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

-58-AT is the change inUT= Thermal Str@SStemperatureE = Elastic modulusThus, ‘T= EQATWhere Ecl = 12,800 for aluminum= 19,500 for steelFor equal AT, the thermal str~sses for a steel tnemberwill be 1.s2 times thatof an aluminum member. Thus for any aluminum alloy with a welded yield strengthin excess of 21 KSI, the safety factor on thermal stresses will be equal to orbetter than that of the equivalent steel structure. Since the welded yieldstrength of S083 plate and shapes are 24 and 21 KSI respectively, thermalstresses are not considered as a design constraint. However, the effectsof thermal expansion on hull deflection should be investigated, since limitingdrafts might he affected.IID.FABRICATION OF LARGE ALUMINUM HULLSThe investigation of the effects of large scale aluminum constructionon presently employed fabricating techniques and shipyard operations consistedof a series of discussions with representatives of four large U.S.shipyards with extensive experience in fabricating aluminum structures.The following paragraphs smarize these discussions.MATERTAL HANDLINGThe material itself poses no particular storage problems. Handlinghowever, requires greater care since the aluminum is more prone to damagethan steel. Plates are handled with suction cups or vacuum lifts. Thisprocess requires additional labor. Aluminum requires no sand blasting orpriming such as steel, but is washed with solvent to remove the oxide filmor other contaminants. Since most yards presently do relatively small amountsof aluminum work per hull, this is generally done by hand. Present techniquescould be updated for a large aluminum hull and mechanically controlled cleaningcould be employed for plates and dipping for all shapes. Larger subassembliescan be handled in aluminum, due to lighter weight, which resultsin a cost savings.ENVIRONMENTAL CONTROLSIn general, most yards have no special enviro~ental controls for temperatureor humidity in the fabrication areas. To minimize thermal effects of thesun, it was generally felt that a shed type covering should be erected over theways. This covering, in conjunction with other protective shielding, would alsodecrease welding time lost due to high winds and inclement weather.WELDING AND CUTTINGGeneral yard experience with aluminum covers thicknesses up to and includingone tich. The present techniques for handling and fabricating are generally basedon material one-half inch thick and below. No special problems are envisonedin fabricating large quantities of thicker material.