DEPARTMENT REPORT UWME-DR-401-103-1 o

_I. VERIFICATION AND APPLICATION

_ OF THE

1 '

_i! IOSIPESCUSHEARTESTMETHOD

,t!

!.

° 'f:

'.:_,: David E. Walrath

Donald F. Adams
_. , , °

DEPARTMENTREPORT

UWME-DR-401-103-1

VERIFICATION ANDAPPLICATIONOF

THEIOSIPESCUSHEARTESTMETHOD

DAVIDE.WALRATH

' DONALDF.ADAMS

i-_l JUNE1984 1

1

i TECHNICALREPORT .

_ NASA-LANGLEY RESEARCHCENTER

HAMPTONVIRGINIA , 23665

GRANTNO.NAG-I-272

;i

COMPOSITEMATERIALSRESEARCHGROUP

MECHANICALENGINEERINGDEPARTMENT

_ UNIVERSITnFYWYOMING

_:._ LARAMIE,WYOMING82071

• I

APPROVEDFORPUBLICRELEASE:DISTRIBUTION UNLIMITED
1 Alpo, t NO I 2. G_etnrnent A¢¢lls,on No. 3. H_,o,.nt_ (::atal_ Ne

I

i:. 4 1"ale and S.t.t,tie S Rel_rz ;::)ate

• Jtme L984

_ Vet lib'allan and Application of the Ioslpescu 6 pr,qo,_,,9 0,_,,,at,,,,co,_

Shear Test Method

:" ? Auti_orls) 8 Performmg@r_lr.zat*(,n .'e_(;,,t NO

U_._._E-J)4R-_ aJ_-195j--J.:,.

" David E. Walrath and Donald F. Adams _ 10 w_k un,t No i

. 9 Petf_rm,ngOr_n,Zat,on NameJIna ,,_oress

ii

Z)epartment: of Mecllanical Engineering 11 Contract or Grant No

tlntversttv at WyomtnR NAG-.I-272

l,aramie, Wyoming 82071 13 Tv_ of Re,on an_me,oOCove,ed

12 SloGnlo;;ngAgency Nlme and A 'dress T_chnJcal

k_ort 6/83-518:)

°.' NASA-Langley Research Center t4. SpOnWl_ga_ncv Cooe

:_" Hampton, VA 23665

. _: i lS Su_Dleme,_,a,¢Notes

==, :,:

_ 16 Abstract

:i'_-. Finite element models were used to study the effects of notch an_le

o_l. Ivariattons on the stress state within an Iosipescu shear to._t specimen. These

=o _. lanalvtical results were also studied to determine the feas bil ity "f usil_4

':,._. Istrain ga_'.e rosettes and a modified extensometer to measure shear ._tt-alli8 l!t

_'." Ithis te_t specimen. Analytical results indicated that notch angle variations

,__- [produc,,d only small differences in simulated shear properti.es. Both strain

"_ ]ga_.e rosett,_ and the modified extensometer were shown to ;_e feasible shear

!: Istraln tranducers for the test method. Correlations of the analytical ,rcsu.lts

_,: lwtth experimental results from shear tests of isotropic (aluminum) a._ _ell as

.:. [,_rtl,,,tt°opic ([O]sT AS4/3501-6) materials were also performed.

-_ "_ _ l'l,e iosipescu shear test fixture was redesigned to in(:orporat_ several

_":i:" mprovcmcnts. These improvements include accommodation of a 50 I._e)'cent larger

sp(:cimen for easier measurement of shear strain, a clamptngmechant_m to relax

-" : strict to_,erances on specimen width, and a self contained altgnment tool for

'_ use du:'iug ._pectmen installation. The inner loading surfaces were al_,, ,loved

: lJurthe_ from the test region. Drawings of this new fixture are Included ]u

>". [the report.

o ,-:, A set of in-plane and Interlaminar shear properties were measured te_. tl,ree

:: graphire fabrlc/epoxv composites of T300/934 composite material. The tbcee

weaw" patterns wereOxtord, 5-harness satin, and 8-harness satin. These tests

*i,. were performed for room temperature/dry conditions.

:.: 17 Key _'_rds(SuG_esv.'dby Autho_ls)| 18. Oisuibut_OnStatement

:" Composites, shear test methods,

h,sipescu shear Unclassified,Unlimited

' 19. Secu,*tVClau,f. 1o!th,sreDot 20. Secur,tvClassf,. (of th_s_lge) 21. No. of Pages 22. P-c(_"

Unclassified Unclassified .I] 2

. "Fo, _alebylb..N: al,onalTechmcalInlotmahoSnexy,reSp. ,,glicld.VIrgln_,l Z2161

NASA-C-|6B (Rev. 10-75)

'_ 0

" _:"'__ _ _al, ._ _,-
t

PREFACE

0

This techtti_al repozt summarizes results of a combined analytical

and experimental study performed for the Nattonal Aeronautics and Space

Administration-Langley Research Center under Grant Number NAG-I-272,

University of Wyoming Project Number 43-8315. Fir. Jerry W. Dedton served

as the NASA Technical Monitor.

Nork conducted as part of this research program was performed by

members of the Composite Materials Research Group (CMRG) within the

blechanical Engineering Department at the University of Wyoming. The CMRG

is led by Dr. Donald F. Adams, Professor of Mechanical Engineering. Mr.

David E. Walrath, CMRG Staff Engineer, served as Principal Investigator

for this program. Al,_o parth, Iparlng It_ this program wer_ Messers. Edwin

H. Odom and Richard S. Zimmerman, CMRG Staff Engineers; Mr. Russ Porter

and Mr. John Hiller, Mechanical Engineering Machine Shop; and Messrs.

Dennis McCarthy, Greg Horrlson, Robert Wakelce, and ,Jeff Kessler,

undergraduate students tn Hechanlcal Engineering.
TABLE OF CONTENTS

Section

I. INTRODUCTION ........................... 1

2. TEST SPECIMEN AND FIXTURE DESIGN ................. 7

:! 2 I Background 7

2.2 Description of the Analysis ................. 8

-_ 2.3 M_terial Properties ..................... 8

_i 2.4 Finite Element Models .................... 13

_ 2.5 Finite Element Stress Results ................ 17

i 2.6 Strain Measurement Analysis ................. 28

__ 2.7 Experimental Veriflcation .................. 40

o_

L

3. SHEAR PROPERTIES OF WOVEN COMPOSITES ............... 61

3.1 Test Matrix ......................... 61

3.2 Test Results ........................ 65

• 4 CONCLUSIONS 75

':o REFERENCES .............................. 79

_° i .. APPENDICES .............................. 83

A. IOSIPESCU SHEAR TEST PROCEDURES ............... 84

B. ALUMINUM ALLOY AND UNIDIRECTIONAL GRAPHITE/EPOXY COMPOSITE

IOSIPESCU SHEAR TEST DATA .................. 97

C. GRAPHITE FABRIC/EPOXY COMPOSITE IOSIPESCU SHEAR TEST DATA . 103

i_

c
g

: SECTION 1

' INTRODUCTION

: Various shear test methods employing some version of a double

_ edge-notched test specimen have been in use for many years. These test

ii techniques include methods first suggested by Arcan [I-3], Iosipescu

t s[a4me ], anbadsic Sleppretzinciple.et. al.Pure[5].sheaAll r lotharding ee of istheseappliedtest tomethaodstest emplo specyimenthe

_t: via force couples producing bending moments, as shown in Figure la for

11 o ehepeoooeus shear loading in the gage section of the test specimen, the bending

moment being zero in this region as shown in Figures Ib and Ic. The

1 ' notches machined in the edges of the test specimen produce a uniform

_I she distribution ar stress whdich istribution would be asproduc oppeodsedin atosptheceimepnaraboli withoutc esdgheaer notcstrhees.ss

The present authors have been studying and using the losipescu

shear test method for a number of years, particularly for measuring

shear properties of composite materials [6-11]. A summary of that work

prior to initiation of the present research program is contained in

Reference [6].

For the past two years, the Composite Materials Research Group

(C_(;) at the University of Wyoming has beel_ studying the Iosipescu

shear test method under g-ant funding provided by the NASA-Langley

t

Research Center. During the first year of this grant, the loslpescu

shear test specimen was modeled using finite element techniques [7].
Pa Pa mmmmtm_,

a-b a-b

I t)

i| t II V

h w

a-b b -- a-b

ii i iii i

a. force Diagram

---p

i

_" Pb --Pb _m _ tm

a-b a-b

• b. Shear Diagram

• Pb

i. ,

mPb mum,

2

.._. c. NomentDiagram

Fteure 1. Force, Shear_ and Moment Dtagrems for the Ioetpeecu

Sheer Test Method.

2

J+ ,

I
_,/_v 2

Various specimen geometry parameters were studied for their influence ou

test results. These geometric parameters included notch depth, notch

root radius, notch angle, and loading point placement. It was found that

notch root radius plays an important role in determining the shear

stress distribution between the notches. A sharp notch root radius

results in shear stress concentrations in orthotropic Iosipescu shear

• test specimens. It was also found that the inner loading points o[ the

Iosipescu shear fixture used at that time were too near the center of

,._ the te_" specimen. Compressive stresses induced by the loading fixture

, extended into the test region of the specimen.

The purpose of the second-year study presented in this report was

! four-fold. First, the test fixture was to be redesigned and rebuilt to

correct various deficiencies detected during prior studies, particularly

!: those involving loading point placement. Since a new fixture was to be

1

built, other features contributing to couvenience of use were also

#

incorporated. Second, the analytical modeling of the test specimen was

_._ to continue in an effort to further understand the influence of test

_ specimen geometry on test results. Third, various shear strain

:. measurement techniques were to be studied, including strain gages and

-_ the modified extensometer discussed in Reference [6]. Finally, a series

of tests were to be performed on woven fabric graphite/epoxy composite

o_'_

_.! materials to measure both in-plane and through-the-thlckness

_i! (interlamlnar) shear strengths and shear modull.

i Finite element models were constructed to analyze 90-degree and D

io

llO-degree included angle notch geometry loslpescu test specimens.

i

. Properties for an isotropic (aluminum) as .ell as an orthotropic

_ (AS4/3501-6 graphlte/epoxy) material were used.

ii 3

!:
Analytically, notch angle was shown to have some effect on the

simulated measurement of shear modulus. However, experimental shear

property measurements on aluminum specimens showed that the difference

in measured properties was small.

A new Iosipescu shear test fixture was designed and built to

incorporate two major changes in the test method. First, the inner

loading points (surfaces) were moved further from the specimen center,

increasing that distance from 2,5 mm (0.10 in) to 6.3 mm (0.25 in). This

was done to minimize the intrusion of loading polnt-lnduced transverse

normal compressive stresses into the test region. The second major

_,: change was to incorporate adjustable clamping mechanisms into the

: fixture halves. These were designed to minimize rotation of the specimen

during testing due to a loose fit between the test specimen and the

fixture. Other changes included increasing the specimen size to provide

! greater area for shear strain instrumentation, and building an alignment °

ii ! tool into the fixture for centering specimens during specimen ,

_, installation.

Oo Experiments on the unidirectional [O]8T AS4/3501-6 graphite/epoxy

composite indicated axial cracks developing at the notch roots. Simple

ii

finite element models including these cracks were analyzed to study the

effect of the cracks on the internal stress state. The cracks were shown

:,: to not significantly alter the stress state in the test region of the

specimen. In fact, by relieving some of the shear stress concentration

at the notch root, the shear stress distribution was improved.

A major portion of the analytical effort was devoted to predicting

d

• _ the possible measurement errors when measuring shear strains with strain

gage rosettes or a modified extensometer. Both strain rosettes and the

4
modified excansometer ware shown Lo be foaaible strain meaauremont

technlquca. Shear modulus determinationa using strain ro_ott_ ,m

i_ . aluminum specimens agreed vary well with handbook values o_ shear

modulus. Similar meaaurementa on undlrectional composite apccl.te_J_ al_o

provided consistent data, which agreed with available shear propertlc_

data in the literature. The modified extensometer was shown to be a very

feasible method for measuring shear strains, but the exact method of

attachment of the extensometer to the specimen must still be designed.

This work is continuing.

. Finally, in-plane and interlaminar shear tests using the redesigned

;_ Iosipescu shear test fixture were performed on three T300/934 graphite

_' fabric/epoxy composite materials. Consistent in-plane shear strength and

_ shear modulus values were measured, with only slight differences between

_: the three materials. Interlamlnar shear strength and shear modull data

_: were somewhat more scattered but still provided useful comparisons of

the three woven composite materials.

_, Analytical and experimental studies of the losipescu shear test

method itself are presented in Section 2 of this report. Section 3

_._ contains the shear test results for the three T300/934 graphite

= fabrlc/epoxy composites. Conclusions of this research program are

summarized in Section 4. Test fixture plans, test procedures, and

individual test specimen results are included in the Appendices.

oi 5

J D

I
fiECTION 2

J

TEST SPECIMENAND FXXTUREDESIGN

" • 2.1 SO__kground

A major thr-st of the present study was to complete the analytical

investigation initiated during the previous year, in order to better

understand the i,nfluence of test specimen design and speclmen-flxture

interaction on Iosipescu shear test measurements, Results to be

presented in this section reflect analytical and experlmental efforts to

understand the influence of notch geometry and loading point placement

.. on the measured shear properties. Two potential methods of shear strain

• measurement were also examined.

An effort was made to interpret the finite element analytical

results in terms of what could be measured in the laboratory. Five basic

, questions were posed:

1) Is the shear stress state in the test region of the specimen

uniform pure shear, and does it reflect the applied shear

stress as determined by the testing machine?

2) _nlat is the effect of inelastic material behavior on test

results?

_,_, 3) What are the load distributions at the inner loading pollers,

t.,

ii.' and do the induced normal stresses intrude into the test

.,i._ region?

: 4) Nhat is the strain distribution in the test region and c_n this

!,!

° strain be accurately measured with strain gages or a modified

Q ....
_ntensame_r?

5) What are th_ dlfferenc_ tn overall test response between

90-dogroe and llO-dogree included ant_le edge-notched spoetmfina?

Those questions will be addressed |.n thlo socclon.

2.2 Dop_llP_t_J_.P)__Jm,Anp=!Y=_t_

The finite clement ana.l,y_{;_ used durhtg tht, fl retie{itch effort was a

3-D, orthotropic, inelastic analy_ls developed by t{,_ CMRG at the

University of Wyoming. This analysis and associated computer program

allows for temperature- and/or moisture-dependent orthotroptc material

behavior. As this analysis has been described elsewhere [12-1.5], a

detailed description will not be repeated here. Briefly however,

elastoplastic material behavior is modeled by use of the tangent modulus

_ . method and incremental loading. The onset of plastic deformation is

determined by a yield surface in three-dimension," space. The analysis

is based on a dlsplacement formulation and employs linear Isoparametric

finite elements.

2.3 Material Properties

i Because the stress-straln response of many composites when

subjected to shear loading is nonlinear (irregardless of the test

• method) it was important to include nonlinear shear behavior in this

: analytical effort. As part of another research program performed for the

Naval Air Systems Command [15], the unidirectional material properties

of Hercules AS4/3501-6 graphlte/epoxy had been modeled using numerical

micromechantcs techniques. As part of the Navy study a complete set of

: three-dlmenslonal material properties, including stlffnesse_, yield

, strengths, and thermal and .noisture expansion coefficients as functions

-: of temperature, was develcped. The elastic coefficients associated with

I

.

L 0
thl_ data base ar_. listed in Table I _or three _mpt,xature_ and two

moisture, eonditio_, A _ubs_t _f th_e data, J.o., tha room tomparat,tre

, stiffness and yield bahavlor for this compoalte materi_al, wan Bqod In

the proaon_ study. Input ,qho_r stress-shear ntrnin material behavior for

_h_ orthotropic analyses _o he pre_cnted l u t:his report t._,_plot_ed in

Figure 2. Although the data plotted in Figure 2 w(:re _;t,nerated uoltt_;

a micromechantcs analysis (predicted knowing only the. properties of th_

constituents, i.e., the fiber and the matrix), this stress-strain

behavior is consistent with actual composite material measurements. A

. typical set of shear test data generated by the CMRG, for a

,:, unidirectional AS4/3501-6 graphite/epoxy composite, is shown in Figure

'i'_ 3. As can be seen by comparing Figures 2 and 3, the input ._aterial

i: properties which were used in the present analytical effort _re

" consistent with actual measured values. The apparent f_ilure a;:'._lns

_ indicated in Figure 3, at approximately 7.J bet_,:_vtwr..redue to failure

! ,

- of the strain gage rosettes, not actual failt, re in the material.

,_ Limited calculations in the linear elastic range ot materia_

_, response w_re also conducted for an unreinforced aluminum specimen usi_g

" known properties of an aluminum alloy taken from Reference[20/. These

,:: properties are listed in Table 2.
TABLE 1

PREDICTED ELASTIC CONSTANTS FOR AN AS4/3501-6

GRAPHITE/EPOXY UNIDIRECTIONAL COMPOSITE LAMINA

Loading Material 21°C, 82°C, 160°C, 21°C,

Case ........ Propert_ ...... pry, Dry_..........Dry. i% M

Longitudinal Ell GPa 142 141 140 141

"l'ension (Hsi) (20.6) (20.5) (20.4) (20.5)

v12 = v13 0.25 0.26 0.25 0.25

= E.. GPa 9 iO 7 79 4.96 8.55

Transverse E2^z " "

Tension JJ(Msl) (1.32) (1.13) (0.72) (1.24)

= G.^ GPa 5 17 3 65 1.93 5.03

Longitudina£ GI2 • •

Shear lJ(Msi) (0.75) (0.53) (0.28) (0.73)

_-:_i _ Transverse G23 GPa 3.38 2.90 I.86 3.I0

i_" Shear (Msl) (0.49) (0.42) (0.27) (0.45)

i_ E22

__ ....... i 0.35 0.35 0.33 0.38

_ v23 2G23

-, IO-9T 10-7

i • Thermal all = 2.146 x - 2.658 x

.... Expans ion

(dry condition) _22 = c_33 ffi4.634 x IO-8T + 3.112 x 10-5

!_ (°c)-I

,_ bloisture _ii = 1.432 x 10-4

Expans ion

', (room temperature) 622 = 833 = 5.120 x 10-3

!

+iI-'-

TABLE 2

•" MECHANICAL PROPERTIES OF 6061-T651 ALUMINUM ALLOY [20]

Tensile Modulus

' E 68.9 GPa

, (i0.0Msi)

Poisson's Ratio

_°:: v 0.33

°

= _, Shear Modulus*

!:

E

4. G ffi2(1 + _) 25.9 GPa

!_.i (3.76 Msi)

Shear Strength

i''o'b _u

_+t_ 207 MPa

: + (30 ksi)

_i:!'. *Shear modulus was not explicitly listed in Reference [20]. Therefore it

+!:, was calculated from the given tensile elastic constants E and v using

tlxewell known isotropic relation G = E/2(I + _).

VJ

_oi:i

:I

,o f

'i

l

i)I'

, °_ 1:_

']

- ;+.. ...... :.,+_+.:_:--,_. ,,,.----,,+-,..,__',++_::.,+-_ "T,,,.__. , " . " ":"--:'+_---_:_ _+'.u++'_'':'_+'+++_-+---_:xt_'.':_-'_ .............. _"-".........++"::--_

+"% 7:----. - + + 'o + e....... ' + ++'=+h + .... -'i' '''+ ........ + ° .... ,...., +,O, 
2.4 Finite Element Models

As discussed in the first-year report [7], three geometric

• variations of the Ioslpescu shear specimen were analyzed. These

variations included notch depth, notch root radius, and notch angle.

Results of this first modeling attempt indicated that a rounded notch

root radius produced a more uniform shear stress distribution within an

isotroplc or an orthotroplc material test specimen. A sharp root radius

tended to cause a shear stress concentration effect.

Shear behavior in the Iosipescu shear test specimen was found to be

: relatively insensitive to notch depth, losipescu had found, using

_i photoelastic techniques, that notch depths between 20 and 25 percent of

i_Jl the specimen width produced an optimum stress state in isotropic i

,__!=_ materials [4]. Finite element analyses performed during the previous '

i_ year [7] tended to verify that conclusion for both isotroplc and

'-"_ orthotroplc materials.

!711. Variations of notch angle were also analyzed using finite element

_ _ techniques during the first year [7] for both isotropic and orthotropic

i_i materials. As expected, the optimum notch angle for isotropic material

_: specimens was found to be 90-degrees. This result agreed with the

'<, analytical and photoelastlc results for Isotropic materials presented in

Reference [4]. However, for orthotroplc materials, notch angles greater

:i than 90-degrees appeared to produce a more uniform shear stress state.

-i Finite element meshes used during this previous investigation were too

. coarse to conclusively demonstrate this notch angle effect°

_: Investigation of the effect of different notch angles on the stress

state within an Iosipescu shear test specimen has be,_n included in this

I present study. Geometric variations were limited to two different notch

I 13
angles. The notch depth was maintained at 20 percent of the specimen

width, and the notch root radius was modeled as 1.3 mm (0.050 in). Late

in the study, tile effect of cracks at the notch root were also examined.

The loading method used in the [oslpeseu shear test is asymmetric,

: as was shown in Figure 1. As such, it was necessary to model the entire

test specimen, not a quarter or half of the specimen as can sometimes be

done based on symmetry arguments. Plots of the finite element meshes

• used, including boundary conditions, for the two notch angles modeled in

"; this study are shown in Figures 4 and 5. As can be seen, the meshes near

_; the notch root are very refined in order to produce as accurate a

.... picture of the local stress state as possible. Subregions at the centers

4¢ of the two models were identified separately, to facilitate a subsequent

._ study of potential strain measurement techniques, including either

strain gage rosettes or a modified extensometer. Each finite element

-_ mesh contains 1716 nodes forming 778 isoparametrie 8-node elements.

_i Although a 3-D finite element analysis was used, these models are

15-

o:_ actudlly 2-D in that only one plane of elements was used for each model.

_. Other investigators have pr vlousl_ analyzed the losipebcu shear

_ test specimen, typically assu_,_ng the model to be symmetric about the

3

_ midlength and/or midwldth lines [16-18]. The imposed boundary conditions

o on these specimens included shear loading at the end, as well as the

_,_ symmetry condition at the center. These were proper assumptions for

J/ those particular test fixtures, but are not proper assumptions for the

, test fixture being studied in the present research effort. Also, the

:; stress state at the loading points was of Interest; therefore it was

necessary to model the actual loading used. Analytical investigations of

other test methods which are very similar to this losipescu shear test

i 14

: ?i
L '"'"' t- ,

i Ii11111_11111' tttittt_llttti n '

I.I I II iiililll_t'8_lm_'l'm Illll

I II II II IL_.i:l/d_m_,(_l I II II I II

i IIIII!1_111111 Ij i , I!

i IIIII1_1111111 I I

__ _¢1111111 I ..I

!1111 i . II ' II

II

IIIIII

Z, ,. IIIIIII II

IIIIII II --x

F+

"!

;" a) Entire HodeI and Imposed Boundary Conditions.

_o

:_ [ /Strain Gage Region

! i " " " l

/ /

i b) Central Test Regloo. Attachment Points

F,

" Figure 4. Finite Element Mesh Used to Model an loslpescu Shear

Specimen Containing 90-Degree Edge Notches,

/-

f ,
Y

i i tltt .... " '

...... li_,i

a) Entire Model and imposed Boundar b,Conditions.
are presented in References [5,19].

As Indicated in Figures 4 and 5, loads were. applied via prescribed

" displacements• Load point nodes on the l¢_t half of the test specimen

were fixed in the y coordinate direction. Load point nodes on the right

-- half of the test specimen were displaced in the negative y coordinate

: direction, reflecting the actual loading method of the test fixture• As

the actual test fixture loads each point In a compressive mode, care

must be taken to ensure no tensile loads develop at the loading points

: during the finite element simulation. No tensile forces were present at

the loading points for any of the cases reported here. All shear test

_!_ simulations consisted of 14 loading increments In order to model the

o inelastic behavior of the test specimen. All loadlngs were simulated at

ambient (room temperature, dry) environmental conditions The finite

i_ element program is capable of modeling nonambient environmental

°_i_ conditions; however this was beyond the scope of the present study.

; 2.5 Finite Element Stress Results

_; Stress versus displacement plots for the 90-degree and the ii0-

: degree notch angle models are shown in Figure 6. The displacements

° _ indicated are the boundary displacements applied to each of the finite

element models. From a testing viewpoint, these values represent the

• simulated displacement measurement of the testing machine, assuming a

: rigid test fixture and load train• The plots of Figure 6 illustrate the

o _ nonlinear response which would be observed by the testing machine

' operator. The applied shear stress is calculated by dividing the

: applied load by the specimen cross-sectional area (between notch roots).

Applied loads were determined from the nodal reaction forces induced by

_" the displacements at the boundaries.
IOS]PESCU STRESS-D_qR.ACEHENT

lKil ' ' J ' I ' ' ' ' 'I" i i' , ,'

-- aid

13 m.._ _,m'm

o ,,.-m_ ElB :

8B -

I OD D "

0 0 .

• 0 0 •- IQ

m

_-' 00 "

i_ El -- i;

:_ _ 0

__f ,m

Figure 6. Predicted Average Shear Stress Versus Fixture

_- Displacement Plots for the 90-Degree and llO-Degree

=: Notch Angle Specimen Geometries.

.

18

i'
Stress distribution contour plots were examined for each of the 14

Increments for both finite element models. Results to be presented here

have been selected from four of those loading Increments, corresponding

to four different regions in the load-displacement regime. Increment 1

results are shown as representing the material tit the linear elastic

:-:, range. These results are directly comparable with those presented by

other authors using linear analyses. Stress contours and distributions

- from Increment 4 are presented since at this applied stress level many

: elements have begun to respond inelast£cally, yet the overall specimen

:: response is still almost linear. Increment 8 results represent a stress

5_ level of obvious nonlinear load-dlsplacement behavior. Finally, results

_' are presented for Increment 12. Stresses at this level of loading are

_.:

? very hlgh and the specimen is near ultimate failure.

)" Knowing the actual state of stress within tile test region is, of

course, cf major importance in understanding the test method. Ideally,

:_'_r the stress state should be a pure shear stress Txy, wlth no

_ _ bendlng-induced axial normal stress c or loading polnt-induced

transverse normal stress o components. Normalized bending stress

;. y

contours Ox/_ for increments I, 4, 8, and 12 are plotted in Figures 7

and 8 for the 90-degree and ll0-degree notch models, respectively.

: Stres_ contours plotted in Figures 7 and 8 and subsequent figures have

been normalized by the absolute value of the applied shear stress _ =

t

_; IXapplledl. Relative to the coordinate system used, as shown previously _t

_' in Figures 4 and 5, actual applied shear stresses were negative. Stress

: values were normalized by the absolute value of the applied shear stress

:i in order to preserve the sign of the normal stresses, negative

indicating compression.

" i

i

I

_ 19

• _-_._-,--_--_----_-_'_ _'--_:_--'-'---_'=_ ......... _i_.£: __._._.___._._____._7____.- _ _.- - - _ •_,--'_ ----_,--c-_-+_-, ....... _;.:_-_ _-_---_, --:.,J

L
- _ii_

'?

r

, °_),U eA -_._a! .h

-I.eI ,C -I.N .¢

-,_ ,D -.NO -D

.-,

:' O,-I P

•I eF ,Me mP

A

" 1.00 =O 1.N 00

, . a) Increment 1, _ = 11.7 HPa b) Increment 4, _ - 44.9 HPa

(1.70 ks/) (6.51 kst)

5..'

?

_: : -3.00 *A -3,00 =A

.._. -l.O0 -I -I,OO -I

,,,. -I .Oe=C -I .eo *C

•._ I •eI O• ,,l

• F

¢

, ,58e oF ,_)O IF

I .m *O I .N eO

_ c) Increment 8, _ = 85.1 MPa d) Increment 12, _ ffi109.2

._ (12.34 ksl) (15.84 k8i)

(.

Figure 7. Normalized Axlal Bendin_ Stress Contours o /_

£or a 90-Degree Notch Iosipescu Shear Test x

r _ Specimen of AS4/3501-6 Graphite/Epoxy.

:i

' " 20

'!

_, ._1_ _-- _ .._ "-
a) Increment 1, 14.5 MPa b) Increment 4, 57.1 MPa

(2.11 ksi) (8.28 ksi)

_'- -3.e9 -n -2.,'_wl -_

( •

-|,00 '_C *1,00 e.¢

-!

_" -."-_OO sD -._ ,,D

-' O. ,rE O. -E

• , I ._O mO I.N -O

; 1

:i c) Increment 8, 95.0 MPa d) Increment 12, 114.0 MPa

....i' (13.78 ksi) (16.53 ksi)

,".i

%,

',i Figure 8. Normalized Axlal Bending Stress Contours o /T for a

_, ItO-Degree Notch Iosipescu Shear Test Specimen of

iI AS4/3501-6 Graphlte/Epoxy.

21
_:,i 'l_h_'"'. . r"

i

i"

r

Looking first at Figure 7 for the 90-degree notch model, It can I)_

seen that the teal region nf the. specimen is essen_lal!y frec of bcnd Jllg

induced stresses in all increments, as indicated by the O.0 COlltOtlr

]=abeled E In Figures 7a-Td. Bending stross,,a did increase at the root.

::i:t of the notchc_, bcln8 as high as 1.0 tlmcf, the applied .hear _res_, u:_

1. indicated by the (; contour at the top notch root in Figure 7b. However,

"t' It will be noted that even slightly removed from the notch root, for all

'.L

four increments, bending stresses are only 0.5 ttme_ the applied shear

i stress or less. Also, a bending stress of 0.5 _ in Increment 1 for

i [

L_

I example, is only 5.9 MPa (0.85 ksi), which is a negligibly low stress in

the fiber direction of a graphlte/epoxy composite. Even in increment 12,

the 0.5 _ bending stresses shown in Figure 7d represent an actual stress

of only 54.6 MPa (7.92 ksl), which is less than 3 percent of the

longitudinal strength of this material.

Similar bending stress results can be seen in the results plotted

!_I for the ii0 degree notch model shown in Figure 8. The O.O stress contour

--_ labeled E actually encloses the center test region in Figures 7a and 7b,

"'. which represent Increments i and 4. Figures 7c and 7d (for Increments 8

j

i and 12) also show that bending stresses were negligible within the

'i

_enter test region. _oSi

!_ Normalized transverse stress, ey/_, is plotted for Increments i, 4,

.... 8, and 12 for the 90-degree notch mod_l in Figure 9. One (.oncluslon

_:.. reached during the analytical study of the previous year [7] was that

°ii:. the inner loading points of the original version of the test fixture

.:{/:! were too close to the center of the test specimen. Inner loading points

'i in the latest version of the test fixture begin at a point 6.3 mm (0.25

'I

i 22
_+ •

" O."P 8,=It

.2'JO =Q ._0 -a

a) Increment I, _ = 11.7 MP._ b) Inereme,t 4+ _ _ 44.9 Xp_

(1.70 ksI) (6.51 ksl)

o

-!

J

D-a _'

-j

._ -_,OO -A -2,00 =A

+'._ -1.50 *B *1.50 -8

. . ,._ -I .QO mC -I .08 -C

::_"+,i" ' -.m -[ -.e_e -e

Y _": _" O. "F e. *iF

-'_"_ ' ._se "0 ._ -0

ii:i_++: c) Increment 8, _ = 85.1 blPa d) Increment 12, T = 109.2

w::,°;+ (12.34 ksi) (15.84 ksi)

_L 'L

_;,++'+"9

+ +:_,

"e',g_g

+

° '2 i

+ l,'igure9. Normalized Transverse Normal Stress Contours

/_" for a 90-Degree Notch Iosipescu Shear Test

+: • S_eclmen of AS4/3501-6 t;r,_l_i_Ite/EpoxCyomposite.

° 23

' +,. ++ +:.+.+.._.:+_. ,_'_-"+:'+'__'-J"+_-_"'_-'+'-'+-_r"" + "'-_ + "" ,; +"--+--"'+_.+_-.'+: ,, ...... '+ .+- + ' ++ 'd' _+++_+ c, +'_....... : "+ .... +

r, ,. o:,. '+'° + l/ .+ ' + .- ° ...... ' +++....:. ,. ° "
in) away from the center of the test specimen, as opposed to the ?.5 mm

(0.; in) distance In tile original fixture. This subject will I,.

dIscuB_ed in more detail l'_ter in th_B _,ectlon. As can be ,_een In I"ll'-r,,

t'

i,

9, tile center 'egion of tile test specimen 1_ subjected to _ stre_n

Y

between 0.25 _ and 0.50 _ (Contours D and E) for Increments 1 and 4 (see

Figures 9a and 9b. The _J stresses are 0.25 _ or less after Increment 4, Y

Figures 9e and qd. It will be remembered that Increment 4 was selected

for presentation since it represents the stress state Just prior to

significant inelastic material behavior. The o stresses ar_ lower

Y

relative to the applied shear stress _ in the subsequent Increments 8

and 12 due to material yielding. Reposltloning the loading points

appears to have improved the overall stress state in the test region as

compared to the results presented in the previous year report [7].

However, some o stress is still present in the test region, becoming

Y

._. progressively less significant when compared to the applied shear stress

-t, .;, _ as the test progressed. It will be noted that these transverse normal

_" stresses are compressive, as expected, and are therefore less important

%_? in terms of inducing transverse failure than if they had been tensile. A

. _ tensile transverse stress is present near the notch root, however; the

_;;: significance of this will also be discussed further in later paragraphs

" Normalized transverse stress o /_ contour plots for the llO-degree

: ' y

_:. notch model are shown in Figure I0. As was true for the 90-degree model,

i_ _ transverse stresses are as high as 0.25 !, as illustrated by contour

,_ y

E in Figure iOa. However, the relative importance of the o stresses as

• Y

compared to the applied stress _ decreases as the test slmulatLon

proceeds. Contour E (O.25 _) moves farther from the specimen center as

'" the o /_ stress ratio decreases at the specimen center, as shown in

Y

o, 24

I

° . -_ " -_.¢,,_,_.,,.____.W, ,-........ ,,.:,.,
!-_;ir

:L -! .00 ..C -t .O0 ,C

-.SOO=P -._ =D

t_T -.a_ ,,[ .._ ,,(

e. ,." 8..F

A I%

a) Increment i, 14.5 MPa b) Increment 4, 57.1 MPa

° - (2.11 ksl) (8.28 ksi)

E

o _:

!.

,

-1.08 "C -"'"'" !._ "C

:'" -._ -D -._OO -D

r"

;, - -.a_ -| -._SO -E

" O. "le O,,,F

o , .&"Se -O ._J_ ',0

c) Increment 8, 95.0 MPa d) Increment 12, 114.0 MPa

o (13.78 kst) (1{).53 ksi)

9

Figure 10. Normalized Transverse Stress Contours ,_/7 for a

J llO-Degree Notch [oslpescu Shear Test S_eclmen

: of AS4/3501-6 Graphlte/Epox_ Composite

25

_i
Figur_s lOb, lOt, and IOd for Increments 4, 8, and 12, respectively.

Again, the transverse normal o stresses are primarily negative

Y

(compresslve), with the exception of two locations near the notch

regions illustrated by the 0.25 _ uontour labeled C in Figure I0. In

comparing Figure IO stress results to the 90-degree notch specimen

transverse stress results shown in Figure 9, it would appear that the

transverse stresses are less significant in the llO-degree notch test

specimen for this particular orthotropic material.

The particular stress contours of interest are, of course, the

shear stress contours. Normalized shear stress contours are plotted for

_ the 90-degree notch model in Figure ii Ideally, there should be a

=_i_ uniform shear stress region of contour value 1.00 throughout the center

_: of the specimen, If so, then the actual shear stress in the test region

_ would match the applied shear stress as measured by the testing machine.

::.

--_ In examining Figure i I for the 90-degree notch model, it can be seen

f that the center test region is being subjected to a fairly uniform shear

\!,- stress, During the initial loading (see Increments i and 4 plotted in

_, Figures lla and lib), some shear stress concentration occurs at the

_ notch roots. This shear stress concentration is as high as -1.25 _ (it

: will be remembered that the applied shear stress is negative), as shown

: by the contours labeled B in Figures lla and lib. This shear stress

concentration is greatly reduced with increasing load, due to the

:_ inelastic material behavior which occurs, as shown for Increments 8 and

12 in Figures llc and lid. At these two applied stress levels, the shear

stress is indeed reasonably uniform, at a value equal to - I,O "t ,

Another way to illustrate the spatial stress distribution is by

. i

means of a stress profile plot at the specimen midlength. Stress profile

26

!.

i
..... '

,"- -I.P5 .R -I._ "A

B

-,.,., '--'

-I.00 ,,C I m eC

_ _'_"_ -,710 SD -,,?'JQ tiC)

"i -.t_XD,,ll -._ -I

:['

"" .rJe -F .L"Je-F

,,, , , , ,,,,

I .l_i 00 1.0@80

a) Increment i, T = 11.7 MPa b) Increment 4, T = /14.9 MPa

. (1.70 ksi) (6.51 ksl)

.(,

i

?.

o°ll

, } -I .P5-A -I .75 ,,R

_ -I .m)',C -I .ee mC

=7 -._,-D -._ .D

--_ +# -._e -l -.50e ,,E

: ._'JOmF .iw'va mF

6 -

_., t ._ "0 1.00 ,'0

i!

i c) Increment 8, T = 85.1 tWa d) Increment 12, T = 109.2 MPa

_-_-"\ii (12.34 ksl) (15.84 ksl)

9

0

D',

%

Figure 11. Normalized Shear Stress Contours _ /T for a

90-Degree Notch Ioslpescu Shear Te_ Specimen .i

o°° of AS4/3501-6 Graphlte/Epoxy Composite.

J

i

"...... S ... .......m+ 7,©7. .... -..... L............. . :c::-----\,
plots for the 90-degree notch model, using the element shear stresses

in the cente_ column of finite elements, are plotted in Figure 12.

During the initial linear portion of the test simulation, Increments i

and 4 plotted in Figures 12a and 12b, respectively, there exists a

shear stress concentration at the notch root of 1.25 times the applied

shear stress. Once significant inelastic material behavior occurs

_iIo (Increments 8 and 12, plotted in Figures 12c and 12d, respectlvely), the

_I shear stress concentration is blunted, the shear stress distribution

_'o_q Similar strc_s contour and stress profile plots are shown for the

L_

ll0-degree notch model in Figures 13 and 14, respectively. As in the

90-degree model, there is some shear stress concentration at the notch

root in the ll0-degree notch model during the initial Increments 1 and i

4, as shown in Figures 14a and 14b. However, this stress concentration

is not a_ high. Otherwise, the behavior of the llO-degree notch specimen

;y_j is very similar to that of the 90-degree notch specimen. A shear stress

_"" _ concentration is present during the initial (linear) increments, _o o

4_ f,.

° _'i although slightly lower than for the 90-degree notch model. As inelastic

-°.: material b_havior occurs, the shear stress approaches a uniform value

o:,: equal to -I.0 i, as shown in Figures 13c, 13d, 14c and 14d.

_,, " An effort was made during the present program to study two

.. available shear strain measurement techniques and to evaluate their

_ °o_" possible usefulness. One easily implemented shear strain transducer is a

,,. _rain gage rosette containing two strain gages oriented at +45 degrees

to the [oadlng direction. One such strain rosette is shown mounted on an

28

_o

(i

e

,, _.-._.,.__m.__%._ ,._,_,_._.._._,,_,_ _ _,,__.._.,__.__,r. __.;..... _.___,.,____
oo*g'Ib ' '#e _

i i i i

9._ -_.5 -1 ._ -I .5 -2.9 -2.5 8._ -J3.5 -1 ._ -! .5 -2.e -2.5

I_II:_Z2:l_ :S_.&'_STRESS N3:__ SI-E:ARSTRESS

a) Increment l, T = 11.7 MPa b) Increment 4, _ = 44.9 MPa

(1.70 ksl) (6.51 ksi)

°

"°"'tQ' o,

, f

. .t

0.0 -_.5 -1,_ -! .5 .-2.0 -2.5 0,_ -0.5 -1.e -I.5 -2,0 -2.5

I_]::_.I"ZED :SI-_AR_TRESS _I"_'T_ SHEARSTRESS

c) ]t,crement :_,7 = 85.1 MPa d) hlcrement 12, 7 = 109.2 MPa

(12.34 ksi_ (15.84 ksi)

Fig,re 12. Normo|Ized Shear Stress Profiles ' /7 for a 90-Degree

Notch [ostpescu Shear Test SpecimeXYot " AS4/3501-.6

(;raph] te/Epo×y ColnDov i t('.

i 2_)
V

j;

+ *1.75 '+A +2.75 -A

: '- -I .P._ =C _ -I ,_S "¢

° _r -I .(_ =D "I *00 "P

: -.750 ..[ -,P50 mE

L

-.5_ mF -.'_I_+ =F

' '_: .I_ -O .IH -0

+ a) Increment l, 14.5 MPa b) Increment 4, 57.1 MPa

'_ (2.11 ksl) (8.28 kst)

':,.

° :i"

'_+2- -! .75 _A -1.75 =_

°+ °'_ '-,.. /" -I .5¢ "B -1,5+ -B

•_+ -.+... !

+_' -I .P.5 -C -I.P.S ',.C

"+ -.75_ mE -.750 "E

°- _ -.SeO -F -,BOO 'iF

'+ ._{_@+O .li_, "G

,_: c) Inereme,t 8, 95.0 HPa d) Increment 12, 114.0 MPa

+ (13.78 ksi) (16.53 ksi)

Figure 13. Normalized Shear Stress Contours T /T for a

llO-Degree Not('b loslpescu Shear TeX_t Specimen

of AS4/3501-6 Graphlte/Epox_ Composite.

'i

%_

30

,)

'+_I_" .., . _ .............. ._- .... _,_-:,,_++"+_; '_'+C'+'_ " "_"'_"='_'+:+_"++"__

°. ...... +._+,++_+i:+_.... ._+r..,,-..+_+_..-+_-+_+,,++-+_++-+-_+!-: _++,_.,++,,,_-++ +; _, .......... ,'+ +. + , o <+ _, .....
.... .'.["_,%,... " ..

/

t

i

.. !

I S

1

•,: i i I .l _ _ ,I t .. i ;

: 8.8 --i_.5 -1.8 -I .5 -2.8 -2.5 0.0 -0.5 -1.0 -I .5 -2.8 -2.5

NOIWIN.]:Z , ED SHEARSTR_S _]:ZED ¢J-IE:AR$'rKESS

a) Increment i, 14.5 MPa b) Increment 4, 57.1 MPa

(2.11 ksi) (8.28 ksi)

3

, :q

1

• .° ,,,

ii ' "

t %

ill : i

-"s. ;-- ; ; • ; • I I - : _ : " I ; ;

'_i 0.0 --0.5 -1.0 -1.5 -2.0 -2.5 0.0 --0.5 -1.i_ -1.5 -2.0 -2.5

c) Increment 8, 95.0 MPa d) h_crement 12, 114.0 MPa

,,.; (13.78 ksl) (16.53 ksl)

' Flgure 14. Normalized .Shear Stres._; Profiles t /_ for a llO-

'ii DAS4 egre/e3501-6 Notch Graloslpes phtte/cEpu oxr Shear_:_,mpo Test s;fre. _ecimen of

;-_' b

:i

_ 31
Ioslpescu shear test specimen of woven fabric T300/934 graphite/epoxy in

Figure 15. This particular Micro Measurements EA-O6-O62TV-350 ._tratn

gage rosette covers an area 1.57 mmx 2.92 mm (0.062 in. x 0.115 in.).

D=Lrln_ col,struction of the finite element model, a set of elements was

defined for both the 90-degree notch and the llO-degree notch models

corresponding to this strain gage area. These areas wure previously

illustrated in Figures 4b and 5b.

The second shear strain transducer that was modeled was a modified

extensometer, described previously in References [6, 8-10]. One version

of this device is shown in Figure 16. The modified extensometer attaches

to four points on the test specimen, as previously illustrated in

Figures 4b and 5b. The four points corresponding to the corners of the

strain rosette were used, thus calculating a shear strain over the same

instrumented area. In the finite element models, these four points

corresponded to four nodes whose displacements were monitored during a

given shear test simulation.

The modified extensometer measures the displacement of the right

set of two attachment points relative to the left set of attachment

points. During a test, the original square defined by the four

attachment points translates, rotates, and deforms, as shown in Figure

17a. Because the modified extensometer is mounted directly on the test

specimen, the deflection measurement of the right side relative to the

left slde is entirely in coordinates relative to the extensometer and

test specimen, as illustrated in Figure 17b. The shear strain is equal

to the angle change, i.e.,

Ay (for small angles) V z tan y = I,

X

32
• Figure 15. Shear Strain Gage Rosette Hounted on an Iosipescu

Shear Test Specimen of Woven Fabric T300/934

Craphite/Epoxy.

2

3

Fisure 16. Modified l_xtensometer Used as a Shear Strain

Transducer.
"T

I

I

I

I

i

I

I

I

a) Actual Motion of the Modified Extensometer.

°_

I

il

I, Ay

I

_ .

, -T

b) Shear Displacement Relative to the Extensometer Coordinate

System.

Figure 17. Shear Strain Measurement with a Modified Extensometer.

34

4
where _ = _hoar t4_raln

Ay _ measured relative vertical displacement

_ L _ horizontal flpac_n8 between extensomotor attachment halves

X

q!

Note that _he oxten_ometor must be free tn rotate with the tev._ region

:° o6 the specimen in this applieatLon. A convenient meatls of attacl,tn_, an

extensometer for this application is current]y being designed.

' Shear stress-straln plots for a unidireetione 1 AS4/3501-6

graphlte/epoxy composite as simulated by what could be measured wlth a

o

tcst_.ng machine, strain gages, and modified extensometer are shown for

the 90-degree notch model in Figure 18. Also plotted in Figure 18 (solid

llne) is the shear stress-straln behavior used as input to the analysis.

The strain gage rosette and the modified extensometer obviously produced

essentially the same response throughout £hls simulated test. In actual

al

' practice, however, the strain rosette itself would have failed at

approximately 6% shear strain as the individual strain gages have a

maximum range of 3%. The two strain gages of the rosette are wired in a

o

half bridge configuration such that the recorded strain for the bridge i is the difference between the two individual strain gage responses. As t

i ° I -he gage will measure positive strain and one gage will measure negative

i=:' strain, the net measured strain is the sum of the absolute values fo[

_' i each individual strain gage. (Thus the full shear strain rauge is 3% +

3% = 6%.) The full-scale range of this strain gage rosette Is more

• limited than that of the modlfled extensometer. The overa]l s_mulated

test performance does deviate from the input material response.

Obviously, the ideal simulated test would exactly track the input

material properties. The simulated tests plotted in Figure 18 measured

_" 35

ii'

I.
IC_IP_ _-DL'_ MODEL

:,,

_-_ Figure 18. SLluttl_lted _;ilear Stress-Strain Plots for an AS4/3501-6

Graphlte/Epo._V Composite Using a Modltled Extensometer

: and a Strain (;a_e Rosette on the 90-Degree Notch

', Ios t pescu bfode l,

*" 36

'J"_ )

,. 777/-----" % , ,7/'o o , . o 
shear modult grt.ater than the input initial shear modulus of 5.17 _;l_j

(0,150 Mst), Tho modified extensometer calculated initial shear modulut_

• was 5.95 GPa (0.863 Mal), an _rror of 15.1 lmrcent. The atralu gage

rosette calculated shear modulus was 5.87 GPA (0.851 Mal), an error of

13.5 percent, tt will be noted that these are analytical (finite

element) predictions, subject to the inaccuracies of the model and

boundary conditions.

Simulated stress-strain plots and input material response are

plotted for the ll0-degree model in Figure 19. Again, the calculated

response of _l_e strain rosette and the modified extensometer differ only

slightly. However, there is some deviation from input material response.

The modified extensometer calculations of initial shear modulus were

greater than the input 5.17 GPa (0.750 Msi) shear modulus, producing a

shear modulus of 5.73 GPa (0.832 Msl); an error of 10.9 percent. The

' strain gage _'osette simulation produced a shear modulus of 5.68 GPa

(0.824 Msi), an error of 9.9 percent.

One-increment (linear elastic) calculations were also performed

using material properties for 6061-T651 aluminum alloy as input. These

input elastlc constants were listed previously in Table 2. Simulated

modified extensometer calculations for the 90-degree notch model

produced a shear modulus of 23.8 GPa (3.45 Msl) as compared _o the input

25.9 GPa (3.76 Msl), an error of -6.1 percent relative to the input

_("

properties. The simulated strain gage calculations showed a modulus of

24.3 GPa (3.45 Msi), an error of -8.2 percent. Shear modulus

calculations for the ll0-degree notch model produced _ simulated

modified extensometer shear modulus of 24.3 GPa (3.45 Msl), an error of

-_8.2 percent. The simulated strain gage rosette measured a shear modulus

:_i 37

• 0
" _ DATA

' , p# D

(,

:-_ 18

:'i G

:' s'Iw_m_1¢£-- 3q_)

',,

¢

" Figure 19. Simulated Shear Stress-Strain Plots for an AS4/3501-6

Graphite/Epoxy Composite Using a Modified Extensometer

_" and a Strain Gage Rosette on the ll0-Degree Notch

,. Iostpescu Node].

,: 38

i
of 23.6 GPa (3.43 Msi), an error of -8.8 percent.

It should be emphasized that the errors in shear modulus

measurement discussed above are analytical predictions, subject not only

to possible errors in the model used to simulate actual test procedures,

but also to errors introduced by the analysis itself. The analysis uses

an incremental loading procedure and the tangent modulus method to

establish the constitutive behavior for a given element [12]. A possible

source of disagreement between input and output shear stress-strain

behavior, as depicted in Figures 18 and 19, is failure of the analysis

to properly track the covstitucive behavior for each element. This

particular topic of research is currently being studied as part of

separate programs. Verification experiments were performed on AS4/3501-6

unidirectional composite Iosipescu shear specimens as well as on

6061-T65I aluminum alloy [osipescu shear specimens, indicating far less

error tha_ predicted by the analysis. These correlations are presented

in the next sub_ection.

To summarize the analytical results presented to this point, two

_I different notch angles have been modeled. Stress contours indicate that

1

ii the shear stresses in the test regions of both specimens were reasonably

_ uniform and free of bending-induced longitudinal normal stresses.

Transverse normal stresses induced at the load points did slightly

_ intrude into the test regions of each geometry. Output results were

_ examined to determine how a modified extensometer or a strain gage

_ rosette would perform in measuring shear strains. Shear moduli values

_ were calculated from these strains and from the applied loads

0

(stresses), for comparison with the Input data. Overall, the llO-degree

_. notch losipescu shear specimen appears to be slightly better than the
90-degree notch _pecimen in terms of uniformity of shear strean and

beLger accuracy of modulus measurement for an orthotropic composite, The

90-degree notch specimen produced less theoretical erzor in modulus

measurement for an isotropic (aluminum) specimen, as would be expected

[41.

A series of Iosipescu shear tests were performed on 6061-T651

aluminum alloy and unidirectional A84/3501-6 graphite/epoxy composite

specimens in order to verify some of the analytical results obtained.

Test specimens were 7.62 cm (3.0 in) long, 1.91 cm (0.75 in) wide.

Aluminum specimens were 0.95 cm (0.375 in) thick; the graphite/epoxy

specimens were 1 mm (0.04 in) thick. Notches were machined with a root

radius of 0.13 cm (0.05 in) to a depth of 0.38 cm (0.15 in). This notch

depth was therefore 20 percent of the specimen width. All specimens were

instrumented with strain gage rosettes as previously shown in Figure 15.

The modified extensometer was not used for these tests as the specimens.

could not accommodate both types of instrumentation simultaneously. The

finite element analyses predicted little difference between strain

rosette and modified extensometer shear strain measurements.

Experimental verification of the modified extensometer is planned as

part of a continuing effort.

Ten losipescu shear specimens of aluminum alloy were tested, five

with 90-degree notches and five with llO-degree notches. The 90-degree

notch specimen is the preferred specimen for testing isotroplc materials

in shear [4]. Specimens incorporating the llO-degree notch were tested

to verify that the analysis correctly predicted shear property

measuremvnt trends. Averages for the five losipescu shear tests on the

4O
aluminum alloy specimens of each notch angle are presented in Table 3.

As expected, the 90-degree notch specimen results were closest to

literature values. The average measured shear modulus (using strain

rosettes) was 25.5 GPa (3.70 Msi), a difference from the literature

(calculated) value of Table 2 of only -2.6 percent. The average measured

shear strength for the 90-degree notch specimens was 219 MPa (31.7 ksi),

a difference of 5.7 pgrcent from the literature value of 207 MPa (30.0

ksi). These results obviously com_, _ quite well.

Measured shear properties for the llO-degree notch aluminum alloy

specimens are also presented in Table 3. The average measured shear

i

i

i_i modulus was 22.3 GPa (3.23 ksi), which is 14 percent lower than the

_I literature value. The measured shear strength using the llOaverage

i_ degree notch specimen was 221 GPa (32.1 ksl), which is 7 percent higher

3

than the literature value. Stress-strain plots as well as tabulated

results for the individual aluminum specimens are shown in Appendix B.

Comparing theoretical and experimental results, the finite element

analysis predicted a shear modulus error (using strain rosettes) of -8.2

percent. The actual experimental difference from published literature

modulus values was -2.6 percent. For the llO-degree notch specimen, the

_. analysis predicted a shear modulus measurement error of -8.8 percent

i.

7

: (again with strain rosettes). The actual experimental shear modulus

-_ difference was -14 percent. Thus the 90-degree notch specimen actually

perlormed better experimentally than the analysis predicted. The

• analysis also underpredlcted the error in using the flU-degree notch

specimen for testing aluminum. However, the analysis did correctly

4

predict the error trends with notch angle, even though there was some

difference between actual and predicted error.

41
TABLE 3

MEASURED SHEAR PROPERTIES OF 6061-T651 ALUHINUH ALLOY

Notch Angle Shear Strength* Shear Modulus*

(Degrees) (MPa) (ksi) (GPa) (Mst)

90 219 31.7 25.5 3.70

ii0 221 32.1 22.3 3.23

Literature Values [20] 207 30.0 25.9 3.76

*Average of five tests

42
Failed aluminum shear specimens are shown in Figures 20 and 21, for

the 90-degree and ll0-degree notch configurations, respectively. The

failure region is obvlously very narrow, extending between notch roots.

These failed specimens are very representative of all I0 aluminum

specimenz tested.

Five Iosipescu shear specimens of unidirectional [O]8T AS4/3501-6

graphite/epoxy composite were then tested, using the 110-degree notch

configuration. These specimens were of the same overall dimensions as

the aluminum specimens, except that their thickness was only 0.i cm

(0.04 in). A complete tabulation of results of these tests is presented

in Appendix B, along with the measured shear stress-strain plots for all

five specimens. The average measured shear modulus was 5.9 GPa (0.85

Msi) and the average shear strength was 108 HPa (15.6 ksi). These values

are comparable to published shear modulus results of 5.9 GPa (0.85 Msi)

[21] and 6.1GPa (0.88 Msi) [22], and shear strength results of I17 GPa

(17 ksi) [23], using other test methods. Two of these unidirectional

specimens failed due to crushing at the inner load points. All five

specimens first cracked at the notch roots, but coutinued to load to

eventual catastrophic failure. An example of this initial crack is shown

in Figure 22. As can be seen in the photograph, a crack has opened near

i the notch root, propagating parallel to the fibers, away from the inner

loading point. A similar crack was present at the bottom notch, although

not shown in Figure 22.

Initial failure of the material in this mode is understandable

(although undesirable) in view of the stress state present at the notch

root. Re-examinlng Figures 9 and I0, i.e., the contour plots of

transverse normal stress, and noting the contour labeled G, it can be

43

_' "": OF POOR QUALIi"_[

Figure 22. lnltlal CrackinS in a _nldlrectlonal [O_ST AS4/3501-6 Graphlte/EpoxY loslpescu Shear Test Specimen.

_5
seen that significant transverse normal tensile stresses are present to

the left of the top notch root and to the right of the bottom notch root

for both the 90-degree and llO-degree specimen configurations. This

stress is probably inherent in the test method and cannot be totally

eliminated. Therefore, an effort was made to understand the effect of

cracking upon the stress state within the test specimen.

Finite element models were generated which contained "cracks" to

the left of the top notch and to the right of the bottom notch, as shown

in Figure 23 and 24. Cracks were modeled by using elements of very low

- " material properties, viz., stiffnesses six orders of magnitude less than

_ stiffnesses of "uncracked" elements. Stiffnesses equal to zero cannot be

!_ used as this will result in zero values on the principal diagonal

of the stiffness matrix, making the problem numerically unsolvable. No

i_ attempt was made to rigorously model stresses near the crack roots, nor

_: to model crack propagation. These two models were merely simple attempts

_ - to understand the effect on test region stresses caused by the geometric

_- influence of the crack.

_,_ Normalized stress contour plots for the 90-degree notch cracked

model are plotted In Figure 25. Normalized axial bending stresses Ox/_

: are plotted in Figure 25a. Comparing Figure 25a to Figure 7a for the

uncracked 90-degree notch model, it is apparent that the presence of the i.

cracks did not significantly alter the bending stress contours. The only

':' apparent influence of the crack was to move the stress contours slightly

away from the notch roots. This is probably an artifact of the model,

" however, as the "crack'* is two elements in height at that point (see

" Figure 23) rather than the very narrow crack present in the test

i specimen (see Figure 22). The finite element mesh was not sufficiently

i46
Figure 23. Cracked losipescu 90-Degree Notch Hodel.

Figure 24. Cracked Tosipescu ] 10--De),reeN_,tch Model.

4 /

.. .J_ _:.. -- @
___-_.._ _ ,00., ,60.,

I

6. =E *,,2'r_ "1[

•5_) g'F II. =F

A

! ._ -O .L_50-O

a) Normalized Axial Bending b) Normalized Transverse Normal

_-p, Stress, _ X /_ Stress, Oy/_

:i

i?:

_k

[, -I.75 :A

-1.25 _B

- 1.00 =C

r-" * .750 "b

_"_ *,500 -E

I °ee -O

c) Normalized Shear Stress,

: •'I x y/V

Figure 25. Normalized Stress Contours for a 90-Degree Notch

Cracked Ioslpescu Shear Test Specimen of AS4/350I-b

Graphlte/Epoxy Composite, _ = 11.4 MPa (1.65 ksi).

J _

,_, _ "_ ,T"_ _ _--.... _ _'_"
reflnt, d to obtain more than qualitative results.

The presence of the er,.ck appeol:8 to merely ahll-t the positions of

' e_=_rtain ._trea_ contours, rather _han significantly al[ering the ;:tres._

profllv.8. Thin ls _een to be true when comparin8 the norm_Jl [a,:d

transverse _trosses plotted in Figure 25b for _he cracked mode] t. th_,

comparable plot for the uneracked model 8hewn in Figure 9a. The

transverse normal tensile stress contour labe]ed G has moved out to the

end of the crack, which it probably caused. Thus the influence of the

crack was to move the undesireable transverse normal _ensi!e stress

;. further from the test region.

_ Normal.ized shear stress contours for the 90-degree notch oracked

} model are plotted in Figure 25c; the comparable uncracked results are

_ plotted in Figure lla. Again, the crack merely influenced the positions

_': of the stress contours, without drastically altering the stress state

_;, within ti,e test region. Shear stresses were, if anything, somewhat more

: uniform in the cracked model than in the uncracked model. This was

3- also indicated in the shear distribution plot for the 90-degree notch

°-" cracked model shown in Figure 26. The shear stress concentration at the

root of the notch was blunted somewhat by the presence of the crack, a_

compared to the 90-degree notch uncracked model shear profile, shown

previously in Figure 12a.

_:. The presence of a crack had very similar effects in the lie-degree

notch model, as can be seen in the stress contours plotted in Figure 27.

Normalized bending stresses o /_ were still small in the test region, as X

shown in Figure 27a, Just as they were in the uncrocked model results,

e

Figure 8a. Normalized transverse normal stresses Oy/_ were still present

in the cracked llO-degree notch model, Figur_ 27b, but did not appear

_k

49

i

"o ...... .- /..'¢"o ' ,, ° ,, : , . o 6) o,
Y__ESOJ 90-D_'O NOTCH

t Qo _lQoeoo joooo a .

oQ OQ#QOmOS

1 i >

Ii

0.0 0.5 1.0 I .5 2.0 2.5

_I_H_L1-ZED SHEARSTRESS

Flgure 26. Normalized Shear Stress Proflle rx /T for a 90-Degree

Notch Cracked Iostpescu Shear TestYspecimen of AS4/3501.6

Graphite/Epoxy, = 11.4 MPa (1.65 kal).

, _ 50
.... ,, F.+..,_.__/ +_+,._. "'"++ +:_" /#":_Y]-[--

a) Normalized Axial Bending b) Normalized Transverse Normal

Stress, Ox/_ Stress, Oy/_

-i .SO "B

-I .aS =C

-I ._ RB

-.7_ mE

- ._eo -F

•itte _G

c) Normalized Shear Stress,

TXV/ t

Figure 27. Norma]ized otre s Contours for a ]]O-Degrec Notch

Cracked iosipescu Shear Testa Spcclmen of AS4/3501-6

Graphite/Epoxy, _ mposJte, _ = ]&.O MPa (2.03 ksl).

! ii_

+ + ° ° " +i+' ;,i " ° u ° o
any more detrimental than for the untracked transverse stress results

plotted in Figure los. Normalized shear stresses, plotted in Figure 27c,

were also relatively unchanged as compared to the untracked result_ of

F!guro 13a. H_,wever, there were still shear stress concentratlons

present at the notch root, shifted to the tip of the modeled crack. The

normalized shear stress profile for the llO-degree notch cracked

specimen is shown in Figure 28. Comparing this plot to the corresponding

uncracked results shown in Figure 14a, it can be seen that the shear

stress concentration has been reduced.

These crack models, admittedly simple preliminary attempts,

indicate that the initial cracking at the notch roots, while disturbing,

is not necessarily detrimental in determining composite shear strength

accurately. Failed unidirectional losipescu shear test specimens

exhibit many smaller cracks throughout the test region, as shown in the

dye-enhan,'ed X-radlograph of Figure 29, indicating failures occur away

from the notch roots. The two major stress relieving cracks beginning at

the left of the top notch and to the right of the bottom notch are quite

obvious. These cracks occurred early in the tests, resulting in

momentary load drops. These are the cause, for example, of the small

discontinuities in the shear stress-displacement plots shown in Figure m

B3 in Appendix B. The specimens continued to load, however, eventually

reaching a final ultimate, catastrophic failure point, failing in shear.

Two of these specimens failed due to crushing at the inner loading

points. Some damage is also apparent at the top edge of the Jpecimen

shown in Figure 29. This crushing is due to an unfavorable load

distribution at th_ inner loading surface, resulting in very high

compressive forces directly at the edge of the loading surface. This was

52

:° . •
__ I1_ I_ NOTCH

Figure 28, Norrnallzed Shear Stress Profile • /_" for a ]]O-Degree

Notch Cracked Iosipescu Shear Tes_Yspeclmen of AS4/3501-6

Graphite/Epoxy, _ - 14.0 MPa (2.03 ksi).

53

t

-4
_igure 29. Dye-Enhanced X-Radiograph of a Failed losipescu

Shear Specimen of [018m AS4/3501-6 Graphlte/Epoxy

Composite, ll0-Degree Notch Configuration.

54
shown analytically by plotting the nodal resultant forces P at the n

center load surface £or each of the two notch angle models. These plots

are shown in Figure 30. The nodal forces have been normalized by the

total force P as applied by a testing machine. Ideally, the distribution

would be constant rather than concentrated as indicated in Figure 30.

Referring back to Figure i, the total force applied at the inner

loading surface is equal to

Pa

Pinner " a - b

where Pinner = total force applied at the inner load surface

a --distan¢.e betwaen outer loading points

b = distance betweo.n inner loading points

Edge crushing had been only a minimal problem with the original test

fixture analyzed in the previous study [7]. One of the tasks of the

present effort included redesigning the test fixture to move the inner

loading points farther from the specimen midline, that is, to increase

b. In the original fixture,

a = 5.1 cm (2 in)

b = 0.51 cm (O.2 in)

Therefore,

Pinner ffiI.Ii

In the redesigned fixture,

a- 7.6 cm (3 in)

b- 1.3 cm (0.5 in)

Therefore,

Plnner = 1.20

55
i O.O I

,-e.I

.-G.2

• --La.g I

i -_.4

-11.5

1t.8 la. I _.2 i_.3 0.4 _.G

D.T_T.eJ_r'.£: _ CEt4rEI_LDE c:X/L3

i-_ a) 90-Degree Notcll Model, P = 180 N (40.8 lb)

"._ •

L_ m

r . . 10.O

: lllJ• o -tD.I

,.. : .-ID.2

iL'

-0.4 _

! .

5

°t-.... I I ' I " -

'- 0,0 I_. l 0.2 0.3 0_4 O.G

1)) I10-Dep, ree Nt, tch Hodt,1, P = 220 N (49.4 lb)

Figure 30. Normalized Nodal Force Distributions Pn/P at

th_' Inner l:_ad Surfaces of all A,$4/350-6

_;raphite/lq_,_xy t:,sipesc,J Shear qpecimen.

_6

i l
Presumably the slight increase in the applied inner load was not

the only factor causing the crushing problems in testing unidirectional

graphite/epoxy coposite specimens. In rounding the notch root, the depth

of the notch was decreased slightly, to less than 20 percent of the

width. The combination of slightly increased inner load and slightly

increased test width (due to decreased notch depth) may have been enough

to cause the crushing failures. It should be noted here that no such

problems were encountered in testing the fabric specimens, as will be

discussed in Section 3.

Several possible solutions exist to alleviate the edge crushing

problem. First, the most obvious solution to the crushing problem is to

increase the notch depth, thus decreasing the specimen width in the test

section. This will result in lower applied loads for a given shear

strength. The previous recommended notch depth ",as 20 percent of the

i_ overall specimen width or height resulting in a test section width equal

i] to 60 oercent of the overall specimen width. Ioslpescu recommended a

ii notch depth of 22.5 percent of the overall width as being optimum [4].

Notch depths up to 25 percent of the overall width will work as well, at

x.

_ :_ the same time decreasing the applied inner load.

:i Second, the ends of the specimens could be tabbed or otherwise

ii' reinforced, to permit them to better withstand the compressive loading

o: forces. Tabbed specimens are commonly used to measure tensile

!.

. properties; therefore no new specimen fabrication techniques need be

:_ developed. However, this solution results in higher testing costs on a

. per specimen basis due to higher specimen preparation costs. One of the

. principal advantages of the loslpescu shear test is its simplicity of

57
uae; tabbed specimen._ add additional compl, ication_,.

A third solution, again involving a change in the test specimen,

would be to test [O/90]ns layup materials rather than unidirectional

materials. This would theoretically noL alter the shear response of the

material, but would greatly increase the specimen's reeistance to

compressive edge loads. One demonstration of this Is given by the shear

test results for woven graphlte/epoxy presented in Section 3 of this

report. However, using special layups to measure shear properties with

the Iosipescu shea_" te_t is no more aLtractive than having to make

special laminates for any other _hear test, e.g., using |+-45Ins

laminates for off-angle shear tests. Again, one major prime advantage of

the loslpescu shear test is the ability, to cut a specimen from the same

unidirectional panel used to measure the longitudinal or transverse

normal properties.

A fourth possibil ity to prevent crushing of the edges of

unidirectional test specimens is to alter the test fixture to help

distribute the inner load to keep compressive stresses below the

critical level. Ideally, the concentrated load distribution currently

present (see Figure 29) should be altered to a constant distribution.

The load distribution can bc altered by changing the fixture loading

surface shape, e.g., using a large radius or a sloped profile. This was

modeled analytically and found to be feasible. Practically, however,

the dimensional changes required to properly contour the loading

surfaces were [ound to be o! the order of 13 lJm (0.0005 itl). Tolerances

on rot_Itlon of the movJ,g fixture half are _f this order. One, other

fixture change would be to ,,ore tht, Inner load points back towards the

mldlength of the spL,rimen as in the orlginal design. However, th_s w_,id
again allow the load-induced compressive stresses to intrude into the

test region as was shown previously [7]. Further lengthening of the

specimen also provides only minimal relief. A more practical solution

is to use a less stiff material at the inner loading surfaces.

Deformation of this material would help redistribute the surface loads

on the specimen and reduce the likelihood of crushing prior to actual

shear failure. Brass inserts 0.05 mm (0.002 in) thick were placed on the

inner loading surfaces for the five tests of unidirectional composite to

achieve the shear failures represented by Figure 29. Further development

of test techniques for measuring unidirectional composite shear

i_-: properties will continue as part of future work.

_ To summarize the results discussed in this section, two different

5 notch angles were modeled for isotropic and orthotropic Iosipescu shear

_ test specimens. While notch angle did affect both simulated and actual

_'_' test results, the differences were not great. It would appear from the

i'_ finite element analyses that the llO-degree notch losipescu shear

specimen was better than the 90-degree notch specimen for shear testing

: _!i orthotropic materials. The 90-degree notch specimen is more accurate for

_!i testing isotropic materials, as theory predicts [4]. This was confirmed

i_ here in the 6061-T651 aluminum alloy also.

=' Cracks emanating from the notch roots were evident in the

=o_! unidirectional graphlte/epoxy composite specimens tested. A preliminary

: analysis of the geometric effect of these cracks indicates that they do

7"

/: not drastically alter the stress state within the test region of the

,j

i specimen. If anything, these cracks appear to make the shear stress

i

I distribution more uniform within the test section.

Finally, an analysis was conducted to define and improve the inner

59
loading point load distribution. Several possibilities are suggested for

eliminating this edge crushing, the most promising being an increase in

the notch depth.

60

o
SECTION 3

SHEAR PROPERTIES OF WOVEN COMPOSITES

3.1 Test Matrix

The modified loslpescu shear test fixture was used to measure the

in-plane and through-the-thlckness (interlamlnar) shear properties of

three woven fabric T300/934 graphlte/epoxy composites. Material

coordinates were defined, with the 1-coordinate direction being parallel

to the warp direction, the 2-coordinate direction being parallel to the

fill direction, and the 3-coordinate direction being perpendicular to

the plane of the plate. Shear stresses were defined in the conventivnal

manner, i.e., that is shear stress is applied perpendicular to the first

noted coordinate direction, parallel to the second coordinate direction.

Thus, a TI2 shear test was performed with the shearing load

perpendicular to the i or warp direction, parallel to the 2 or fill

direction. All three fabrics were tested in both of the In-plane shear

l

directions and in two of the possible four interlaminar directions. A

matrix of the tests performed on these three fabric composites is

presented in Table 4.

The three fabric composites consisted of three different weave

patterns as listed in Table 4, viz., an Oxford weave, a 5-harness satin

weave, and an 8-harness satin weave. All three laminates were fabricated

of Union Carbide T300 graphite fiber and Fiberite 934 epoxy resin.

NASA-LaIlgley fabricated the laminatcs and performed the fiber volume

measurements listed in Table 4.

Test specimens were machined by the CMRG at the University of

Wyoming using procedures described in Appendix A. In-plane (12 and 21)

shear specimens were 7.6 cm (3.0 in) long, 1.91 cm (0.75 in) wide, and
TABLE4

IOSIPESCU SHEARTEST MATRIXFOg THREET300/934

GRAPHITE/EPOXYFABRIC COMPOSITES

(llO-DEGREE NOTCHANGLESPECIMENS)

Weave Fiber Volume Shear Test No. of

Pattern (_) Orientation Shear Tests

Oxford 55.7 12

21 5

13 5

23 6

5-Harness 54.8 12 5

Satin 21 6

13 5

23 5

8-Harness 56.7 12 5

Satin 21 4

13 5

23 5

62
J

of as-recelved thickness, nomlnally 0.25 cm (0.[0 _n). !nter!aminar

loslpeseu sh,_ar specimens wore 7.6 cm (3.0 i_L) loi|g, !._ em (O.5 in)

wide, and nominally 0.328 cm (0.13 in) thick. The _,terlamJnar specimen

width was achieved by staci_Ing layers of the 0.25 cm (0.I0 in) thick

laminates, bon_ed together with an epoxy adhesive, as described in

Appendix A.

The llO-degree notch angle was used in testing these specimens,

machined to a depth equal to 20 percent of the overall width. The

analysis indicated that notch angle did not significantly affect tes_

results; the 90-degree notch is the preferred geometry. The 20 percent

notch depth was also sufficient; no edge crushing was observed in any of

these test specimens.

Each of the woven fabric shear test specimens was instrumented with

a Micro Measurements EA-O6-062TV-350 strain gage rosette for shear

strain measurement. These rosettes measure 1.57 mm x 2.92 mm (0.062 in x

0.115 in) and contain two 350-Ohm strain gages oriented at ±45 degrees.

These strain gages were wired in a half-brldge configuration. One

instrumented test specimen was shown previously in Figure 15. Testing

was performed according to the procedures described in Appendix A.

3.2 Test Results

Avera@ed shear strengths and shear moduli for the three graphite

fabrlc/epoxy composites are plo_ted in Figures 31 and 32, respectively,

and tabulated in 'Fable 5. Complete results for each individual test

specimen are included in Appendix C, including tables of strengths and

modull as well as the shear stress-straln and shear stress-displacement

:3

plots.

As shown in Figure 31, the in-p]ane 12 and 21 shear strenKths for
u) Wqpmo I/) m

ii" "i' r'r'_'i'_i' ' T't'rTr"

' _i.--." _............ ;,,.-:_ ,:: _ Le

i _t111111!11il IH11111 IIi1I 11IIii11II!11 ! I!11III11IIIIII ! Ii=' .°

|llJJ........... lilllllllllllllliilillillllllilllliili!llll_ll!!,_o l ,,'-'

4-_, 0

_U

. _-I IJ

"!lil!!_ii!l!lilili_!i!i!il',illll]"_!iillllll/illl' '_°'_

" I_ H iB _ ':

°i'

°1' 6_

___j.__.._._ ._, .... -._-,o-'_:" 2"CZ-.;_:_-_ _i ..........
¢_ gnqnooH

dl m m

,,- m W

_ -I _''_ ,_-rt-r-r-r] _

: N

• _i Q

_,'.._, _ _ _ _ N///Zj//I// _ _//ZI//___///2°

I=

• _

o ,; o _ o

_ _tlIIIWIlII]IilI!!I IUlIIIlIIIIIltlIIlIII _°.."

_'_', __I I I I_t _]_J_.,! I i I _I I I _ _'

'

_J

• • e • _

i-,

:,i-] i ........ ' :,o , ' " ' , ...... " " ......"'"'" ' 
TABLE 5

K_ERAGEIOSIPESCU SHEAR STRENGTHSAND SHEARMODULIFOR

T300/934 WOVENGRAPHITE/EPOXYCOMPOSITES

Weave Test Strength Modulus

Pattern Orientation ......(MPa) ......_ksi) .....(GPa___ (Msi_,

Oxford 12 104 15.1 4.5 0.65

21 101 14.7 5.0 O. 72

_; 13 37 5.31 3.4 0.49

_'- 23 35 5.1 4.6 0.67

...._

5-Harness 12 112 16.2 5.7 O. 83

_ 21 122 17.7 5.4 O. 78

_, 13 46 6.6 3.5 0.51

_" 23 47 6.8 3.4 O. 49

-_

Y

. 8-Harness 12 120 17.4 5.3 O.77

_' 21 128 18.6 5.2 0.76

'_ 13 40 5.8 2.8 O.40

_. 23 39 5.6 3.6 0.52

>

_ ,! 66

_,,_
the Oxford weave material were virtually the same, as would be expected

due to stress symmetry considerations. This same consistency was true

for the 5-harness and 8-harness weave materials as well. The

interlaminar strengths were considerably lower than the in-plane

strengths for each material, but again were virtually the same when

comparing the 13 and 23 strengths for each material.

Similar results were obtained for the average shear moduli plotted

in Figure 32, although there was somewhat more scatter in the data.

In-plane (12 and 21) shear moduli were virtually the same for each

material. There does at first appear to be some difference between

interlamlnar (13 and 23) shear moduli for the Oxford and 8-harness weave

materials. However, these differences were within the data scatter.

Interlamlnar (13 and 23) shear modull for the 5-harness weave material

were also virtually identical.

In comparing the three materials to each other, it would appear

that there was little difference in interlamlnar (13 and 23) shear

strength between the three weave patterns, as shown in Figure 31. There

does seem to have been a gradual increase in the In-plane shear

_ strengths in going from the Oxford to the 5-harness satin to the

I 8-harness satin weave materials. The improvement is slight, but

i apparent, with the 8-harness weave material approaching or equaling the

o!

117 MPa (17 ksi) in-plane shear strength of many unidirectional

graphlte/epoxy composites [23]. Average shear modull for the various

shear directions were approximately equal among the three different

materials, within data scatter.

Shear moduli were calculated in the conventional manner, i.e., as

the initial slope of the shear stress-straln curve. However, the

67
determination of the shear strengths was subject to some interpretation.

The major problem involves the definition of shear failure. In

fiber-reinforced composite materials, a local shear failure may occur,

followed by a local reorientation of the fibers which then begin to load

in a tensile mode. These fibers, loading in a tensile mode, prevent

ultimate fracture in the test specimen, even though the material has

failed locally due to shear stresses.

This type of behavior, i.e., local shear failure followed by fiber

reorientation, was evident in the shear stress-strain and shear

stress-displacement plots for the three graphite fabric/epoxy composites

tested during this program. Representative in-plane shear stress-strain

and shear stress-displacement plots are shown in Figure 33 for one of

the Oxford-weave test specimens. Similar plots for all of the tested

specimens are presented in Appendix C.

The shear stress-strain plots (a typical example being given in

Figure 33a), exhibited linear response in only a small initial portion

of the test. The shear stress-strain curve was smoothly curved,

exhibiting no clearly defined yield point. Strains continued to increase

to a value of 6 percent, at which level the maximum shear strain

• easuring capability of the strain rosette was reached. Stress continued

to increase, as indicated by the vertical portion of the stress-strain

pl(,t of Figure 33a, until the specimen reached a maximum value and

stress dropped.

In studying the shear stress-d£splacement plot of Figure 33b, it

can be seen that the shear stress initially increased smoothly with

increasing displacement or crosshead travel of the testing machine.

However, beyond approximately 100 _IPa (15 ksi) the shear stress remained

68

_:__ ....... _...._.; _c,_f _ _, _---- _ _r'-. _ .......... -_ .... _ .... -,_-- ......... "_-_'_-_' ' "_'_d _ __ " _ - _- _- "_'_._-''_'_
NAPI24

U_ I 1 e , I I u u i | 1 • n J

tIN IE

1 .I

E

• ' ' I a

a) Shear Stress-Stra£n

|Elm |'l . ,

i " I

t0

118

a a

" b) Shear Stress-Displacement

• Figure 33. Typical In-plane (12) Iosipescu Shear Results for

an Oxford Neave T300/934 Graphlte/Epoxy Composite,

Spec".men Number NAPI24.
practically constant with increasing displacement for a considerable

• portion of the curve. Shear stress then began to increase again, reached

a maximum, then dropped. The actual shear failure of this material wa_

at the first flattened portion of the shear stress-dlsplacement plot.

-.... During that portion of the test the fibers went through some local

_ reorientation, at which time they began to carry a portion of the load

in a local tensile stress mode. Overall specimen stress then continued

to increase with continued displacement until gross specimen failure

occurred. The difference between the interpreted shear failure and the

ultimate stress calculated based on the maximum load attained was small

o_ for this particular test specimen. However, a much greater difference

:r

_- was encountered when testing interlaminar shear specimens. A similar

)

,. shear strength definition problem has also been encountered in shear

_o,_ testing glass-reinforced sheet molding compounds, as described in

i References [9,10]. Strengths reported here for the graphite fabric/epoxy

_!_ laminates were based on the initial shear stress value prior to fiber

i- ,_

_i reorientation rather than the maximum load attained.

_ Representative failures for In-plane and interlaminar test

specimens are shown for the 8-harness satin-weave material in Figures 34

J_ and 35, respectively. The In-plane (12 and 21) shear failures shown in

_ Figure 34 occurred along a path between the notch roots. Failure in both

_: instances appeared to be on the 21 shear plane, as indicated by the

i

°i_ horizontal cracks shown in Figure 34a and the vertical cracks shown in

_,i Figure 34b. Failures in the interlamlnar (13 and 23) specimens, such as

j_

• shown in Figure 35, occurred between the notch roots and consisted of

o cracks perpendicular to the direction of shear loading, marked by arrows

_ " In Figure 35. Some cracks also occurred in the bond lines between

_ 7_
a) In-Plane (Z2) Shear Orientation

!

_-'1 ! '

b) In-Plane (21) Shear Orientation

Figure 34. Typlcal Failures for In-Plane Zoslpescu Shear Test Specimens

of 8-Harness Satin-Weave T300/934 Graphlte/Epoxy Composite.

_ 71

_m
i

: i_,_ ...,• .

_. , ,q .

g -..-_i_.-

- . ;:

t  ̧_ _ _ .

•_, a) Inter.laminar (13) Shear Orientation

"i

'!

7

; b) Interlaminar (23) Shear Orientation

,.o

Figure 35. Falled Interlamlnar Iosipescu Shear Test Specimens of

8-Harness Satin-Weave T300/934 Graphite/Epoxy Composite.

" __ 72
various laminate layers. It will be recalled that layers were stacked to

achieve the desired specimen width for the Interlamlnar shear specimens.

In future woi:k, particularly for 3-0 weave patterns, the stacking of

layers to achieve a desired Interlaminar shear specimen thickness will

probably not be practical. Laminates will have to b_ fabricated to the

desired thickness (laminate thickness being interlaminar shear specimen

width). The newer losJpescu shear fixture will accommodate specimens of

various width,s, as described in Appendix A.

Overall, a representative and consls=ent set of shear properties,

including both in-plane and interlaminar properties, was obtained for

each of the three different weave patterns. The different weave

geometries did not appear to greatly alter the shear properties of the

material, although slight differences in in-plane shear strength were

observed.

The losipescu shear test method performed very well in measuring

the in-plane shear properties of the three materials, and reasonably

well in measuring the interlaminar properties. In future test work, it

would be desirable to cut Interlaminar loslpescu shear specimens of

woven composites from thicker laminates rather than from bonded, stacked

sheets of thinner laminates.

7_I
SECTION 4

CONCLUSIONS

Overall, most project objectives were achieved during this secondyear research effort. The Ioslpescu shear test fixture was completely

redesigned, incorporating some of the following features:

_ a) Inner loading surfaces were moved farther from the test

:_- region.

_'..- b) Test specimen size was increased by 50 percent to provide more

_:

, i_ room for shear strain measurement, instrumentation,

_ c) A clamping mechanism was incorporated to remove the necessity

_ for strict tolerances on specimen width, resulting in less

'" expensive specimen fabrication.

:.. d) The test fixture now will accommodate a range of specimen

widths.

_ Fixture drawings, specimen fabrication methods, and testing procedures ,.

: are all included in Appendix A.

A finite element analysis was performed to determine the stress

,: state within two different losipescu shear test specimen geometries.

,, These specimens were also analyzed to determine the feasibility and

• potential accuracy of using gages or a modified extensometer for shear

strain measurement. I_: was found that the notch angle does affect the

stress state within the test region, as would be expected. Results
:" indicated that a 90-degre_ notch is the most suitable angle for teL.ring

isotropic materials, but a llO-degree notch may he n_._re suitable for

.... shear testing of highly orthotropic unidirectional componite materials.

- However, the difference l,s nmall.

Both a modified extensom_ter a,td strain gage rosettes were found,

analytically, to be sultablo for measuring shear strain in the

., losipescu specimen. Strain gage rosettes hav_ proven very usable in past

work, and were used extensively in this present program as well.

However, they lack sufficient shear straln measurement range for highly

nonlinear shear behavior, as in shear testing at elevated temperatures.

i" Work is proceeding to design a suitable attachment mechanism for the

. T modified extensometer to take advantage of its greater shear measurement

t.

range.

q

_;' Some preliminary work was done to model the effect of cracks at the

i.i_ notch roots, observed in tests of unidirectional graphlte/epoxy

_o_. laminates. It was found that the cracks did not significantly alter the

7_

=_ :. shear stress distribution within the test region of the specimen; if

._ anything the shear stress distribution was improved. This cracking is

apparent only in shear testing of unidirectional composites and was not

i"

:_ a factor in tests of the woven fabric materials.

In-plane and Interlamlnor shear properties were measured for three

...._: fabrlc-reinforced graphlte/epoxy composites. The three different weave

_; geometries performed essentially the same in shear. However, the

o ' 5-harness and 8-harness satln-weave materials did exhibit slightly

h/gher in-plane shear strengths then the Oxford weave material.

Work to be accomplished in the third year of this program includes

_- shear properties measurement for a wider variety of weav? patterns. In a

"ii 76

' _ ""_ '_-%7"'"-'_'_L_"_'-_-_'_,r_;_-_._.-_-_ ' _,X_:_ ....................

_'" o "'o_6°'_o_,,_, °. ,,_._ _ '•:. 0 ,o .... °o _ • o _ -o , , --,--. , -,,
parallel task, development will continue on _he modified extensometer

as a shear straln transducer. Although little further analytical work Is

planned, analynes do exist for modeling these woven composl_e materlala

, to study the effects of weave geometry on the various material

properties. The same 3-D finite element program and associated plotting

software used in the present study to model the los£pescu shear teat

specimen could also be used to perform micromechanics studles of woven

fabric composites. These analytical efforts may be further explortd as

time permits.

:i

e-;

g_

i"

2
REFERENCES

]. Arcan, M. and Goldvnberg, N., "i)t_ a Basic Criterion for Se]ec_lng

Shear Te_tiug Standard for Plastic Materials," (In Freuch) ISO/TC

61-We 2 SP. 171, Burgens_ock-SwttzerJand, 1957.

2. Goldenberg, N., Arcan, M. and Ntcolau, E., "On the Moat SuitabLe

Specimen Shape for Testing Shear Strength of Pl.astic_,"

International Symposium on Plastics Testing and Standardizaticn,

ASTM STP 247; American Society for Testing and Materiale, 1958, pp.

115-121.

f

3. Arcan, M., Hashin, Z. and Voloshin, A., "A Method to Produce

= Uniform Plane-stress States with Applications to Fiber-reinforced

: Materials," E_erlmental Mechanics, Vol. 18, No. 4, 1978, pp.

Y 14I-146.

.... 4. losipescu, N., "New Accurate Procedure for Single Shear Testing of

_ Metals," Journal of Materials, Vol. 2, Ne. 3, September 1967, pp.

.- 537-666.

v:

5. Slepetz, J. M., Zagaeskl, T. F. and Novella, R. F., "In-plane Shear

L

_, Test for Composite Materials," Report No. AMMRC TR 78-30, Army

Materials and Mechanics Research Center, Watertown, Massachusetts,

July 1978.

° 6. Walrath, D. E. and Adams, D. F., "The loslpescu Shear Test as

Applied to Composite Materlals," Experimental Mechanlcs, Vol. 23,

No. I, March 1983, pp. 105-110.

7. Walrath, D. E. and Adams, D. F., "Analysis of the Stress State in

: an losipescu Shear Test Specimen," Report UWME-DR-301-102-1,

-_ Department of Mechanical Engineering, University of Wyoming,

Laramie, Wyoming, June 1983.

i

i 8. Adams, D. F. and Walrath, D. E., "loslpescu Shear Properties of SMC

Composite Materials", Co_osite Materials: Testing and _

;i (Sixth Conference), ASTM STP 787, 1982, pp. 19-33.

:< 9. Walrath, D. E. and Adams, D. F., "Shear Strength and Modulus of

SMC-RSO and XMC-3 Composite Materials," Report UWME-DR-O04-i05-1,

Department of Mechanlcal Engineering, University of Wyoming,

Laramie, Wyoming, March 1980.

I0. Walrath, D. E., and Adams, D. F., "Static and Dynamic Shear Testing

of SMC Composite Materlals," Report UWME-DR-O04-103-1, Department

of Mechanical Engineering, University of Wyoming, Laramie, Wyoming,

May 1980.

IONALLYBLANK
Ii. Walrath, D. E. and Adams. D. F., "Damage Mechani_m_/Fal!ure

Mechanica of Carbon-Carbon Composite Mat_rlala," Report

UWME-DR-904-!OI-!, Department of Mechanical Engineering, Unlver_tty

of Wyoming, La_mle, Wyoming, September, 1979.

12. Monib, M. M. and Adams, D. F., "Three*Dlmen_onal Elastop]a_tlc

Finite El_mont Analysis of Laminated Composites," Ropor_

UWME-DR-O01-!02-_, On_vcr_t_y of Wyoming, Departmen_ of Mechanical

Engineering, November 1980.

13. Grimes, G. C., Adam_, D. F. and Dus_blon, E. C., "The Effect_ of

D£scontinuttles on Compression Fatigue Properties of Advanced

Composites," Northrop Technical Report NOR 80-158, Naval Air

Systems Command, Contracts N00019-79-C-0275 and N00019-79-C-0276,

October 1980.

14. Ramkumar, R. L., Grimes, G. C., Adams, D. F. and Dusablon, E. G.,

Effects of Materials and Processes Defects on the Compression

Properties of Advanced Composites," Northrop Technical Report NOR

82-103, Naval Air Systems Command, Contracts N00019-80-C-0484 and

N00019-80-C-0490, May 1982.

15. Adams, D. F., Ramkumar, R. L. and Walrath, D. E., "Analysis of

Porous Laminates in the Presence of Ply Drop-off_ and Fastener

Holes," Northrop Technical Report NOR 84-113, Naval Air Systems

Command Contracts N00019-82-C-0156 and N00019-82-C-0063, May 1984.

16. Bergner, Jr. H. W., Davis, Jr. J. G. and Herakovich, C. T.,

"Analysis of Shear Test Method for Composite Laminates," Report

VPI-E-77-14, Virginia Polytechnic Institute and State University,

Blacksburg, Virginia, April 1977.

17. Herakovich, C. T. and Bergner, Jr. H. W., "Finite Element Stress

Analysis of a Notched Coupon Specimen for In-plane Shear Behavior

of Composites," Composites, July 1980, pp. 149-154.

18. wang, s. s., Goetz, D. P. and Corten, H. T., "Shear Fatigue

Degradation and Fracture of Random Short-Fiber SMC Composite,"

Journal of Composite Materials, Vol. 18, January 1984, pp. 2-20.

19. Marloff, R. H., "Finite Element Analysis of Biaxlal Stress Test

Specimen for Graphlte/Epoxy and Glass Fabrlc/Epoxy Composites,"

Composite Materials: Testing and Design (Sixth Conference), ASTIr

STP 787, 1982, pp. 34-49.

20. Metals Handbook, Volume 2 - Propertles and Selection: Nonferrous

Alloys and Pure Metals, Ninth Edition, American Society for Metals,

1979.

21. Renton, W. J. and Ho, T., "The Effect of Environment on the

Mechanical Behavior of AS/3501-6 Graphlte/Epoxy Material," Final

Phase I Report, NASC Contract No. N00019-77-C-0369, June 1978.

8O

,°
22. Knight, M., "The Determlnatiotl nf [ncerlamlnar Modu!i of

G_aphlte/Epoxy Composites," 5th Mechanics of Eo_nposlte_ Review,

l)ayton, Ohio, 1981.

23, grimes, G C. and Adams, D. F., "Investlgation of ComproHston

Fatigue Proportloa of Advanced Eompoaltes," Northrop Technical

Report NOR_79-17, Nav_! Air Sy_emo Cogna_d Contra¢_

NO0019=17-C-O518 and N00019=77_C=05i9, Oc_obor 1979,

!_ 81

J

APPENDIX A

IOSIPESCU SHEAR TEST PROCEDURES

A.I. Test Fixture

The losipescu shear test fi×ture is designed to test flat specimens

nominally 7.62 cm (3 in) long, nominally 1.91 cm (0.75 in) wide, and up

to 1.27 cm (0.5 in) thick. A test fixture is shown in Figure AI. This

test fixture is designed to be used in a testing machine set up in a

compression mode. The fixture can be inserted between two flat

compression plattens. However, it is usually more convenient to attach

the right fixture half to the upper testing machine load surface using

the center hole provided in the fixture. This fixture has been loaded to

22 kN (5000 Ibs) applied force without damage to the fixture.

Machine drawings of this test fixture are included as Figures A2

through A6. All parts are fabricated from low carbon cold rolled steel

with the exception of the linear bushing and post. These items are

manufactured by Thompson Industries, Manhasset, New York, and may be

purchased from any of their distributors.

The fixture as shown it, Flgure_ is designed to test specimens

nominally 1.91 cm (0.75 in) in width. The wedge clamp blocks allow

approximately I mm (0.04 in) variation on that width. Only light

clamping is required, to ensure that no specimen rotation tJkes place

during the test. Narrower specimens may be tested by using thicker

wedges, changing the height dimension of the wedge in Figure A3.

A. 2. Tept Specimen Fabric:_t.i9_!

loslpescu shear specimens for use with the present test fixture are
B

5

___/, ̧
i:r

_ F -r-r ! _ -- 1!'1I

!-" _. / : f s n_;J ,'l

i I ]-- -I.]-t- 4- _1_ _ ..... ..,,

i=' _, _ ._#-I j - _ .....

i_:-" DRILL r,, TAP ..__._/i._ L'_-- _

c | ...... r .....

, , 5/t_=24 tlllF ....

O.250

3

i: =.'i_

H}- DRILL G T_,P

i -. i/4-20 UNC

' "-"" 1/2 DEEP

_" 4 PLACES

_" .-4,.--t. 250--'o" "= --0. 375

! .... _. t _ I

-----*-o.soo POTFA:E 0 i

' °"...... ._3.5"o o _ (tVP) {

•_,..... : _ 112_IA _ i

FRONT FASF_ _; 0.500 _'=-_- 0 Z50 |

°, _' ',.-. 1 -- "- - 318 _IA i _ _ ' ' r ..x l

'!!" - - ' lO 0 LE_ _. 'V'A

° :': " _A I_

:°- I_ l-;

:. f 1 ..... I. R7B.....

_, ) ,,

° " _ t

o (" _.: _ -_-

: L .... ._ COMPO,_ZTEMATERIALS RESEARCH8ROLIP

UrlIVERSZTY OF WYOMINg

! o e,: |

i _o:," "_ --0,425 +O.OOl L'NAWIN_ # 1

'>,; ' P -0,00! TE_T FIXTURE HALF

i /''' 3ECTIOII A-A 2 RE_'D FULLSIZE; CIHENSIO_SIN INCHES

ALL TOLENAN;ES t.O.O05

; UNLESS NOTEE OTHERWISE

; o

7 Figure A2. Iosipeecu Shear Test Fixture Half

0

" 86

,(

!,

N:"__°-':: = .... -"_%_-:;7 _"C_'_-_-'--'----_'-x"_2_ _- __c-_--_-,,.-_- - _-,_ ;'-..-_ ,.x_,=___,,_,___ .-_"_:--'_-_- =;2_C-............. -,-,,.-_.,.,s-_-45.::: :.'=.=-_>
+REAMOia+pz+ -LI-_'_

+o o++x+

5/16-24 UNF o DOWELPINS

_ il BRAZED

"-SCREWDRIVER SLOT

I/tfi W X 1/8 DP

ALIGNMENTSLEEVE ALIGNMENTPOST

I REO'D ! REO'D

:: -._o_oo_- F--,ooo_

5/18-24 UNF 0.750 \ 2 PEm'D

_" . DEB

++ l

i_?

!+4

_n

0

o WEDGEADJUSTMENTSCREW

o (OPTIONAL-MODIFY 3/B X 2

" _ _ " .,-, SOCKETCAPSCREW)

i-- =_, _ -,o

_ _ o SNAPRING GROOVE 2 REe'I_

!;_- ', _ o + 0.225 DIA THREADED

• ____ ; /0.026 HIDE /-'5/t6-24 UNF

,.... / 1. 200 LONg

E_

COMPOSITEMATERIALSRESEARgHgROUP

UNIVERSITYOF WYOMINg

----'_" 0. 375r"* --

t.427 t.375 _ DRAWING @ 2

• 0.003' FULL SIZE; DIMENSIONSIN INCHES

-0.000

.......... 2.375 ..........

I

t

i Figure A3. Iostpescu Shear Test Fixture Alignment: Tool

_"i Assembly and Clamp Assembly.

i 87

+ jm4b + : .9

........... *+ ............ + + P ++ '' +. <' + _ + + + ....

t.' 0 ,J _ " - +......... "u_ ' '+

•u ', , , _ s oo o ,, o--u ,_+ ,

Q

,_ I I I I

I I I I

--.! _ ! t..

o.,_,,,T;J,, _ _ t/4"20 UNC_._---./

_/2 DEEP

2 PLACES ............................

0.375-_; "_'-"1.250_--_-

k- _ h

O.500 O.375-- _ t. 250

i

_ _ _ | _

t/4 DIA.

' 4 PLACES

Z

L_i

_-, _ -_'

i

•,-----,._oo_.-I _ -

COHPOSITE HATERIALS RESEARCHGROUP

UNIVERSITY OF HYOHING

DRAWING f 4

LEFT SIDE SUPPORT

t RE_'D

"'. FULL SIZE: DIHENSIONS IN INCHES

F18ure AS. Iosipescu Shear Test Flxture Fixed Half

tlount tng Bracket

,. 89

,o
................ 4,000

'l il .........

II tI

i _4

, ,'(':_.)_ t "" " o'_

I

; I

I1_ o \ i'

ea ,\ i

r _

_L \ T

-_ 0.650 "_--"-1.250--'-_ \ DRILL t/4

_...__C°BORE3/8 ...... 0.7496 DIA +0.0004

1/4 DEEP -0.0000

2 PLACES __ __

COM_'OSITEMATERIALSHESEAfiCH6ROUP

UNIVERSITYOF WYOMZNS

DHAWING 111b

BASE PLATE ASSEMBLY

t. REQ'D

FULL SIZE: DIMENSIONSIN INCHES

0

p..,

3/4 _IA X 4 1/2 LOH_

THOHPSOtSOLI ! E 60 -----""

:, SHAFT (CLASSL) ""_--

DRILL & TAP

!: I/,$-2UN8 F'

{ I

-_",; Figure A6. Ioslpescu Shear Test Fixture Base and i'

.!.i Post Assembly

-I 90

.._,_ Ik "_J
7.62 cm (3 in) long, 1.9] cm (0.75 in) wide, and of any thlckne_.s up to

ir

1.27 cm (0.5 in) thick, as shown In Fll_;ureA7, Very thin apec!mens may be

= 'i" tested, buc care. m,mt I)e take. to enaure compressive buckling does not

.

" occur. Thla can be dora;, with bonded t_bfa or backup plates.

" Composite specimens are typically cut with diamond abrasive

• tooling; metal spec in:en:; are typically prep_red till.rig conventional

:. metalworking tools. Notches ore ground in the. composite specimens using

=

a 60-grit abrasive wheel in a standard surtace or tool grinder. This

o-.

"r wheel is dressed to grind the prescribed notch angle and root radius

": shown in FigureA7 Care must be taken to avoid delamtnating specimens.

ko

" Stackiag and clamping specimens has been found to be effective. Notches :'2

%,-

_?: are usually cut in metal specimens with a 90 ° milling cutter with proper

_ root radius ground onto the cutter if possible.

--=_S

i: Shear tests may be performed with the losipescu shear fixture In

_i_ any of th_ six material shear coordinate planes. It Is conventional to f

_;.' define a material coordinate system where the 1-coordinate is parallel

?'i

:- to the principal in-plane material direction, the 2-coordinate is the

o17.

i other In-plane axis, and the 3-coordinate is perpendicular to the plane

of the plate. The shear stress is then defined as being applied

................... perpendicular to the ftrat coordinate, parallel to the second. Therefore

:2

o

12 and 21 are the in-plane shear components while the tnterlaminar shear

o components are denoted 13, 31, 23, and 32. Specimens to impose any one

."o _i, • of these six sht:ar components can be fabricated from thin laminates by

, ij "_'

"; stacking and bonding sufficient layers of tlle laminated plate to obtain

':, the deslrvd specimen width, as indicated in Figure AS. An in-plane 12 or

°" 21 specimen Is slmply cut from the plate, as shown In Figure ABa.

Interlaminar shear specimens 13, 31, 23, or 32 are cut from thick plates

,' 91
I

Figure A7. [osipescu Shear Test Specimen

t ffi 1.27 cm (0.5 in)

h ffi 1.91 cm (0.75 in)

d = 0.38 cm (0.15 in)

L ffi 7.62 cm (3.0 in)

r = 0.13 cm (0.05 in)

92
2 t

.... OR

a, ONElAYER 12 OR 2t

1 2

OR

!i_ 3 3

dldfjlrlipllpj ,lpl

%

:,: _,30 layers

_.

_?:_ _

_:": b. 31 OR 3P

•:r 3 3

,_!

,,, OR

U;

-: t 2

?

o :i;

'- ' _8 layers

_:_

/:_' A

',?

",_ _- 13 OR23

e

Figure A8. Iostpescu Shear Test Specimen Configurations

Assuming t = 2.5 mm (0.1 in)
L formed by _tacktng and bonding aufficient layors of the thinner plates

; _o obtain the desirad thickness, as shown in Figures Agb and Age.

i'

However, the specimen [ype depicted !n Figure ASb has been shown to be

i very fragile [9,10], producing poor results, and is therefore not

!

recommended. The _pec!men type of Figure Age ls preferred.

i

_' Specimens may be instrumented with strain gages, as shown in Figure

i_ 9 or a modified extensometcr may be used, as shown In Figure /_0.

[ ,,

v,,,. Further discussion of these shear strain methods may be found in

F_ Reference [7]. A more convenient mechanism for attaching an extensometer

! ,.

i _: to measure shear strains in the Iostpescu shear test specimen is

currently being designed.

io*

i ':::: Test Procedures

c

i-f Specimens should be centered in the test fixture using the lift-up

--_: alignment tool to Index on the lower specimen notch. The wedge clamps

_: are then tightened to hold the specimen firmly in place. These clamps

. need only be tightened "finger tight". The objective is to prevent the

specimen from rotating during the test. Over tightening the wedge clamps

_, may result in excessive transverse compression loading of the specimen.

: Tests may be performed at any desired loading rate. A convenient

quasi-statlc rate is I mm/mln (0.04 In/mln). Cyclic loading is also

possible by making appropriate provisions for attaching the fixture In

_ i: the test machine. i/

Shear stresses are calculated by dividing the applied load P by the

cross-sectional area between the notch tips, i.e.,

p

i " wt

i _ UItimate shear strength is not necessarily related to the maximum force

!_i reached, as discussed in References [7,9,10]. During and after actual

L

94

; _
1_ she.ar £atl_urc, the i:t.,i_orclag libels tn _ composic_ mat_rtal may t

reorient, suh_,,quonLly I.,_irlng .-toil., p_rClon o_ t h_ npplh,d fcJrco J-n n

rell_ll.e mode. Tho IJctl4H- _.i[ whlela tlii_t hnppenn e;in utlt, nll y b_ dol_,Hi!lrl_od

f|'i_ll! ;i l_t_ld_ ([Itl:itii:i) _t_t'_}ti_;*[l,_pi;It'i'tll_llt p!ot_ t,_amp!_el_ ,;,f which _] 1'[__

;ili4,Wli i.lrl F[I;uI._O 33, 'rl., iJ,, l iil ;il whhtli l.lit_ litlcottn:ditip_lll2(,iili_lt plot

illirilpl:ly ¢lllllilll, tl /ilopu lti till, ltlll!!!- _+!{ i_lih,h oito_lr f_iilul:c, o(',[.'ur._i, !'lb,,,r

i_.t_llrioill.ill= loll dtl_,_ iiiJl= ll¢._t_l_;-i_iiil: 1171y !ict,)lir ll! I;1] [- C.tinl|)tl_i_l_tlltl lill-!lli.:l{t,

_tl'_2.'-it# lliay be tllc _tetU__ll uhc'<tr _lt°t, lll;t[l Ill '<l¢lllllJ c,'lfl(_f_, '|'#jt-il. tt,;.)tjil'::

"'i

'ii

t

.!

1

!

t

L

{;

t"

I:

1
APPENDIX B

ALIIM[Ni_ ALLOY AND ONII)IREGT[ONAL

GRAPHITE/EPOXY COMPOSITE IOSIPESCO

SHEAR TEST DATA

©

• o - .. • <,. ' '+ . 'If' ' ' + •
,: TABLEB1

_ SHEARSTRENGTHAND SHEARMODULUSFOR 6061-T651

:, ALUMINUMALLOYIOSIPESCU SHEARSPECIMENS

_. Specimen Notch Angle Strength Modulus

_ No. : (Degrees) (MPa) (kSI) {GPa) {Msl)

' 1 90 221 32.0 25.5 3.70

2 213 30.9 25.0 3.62

3 217 31.5 25.5 3.70

_ 4 221 32.1 27.2 3.95

°;. 5 22_..£o 32.__.9 24._.._4 3.5__4_

_" Avg. 219 31.7 25.5 3.70

Std. Dev. 3 0.5 I.I 0.15

'f'"_ 1 ll.O 225 32.6 23.3 3.38

;' 2 219 31.8 22.I 3.20

i_,:" i; 3 218 31.6 22.9 3.32

° ::' 4 220 32.0 21.7 3.15

, _:_ 5 ?23 32.3 21.5 3.12

, Avg. 221 32.1 22.3 3,23

Std. Dev. 3 0.4 0.8 0.11

£I

t

......... I.\,,_. !., \','K riOT __,_::'n

" t)_

98 _INTIENTIONALLV BLANK

ira,

2_

•. " 0000000:
gla-_ NOTCH .ad__

Strain Gage Amplifier

Saturation

Figure BI, Iosipescu Shear Stress-Straln Results for 6061-T651

Aluminum Using a 90-Degree Notch Specimen.

<,,

)_ 99
118- DEG blTrOq ALUHINU_

Strain Gage Amplifier

Saturation

Figure B2. loslpescu Shear Stress-Strain Results for 6061-T651

Aluminum Using a ll(}-Oegree Notch Specimen,

100

_,54_' _ _ -_ _
TABLE B2

SHEAR STRENGTH AND SHEAR MODULUS FOR [O]8T

AS4/3501-6 GRAPHITE/EPOXY COMPOSITE

Specimen Strength Modulus

Orientation No, _ ..... _ (ksi____(GPa_____(Mss_

12 I 101 14.6 6.5 0.95

2 112 16.3 6.0 0.87

3 108 15.6 5.8 0.84

4 114 16.5 8.1" 1.17"

5 104 15.1 5.3 0.77

Avg. 108 15.6 5.9 0.85

Std. Dev. 6 0.8 0.5 0.07

*not included in average

J

i lO1

I'

,9

f_
: 1! O-DEG NOTCH AS4/'350 !--6

: Figure B3. [ostpescu Shear Stress-Strain Results for JOisT

AS4/3501-6 (;raphite/Epo×y. Composite Using

a llO-l)egree Notch Specimen.

;_i, 102
APPZNDIX C

GRAPHITE FABRIC/EPOXY COMPOSITE

IOSIPESCU SHEAR TEST DATA
TABI.E CI

SHEAR STRENGTH AND SHEAR HODULUS FOR OXFORD-WEAVE

T300/934 GRAPIIITE/EPOXY COMPOSITE

Test Spec imen St rength Modulus

O.r_i_e.n.t a t ion ....... No. ......................... (±'qPa)........ (ks_t)_...... (.MPa) ....... (313.i)

12 2 103 15.0 4.3 0.63

3 106 15.3 4.7 O. 68

==' 4 105 15.2 4.8 0.69

5 104 15.1 4.2 0.62

_, Avg. 104 15.1 4.5 0.65

i_ Std. D_-v. 1 0.1 0.3 0.04

21 1 100 14.5 4.6 0.67

2 I00 14.5 4 7 0.68

3 98 14.2 5.4 0.78

Z_;.... 4 103 15.0 5 2 0.75

_ 5 104 15. I 5.0 0.72

: ' Avg. i01 14.7 5.0 0.72

, ! . Std. Dev. 3 0.4 0.3 0.05

13 1 40.4 5.86 3.7 0.54

2 35.3 5.12 3.3 0.48

! ; 3 39.0 5.66 3.0 0.44

:" 4 36.1 5.24 3.0 0.44

5 33.0 4.78 3.7 0.54

': Avg. 3-6".-8 5--_'3-3 -3.-4 0-.-4-9

Std. Dev. 3.0 0.43 0.3 0.05

23 1 31.2 4.53 3.2* 0.46*

2 31.3 4.54 4.2 0.61

3 35.4 5.13 4.8 0.69

4 35.2 5.I0 4.7 0.68

6 36.1 5.23 4.7 0.68

7 40.? 5 8.3 3.4. 0._49"

Avg. 34.9 5.06 4.6 0.67

Std. Dev. 3.4 0.49 0.3 0.04

_no-t- -inc-fude-d- -i-n--a v e r a g e .... , ....... ' .... " .....

]04
IEII

Q m

• == R 76 Im

b) Stress-Displacement

Figure Cl. In-plane (12) Ioslpescu Shear Results for Oxford-Neave

T300/934 Graphlte/Epoxy Composite.

105
a) Stress-Strain

b) Stress-Displacement +.

Figure C2. In-plane (21) loslpescu Shear Results for Oxford-

! Weave T300/934 Graphite/Epoxy Composite.

• lOt_

1 ..)
/

7B _ rt-r--/--r-_-1--T--r--r---r- i_1-l_-Pr-_ 1o

t

,_a. _ ' • I I I _. l , I I i t ' " • -| ' i • • a

'_ • I0 M _IB 40

_.t _ S*rRAX¢E.N 4n_

_. a) Stress-Strain

/i'

-,,,_, 711 -I I ," i i i "i i' I' I I i = i

;i • ' -- 1U

"• I18

/.-!!

!i

.. ll _6 60 76

b) St tess-Displacement

r

i Figure C3. Tnterlamlnar (13) losipescu Shear Results for OxfordWeave T300/934 Graphite/Epoxy.

1.07
9 ,.,I.*,*I*,,_I .... I.,. I

a) Stress-Strain

b) Stress-Displacement

Q

Figure C4. Interlamtnar (23) [osipescu Shear Results for

Oxford-WeaveT300/934 Craphite/Ep¢,xy.

108

- J
TABLE C2

S_IEAR STREN(_TIt ANO ._I[F,A_ MODULOS FOR 5-HARNESS

SAT_N-WEAVE T300/934 (;RAPIIITEIEPOXY COMPOSITE

Ten t Spec lmeu St rengl:h Hodu tu.

12 1 107 15.5 5.2 0.7b

2 115 16.7 5.8 0,84

3 112 16.2 5.9 0.86

4 115 16.7 5.7 0.83

5 III 16.1 0.0 0.87

Avg. 112 16.2 5.7 0.83 L

Std. Dev. 3 0.5 0.3 0.04 [

I

17.3 5.5 0.80 1

21 1 119

2 129 18.7 5.2 O. 75

3 125 18,1 5.7 0,82

4 125 18.1 4.8 0.70

5 116 16.8 6.1 0.88 6 119 172 4.9 o.71

Avg. 12--_ _ 5.---4 0.78

Std. Dev. 5 0.7 0.5 O.07

13 1 36,1" 5.23* 3.0 0.44

2 45.9 6.65 2.9* 0.43*

3 51.6" 7,49* 3.9* 0,57* i

5 46.3 6.72 3.6 0.52

6 43.6 6.33 3.9 0.56

Avg. 45.3 6.57 3.5 0.51

Std. Dev. 1.4 0.21 0.4 0.06

23 1 47.6 6.90 2.9 0.42

2 41.2 5.97 3.2 0.47

3 49.0 7.11 3.8 0.55

4 50.4 7.3t 3.2 0.46

5 45.8 6.64 3.7 0.54

Avg. 46.8 6.79 3.4 O. 49

Std. Dev. 3.6 0.52 0.4 0.06

*not included in average

109
IIIO lS

G

,'i a) Stress-Strain

,_,_ Imm T'-r-'_ i -i i ' ' ' w.-i

I

G

• Q

b

b) Stress-Displacement

o

: Figure C5. In-plane (12) losipescu Shear Results for 5-Harness

Satin-Neave I'300/934 Graphite/Epoxy Composite.

.... ] l0

'::'..it
a) Stress-StraLn

ICdm

8m

G

Q Q

I)2Hq..A,C:8_D_,Q¢,._ ,1_1)

b) Stress-Displacement

Figure C6. In-plane (21) Iosipescu Shear Results for 5-Harness

Satin-Weave T300/934 Graphite/Epoxy Composite.

111
-- 10

16Q

IU 28 _ 4U

°\i, a) Stress-Straln

i

• 'TE _ , , , , i , ", , , i , ', , , 1

L O

.... 2 _

o _

?i'

:_' • a

o_ • 21S 60 715

" b) Stress-Displacement

Figure C7. lncerlamlnar (13) loslpescu Shear Results for

_._ 5-Harness Satln-Weave T300/934 Graphlte/Epoxy

?_;i Composite.

,_:; 1]2

i,

° 'i
7E

N

-_ a a

..... a) Stress-Straln

6

.....i

Q IK* ' ' * l * L , , I i ' ' ' I ' ' • n,

• _15 m 76 I_

b) Stress-Displacement

Figure C8. Interlaminar (23) Iosipescu Shear Results for

5-Harness Satin-Weave T300/934 Graphite/Epoxy

._ Composite.

113

i
TABLE C3

SHEAR STRENGTH AND SHEAR MODULUS FOR 8-HARNESS

SATIN-WEAVE T300/934 GRAPHITE/EPOXY COMPOSITE

Test Specimen Strength Modulus

Orientation No. (MPa) (ksi.) (GPa) (Msi)

12 1 120 17.5 6.0 0.87 ,

2 121 17.6 5.6 O.gl

3 120 17.5 5.1 O.74 i

4 122 17.7 5.0 0.73

5 114 16.5 4.8 O. 70

Avg. 120 17.4 5.3 O. 77

Std. Dev. 3 0.5 0.5 0.07

21 2 107 15.5 5.2 0.76

3 108 15.7 5 • 1 O. 75

4 150 21.8 5.7 0.82

5 148 21.5 4.8 O.70

Avg. 128 18.6 5.2 O. 76

Std. Dev. 24 3.5 0.3 0.05

13 1 35.7 5.18 2.8 0.40

2 41.4 6.00 2.5 0.36

3 44.6 6.47 3.1 0.45

4 36.2 5.25 3.7* 0.54'

5 42.3 6.13 2.3* O.33*

Avg. 40.1 5.81 2.8 O.40

Std. Dev. 3.9 0.57 0.3 0.05

23 1 36.2 5.25 3.0 0.43

2 28.4* 4.12" 3.7 O.53

3 37.3 5.41 3.8 0.56

4 42.0 6.09 3.9 0.57

5 47.0* 6.82* 2.8* 0.4]*

Avg. 38.5 5.58 3.6 0.52

Std. Dev. 3.1 0.45 0.4 0.06

*not included in average

114
16

o_'

G

:0il

a

8 11s _ "/Is I_

a) Stress-Strain

"

J'<_ _i V , , , . I , , i . I , i i * " Q

" ! b) Stress-Displacement

I

i

_., Figure C9. In-plane 8-Harness (Satin 12) -Wloeavslpeseu e T30Shea 0/934r ReGsults raphite/Epoxy for

! Compost re.

° i 115

1
Q Q

a) Stress-Strain

_ L_'''i'''J i,,,,l,,,, I,,,

" F 1

iim

io

im

Q a

b) Stress-Dtsp]acement

Figure CIO. In-plane (21) Ioslpescu Shear Results for 8-Harness

Satln-Weave T300/93_ Graphlte/Epoxy Composite.

116
7G , , , _ j '. .' '. "i'i' I , , , j . , , ,

-- IU

8

Q ; . . • I .... ,J , i,i i I .... a

a) Stress-Strain

7B ' ' ' ' I i , , , I l , i i

s

i .I

Q . , I .... I .... a

0 a _m 7_

I>:_Si=I.AClDE] " __[-ne3 :m)

b) Stress-Displacement

Figure Cll. lnterlamtnar (13) Iosipescu Shear Results for

8-Harness Satin-Weave T300/934 Graphite/Epoxy

Composite.
7E Cl , , i | I ITI'" i i i'i F| I I I J | l i ! I

E

-- IU

I" I

6

:z

II Q

a-_ _ ¢£.-Qs)

a) Stress-Strain

1'°

0 .,,,I .... I..,, Q

8 I m

L

b) Stress-Displa_ement

Figure C12. Interlaminar (23) Iosipescu Shear Results

for 8-Harness Satin-Weave T300/934 Graphite/

Epoxy Composite.

118