CREEP COMPRESSION BEHAVIOR OF POLYURETHANE FOAM

CREEP COMPRESSION BEHAVIOR OF POLYURETHANE FOAM FROM CRYOGENICS TEMPERATURE : SIZE EFFECTS Anne-Gaëlle DENAY1 (PhD student), Annette Roy1, Gaëlle ALISE1, Sylvie CASTAGNET² SUPERVISORS : S.CASTAGNET2, A. ROY1,G. ALISE1 2ENSMA URP 3346 DEPARTEMENT PHYSIQUE ET MECANIQUE DES MATERIAUX 1 AV . CLEMENT ADER, 86961 FUTUROSCOPE CHASSENEUIL CEDEX 1CRITT MATÉRIAUX POITOU-CHARENTES, BP 115, AV. M ALLET, 17 300 ROCHEFORT CEDEX, FRANCE

CONTEXT

Polyurethane foams are widely used for impact applications as well as for thermal insulation, as addressed in the present study for storage and transport by methane carrier of liquid natural gas : LNG (T° = -170°C ). Although initially used for interesting thermal properties, the polyurethane foam also has an important mechanical role. It must be especially resistant to compression and creep, (under the LNG weight over long periods at -170°C, followed by unloading and heating stages ,up to 80°C, when the tank is empty). The general issue of this study deals with the deformation mechanisms and kinetics of pure and glass fiber reinforced polyurethane foams under creep loading (0,25MPA), especially at very low temperatures; and characterize size effect to indentify a minimal representative surface.

OBJECTIVES OBJECTIVES The main objective of this study is to predict long term behavior of PU foam at very low temperatures. Time-Temperature Superposition Principle (TTSP). We decided to use the Time Temperature Superposition Principle (TTSP), and inform this model with experimental results of Dynamical Mechanical Analysis (DMA). However, this experimental technique is only possible on samples of limited dimensions. (Cube of side 6 mm). However, this experimental technique is only possible on samples of limited dimensions. (Cube of side 6 mm). Therefore, it is necessary to ensure that the samples are mechanically representative, and thus to study the effects of scale. To determine a minimum representative volume, we conducted two series of test, monotonic compression with mechanical and optical analysis.

MATERIALS AND METHODS

 Thermoset PU foam  Monotonic compression tests on cubic samples of polyurethane foam , with edges equal to 20,30,40, and 50mm. The strain  Blowing agent = Solkane 141b (1,1 rate is the same for all dimensions of samples ( 1.66.10-3.s-1 ).  Determination of mechanically representative volume. dichloro-1-fluoroethane)  Density : 110 kg/m3 for PU foam,  Full Field measurements of deformation, followed by markers (optical analysis), on monotic compression (PU cube, edge = 50mm), analysis of quadruplets on surface (accuracy of measure : 0.02%).  Determination of deformation heterogeneity .

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 Cellular microstructure :

 Multiscale analysis on creep tests at stress = 0.25Mpa, analysis of the strain response for areas of varying sizes (measurements on a single sample, less strain gradient as above).  Determination of mechanically representative surface and correlation with previous results.

 Closed and spherical cells  Mean cell diameter = 350µm

RESULTS Full Field measurement of deformation

Monotonic compression

Stress - strain curve for each quadruplets.  Repeatability : 5 samples per dimension  On graph : average curve.

1.18 MPa levels deformation

0.4 MPa

numbers of quadruplets

ε