When an elastomer imbibes a solvent and swells, a force is generated if the elastomer is constrained by a hard material. The magnitude of the force depends on the geometry of the constraint, as well as on the chemistry of the elastomer and solvent. This paper models an elastomer crosslinked on the exterior surface of a metallic tubing. The elastomer then imbibes a solvent and swells. After the swollen elastomer touches the wall of the borehole, a significant amount of time is needed for the solvent in the elastomer to redistribute, building up the sealing pressure to the state of equilibrium. The sealing pressure and the sealing time are calculated in terms of the geometric parameters ͑i.e., the thickness of the elastomer and the radii of the tubing and borehole͒, the number of monomers along each polymer chain of the elastomer, and the affinity between the elastomer and the solvent.
Cyclic loading of bone during daily activities can lead to fatigue degradation and increased risk of fracture in both the young and elderly population. Damage processes under cyclic loading in trabecular bone result in the reduction of the elastic modulus and accumulation of residual strain. These effects increase with increasing stress levels, leading to a progressive reduction in fatigue life. The present work analyzes the effect of stress and strain variation on the above damage processes in bovine trabecular bone, and develops a phenomenological model relating fatigue life to the imposed stress level. The elastic modulus reduction of the bone specimens was observed to depend on the maximum compressive strain, while the rate of residual strain accumulation was a function of the stress level. A model was developed for the upper and lower bounds of bone elastic modulus reduction with increasing number of cycles, at each stress range. The experimental observations were described well by the model. The model predicted the bounds of the fatigue life with change in fatigue stress. The decrease in the fatigue life with increasing stress was related to corresponding increases in the residual strain accumulation rates at the elevated stress levels. The model shows the validity of fatigue predictions from relatively few cyclic experiments, by combining trends observed in the monotonic and the cyclic tests. The model also presents a relatively simple procedure for predicting the endurance limit for bovine trabecular bone specimens.
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.
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