ao 7 gs Report 2092. fi Trax. i! ‘DV aval ire \ be © Cc Ss WEE” py, \CSOLLECTiog eae HYDROMECHANICS EVALUATION OF STRESSES IN WEB-STIFFENED CYLINDRICAL SANDWICH SHELLS SUBJECTED TO UNIFORM O EXTERNAL PRESSURE AERODYNAMICS Bh O James A. Nott and Gerald D. Ward STRUCTURAL MECHANICS . = Distribution of this Document is Unlimited APPLIED MATHEMATICS Oo : STRUCTURAL MECHANICS LABORATORY ce STICS AND = RESEARCH AND DEVELOPMENT REPORT (CE BRATION = i; DS: September 1965 Report 2092 0.2093 EVALUATION OF STRESSES IN WEB-STIFFENED - CYLINDRICAL SANDWICH SHELLS SUBJECTED TO UNIFORM EXTERNAL PRESSURE by James A. Nott and Gerald D. Ward Distribution of this Document is Unlimited September 1965 Report 2092 S-FO13 03 02 Task 1956 TABLE OF CONTENTS Page INISURNCI, Whoo oacssoCsoudsUDoRoOOD OOOO OO UBC U DO OUDO OOOO OOH OOUD ONO 1 ADMINIS HR ATyIA Ese: ORMATHION ie rerctretone icine hehe Roneic ren icletclcnlemeleneretctcne 1 ONAN RODUGIMION saggdoogc0ddancnc0d0Dd G0 DD [Kb ERD DDD ODDO ADDOODOOONO’ 1 DAISGRUPTION Ole MODUS csooccoorocvcvo0cdoonooogddeooobaoUDO0 DODO 2 TNSTRUMENDATTONSAND STE SiveP RO CEDURES eeriamerrycrt tarry ter einai ae 3 IUEISIE IRISUICIUS - 15 5 Obed GOO BOS O COMO OOO OOOO OU. U.0.0 DOOO-OO TUCO me a6.006 3 DIESOUSSION scoaaesco False tats oi a empSepto taptestotner cet ARSON o.oo ce tebeheiantans, eovewa tenors penenene 3 GONGEUSTONS se sie cebieuaipedosieiis Gch cones a Peortavosuauencotomel ou suadl Vor sueteie ch oneichews fem eae aie 4 REBERENGES® 2 custe ro tencvole-arlest cevienenetiototie. 0) ey ouster cteiieitel cvs tensor ccm Na ania otucle pcan emt 13 LIST OF FIGURES Page alan i > WMoclol iiineEMSOMNS cooocvoccvvcoo0e dC DDD DDD DD OD DDNOONDND 5 lnibar) 2 so SiR Wools gure@re IbmstemUINEMCEeLON saoosconcacocv00008 5 Figure 3 - Circumferential Strains on Outer Surface of Outside Slo sooooocncHpcodoo ODO DO OO DDDOOD DDC OODODOOODODNDS 6 Figure 4 - Circumferential Strains on Inner Surface of Outside SHVeM ks Fccraenecastena icitolie coins settewshia bench Caylee Rseoleuse-b ete ucn-Mneremeucer one 7 Figure 5 - Circumferential Strains on Outer Surface of Inside SIGN Seadoo soccodscooncs coco dd ocd AUUMOG OO Ud Od od OC 8 Figure 6 - Circumferential Strains on Inner Surface of Inside SHEA oS 55. cray.siver eves eves sts to ede sea te er euestecaet areas eueel aman ieee mere er ausie 8 Figure 7 - Longitudinal Strains on Outer Surface of Outside SINC, 1h.566.660050000000900000000000000000000060000006 9 Figure 8 - Longitudinal Strains on Inner Surface of Outside SHV Geos oaoudcD eos ooD DODO HS OODUa DU OO ODGODUO ODDO DdOON 10 Figure 9 - Longitudinal Strains on Outer Surface of Inside SOV) Le Nee nO eReNEnC Ore mac ror own Siaioetto Sera Oe Clore eeced-O'o! d'buo 6100-0. nal Figure 10 - Longitudinal Strains on Inner Surface of Inside SIGMA, | eactees ons ieh eeu at aiseus) eles sitehel suet ohenensueneuenstaretoheite seaemetomemenoneten ote te 12 ata ABSTRACT Four cylindrical web-stiffened sandwich models were tested under external hydrostatic pressure. Experimental strains were recorded on both outside and inside shells and compared with theoretical strains computed from existing formula developed at the David Taylor Model Basin. The differences between experimental and theoretical results were within the range of experimental error. ADMINISTRATIVE INFORMATION This investigation was conducted under the sponsorship of the Bureau of Ships, Code 442, Project No. S-F013 03 02, Task 1956. INTRODUCTION In recent years, the Navy has shown great interest in the explor- ation of the depths of the ocean by means of deep-diving manned sub- marines. Since the pressure hulls of these submarines are weight critical and often involve the use of thick plates, new types of structures are being investigated to reduce fabrication difficulties and to produce hulls with improved strength-to-weight ratio characteristics. One of these structures is a cylindrical sandwich shell consisting of two concentric cylinders connected by annular webs; this type is illustrated in Figure l. To evaluate the structural strength of a cylindrical sandwich shell, the locations and magnitudes of maximum stresses must be determined. Anal- yses for stress distribution in sandwich shells loaded under external hydrostatic pressure were carried out in References 1 and 2, The maximum stresses occur in the shells at locations next to the webs and midway be- tween adjacent webs. The stresses in these locations are of interest for the purposes of structural design. A graphical analysis for determining * References are listed on page 13. these stresses is also shown in Reference 2. From the stresses obtained by use of this emety7ois .” theoretical strains can be computed and com- pared directly with observed data. To evaluate the theoretical analysis, four sandwich-type models were fabricated from epoxy resin and tested under external hydrostatic pressure. Strains were recorded at locations next to the webs and midway between the two webs on both outside and inside shells. A longitudinal strain distribution along a web spacing was also measured in one model. This report presents the experimental strains and a comparison of observed and theoretical values. DESCRIPTION OF MODELS Four models, designated SER-1, SER-2, SER-3, and SER-4, were fabricated from epoxy resin. The composition of the epoxy resin was 50 percent Versamid 125 and 50 percent Epon 828. A sandwich-type con- figuration for the models was constructed by joining a series of channel- shaped rings together. These rings were individually formed by pouring liquid resin into a mold, allowing the resin to harden at room temperature for 24 hr, and then post curing the rings in an oven for 8 hr at a tem- perature of 130 F. Each ring was then machined to the final required dimensions. The dimensions of these rings are shown in Figure 1. Specimens were made to determine the material properties of the epoxy resin. A Young's modulus of 328,000 psi and a Poisson's ratio of 0.4 were determined from separate tests using a compressometer, deflectom- eter, and a Tuckerman optical strain gage. These values were used for determining the theoretical strains presented in this report. The design of the four models was oriented to study the effects of shell lengths on stress distributions in the sandwich shells. The basic design of the shell thicknesses and the radii was fashioned after a geometry for a proposed deep-diving oceanographic hull stmucture.~ On each of the four models, the outside radius was 5.40 in., the inside radius was 4.11 in., the outside and inside shell thicknesses were 0.163 in., and the web thickness was 0.138 in. Only the web spacing in the four models varied. The spacings (dimension Le shown in Figure 1) were 0.75 in. for Model SER-1, 1.00 in. for Model SER-2, 1.25 in. for Model SER-3, and 1.50 in. for Model SER-4. INSTRUMENTATION AND TEST PROCEDURE Each model was instrumented with foil-type strain gages 0.063 in. in length. These gages were located on the two shells of each model in areas of critical stress. The middle ring (Ring 5) on each model was in- strumented at locations next to the web and midway between adjacent webs on the O- and 180-deg orientation. Check points were instrumented at locations midway between the webs on an adjacent ring (Ring 6). Additional gages were also placed on the outside surfaces of the models next to the webs at the 45-, 90-, and 135-deg orientations on Ring 5. Model SER-2 was instrumented with additional longitudinal gages covering the area be- tween midbay and the web juncture. After the models were instrumented, the rings were bonded together with the same type of epoxy resin used in the models. Figure 2 shows the four models before testing. The models were tested hydrostatically in a pressure tank to obtain elastic strain data. Two pressure runs were made on each model to a pressure of 100 psi, and strains were read at each 10-psi increment. TEST RESULTS The strain recordings obtained during the second run of each test were used to compute strain sensitivities. These strains were plotted as a function of x/2 (where x is the distance from the web to the center of the strain gage and 2 is the unsupported length of the bay) and are shown in Figures 3 through 10. The solid line represents theoretical strains computed by utilizing Reference 2. The dotted vertical lines in these figures represent the fillet at the intersection of the web and shell. DISCUSSION The primary purpose of this investigation was to establish experi- mental verification for the analysis of deformations in web-stiffened sand- wich cylinders. In general, excellent agreement was obtained as shown in Figures 3 through 10. Data on the longitudinal strain gradient between webs pro- vided by the additional longitudinal gages on SER-2 agreed well with the theoretical values. The largest discrepancies occurred at the intersection of the shell and web where the fillet was located. This fillet (Figure 1) was incor- porated to reduce the effects of shear and possible stress concentrations due to undercutting or voids that could have developed during fabrication. Observation of the experimental strains suggested that a portion of the fillet acted as a stiffener. This effect is less noticeable or negligible on the two models with longer bay lengths. CONCLUSION Theoretical analysis as given in Reference 2 will adequately predict the elastic axisymmetric behavior in web-stiffened cylindrical sandwich shells subjected to hydrostatic pressure. SSNS SSS MISES ESS] (0.8 OD ——= MODEL LENGTH MODEL L¢ (IN) > Psp-312652 || Figure 2 - SER Models after Instrumentation IT9YS apts3ino FO sd¥FIng 193nO uo SuUTeI4S [TeTUSLEeFuMIDIT) - i x os'O 8vO bb'0 Ob'0 9£'0 ze'0 820 b2'0 ozo gro rae) 800 ¢ oinsty b00 2 39N34343u=— TWLN3WIN3dxX3 O ISd/NI/NI 77 NI NIVYLS TT°YS Spts3no FO sdeFInsg rouuT uo SUTeI}S TeTJUsLOFUMIIT) - p oin3sTty ISd/NI/NI 77 NI NIVYLS O EXPERIMENTAL a— REFERENCE 2 STRAIN IN A IN/IN/PSI fe) 0.04 0.08 0.12 0.16 0.20 0.24 0.28 0.32 0.36 0.40 0.44 0.48 0.50 T O EXPERIMENTAL = REFERENCE 2 STRAIN IN LL IN/IN/PSI Figure 6 - Circumferential Strains on Inner Surface of Inside Shell STRAIN IN t IN/IN/PSI oO EXPERIMENTAL — REFERENCE 2 [o} 0.04 0.08 0.12 0.16 0.20 0.24 0.28 0.32 0.36 0.40 0.44 0.48 0.50 os Se Figure 7 - Longitudinal Strains on Outer Surface of Outside Shell O EXPERIMENTAL — REFERENCE 2 CLE EL TT) LE) EO) Co CLEA CT EVERETT CAT) LTT YE PE ET) et ALLL GA rr ETT CT ae [o) fe) + ISd/NI/NI 77 NI NIVYLS x|s Figure 8 - Longitudinal Strains on Inner Surface of Outside Shell 10 STRAIN IN £l IN/IN/PSI -60 O EXPERIMENTAL -50 — REFERENCE 2 Figure 9 - Longitudinal Strains on Outer Surface of Inside Shell Wh o EXPERIMENTAL REFERENCE 2 +20 ISd/NVNI77 NI NIVYLS 0.40 0.36 0.16 0.08 0.04 as A Figure 10 - Longitudinal Strains on Inner Surface of Inside Shell 2 REFERENCES 1. Pulos, John G., "Axisymmetric Elastic Deformation and Stresses in a Web-Stiffened Sandwich Cylinder under External Hydrostatic Pressure,"! David Taylor Model Basin Report 1543 (Nov 1961). 2. Nott, James A., "Graphical Analysis for Maximum Stresses in Sandwich Cylinders under External Uniform Pressure," David Taylor Model Basin Report 1817 (May 1964). 3. Hom, Kenneth and Blumenberg, William F., "Hydrostatic Tests of Structural Models for Preliminary Design of a Web-Stiffened Sandwich Pressure Hull," David Taylor Model Basin Report 1763 (Sep 1963). 13 bain (eet he a sy;" Oi teh rete Twa ER ary + cot fe cou ce ‘oi 1 a CED, Witdebes We anion iret bya wn o Ht vi Weyer eke my La p t ce as ay & Ao hae ae ge AF ong Y nedieet afk SER rt a sc: a Berti ae Wit ait fs . iy (ee LT EM Se aais dv bib shh ‘ani eM el ane ane 197 rea “nave 'f EDOM Fm (Gey B4% - A bt ° 2 j ‘ i er } b Ly “d ‘ =. i ’ } ss abe 4 7 r 7 J A } 7s iad ‘ si Ai exe 7 a N phy, - * ~ 1 i { j oP e ee i if 2 ey A A A Pi rey ‘ ; tick «Se j “(Laie 4 : hice - ant ay Copies 14 a ee NO j=) fo a et lO) INITIAL DISTRIBUTION CHBUSHIPS 2 Sci & Res Sec (Code 442) 1 Lab Mgt (Code 320) Tech Lib (Code 210L) Ships Res Br (Code 341) Appli Sci Br (Code 342) Prelim Des Br (Code 420) Prelim Des Sec (Code 421) Ship Protec (Code 423) Hull Des Br (Code 440) Hull Struc Sec (Code 443) Sub Br (Code 525) CHONR, Head Struc Mech (Code 439) CNO (Op O7TB) CDR, USNOL CDR, USNRL (2027) CDR, USNOTS, China Lake CO, USNUOS CO, USNUSL CHBUWEPS, SP-001 CDR, DDC NAVSHIPYD PTSMH NAVSHIPYD MARE NAVSHIPYD CHSN NAVSHIPYD NY USNASL SUPSHIP, Groton ee e Elec Boat Div, Genl Dyn Corp SUPSHIP, Newport News NNSB & DD Co SUPSHIP, Pascagoula DIR DEF R & E Attn: Tech Lib CO, USNROTC & NAVADMINU, MIT O in C, PGSCOL, Webb DIR, APL, Univ of Wash, Seattle 15 Copies 1 NO NAS, Attn: Comm on Undersea Warfare DIR, WHOI Dr. R. DeHart, SWRI Prof. J. Kempner, Brooklyn Polytechnic Inst Mr. J. L. Mershon, AEC act) PUR a ital TRE tray.) ae a DPR ANP : PAE wat rin Soha nip! oll ii