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;t .', :~.<' . RHEOLOGICAL PROPERTIES AND IMPACT BEHAVIOR> -. ~ Multi-comp~nentThermoplasticComposites . - '.' .

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5th Annual ASM/ESD Advanced Composites Conference/ExpositionDearborn - September 26, 1989

stephen Burke DriscollLisa FedericoDaniel GallagherDouglas Harrington

Dr. R.M.V.G.K. RaoNational Aeronautical

J".

Labo rata r::r.

The University of Lowellin Massachusetts

Bangalor~,. India

Introduction: "',:"

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The steady growth of reinfgfced plastics/composites has beenv~ri encouraging and no s~Q~down is predicted for the comingdecade. In fact new develqpments in materials, complemented .tby innovations in processing, wilT-enhance the stature ofRP/Cs in the years ahead.:One important member of thiscomposite field is thermoplastic sheeting. ~.j\'.J'-. ..

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starting with the PPG co-developed AZDEL* polypropylene glassmat product and further enhanced by Allied STX* stampablenylon and Phillip's RYTON PPS a decade ago, Glass MatThermoplastics (GMT) now inclupe the recently expanded GE's

. Technopolymers product line of AZDCL*, AZMET* semicrystallinePET-based sheeting, and AZLOY* amorphous PC/PBT. Also/joiningthe competition is Exxon's TAFFEN* random-chopped glass PPsheeting. BASF has announced plans to introduce its TPCseries of nylon and PP impregnated random or unidirectionalglass me:ts. .'

The developments in the material side of the TPC have beenmatched by similar innovations in processing. The early1980's witnessed many developments, including:II, .

1) Yates' development of the ROLL-TRUSION* process, asreported by Driscoll and plumer (1)

2) the concurrent announcement by ICI for roll-forming PEEKcomposites

3) other us ARMY-AMMRC funded techniques, such as Madenjian's- fluidized bed-coating operation (2) .

4) Muzzy et. al., published recently a paper onelectrostatic prepregging using LARC-TPI and PEEK (3)

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Each composite system and process/fabrication-approach has.resulted in enhanced performance. The use of hybrids offillers and reinforcing agents as well as different resinssystems (or thermoplastic alloys) as the impregnating matrixallows the materials engineer to build-in selectedperformance credentials demanded by the design and processingengineers. The scope of this interim report on thesethermoplastic composite constructions is to detail what canbe done and to report briefly on some selected results.

The ASTM D-20 Committee of Plastics founded ten years ago inthis hotel the D 20.10.15 Section on Dynamic Mechanicalproperties. In the past decade a family of testing protocolshas been authored by representatives of material suppliers,fabricators, and users of plastics materials. The publi~hed

A~TM documents include:

D 4065D 4092D 4440D 4473

Dynamic Mechanical proper~~~sGlossary of Terms and DefAnJ,.tionsMelt Viscosity-~Cure Behavior of Thermosett~.

0~26jects being balloted include:'..'. x-lO-IIS Dynamic Tension

X-lO-li6 Dynamic Three PointX-lO-12l Dynamic ~ompressionX-lO-lS? Dynamic Torsion

Bending

These documents allow the mat~rials-design-processingengineer to characterize the ~mportant rheological propertiesof a material and to translate this viscoelastic behaviorinto p~actical term of design worthiness and processability.

Although an important aspect of composite performance isprocessability, an equally invaluable assessment of thefunctional behavior is demanded. This paper will addressbriefly this second area of interest.

Dynamic mechanical testing of composites is based on a ,

controlled deformation of the material system - and measuringthe response to that mechanical deformation. The degrees offreedom in rheological testing include the frequency, thetemperature, the strain amplitude of deformation, and thetime factor. .

ASTM cautions very clearly that testing should only be doneat very low frequencies in order to avoid masking importanttransitions. The temperature gradient shoulD also be limitedto 3 to 5 C/minute to ensure that the material is indeed atthe reference temperature. (The following examples have been.tested at low frequencies. (1 to 10 radians/second) andthermal ramps of 3 C/minute.)

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Experimental:

A Rheometries Mechanical Spectrometer (Model RMS 605) wasused in the forced-oscillatory deformation of torsionalsamples. The strain amplitude (typically below 0.5%) is afunction of the sample geometry. Although the torsionalgeometry was selected, dynamic three-point bending would havebeen equally appropriate. In fact, using both would alloweasy determination of Poisson's ratio.

Analogous to the sensitivity of thermoset composites to resintype, curing agent, fiber reinforcement / direction and agingproblems, TPC's are similarly susceptible to the inherentvariations in the polymer's architecture (molecular weight,its distribution, and branching) as well as alloy/blendcompositions. These material-dependent features can be easilymonitored using ASTM D 4440 (dynamic, frequency sweep testmode, parallel -plate geometry)., (4, 5) . .

consequentlY,;:.,rt?:Reengineer does have a powerful ~malytica~l'tool for moni'~~ting the material during processVng (crit:<~~~\viscosities af5~'~function of processing temperatures) as'9:ellas~,mea.~.>UJ:;),-..(lg,.:;~:h:jt:resultant functional performance of theS-~

fabricated p~b:duct;' Toill'tfs~rate--how.the fabc.i~ation scp.emecan be used ef'fect1vely to d1rect these propert1es, a se_i:'-lt~(sof TPC's was ~~~pared using different symmetrical and -'- , .

asymmetrical ~~semblies of: .

ULTEM* polyetherimide impregnated graphite clothVICTREX* PEEK impregnated unidirectional graphite

tapes -

Sample Construction

123456789101112

All ULTEM*,cloth: AAAAAAAAll PEEK* Unidirectional:A/BBBBB"/AA/BBBBB=/AB"/AAAAA/B"A/B"/A/B"/A/B"/AAAA/B "/ AA/B "

B"/A/B"BtlB"B"/AB::z/A/B"B"B=B=/AB"/AA/B"B"/AAB""/AA/B::zB=/AAB=B=B::zB=B=/B"/B=

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Briefly, the data generated by D 4065 and X-IO-IS7 showsseveral important thermomechanical characteristics:

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1. the modulus as a function of temperature

2. various thermal transitions, including Tg and thebeta peaks

3. indications of maximum continuous use temperature

4. trends for predicting creep and impact behavior

The following is a summation of these rheological testresults:

.,.

SHEAR MODULUS, G' (E10 dynes/sq. em.)AS FUNCTION OF TEMPERATURE (C)

Material RT 100 150,-. 200 300

unidirectionalMD 2.745 1.6T.O 2.3Quasi- -..1:a

Epoxy/Graphi te;;'_Compos1 te2.5 ~,~ 1.61 .5 J.~''; 1 .31 .9 :a.c1'. 1 .01~ 5 . " - -. ';4:" J5:~;--- 1. 3

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THERMOMECHANICAL BEHAVIOR

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-- "-

The,-,':;s.:e;:condtopic to be discussed is the concept;,qfins,t.r'.1.1mentedimpact behavior (ASTM D 3763)withO:.4=!mphasis onlow'~;fqlQw-,".=-.$llb_-:-cr i tical impacts. The his to r i caltdJackg round,rafiO'nal, andcases tudTes"-bf':"-in-s-trumeated imp-ctdtLtesting

haV"~~-i~:;beendocumented in ASTM STP 936.. (6) Haw~~icir: 1988pre,s,~nted a well-documented paper on ~nstrumen;t~d ~mpactte~6tng of asymmetrical thermoset composites.f«O) Rao,sponsored by a united Nations UNIDO Research ;Re:llowship atThe university of Lowell, investigated this ~me concept, butfocused on low-blow impacts of fibrous glass; carbon fiber,and Kevlar*/epoxy composites.i

His study of 10- and 20- plies of glass/epoxy and 15-layeredKevlar*/epoxy showed that the deflection and yield energyincreased while the percent energy absorbed decreased withavailable incident energy. For these materials the repeatedor multiple-blow impact energy approached the single-blowpenetrated energy as the drop height increased.

The deviations between the multiple-blow and single impactevent narrowed as the drop height increased. Conversely, thedeviations increased at the lower drop heights. Thus, the",4 H" value can be used either to magnify or narrow thedeviations between single and repeated drop height tests.Rao's idea of a FICTITIOUS IMPACT LENS (FIL) is useful fordistinguishing between the impact response of variouscomposites, especially those having apparently similar energyabsorption capability. Together with the Ductility Index (DI)the drop increment is a powerful testing tool forcharacterizing impact behavior of composites since t~e FILmagnifies or contracts the differences in impact response.

ULTEM* Cloth/PEEK* unidirectional Construction

1 219 210 0.5852 150 300+ 0.1323 214 230 0.3104 211 211 0.4055 214 226 0.4686 215 224 0.4697 212 227 0.4628 210 228 0.2589 210 234 0.27610 212 224 0.32611 211 224 0.32412 165tt 209 0.161

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Another example of this FIL-concept is the single-blow vs.repeated 'or multi-impa~t of selected thermoplastic "stack~".The symmetrical and asymmetrical assemblies were impactedusing a Rheometries Instrumented Impact Tester (Model RDT5000); the thickness was kept constant and all tests wereconducted at ambient conditions.

First, a series of increased thickness and 5-ply assembliesof PC and SMA were impacted. Although the SMA was initially"weaker" this deficiency (as a function of thickness)decreased with increased thickness, and the five-plyconstructions exhibited energies of 3030 in-lb for SMA and3370 in-Ib for PC.

.,.

Second~ a series of symmetrical and asymmetricalconstructions were impacted at 8000 ipm: ,.

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PC /3 - S MiiJ)i,~

SMA/3-pc7sMAPC/SMA/~~/SMA/PCSMA/PC/-SMA/PC/SMA,,,'-" ,~ ,,--.,

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Energy (,in-~b)

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Since these multi-ply constructions exhibited similar impactbehavior, a third series was tested - both at theconventional Izod impacting speed (8000 ipm) and at varyingdrop heights. The results of ithese single-blow and repeateddrop tests are noted below:

Height (in) Energy (in-1b)

PC/PC/PC PC/SMA/PC SMA/PC/PC

5 210 260 2506 310 310 3107 400 370 3708 400 430 4309 480 470 47010 540 540 53011 600 590 58012 640 630 64013 680 680 69014 730 730 76015 780 800 79016 850 88017 620 90018 950

Cumulative. energy: 7430 7590 . 5820.

Single-blow impact energy at 24 inches = 8000 inches/minute1210 1220 1230

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The conclusions of this preliminary work are:

1. dynamic mechanical testing is a powerful .

analytical technique for chara~terizingthe rheological properties ofthermoplastic composites - especiallyd~e to varied, lay-up ofdirectionalized reinforcements.

2. instrumented impact testing has been shown to beeffective in discerning significantdifferences among thermoplastic andthermosetting composites which exhibitapparently similar behavior at isolatedconditions

Obviously, the results of these,~.limited studies areencouraging but we must tempe~,a~r enthusiam until wecomple te the total pro ject whi'ch\ encompasse s :\.',

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,L. individuaL materials ".\:~2. fabrication s~hemes' ".

3. orientation of reinforcement4. geometry / thickness of the assemblies as well as

impacting probe/support ring ratio5. impacting rates '

6. single vs. multiple impact events

We look forward to sharing wfth you these results at afuture meeting.

References:

1. Driscoll, Stephen Burke; Plumer, John; and Yates, Mark;Roll-Trusion* - A New Manufacturing Technology,SPI-RP/C 1983, Paper 20-B

2. Madenjian, Arthur, UL Master's Thesis, 19853. Muzzy, John at. al., Electrostatic Prepregging of

Thermoplastic Matrices", SAMPE JOURNAL, 25, No.5,September/October 1989, pp 15-20 --

4. Driscoll, Stephen Burke, Using Rheological Measurementsfor Quality Assurance, ASTM, STP 846, 1984, pp. 83-102

5. Driscoll, Stephen Burke, Using ASTM D 4065 for PredictingProcessability and Properties, ASTM STP, 1985, pp.144-161

6. Driscoll, Stephen Burke, Variable Rate Impact Testing ofPolymeric Materials - A Review, ASTM STP 936, 1986,pp. 163-186

7. Haw k e s, ,J0 h n , Imp act Res i s tan c e ..::Pol yet h y 1en e H y b rid

Composites, SPE ANTEC 1988, pp 1910-1912

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