DTIC ADA246304: Ocean Engineering Studies Compiled 1991. Volume 7. Acrylic Windows- Diverse Design Features and Types of Service

313 Pages·31.8 MB·English

by  Defense Technical Information Center

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Ocean Engineering
Studies
Compiled 1991
Volume VII: Acrylic Windows-
Diverse Design Features
Accesion For 1
NTIS CRA&I and T)pes of Service
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By
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J. D. Stachiw
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PUBLISHED BY
NAVAL OCEAN SYSTEMS CENTER
SAN DIEGO, CALIFORNIA
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Foreword
For successful operation, all manned diving systems, submersibles, and hyperbaric chambers re-
quire pressure-resistant viewports. These viewports allow the personnel inside the diving bells and sub-
mersibles to observe the environment outside the pressure-resistant hulls. In addition, on land, opera-
tors of hyperbaric chambers can observe the behavior of patients or divers undergoing hyperbaric
treatment inside the chambers.
Since the viewports form a part of the pressure-resistant envelope, they must meet or surpass the
safety criteria used for designing either the metallic or plastic composite pressure envelope. The
ASME Boiler and Pressure Vessel Code Section 8 provides such design criteria, and the chambers/
pressure hulls designed on their basis have generated an unexcelled safety record.
The viewports, because of the unique structural properties of the acrylic plastic used in co«i«i»~ici-
ing the windows, could not be designed according to the same criteria as for the pressure envt. s
fabricated of metallic or plastic composite materials. To preclude potential catastrophic failures of
windows designed on the basis of inadequate data, in 196S, the U.S. Navy initiated a window testing
program at the Naval Civil Engineering Laboratory and the Naval Ocean Systems Center. Under this
program, window testing was conducted until 1975.
The objective of the window testing program was to generate test data concerning the structural
performance of acrylic-plastic windows fabricated in different shapes, sizes, and thicknesses. Candi-
dates for investigation included the effect of major design parameters, like the thickness to diameter
ratio, bevel angle of bearing surfaces, and the ratio of window diameter to seat-opening diameter on
the structural performance of the windows; and empirical relationships were to be formulated between
these variables and the critical pressures at which windows fail. To make the test results realistic, the
test conditions were varied to simulate the in-service environment that the windows were to be sub-
jected. Thus, durinp testing, the windows were subjected not only to short-term pressurization at
room temperature, but also to long-term sustained and repeated pressurization at different ambient
temperatures.
On the basis of these data, empirical relationships were formulated between design parameters and
test conditions. Committees in the Pressure Technology Codes of the American Society of Mechani-
cal Engineers subsequently incorporated these relationships into the Safety Standard for Pressure Ves-
sels for Human Oc-upancy (ASME PVHO-1 Safety Standard). Since that time, this ASME Safety
Standard has formed the basis — worldwide — for designing acrylic windows in pressure chambers for
human occupancy. Their performance record is excellent; since the publication of the Safety Stan-
dard in 1977. no catastrophic failures have been recorded that resulted in personal injury.
The data generated by the Navy's window testing program were originally disseminated in technical
reports of the Naval Civil Engineering Laboratory and Jnt Naval Ocean Systems Center, and were
made available to the general public through the Defense Technical Information Center. Some of the
data were also presented in technical papers that subsequently were published in the Transactions of
the American Society of Mechanical Engineers. To facilitate distribution of these data to users inside
and outside of the Department of Defense, the technical reports have been collected and are being
reissued as volumes of the U.S. Navy Ocean Engineering Studies.
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Volume VII of the Ocean Engineering Series is a compilation of several technical reports and pa-
pers dealing with different aspects of the acrylic plastic window technology. The first report describes
in detail the development of a fabrication technique for casting thick spherical shell windows in per-
manent metal molds to net dimensions and the subsequent experimental evaluation of their structural
performance. The second report summarizes the results of a testing program that analyzed the frac-
ture toughness of spherical shell windows under point impact generated by simulated collisions between
submersibles equipped with spherical bow windows and massive obstacles, like ships, offshore plat-
form, docks, and rocks.
The third report presents experimental data on the effect of bubble inclusions in acrylic castings
on the mechanical properties of cast acrylic plastic. These data are particularly valuable for setting
acceptance limits in quality assurance programs for fabricating large acrylic windows from (1) mono-
lithic casting or (2) multiple segments joined by adhesive bonding.
The fourth report presents the designer with information on how weathering and long-term sus-
tained loading degrade the structural properties of acrylic plastic. On the basis of such information,
the designer can apply the appropriate safety factors to design stress values so the acrylic structure
can, even after 10 or 20 years of service, safely carry the load for which it was designed. The data
contained in this report are further augmented by technical papers on the same subject published in
the Transactions of ASME.
The remainder of the technical papers deal with various design and fabrication aspects of acrylic
windows and pressure hulls. Of particular interest is the paper on the design and performance of
plane disc windows with twin conical bearing curfaces. These windows are installed in diving bells and
personnel transfer capsules where the window is subjected to pressurizations from either side.
Another paper covers the design and performance of hyperhemispherical windows that find application
as observation domes on submersibles or nonpenetrating periscopes on submarines. There are also
several papers of interest to designers of acrylic spherical hulls; one addresses the effect of multiple
penetrations, another the incorporation of polycarbonate plastic inserts, and still another the increase
of wall thickness on the structural performance of acrylic spherical hulls.
The pressure and duration of loading data summarized in the reports apply directly to windows of
any size with an identical t/Di ratio, while the displacements shown must be multiplied by a scale fac-
tor based on the ratio of minor diameters on the test and operational windows. To date, these test
data have been used successfully in designing windows and pressure hulls in sizes up to 96 inches for
tourist submarines.
J. D. Sttchiw
Marine Materials Office
Ocean Engineering Division
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TABLE OF CONTENTS: VOLUME VII
NUC TP 410 Development of a Precision Casting Process for Acrylic Plastic
Spherical Shell Windows Applicable to High-Pressure Service
NUC TP 486 Acrylic Plastic Spherical Windows Under Point Impact Loading
NUC TP 305 Effect of Bubble Inclusions on the Mechanical Properties of Cast
Polymethyl Methacrylate
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NOSC TR 1303 Crazing and Degradation of Flexure Strength in Acrylic Plates
as a Function of Time
Transactions ASME Effect of Weathering and Submersion in Seawater on the Mechanical
Properties in Acrylic Plastic
Transactions ASME Effect of Weather, Age, and Cyclic Pressurizations on Structural
Performance of Acrylic Plastic Spherical Shells Under External
Pressure Loading
Transactions ASME Polycarbonate Plastic Inserts for Spherical Acrylic Plastic Shells
Under Hydrostatic Loading
Transactions ASME Spherical Acrylic Pressure Hulls With Multiple Penetrations
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Transactions ASML Acrylic Plastic Spherical Pressure Hull for 2439 m (8000 ft)
Design Depth: Phase I
Transactions ASME Structural Performance of Acrylic Plastic Plane Disk Windows
With Twin Conical Bearing Surfaces.
Transactions ASME Hyperhemispherical Viewports for Undersea Applications
Transactions ASME The Origins of Acrylic Plastic Submersibles
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NUCTP 410
DEVELOPMENT OF
A PRECISION CASTING PROCESS FOR
ACRYLIC PLASTIC SPHERICAL SHELL WINDOWS
APPLICABLE TO HIGH-PRESSURE SERVICE
by
Jerry D. Stachiw
Ocean Technology Department
May 1974
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Approved for public diatnbutie-n ualimiUd
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NAVAL UNDERSEA CENTER, SAN DIEGO, CA. 92132
AN ACTIVITY OF THE NAVAL MATERIAL COMMAND
ROBERT H. GAUTIER, CAPT, USN Wm. B. McLEAN, Ph.D.
Commander Technical Director
ADMINISTRATIVE INFORMATION
The research described in this report covers the time period from June
1972 to December 1973. The research has been jointly supported by the Director
of Naval Laboratories and the Naval Facilities Engineering Command, under
NAVFAC project number 165869.
Acknowledgment
The precision casting process for acrylic plastic spherical shell windows
was developed by Mr. Bruce Beasley at Polymer Products, Oakland, California.
The hydrostatic testing of the cast window specimens was conducted at Southwest
Research Institute, under the personal supervision of Mr. J. Jones, and <tt Naval
Civil Engineering Laboratory by Mr. K. O. Gray. The molds were fabricated by
Adroit Engineering, San Diego, California, according to specifications provided
by NUC.
Under authority of
H. R. TALKINGTON, Head
Ocean Technology Department
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UNCLASSIFIED
SECURITY CLASSIFICATION OF THIS PAGE rWi«n Dai* Enterrd)
REPORT DOCUMENTATION PAGE READ INSTRUCTIONS
BEFORE COMPLETING FORM
I. REPORT NUMBER 2. COVT ACCESSION NO 3. RECIPIENT'S CATALOG NUMBER
NUCTP410
*. TITLE CndSumtttt,) S. TVPE OF REPORT A PERIOD COVERED
Development of a Precision Casting Process Research and Development
for Acrylic Plastic Spherical Shell Windows June 72 to December 73
I, PERFORMING ORG. REPORT NUMBER
Applicable to High-Pressure Service
7. AuTMORf«; B CONTRACT OR GRANT NUMBERED
Jerry D. Stachiw
I. PERFORMING ORGANIZATION NAME AND ADDRESS 10 PROGRAM ELEMENT. PROJECT, TASK
AREA * WOIK UNIT NUMBERS
Naval Undersea Center
NAVFAC Project Number
San Diego, California 92132
165869
II. CONTROLLING OFFICE NAME AND AOORESS 12. REPORT OATE
Naval Facilities Engineering Command, Wash.,D.C. 20360 May 1974
II. NUMBER OF PAGES
Director of Naval Laboratories, Wash., D.C. 20390 58
I« MONITORING AGENCY NAME * AOORESVlf dillrnnl Inm Controlling Ollirt) IS. SECURITY CLASS. fW MM« M*wr|
UNCLASSIFIED
IS. OECLASSIFICATION DO«NORAOING
SCHEDULE
If. DISTRIBUTION STATEMENT (ul rni« K*pe,t,
Approved for public release; distribution unlimited.
IT DISTRIBUTION STATEMENT (ml rh, M|»KI 1>l»,td In Blurt 20. If «ll»nl tot* R./totl)
II SUPPLEMENTARY NOTES
II ([yiOdllCaUHMWIM aary and ttWmltly mv mlmt # »uma*tt
Acrylic hulls pressure vessel windows undersea habitat windows
Acrylic plastic submersible windows acrylic plastic castings
viewports hyperbaric chamber windows
pressure testing spherical shells
IB ABSTRACT tCmmltmu» an #•»•*•• •!•* It »•c»t»*#Y 9*4 idamttty ma mlatk
A casting technique was developed that allows casting of acrylic plastic spherical
shell sector windows to curative and thickness tolerances generally found only in machined
windows. By means of ths technique, 18-inch OD X 10-inch ID windows were made; after
a minor polishing operation, they met the ASTM-D-702 specification for optical clarity. The
mechanical and physical properties of the castings were in the same range as those of com-
mercially available cast plates and sheets, (cont'd)
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00 , 'ST» M73 «"•▼••* ©'««ov as ii oat«.!Tt UNCLASSIFIED
MCUMTV CL AUlFICATlO« OF TMII PACE IBW« Data EMPMNB i
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