resin ,the gela-without being influenced by the reinfoced fibertionof cure processbundles.ThelTYHCNM H Ge monitored resultsIn order to present the variation w ithinof carbon fiber reinforced/ bismaleimide BMI )the cure process more distinctly , every dataresin matrix composite by dielectric sensor ispoint in fig.5 are replaced by the mean valueshown in fig. 7 , which includes the minimum-66-High Technology Letters , Vol.6 ,No.2 , April. 2000point of viscosity ,the gelation point and thecomposite to compact ，thereby compressingend point of cure reaction. We can conclude byhe fiber network , elastic deformation occurscomparing fig.6 with fig.7 that the trends ofin the fiber bundles and part of the applied loadtwo curves of the same kind of composite mon-is carried by the fibers. As a result of this , mi-itored by different sorts of sensor are almostcrobend of the fiber optic can be reinforced bysame. The heating-up rate in fig.7 is less thanthe elastic deformation of the fiber network ,that in fig.6 , thus the cure process shown inthus the power attenuation is enhanced. Thefig. 7 logs behind the cure process shown infinial fiber volume fraction of the composite isfig.6 , Certainly the minimum viscosity time ,determined by the deformation characteristicsgelation time and cure end time in fig.7 log be-of the fiber strcture. W hen the cmposite lami-hind the corresponding points in fig. 6.nate is compacted , the microbend attenuation2.8-200attains maximum without varying. Thus thetime at w hich compaction is achieved should becorrectly judged from the curve of microbendattenuation.It is found by multi experiments that the100measured results will be distinct if the fiber op-7tic is intersected with the fiber boundles of theadjacent plies. The reason of this situation isthat the fiber optic across the fiber bundles of1050the plies can be strongly supported by the fiberTime/minbundles，and thus the microbend is easilyformed. One of the best measured results isshown in fig. 8，the applied pressure isFig.7 Experiment results of dielectric monitoring0.1MPa ; the layup of the plies is 0/0/0/90/cure process of BMI- I /T300 prepreg90/ F0/90/90/0/0/0 ; fiber optic is embed be-tween the two middle plies and is perpendicu-The microbend fiber optic sensor canlared with the fiber bundles of the two adja-monitor the changing process of thickness ofcented plies. Gutowski has found by compua-composite laminate caused by ex ternal pressuretion and ex periment that under the external .when the resin matrix is at the fluidity stage.pressure ,the deformation of fiber bundles of[n terms of the model about resin flowingcomposite is enhanced slowly in the beginningthrough laminates presented by Gutowskt 11 ,but subsequently enhanced fastly11. This reg-The uncured composite with viscous resin ma-ular parten w hould lead the phenomenon thattrix can be modeled as a porous ,nonlinear elas-the microbend attenuation enhances relativelytic media that is filled with a viscous liquid.slowly after initial decreasing process , then en-When pressure is applied , it must be shared byhances fastly ,as shown in fig. 8. When theboth the resin and the fiber structure.composite laminate is nearly compacted ，theIn terms of the experiment results of mi-varing rate of microbend at tenuation declinescrobend of fig. 8. Initially ,as the viscosity isto 0 because of the ending of deformation olowered and the fluidity of resin is enhanced ,fiberTh. the. roints at which thethe force of the plies acting on the fiber optic iscomTYH中国煤化工tarted and complet-weaken. Thus the microbend of fiber opticed cuCNMH Gm fig. 8. The smallshould be weaken , the power attenuation ofpeak value of the curve in the early stage istransmitted lights also be faded. The loss incaused by heat expansion of the plies. the fluc-resin caused by pressure gradient will allow thetuations occured in anaphase are caused by the一67一High Technology Letters , Vol.6 , No.2 , April.2000fluctuation of temperature control system .resin matrix ; The applied pressure can be ad-200justed according to the change rate of thickness180of laminate and the temperature can be sec-.5160ondary elevated on time according to the moni-140tored compaction point of laminate so as to120. 100.5国avoid the resin being excessively lost. M ore-8C+1over , when the end point of cure process is6monitored , the cure operation can be terminat-1.540ed on time so that the cure cycle can be saved .020406080100120140160180If these key operation steps are effectively con-Time/mintroled , the quality of products whould be en-sured and the production costs w hould beFig.8 Experiment results of micobend sensor forsaved , as be expatiated in front.BMI-I/T300 prepregMoreover ,our work lay a foundation forapplying the fiber optic sensors in intelligent3 Conclusiononline system which can real time monitor and .feedback control the curing process of comp0s-Smart materials and structures containingites-12]. Every variables of the composite canfiber optic sensors are rapidly developed andbe gathered by fiber optic sensors every severalhighly regarded in the fields of aircraft , as-seconds and processed by computer ，then thetronayigation etc since these years. Accordingto the latest tendency of smart technologiescorresponding operating orders established ac-cording to the tendencies of variables are feedand structures ，we have systematically ex-plored the technology of monitoring the param-back to the curing system by the intelligent on-eters by using multimode fiber optic ，andline monitoring system. Thus the operationfound that multimode fiber optic sensors can beconditions at every intervals can be automati-applied in monitoring cure process of compos-cally adjusted to make the curing operationite. The apparatus which are employed in ourproceeding along the optimum course.In this paper ,the two sorts of fiber opticexperimenrts are desirable in sensitivity andrealibility , simple in structure and economic insensor are ex perimentized apartly ，but theycan be setted in the same cure system andcost.In this paper , two specially manufacturedmonitor the different variables simulately. Fur-types of fiber optic sensor are presented. Thethermore ,the laser light emited from the lightviscosity process including the nadir of viscosi-source can be split into two beams and be ripty , the gelation point and the end time of cureinto two fiber optics separately without em-process can be monitored by speckle spatialploying two lasers. It is also found that thespectrum( SSs ) fiber optic. The compressionmeasured results have nothing to do with theprocess caused by external pressure ，incudingtransmitted light intensities. therefore it is un-starting point and ending point of compressionnecessary to set reference light to compensateof laminate can be monitored by microbend at-the light fluctuation of the transmitted light.tenuation fiber optic sensor. The monitored re-On the other hand ,the monitoring system em-sults were found to be accurately repetitive byploy1 ov rerimont has the design fea-several exeriments. Therefore，we can deter-tur中国煤化工laser diode is em-minate the time at w hich intermediate constantploydMYHCNMHGparts of gatheringtemperature stage begins and the time atand processing signals can be integrated basedw hich operation pressure is applied accordingon chip microcomputer. The fiber optic linksto the early declining process of viscosity ofat the inlet port and the outlet port of the com--68-High Technology Letters , Vol.6 ,No.2 , April. 2000posite laminate can be realized by connection-sensor and composite cure monitor for smartpeg and pinboard. Thus the total reability ofstructure applications , Smart Sensing. In : Pro-cessing，and Instrumentation II ，James S.the monitoring will be greatly elevated and theSirkis ,ed. SPIE. 1994 ,2191 46investment will be saved .[6] Kai-Yuen Lam , Afromowitz M A. Cure SensorAfter the end of cure , the fiber opticAppl. Opt. , 1995，34 :5635maintains the performance of optical w aveg-[7]RawsonEG,GoodmanJW,NortonRE.J.uide which can be used in sensing vibration ,Opt. Soc. Am. , 1980 , 70 :968stress and fatigue etc during service of compos-[ 8]Zhang N M. High Technology Letters , 1998 ,8ites13]. Therefore , fiber optic sensors have( 10):35multiuses of monitoring the parameters of the[9 ] Tim Clark , Herb Smith. M icrobend fiber opticsensors( Eric Udd ed ). John Wiley & Sons ,composites from producing stage to serviceInc. ,1994 319stage that other sensors can not possess.[ 10 ] Suopajarvi P , et al. Optical Engineering，1995 ,34( 9 ) 2587References[ 1 ] Ciriscioli P R , Springer G S. SmartAutoclave[ 11 ]GutowskiT G , Morigaki T ,Cai A. Journal ofCom posite Materials , 1987 ,21 :172Cure of Composites , Lancaster ,PA : Technom-[ 12]Ciriscioli P R ,George s. Journal of Com positeic Publishing Co , Inc. 1990Materials , 1991 ,25( 10 ):1542[2]Ciriscioli P R , SpringerG s. SAMPE Journal ,[ 13 ]Spillman W B ,Jr. Et. al. Fiber optic vibration .1989 ,25 :35sensors for structural control applications. In :[3 ] Eric Udd. Overview of fiber optic smart struc-Proc. Damping’' 89 Conference , 1989 , Vol.ture for aerospace application. In : Fiber OpticII ICA1- ICA21Smart Strucetures And Skins I , E. Udd ，ed.SPIE.1988 ,986 ,2Li Chensha , born in 1969 , graduated from Xi'. [4] MilkovichS M ,et. al. In Situ Sensors for Intel-an Jiaotong University in 1991. He received his Phligent Process Control for Fabrication of Poly-D. degree from Harbin Institute of Technology inmer- M atrix Composite Materials ，Smart Sens-1999. Now he works as a post-doctor in Tsinghua U-ing. In : Processing , and Instrumentation II ，niversity. His main research interests is smart mate-James S. Sirkis ,ed. SPIE. 1994 ,2191 ,349rial system and structure .[5] May R G ,et. al. Combined fiber optic strain中国煤化工MHCNMHG一69一