SECTION 1 - Boat Design Net

Pt B, Ch 12, Sec 2Table 4 : BalsaVoluminal mass (kg/m 3 )80 96 112 128 144 160 176 192 240Young modulus (MPa), parallel tosandwich in-plane E 1 , E 223 33 42 51 61 71 80 89 116Young modulus (MPa), normal tosandwich in-plane E 31522 2145 2768 3460 4083 4706 5328 5882 7750Shear modulus (MPa), normal tosandwich in-plane G 13 , G 2357 80 103 127 150 174 197 218 286Shear modulus (MPa), parallel tosandwich in-plane G 1240 55 70 90 105 120 140 150 200Coefficient ν 12 , ν 21 0,015 0,015 0,015 0,015 0,015 0,015 0,015 0,015 0,015Breaking compressive (MPa), normalto sandwich in-plane σ 33,53 5,12 5,95 8,17 9,69 11,35 12,80 14,32 18,96Breaking traction (MPa), parallelto sandwich in-plane σ 1 , σ 20,28 0,34 0,42 0,51 0,56 0,64 0,69 0,78 1Breaking compressive (MPa), parallelto sandwich in-plane σ 1 , σ 20,48 0,58 0,71 0,87 0,95 1,1 1,17 1,33 1,7Shear breaking (MPa), throughsandwich thickness τ 13 , τ 230,94 1,1 1,33 1,62 1,73 1,93 2,05 2,33 2,93Shear breaking (MPa), parallel tosandwich in-plane τ 120,7 0,9 1,2 1,5 1,8 2 2,3 2,5 3,4The values presented in this table are given for general guidance only.Note 1: τ 13 and τ 23 are identical to respectively τ IL2 and τ IL1Young modulus (MPa), parallel to grain E 1 60004.4 Natural materials4.4.1 GeneralThe natural material used is the wood, and so the mechanicalcharacteristics of wood as core are intrinsically linked tothe structure of wood used.Two main technics are used to make sandwich with woodcore which differ from the wood grain orientation in relationto the sandwich plane:• wood grain running normal to the sandwich plane(balsa). In this case, the wood core behaviour is similarto foams or honeycombs.• wood grain running parallel to the sandwich plane(cedar for example). In this case, in addition to ensuringstiffness and shear resistance of the sandwich, the woodcore directly takes part to the global sandwich bendingdue to significant stiffness.4.4.2 BalsaThe main mechanical characteristics of balsa are:• high compressive and shear strength• high stability where heated.Balsa is available in a large range of density and thickness.Where balsa is used with high density and thickness, thegrain may be transversally solicited by the global sandwichbending.For information, the standard mechanical characteristics ofthe balsa core material in relation to their density are givenin Tab 4.4.4.3 Red cedarRed cedar is generally used in typical construction, named“strip planking”. With its wood grain running parallel to thesandwich plane, the cedar is also participating to bendingstress located perpendicular to the cedar grain where itsresistance is weaker.For information, the main mechanical characteristics of redcedar, for a voluminal mass equal to 350 kg/m 3 , are in Tab 5.Table 5 : Red cedarYoung modulus (MPa), perpendicular to grainE 2 , E 3300Shear modulus (MPa) G 12 350Shear modulus (MPa) G 23 250Shear modulus (MPa) G 13 350Coefficient ν 12 0,47Coefficient ν 21 0,02Breaking traction (MPa), parallel to graindirection σ 140Breaking traction (MPa), perpendicular tograin direction σ 21,5Breaking compressive (MPa), parallel to graindirection σ 125Breaking compressive (MPa), perpendicularto grain direction σ 22,5Breaking, shear stress (MPa) τ 12 , τ 13 , τ IL2 5Breaking, shear stress (MPa) τ 23 , τ IL1 10The values presented in this table are given for generalguidance only.284 Bureau Veritas Rules for Yachts July 2006 with February 2008 Amendments