A comprehensive study has been conducted to develop proper test methods for accurate determination of failure strengths along different material directions of closed-cell polymer-based structural foams under different loading modes. The test methods developed are used to evaluate strengths and failure modes of commonly used H80 polyvinyl chloride (PVC) foam. The foam's out-of-plane anisotropic and in-plane isotropic cell microstructures are considered in the test methodology development. The effect of test specimen geometry on compressive deformation and failure properties is addressed, especially the aspect ratio of the specimen gauge section. Foam nonlinear constitutive relationships, strength and failure modes along both in-plane and out-of-plane (rise) directions are obtained in different loading modes. Experimental results reveal strong transversely isotropic characteristics of foam microstructure and strength properties. Compressive damage initiation and progression prior to failure are investigated in an incremental loading–unloading experiment. To evaluate foam in-plane and out-of-plane shear strengths, a scaled shear test method is also developed. Shear loading and unloading experiments are carried out to identify the causes of observed large shear damage and failure modes. The complex damage and failure modes in H80 PVC foam under different loading modes are examined, both macroscopically and microscopically.

Light-weight polymeric foams are frequently used in composite sandwich construction in which foam core material properties could significantly influence the overall performance of the sandwich structure. Foam mechanical properties usually depend on a number of factors, including foam density, cell microstructure, and properties of foam–matrix polymer. Although the properties of foam–matrix polymer are determined mainly by the properties of the foam base (parent) polymer, they are also affected by other factors such as foam processing conditions. With the large number of material and microstructure parameters that influence foam properties, modeling mechanical behavior of polymeric foams could be quite involved, especially if foam behavior is anisotropic. This paper describes an effort to predict static elastic stiffness of closed-cell PVC foams. PVC foams are modeled as transversely isotropic materials with properties in the foam rise direction different from those in the planar (plane of isotropy) directions. An engineering approach, based on fibrous composites, is developed to predict in-plane and out-of-plane stiffness of PVC foams. The validity of the engineering model for the PVC foam stiffness is first demonstrated through comparison with test results on DIAB H80 foam obtained from a systematic in-house test program. Comparison of the predictions with the stiffness properties reported by a PVC foam manufacturer for various other density foams is also carried out. Good agreements are obtained for the cases studied. Comparison of stiffness predictions obtained in the paper with predictions from other published models of isotropic foam behavior is presented.

This is part of a series of articles on the properties of a thermoplastic polyamide matrix [PACM-12, DuPont, poly(bis-4-4'-dicyclohexylmethane) n -dodecanediamide]/graphite fiber (AS4, Hercules) composite. The structural characterization of the neat resin by differential scanning calorimetry (DSC) and X-ray diffraction as a function of processing history is described here. PACM-12, considered a representative thermoplastic matrix polymer for advanced composites, as well as an engineering plastic, is partially crystalline (ca. 20%) under normal composite processing conditions, but can be quenched to a completely amorphous state. The complex DSC results are shown to result, at least in part, from the presence of a different crystal structure in slow cooled PACM-12 than in quenched, annealed or fiber samples, to a melting-recrystallization-melting process during heating and to the effect of heating rate.

A study has been conducted to develop proper test methods and to utilize the tests to evaluate three-dimensional mechanical behavior of a polyvinyl chloride structural foam (Divinycell H80 with nominal density of 80 kg/m 3 ). Transversely isotropic foam microstructure was examined and it revealed that the cell size aspect ratio in in-plane directions was near unity but greater than one in the out-of-plane (rise) direction. Foam stiffness properties, i.e. moduli and Poisson's ratios, were obtained in different loading modes, along both in-plane and out-of-plane directions. The influence of test specimen geometry on compressive properties was studied. Foam specimens with both straight-side and reduced gage sections were designed, fabricated and tested. The effect of specimen gage-section aspect ratio was identified as a critical geometric parameter, affecting foam compressive properties. For foam tensile properties, specimens with different cross-sectional dimensions in the gage section were used. The results revealed transversely isotropic characteristics of the foam material. To evaluate foam shear properties a scaled shear test method was developed. The results indicated a significant difference in in-plane and out-of-plane foam shear stiffness properties.

Synthetic fiber mooring rope is an important emerging technology helping enable the economical exploration and production of petroleum from offshore deepwater reservoirs. Polyester moorings have been used successfully for years in Brazil and were recently approved by the MMS for use by two MODU drilling operations in the Gulf of Mexico. One of the unknown issues associated with the use of synthetic fiber mooring ropes is how to account for damage and the associated lifetime and reliability predictions. The MMS has sponsored research to address the damage tolerance issue including the activity reported in the current paper. This paper describes the results of controlled, damage-tolerance, static tension tests on elements and subrope components taken directly from representative polyester mooring rope products. The results should serve as a foundation for further research into the behavior of ropes with damage including more sophisticated analytical modeling. Introduction Considerable emphasis is being placed worldwide on the economical recovery of petroleum resources from deepwater. The definition of deepwater has expanded in the last decade to now include depths as great as 10,000 feet and deeper. Many different concepts have been proposed for deepwater platforms including FPSO's SPAR's, and TLP's. Each concept depends on the use of a mooring line or tether to keep on station. The taut leg mooring line concept in which multiple light-weight synthetic fibers such as polyester are used as a rope suspended from the platform to the seabed at an angle of approximately 45-degrees from vertical is a very attractive candidate and the concept is growing in popularity. Petrobras has made a major commitment to this concept1 with over 1½ dozen platforms so anchored and there is considerable interest emerging in using the synthetic fiber mooring rope in other parts of the world including the Gulf of Mexico. The American Petroleum Institute has prepared guidelines for the design, manufacture, installation and maintenance of synthetic fiber mooring ropes2. The Minerals Management Service (MMS) recently approved the use of FPSO systems in central and western Gulf of Mexico regions3 and two MODU drilling platform have recently been given approval to use polyester mooring rope in Gulf of Mexico deepwater drilling programs. The MMS is interested in the durability of synthetic fiber mooring ropes and has been proactive in sponsoring research and testing to characterize handling and installation damage4 and to assess the effects of damage. Damage can result from handling the rope during installation, be the consequence of wear experienced during service, or be caused by ingress of sand or marine growth. The integrated program involves testing small-scale rope components (the focus of the current paper), analytical modeling, and a largescale test program. Results from the current study will be used in subsequent validation of an analytical model. The ultimate goal of the program is to develop guidelines for addressing safety and reliability issues associated with damage.