Fracture Toughness of Thin Plates by the Double-Torsion Test Method

Double torsion testing can produce fracture toughness values without crack length measurement that are comparable to those measured via standardized techniques such as the chevron-notch, surface-crack-in-flexure and precracked beam if the appropriate geometry is employed, and the material does not exhibit increasing crack growth resistance. Results to date indicate that 8 2 are required if crack length is not considered in stress intensity calculations. At L/W = 2, the normalized crack length should be 0.35 80) nonlinear effects were encountered

Intermediate Temperature Carbon - Carbon Composite Structures. CRADA Final Report

The objective of this Cooperative Research and Development Agreement (CRADA) between UT-Battelle, LLC (the "Contractor") and Synterials, Inc. (the "Participant") was to demonstrate promising processing methods, which can lead to producing Carbon-Carbon Composites (CCC), with tensile and interlaminar properties comparable to those of organic matrix composites and environmental stability at 1200 F for long periods of time. The participant synthesized carbon-carbon composites with two different fiber coatings and three different matrices. Both parties evaluated the tensile and interlaminar properties of these materials and characterized the microstructure of the matrices and interfaces. It was found that fiber coatings of carbon and boron carbide provided the best environmental protection and resulted in composites with high tensile strength

Oxidation induced stress-rupture of fiber bundles

The effect of oxidation on the stress-rupture behavior of fiber bundles was modeled. It is shown that oxidation-induced fiber strength degradation results in the delayed failure of the associated fiber bundle and that the fiber bundle strength decreases with time as t{sup {minus}1/4}. It is also shown that the temperature dependence of the bundle loss of strength reflects the thermal dependence of the mechanism controlling the oxidation of the fibers. The effect of gauge length on the fiber bundle strength was also analyzed. Numerical examples are presented for the special case of Nicalon{trademark} fibers

Optimization of Pseudo-Porous SiC Fiber Coatings for SiC/SiC Composites

The objective of this Cooperative Research and Development Agreement between Lockheed Martin Energy Research Corporation and Hyper-Therm High-Temperature Composites, Inc. was the optimization of the microstructure of pseudo-porous SiC fiber coatings for SiC/SiC composites. Extensive interfacial test characterization was conducted through single-fiber push-out tests and analytical electron microscopy to assess the effect of various microstructural features of the fiber coating on the interfacial properties of the composite. The thermal stability of these coatings and their interfaces was also investigated after exposure to air at elevated temperatures

The Mechanics of Creep Deformation in Polymer Derived Continuous Fiber-Reinforced Ceramic Matrix Composites

The objective of this Cooperative Research and Development Agreement between Lockheed Martin Energy Research Corporation and Dow Corning Corporation was to study the effects of temperature, stress, fiber type and fiber architecture on the time-dependent deformation and stress-rupture behavior of polymer-derived ceramic matrix composites developed by the Dow Corning Corporation. Materials reinforced with CG-Nicalon{trademark}, Hi-Nicalon{trademark} and Sylramic{reg_sign} fibers were evaluated under fast fracture, stress-relaxation, and stress-rupture conditions at temperatures between 700 C and 1400 C in ambient air and for stresses between 50 and 200 MPa. Some of the stress-rupture tests conducted as part of this program are among the longest-duration experiments ever conducted with these materials. The possibility of using accelerated test techniques to evaluate the very-long term stress-rupture/creep behavior of these materials was investigated by means of stress-relaxation experiments. However it was found that because these materials exhibit non-linear stress-strain behavior at stresses larger than the matrix cracking stress and because of environmentally-induced changes in the micro and mesostructure of the material, particularly at elevated temperatures, this approach is impractical. However, the results of stress-relaxation experiments will be useful to predict the behavior of these materials in applications where stresses are thermally-induced and therefore driven by strains (e.g., when components are subjected to thermal gradients). The evolution of the microstructure of the fibers, matrix and fiber-matrix interface was studied as a function of stress and temperature, using analytical electron microscopy. The results from these analyses were essential to understand the relationships between environment, stress, temperature and processing on the microstructure and properties of these materials

Characterization of Min-K TE-1400 Thermal Insulation

Min-K 1400TE insulation material was characterized at Oak Ridge National Laboratory for use in structural applications under gradient temperature conditions. Initial compression testing was performed at room temperature at various loading rates ranging between 5 and 500 psi/hour (≈35 and 3500 kPa/hour) to determine the effect of sample size and test specimen geometry on the compressive strength of Min-K. To determine the loading rates that would be used for stress relaxation testing, compression tests were next carried out at various levels followed by stress relaxation under constant strain at temperatures of 650, 850, and 900oC. Additional high temperature compression testing was performed with samples loaded at a rate of 53 psi/hour (365 kPa/hour) in three load steps of 50, 100 and 200 psi (345, 690, and 1380 kPa) with quick unload/load cycles between steps and followed by a hold period in load control (3 to 100 hours) to allow for sample creep. Testing was carried out at 190, 382, 813, and 850oC. Isothermal stress relaxation testing was performed at temperatures of 190, 382, 813, and 850oC and initial loads of 100 and 200 psi (690 and 1380 kPa). Gradient stress relaxation testing was intended to be performed at temperatures of 850/450oC and 450/190oC with initial loads of 100 or 200 psi (690 and 1380 kPa) performed under constant strain utilizing a twelve-step loading scheme with loading every half hour at a rate of 5.56% strain/hour

Roadmap to NRC Approval of Ceramic Matrix Composites in Generation IV Reactors

This report provides an initial roadmap to obtain Nuclear Regulatory Commission (NRC) approval for using these material systems in a nuclear application. The possible paths taken to achieving NRC approval are necessarily subject to change as this is an on-going process that shifts as more data and a clearer understanding of the nuclear regulations are gathered

Characterization of Min-K TE-1400 Thermal Insulation (Two-Year Gradient Stress Relaxation Testing Update)

Min-K 1400TE insulation material was characterized at Oak Ridge National Laboratory for use in structural applications under gradient temperature conditions. A previous report (ORNL/TM-2008/089) discusses the testing and results from the original three year duration of the project. This testing included compression testing to determine the effect of sample size and test specimen geometry on the compressive strength of Min-K, subsequent compression testing on cylindrical specimens to determine loading rates for stress relaxation testing, isothermal stress relaxation testing, and gradient stress relaxation testing. This report presents the results from the continuation of the gradient temperature stress relaxation testing and the resulting updated modeling