2 Matching Results

Search Results

Advanced search parameters have been applied.

Prediction of long-term failure in Kevlar 49 composites

Description: Creep rupture data in Kevlar 49 epoxy usually exhibit considerable scatter: the coefficient of variation (CV) about the mean failure time at a given stress exceeds 100%. Quasi-static strength data, in contrast, shows little scatter: <4% CV for pressure vessels and <10% for impregnated strands. In this paper analysis of existing creep rupture data on Kevlar epoxy vessels at four storage pressures has produced an interesting and useful result. It was found that a significant portion of the scatter in failure times for pressure vessels is due to spool-to-spool variation in the eight spools of Kevlar fibers used to wind the vessels. The order rank of mean times to failure was consistent over a pressure range from 3400 to 4300 psi, 68 to 86% of short term burst. Also, the coefficient of variation about the mean failure time for each spool was less than that for the total sample. The statistical inference that the sample is nonhomogeneous was supported by a nonparametric check using the Kruskal-Wallis test, and by a parametric analysis of variance. The order rank found in long-term tests did not unequivocally agree with static strength ranks; several spool sets were distinctly high or low. The implication is that, while static strengths are not valid predictors of long-term behavior, short term creep rupture tests at high stress definitely are. The material difference which causes the spool-to-spool variations has not yet been identified for all eight spools. However, it appears that Kevlar behavior at lower pressures may be predicted through the use of curves fitted to the data for each spool. A power law relating failure time to pressure, t = t/sub 0/(p/p/sub 0/)/sup m/, was found to fit the data reasonably well. The implication is that, both in composite vessel design and in creep rupture experiments, the pressure ...
Date: January 1, 1982
Creator: Gerstle, F.P. Jr.
Partner: UNT Libraries Government Documents Department

Process development for electron beam joining of ceramic and glass components

Description: The purpose of this project is to develop and extend the electron beam joining process to applications related to Mo/Al{sub 2}O{sub 3} cermets for neutron tube fabrication, glass seals for flat panel displays, and ceramics for structural applications. The key issue is the identification of the allowable operating ranges that produce thermal conditions favorable to robust joining and sealing. High strength, hermetic braze joints between ceramic components have been produced using high energy electron beams. With a penetration depth into a typical ceramic of {approximately} 1 cm for a 10 MeV electron beam, this method provides the capability for rapid, transient brazing operations where temperature control of heat sensitive components is essential. The method deposits energy directly into a buried joint, allowing otherwise inaccessible interfaces to be brazed. The combination of transient heating, with higher thermal conductivity, lower heat capacity, and lower melting temperature of braze metals relative to the ceramic materials, enables a pulsed high power beam to melt a braze metal without producing excessive ceramic temperatures. The authors have demonstrated the feasibility of this process related to ceramic coupons a well as ceramic and glass tubes and cylindrical shapes. The transient thermal response was predicted, using as input the energy absorption predicted from the coupled electron-photon and thermal transport analysis. The joining experiments were conducted with an RF linear accelerator at 10--13 MV. Joining experiments have provided high strength joints between alumina and alumina and between alumina and cermet joints in cylindrical geometry. These joints provided good hermetic seals.
Date: November 1, 1997
Creator: Turman, B.N.; Glass, S.J.; Yang, P.; Gerstle, F.P.; Halbleib, J.A.; Voth, T.E. et al.
Partner: UNT Libraries Government Documents Department