Fatigue life tests of polyester film tape recorder belt

Karsh, I.

English

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JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
PASADENA, CALIFORNIA
N68-I5504
(ACCESSION NUMBER) (THRU)
I /7 ,_
-d_ P_.5- /
https://ntrs.nasa.gov/search.jsp?R=19680006035 2020-03-12T12:05:37+00:00Z
ux-cLA,SS FTED Kinel0gic Document 118001
Issued i0 November 1966
Copy Number
FINAL ENGINEERING REPORT
COMPARISON FATIGUE LIFE TEST OF
SEAMLESS POLYESTER FILM BELTS
FABRICATED BY AN ALTERNATE SOURCE
JPL PURCHASE ORDER DT-377029
Work Period: 1 July 1966 - 31 October 1966
PREPARED FOR:
Jet Propulsion Laboratory
California Institute of Technology
Pasadena, California
JPL SUBCONTRACT DT-377029
PREPARED BY:
Kinelogic Corporation
29 South Pasadena Avenue
Pasadena, California 91101
(Z i._) 684-0434
TWX 919-588-3287
l'his work wa_ performed for the Jet Propulsion _,
California Institute of Technology, spor._,ced b7 the :f
National Aeronautics and Space AdmLqbttatto_ mad_
Contract NAS7-100. -
UNCLASSIFIED
f
Copy Number
I-3
4
5
7
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DISTRIBUTION .
Recipient
Jet Propulsion Laboratory, California
Institute of Technology, Pasadena, Calif.
I. Karsh, Project Manager, Kinelogic Corp.
J. Oreenhalgh, Director of Contract Admin-
istration, Kinelogic Corporation
T. Sinoos, Administrative Assistant to the
Director of Engineering, Einelogic Corp.
Engineering Files, Einelogic Corporation
Publication Files, l<inelogic Corporation
"ii ....;
APPROVALS
Prepared by: ]-n "
\
Prelect Engineer
Approved by:
Director of Engineering
Approved by:
/_a m_s Oreenhalgh ,,'I/
_irectorfho_tractA_i_istration
Approved by:
Director o_
iii
TABLE OF CONTENTS
SECTION
lo
2.
3.
APPENDIX
A.
B.
TITLE
CONTRACT FULFILLMENT
SUMMARY
TECHNICALACTIVITY
3.1
3.2
3.3
3.4
Introduction
Test Procedure
Test Results
Interpretation of Results
and Conclusions
Calculation by.Least Squares Method
Test for Difference of Standard
Deviation (Variance)
References
PAGE
1
1
2 "
2
3
4
FINAL ENGINEERING REPORT
COMPARISON FATIGUE LIFE TEST OF
SEAMLESS POLYESTER FILM BELTS
FABRICATED BY AN ALTERNATE SOURCE
.JPL PURCHASE ORDER DT-377029
I. C O_'TRACT FULFILLMENT"
This final engineering report is submitted in fulfillment of Jet
Propulsion Laboratory purchase order number DT-3770Z9, item 2, bY
Kinelogic Corporation.
2. SUMMARY
During the period beginning 1 July 1966 and ending 31 October 1966,
Kinelogic Corporation has performed work for the Jet Propulsion Laboratory
of the California Institute of Technology in accordance with purchase order
DT-3770Z9.
In accordance with the purchase order, $PL provided a sample lot
of seamless polyester film belts from an alternate source. Tests were
conducted on the alternate source belts under conditions which duplicated
tests performed as part of an earlier study of fatigue life of belts by Kinelogic
Corporation. It was found that the alternate sou_rce belts had a significantly
longer life than did the control group belts. It was determined that the
variability of life within each sample lot does not differ significantly between
samples. The alternate source belts may be expected to have a life
approximately four times that of the control group belts when used under
identical conditions.
_
5
2. SUMMARY (Continued)
The material sources and fabrication techniques and conditions
of the alternate source belts were not disclosed by JPL and were not
investigated as part of this program, and therefore, no discussion of the
relative merits of the process is contained'in this report.
3. TECHNICAL ACTIVITY
3. 1 INTRODUCTION
Seamless polyester film belts have a finite life which is predictable
based upon analysis of statistical data. This report is one of a continuing
series of reports for programs in which data is collected and analyzed. This
section of the report is divided into three subsections which discuss (3. 2)
the test procedure used in the testing program, (3. 3) the results of the tests
which were conducted, and (3.4) the interpretation of the data and conclusions
drawn based upon that data.
-2-
3. 2 TEST PROCEDURE
The fatigue life testers used for testing the alternate source belts
have been adequately described in the final report of an earlier studYl. The
basic idea of the testers is to drive the belts at a relatively high surface speed
with a large diameter drive pulley. The belt passes over a series of small-
diameter test spindles to cause the fatigue stresses. Provision is made for
automatic shut-down of the tester when the belt has failed. An elapsed time
indicator in parallel with the motor measures the time to failure.
The severity of fatigue stressing mawr then be varied by the following
three parameters:
i.
2.
The tension put into the belt at installation,
the size of the test "spindles (which determines
the bending stress),
3. the belt path which determines whether the
bending stress is undirectional or bidirectional.
The test conditions which were used in the earlier test program 1
o
which were used as the control group for this program are as follows:
0
2.
3.
4.
5.
Installed Stress:
Material Thickne s s :
Test Spindle Diameter:
Stress Cycling Rate:
Threading Pattern:
4, 375 PSi
0. 001 inch
• 0. 200 inch
1,940 stress cycles per minute
Serpentine
This set of conditions was selected to provide a test at a stress level
slightly above the endurance limit, thereby affording a compromise between
-3-
7
3. 2 TEST PROCEDURE (Conti,_ued)
economy in testing time and testing significance.
The alternate source lot of belts were installed and operated to
failure on the same equipment and under the same conditions as used in
the earlier study I.
3. 3 TEST RESULTS
The life of each test belt from the control group tests are tabulated
in Table I.
TABLE I
RANK STRESS CYCLES x 106
.0.349io
2. 2.24
3. i0.0
L
4. 10.3
s
5. 12.8
The cumulative failure plot for this test is shown in Figure i.
Also shown in Figure 1 are the best-fit straight-line and the prediction
interval determined from these five test points. The best-fit straight-line
is calculated by the method of leasts squaresi; the usual method employed
for fitting a curve to data which is varying in a random manner but, with
an underlying functional relationship. The prediction interval is then
calculated from the variabilit.y of the test points about the best-fit line.
-4-
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3. 3 TEST RESULTS (Continued)
The prediction interval in Figure 1 is based upon a 90_0 confidence level.
This means that at least 90% of all subsequent test points will fall inside
the prediction interval of Figure I, if the sample is basically unchanged
from the original. Conversely, if the test points fall Outside the prediction
interval, it can be said that at the 90% confidence level, a significant
difference exists between the two samples, i
The lives of the ten belts tested in this study are tabulated in
Table If, and are shown in the cumulative fa'ilure plot, Figure 2.
.RAN_
.
2.
TABLE II
STRESS CYCLES x i0_;
1.33
4.82
3. 12.7
4. 15.6
5. 18.2
o
6. 18.6
7. 20.2
8.
.
I0.
27.2
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43.0
60.4
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10
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........... . w
3. 3 TESTS RESULTS (Continued)
Also shown in Figure 2 are the best-fit straight-line and prediction interval
of the control group lot. These are transferred from Figure I. The
best-fit straight-line for the alternate source lot is also shown in Figure 2.
This line has been calculated by the method of least squares 2. (See
Appendix A.) The values-for ordinate (x) and absissa (y) are measured on
the uniform scales to the right and top of the graph grid pattern respectively.
These scales are in units of standard deviation and the slope of the straight-
line plot (measured in units of standard deviation) is the standard deviation
of the test sample. The slope of the control group was I. 634 and the slope
of the alternate source group was I. 067. The slope, determined by the
of all tests used in the earlier studyi, was 1.20.average
The standard deviation is a quantified measure of the variability of
the sample. The standard deviations determined by the two samples are
not equal. The "F" test is utilized to determine whether the two values have
a statistically significant difference 3. If the #alue calculated from the ratio
of the two sample variances(square of standard deviation) exceeds the tabular
value, a statistically significant difference exists between the samples. The
difference was found not to be significant when compared to the original test
!
and also as compared to the grand average of all useable test data in the
earlier study I at the 90_/0 confidence level. (See Appendix B.)
3.4 INTERPRETATION OF RESULTS AND CONCLUSIONS
The comparison sample of seamless polyester film belts, which _}ere
fabricated by another source, was found to be significantly lo:nger lived than
- 8 -
3. 4 INTERPRETATION OF RESULTS AND CONCLUSIO_-S
the control group sample. The improvement was found to be a uniform
four-fold increase throughout the life of the sample. The life of belts
with'fatigue life characteristics similar to this sample should be four
times that predicted on the basis of the earlier study I.
A four-fold increase in life, while not large, can make the difference
between an acceptable and an unacceptable application. Since seamless
polyester film belts are widely used in low power, low weight applications
of instrumentation recorders, any increase in servicability or reliability
should be identified and utilized. Any differences in materials or fabricating
conditions between those used in the reference study and those used by this
other source should be investigated to determined the cause of the improvement.
-9
REFERENCES
i,
,
Final Report on Fatigue Life of Polyester and
Polyimide Film Belts, Tape Recorder Belt Study,
JPL Subcontract No. 950899.
Page 262, Engineering Statistics, A. H. Bowker and
G. J. Zieberman, Prentice-Hall, Inc. ; 1963.
3. Page 186, ibid 2.
i""
Page 1 of 2
APPE_'DIX A
CALCULATIONS BY LEAST SQUARES METHOD
2 2
x. Yi x.x. x yl l 1
0.67 0. 59 0. 3953 0. 4489 0. 3481
i. 35 1.87 2. 5245 1.8225 3. 4969
i. 85 I.'87 5. 3095 3. 4225 8. 2369
2. 23 3.01 6. 7123 4. 9719 9. 0601
2. 50 3. 21 8. 0250 "6. 2500 I0. 3041
2. 77 3. 25 9. 0025 7.6729 I0. 5625
3. 00 3. 32 9, 9600 9. 0000 i i. 0224
3. 26 3.60 ii. 7360 i0.6276 12. 9600
3. 52 4.06 14. 2912 12. 3904 16. 4836
3.86 4.47 17. 2542 14. 8996 I 19. 9809
!
2 2
_x. _-x _x ._yI _'_-Yi "- iYi
25. 01 30. 25 85. 2105 71. 5073 102. 4555
o
Page 2 of 2
APPENDIX A
_- = . )2
__(xi x)2 _x. 2 (r2 x.
1 l
n
Z(y i _ _)2 = _Yi - (_Yi
n
- _X
C
Slope = b =
= 71. 5073 - (25.01) 2
i0
= 71.5073 - 62.5500
= 8.95729
= 102. 4555 - (30. 25) 2
i0
= 102.4555 - 91.50625
= 10.94925
Yi - (tLx.)1(_lYi)
n
= 85.2105 - 25.01 x 30.25
I0
= 85.2105 - 75.65525
= 9. 55525
" (Yi - = 9. 55525
8. 95729
= .1.066756
Page 1 of 1
APPENDIX B
TEST FOR DIFFERENCE OF STANDARD DEVIATION (VARIANCE)
Comparison of Test of Control Group to Alternate Source Belts
Sample
Control Group
Alternate Source
S_:_ " S 2 ;:_
-]
I. 634 2. 669956 I
>
I. 067 I. 138489 j
F
2. 345
Maximum value of "F" caused by chance at 90"/0 confidence Level:
F0.1,4, 9 : 2.69
There is no significant difference in standard deviation between
the two tests at the 90°7o confidence level.
, Comparison of New Sample of Alternate Source Belts to the Average of
the Earlier Standby Belts
I S iS I
Control Group 1.200 1.440000 1 1.34957825
Alternate Source 1. 067 1. 138489
i
Maximum value of "F" caused by chance at 90% confidence level:
F0. 1, 100,9 : 2. 19
There is no significant difference in standard deviation between
the alternate source belt sample and the average of the contrbl
group belt sample at the 90o70 confidence level.
':_'Sis the sample standard deviation and S 2 is the variance. In
the "F" test the variances are compared.


Comparison Fatigue Life Test of Seamless Polyester Film Belts Fabricated by an Alternate Source Final Engineering Report, 1 Jul. - 31 Oct. 1966

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