Flexural behavior of steel fiber reinforced concrete: testing and modelling

In this paper the results of tests performed on specimens and structural elements made of steel fiber reinforced concrete are presented. Fiber content ranged from 0 to 60 kg/m3 of concrete. Using the results of the uniaxial compression tests performed under displacement control condition, a stress strain relationship for fiber concrete in compression was derived. Three point bending tests on notched beams were carried out in order to simulate the post cracking behavior and to evaluate the fracture energy. Based on the constitutive relationships derived from the experiments, a layered model for the analysis of steel fiber reinforced concrete cross sections was developed. The model performance and the benefits of fiber reinforcement on thin slabs reinforced with steel bars were assessed by carrying out tests on slab strips. The main results are presented and discussed

The effects of an aggressive environment on the subcritical crack growth of a continuous-fiber ceramic composite

Time-dependent crack growth measurements of ceramic composites in aggressive environments are being conducted on materials consisting of CVI SiC reinforced with Nicalon fibers (SiC/SiC{sub f}) having C and BN fiber-matrix interfaces. Crack velocities are determined as a function of applied stress intensity. Results have been obtained for crack velocity-stress intensity relationships in pure Ar and in Ar plus 2000 ppM O{sub 2} atmospheres at 1100{degrees}C. A 2D micromechanics model is used to represent the time-dependence of observed crack bridging events and is able to rationalize the observed phenomena

EVALUATION OF CONCRETE PROPERTY DATA AT ELEVATED TEMPERATURES FOR USE IN THE SAFE-CRACK COMPUTER CODE

Design and analysis of Hanford double-shell waste storage tanks has made use of the finite element computer code SAFE-CRACK as a check of the concrete portion of the tank design after cmpletion of design. Rockwell Hanford Operations, the site contractor responsible for operation of the tanks, has requested Battelle Pacific Northwest Laboratory (PNL) to evaluate the use of the Hanford concrete property data at elevated temperatures by the SAFE-CRACK code. The purpose of this investigation is to evaluate the proper use of the mathematical expressions in SAFE-CRACK to best define the physical concrete properties extrapolated from the documented concrete property data when subjected to elevated temperatures and cyclic temperature variations

Dimensional stability and tensile strength of irradiated Nicalon-CG and Hi-Nicalon SiC fibers

Nicalon-CG and Hi-Nicalon fibers were characterized by measuring their length, density, and tensile strength in the unirradiated, thermal annealed, and irradiated conditions. The irradiation was conducted in the EBR-II to a dose of 43 dpa-SiC at a nominal irradiation temperature of 1,000 C. The annealed specimens were held at 1,010 C for 165 days to approximately duplicate the thermal exposure of the irradiated specimens. The results indicate the fibers that perform best in an irradiation environment are those that approach stoichiometric and crystalline SiC. Hi-Nicalon exhibited negligible densification, accompanied by an increase in tensile strength after irradiation. Nicalon-CG possessed a higher tensile strength than hi-Nicalon in the unirradiated condition, but was significantly weakened in the annealed and irradiated conditions. In addition, Nicalon-CG exhibited unacceptable irradiation-induced shrinkage. Loss o fiber tensile strength after irradiation is shown to reduce the flexural strength of irradiated composites and Nicalon-CG fiber shrinkage observed in irradiated composites

Materials characterization of cermet anodes tested in a pilot cell

Cermet anodes were evaluated as nonconsumable substitutes for carbon anodes using a pilot-scale reduction cell at the Reynolds Manufacturing Technology Laboratory. After pilot cell testing, tile anodes were subjected to extensive materials characterization and physical properties measurements at the Pacific Northwest Laboratory. Significant changes in the composition of the cermet anodes were observed including the growth of a reaction layer and penetration of electrolyte deep into the cermet matrix. Fracture strength and toughness were measured as a function of temperature and the ductile-brittle transition wasreduced by 500C following pilot cell testing. These results imply difficulties with anode material and control of operating conditions in the pilot cell, and suggest that additional development work be performed before the cermet anodes are used in commercial reduction cells. The results also highlight specific fabrication and operational considerations that should be addressed in future testing

The effects of an aggressive environment on the subcritical crack growth of a continuous-fiber ceramic composite

Time-dependent crack growth measurements of ceramic composites in aggressive environments are being conducted on materials consisting of CVI SiC reinforced with Nicalon fibers (SiC/SiC[sub f]) having C and BN fiber-matrix interfaces. Crack velocities are determined as a function of applied stress intensity. Results have been obtained for crack velocity-stress intensity relationships in pure Ar and in Ar plus 2000 ppM O[sub 2] atmospheres at 1100[degrees]C. A 2D micromechanics model is used to represent the time-dependence of observed crack bridging events and is able to rationalize the observed phenomena

PHYSICAL EFFECTS OF THE HANFORD WINDSTORMS OF JANUARY 11, 1972 AND JANUARY 21, 1972

The windstorm of January 11 caused a minor amount of damage to the Hanford Reservation and Hanford vicinity. Damage sustained to Hanford Reservation structures (roofing, flashing, fences, windows) was approximately $20,000. One building did receive structural damage to roof members. Evidence that wind pressures did not reach 30 lb/ft{sup 2} during the January 11 windstorm was provided in the fact that specially designed exterior wall panels did not fail. These panels were designed and carefully proof-tested to insure that they would fail at a loading of 30 lb/ft{sup 2} as a requirement of structural safety in the original design-construction program in 1952-1954. There was one power outage on the Hanford Reservation due to the January 11 windstorm (Rattlesnake Mountain Observatory). Damage to power lines and electrical facilities amounted to about$1600. Damage to structures in the Hanford vicinity (excluding the Hanford Reservation) from the January 11 windstorm was estimated to cost $13,000. This does not include damage to private residences, etc., which has been estimated by others to be near$250,000. Power line damage in the Hanford vicinity amounted to about $80,000, of which$60,000 was accounted for in the loss of four transmission towers in the tie-line between Priest Rapids and Wanapum Dams. The January 21 windstorm, which struck Toppenish, Washington, was a straight-wind of the catabatic foehn type and not a tornado-type wind as described in newspaper accounts. No funnel cloud was associated with this windstorm. The maximum gust was about 85 mph at 30 ft above the ground. Cost estimates of damage in Toppenish were not available. There were no power outages or structural damage on the Hanford Reservation from the January 21 windstorm. Total damage to the Hanford Reservation from the two windstorms was estimated to be about $22,500

Thermal conductivities of thin, sputtered optical films

The normal component of the thin film thermal conductivity has been measured for the first time for several advanced sputtered optical materials. Included are data for single layers of boron nitride (BN), aluminum nitride (AIN), silicon aluminum nitride (Si-Al-N), silicon aluminum oxynitride (Si-Al-O-N), silicon carbide (SiC), and for dielectric-enhanced metal reflectors of the form Al(SiO{sub 2}/Si{sub 3}N{sub 4}){sup n} and Al(Al{sub 2}O{sub 3}/AIN){sup n}. Sputtered films of more conventional materials like SiO{sub 2}, Al{sub 2}O{sub 3}, Ta{sub 2}O{sub 5}, Ti, and Si have also been measured. The data show that thin film thermal conductivities are typically 10 to 100 times lower than conductivities for the same materials in bulk form. Structural disorder in the amorphous or very fine-grained films appears to account for most of the conductivity difference. Conclusive evidence for a film/substrate interface contribution is presented

Composite materials for fusion applications

Ceramic matrix composites, CMCs, are being considered for advanced first-wall and blanket structural applications because of their high-temperature properties, low neutron activation, low density and low coefficient of expansion coupled with good thermal conductivity and corrosion behavior. This paper presents a review and analysis of the hermetic, thermal conductivity, corrosion, crack growth and radiation damage properties of CMCs. It was concluded that the leak rates of a gaseous coolant into the plasma chamber or tritium out of the blanket could exceed design criteria if matrix microcracking causes existing porosity to become interconnected. Thermal conductivities of unirradiated SiC/SiC and C/SiC materials are about 1/2 to 2/3 that of Type 316 SS whereas the thermal conductivity for C/C composites is seven times larger. The thermal stress figure-of-merit value for CMCs exceeds that of Type 316 SS for a single thermal cycle. SiC/SiC composites are very resistant to corrosion and are expected to be compatible with He or Li coolants if the O{sub 2} concentrations are maintained at the appropriate levels. CMCs exhibit subcritical crack growth at elevated temperatures and the crack velocity is a function of the corrosion conditions. The radiation stability of CMCs will depend on the stability of the fiber, microcracking of the matrix, and the effects of gaseous transmutation products on properties. 23 refs., 14 figs., 1 tab