The Performance, Safety and Production Benefits of SPS Structures ...

APPENDIXSPS TECHNOLOGY DEVELOPMENTMATERIAL CHARACTERISATIONThe polyurethane elastomer core is an engineered plasticthat has been developed by Elastogran GmbH inaccordance with Intelligent Engineering’s materialcharacterisation specification for the anticipated extremesof the full range of operating temperatures between -45ºCand +100ºC. Mechanical properties of the elastomer,including density, tensile strength (as illustrated in FigureA.1(a)), compressive strength, shear modulus andPoisson’s ratio were verified in accordance with theappropriate ASTM or DIN standards and are summarisedin Table A.1.Mechanical PropertiesThermal PropertiesTable A.1 Characteristic Elastomer Material PropertiesTest ResultsDensityρ e = 1150 kg/m 3Tensile BehaviourProperty -80 o C -60 o C -40 o C -20 o C 23 o C 60 o C 80 o CE (MPa) 3859 2924 1765 1164 874 436 248σ y(MPa)38.9 29.5 28.4 23.0 16.1 8.1 6.2ε u (%) 7.2 11.1 13.2 15.1 32.1 43.1 47.4Compressive BehaviourProperty -80 o C -60 o C -40 o C -20 o C 23 o C 60 o C 80 o CE (MPa) 3878 2813 1347 1166 765 501 336σ y(MPa)52.1 33.5 30.9 21.4 18.0 10.2 7.9Shear Modulus (Torsion Pendulum Test)Property-80 o C-60 o C -40 o C -20 o C 23 o C 60 o C 80 o CG(MPa)1386 955 559 429 285 180 135Poisson Ratioν = 0.36Thermal Expansion CoefficientProperty -30 o C -10 o C 10 o C 30 50 o C 70 o Co Cα (x10 -6 m/m·oC) 96.1 120.1 133.6 148 162.5 184.7.7Specific HeatProperty -20 o C 23 o C 60 o C 80 o Cc (J/kg·oC)1217 1414 1588 1687Thermal Conductivityk = 0.1774 W/m² o C (R-value/mm thickness = 0.032 o F·ft 2·h/Btu)STRUCTURAL BEHAVIOUR AND PERFORMANCEClassification rules commonly specify minimum plateslenderness parameters to preclude local failures becausesuch failures prevent the flexural and compressionmembers (stiffened steel plates, girders, transverses)from reaching their maximum strength. For the SPSsystem, in a parallel manner, a minimum bond strengthand a modulus of elasticity of the core material arerequired to preclude local failures and to limit sheardeformations in the core that reduce this strength. Thesevalues have been determined analytically and verified bytests.Bond at the interface between the core and face plates isrequired for composite action under normal operatingloads, which may include dynamic loading events likewave action or impact loads (grab or heavy cargo) thatoccur frequently; and must be maintained for the fullrange of normal operating temperatures. More than onethousand tests have been conducted in shear and directtension (direction of load transfer across the interface) onbond strength test specimens, as illustrated in FigureA.1(b), with a variety of surface preparations (primedsurface, commercial bonding agents, surface roughness,casting conditions, elastomer properties, ambienttemperatures, base metals, and on samples subject toadvanced corrosion, seawater and chemicals to determinethe bond strength for anticipated fabrication andoperating conditions. Based on the results of these tests,specifications for surface preparation and design valueshave been established.The characteristic flexural and compressive strength ofSPS plates was established by tests as illustrated inFigures A.1(c) and (e). Compression tests includedstocky columns, which gives cross sectional compressivestrength (no buckling) and more slender columns thatfailed by either inelastic or elastic global buckling. Thetests verify that SPS plates with a core modulus ofelasticity greater than the minimum specified can obtainthe flexural (plastic moment capacity) or compressivestrength without local buckling, de-lamination of the faceplates or any other local failure modes generallyassociated with laminates. Analytical predictions ofstrength calculated from commercially available finiteelement programs, verified against the test results, werein close correspondence with mean test-to-predictedratios of 0.98 and 1.05 and coefficients of variation lessthan 5% for flexure and compression respectively.Additional full-scale ultimate (proof) load tests, like thelashing pot test shown in Figure A.1(d), are conducted asrequired.The same finite element programs are being used forparametric model studies to develop design equations forClassification Rules for determining the scantlings forSPS ships and SPS ship components. IntelligentEngineering is currently working with Lloyd’s Registeron developing a set of rules and regulations for sandwichplate ship structures. Until these rules are available, SPSships can be designed and assessed by direct designcalculations, which establish equivalency to comparativesteel ships. Intelligent Engineering has receivedapprovals from major ship classification societies for theuse of SPS in new builds and the rehabilitation of shipswith over 26,000 m² of SPS decks, hulls, tank tops,bulkheads, bow fingers and funnel casings in service on30 projects.13