INFORMATION REVIEWED AND REAFFIRMED 1965

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PISSN'S RATIS FP GLASS-FABRICABASE PLASTIC LAMINATES N.

ne f a Series Issued in Cperatin with the ANC-17 PANEL N PLASTICS FR

Illilaniumr wl I FREST PRliUCTS.LABRATRT MADISN S.

1 PISSN'S RATIS FP GLASS-FABRICABASE PLASTIC LAMINATES N. 186 January 1957 INFRMATIN REVIEWED AND REAFFIRMED 1965 This Reprt is ne f a Series Issued in Cperatin with the ANC-17 PANEL N PLASTICS FR AIRCRAFT f the Departments f the AIR FRCE, NAVY, AND CMMERCE 11 I Illilaniumr wl I FREST PRliUCTS.LABRATRT MADISN S. WISCNSIN UNITED STATES DEPARTMENT F AGRICULTURE FREST SERVICE In Cperatin with the University f Wiscnsin

2 PISSN'S RATIS FR GLASS-FABRIC-BASE PLASTIC LAMINATES1 By RBERT L. YUNGS, Technlgist 2 Frest Prducts Labratry, Frest Service U. S. Department f Agriculture Summary Pissn's ratis were determined by test fr several glass-fabric-base plastic laminates after nrmal cnditining. Lads were applied parallel and perpendicular t the warp directin t btain Pissn's ratis alng the natural axes f the materials. A few tests were als made t determine the effects f wet cnditining and type f resin n Pissn's ratis. Fr mst f the laminates investigated, the Pissn's ratis were abut 1/8. Intrductin Values f Pissn's rati are frequently required in the calculatin f the elastic and strength prperties f glass-fabric-base plastic laminates. 1 This prgress reprt is ne f a series (ANC-17, Item 56-4) prepared and distributed by the U. S. Frest Prducts Labratry under U. S. Navy Bureau f Aernautics N. NAer 1683 and U. S. Air Frce Cntract N. D 33(616) Results here reprted are preliminary and may be revised as additinal data becme available. 2 Maintained at Madisn, Wis., in cperatin with the University f Wiscnsin. Rept. N Agriculture-Madisn

Pissn's ratis have previusly been btained fr parallel laminates reinfrced with 162, 181, and 143 glass fabrics, 3 and values based n these data are included in this reprt.

3 Few data are available n Pissn's ratis fr such laminates, and data frm different surces are nt cnsistent. In sme cases the use f an apprximate value is satisfactry, but in ther cases a mre reliable value is required. Pissn's ratis have previusly been btained fr parallel laminates reinfrced with 162, 181, and 143 glass fabrics, 3 and values based n these data are included in this reprt. Limited data n Pissn's rati fr a few laminates at lw stress levels are als presented in the ANC-17 Bulletin. 4 The wrk here reprted was dne t determine Pissn's ratis fr several different laminates, with the principal stresses applied bth parallel and perpendicular t the warp directin. Mst f the tests were made n parallel laminates after nrmal cnditining. A few tests, hwever, were cnducted t investigate the effects f wet cnditining and the type f resin used. This research was cnducted at the Frest Prducts Labratry frm July t Nvember 1956, at the request f, and in cperatin with, the ANC-17 Panel n Plastics fr Aircraft. Descriptin f Material ne glass-fabric-base plastic laminate 1/8 inch thick, 18 inches wide, and either 18 r 24 inches lng was made with Selectrn 53 resin and each f the fllwing reinfrcements: (a) Plain weave 112 Vlan A (b) 4-harness satin weave Ericksn, E. C.., and Nrris, C. B. Tensile Prperties f Glass- Fabric-Laminates with Laminatins riented in Any Way. Frest Prducts Labratry Reprt N. 1853, Nvember U. S. Frest Prducts Labratry, ANC-17 Panel n Plastics fr Aircraft. ANC-17 Bulletin, Plastics fr Aircraft; Part I, Reinfrced Plastics. Issued by Departments f the Air Frce, Navy, and Cmmerce Rept. N

(c) 8-harness satin weave (d) Unidirectinal weave 181 Vlan A 182-114 184 Vlan A 143 Vlan A In additin, ne laminate 1/8 inch thick, 18 inches wide, and 18 inches lng was made with 181 Vlan A fabric

4 (c) 8-harness satin weave (d) Unidirectinal weave 181 Vlan A Vlan A 143 Vlan A In additin, ne laminate 1/8 inch thick, 18 inches wide, and 18 inches lng was made with 181 Vlan A fabric and Epn 828 resin with Curing Agent CL. All panels were parallel laminated except the ne reinfrced with 143 Vlan A fabric, which was crss laminated. Selectrn 53 resin is a laminating resin f the plyester (alkyd-styrene) type cnfrming with the requirements f Military Specificatin MIL-R- 7575A. Epn 828 is an epxy laminating resin f the type required by Military Specificatin MIL-R-93A. Laminates made with fabric having 114 finish, an lder type f fabric finish, are generally affected mre by wet cnditining than laminates made with Vlan A r ne f the ther imprved finishes. Fr determinatin f Pissn's ratis f nrmally cnditined specimens, hwever, fabric finish is nt cnsidered imprtant. Fr this reasn, fabric having 114 finish was used in sme f the laminates frm which specimens were t be made fr test after nrmal cnditining, in rder t use glass fabric n hand. Laminates that were t be cut int specimens fr tests after either nrmal r wet cnditining were reinfrced with fabric having Vlan A finish. Plyester laminates were prepared by means f the usual wet lay-up prcedures. The resin was catalyzed with.8 percent f benzyl perxide, by weight, and the resin and fabric were laid up between cellphane-cvered aluminum cauls. The laminates were cured fr 9 minutes in a press at a pressure f 14 punds per square inch and a platen temperature that was gradually increased frm 22 t 25 F. The epxy laminate was prepared by wet lay-up prcedures with Epn 828 epxy resin cntaining 14 percent by weight f curing agent CL. The resinfabric assembly was cured in a press at 215 F. with cntact pressure fr 12 minutes fllwed by a pressure f 25 punds per square inch fr 48 minutes. This laminate was nt pst-cured. Fabricatin details fr this Rept. N

type f epxy laminate are siven in Frest Prducts Labratry Reprts Ns. 182-5 -- and 1824-C.a Infrmatin n the cnstructin and physical prperties f the laminates is listed in table 1.

perpendicular (9 ) t it. Five specimens were cut frm the 143 crss laminate in the directin, which was parallel t the warp f the face laminatins.

5 type f epxy laminate are siven in Frest Prducts Labratry Reprts Ns and 1824-C.a Infrmatin n the cnstructin and physical prperties f the laminates is listed in table 1. Test Specimens Frm each panel except thse reinfrced with 143 r 181 fabric, five specimens were cut with their lngitudinal axis parallel ( ) t the warp directin and 5 with their lngitudinal axis perpendicular (9 ) t it. Five specimens were cut frm the 143 crss laminate in the directin, which was parallel t the warp f the face laminatins. Ten specimens were prepared frm each f the 181 parallel laminates in the directin, and thse frm each panel were numbered cnsecutively. dd-numbered specimens were tested after nrmal cnditining, and even-numbered specimens were tested after wet cnditining. Each specimen was 16 inches lng and 1-1/2 inches wide and was necked dwn at the center t a minimum sectin.8 inch wide and 2-1/2 inches lng. The minimum sectin was cnnected t the wide ends by circular arcs f 2-inch radius that were tangent t the minimum sectin. Specimens were cut t apprximate size n a bandsaw and finished t final size and shape with an emery wheel munted n a shaper head. Tw metalectric strain gages were munted near the center f the minimum sectin n each side f each specimen; ne t measure elngatin and ne t measure cntractin. n specimens that were t be tested after nrmal cnditining, 1-inch SR-4, Type A-1 strain gages were munted lngitudinally t measure elngatin, and 1/2-inch, Type A-5 strain gages were munted transversely t measure cntractin. n specimens that were t be tested after wet cnditining, 1-inch, Type AB-3 strain gages were munted lngitudinally t measure elngatin, -Yungs, R. L. Supplement t Mechanical Prperties f Plastic Laminates. Frest Prducts Labratry Reprt N. 182-C, August Yungs, R. L. Supplement t Blt-Blearing Prperties f Glass-Fabric- Base Plastic Laminates. Frest Prducts Labratry Reprt N C, February Rept. N

and 1/2-inch, Type AB-5 strain gages were munted transversely t measure cntractin. Specimens that were t be tested after nrmal cnditining were cnditined fr at least 2 weeks at 75 F.

Testing Prcedure Specimens were remved frm the cnditining area ne at a time and measured fr thickness and width at the minimum sectin by means f a micrmeter caliper.

6 and 1/2-inch, Type AB-5 strain gages were munted transversely t measure cntractin. Specimens that were t be tested after nrmal cnditining were cnditined fr at least 2 weeks at 75 F. and 5 percent relative humidity. Specimens t be tested after wet cnditining were cnditined fr 6 days at 1 F. and 1 percent relative humidity. Testing Prcedure Specimens were remved frm the cnditining area ne at a time and measured fr thickness and width at the minimum sectin by means f a micrmeter caliper. They were then placed in Templin grips in a hydraulic testing machine and laded in tensin at a cnstant head speed f.35 inch per minute. ne specimen f each lad-directin r cnditining grup f each laminate was munted in the testing machine and laded until it failed. These tests were made t shw the stress at which the initial and secndary prprtinal limits ccurred in rder t serve as a guide fr Pissn's rati tests. Specimens fr determinatin f Pissn's rati were munted in the testing machine, given a small initial lad, then laded and unladed fur times in ne cntinuus peratin with n intentinal rest r recvery perids. In the first tw runs, lads reached abut three-furths f the secndary prprtinal-limit lad f the specimen, as previusly, determined frm the cntrl test fr the grup. In the third and furth runs, lads reached abut the secndary prprtinal limit lad. Each lading started at the-initial lad, and each unlading except the last ended at the same lad. Elngatin and cntractin strain data were taken during the first lading run, the first unlading run, the secnd lading run, the furth lading run, and the furth unlading run with the metalectric strain gages munted n the specimens. Tests f nrmally cnditined material were cnducted n three specimens at each angle f lading frm each laminate. Tests f wet-cnditined material were cnducted n fur specimens f each 181 laminate. Rept. N

Calculatin f Pissn's Ratis Elngatin and cntractin strain data fr each specimen were pltted t the same vertical lad scale and suitable hrizntal strain scales, as in figure 1.

Initial and secndary slpes were clearly evident n the elngatin curve fr the first lading f each specimen, but were s indistinct n subsequent ladings that n attempt was made t distinguish between

7 Calculatin f Pissn's Ratis Elngatin and cntractin strain data fr each specimen were pltted t the same vertical lad scale and suitable hrizntal strain scales, as in figure 1. Straight lines were drawn thrugh the pltted pints t indicate the slpes f the elngatin and cntractin curves fr each run. Initial and secndary slpes were clearly evident n the elngatin curve fr the first lading f each specimen, but were s indistinct n subsequent ladings that n attempt was made t distinguish between them, since this distinctin wuld have had n significant effect n the values f Pissn's rati calculated frm them. All unlading runs were characterized by a single slpe. Pissn's ratis were then calculated fr the initial and secndary prtins f the first lading run and fr the first unlading run, the secnd lading run, the furth lading run, and the furth unlading run by dividing the strain in cntractin perpendicular t the directin f lading by the strain in elngatin parallel t the directin f lading. The rati f cntractin in the perpendicular-t-warp directin, ft, t elngatin prduced by a tensile lad in the parallel-t-warp directin, a, was designated as Flap. The rati f cntractin in the parallel-t-warp directin, a, t elngatin prduced by a tensile lad in the perpendicular-t-warp directin, f3, was designated as t.ipa. Average values f flap and liga were calculated fr the crrespnding phase f lading r unlading f all specimens in a grup. The indicatins f the metalectric strain gages used t measure elngatin and cntractin strains were subject t errr resulting frm transverse sensitivity. This was particularly significant fr the gages measuring cntractin strain, which was quite small relative t the elngatin strain. Each average value was therefre adjusted t eliminate this errr by means f the relatinships presented by Baumberger and Hines. Presentatin and Discussin f Results Values f Pissn's rati calculated fr each f the laminates tested in this wrk are presented in table 2. Als included in table 2 are values?baumberger, R., and Hines, F., Practical Reductin Frmulas fr Use n Bnded Wire Strain Gages in Tw-Dimensinal Stress Fields. Experimental Stress Analysis 2:1: Rept. N

significance. Mdulus f elasticity values calculated frm the Pissn's rati elngatin data f this reprt are als presented in table 2.

8 f Pissn's rati based n previus similar tests f laminates reinfrced with 162, 181, and 143 glass fabrics. These values were adjusted fr transverse sensitivity in rder t make them mre clsely cmparable t the values btained in this wrk, althugh it is prbable that the adjustment is f slight practical significance. Mdulus f elasticity values calculated frm the Pissn's rati elngatin data f this reprt are als presented in table 2. A set f typical lad-strain curves in elngatin and cntractin are shwn in figure 1. These curves are based n data btained in tests f a 181 epxy laminate, and are similar in frm t thse based n plyester laminates tested in this wrk and t thse based n a 181 plyester laminate previusly tested. 3 The data f table 2 shw that the Pissn's rati was highest fr the initial prtin f the first lading and lwest fr the secndary prtin f the first lading fr each material except the 143 parallel laminate that did nt have tw distinct slpes in the first lading curve. In subsequent runs, the Pissn's ratis fr bth lading and unlading remained abut equal t the average f the Pissn's ratis fr the initial and secndary slpes f the first lading. Since a structural cmpnent is usually subjected t repetitins f lad, the Pissn's rati value based n ladings after the first applicatin f lad will prbably be the prper value t use in design. The data f table 2 indicate that a Pissn's rati f 1/8 wuld prbably be suitable fr mst f the laminates investigated. This is true fr bth Flag and ppa. The utstanding exceptin t this was the 143 parallel laminate, fr which p. cri_i was abut 1/4 and ppa abut 1/16. An exceptin might als be made fr the 182 laminate, fr which 1.1. was abut 1/7 and p.pa abut 1/1. The data n 181 plyester and epxy laminates tested in bth the dry and wet cnditins indicate that wetting prduced a slight increase in Pissn's rati in all lading and unlading runs fr bth types f laminate, althugh this increase was s slight that it wuld have little effect n mst design calculatins. These same data indicate that Pissn's rati was higher fr the epxy laminate than fr the plyester laminate in all lading and unlading runs in bth the dry and wet cnditins. Again, this difference prbably has little practical significance. Rept. N

It has previusly been bserved that the tensile mdulus f elasticity f glass-fabric-base plyester laminates that have been preladed in tensin t a high stress level is generally nly slightly higher than

Few data are available, hwever, n the effect f tensile prelading n the prperties f epxy laminates.

9 It has previusly been bserved that the tensile mdulus f elasticity f glass-fabric-base plyester laminates that have been preladed in tensin t a high stress level is generally nly slightly higher than that based n the secndary prtin f the first lading curve. Similar relatinships were bserved in this research. Few data are available, hwever, n the effect f tensile prelading n the prperties f epxy laminates. Table 2 lists ratis f mdulus f elasticity btained fr the furth lading t the secndary mdulus btained fr the first lading. The rati varies smewhat amng laminates, the final mdulus f elasticity f plyester laminates being abut 3 t 1 percent higher than the secndary mdulus fr the first lading. There was, hwever, a distinct difference in this respect between the 181 plyester laminate and the cmparable 181 epxy laminate. The average rati was abut 1.6 fr the plyester laminate and 1.17 fr the epxy laminate. Similar relatinships might be expected fr plyester and epxy laminates reinfrced with ther fabrics, althugh the differences may vary. Thus, while the secndary tensile mdulus f elasticity might be used as a design value fr plyester laminates, it is pssible that it may be t cnservative fr epxy laminates. Cnclusins Results f this wrk indicate that a value f 1/8 wuld be satisfactry fr Pissn's rati f mst glass-fabric-base plastic laminates when laded at either r 9 t the warp f the fabric. Fr the parallel-laminated 143 laminate, Pissn's ratis f 1/4 fr lading and 1/16 fr 9 lading were indicated. Fr the 182 laminate, Pissn's ratis f 1/7 fr ' lading and 1/1 fr 9 lading were indicated. Pissn's ratis were slightly higher fr a 181 epxy laminate than fr a cmparable plyester laminate. Pissn's ratis f the 181 laminates were increased smewhat by wet cnditining. In neither case, hwever, was the difference great enugh t have any significant effect n mst design calculatins. 8 Werren, Fred. Effect f Prestressing in Tensin and Cmpressin n the Mechanical Prperties f Tw Glass-Fabric-Base Plastic Laminates. U. S. Frest Prducts Labratry Reprt N. 1811, September 195, and Supplement A, June Rept. N

The ratis f tensile mdulus f elasticity f the furth lading run t the mdulus f the secndary prtin f the first run were cnsiderably higher fr the 181 epxy laminate than fr the

10 The ratis f tensile mdulus f elasticity f the furth lading run t the mdulus f the secndary prtin f the first run were cnsiderably higher fr the 181 epxy laminate than fr the cmparable 181 plyester laminate r ther plyester laminates. The secndary tensile mdulus f elasticity f this epxy laminate may be t cnservative t use as a design value. Rept. N

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PUCICLING Of SIMPLY SUPPORTED RECTANGULAR SANDWICH PANELS SUBJECTED TO EDGEWISE PENDING. March No ICUL'I',.LL ROOM

ICUL'I',.LL ROOM PUCICLING Of SIMPLY SUPPORTED RECTNGULR SNDWICH PNELS SUBJECTED TO EDGEWISE PENDING March 1959 N. 1868 This Reprt Is One f a Series Issued in Cperatin with the NC-23 PNEL ON COMPOSITE