An investigation to determine the physical properties of low pressure molded laminates and their use as structural materials

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AN INVESTIGATION TO DETERMINE THE PHYSICAL PROPERTIES OF1 LOW PRESSURE MOLDED LAMINATES AND THE IK USE AS STRUCTURAL MATERIALS

A Thesis Presented to the Faculty of the School of Engineering The University of Southern California

In Partial Fulfillment of the Requirements for the Degree Master of Science in Mechanical Engineering

*>7 Kenneth Brown January 1950

UMI Number: EP60493

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This thesis, w ritte n by

......... Kenneth_ Brown............. under the guidance of h.X$... F a c u lty C om m ittee, and approved by a l l its members, has been presented to and accepted by the C o u n cil on G ra d u ate S tudy and Research in p a r t ia l f u l f i l l ­ ment of the requirements f o r the degree of

Master of Science in Mechanical Engineer ing^..«..Emory___S^..-BQgardus DEAN D a te ...^ ..t. __

n F a c u lty C om m ittee

/

TABLE OP1 CGLTEUTS CHAPTER

PAGE

I. . THE PROBLEMS ARD DEPTHTTIOHS OP5 TERMS USED The problem * *

. .

............................

1

Statement of the p r o b l e m .................

1

Importance of the s t u d y ...................

1

Organization of the t h e s i s ...............

2

Definitions of terms used ...................

3

Low pressure molded laminates .............

3

Polyester resins

3

.........................

Phenolic resins ............................ II.

HISTORY OP L A M I N A T E S ......................... General characteristics of laminates

4 5

. . . .

8

.......................

8

Electrical properties .....................

9

Thermal properties

.......................

9

Chemical properties .......................

9

THE R E S I N S ....................................

10

Types of r e s i n ..............................

10

General properties

III.

1

Polyester resins

.........................

10

Phenolic resins ...........................

10

Characteristics and selection of polyester r e s i n s ....................................

11

Discussion of polyester resins

11

Polyester resins available

..........

...............

12

ii CHAPTER

PAGE Selectron 5003 ..............................

13

Curing characteristics .........

14

Catalyst IV.

.

THE RE INF OK C E M E N T ..............................

16

Function . . . . . . . . . . . . . . . . . .

16

Paper reinforcements .......................

16

Cotton fabric reinforcements ...............

17

Fiberglas reinforcements . . . . . . . . . .

17

Selection and weave of reinforcement material

18

S e l e c t i o n ..................................

18

PI ain weave

18

Uni-directional weave

..................... .

18

.....................

21

METHODS GP F A B R I C A T I O N .........................

22

Lay-up impregnation

VI.

16

Function and types . . . . . . . . . . . . . .

Long shaft satin w e a v e ................ ...

V.

15

.......................

24

Hand impregnation .prior to l a y - u p ........

24

Controlled impregnation prior

29

tolay-up.

. .

TEST PROCEDURES FOR PHYSICAL PROPERTIES. . . . .

30

Flexural properties of l a m i n a t e s .............

30

S p e c i m e n ....................................

30

Experimental procedure .....................

30

Modulus In f l e x u r e .........................

32

Tensile properties of laminates

.............

34

iii CHAFFER

FAGE S p e c i m e n .............................

34

Experimental procedure ...................

34

Compressive properties of laminates

. . . .

33

S p e c i m e n ..................................

35

Experimental procedure ...................

35

Impact properties of laminates .............

35

S p e c i m e n ..................................

35

Experimental procedure ...................

35

Bearing strength of laminates

VII.

.............

37

S p e c i m e n ..................................

37

Experimental procedure ...................

37

Shear strength of l a m i n a t e s ...............

40

S p e c i m e n ..................................

40

Experimental procedure ...................

41

RESULTS OF' THE IB VEST IGAT I C E .................

43

Effects due to a n i s o t r o p y .................

43

Effects due to laminate and fabric thickness

VIII.

v a r i a t i o n s ................................

45

Stress-strain curves .......................

45

Edgewise compression properties

. ........

46

Elexural properties.........................

47

Comparison of laminates end aluminum . . . .

47

SUMMARY AMD C O N C L U S I O N .......................

51

BIBLIOGRAPHY

.........................................

54

iv CHAPTER A P P E N D I X .............................................

PAGE 56

LIST OF TABLES TABLE

PAGE

I.

Properties of F i b e r g l a s .......................

20

II.

Times and Temperatures for Curing Laminates * .

25

III.

Ultimate Strengths and Yield Strengths of Laminates and 24S-T Alclad Alluminum Alloy . .

IV.

57

Load Deformation and Stress Headings for Flexure Tests of Laminates Constructed with 181 F i b e r g l a s ................................

V.

58

Load Deformation and Stress Readings for Tension Tests of Laminates Constructed with 181 Fiberglas

VI.

.

............................

59

Load Deformation and Stress Headings for Compression Tests of Laminates Constructed with 181 F i b e r g l a s ......................... ..

VII.

60

Load Deformation and Stress Headings for Edge­ wise Compression Tests of Laminates Con­ structed with 181 F i b e r g l a s .................

VIII.

61

Load Deformation and Stress Readings for Shear Tests of Laminates Constructed with 181 F i b e r g l a s ....................................

IX.

62

Load Deformation and Stress Headings for Bearing Tests of Laminates Constructed with 181 F i b e r g l a s ............................

63

ii TABLE X,

PAGE Impact Strength Readings for Laminates Constructed with 181 F i b e r g l a s .................

XI.

64

Modulus in Flexure Values for Laminates Constructed with 181 F i b e r g l a s .................

64

LIST OF FIGURES FIGURE

.

PAGE

1.

Chemical Formula of Selectron 5003 ................

14

2.

Types of Fiberglas L e a v e ..........................

19

3.

Vacuum B a g .........................................

23

4.

Lay-up Impregnation.................................

26

5.

Hand Impregnation Frior to L a y - u p ...............

27

6.

Controlled Impregnation Frior to Lay-up

.........

28

7.

Flexure Specimen ...................................

31

b.

Baldwin Southwark Universal Testing Machine . . .

33

9.

Tension S p e c i m e n ...................................

36

10.

Impact S p e c i m e n ...................................

36

11.

Impact Testing M a c h i n e .............

38

12.

Bearing Specimen ..................................

39

13.

Bearing Test J i g ..................................

39

14.

Johnson-type Shear T o o l ..........................

42

15.

Stress Deflection Curves for Laminates using 181 F i b e r g l a s ......................................

16.

Stress Strain and Stress Deflection Laminates using 116 Fiberglas

17.

Laminates using 162 Fiberglas 18.

66

Curvesfor

.................

Stress Strain and Stress Deflection Laminates using 164 Fiberglas

Curvesfor

.................

Stress Strain and Stress Deflection

65

67

Curvesfor

.................

68

ii FIGURE 19.

FAGS

Stress Strain and Stress Deflection Curves for Laminates using 143P Fiberglas .................

20.

Stress Strain and Stress Deflection Curves for Laminates using

21.

70

TypeFiberglas .

............

71

Comparison of Modulus of Flexure of Laminates using Different

23.

143CFiberglas .................

Comparison of Impact Strengths of Laminates using Different

22.

69

TypeF i b e r g l a s .................

72

Comparison of Maximum Shear Strengths of Laminates using Different

TypeF i b e r g l a s .................

73

CHAPTER I THE PROBLEMS AND DEFINITIONS OF TERMS USED During the last decade much progress has been made in determining the properties and uses of low pressure molded laminates.

This information and research data is not com­

plete, however, as laminates have been and are being used only as a semi-structural material. I.

THE PROBLEM

Statement of the problem.

It is the purpose of this

study (1) to give the materials to be used in construction of the strongest low pressure laminates; procedure for testing these materials;

(2) to describe the

(3) to experimentally

determine the physical properties of the laminates; and (4) to determine, by comparing the laminates with an aluminum alloy, whether they can be used as a structural material. Importance of the study.

Plastic airframes have been

a dream of theorists for many years, but a dream that has never been fulfilled.

They are nearer practical realization,

however, becaaise of recent and continued developments in low pressure bonding of reinforcing materials with synthetic, thermo-setting resins.

A number of aircraft companies are

conducting research pertaining to development and practical

2 application of this new process of fabricating large, inte­ gral aircraft components by the singularly simple method of laminating alternate layers of reinforcing material and synthetic resins.

Successes already attained in this field

have caused some engineers to predict that full development of plastic laminates will bring a change in the aircraft field as remarkable as the swing from fabric and dope con­ struction to all-sheet metal. Process engineering laboratories have found that laminates can be successfully used in the manufacture of comparatively large aircraft parts.

No effort lias been

made, however, to utilize laminations in areas of high stress.

In this study an attempt was made to determine all

the necessary physical properties of the strongest laminates, and show how the strength and weight factors of these nev; materials compared structurally with those of aluminum sheet construction. Organization of the thesis.

This thesis presents the

results of an experimental investigation to determine the physical properties of low pressure molded laminates, and the possible usage of these laminates as structural m a ­ terials.

Six types of laminates were used, allowing a wide

range of properties to be Investigated.

The primary object

of the study was to determine whether low pressure molded

3 laminates could be used for structural purposes,

It was first

necessary to determine the resin and reinforcing material that would give maximum strength, and then investigate the physical properties of the laminates*

The results are pre­

sented in tabular and graphical form in the Appendix. 11.

l)Er'In IT IOil S Cl' TKuho USilD

how pressure molded laminates.

The term, low pres­

sure molded laminates, includes all those structures molded to their final form in the range of pressures from four hundred pounds per square inch down to and including pres­ sures obtained by the mere contact of the plies.

They are

constructed by laying up or stacking a base material that is impregnated with one or more of the group of synthetic, thermosetting type resins.

The impregnant (which usually

serves also as the bond) is cured under pressure, at tempera­ tures and for time intervals appropriate to the particular1 resins and bases selected.

An example Is a structure com­

posed of Fiberglas or cloth base impregnated with polyester or phenolic resin. Polyester resins.

This report was based on laminates

using polyester resins which by general definition refers to low molecular weight liquid or viscous products which may be cured to a solid form by the application of heat or a

4 catalyst or a combination of both.

A typical polyester is

made by condensing an unsaturated dibasic acid, maleic anhydride, with a glycol, Phenolic resin*

such as

such as diethylene glycol.1

Phenolic resin is the result of the

reaction of acetylene and p-tert-butylphenal in the presence of zinc naphthenate•2

However, no tests were run with the

laminates using phenolic resins.

1 A. M. Beavers, "Basic Chemistry of the Polyester Laminating Resins," (unpublished paper read before the meeting of the Society of Plastics Industry, Trenton, New Jersey, April 12, 1949). 2 Bred B. Stanley, "Phenolic Resins," Modern Plastic Encylopedia, 1948 edition, p. 678.

CHAPTHK II HI ST GilY GT' LAlv'ilKATiiS From the period of their first appearance several decades ago until the beginning of world bar II, available forms of laminates were confined almost exclusively to simple structures.

These were sheets, rods, tubes and a few special

cross sections and contours molded at pressures between twelve hundred and two thousand pounds xjer square inch.

The

one very important exception to this type was the rolled or wrapped type tubiiv using the phenolic resin with both paper and fabric base construction.

These products had extremely

high electrical and mechanical properties, and were developed by the high pressure laminators.

For these reasons, they are

seldom classified as low pressure laminates.

nevertheless,

they may be regarded as the forerunners of low pressure laminates of more complex form. laminates,

During the early growth of

end until the beginning of World bar II, the de­

velopment was characterized by a steady, tion along the following lines: resins and bases,

somewhat slow; evolu­

(1) A gradual improvement in

end increasingly better manufacturing con­

trol of laminated products:

(2) Additions to the number of

standard and special grades of laminates used for industrial purposes:

(3) A widening of the range of sizes of sheets,

rods, and tubes, and an increase in the number of special

6 forms such as square and rectangular tubes, channels, angles and other simple cross sections:

(4)

The extension of

forms to include custom molding of a number of simple shapes of small and medium size under high pressure.

(Like powder

molded products, these required a minimum of fabricating or finishing operations after removal from the mold):

(5)

An

extension of the laminates to a wide range of industrial applications. The outbreak of V^orld War II found the laminates solidly established in the industrial field.

They were of

such great importance as industrial materials, that they were among the first to be placed on the critical list by

the

War Production Board, and until the close of the war they were rigidly controlled and allocated to top priority pro­ jects. With the war came a great amount of technical data on laminates from the increased research, testing and devel­ opment programs.

Every section of the plastic industry was

profoundly affected but none more than the laminating group. Coordinated with development programs, initiated by manu­ facturers of laminates, were similar projects carried on by manufacturers of resins and base materials, and of pro­ cessing, fabricating and testing equipment.

Superimposed

upon these were broad, over-all programs conducted or super­ vised by various civil or military government agencies.

7 These agencies were to explore the possibilities of new materials and processes and to test thoroughly the estab­ lished types of laminates for new app lie at ions, especially in the expanded field of aircraft construction.

The result

of this expansion upon the manufacture of low pressure laminates may be summarized as follows:

(1)

An enormous

increase in the production volume of the established low pressure rolled tubes of industrial grades and their exten­ sion in their fields of application.

(2)

The modification

of the familiar phenolic resins and the development of suit­ able base material to permit the molding of small, medium and large size structures of intricate contours at pressures as low as fifty and seldom higher than two hundred pounds per square inch.

This process was termed,

11low pressure molding, “

to distinguish it from the established processes using pres­ sures from twelve hundred to two thousand pounds per square inch which thereafter were called ‘‘high pressure molding'1. (3)

The development, testing and immediate application of a

new family of thermosetting resins of the alkyd type desig­ nated by the term, "thermo setting vinyl polymer,*1 (unsat­ urated polyesters).

These new resins were superior to the

phenolics for the low pressure molding and laminating pro­ cesses because of the high bond strength obtained by molding at pressures from fifteen pounds per square inch down to and including the pressure developed by mere contact of the

8 plies.

This high bond strength was combined with exception­

ally high values for the mechanical properties including tensile and impact strengths. Thus, the ond of tho war found tho laminating indus­ try with greatly expanded facilities for processing the established materials, and in possession of a large group of new materials. In the post war era all of these new laminates have found applications in the industrial field, but none more than the polyester impregnated structure.

Because of the

simplicity of the laminating process and the low cost of equipment, this material is in greater demand than any other type of laminate. 1.

GENERAL CHARACTERISTICS Of LAHIEATES

The following basic properties have been found to exist in all types of laminates.3

However, due to the large

number of laminate types available, the values of these properties may be varied over a fairly wide range. General properties.

For most types and grades lami­

nates are approximately half the density of aluminum. pared to this metal they also have a favorable weight-

S Ibid., pp. 667-68.

Com­

9 strength, ratio over a temperature range extending from sub­ zero to about two hundred fifty degrees .Fahrenheit,

dome

grades, however, can exceed this temperature range,

They

also have good dimensional stability within the operating range of temperatures end under extremes of humidity.

The

properties of absorbing and dampening vibrations of audio end other frequencies have proven exceedingly good. Electrical properties.

Laminates have been found to

have high dielectric strength and excellent moisture re si st anc e . Thermal properties.

Laminates possess low heat con­

ductivity and are superior to other nonporous materials as heat insulators.

They have good heat resistance which per­

mits high service temperatures, and they have favorable coefficients of thermal expansion which ensures good dimen­ sional stability in relation to temperature changes within the operating range. Chemical properties.

Under conditions of total

immersion and over a wide range of temperatures laminates are only slightly affected by, or are completely inert to, a large number of common solvents and reagents.

CHAPTER 111 THE RESITS Two different rosins arc available for fabricating laminates and each of these is produced in a slightly dif­ ferent, composition.

This chapter will describe the two

types and give the conclusions for the selection of resin for this investigation. I. Polyester Resins.

TYPES OF RESIN Polyester resins are unsaturated

resins that do not produce water during curing, and thus differ from the ordinary thermosetting resins which cure by a condensation reaction involving liberation of water.

For

this reason the laminates produced by the use of this pro­ duct may be cured by application of heat or a catalyst with very low pressures of from fifteen pounds per square inch down to and including pressures obtained by the mere contact of the plies. Phenolic resins. products,

Phenolic resins are condensation

and therefore a certain amount of water is given

off during the curing operation.

For this reason, unless

special grades and techniques are used, some pressure is re­ required during the final curing operation.

This pressure

11 will range from four hundred, pounds per square inch down to twenty-five pounds per square inch. It can be readily seen that laminates using phenolic resins will require more costly and more intricate equipment to fabricate.

The aircraft industry has therefore foaind

much more use for laminates using the polyester resins. For many yeans it was thought that the higher the laminating pressure the stronger the laminate.

However,

it

has been found that the breaking loads of resin bonded laminates are not affected by laminating pressures ranging from ten to one hundred pounds per square

inch.4

p or these

reasons polyester type resins were used for bonding the laminates for this investigation. ll •

GIh'iHhGihh 1 i.xCG ni.D SxiinD G J.ION Ux* a-Orj n D l r m o r i < 0 Discussion of polyester resins.

Polyester resins,

generally known as contact pressure or impression molding resins, are classified by the chemist as modified alkyd resins, alkyd styrene resins, unsaturated polyester resins and allyl resins. These resins,

supplied in a fluid state, range in

4 J. M. McColgan and D. H. Stutzman, "Plastic Laminates - Physical Properties end Data Presentation," (unpublished Research, North American Aviation, Incorporated, Report No. EA-47-19S, Inglewood, California, March 1947), P . 11.

12 viscosity from that of water to that of cold molasses (from twenty to six hundred thousand centipoises)•

Very slight

pressure is required during the curing cycle to produce a hard, dense plastic.

No volatiles are released during the

curing operation, therefore one hundred pounds of uncured resins produce one hundred pounds of cured plastic. The original liquid can be diluted with suitable solvents but such modifications should always be made with­ in the limitations approved by the resin manufacturer. Curing temperatures are usually in the r ange from 225 degrees to 275 degrees Fahrenheit.

At the start of the

curing cycle the liquid flows readily, but at the inter­ mediate stage it becomes gelatinous.

Further heating im­

parts hardness and strength. The polyester resins are obtainable in two forms; Rigid Polyester which will convert to a hard, infusible state used for rigid and stressed structures, and Flexible Polyester which converts to a flexible cured product suit­ able for products requiring a flexible, non-stressed sheet. Polyester re sins available.

Five types of polyester

resins are manufactured with trade names of Plaskon, Laminar, Faraplex, Vibrin and Selectron.

Each company produces the

resins in either the rigid or the flexible form, however, in regard to present demands, the rigid polyester is the

13 is the most used product. is hased upon ^electron. of its availability.

The data presented in this thesis This v/as chosen primarily because

However,

all other types mentioned

will meet the Air Force specifications thereby producing approximately the same resuits.5 3electron 5QQ5.

Solectron 5003 is the name applied

to a clear, transparent, fast-curing thermosetting resin developed and distributed by the Pittsburgh Plate Glass Company.^

This resin is of the copolymer type.

It Is

furnished and applied at one hundred per cent solid and is cured at moderate temperatures.

It may be cured in the pre­

sence or absence of pressure end with or without pigments, dyes, fillers and reinforcing materials.

Selectron 5003

is produced by condensing maleic anhydride with diethylene glycol.

The chemical reaction involved is shown in Figure

5 J. M. McColgan, uAn Evaluation of Representative Commercial Resins for Laminating Fiberglas Fabrics,” (unpublished Research, North American Aviation, Incorporated, Report No. HA-46-690, Inglewood, California, August 1946), pp. 15-16. ^ Technical Report of the Pittsburgh Flate Glass Company, (Pittsburgh, Pennsylvania: November 1, 1947), pp. 1-2. r/

Technical Report of the Rohm and Haas Company, Periodical Paraplex Hews Letter Ho. 1, (Philadelphia, Pennsylvania, April 6, 1949).

14

0 0 0 w , \ // c G 1 1

ii

jTh

•o d

I

+

CH + n

H0CII2CH20CH2CE20K

(n-l)HgO

0 0 r 11 11 i HO jCHgCKgOCHgCEgOC - CH = CH-C-C 1 -HO FIGURE 1 CHEMICAL FORMULA OF SELECTRON 5003

Curing characteristics.

The curing characteristics

ox ^electron 5003 follows the same general pattern as all other types of resins.

The curing cycle involves conversion

to a gel, followed immediately and, in some cases, almost simultaneously by further polymerization into final ther­ moset form.

During the polymerization process the resin

undergoes a gradual shrinkage.

Ultimate strength, hardness

end other characteristic properties, develop) during the later stages of the cure. Standards of gel time and minimum cure are given by the manufacturer for each type of resin.

These are

essential to the design or selection of equipment for the handling of the resin, particularly in continuous fabrica­ tion processes.

The gel time is defined as the total

15 elapsed time required for the conversion of the catalyzed resin contained in a tube of standard dimension immersed in a liquid bath maintained at constant predetermined tem­ perature.

Solectron 5005 has a minimum curing time of

fifteen minutes and a gel time of eight minutes. Cats-lyst. catalysts,

Selectron 5003 Resin requires peroxide

such as benzoyl peroxide.^

Dissolved in proper

concentration preparatory to use, these catalysts permit rap>id curing of the resins at moderate temperatures. Granular benzoyl peroxide dissolves readily enough in Selectron 5003 resin.

In laboratory work, as was performed

in these tests, it is usually desirable to use a paste type catalyst such as Luperco ATC; benzoyl peroxide ground and suspended in an inert carrier.

The paste type material

dissolves more rapidly and was generally more convenient to use •

Technical Report of the Pittsburgh Plate Glass Company, o p . cit., p. 2.

CHAPTER IV THE REINFORCEMENT 'Three types of reinforcement material are commonly used in the fabrication of low pressure laminates.

The

function of these materials and a brief description of each will be discussed in this chapter. I. Function.

FUNCTION AND TYPES

The filler in a laminate sheet, tube or

rod has two functions:

(1) It serves as a medium for dis­

persing a uniform amount of resin over a large expansion of area; and (2) it gives the finished product characteristics^ such as strength, heat resistance and mechanic si rigidity. Paper reinforcement s.

Any type of paper may be used

as a base material for laminates, however only specially prepared material is of any use to manufacturers or de­ signers.

Paper laminates have been found to have from

forty to sixty per cent less strength than Fiberglas rein­ forced laminates.®

If good electrical properties are re­

quired, and not too high a strength, alpha cellulose papers can be employed.

Rag base papers can be used in applica-

® Philip M. Field, "Basic Physical Properties of Laminates," Modern Plastics, 20:96, August 1943.

17 tions requiring intricate molding and to sheet stock lamin­ ates which will require difficult machining operations for finishing.

Sulfite papers are used frequently for laminates

that do not require high strength or electrical properties, hut which are to be punched.

Creped paper can he used to

some extent for forming or molding into odd shapes. Cotton fabric reinforcements.

The use of cotton

fabrics for laminate reinforcements, covers nearly the entire range of standard types of cotton cloth construction. Various weaves are employed, from the very open to the tight, and from those possessing equal strengths in two directions to the extremely strong uni-directional cloths. The cloths may he aesized or bleached in order to obtain desirable properties in the finished laminate, such as water resistance, low electrical loss or better machining quali­ ties.

Cotton cloths have been .round to have lower strength

characteristics than paper v/hen used as a reinforcement for laminates.^0 fiberglas reinf or c ement s.

G-lass cloths are finding

an increasing variety of uses as laminate filler.

Of

special significance has been the realization of the depen­ dence of the properties of finished laminated parts on the Ibid., p . 98.

18 type and construction of the glass fiber fabric which can be used.

The strength as well as electrical characteristics

of laminates have been found to be greatly increased with the use of Fiberglas reinforcements. II.

SELECT IOH hhD WEAVE OF REIKFOECEMEHT MATERIAL

Selection.

Faper and cotton cloth reinforcements

have been found to have little value because of their re­ latively low strength characteristics.

Glass fabrics, on

the other hand, are proving very useful with their high strength projoerties.

At the present time laminates are

being used only as a semi-structural material but because of their high structural strength Fiberglas reinforcements were used in this investigation.

Fiberglas cloth is made

in a variety of weaves end thicknesses,

and for this study

six types were chosen which were representative of all weaves available.

The types of weave are illustrated in

Figure 2 and the properties of Fiberglas cloths are given in Table I. Plain weave.

Cloth with plain weave is constructed

by each warp and fill thread passing over one thread and under the next thread.

Both the warp end the fill thread

are constructed from the same size yarn. Long shaft satin weave.

Satin weave fabrics are

S

quare

w ovprv

iv e a v e

L otiu-SHf)P T SAT IN \UEA ^•-'

iTT17r7NNNNr-r-p^'EN •VV/-■EiNt. C r /OA.'K U-'^'A VE

'/CURE

YPt5 Of

2

20

TABLE I PROPERTIES OF FIBERGLAS Fiberglas cloth no*

Yarns

VS/arp Fill Square woven fabrics 116 450-1/2 450-1/2

Thickness (inches)

Breaking strength (lbs/inch width) Fill Warp

.004

150

100

162

225-2/5

225-2/5

.015

450

350

164

225-4/3

225-4/3

.015

500

450

.009

610

56

.0085

310

310

Uni-directional fabrics 143

225-3/2

450-1/2

Bong-shaft satin weave fabric

181

225-1/3

225-1/3

21 those in which each warp and fill yarn goes under one and over three, five, or seven yarns according to type designed as four shaft,

six shaft, eight shaft, etc.

The eight shaft

design offers the best possibilities in glass fabrics for plastic reinforeernents.

This construction is a variation of

plain weave, having substantially the same strength yarn in warp and fill.

They are woven so that each warp and fill

yarn goes under seven and then over the eighth yarn instead of going over one yarn and then under the next one, as in the case of the plain weave. Uni-directional weave.

In uni-direction cloth, fill

yarns are very thin as compared to warp yarns.

They are

woven so that each warp and fill yarn goes under two and then over the third yarn.

This type of fabric will give

maximum strength in one direction only, unless they are cross laminated, whereby giving approximately balanced strength properties.

CHAPTER V METHODS OF FABRICATION

Low pressure laminate□ aro fabricated by throe different methods.

These three methods and the molding process

are discussed in this chapter. The laminates were prepared by saturating the base material, Fiberglas, with Selectron 5003 resin, building up the plies to a suitable thickness and curing under pressure. It was only necessary that pressure be adequate to eliminate irregularities in the surface end to assure contact between the several plies.

Pressures were supplied to the specimens

tested in this study by use of a vacuum bag which is illus­ trated in Figure 3.

The vacuum bag process consisted of

placing the reinforcing material, impregnated with resin, within the mold.

The laminate was then covered with a flex­

ible air-impermeable sheet material called Polyvinyl Alcohol Sheet. mold.

The edges v/ere tightly clampted to the edge of the Air was then exhausted from the interior of the bag

by a vacuum pump, and this placed the atmospheric pressure of approximately ten pounds per square inch over the surface of the laminate.

This firmly compressed it against the con­

tours of the mold and at the same time exhausted any air within the resin or reinforcement. placed in an oven for curing.

The laminates were then

o

lA/nn

d

v a

£ 3 y n 9 /j

3J.&A J f W J

9Vtf

3dOl3AN3J

3 J3J~! 850

60 TABLE VI LOAD DEFORMATION ALL STRESS READINGS EGA COIviFRESSlOK TESTS OF LAMINATES CONSTRUCTED UTTII 181 FIBERGLAS

Load (lb) 5 6

9 12

15 18 21

24 27 50 55 56 56 •5 Note:

Deflec­ tion Stress (in) (psi) .0015 2,998 .0029 5,980 .0040 8,980 .0062 11,980 .0078 14,980 .0090 17,950 .0 1 0 0 20,980 .0125 25,970 .0158 26,950 .0155 29,950 .0174 52,920 .0198 55,900 56,200

Load (lb) 5 6

9 12

15 18 21

24 27 50 55 56 56.4

=

b = d

Deflec­ tion Stress (psi) (in) .0015 .0029 .0059 •0060 .0072 .0085 .0098 .0 1 1 0

.0128 .0146 .0169 .0187

2,440 5,950 8,920 11,900 14,850 17,820 20,800 25,800 26,850 29,850 52,670 55,620 56,550

Goad (lb) 5 6

9 12

15 18 21

24 27 50 55 56 57.2

Deflec­ tion Stress (psi) (in) .0017 .0051 .0045 .0070 .0082 .0095 .0105 .0127 .0141 .0165 .0185

5,060 6,150 9,180 12,250 15,500 18,530 21,400 24,500 27,250 30,500 33,700 .0201 36,750 57,900

Load Column x 10°

S -

A

Specimen 5

Specimen 2

Specimen 1

1.02 square inches 1.00

inches

= 1 . 0 2 Inches

F (ultimate) = 56,250

A

56 ,250 1.02

56,200

61 LABLE VII LOAD DJlb'CiL.*A'l'10b ALD BlitLSS iiLADILUS iGA DDG-iAvISL GGiuPrlLSD IOb TLSl'S CL LAD ILATLS CObSLiiuCiLD ViilTH 181 AlBmAG•LAS

Specimen 1 Load (lb)

Specimen 2

Deflec­ tion Stress (in) (psi)

1 2

1,990 3,990 5,960 7,960 9,950 11,920 13,900 15,920 17,900 19,890 21,900 23,600

.0012

.0038 .0057 .0080

3 4 5

.0102

.0125 .0146 .0169 .0182 .0205 •0226 • *“

6

7 8

9 10 11 11.8

tote :

Load (lb) 1 2

3 4 5 6

7 8

9 10 11 11.6

-

P A

.503 square inches

b =

1.000

d

.503 inches

-

1,960 3,920 5,890 7,850 9,800 11,750 13,700 15,700 17,680 19,600 21,600 22,650

.0010

.0032 .0051 .0077 .0100

.0119 .0143 .0163 .0178 .0198 .0219

Load (lb) 1 2

3 4 5 6

7 8

9 10 11

11.9

Deflec­ tion Stress (in) (psi) .0010

.0030 .0051 .0077 .0100

.0117 .0142 .0161 .0176 .0193 .0216 M —

Load Column x 103

S :

A

Deflec­ tion Stress (in) (psi)

Specimen 3

inches

F (ultimate)

=• 11,870

11 •

,870 503

23 ,600

1,955 3,910 5,860 7,830 9,780 11,720 13,650 15,600 17,580 19,500 21,500 23,400

62 TABLE VIII LOAD AND STRESS HEADINGS FOR SHEAR TESTS OF LAMINATES CONSTRUCTED EITK 181 FIBERGLAS

Specimen 1 Load Stress (lbs) (psi) 1225

18,600

So€scimen 2 Load Stress (lbs) (psi) 18,750

1316

Specimen 3 Load Stress (lbs) (psi) 1310

18,650

SAMPLE CALCULATIONS

£ A

Ss A

=

(b)(d)

Ss

=

b = .520 incbes d = .135 inches P (ultimate)

=

1225 pounds

1225 (.520)(.135)

= 1«>600 psi

63 TABLE IX LOAD DLF GriiuAlIGL .-iBD ci'liiJiSS BLADli’ iGS jLrOri BEa KIjaGt TL b IS 01'* BAmIhaTBS C 01.Bin U Of BD aITH 161 I*lDEixo L a 3

Specimen 2

Specimeni 1 Load (lb)

Deflec­ tion Stress (in) (psi) .0058

100 200

.0122

300 400 500 600 650

.0184 .0245 .0308 •0366 • ***•

6,360 12,750 19,100 25,500 31,820 38,200 41,700

100 200

300 400 500 600 640

F td

3

t =

.125 inches

d =

.127 inches

P (ultimate)

Load (lb)

=

Deflec­ tion Stress (in) (psi) .0047 .0115 .0173 .0230 .0297 .0353 --

6,250 12,500 18,750 25,000 31,220 37,500 40,000

650 (.125) (.127)

Specimen 3 Load (lb) 100 200

300 400 500 600 680

=

Deflec­ Stress tion (in) (psi) .0062 6,590 .0132 13,180 . 0 2 0 2 19,720 .0253 26,150 .0318 32,900 .0385 39,500 —_ 44,500

41,700

650 pounds

Bearing strength at which the hearing hole is deformed four per cent of its diameter

—

5250 j:>ounds per square inch.

64 TABLE X IBP ACT STRELGT K READINGS FOR L AMI h ATE S CONSTRUCTED WITH 181 FIBERGLAS

Specimen 1

Specimen 2

(Pounds 1 c3P Inch)

Impact Strength 19.2

3p>ecirrien 3

20.3

table

18.9

a

i

iViOuuLuS IN j?LEXUEE Vj-xLUiiiC? i Oxi LAMINATES CONSTRUCTED RITE 181 FIBiUEGLAS

Specimen 1

Specimen 2

Modulus in Flexure 3,520,00

Specimen 3

(pounds Per Square Inch)

3,250,00

2, 930^ 000

SAMPLE CALCULATIONS

EB

3 4 b" d 3 ( - f )

=

L = 2 inches L = ,550 inches 1 ~ •135 inches P =

1 6 0 p o un ds

I -

.0730 inches

| = 2200

u, _

2

B " W (T 5 5 0 T n W T

3,520,000

/ooaa \ (2200)

TH0C/SAMOS) (M JWCH ScpUA PC pep

CL t.. CQfrf. PJ?£SS/QtS

5 T f ? £ S S „ Po(//VOS

b -j-

T P A/S /O/y

c".\ &PA P/A /G d - eocpiv/sp e-I- p l e x Uf$£

L.:.