A Theoretical Investigation of Composite Overwrapped Pressure Vessel (COPV) Mechanics Applied to NASA Full Scale Tests

A theoretical investigation of the factors controlling the stress rupture life of the National Aeronautics and Space Agency's (NASA) composite overwrapped pressure vessels (COPVs) continues. Kevlar(TradeMark) fiber overwrapped tanks are of particular concern due to their long usage and the poorly understood stress rupture process in Kevlar(TradeMark) filaments. Existing long term data show that the rupture process is a function of stress, temperature and time. However, due to the presence of a load sharing liner, the manufacturing induced residual stresses and the complex mechanical response, the state of actual fiber stress in flight hardware and test articles is not clearly known. This paper is a companion to the experimental investigation reported in [1] and develops a theoretical framework necessary to design full-scale pathfinder experiments and accurately interpret the experimentally observed deformation and failure mechanisms leading up to static burst in COPVs. The fundamental mechanical response of COPVs is described using linear elasticity and thin shell theory and discussed in comparison to existing experimental observations. These comparisons reveal discrepancies between physical data and the current analytical results and suggest that the vessel's residual stress state and the spatial stress distribution as a function of pressure may be completely different from predictions based upon existing linear elastic analyses. The 3D elasticity of transversely isotropic spherical shells demonstrates that an overly compliant transverse stiffness relative to membrane stiffness can account for some of this by shifting a thin shell problem well into the realm of thick shell response. The use of calibration procedures are demonstrated as calibrated thin shell model results and finite element results are shown to be in good agreement with the experimental results. The successes reported here have lead to continuing work with full scale testing of larger NASA COPV hardware

Use of Modal Acoustic Emission to Monitor Damage Progression in Carbon Fiber/Epoxy Tows and Implications for Composite Structures

This slide presentation reviews the use of Modal Acoustic Emission to monitor damage progression to carbon fiber/epoxy tows. There is a risk for catastrophic failure of composite overwrapped pressure vessels (COPVs) due to burst-before-leak (BBL) stress rupture (SR) failure of carbon-epoxy (C/Ep) COPVs. A lack of quantitative nondestructive evaluation (NDE) is causing problems in current and future spacecraft designs. It is therefore important to develop and demonstrate critical NDE that can be implemented during stages of the design process since the observed rupture can occur with little of no advanced warning. Therefore a program was required to develop quantitative acoustic emission (AE) procedures specific to C/Ep overwraps, but which also have utility for monitoring damage accumulation in composite structure in general, and to lay the groundwork for establishing critical thresholds for accumulated damage in composite structures, such as COPVs, so that precautionary or preemptive engineering steps can be implemented to minimize of obviate the risk of catastrophic failure. A computed Felicity Ratio (FR) coupled with fast Fourier Transform (FFT) frequency analysis shows promise as an analytical pass/fail criterion. The FR analysis and waveform and FFT analysis are reviewe

Developing Novel Acoustic Emission Procedures for Failure Prediction of Carbon-Epoxy COPVs and Related Composite Materials

No abstract availabl

Composite Overwrapped Pressure Vessel (COPV) Stress Rupture Testing

This paper reports stress rupture testing of Kevlar(TradeMark) composite overwrapped pressure vessels (COPVs) at NASA White Sands Test Facility. This 6-year test program was part of the larger effort to predict and extend the lifetime of flight vessels. Tests were performed to characterize control parameters for stress rupture testing, and vessel life was predicted by statistical modeling. One highly instrumented 102-cm (40-in.) diameter Kevlar(TradeMark) COPV was tested to failure (burst) as a single-point model verification. Significant data were generated that will enhance development of improved NDE methods and predictive modeling techniques, and thus better address stress rupture and other composite durability concerns that affect pressure vessel safety, reliability and mission assurance

Utilization of Fiber Optics in Large Scale Landline Telemetry Systems

International Telemetering Conference Proceedings / September 28-30, 1982 / Sheraton Harbor Island Hotel and Convention Center, San Diego, CaliforniaThe large-scale landline telemetry system may benefit from the application of fiber optics. With present technology, practical means exist to design, implement, and test longdistance, data-transmission systems using fiber optics. Fiber optics and Computer Automated Measurement and Control (CAMA) equipment provide application and tradeoff advantages over a hard-wire system. Procedures for equipment verification must be developed to confirm and verify system performance of the design criteria. Practical computations may be made using values representative of actual system performance. A solution is provided to a typical data transmission problem.International Foundation for TelemeteringProceedings from the International Telemetering Conference are made available by the International Foundation for Telemetering and the University of Arizona Libraries. Visit http://www.telemetry.org/index.php/contact-us if you have questions about items in this collection

AMSSM Scientific Statement Concerning Viscosupplementation Injections for Knee Osteoarthritis: Importance for Individual Patient Outcomes.

OBJECTIVE: Osteoarthritis (OA) is a disabling disease that produces severe morbidity reducing physical activity. Our position statement on treatment of knee OA with viscosupplementation injection [hyaluronic acid (HA)] versus steroid [intra-articular corticosteroid (IAS)] and placebo [intra-articular placebo (IAP)] is based on the evaluation of treatment effect by examining the number of subjects within a treatment arm that met the Outcome Measures in Rheumatoid Arthritis Clinical Trials-Osteoarthritis Research Society International (OMERACT-OARSI) criteria, which is different and more relevant than methods used in other reviews which examined if the average change across the treatment groups was clinically different. DATA SOURCES: We performed a systematic literature search for all relevant articles from 1960 to August 2014 in the MEDLINE, EMBASE, and Cochrane CENTRAL. We performed a network meta-analysis (NMA) of the relevant literature to determine if there is a benefit from HA as compared with IAS and IAP. MAIN RESULTS: Eleven articles met the inclusion criteria from the search strategy. On NMA, those subjects receiving HA were 15% and 11% more likely to respond to treatment by the OMERACT-OARSI criteria than those receiving IAS or IAP, respectively (P \u3c 0.05 for both). CONCLUSIONS: In light of the aforementioned results of our NMA, the American Medical Society for Sport Medicine recommends the use of HA for the appropriate patients with knee OA

AMSSM scientific statement concerning viscosupplementation injections for knee osteoarthritis: importance for individual patient outcomes.

Osteoarthritis (OA) is a disabling disease that produces severe morbidity reducing physical activity. Our position statement on treatment of knee OA with viscosupplementation injection (hyaluronic acid, HA) versus steroid (intra-articular corticosteroids, IAS) and placebo (intra-articular placebo, IAP) is based on the evaluation of treatment effect by examining the number of participants within a treatment arm who met the Outcome Measures in Rheumatoid Arthritis Clinical Trials-Osteoarthritis Research Society International (OMERACT-OARSI) criteria, which is different and more relevant than methods used in other reviews which examined if the average change across the treatment groups were clinically different. We performed a systematic literature search for all relevant articles from 1960 to August 2014 in the MEDLINE, EMBASE and Cochrane CENTRAL. We performed a network meta-analysis (NMA) of the relevant literature to determine if there is a benefit from HA as compared with IAS and IAP. 11 papers met the inclusion criteria from the search strategy. On NMA, those participants receiving HA were 15% and 11% more likely to respond to treatment by OMERACT-OARSI criteria than those receiving IAS or IAP, respectively (

Numerical description of coalbed methane desorption stages based on isothermal adsorption experiment

Quantitative description of desorption stages of coalbed methane is an important basis to objectively understand the production of coalbed methane well, to diagnose the production state, and to optimize the management of draining and collection of coalbed methane. A series of isothermal adsorption experiments were carried out with 12 anthracite samples from 6 coalbed methane wells located in the south of the Qinshui Basin, based on the results of isothermal adsorption experiments, and an analytical model was developed based on the Langmuir sorption theory. With the model, a numerical method that adopts equivalent desorption rate and its curve was established, which can be used to characterize the staged desorption of coalbed methane. According to the experimental and numerical characterizations, three key pressure points determined by the equivalent desorption rate curvature that defines pressure-declining desorption stage, have been proposed and confirmed, namely, start-up pressure, transition pressure and sensitive pressure. By using these three key pressure points, the process of coalbed methane desorption associated with isothermal adsorption experiments can be divided into four stages, i.e., zero desorption stage, slow desorption stage, transition desorption stage, and sensitive desorption stage. According to analogy analysis, there are differences and similarities between the processes of coalbed methane desorption identified by isothermal adsorption experiments and observed in gas production. Moreover, it has been found that larger Langmuir volume and ratio of Langmuir constants are beneficial to earlier advent of steady production stage, whereas it is also possible that the declining production stage may occur ahead of schedule