design considerations for aluminum hull structures - Ship Structure ...

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-16-l?igures5, 6, 7 ati 8 present fatigue curves for 5083-H113, 5086-H32and 5456-H321 aluminum as well as structural steel alloys. These curvesevaluate the effects of stress ratio, weld bead removal and s~face notches~to the extent of available test data. The letter M corresponds to theR.R. Moore rotating beam fatigue test, and the letter K refers to the Krousereversed beam bending fatigue test. Axial tension-compression fatigue testsgive results appfioxima.telyequal to reversed beam bending results for completestress reversal. Most complete reversal tests utilize the M30re orKrouse procedure. Where undefined, the curves for complete stress reversalare probably developed from axial.or Krouse bending tests. The factor KTdefines the stress concentration factor at the root of the notch.Equivalent curves of Figures 5, 6 and 7 are nearly coincident, and thefollowing discussion applies to the three aluminum alloys. The endurancelimit fatigue band covers the range from 35 KSI to 6.5 KSI, the upper boundcorresponding to a stress ratio of 0.S and tie lower bound correspondingto as-welded material or sharp-notched material subjected to complete stressreversal. The effect of stress ratio and notches on the fatigue strengthof unwelded material is obvious from the curves. A very significant observationis that the fatigue strength of butt-welded specimens with the weldbead removed is 50 to 80 per cent greater than the fatigue strength ofas-welded specimens, although the static strength of as-welded specimensis slightly higher than that of specimens with the bead removed. Thereasons for this phenomenon and the different values from different testprocedures for complete stress reversal will be discussed later in furtherdetail.The S-N curves for steel, Figure 8, follow the same trends as thealuminum curves. However, the magnitudes of the curves for butt-weldedmild steel and high tensile sfieelare somewhat higher than the equivalentmagnitudes for aluminum, the lower bound for steel being IS KSI. This isto be expected, since welding of structural steel results in a 100 per centefficient joint, wh~reas welded aluminum joints exhibit somewhat less than100 per cent static efficiency. The metallurgical explanation for thedifferent weld strengths is beyond the scope of this study; however, itseffect is clearly described by the fatigue curves. The limited fatiguedata presented for steel is obtained from References (29) and (3o), andis used for comparison purposes only. A complete evaluation of thefatigue strength of structural steel is not intended for this study.Figure 9 indicates the detr~ental effect of fresh or salt waterspray on the fatigue strengths of unwelded mild steel and ~083-Hl13aluminum alloy, Reference (13). Both metals have large reductions infatigue strength from water spray, but the reduction in the endurancelimit of aluminum to 4.5 K51 is a major concern in the application ofaluminum in marine environment. References (14) and (23) indicate thatthe extreme reduction in fatigue strength due to water spray is causedby surface oxidation leading to fine cracks. Some methods for minimizingthe reduction in strength are protective coating, surface compressivestresses, etc., Reference (23). The fatigue limit of butt-welded aluminumalloy with notches, subjected to water spray and slow complete stressreversal in a corrosive atmosphere, is as yet undetermined, but it isexpected that such a value would be very low.The following paragraphs explain the reasons for the trends inFigures 3 through 9, and discuss the maw variables that have not beenevaluated quantitatively. The effects of alloy composition, grain size
\ \\.-.-. 1505? U241T \l“--”-””-”--’-H’y\\YK~~. - . . .. . . . . . . - ,-. .— -\.\—-17-10:’’””””” ““”-l”--”---+-””-”+ -t+----”’-””-*----- 1““-”--–-”~”1+””+-” ““””””+01- I --------~o;. /# i~,03 106 1Oe ELmER OFcYcLES(N)FIG. 3 S-N Fatigue Curves for Unwelded 5000 SeriesAluminum Alloys and Structural Steel50ho30120100,03 , ~4 1$ 106NUM8EFl OF ~CI,ES(N),07 108 SLFIG. 4 S-N Fatigue Curves for Welded 5000 SeriesAluminum Alloys and Structural Steel
Page 5: CONTENTSI.. II.III.Iv.v.VI ●VII.I
Page 9 and 10: LIST OF FIGURES(Cent’d)FIGURE NO.
Page 11 and 12: I. INTRODUCTIONThis report summariz
Page 13: art in fabricating and maintaining
Page 16 and 17: MONTEROSSO GRANA /17VALGRANA / CARA
Page 18 and 19: -8-Numerous references have been re
Page 20 and 21: .10.TABLE 2. Mechanical Properties
Page 22 and 23: TABLE 2 Mechanical Properties of Al
Page 24 and 25: TABLE 3 Mechanical Property Limits
Page 28 and 29: -18-ti-’”’-”-””””-L
Page 30 and 31: -20-60 .r---.— ..,.— -——,L-
Page 32 and 33: .22-each stress level, rate of load
Page 34 and 35: -24-!Z456-H321 = 0.485083-H321 = 0.
Page 36 and 37: -26-(c)Members with partial or cont
Page 38 and 39: -28-AllOyS 5083 and 54.56(~ content
Page 40 and 41: -30-The previous paragraphs have de
Page 42 and 43: -32-The problem of cargo hold abras
Page 44 and 45: -34-The question of residual stress
Page 46 and 47: .36-Each alloy was given a relative
Page 48 and 49: -38-GENERAL OBSERVATIONSFYior to a
Page 50 and 51: -40-The question of comparative imp
Page 52 and 53: -42-(d)(e)Poor quality welds due to
Page 54 and 55: -44-The ABS criteria noted above we
Page 56 and 57: -46-DNV would consider fatigue in e
Page 58 and 59: -48-is less, for the exposed side s
Page 60 and 61: Equation (2):-50-Hu1l SMa~um = Hull
Page 62 and 63: -52-Another aspect of vibrations wh
Page 64 and 65: -54-000000000Bottom Shell PlateSide
Page 66 and 67: -56-at the deck and keel. This stre
Page 68 and 69: -58-AT is the change inUT= Thermal
Page 70 and 71: -60-SUl@!ARYAll parties contacted f
Page 72 and 73: -62-(c)(d)(e)(f)T~e exterior side o
Page 74 and 75: TABLE 12 Aluminum Bulk Carrier - Su
Page 76 and 77:
.66-INSUT.ATION AND SHEATHINGShell8
Page 78 and 79:
-68-(b)(c)(d)(e)(f)(g)(h)(i)(j)At l
Page 80 and 81:
-70-IIF.INSTALLATION OF SYSTEMS AND
Page 82 and 83:
Rudder Assembly -carrier should be
Page 84 and 85:
-74-(b)MechanicalTensile Strength 6
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-76-(e)The steel piping must be of
Page 88 and 89:
-78-Other Piping Systems and Valves
Page 90 and 91:
-80-struetion for the aluminum hull
Page 92 and 93:
-82-Large heavy type machine~ must
Page 94 and 95:
suffers attack in an alkaline envir
Page 96 and 97:
-86-REPAIRSObtaining proper repairs
Page 98 and 99:
-88-The design of the midship s~cti
Page 100 and 101:
-90-assuming the increase is applic
Page 102 and 103:
LIGHT SHIP WEIGHT ESTIMATE-92-In or
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-94-TABLE 20 Aluminum Bulk Carrier
Page 106 and 107:
TABLE 22 Trim and StabilityFull Loa
Page 108 and 109:
-98-TABLE 24 Price of Steel Bulk Ca
Page 110 and 111:
GaseNumber. . . -.,- .TABLE 27 Comp
Page 112 and 113:
-1o2-TABLE 28CarriersComparison of
Page 114 and 115:
12 ---n..T.[T7%l,=LEGS IU ORF=ErY
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-106-such as iron ore, on two of th
Page 118 and 119:
-108-7)is,zg~ gg~5e mzz~E’4E!~K2j
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-11o-(a)(b)(c)(d)Inerting system fo
Page 122 and 123:
-112-fatigue, particularly in the p
Page 124 and 125:
-114-2k* Installation of Systems an
Page 126 and 127:
-116-LIST OF REFERENCES(7)Fatigue P
Page 128 and 129:
-11.8-LLST OF REFERENCES(Cent’d)(
Page 130 and 131:
-120-ADDITIONAL SOURCES OF INFORMAT
Page 132 and 133:
-122-redistribution of the still wa
Page 134 and 135:
-124-APPENDIX BEXCERPTS FROMRULES A
Page 136 and 137:
-126-92.07-10(d)(~) Interior stairs
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-128-~gE1+0102030- .. ..—405060
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ectintyclassification4KEYWORDSROLEL
Page 142:
SHIP STRUCTURE COMMITTEE PUBLICATIO
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