Transcription

SAMPE JOURNAL SEPTEMBER/OCTOBER 2020SAMPE Europe 20 Amsterdam.48SAMPE Graphene Leadership Summit.58CAMX 2020 Virtual Event.60PAGE6Adhesives & MaterialBonding PreparationSOCI E T Y FO R TH E A DVA NCE M E NTO F M ATE RI A L A N D PROCE S S E NG I N E E RI NG

TABLE OF CONTENTSSE PTE MBE R/OCTOBE R 2020 Vol. 56, No. 5 www.sampe.orgDEPARTMENTS NEWS522Welcome to SAMPE!Our New CEO-Zane Clark3 Technical Director’sCorner46SAMPE 2021 Long BeachCall for Abstracts48SAMPE Conference 20AmsterdamPAGE506Composite Bonded JointsUpdate Your Profile Today!5216OPTIMUM NUTPLATE26AUTOMOTIVE ENGINEERING34PERFORMANCEWITH PLASMAREPAIRPlasma SurfacePreparation forOptimum NutplatePerformanceTowards a New Era inAutomotive Engineeringwith PlasmaBonded StructuralRepair of Carbon FiberBicycle FramesIndustry Announcements54 Welcome SAMPE NewMembersInterlocking Fiber Configuration Effect on Mode-IDisbond Arresting in Composite Bonded JointsFEATURESAttention SAMPE Members58SAMPE GrapheneLeadership Summit59Team SAMPE60CAMX 2020 Orlando, FL64CAMX 2020 Orlando, FLVirtual Exhibitor ListingsBONDED STRUCTURAL68Advertiser Index69Resource Center72SAMPE Virtual EventsCalendarJOURNAL ASPECTS: The subject of “adhesives and material bonding preparation” various materials together so that they maintain structural adequacyover time and load history, depends upon many factors as well as applications. The cover photo, courtesy of Masterbond, Inc. demonstrates that even smallelectrical components require specialty encapsulant adhesives to protect electrical components. Composites involve fibers and resins within laminatedstructures. Consequently, composite joint bonds often require designs that will arrest, or stop, any crack growth. The team from the University of Tokyo,JAXA and JSTB developed a unique process for controlling such adhesive areas where a crack might develop. Cleaning surfaces of planned adhesivebonded regions is a critical aspect and Surfx Technologies LLC has developed such methods for aerospace “nutplates” which are commonly used. Plasmatreating has also become quite popular as shown in the photo cleaning an automotive composite structure (courtesy Plasmatreet GmbH’s applicationarticle). Repairs -- for the most part, if a structural composite is damaged to the extent repair is possible, adhesive bonding often is used to effect near100% recovery to initial capability. Carbon fiber composite bicycles often undergo some damage during their history -- and a graduate student at PennState (PSU) has demonstrated adhesive bonded repairs to a composite frame.w w w. s a m p e . o r gS E P T E M B E R /O C TO B E R 2 0 2 0 SAMPE JOURNAL 1

FEATUREOptimum Nutplate PerformancePlasma Surface Preparation forOptimum Nutplate PerformanceThomas S. Williams, Graham Ray, Demetrious L. Lloyd and Robert F. HicksSurfx Technologies, LLC, Redondo Beach, CAABSTRACTNutplates are commonly used on aircraft to allow installation and removal of components and panels for maintenance and repair. The use of bonded nutplates overriveted ones reduces manufacturing complexity and leads to weight savings. In this work,plasma surface preparation has been examined for bonding stainless steel nutplates toaluminum structures. Preparation of these bond surfaces is often accomplished throughan abrasion process or using only a solvent wipe. These methods are difficult to controland can lead to variation in the performance of bonded nutplates. Successful installation of bonded nutplates requires the generation of a highly clean and active bondingsurface. A small, portable plasma device was used to clean individual nutplates withina few seconds. In addition, a handheld plasma tool was used to prepare the nutplateinstallation site. The plasma process eliminates operator variability by removing surfacecontaminants in a matter of seconds with no other cleaning steps required. The bondsurface is rendered active for bonding and converted to a high surface energy, hydrophilic state. This new technology eliminates interfacial bond failures while increasing pushoff strength from 441 34 lbs to 845 74 lbs and torque-out strength from 100 18 in·lbs to159 27 in·lbs when compared with abrasion. Furthermore, the plasma has been shown toreduce preparation time, decrease variability and lower the instances of nutplate failuresboth in manufacturing and in the aircraft service environment. Transitioning to a plasma-based surface preparation thereby offers the potential to save millions of dollars overthe life cycle of an aircraft.16 SAMPE JOURNAL S E P T E M B E R /O C TO B E R 2 0 2 0w w w. s a m p e . o r g

INTRODUCTIONBonded fasteners, such as nutplates, are used extensively in aerospace manufacturing. Nutplatesare bonded to an aircraft structure and receive bolttype fasteners to hold removable components onthe aircraft. Significant effort has been expendedin recent years to understand the surface preparation mechanisms and bonding properties of thesenutplate assemblies. Throughout the industry, failures of bonded nutplates have been reported as asignificant source of unscheduled maintenance onmodern aircraft1-3. Subsequent failure analysis indicated that surface preparation is a critical factorin the performance of bonded nutplates.Although bonded nutplates eliminate the needto drill extra rivet holes, the typical surface preparation processes used prior to installation are stillsomewhat labor intensive. Prior to applying adhesive to the nutplates, they must be cleaned. Thisoften involves the use of solvent wiping, sandingor even grit blasting. The structural component towhich the fastener is bonded can consist of a variety of materials including thermoset and thermoplastic composites along with a variety of differentmetals. These structural elements must also beprepped prior to installation of the fastener. One ofthe most common surface preparation methods ishand sanding. This process is subject to operatorvariability, which can lead to improperly preparedsurfaces with weak bonds that fail after installation and result in time consuming and expensiverepairs.Among alternative surface preparation techniques, atmospheric pressure plasma has beenshown to be an effective method for forming strongadhesive bonds between a wide variety of dissimilar adherend materials4-12. Plasma treatment canreduce the water contact angle of metal and composite surfaces below 20o, yielding a high energysurface which is ideal for bonding. Plasma activation was explored as a method for surface pretreatment prior to the installation of adhesively bondednutplates on BMI and epoxy composite substratesusing CB301 and CB200 adhesive9,10. Plasma activation of the BMI substrates showed a numberof beneficial results when compared to surfacepreparation by solvent wiping and abrasion. Plasma activation of the BMI was shown to drive bondfailure away from the interface and to increasethe strength of the BMI-nutplate bond. Plasmatreatment increased mechanical loads by 25% forpush-off and 23% for torque-out tests on average6.ADVANCED NONWOVENS FORCOMPOSITESFROM TECHNICAL FIBRE PRODUCTS INC.MULTIPLE BENEFITS FROM USING A SINGLE MATERIAL!HIGH QUALITY SURFACE FINISHELECTRICAL CONDUCTIVITYADHESIVE CARRIERFRACTURE TOUGHNESS IMPROVEMENTRESIN FLOW MEDIAEMI SHIELDINGFIRE PROTECTIONABRASION RESISTANCECORROSION [email protected] 1 518 280 8500 TFP IS A JAMES CROPPER COMPANYSAMPE Journal Print Ad - 2019.indd 3w w w. s a m p e . o r g11/02/2019 10:06S E P T E M B E R /O C TO B E R 2 0 2 0 SAMPE JOURNAL 17

FEATURE / OPTIMUM NUTPL ATE PERFORMANCESimilar results have been observed on other substrate materials including bare metal, anodizedand primed aluminum 70758.Through this work, it has been observed thatproper preparation of the nutplate surface is essential for achieving strong, reliable bonded nutplates.Analysis of the specimens after mechanical testingindicated that the nutplate interface is often theweak link of the bonded assembly. Consequently,there has been a need to develop an alternativenutplate surface preparation technique. Preparation of the nutplate via solvent wiping consistently resulted in interfacial bond failures when usingCB301 adhesive6,7. While grit blasting was capableof producing strong bonded nutplates, this method is time consuming and impractical in most nutplate installation settings. Meanwhile, plasma wasshown to rapidly produce strong bonded nutplatesand to eliminate the occurrence of interfacial failures at the nutplate surface.In order to improve on the drawbacks that areinherent in manual abrasive preparation methods,Surfx Technologies has produced two purpose-builtplasma devices for optimal surface preparation ofthe nutplate and structure. In order to establish adependable, high quality bond, a portable plasmadevice has been developed that cleans a nutplateseconds. Used in concert with a handheld plasmasource for the substrate, a fast and reliable surfacepreparation technique is realized for installingbonded fasteners on aerospace structures.Additional work was needed to expand thescope of these previous studies by exploring additional substrates and adhesives as well as optimizing the plasma process conditions. This workcontinues the examination of atmospheric plasmacleaning and activation for bonded nutplate installation. The novel plasma devices have been usedto demonstrate this plasma technique as a replacement for abrasion processes. The plasma processcan also be tailored to any specific combinationof adhesive, fastener type and substrate material.Below, results are presented for the surface preparation of unprimed, stainless steel nutplates andaluminum substrate coupons using atmosphericpressure plasma.EXPERIMENTAL METHODSMaterialsDome-style (CB6010 CR3) and open-end style(CB6003 CR4) nutplates were used along withCB301 epoxy adhesive from Click Bond, Inc. andEpibond 1544-1 epoxy adhesive from Huntsman.Aluminum sheets made from alloys 7075, 6061and 2024 were used for substrate materials. Thesubstrate materials were machined into 2” x 8”coupons. A schematic of the test coupon with thelocations of the five holes is shown in Figure 1. Fiveequidistant holes were drilled into the center of therectangular coupon.Solvent WipingSubstrate surfaces were cleaned with Dysol DS-108solvent or isopropyl alcohol (IPA) using DuPontSontara lint-free cloth wipes. This process consisted of three steps: a one directional dry wipe, a onedirectional wipe with the cloth saturated with thesolvent, and a final one directional dry wipe.Grit BlastingPrior to bonding, one subset of the nutplates andsubstrate coupons were grit blasted using a King#4004-0 grit blasting cabinet. Grit blasting was performed using fresh Elfusa ALR 240 grit aluminumoxide media with an air compressor regulated to 80lbs. of pressure. Each item was grit blasted with thegun nozzle kept between 45 and 90 degrees to thebonding surface. An approximate distance of 10 cmwas maintained between the nozzle and the surface. Samples were abraded until a matte finish wasFigure 1. Schematic of nutplate test coupon with dimensions.18 SAMPE JOURNAL S E P T E M B E R /O C TO B E R 2 0 2 0w w w. s a m p e . o r g

achieved. Residual debris was removed with clean,dry air. Grit blasted parts were finally wiped withlint-free towels soaked in DS-108 prior to bonding.The surface was solvent cleaned until no residuecame off the surface, and finally dry wiped with aclean cloth.Plasma Surface ActivationA Surfx Technologies Atomflo plasma controller was used for the preparation of both thesubstrate and the nutplate surfaces. The Atomfloactively controls and monitors all plasma processconditions and logs this information for futurereference. Plasma activation of the nutplates wasachieved using the Nutplate Plasma Cleaner , orNPC. The NPC, also developed by Surfx, is a surfacepreparation tool specifically designed for nutplatesand other bonded fasteners. An image of this tool isprovided in Figure 2. Industrial grade helium andoxygen were fed into the NPC at 30 liters per minute (LPM) and 0.2 LPM, respectively. The plasmawas ignited using 80 W of RF power at 27.12 MHz.Unless stated otherwise, the nutplate was insertedinto the NPC for 5 seconds and then removed.Figure 3 shows an image of the NPC in use. Thenutplate is seated into the NPC and a plasma discharge is generated beneath the bonding surface.Reactive species from the plasma rapidly removesurface contaminants leaving behind a clean andactive surface. The high surface energy impartedby the plasma cleaning process is ideal for adhesivebonding applications. The NPC can be configuredto treat any size and style of fastener.Plasma activation of the substrate coupons wasachieved with the Surfx Aircraft Plasma Cleaner ,or APC. The APC features a hexagonal, showerheadplasma source affixed to a flexible handle. An imagew w w. s a m p e . o r gFigure 2. Surfx Nutplate PlasmaCleaner with nutplate inserted.Figure 3. Nutplate Plasma Cleaner cleaning a nutplate and exhibiting bluelight from the plasma glow.S E P T E M B E R /O C TO B E R 2 0 2 0 SAMPE JOURNAL 19

FEATURE / OPTIMUM NUTPL ATE PERFORMANCEFigure 4. Aircraft Plasma Cleaner with 1” wide hexagonal showerhead plasma source.of this device is presented in Figure 4. The handlecontains integrated timer and status lights to assistthe user by presenting all system information necessary to operate the tool. A built-in timer functionallows the user to initiate a 5 second blinking light.The width of the hexagonal showerhead pattern is1”. Standoff pins around the plasma head maintaina 2 mm distance when the APC is pressed against thematerial being activated. The plasma was operatedat 165 W of RF power using 30 LPM of helium and0.58 LPM of oxygen. To prepare the material surface,plasma is generated inside the source and the reactive gasses flow out onto the substrate below. Theshowerhead end of the device was placed directlyonto the substrate and centered around the nutplateinstallation hole. The plasma was kept over each installation site for a period of 5 seconds.Hand AbrasionA subset of the nutplates and structure couponswere prepared using manual abrasion. Abrasion ofthe substrates was achieved using Scotch-Brite 7447 pads. Prior to abrasion, the solvent wipingstep was performed, and the surface was abradedby hand until a matte finish was visible. Followingabrasion, another solvent wipe step was performedand repeated until no residue was observed on thewipe. It was then given a final dry wipe.Bond ProcedureAll samples were bonded within 20 minutes of thesurface activation processes. A set of at least fivebonded nutplates was produced for each test. Adhesive was applied to the nutplates in a single beadaround the elastic fixture of the nutplate. The fixture was then pulled through the installation holein the structure coupon until the nutplate sat firmlyagainst the surface with a visible bead of adhesivearound the edges. Coupons were then allowed tocure for a minimum of 72 hours before testing.Water Contact AngleWater contact angle (WCA) of the test couponswas measured using a Surface Analyst (modelSA3001) manufactured by BTG Labs. The WCA of20 SAMPE JOURNAL the nutplates before and after surface treatmentwas obtained using a Krüss DSA15B EasyDrop digital goniometer with DSA3 software package.Push-Off TestingPush-off testing followed the requirements ofNASM 25027 (reference para. 4.5.3.5)13. Mechanicalpush testing was performed on an Instron (model 3369). A custom push off tool sized for the nutelement of the nutplate was attached to a 50 kNload cell. It was lowered into the nutplate until itengaged the nut. Load was applied at a rate of 0.05inches per minute until failure occurred.Torque Out TestingTorque out testing followed the requirements ofNASM 25027 (reference para. 4.5.3.4)13. The substrates were placed into a test fixture which consisted of a channel to hold the test coupons andfixturing for mounting a 0-100 ft·lb torque wrenchwith memory needle made by CDI (model 1003LDFNSS). The torque wrench was attached to an extractor tool which allowed it to engage with thenut element to perform the toque-out test. Priorto testing, the torque wrench memory needle wasset to zero, and then torque was applied to the nutplate until the joint failed.Failure Mode AnalysisFollowing mechanical testing, the failure modeof the disbanded assembly was analyzed. Imageswere taken of the bond region for each substrateand nutplate. Four different failure modes wereidentified: interfacial/adhesive failure at the substrate, interfacial/adhesive failure at the nutplate,cohesive failure within the adhesive and mechanical failure of the nutplate. Images of each substratewere processed through an internally developedcomputer algorithm, which overlaid the variousfailure modes as different colored pixels on theoriginal image. These results were visually checkedagainst the substrate and nutplate to confirm accuracy. Finally, the number of pixels of a given colorwas compiled and divided by the total number ofpixels to yield the percentage of each failure mode.S E P T E M B E R /O C TO B E R 2 0 2 0w w w. s a m p e . o r g

RESULTS AND DISCUSSIONWater Contact AngleWater contact angle measurements as a function ofthe nutplate surface preparation are summarizedbelow in Table 16,7. The nutplates with no surfacepreparation exhibited a WCA of 139 2 . This is avery large contact angle that suggests the surfaceof the nutplate is contaminated during storage resulting in a non-wetting and extremely hydrophobic surface. A solvent wipe of the nutplate surfaceresults in a contact angle which is still hydrophobic. Plasma activation of the nutplate produces ahydrophilic surface by decreasing the WCA from114 2 after DS-108 wiping to less than 5 afterplasma activation. The nutplates which were activated by the NPC exhibit super hydrophilic wettingbehavior which is also significantly lower than gritblasting which yielded a 33 3 WCA.Figure 5 shows images taken from the Krüssgoniometer of water droplets on the stainless steelnutplates. The droplet on the left of Figure 5 wasmeasured after solvent wiping with DS-108 and thedroplet in the image on the right was after cleaningwith the Nutplate Plasma Cleaner. The water droplet is observed to bead up on the solvent wipedsample. The water exhibits a very large contactangle that indicates a non-wetting, hydrophobicsurface. This is in stark contrast to the behavior ofthe nutplate after cleaning and activation with theNPC. The water droplet spreads out on this surfacedue to the strong attractive forces between the water and the nutplate surface. This is indicative ofcomplete wetting and is a necessary condition forproducing a strong adhesive bond.The Aircraft Plasma Cleaner (APC) has beendemonstrated to activate a wide variety of thematerials that are typically used as the structuralcomponents for nutplate assemblies. This includesmultiple composite resin systems and aluminum70758-10. Data gathered previously using 7075 aluminum8 is presented alongside data for aluminumalloys 6061 and 2024. The effects of plasma surfacepreparation compared to hand abrasion and solvent wiping are summarized in Table 2. The watercontact angle on the bare aluminum 7075 was reduced from 71 7 to 45 4 following surface abrasion. The contact angle was improved by a 5 secondexposure to the APC in lieu of the abrasion process.This yielded a wetting angle of 10 1 . Anodizedaluminum 7075 had its WCA reduced from 55 4 to 42 1 following surface abrasion compared to25 1 after plasma treatment. It should be notedthat the abrasion process has a damaging effecton the anodization layer which is removed duringsurface preparation. Meanwhile, cleaning and activation with the APC uses a non-ablative processwhich leaves the anodization intact. For the 6061w w w. s a m p e . o r gNutplate Prep