Investigation on the behaviour under fatigue loading of orthogonally placed plates of glass reinforced polyester

TECHNISCHE HOGESCHOOL DELFT

AFDELING DER SCHEEPSBOUW- EN SCHEEPVAARTKUNDE LABORATORIUM VOOR SCHEEPSCONSTRUCTIES

RapportNr.

SSL 211

INVESTIGATION ON THE BEHAVIOUR UNDER

FATIGUE LOADING OF ORTHOGONALLY PLACED

PLATES OF GLASS REINFORCED POLYESTER

November 1977

TECHNISCHE HOGESCHOOL DELFT

AFDELING DER SCHEEPSBOUW- EN SCHEEPVAARTKUNDE LABORATORIUM VOOR SCHEEPSCONSTRUCTIES

Rapport Nr.

SSL 211

iNVESTIGATION ON THE BEHAVIOUR UNDER

FATIGUE LOADING OF ORTHOGONALLY PLACED

PLATES OF GLASS REINFORCED POLYESTER

/

ir. H.G. Scholte

R.T. van Leeuwen

Project: SC 75-06

Report 211

Contents _Page

Summary.

Specification of material and specimens. - 2

Test Procedure. ₃ - Supporti ₃ - Load ing. ₃ - Frequency. ₃ - Measurements. ₄ Test res'ults. ₅ - Static tests. - 5 - Fatigue tests. 7

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Summary

In order to get more. knowledge about the behaviour of the structural detail's of a glass reinforced polyester minesweeper under cyclic lòading a fatigue testing program has -been carried out.

On request of the Dutch Navy the fatigue strength of -the shell-bulkhead connection was investigated by the Ship Structures Laboratory of- the

Delft University of Technology.

After testing. some specimens under static tensile and static compression load, eleven specimens were subjected to alternating loading to determine

the loads corresponding to fatigue life over a range up to jp7 -number of

cycles-. .

-For one specimen fatiguing was not continued till failure. After a number

of 10 cycles- this specimen was subjected to a static tensile test-. No -significant reduction of the static tensile strength was found.

Under fatigue loading delamination in the connection of bulkhead and shell

will happen in a very early st-age and at low values of the tensile load component of the double load amplitudes.. In almost all tests considerable

delamination and crack initiation was found within a number of cycles

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Specification of material and specimens

Material and specimens are specified in note 511 562 STCAN of 9.7.75 on page 3 and 4. (Plan E 0019-050 DdAÑ CHERBOURO).

According to this note the material composition of the specimens is:

- ttra-hydrophtalique polyester resin (Norsodyne 29.4 T)

- woven roving cloth of 830 g/rn2

- glass-resin ratio: 45-50% glass content.

The specimens were fabricated at DCAN at Cherbour.g.

Form and scantlings of the specimens are shown in figure 1.

For additional reinforcement glass pins were set in the corner of the specimens to connect corner profile with bottomplate. They were glued

in situ with Araldite AW 106 and harder HV 953 U.

The specimens were señt in two.cônsignmen.ts of six testpieces to Deift.,

while one specimen (no. 0) was sent befOre at convenience of the laboratory

in manufacturing the necessary accessories.

The first consignment (with. specimens 1, 2, 3, 4., 5 and 12) was received

at 30-8-1976, while.the second consignment arrived at 28 of September.

A careful inspection, during the test program showed that the specimens. 1, 2,

3, 4,, 5 and 12 were. made out óf one largerplate connection, while the

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Test Procedure

P22

;Glass rein:forced polyester has .a relatively low inddulus of elasticity.

Therefore a large deflection can be expected when the specimens are

subjected to tensile and compression loading.

To avoid that under cyclic loading the deflection would cause Ïarge

secondary axial stresses in the bot.tompiate., special support.s were made

(figure 2). With these supports the specimens could be considered as

completely free supported, so that secondary bendingand axial stresses were avoided or kept negiectably small. During the whole investigation

checking of secondary stress showed values less than 10/00 of the

primary bending stress

Only specimen O was supported by normal round bars sincé the large loads in the static compression test could have damaged the specially constructed

supports.

Load Ing

Ali specimens were tested on an Amsler pulsator with a maximum capacity

of 350 kIl. The hydraulic power steering was effectuated by a low frequency

power supply unit. Whéreas the combined system of pulsator and power supply is single working the desired mean value of the double load amiitude was

obtained with a counter pressure on the loading frame by means of a second actuátor_únderconstant_hydraui±c_pressure in open connection with ap accumulator. A view of the testing arrangement with measuring apparatus

is given in figure 3.

Regulation of the loading was carried out by hand. For this prpöse the

load force acting upon the test piece was measured with a load.celi.

The static load value or in case of cyclic loading, the minimum and maximum values as well as the displacement of the load frame were indicated on

digital voltmeters. Based upon this indication the upper and lower values

of the. double load amplitude were adjusted at the regulation desk by hand

until the right load values were obtained.

In all tests the distance between the supports was 400 mm, according to

figure 2.

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was dependent directly from the displacement and indirectly from the load amplitude. So the frequency was not kept constant during ail _tests, but varied from O,6Hz.at high loads with large deflection _{up to 1,15 Hz}

at th lower loads with smal,l displacements.

Measuements

For yerification and for analysis afterwards many measurements have been made, They were also recorded at regular time intervals during the fatigue

tests and continuously in the static tests.

As shown in figure 4 the l'oad force and the displacement of the load frame

were not only measured by digital voltmeters but they were also recorded

in analog and in digital registration.

Additionally to this the axial and bending stresses of the supports were

measured and registrated. The reason was not only to have a verifcation

of the load cell, but even more to be informed about the response of the

test specimens. The stresses in the support were measured by a couple of strain gauges on each support.

The added output. of strain gauges on a support was a measure for the load bearing reaction force of the concerned support, whereas the sum of all

these reaction forces had to be equal to the applied load force. However, the ¿if ference in the output of the strain gauges on either side of the

supports was a measure for the bending load upon the support and therewith a measure for the secondary load and stress in the test specimen.

Additionally to the electronic measurements of loads and displacement, the test specimens were examined visually on crack development and delamination. At every inspection the number of cycles and crack lengths was noted.

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Test results

The particulars of test condition and thé main results of the tests are given in the table in figure 5.

In the second column of the table the dates of testing are mentioned,, showing the sequence of the different tests.

Preceding to thé fatigue tests specimen O was subjected to static

corn-pression load and specimen I to static tensile load to be informed about

the static strength.

When starting the fatigue testing, by misunderstanding the first experiments

with specimens 2 and 3 'were carried out with a ratio of minimum and maximum load R

=-4

instead of R -1. However, it has the advantage that some

information is obtained about the effect of a change of the mean load value. To keep the total testing time within reasonáble limits, it was decided at

the first instance that the tests should concern the fatigue life up till

about I0 cycles. On account of this consideration and also to gain in a

short time more information about smaller fatigue lives at higher load

amplitudes., the fatiguing of specimen 6 was interrupted when after one wéek

the crack propagation was reduced to a very low level. The fatiguing of this specimen was continued after testing specimens 7, 8 and 9.

Early at December 1976 the Dutch Navy informed us that more information about larger fatigue lives up till cycles would be very welcome.

So it was decided in principle to test the remaining specimens 10, II and 12 'at lower load amplitudes in order to get some test points of about I0

cycles. However,, since the resulting expansion of the test duration would

be considerable, the experiments had to be interrupted for a period of about 10 weeks in favour of other planned research activities of the

labor-atory.

Static tests

Before starting the fatigue tests two specimens were subjected to static

loads. The results are presented in figures 6-9.

Specimen O was tested under compression load. The specimen was supported

by round bars, the distance between the bars was 400 xmn.

The load force was increased continuously with a constant load speed of

0,6 kN per second. . .

At a load force of 90 kN a small crack developed with a loud cracking noise

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The crack appeared over the full breadth of the specimen with a length just equal to the thickness of the bulkhead plate.

The compression strength was 154 kN, At this load force failure of the bottom plate was initiated by rupture of the glass filaments at the lower

side..

When the specimen was unloaded, cracks developed between the vertical bulkhead plate and one of the connecting profiles. Figure 7 shows the

specimen after the test.

A static tensile test was carried out on specimen 1. Equal to the

compres-sion test the load force was increased with a constant speed of about

0.,6'kN per second. The ultimate tensile strength was found to be 50,7 kN..

The results were presented in figure 8 where besides the load curve also the crack pattern is drawn. The numbers 1-19 on the load curve correspond

to the different phases of crack initiation and crack develópment as given

in the drawing of the crack pattern.

From the figure it can be seen that the first crack was initiated at a load fórce of about 45% of the ultimate load strength. The cracks dit not

develop very homogeneously, but abruptly with small intervals as is ref

lect-ed by the points of load relief in the load curvê.

Special. attention is drawn, at the points 8, 9, 10 and 1.3 indicating the moments. that clouds of dust were observed, due to the release of the glass

pins at the surface of the corner connection. Considering the initiation

and propagation of crack "A" it can be expected that farther inside the

corner profile or in the bottompIate the release of the pins started earlier.

/

1-Ibwever, it was not possible to observe more detailed the behaviour of the

glass pins during the test and the influence on the test results. Figure 9

shows that. 6 pins were pulled eut of the corner profile and only two pins

out of the bottomplate.

In order to get information about the influence of fatigue on the. static

tensile strength, specimen 11 was tested under static tensile load after

10 cycles of fatigue loading. At that moment already large fatigue cracks

had developed (see figure. 18').

The result of the static tensile test is presented in figure 10. .

The ultimate load strength was 55,1 kIT; about 10% larger than the ultimate

strength of specimen 1 without fatigue. However, this difference may be due

to the fact that both specimens were made out of different charges.'

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found due to fatigue.

Since the cracks in specimen 11 developed during the fatigue _{test and not}

in th _{static tensile test, the load curve in figure 10 shows no points}

of lod relief,. The kink in the load curve at a load force of about 35 kN

can be attributed to a certain plastic deformation due to the combined influence of the tensile load component, the development of _{cracks and the} pulverization of the resin in the crack(tip)s.

The/hotoraphsin the figures 11, 12 and 13 show specimen 11 in the

differ-ent phases at the point of failure. The marks on the specimen show the

presence of cracks resulting from the fatigue tesit.

Fatigue tests

The results of the endurance tests are presentedin figure _{23. The figure}

shows a ood relation between load amplitude and fatigue. life. _{I.t is notable}

that the specïthens out of one single charge showso good _{a relation that it}

seems to be significant.

Although there is not much more to comment on in this f igure , it is however

useful to tell somewhat more about the behaviour of _{the specimens undèr} fatigue loading since the crack growth is very characteristic.

Particulars about the crack growth are given in the figures 14-22.. It is

remarkable that in a very early stage of loading and fatiguelife _delamination

occurs and crack initiation starts. The whole process of crack growth differs completely from the crack growth in a homogeneous material as steel.

In steel normally one crack will arise at apoint of stress concentration

and propagate in a direction perpendicular onthe direction 6f _{the largest}

working strain amplitude. Totally different, in the _{nonhomogeneous material} of glass reinforced polyester a complete crack pattern with some dominating cracks can be watched. These cracks develop not perpendicular _{on the direction}

of the largest working strain amplitude in the _{structural detail but between}

and following the layers of reinforcements.. The cracks arise due to shear

forces in the resin between the layers of reinforcement and due .to the

tensile stresses in the resin in a direction perpendicular on these layers

of reinforcement.

To give some information about the crack growth for different _{load amplitüdes}

and fatigue lives, the most characteristic and important cracks in five specimens are sho'm in the figures 14-18. The location of _{the cracks and}

several values of crack length are presented. Also the measured displacement of the load frame is given according to the tensile _{part of the double load}

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the other specimens,which are not presented in these figures. Watching the development of the cracks, many remarks can be made.

Large cracks arise and propagate primarily between corner profile and bottomplate or bulkhead. Secondary identical cracks develop between corner

profile and the smaller reinforcement in the corner. Sometimes a large crack

develops at about half the thickness in the corner profile. SchematIcalLy these locations of the large cracks are shown at the positions marked A, B

and _{in figure 21.. Besides, anywhere in the rounding of corner profile' and}

smaller reinforcement a lot of smaller cracks could exist.

Additional to the cracks in the corner many small cracks were found at the end of the corner profile. The occurrences of these craks are sampled in

the table in figure 22. The table shows that in all specimens delamination

and cracks were found between the end part of the corner profile and the

bottomplate, although the crack growth got never a serious or dominating character. The other places of discontinuity at the end of corner profile and reinforcement showed small cracks only in a few cases.

As indicated in the table of figure 22 the five last tested specimens had already cracks or small spots of delamination before being loaded. It ïs

concluded that ¡these defects were caused by enclosure of air or by local

insufficient adhesion to each other of two layers of reinforcement or of

two parts of the specimen. That such defects were not òbserved in the earlier tested specimens may be due to a growing experience and caution in examining the specimens on search for cracks. Therefore, in all

pro-bability, it may be assumed that the earlier tested specimens had the same

defects _{dur ing}

the start of the fatigue test has been defects., which already were present.

in total about eight similar defects were detected before testing in the

center of the corner (position A, B or C according tà figure 21) of the

last five specimens..

However, as far as could be observed and considering the crack initiation

at starting the tests before the full load, amplitude was setted, these

defects did not have a significant effect upon the results.

Although in the figures 14-18 the location of cracks,, the crack length

and the crack growth are presented, it must be realised that the real crack pattern and crack propagation is much more complicated than shown in these

figures.

So, it appeared that many times a crack front is not a straight line and that at any given moment the crack length at the frontside may differ sub-stantially from the crack length at the back of the specimen. However, there

Project: SC 75-06

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is not so much difference when comparing frontside. with back over the total

fatigue life of a specimen. in that case the tendencies in crack development are equal for both sides of the specimen. Where these particulars of the

different. specimens all have the same character withòút significant differ-ences, the presentation of crack growth at both sides of. the specimen and the. relation between is restricted to one specimen. So the five largest and most, important cracks of specimen 9 are given in figure 20. The locations of

these cracks are shown more detailed in the figures 17 and 19.

Figure 19 shows the crack pattern at both frontside and back of specimen 9. A comparison of both sides shows another difficulty in describing the cracks. Many times a crack develops in a plane between two layers of.reinforcement.

In that case a crack that extends over the full breadth of the specimen from one side to the othei side can be identified very easily. But sometimes (local) delanination between three or more adjacent layers of reinforcement

can result in a shift of the crack propagation out of the plane wher.e the

crack started to a plane between other layers o.f reinforcement. Otherwise

such adelamination may connect two cracks which started in different planes.

In bo.th cases the identification of a crack and its particulars as length,

urface and propagation will have a somewhat arbitrary character.

The examination of the specimens during the tests was not restricted to

crack growth only, .but also the. behaviour of the glass pins and their effect

upon the crack propagation was included. Although the observers got thì feeling that the pins had a positive effect upon the resistance against tensile load and fatigue, the burden of the proof is still with them.

The frontlines of the cracks were indeed capricious but the form of the lines showed no relation to the location of the pins. Besides, it was impossible to measure if crack opening at the location of the pins was less than elsewhere.

Likewise, i,t was very difficult and almost impossible to notice the pins

coming loose from bottomplate or even from the corner profile. Only at the

last phase of the fatigue life s.lipping of an increasing number of pins in the corner profile could. be observed. In all specimens,, except I and 2,, most

of the glass pins were pulled out of the bottomplate and only a few pins were

tor.n out of the. corner profile.

Lastly the reduction in rigidity has to be mentioned. In the figures 14-18 the deformation or deflection of the specimens due to th tensile part of the load compònent during the test is given. Halfway of' the fatigue life the de-formation is about 3 times larger than at the beginning., reducing the

Project; SC 75-06 F0 -Report 211

the relation between load and deflection is influenced by the loading

Project: SC 75-06 . 11

-Report 211

Conclusions and remarks

In static testing the compression strength was about 3 times as high

as the tensile s.trength.

Tensile strength and fatigue strength. are strongly dependent on the strength properties of the resin.

Fatiguing does not cause a reduction in static tensile stiength.

4.. It is notable that the results of the specimens out of one single

charge show, so good a relation that it seems to be significant.

Delamination occurs and crack initiation starts at very low tensile

loads and in a very early stage of fatigue life.

Under fatigue loading many cracks develo,p in planes between the layers

of reinforcement. The cracks show a large preference to the planes beieen the composing parts of the structure.

7 The glass pins .did not show a measurable effect upon the resùlts.

In the static tensile test the pins released at a value of about 80%

of the ultimate tensile load.

In fatigue test the pins releasd in the last phase of the fatigue

life.. .

8. Some specimens had small defects due to enclosure of air or by local insufficient adhesion of adjacent layers of reinforcement or of two

parts of the structure; no significant influence, upon the t'est results was found.

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20

A-A

'y

"f'

_'4,4

"a

L

î

j

Reinforcement

50 X 50 X ₅ 600

Figure 1.

TEST SPECIMEN.

o

C"

Q

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/

train gauges.

400

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i

/

Project: SC 75-06 Report 211 I, regulation desk

V

djgital oJ.tmeter str. g.

md

number of cycles load cell multiplexer _.peak_ detector puncher

strain gage indicators

j-time

actuator

dis lacement transducer

amplifiers

analog recorder

Figure 4. SCHEME 0F MEASURING ARRANGEMENT.

supports with load cell

w

digital

Figure 5. TEST PROGRAN AND RESULTS. Specimen No. Date of test Load in kÑ Freq. in Hz Number of cycles X 10 . Static P Dynamic . ¡P min. max. Crack . . . . initiation Crack . ,. . . initiation Failure 0 20/09/76 -154 _00 1 24/09/76 + 50,7 +22 2 29/09/76 -11 /+22 1 at start 46 3 30/09/76 - 8,7/+17,4 1 at start

1230

4 21/10/76 -22 ¡+22 +24 0,6 at start 40 5 25/10/76 -20,51+20,5 +18 0,7 at start 81 6 29/10/76 -17 ¡+17 0,9 51 (583) cont. 25/11/76 H ti 1,05 Ì.667 7 8/11/76 -19,51+19,5 +15 0,8 at start 415 8 17/II/76 -25 ¡+25 +21 0,6, at start 106 9 22/11/76 -28 ¡+28 +25 0,55 at start 44 10 17/12/76 -15 ¡+15 1,15 110 3.905 11 21/04/77 -14,5/+14,5 1,1 106 10.430 17/08/77 + 55,1 1.2 9/02/77 -15 _¡+15 +12 1 at start 534

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specimen O

loading speed 0,6 kN/sec.

Figure 6. SPECIMEN O UNDER COMPRESSION LOAD.

2 3 5 _{lI0 15}

deflection in mm.

hard crack at load of 90 kN due to delamination between both plates. failure of bottomplate at maximum load.

delamination between reinforcement and vertical plate due to

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30 Q) 25 o L41 -ci cj o r- 20 Specimen .1 loading speed 0,62 kN/sec. 13

I0. /

₁₆ deflection in mm.

thé numbers in the figure correspond to the different phases in crack propagation

- at 8, 9, 10 and 13 clouds of dust were observed

- at 16 a white delamination spot was observed

Figure 8. SPECINEN I UNDER TENSILE LOAD.

Project: SC 75-06 ReporL 211 r-18 14

fi&

14 18 ¿rackHRIS t I t I

II

I

l_j_J

2 3 4 5 lO 15 ig

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Figure lO.

SPECIMEN Il AFTER _{CYCLES FATIGUE LOADING IN A STATIC TENSILE}

TEST.

2 3 4 5 Io

Project: SC 75-O6 Report 211 SPECIMEN. 11 LOAD: 0kg SPECIMEN. 11 LOAD: p6000k5

Project: SC 75-06 Report 211 SPECIMEN. 11 LOAD: +525o SPECIMEN. 11 LOAD 0k3

-J

Project: SC 75-06 Report 211 SPEC (MEN 11 LOAD: +5250kq

-J

tK,.

SPEC (MEN. 11 LOAD: t525ok9

-J

Specimen 3 A' q

t

P = +17,5 kN max IP

_=-8,7kN

min displacement due to tensile load component

Q______ _Á

I I

It

I I -tI

numher of cycles

A

Figure 14. FATIGUE- RESULTS OF SPECIMEN 3.

CRACK PROAGATION ANT) DEFLECTION OF SPECIMEN.

t I

tI 11111

I I i

111111

o

o

X Gc 106 o a X 15 10 x A EL) -x A _A 4 A A

X- ....-o

3 4J

o

2 L) Ct I C) A X t I

ti

t

I II'

t I I i o

lt p_max = +20,.5 kN

I P . = -20,5 kN

min

lt

displacement due to tensile load component

o

e

10

e

_15

Io 3 2 (DPI e o O 'PI (D r?C) ts...

Ç/)

Io io

iû

number of cycles

Figure 15. FATIGUE RESULTS OF SPECIMEN 5.

CCK PROPAGATION AND DEFLECTION 0F SPECIMEN.

e

_o

Specimen 5 R = -1 Ql 5

e

4

o

A o

e

A O _AA

_o

A

_o

o

ej number of cycles Figure 16. FATIGUE RESULTS 0F SPECIMEN 7.

CCK PROPAGATION AND DEFLECTION 0F SPECIMEN.

o

15

-

10 - o C L. rtC Lr A A

o

A

J

I

II

o

I I

II IIIII

I A t J I

IIII

L Io 102

o

I _max = +19,5 kN min = -19,5 kN displacement due to

tensile load component

I-

e

-j

56

:j

2 C-) 106

Specimen 9

R = -1

s, 4

=+28kN

max

=-28kN

min displacement due to

tensile load component

e

e

e

e

e

...88

₈ ... 8 -

_o

₈

o

o

o

e

o

t _L I I I I t I t I i I I I t I I i_ t ICI t I J t t I I I I I I I i i t 10 102 number of cycles

Figure 17.

FATIGUE RESULTS OF SPECIMEN 9.

CRACK PROPAGATION AND DEFLECTION OF SPECIMEN.

5 10 b 8

J4

o

3 CS 2 o

Specimen 11 R = -1

& o

-A

I I I

iiiil

102 A' Figure 18.

TP

= max

IP.

= min 1î

+14,5 kN

-14,5 kN

displacement due to tensile load component

IO

o

FATIGUE RESULTS 0F SPECPEN 11.

CRACK PROPAGATION AND DEFLECTION OF SPECIN.

o

o

o I o I _E o -1 C,

o

A A LA A L A 106 A

o....--...

A . d.... I I

?IfII

I I I

fiuti

io7

15 E o 5 EC.) f-A A 4 L 1-J 3 C-) 2 C.)

Project: Sc _75-06 Report 211

L

--J I

Crack pattern at backside after .44 X _cycles

e

Crack pattern at frontside after 44 X 10 cycles

Figure 19. LOCATION OF CRACKS IN SPECIMEN 9. COMPARISON OF FRONTSIDE AND BACK.

.-. I. ---.

_____.1.;_.

/ ¡

/

:,'

r

I

/

i___

-i

-î-

_-

_..

/

....

.-.-. I t i I I I 102 Specimen 9 R = -1 P' = +28 kN/-28 kN 10

crack at front side and back side (see figure 19 for the

location of the cracks)

number of cycles

Figure 20. CRACK PROPAGATION IN SPECI1E 9. COMPARISON OF FRONTSIDE AND BACK.

A 10 ._I 4-J JJ E (J -.4 Ln I C o.' o

e

-1 5 -I 4 L: 3 . L. Q

i

15

dO

o E I I i I I 1111 I I _I ,t I i iO

A Cracks between corner profile

and bottomplate or bulkhead.

B Cracks between corner profile and smaller reinforcement.

C Cracks at ábòut half thickness df corner profile.

2

2

--28/is

C

Figure 2L PLACES OF CJ-1APACTERÏSTiC C1LCKS

CRP-SPECPIENS UNDET. TENSILE AND

I Craks between the end of

corner profile and bottomplate. 2,3 Cracks between corner profile

and the end of the smaller

reinforcement.

4 Cracks between the end of corner profile and bulkhead.

2

IN

FATIGUE LOADING.

1, 2., 3 and 4 are locations of cracks accdrding to figure 21; L = left side; R _{= right side.; F = front; B = back.}

first observation of crack; D = defect observed before test; S = at start; 80 = at 80% of fatigue life.

crack length at first Observation and at nd of test in case cf crack propagation.

Figure 22: RACKS AT T1 DISCONTINUOUS ENDS OF THE

ÒONNECT INC GRP-ANCLE. CRACK* POSITION TEST SPECIMEN 3 4 5 6 7 8 9 10

JI... 12

_Total I 1. LF S: 9 S:1O2O S: 28 12: 4 20: 4 8

6:612

S:528

1O:36 1 LB S:12--16 80:1822 S:4175 20:10 4: 410

D:37O

50:64-15 8: 4 D: 54-17 1: 10 [ D: 3 cracks RF 5: 4 80: 6 S: 37 5:4] I S: 1217 40: 3 S:2 9 8: 4 95: 10

_r

S: 9 RB S: 7 S: 94-12 5:5-*12 S: 4 8

6:612

S:2-± 9 3:34-8 D:1O4-12 3: 3 _J x: 8 " 2. LF S: 4 20: 6 LB _{D: 74-17 D: 4 cracks} RF S: 6

D:9

. S: 2 RB 4.: 4-- 6 D: 7 D: 4

x:

i 3; LF S:5 9 S: 8-»15

i

LB

_S:418

15:1316 4: 5 (SD: O cracks RB . S:. 5 ¡ . ) x: i 4. LF 60; 21 95:27 LB S: 914 35: 20 95:27 S:32-39 D: O cracks

S:3

RB S: 18 . x: 3

z

n X 50

D

D

= -1

max

P. IT'

_{min max}

=-iû

Figure 23.

FATIGUE 0F GLASS

number

LIFE 0F THE

REINFCICE1D I i r t i t

ti

106

of cycles

CONNECTION 0F ORTHOGONALLY PLACED PLATES

POLYESTER..

D

3 P max

lo

_.____,___3

11 (Dpi

-e o

O L.a. r? r) r? Ö

J

o

o' 30 2 -C

2

20L_

-o o 10 P

min

.

IP