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DEPARTMENT OF DEFENCE"! llQTflDEFENCE SCIENCE & TECHNOLOGY ORGANISATION I !! # I VFlow Testing of Cytec FM300 andFM300-2K Structural AdhesivesRoger Vodicka/DSTO-TN-0383,-"DISTRIBUTION STATEMENT A:Approved for Public Release Distribution Unlimited20010927 109
Flow Testing of Cytec FM300 and FM300-2KStructural AdhesivesRoger VodickaAirframes and Engines DivisionAeronautical and Maritime Research LaboratoryDSTO-TN-0383ABSTRACTThe flow of Cytec FM300 and FM300-2K structural film adhesives was examined usingflow tests employing an autoclave or by using dead-weights to apply pressure. Theeffect of ageing the adhesive at room-temperature was examined for periods of up to60 days. FM300 adhesive was found to show rninimal changes in flow and it wasdifficult to determine the adhesive age from the flow test results. The effects of ageingon FM300 are most likely to appear in the results of mechanical tests such as the shortoverlap shear test. FM300-2K showed a more consistent change in flow with age. Theflow of FM300-2K changed markedly over the ageing period (about 30-40% change inarea flow) and decreased in an almost linear fashion with age. This makes it viable todetermine the effects of ageing on FM300-2K based on the results of flow tests. Bothtypes of pressure application (autoclave and dead-weights) are suitable for flow testingand offer key advantages and disadvantages. If an autoclave is available it is preferableto perform flow tests at 100 kPa.RELEASE LIMITATIONApproved for public release'DEPARTMENT OF DEFENCEDEFENCE SCIENCE J TECHNOLOGY ORGANISATIONDSTOAQfoi- iz-di oö
Published byDSTO Aeronautical and Maritime Research Laboratory506 Lorimer StFishermans Bend Vic 3207 AustraliaTelephone: (03) 9626 7000Fax: (03)9626 7999 Commonwealth of Australia 2001AR-011-946July, 2001APPROVED FOR PUBLIC RELEASE
Flow Testing of Cytec FM300 and FM300-2KStructural AdhesivesExecutive SummaryEpoxy film adhesives are used throughout the F/A-18 aircraft for adhesive bonding ofhoneycomb sandwich structures and other components. These film adhesives givehigh temperature properties and are typically cured at 120 C or 177 C.Two commonly used film adhesives are Cytec FM300 and FM300-2. Cytec FM300 wasused in the original manufacture of most of the bonded F/A-18 components includingthe rudder and horizontal stabilator. FM300-2 is now used as a lower-temperaturecuring alternative to FM300 for certain repair operations.The storage of film adhesives at -18 C is required, as any exposure to elevatedtemperatures will advance the cure state of the adhesive. An advanced state of curemakes the adhesive difficult to process as it will be less inclined to flow and 'wet out'the bonding surfaces. This can cause reductions in mechanical properties such as shearstrength. Material which has been stored for some time may need to be tested to ensurethat it is still within life. The use of adhesive flow tests can form part of a suitableacceptance criteria for film adhesives. A flow test examines the amount of adhesiveflow which occurs for a given processing pressure under a given temperature curecycle.This work examines the different types of flow tests that are available and examinesthe changes in flow of Cytec FM300 and FM300-2K when exposed to periods of roomtemperature for up to 60 days. FM300 adhesive was found to show minimal changes inflow and it was difficult to determine the adhesive age from the flow test results. Theeffects of ageing FM300 for up to sixty days on mechanical properties would need to bedetermined before the material could be re-qualified for use. FM300-2K showed a moreconsistent change in flow with age making it viable to determine the effects of ageingon FM300-2K based on the results of flow tests.The costs and logistics of storing film adhesives for use in repair operations are highand significant cost savings are possible if the film adhesives can be effectively usedbeyond the manufacturer's stated shelf life. This report has identified some importantissues associated with the re-lifing of two of the main film adhesives used by theRAAF.
AuthorR. VodickaAirframes and Engines DivisionRoger Vodicka graduated BSc. (Hons.) from Monash Universityand joined AMRL in 1990. He has previously worked on a rangeof projects at AMRL including adhesively bonded composite repairtechnology, battle damage repair methods, effects of environmenton the durability of composite materials as well as the durability ofhoneycomb sandwich structures. He is currently the task managerfor the Composite Repair and Engineering Development Program(CREDP).
Contents1. INTRODUCTION12. MATERIALS USED2.1 Adhesive Cure and Processing223. ADHESIVE AGEING24. FLOW TEST TECHNIQUES4.1 Autoclave Based Flow Test4.2 Dead weight flow method4.3 Measuring Flow4.3.1 Flow Change by Weight4.3.2 Flow by Change of Area3345555. RESULTS5.1 FM300 Autoclave Cure5.2 FM300 Dead Weight Cure5.3 Autoclave Cure FM300-2K5.4 FM300-2K Dead Weight Cure557896. DISCUSSION107. CONCLUSIONS128. RECOMMENDATIONS129. ACKNOWLEDGMENTS1310. REFERENCES13APPENDIX A:15FLOW TEST PREPARATION PROCEDURE
DSTO-TN-03831. IntroductionStructural film adhesives are used extensively in the aerospace industry for adhesivebonding of both metallic and composite materials. They are convenient and practicalto use since they allow the adhesive to be used in the form of a sheet rather than aviscous liquid allowing easier manufacture and control of the amount of material used.Epoxy film adhesives are used throughout the F/A-18 aircraft for adhesive bonding ofhoneycomb sandwich structures, metal to metal bonding and metal to compositebonding. These film adhesives give high temperature properties and are typicallycuredatl20oCorl77 CTwo commonly used film adhesives are Cytec FM300 and FM300-2K. Cytec FM300 wasused in the original manufacture of most of the bonded F/A-18 components includingthe rudder and horizontal stabilator. Cytec FM300-2K is a lower-temperature curingadhesive and has been approved as a substitute for FM300 when used for structuralrepairs to some honeycomb components, providing revised repair guidelines are used(ie: the Boeing Bonded Joint Analysis Methodology BJAM). The lower temperaturecure of FM300-2K (120 C) is an advantage during repair of honeycomb sandwichstructure as it reduces the risk of boiling any water that may be present within thehoneycomb. High pressures can arise from steam at high temperatures and this cancause the failure of a component due to the bonded skin separating from thehoneycomb core or the core itself can be damaged.The storage of film adhesives at -18 C is required, as any exposure to temperature willadvance the cure state of the adhesive. The epoxy adhesive undergoes an irreversiblechemical reaction (ie: curing). An advanced state of cure makes the adhesive difficult toprocess, as it will be less inclined to flow and 'wet out' the bonding surfaces. This canalso cause reductions in strength properties such as shear strength. Cytec FM300-2Kwill remain in useful life for up to one year at -18 C according to manufacturer'srecommendations. FM300 has a shelf life of 6 months at -18 C. If the temperature ofstorage increases, the effective 'life' of the material will be reduced. FM300 can remainin life for up to 30 days when stored at 21 C. FM300-2K can remain in life for up to 10days at 24 C. It is therefore vital to ensure that any adhesive used for aircraft repairand manufacture is within shelf life.Material that has been stored for some time may need to be tested to ensure that it issuitable for use on aircraft. Material which is outside of the manufacturers stated shelflife can be re-qualified for further use provided certain acceptance tests are passed.Such testing may include the use of flow tests or mechanical tests such as the shortoverlap shear strength test. RAAF Standard (ENG) A5007 describes the standards thatshould be used when film adhesives are received, stored and used. The use of adhesiveflow tests is listed as one of the acceptance tests required to re-qualify film adhesives. Aflow test examines the amount of adhesive flow which occurs for a" given processingpressure under a given temperature cure cycle.This work examines the different types of flow tests that are available and examines thechanges in flow of Cytec FM300 and FM300-2K when exposed to room temperature forperiods of up to 60 days.
DSTO-TN-03832. Materials UsedTwo types of epoxy film adhesive used for F/A-18 manufacture and repair areexamined in this study. Both are manufactured by Cytec-Fiberite in the U.S.A. Thematerial batches used in the study are shown in Table 1.Table 1 Details of film adhesives used for flow testingNameAreal WeightDate ofManufactureProduct # - Batch Roll/Can/Sheet(lbs/ft*)FM3002-K0.1025th January 4169-00531-000041999FM3000.1020* July 19994279-01042-00009B2.1 Adhesive Cure and ProcessingThe cure cycles for both adhesive materials employ a ramp to the cure temperature at3 C per minute followed by a dwell at the cure temperature. In all cases in this study itwas only necessary to cure the adhesive to the gel stage (ie: where no further flowoccurs). FM300 was cured for 30 minutes at 177 C while FM300-2K was cured at 120 Cfor 30 minutes.The cure pressure is another important aspect of adhesive processing. It ensures thatthe adhesive flows and is compacted to the desired bondline thickness. Bondlinethickness is often controlled using a scrim cloth. A scrim cloth is typically a wovennylon fabric weave placed within the film adhesive at time of adhesive manufacture.The 'K' suffix denotes a knit weave for the scrim fabric. A mat scrim cloth is denoted'M'. Adhesives can also be supplied without a scrim cloth (unsupported) and have a'U' suffix. The scrim cloth will affect the result of any flow test so it is vital to ensurethat flow tests are compared for the same resin system, identical scrim cloth as well asthe same test procedure and cure conditions. Pressure can be applied in a number ofways depending on the process. This includes using an autoclave, mechanical press orthe use of dead weights. The last method is unlikely to be used in the manufacture orrepair of aerospace parts.3. Adhesive AgeingBoth adhesive systems were aged by exposing them in the laboratory environment forperiods of between zero and sixty days. A baseline test using fresh materialrepresented zero days of exposure. Laboratory air temperature was approximately
DSTO-TN-038321 C. Adhesive discs were aged inside sealed aluminium coated plastic bags to preventcontamination and moisture uptake.A period of sixty days was chosen since this is the maximum amount of time that theadhesives are likely to be re-qualified. Some practices allow a material to be requalified for another 50% of its original shelf life. For FM300 this represents thematerial being re-qualified more than twice. For FM300-2K the sixty day periodrepresents a large period in excess of its original shelf life (ie: ten days).4. Flow Test TechniquesThe flow test technique used here is based on the Boeing Support Standard BSS 7240'Adhesive Flow Test' that is recommended by CytecFiberite [1]. The standard requiresthe use of a 1.5" (38 mm) diameter disc of material placed between mylar separatorfilm which is then cured according to the manufacturer's recommendation. The flowwas then measured by calculating the increase in adhesive area. This was done bycomparing the adhesive flow with a simple series of concentric circles that mark therelevant flow levels.The technique used in this study is a slightly modified version of the Boeing standard(See Appendix A). Teflon coated fibreglass was used as the separator film and a 32mmdiameter adhesive sample was cut out for the test using a hole punch. Care was takento ensure that the adhesive was cut cleanly. Samples were placed under pressure usingeither an autoclave or by placing dead-weights on the material discs. They were thencured using the cure cycles defined in Section 2.1.4.1 Autoclave Based Flow TestTwo autoclave pressures were used, 100 kPa and 280 kPa (280 kPa is recommended bythe manufacturer). It was found that 6 discs of material could easily be cured on asingle aluminium plate. This made it easy to perform a number of replicates at thesame time. The test setup is illustrated in Figure 1. The whole setup was covered invacuum bagging material before processing as per standard autoclave curing practice.
-TN-0383Breather material/WWMttMMffl, v .v .V:V V TeflonCoatedGlassi"-—. 6mmMachinedAluminiumSheetitw- -»132mm DiameterFilm Adhesive1 Aluminiumopiate-izure 1 Test setuv for autoclave-llased adhesive flow test.4.2 Dead weight flow methodAnother technique was also trialed which did not require the use of an autoclave or amechanical press. In this technique pressure to the disc of adhesive was applied using adead weight. Heat was then applied as per the manufacturer's recommend cure cycleusing a heater blanket. Heater blankets are typically used by the RAAF for adhesivelybonded repairs and are generally more available and less expensive than an autoclaveor mechanical press. As per the method above, a 32mm diameter disc of material wasused and placed between teflon coated fibreglass. In this study two dead weights wereused to simulate pressures of 100 kPa(8.35 kg dead weight) and 280 kPa (22.27 kg deadweight). The test setup is illustrated in Figure 2.Honeycomb core 37mm m DiameterFilm AdhesiveHeater BlanketFigure 2 Test setup for dead-weight adhesive flow testAluminium /plate
DSTO-TN-0383Temperature was applied using a heater blanket and controlled using a MACBONDER[2] temperature controller. A thermocouple was placed on the 6mm thick aluminiumsheet directly above the adhesive disc. A piece of honeycomb core was used tothermally insulate the large dead weight from the test area4.3 Measuring FlowThere are a number of ways to measure the resulting flow after the adhesive has beenprocessed. These include flow change by weight and change by area.4.3.1 Flow Change by WeightIn this measurement method the sample disc is weighed prior to testing on a fourfigure balance. After processing the cured disc is cut using the same size hole punch asfor the original disc (ie: 32mm) and this cut-out is then weighed. The cut-out sectionmust include the entire scrim cloth. The flow is then a percentage of the original weight„, „,, Mass of flow cutout. *, nnie: %flow (lr-r—)*100.original mass4.3.2 Flow by Change of AreaThe change in area after the material is cured can be calculated using a number ofmethods. The Boeing Support Standard BSS 7240 'Adhesive Flow Test' uses a series ofconcentric circles over which the adhesive disc is placed. The circles then indicate thepercentage flow.Another way is to measure the average diameter of the disc before and after processing, „Final Flow Area *,. Aand express the flow as:;—* 1UU.Ongmal AreaIn this study an average flow area was calculated by measuring the flow disc diameterat four points. In most cases the flow disc was roughly circular and a good estimate ofarea could be gained using this technique.5. ResultsResults are shown for both processing techniques (autoclave and dead weight) and forboth methods of calculating the flow (weight and area). The results are plotted againstthe ageing period of the adhesive at room temperature. Tests were conducted duringthe period December 1999 and March 2000.5.1 FM300 Autoclave CureFigure 3 shows the flow test results for cure of FM300 in the autoclave at 100 kPa.Measurements of both area and weight were taken and are plotted on alternate y-axes.
DSTO-TN-0383The change in flow over the ageing period is very low and there are some large errorbars which make it difficult to assess any changes due to ageing.77.2700Weight flow — Area flowA—77.076.869076.668076.467076.2 H 660 T1650 1020:405060Time (days)Figure 3 Flow test result for 100 kPa autoclave cure ofFM300.Figure 4 shows the flow test results for autoclave cure at 280 kPa. The flow by weightsees an increase after 30 days while the flow area peaks around the 20 to 30 day times.There is also less correlation between the weight and flow area measurement whencompared to all the other results. Again the change in flow is very small over theageing period and the sizes of the error bars make it difficult to assess actual flowchanges.79.5-Area flow980-A— Weight flow79.0-96078.5-940 gS 920 303T]900 Qg 78.0CO"Ö 77.5-88077.086084076.02030 rsoTime (days).Figure 4 Flow test result for 280 kPa autoclave cure ofFM300.82060
DSTO-TN-03835.2 FM300 Dead Weight Cure63-310 A— Weight flow62-Area flow30061 - 29060'280j 59'O 3270 a 2!o260 .2 57 D5 56.250 S55'24054.230S352-—r -r-—T-1020305040-160220Time (days)Figure 5 Flow test result for 100 kPa dead-weight cure ofFM300.Figure 5 shows the flow test result for the dead-weight cure of FM300 at 100 kPa. Theflow sees an initial rise after 10 days followed by a marked decrease after 60 days. Thelevel of flow is also much less than that seen when using an autoclave for the samegiven pressure.65330- Weight flow- Area flow64-32063 310 5 62300Ol 61290vg 602805927058—r—10—r20—r 3040—r—50Time (days)Figure 6 Flow test result for 280kPa dead-weight cure ofFM300.60 a cu
DSTO-TN-0383Figure 6 shows the flow test result for the dead-weight cure of FM300 at 280kPa. Theresults show an increase in flow after 10 days. After 20 days the flow is back to thesame level as zero days of ageing. Small decreases are then noted when ageingcontinued to 60 days. The change in flow over the ageing period is small and the size ofthe error bars makes it difficult to detect the age of the material by its flow.5.3 Autoclave Cure FM300-2K84-i—A— Weight flow— —Area flow8310008290081 80 79''ÖS78-o800*o700 *6007675-50074203050Time (days)Figure 7 Flow test result for 10 OkPa autoclave cure ofFM300-2KFigure 7 shows the results of flow tests for the lOOkPa autoclave cure of FM300-2K. Theflow sees a steady, almost linear, decline in flow over the entire ageing period. Themagnitude of the change in flow is significantly greater over the ageing periodcompared to FM300.
DSTO-TN-038385'1300*— Weight flow — Area flow84 120083'5o1100 vS821000 *5 eno 900 0Time (days)Figure 8 Flow test result for 280 kPa autoclave cure ofFM300-2KFigure 8 shows the results of flow tests for FM300-2K cured in the autoclave at 280 kPa.For the first 10 days the flow is essentially unchanged. After this the flow sees a lineardecline in flow up to the 60 days of ageing investigated.5.4 FM300-2K Dead Weight CureTime (days)Figure 9 Flow test result for 100 kPa dead-weight cure ofFM300-2K
DSTO-TN-0383Figure 9 shows the results of flow tests for the 100 kPa dead-weight cure of FM300-2K.The flow is unchanged after 10 days and then sees a linear decline until 60 days. j 360—*— Weight flow— — Area flow- 35034033032064310 !626300 CDs290 M-Tl280 Ö270 *s 58-I 60Time (days)Figure 10 Flow test result for 280kPa dead-weight cure ofFM300-2K.Figure 10 shows the results of flow tests for the dead-weight cure of FM300-2K at280 kPa. The flow is unchanged after five days but then sees a linear decline for ageingperiods up to the 60 days investigated.6. DiscussionThe results shows that the difference in measuring the flow using area or weight doesnot seem to have a great bearing on the outcome of the results. The area can be difficultto measure if the flow is not perfectly circular. The weight can also be difficult tomeasure if the cured adhesive fractures when the hole punch is used to cut thematerial. The exception to this was the result of curing FM300 at 280 kPa in anautoclave. It is not known why these results are inconsistent.The results for FM300 suggest that the flow can increase for ageing
The flow of Cytec FM300 and FM300-2K structural film adhesives was examined using flow tests employing an autoclave or by using dead-weights to apply pressure. The effect of ageing the adhesive at room-temperature was examined for periods of up to 60 days. FM300 adhes
