In recent years, fiber-reinforced composites have become more accepted for aerospace applications. Specifically, during NASA's recent efforts to develop new launch vehicles, composite materials were considered and baselined for a number of structures. Because of mass and stiffness requirements, sandwich composites are often selected for many applications. However, there are a number of manufacturing and in-service concerns associated with traditional honeycomb-core sandwich composites that in certain instances may be alleviated through the use of other core materials or construction methods. Flutedcore, which consists of integral angled web members with structural radius fillers spaced between laminate face sheets, is one such construction alternative and is considered herein. Two different fluted-core designs were considered: a subscale design and a full-scale design sized for a heavy-lift-launch-vehicle interstage. In particular, axial compression of flutedcore composites was evaluated with experiments and finite-element analyses (FEA); axial compression is the primary loading condition in dry launch-vehicle barrel sections. Detailed finite-element models were developed to represent all components of the fluted-core construction, and geometrically nonlinear analyses were conducted to predict both buckling and material failures. Good agreement was obtained between test data and analyses, for both local buckling and ultimate material failure. Though the local buckling events are not catastrophic, the resulting deformations contribute to material failures. Consequently, an important observation is that the material failure loads and modes would not be captured by either linear analyses or nonlinear smeared-shell analyses. Compression-after-impact (CAI) performance of fluted-core composites was also investigated by experimentally testing samples impacted with 6 ft.-lb. impact energies. It was found that such impacts reduced the ultimate load carrying capability by approximately 40% on the subscale test articles and by less than 20% on the full-scale test articles. Nondestructive inspection of the damage zones indicated that the detectable damage was limited to no more than one flute on either side of any given impact. More study is needed, but this may indicate that an inherent damagearrest capability of fluted core could provide benefits over traditional sandwich designs in certain weight-critical applications.
Fluted-core sandwich composites consist of integral angled web members spaced between laminate face sheets, and may have the potential to provide benefits over traditional sandwich composites for certain aerospace applications. However, fabrication of large autoclave-cured fluted-core cylindrical shells with existing autoclaves will require that the shells be fabricated in segments, and joined longitudinally to form a complete barrel. Two different longitudinal fluted-core joint designs were considered experimentally in this study. In particular, jointed fluted-core-composite panels were tested in longitudinal compression because longitudinal compression is the primary loading condition in dry launch-vehicle barrel sections. One of the joint designs performed well in comparison with unjointed test articles, and the other joint design failed at loads approximately 14% lower than unjointed test articles. The compression-after-impact (CAI) performance of jointed fluted-core composites was also investigated by testing test articles that had been subjected to 6 ft-lb impacts. It was found that such impacts reduced the load-carrying capability by 9% to 40%. This reduction is dependent on the joint concept, component flute size, and facesheet thickness.
Foams made from engineered thermoplastic resin systems possess high glass transition temperatures. When compared to most thermoset resins, it was anticipated that lightly cross-linked foam candidates might survive high temperature/ pressure cures. This is especially true if the viscosity decline (i.e., loosening of weak secondary bonds) during sandwich bond cycles were found to be gradual enough to be controllable. To test this supposition, a low-cost five-step screening down-select methodology was utilized: (a) survey and evaluate vendor data, (b) pre-screen candidate foams using a vertical flame test, (c) characterize basic material properties using room temperature quasi-static compression testing, (d) evaluate failure mechanisms via elevated temperature compression testing, and (e) validate material functionality by conducting flat and contoured autoclave sandwich panel bond trials. None of the three candidate materials evaluated individually met all research requirements. Still, the population taken as a whole exhibited the potential for fulfilling the study's objectives. It is hypothesized that foam chemistry modifications, cell structure manipulation, and/or additional cure cycle process parameter management could lead to extended usage of foam in structurally demanding applications.
Fluted-core sandwich composites consist of integral angled web members spaced between laminate face sheets, and may have the potential to provide benefits over traditional sandwich composites for certain aerospace applications. However, fabrication of large autoclave-cured fluted-core cylindrical shells with existing autoclaves will require that the shells be fabricated in segments, and joined longitudinally to form a complete barrel. Two different longitudinal fluted-core joint designs were considered experimentally in this study. In particular, jointed fluted-core-composite panels were tested in longitudinal compression because longitudinal compression is the primary loading condition in dry launch-vehicle barrel sections. One of the joint designs performed well in comparison with unjointed test articles, and the other joint design failed at loads approximately 14% lower than unjointed test articles. The compression-after-impact (CAI) performance of jointed fluted-core composites was also investigated by testing test articles that had been subjected to 6 ft-lb impacts. It was found that such impacts reduced the load-carrying capability by 9% to 40%. This reduction is dependent on the joint concept, component flute size, and facesheet thickness.
The Oropendola Field is located in the Llanos Basin of Colombia and production from the wells is typically augmented by means of artificial lift methods, particularly the jet pump. During a recent routine wireline campaign to install a jet pump in a sliding sleeve, difficulty was experienced in releasing the assembly from the running tool and so it was extracted, but became lodged and eventually the running tool released leaving a fish in the hole. There followed several unsuccessful attempts to recover the fish but with each successive attempt the situation kept deteriorating and so fishing operations were suspended while the options were considered:• Continue with fishing operations to try to clean up the well. • Work the well over.The latter option was considered financially unattractive so the former choice was made but the situation was so complex that it was decided to bring into the country a heavy duty Wireline fishing specialist to assist. His brief was to evaluate the well along with the client and the local wireline personnel, to put a plan in place for the recovery process to begin and to supervise operations to clean the well up. After a full review of the equipment available and the number and type of fish that needed to be recovered, an operational plan was compiled and operations begun using the on site wireline unit and ancillary equipment. Early problems with the relatively low strength of standard pulling tools lead to a further review of tooling and a set of heavy duty fishing tools being imported, upon receipt of which operations continued. After a total of 59 trips into the well, with no miss-runs and no failures, all of the fish were successfully recovered and a new jet pump assembly was run and landed successfully allowing the well to be brought back into production 26 days after arrival of the specialist on site.In this paper the authors will review the operations that lead to the complex fishing problem, the tools imported and the reasons for them. They will go on to describe in detail the fishing operation which utilized equipment with lower than ideal load capabilities and the detailed evaluation process of each wireline tool string run which eventually lead to the well being cleaned up and its production capacity restored
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