the effect of different surface treatments of...

QUARTERLYISSN 1232-9312 1/2018(108)

Journal of MachineC o n s t r u c t i o n and Maintenance

p. 83–89

Mariusz KŁONICALublin University of Technology, PolandDepartment of Production Engineering [email protected]

ThE EFFECT OF DIFFERENT SURFACE TREATMENTS OF 316l STEEl ON ADhESIVE JOINT STRENGTh

Key words: surface layer, surface roughness, 316L steel, adhesive joint.

Abstract: The present paper examines selected strength test results of adhesive joints of 316L steel after different types of surface treatment. The analysis focuses on the effect of surface layer treatment on the value of selected 2D and 3D surface roughness parameters with regards to adhesive joint strength. In addition, the Abbott-Firestone curve (bearing area curve) is examined in order to provide information on the state of the surface in terms of its suitability for adhesive joining. Experimental data from shear strength tests of 316L steel specimens bonded with Loctite EA 9466 was subjected to comparative analysis. The final section draws conclusions from the study.

Analiza porównawcza przygotowania powierzchni stali 316l na wytrzymałość połączeń klejowych

Słowa kluczowe: warstwa wierzchnia, chropowatość powierzchni, stal 316L, połączenie klejowe.

Streszczenie: W pracy przedstawiono wybrane wyniki badań dotyczące skuteczności klejenia stali 316L po różnych sposobach przygotowania powierzchni. Analizowano wpływ przygotowania warstwy wierzchniej na wartości wybranych parametrów chro-powatości powierzchni 2D oraz 3D w aspekcie wytrzymałości połączeń klejowych. Ponadto analizie poddano krzywą Abbotta--Firestone`a (krzywa udziału nośnego), która zawiera informacje o stanie powierzchni w aspekcie jej przydatności eksploata-cyjnej. Zestawiono wyniki uzyskanych naprężeń ścinających w badaniach eksperymentalnych dla próbek wykonanych ze stali 316L z udziałem kleju Loctite EA 9466. Pracę zakończono wnioskami.

© 2018 Mariusz Kłonica This is an open access article licensed under the Creative Commons Attribution International License (CC BY)

https://creativecommons.org/licenses/by/4.0/

Introduction

Adhesive joining is found in an increasing scopeof applicationsonaccountofnumerousadvantagesofthis method [5, 7, 9]. Cost-wise, the method enablesreducing costs of joint assembly, which furthermoreleads to lowering assembly and production costs of technical objects where adhesive joining is applied [6,8].Inaddition,themassofsuchobjectsisreduced.Whatismore,adhesivebondingiscapableofformingjointsbetweenadherendsdissimilarinmaterial,shape,or dimensions. Nowadays, the range of adhesives is

enormous,hencetheselectionofanoptimalsolutioninagivencaseisfacilitated[13,14].

Unlike in welding or pressure welding, adhesivejoiningdoesnotleadtostructuralchangesinthesubstratematerial, nor does it require elevated temperature inthe joint area, which could be the cause of thermaldeformation [5, 7]. When bonding with adhesives,no holes need to be drilled in substrate material (as in riveted joints), which may lead to weakening of thecross-section and unfavourable stress-concentration inthe joint.An adhesive joint is capable of dampeningvibration,sealing,andair-tightsealingstructures.Proper

84 Journal of Machine Construction and Maintenance | 1/2018

surfacepre-treatmentiscriticaltoadhesivejoining,andit must produce a proper surface texture and its multi-directionallay.

The geometric structure of a surface is generally describedbyitsthreemainproperties:shape,waviness,and roughness [1–4]. Surface roughness is mostfrequently evaluated in testsbyquantitativemeasures,referred toas2D(profilemethod)or3D(stereometricmethod) surface roughness parameters. There are 4groups of surface roughness parameters: measured in the vertical direction (amplitude parameters – account forchangesinheight),measuredinthehorizontaldirection(spatialparameters–describechangesinwidth),hybridparameters and functional parameters connected with

materialratio,calculatedontheAbbott-Firestonecurve[1,4,10–12].

Theaimofthearticlewastoaconductcomparativeanalysis of 316L steel adhesive joints bonded withLoctite EA 9466 reflecting the impact of differentsurfacetreatmentmethods.

1. Methodology of measurements

The chemical composition and selected properties of316Lsteel,thesubstratematerialintests,areshowninTable1.Thetablewasbasedonthematerialdatasheet.

Table 1. Chemical composition and selected properties of 316L steel (according to material data sheet)

316LsteelElement C Si Mn P S Ni Cr Mo NValue[%] 0.011 0.54 1.03 0.040 0.001 10.18 16.71 2.05 0.020TensilestrengthRm[MPa] 592ContractualyieldstrengthRp0.2[MPa] 290Hardness[HV] 148

Table 2 shows different variants of surfacelayer preparation of 316L steel substrate specimens.Specimenssized100x25mmand1.5mminthicknesswere subjected to 5 variants of surface treatment,followed by degreasing with Loctite 7061 degreasingagent.Thedegreasingprocessconsistedoftwostages:first thesampleswere treatedwithdegreasingsolutionandwipedwithapapertowel(repeatedtwice),then,afterthe second application of Loctite 7061, the substancewaslefttoevaporate.Treatmentoperationsinvolvedtheuseofnon-wovenabrasivefabric(P280andP100)oranabrasivetool,andtheywerecarriedoutmanually.Sandblastingwasconductedatthepressureof0.8MPa.

Table 2. Substrate surface treatment variants

Variant SurfacetreatmentT1 UntreatedT2 AbrasivefabricP280T3 AbrasivefabricP100T4 AbrasivetoolP320T5 Sandblasting

Following surface treatment, the specimens weresubjected to surface roughnessmeasurements, and theobtainedresultsunderwentfurtheranalysis.

The set-up utilised in the surface roughness measurements conducted in the study was roughness,contour, and a 3D topography measurement systemT8000 RC-120-400 by Hommel-Etamic. The systemwas fittedwith a 2 µm contour probe.The roughnesssamplingcut-offwasobtainedfromliterature[4].

The contact measurement method consists in reflectingpeaksandvalleysonthespecimensurfacewithameasuringtip(contourprobe)ofaspecifieddiametermovingonthesurfaceofaspecimenataconstantspeed.The measurement is taken in a specified direction inthe 2D profile; whereas, the 3D stereometric methodemploysaline-profilingmethodcarriedoutonaspecifiedsurface.Thespecimenswerescannedintheareaof4.8mmx4.8mm.2Dsurfaceroughnessparametersweretakenintenrepetitionsforallsurfacetreatmentvariants,and their mean values, including standard deviation,werepresentedintheformofgraphs.

Surface roughness parameters measurementprovides a thorough evaluation of its microgeometry.Surface topography, particularly roughness, andwaviness is characterised by a number of parameters.Theconducted tests focusedon the following3Darearoughness parameters of the surface:

-Sq–rootmeansquareheight,-Sz–maximumheight,-Sa–arithmeticalmeanheight.The tests conducted for the sake of this study

involvedthemeasurementofthefollowing2Dsurfaceroughness parameters:

-Ra–arithmeticmeandeviationoftheroughnessprofile,

-Rk–coreroughnessdepth,-Rt–totalheightoftheprofile,-Rz–maximumheightoftheprofile.Figure 1 shows a schematic representationof the

testedsinglelapadhesivejoint.Bondlinethicknesswasgk=(0.07–0.09)mm,andtheremainingdimensionsareshowninFig.1.

Journal of Machine Construction and Maintenance | 1/2018 85

Fig. 1. Schematic representation of the single lap adhesive joint

Theadhesivewascuredatambienttemperatureof(22–24)°Candtherelativehumidityof(45–55)%.Thevalueofloadappliedtothejointduringcure,expressedinMPa,wasspecifiedat0.2MPa,andthecuringtimewas168h.

Table3showsselectedpropertiesofcuredLoctiteEA9466adhesivecomposition.

Table 3. Selected properties of cured Loctite EA 9466 adhesive [15]

Physical properties LoctiteEA

9466Tensilestrength(ASTMD882),N/mm2 32Elongation(ASTMD882),% 3Tensilemodulus(ASTMD882),N/mm2 1718Shorehardness(ASTMD1706),DurometerD 60

Theinstrumentusedtoproduceanimageof316Lsteel substrate surface was a Keyence VHX-5000microscope.

Adhesive joint shear strength was evaluatedaccording to the standardDINEN 1465 bymeans ofa Zwick/Roell Z 150 material testing machine. Theinitialdistancebetweengripswasequalto85mm,andthetraversespeedwassetto2mm/min.Eachseriesoftestswasconductedontenspecimens.

2. Test results

Table4shows3Disometricimagesof316Lsteelsubstrate specimens after particular surface treatment operations, selected 3D area roughness parameters, aswell as microscopic images of specimens magnified1000times.

TheobservationsandanalysisoftestresultsshowthatitisthesurfacetreatmentvariantT5(sandblasting)

thatprovidesthebestresultsofsurfacepreparationforadhesivebonding.ItmaybenotedthatthevalueofSaarea roughness parameter is 6 times higher comparedto the untreated surface T1.As a result of kinematictoolinterference, thegeometricstructureof316Lsteelspecimensurfacesubjectedtoabrasivefabrictreatmentshowsdistincttoolmarks.

Table5showsselectedsurfaceroughnessprofilesof316LsteelspecimenandincludestheAbbott-Firestonecurve(bearingareacurve)calculatedforallthesurfacetreatment variants. An interesting observation is thepositivecorrelationbetweenthesurfaceprofilesandthesubstratebondsurfacetexturing.

TheAbbott-Firestone curve contains informationregarding the state of the surface with respect to its suitability for bonding. The selected parameter of theAbbott-FirestonecurvewasRk–coreroughnessdepth,i.e.thepartoftheprofileexcludingextremepeaksanddepths.

Figure 2 shows the effect of different surfacetreatment variants of 316L steel substrates on the Rksurfaceroughnessparameter.

The conducted analysis evidences a 36-foldincreaseinthevalueofRkforsurfacetreatmentvariantT5incomparisonwiththeuntreatedvariantT1.Inthefirstfourvariants(T1-T4), thestandarddeviationdoesnotexceed0.07.

Figure 3 shows the impact of particular surfacetreatment methods on the value Ra of the surfaceroughnessparameter.

BothRkandRaparametersseemtoshowasimilarrelationship with the particular surface treatment variants. In T2-T4, the value of surface roughnessparameter Ra ranges between (0.14–0.19) µm. Thescatterofresultsisthestandarddeviation.

Fig.4showstherelationshipbetweenRz/Rtsurfaceroughness parameters and different surface treatment methods.


Table 4. Isometric images and images of the specimens’ surfaces


Fig. 2. The effect of surface treatment on surface roughness parameter Rk

Fig. 3. The effect of surface treatment on the value of surface roughness parameter Ra


Table 5. 2D surface roughness parameters and the Abbott-Firestone curves

Fig. 4. The effect of surface treatment on the value of surface roughness parameters Rz and Rt

Fig. 5. Shear stress of 316L steel adhesive joint specimen bonded with Loctite EA 9466


The analysis of results indicates a small increase ofRtcomparedtoRz.ThestandarddeviationforRtistwiceashighasforRz.Inaddition,anotableincreasein the values of both surface roughness parameters isobserved for the T5 surface treatment method. Thevaluesoftheparametersinquestionincrease15x.

Figure5 showsshear stressvaluesobtained fromstrength tests of 316L steel adhesive joint specimensbondedwithLoctiteEA9466.

The strength tests conducted in the study show that the highest shear failure stress is obtained for the surfacetreatmentvariantT5–sandblasting.Theaveragevalueofthesestrainsamountstoapprox.31MPa,whichexhibits a 130% increase in the value of shear failurestress in comparison with untreated specimens (T1).Moreover, the repeatability of measurements for allsurfacetreatmentvariantswasverygood,asconfirmedby the level-2 standarddeviation.The lowest increasein the value of shear stresswas observed for samplessubjected to variant T2 of surface treatment, whichproduceda70%increaseinshearstresscomparedtoT1.

Conclusions

The tests and analyses conducted as a part of the research work presented in the present paper allowed us to formulate the following conclusions:1. Theresultsofsurfaceroughnessprofilemeasurements

indicatesandblastingasthemosteffectivemethodofproducing the desired surface texture of the analysed specimens.

2. The highest surface roughness and area roughnessparameterswereobtainedforspecimenssubjectedtotheT5surfacetreatmentmethod(sandblasting).

3. Thehigheststrengthofadhesivejointswasobservedinsandblasting-treatedspecimens(T5).Theincreasein joint strength amounted to 130%, compared tojointswhosesubstrateswereuntreated(T1).

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