Boatbuilding materials and methods Markku Hentinen 2016

Transcription

1 Boatbuilding materials and methods Markku Hentinen 2016 Aalto Kul Typical materials Fibre reinforced plastics FRP > 90 % of recreational boats Aluminium: major part of workboats; small recreational boats; megayachts ABS-plastic: small leisure boats Wood: one-off + small boats Steel: one-off, megayachts Additionally: polyethen, ferrocement 2. Properties affecting material selection Price Manufacturing method/process (investments, skills needed) Strength, stiffness in relation to weight: T /, / ², E/ ³ T = allowable stress in Tension, C = allowable stress in Compression, = allowable stress in Bending, = density Weathering resistance, surface quality (gloss), ease of maintenance

2 Steel High specific strength and stiffness in tension & compression, lower in bending: = 410 MPa (High-tensile >480 MPa) y = 235 MPa (NV-NS, Cor-Ten), High-tensile >340 MPa (NV-HS) = 22 % E = about 210 GPa (3 that of Aluminium) Toughness: large reserve to ultimate strength; ductile Good local strength and abrasion resistance (f.ex. Ice breaking) Good fire resistance (n on-combustible, low price Corrosion: have to be coated (epoxy primers), needs servicing, added thickness for corrosion Condensation insulation needed Stainless steels: AISI 304, AISI 316 (best corrosion resistance as welded), AISI 329 (highest strength) Manufacturing: Welding: arc welding (rod electrode), MIG, even TIG cracks, fatigue, corrosion Expanded surfaces easy, double curvature difficult/expensive longitudinal or transverse stiffening, see ship structures

3 Aluminium Sea-water resistant grades (AlMg3, 4.5 and AlSi1Mg) plates, extruded profiles = 235 MPa E = 70 GPa y = 170 MPa Corrosion: mainly galvanic (to be insulated from more noble metals and carbon fibres; leaks in the electrical system dangerous) Welding: MIG/TIG; cracks, fatigue Riveting: no strength loss in hardened alloys, but risk for leaks Expanded surfaces easy, double curvature more difficult

4 Thermoplastics (recyclable) ABS (acryl-nitril-butadien-stryren) = 30 MPa E = 1.6 GPa Ductile, high impact strength (not below 0 C) Strength values sensitive to temperature Creep may be a problem Must be UV-protected Scantlings and manufacturing process need know-how High cost of moulds Manufacturing techniques: Thermoforming of ABS-sheets; ABS-PU-ABS sandwich also possible (Terhi-boats) Polyethen PEL = 7.5 MPa E = 180 MPa PEM = 13 MPa E = 350 MPa Ductile (even better than ABS), high impact strength; otherwise low strength values Sensitive to UV Creep may be a problem Easy recycling Manufacturing techniques: rotation moulding of granulates, or welding of sheets and pipes or profiles

5 Ferrocement and wood Ferrocement C = 35 MPa Amount of steels is critical for tensile strength Manufacturing: Steel rods, nets, floating the concrete Wood Traditional building also new ones methods, but New adhesives Mechanical properties: large variation Weathering resistance: must be protected, impregnated Limitations to form-giving

6 WOOD Mechanical properties: affected by density, humidity and orientation (anisotropic). High specific values in bending, lower in tension and compression = (humidity %) (MPa) (humidity 12 %) y = (MPa) (MPa) E = (MPa) (MPa) In compression = (MPa) depending on the direction (humidity %) is the density of owen-dried wood (g/cm³) Creep to be taken into account Weathering resistance: to be shielded (oxygen ingress blocked), impregnated (preventing water ingress), or to be treated with antirot agents Limitations to form-giving

7 Traditional planking, or Cross-lamination of plies

8 Reinforced plastics The material gets its final characteristics at the boatyard; quality control is critical Mechanical properties: very large scale, anisotropic: oriented strength and stiffness Suitable for sandwich construction Good surface quality and weathering resistance See separate slides. COMPARISON OF DIFFERENT MATERIALS REQUIRES MANY FACTORS TO BE TAKEN INTO ACCOUNT; THE RESULT IS ALWAYS A COMPROMISE

9 Specific strength values Specific strength Tensile loading UD-laminate Specific strength Bending UD-laminate Biaxial optimised laminates AlMg3 Biaxial optimised laminates Cor-ten Steel (345 Mpa) AlMg3 Woven rowing laminates Wood Woven rowing laminates ABS Mat laminate Steel (210 Mpa) Cor-ten Steel (345 Mpa) Wood Steel (210 Mpa) ABS Mat laminate Ferrocement Ferrocement Specific stiffness Specific stiffness