A simple and convenient method of analysis for studying two-dimensional mixed-mode crack problems is presented. The analysis is formulated on the basis of conservation laws of elasticity and of fundamental relationships in fracture mechanics. The problem is reduced to the determination of mixed-mode stress-intensity factor solutions in terms of conservation integrals involving known auxiliary solutions. One of the salient features of the present analysis is that the stress-intensity solutions can be determined directly by using information extracted in the far field. Several examples with solutions available in the literature are solved to examine the accuracy and other characteristics of the current approach. This method is demonstrated to be superior in its numerical simplicity and computational efficiency to other approaches. Solutions of more complicated and practical engineering fracture problems dealing with the crack emanating from a circular hole are presented also to illustrate the capacity of this method.

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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.

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.

Thia paper waa selected for presentation by lhe OTC Program Committee following revi_ of information con18ined in an abstract aubmlned by the authorIal. Conlenta of the paper, aa presented, have not bean reviewed by the OIIshore Technology Conference and are aubjact to correction by the euthor(a). The material, aa presented, does not _ r i l y reflect any poaition of the OIIshore Technology Conference or na oHlcera. Electronic reproduction, distribution, or storage ot any perl of thia paper tor commercial p\lfP088l without the written conaant oflhe OIIshore Technology Conference Is prohibited. Permiaalon 10 reproduce in print ia reatricted to an abatract of nof more than 300 words; iIIustrationa may nof be copied. The abstract must conlain conspicuoua acknowtedgmanl of where and by whom the paper waa presented. ABSTRACTComposite production riser (CPR) joints are being seriously considered in the development of deep water tension leg platforms (UPs), because of their inherent light weight, superior fatigue and corrosion resistance, and outstanding specific strength and stiffness properties. Current efforts on the development of CPR joints have been mainly focused on lowcost manufacturing and failure strength evaluation of CPR tube body and CPR joint connection. The important issue of system dynamics of UPs containing multiple CPR strings, has not been addressed.In this paper, system analysis of a UP containing 16 CPR strings and 12 tendons subjected to Gulf of Mexico environment loading have been conducted. The riser system is configured for 3,000 ft water depth with CPR joints, standard steel riser joints, splash zone joints, stress joint, and top tensioners. The study embraces several disciplines, including naval architecture, riser dynamics analysis, and composite failure mechanics to develop an iterative algorithm for evaluation of the top tension and stress joint requirement. Specifically, optimum top tension requirements have been determined based on riser dynamics and the failure envelope of the CPR joints. For comparison, the optimum top tension requirements are further used to size the UPs with all-steel riser and with CPR. For the 3,000 ft water depth case study, reduction in riser weight is magnified by 3.31 times in the UP size. It is demonstrated that the weight reduction in the riser string is nonlinearly related to the tensioner requirement and UP size.