Sf Etris

Heat Transfer in Fibrous Materials

In fibrous material different types of heat transfer are present: conduction in solid phase constituting the insulation, radiation in the material, and heat transfer in the gas confined in the insulation. In this report the mechanisms of heat transfer are calculated theoretically. These calculations are verified experimentally by measurements on a glass fiber insulation in a specially constructed guarded hot plate apparatus. It is shown that the theories give a complete and consistent explanation of the influence of the mechanisms of heat transfer on the effective thermal conductivity of fibrous material.

Probabilistic Updating of Flaw Information

The prediction and control of flaws in welds occupy an important role in design against fatigue and fracture failure. However, the present NDT devices can detect only a fraction of the flaws and they do not give the actual size of flaws detected. Using Bayes Theorem, a framework is proposed whereby distributions of flaw size and density are updated from NDT inspection data and the level of repair. The concept is equivalent to a filtering process where the detectability function of the NDT device acts as the filter. The information derived will help planning of NDT inspection programs and consistent code specifications.

Effect of Pyrolytic Temperatures on the Longitudinal Strength of Dry Douglas-Fir

Compressive and tensile strength of dry Douglas-fir was measured through rapid constant deformation rate tests at temperatures from 25 to 288°C, at initial thermoequilibrium and after 2 h of heating. The tensile strength decreased slowly with increasing temperatures to 175°C. Above 175°C, the tensile strength reduces rapidly. This is attributed to alteration of the cellulosic fraction of wood. The compressive strength decreases more uniformly with temperatures increasing to 288°C due to changes occurring in all three basic wood components with change in temperature. A first-order reaction equation for bond rupture/formation was adopted to describe the response. Including only terms for bond rupture resulted in good correlation to the observed strength response at reaching thermoequilibrium.

Effect of Specimen Geometry on Hot Torsion Test Results for Solid and Tubular Specimens

Hot torsion tests have been carried out on aluminum, stainless steel, and silicon steel specimens using a wide range of gage length: radius ratios and bore diameters. For stainless steel, which dynamically recrystallises, a higher strain to maximum stress was found for specimens with a gage length : radius ratio A new effective radius is proposed for calculation of strains, strain rates, and shear stresses from torque-twist data for solid and tubular specimens.

Finite Element Modeling of Magnetic Field/Defect Interactions

Defect modeling and the prediction of magnetic field/defect interactions is of importance to the further refinement of electromagnetic methods of defect detection and categorization. Finite element methods are particularly suited to the analysis of field distributions within magnetic structures having complex boundary geometries and nonlinear B-H characteristics. This paper describes operational aspects of the finite element technique and shows how such methods can be applied to the analysis of electromagnetic methods of nondestructive testing, by predicting the magnetic field distribution around a rectangular slot in the surface of a circular ferromagnetic bar carrying an axial magnetisation current.

Capillary Porosity in Hardened Cement Paste

The porosity and pore size distributions of cement pastes of water/cement ratios of 0.35 and 0.55 were measured by high pressure (50,000 psi) mercury porosimetry. Measurements were made on pastes hydrated from 8 hours to 90 days. The variation of mercury porosity with maturity was found to correlate well with generally held concepts of the hydration of cement paste. Differences in the pore size distributions between pastes of different water/cement ratio lie mainly in the region of large pores.

THE INFLUENCE OF LOADING VARIABLES ON ENVIRONMENT-ENHANCED FATIGUE CRACK GROWTH IN HIGH STRENGTH STEELS

An experimental program was carried out to further determine the range of applicability of the superposition model, proposed by Wei and Landes, for estimating the effects of cyclic loading variables and chemical environment on fatigue crack growth. AISI 4340 steel, tempered at 200 deg F and 500 deg F, and RQ360A steel were used in this investigation. The influences of frequency, stress ratio, and cyclic-load waveform were examined. The results showed that the superposition model provides correct estimates of the trend and the order of magnitude for the influences of these variables within the applicable range provided that steady-state crack growth data are used. Data on the AISI 4340 steel suggest the presence of some synergistic effect of fatigue and environmental attack. Modification of this model will be needed to incorporate this effect and to improve the accuracy of predictions. Environment can affect fatigue-crack growth at K levels below the K level for stress corrosion cracking. Data obtined on the RQ360A steel indicate that the environmental effect can depend on frequency and cyclic-load waveform. These results are in agreement with published results on highly alloyed steels. Further basic studies will be needed to clarify these effects and to develop viable prediction procedures. Nonsteady-state crack growth in fatigue was observed. This state of carck growth would occur at the start of testing and following test interruptions. This phenomenon must be recongnized, and be taken into consideration in data acquisition and subsequent utilization. /Author/

The Influence of Interstitial Content on the Ductile-Brittle Transition Temperature of Fe-25Cr Ferritic Stainless Steels

The low temperature ductility of several vacuummelted, 25 percent chromium, ferritic stainless steels containing between 300 and 900 ppm total interstitials (C + N + O) has been investigated in the water-quenched condition using impact and tensile tests. In the low interstitial content alloys, the ductile-brittle transition temperature was markedly influenced by changes in interstitial content and grain size, whereas for the high interstitial contents such changes were not as significant. Tensile tests on the same alloys indicated that the yield stress was not sensitive to variations in either interstitial content or grain size. It is shown that increasing the interstitial content in these high chromium ferritic steels effects an increase in the amount of second phase present, particularly at the grain boundaries. Such particles enhance cleavage fracture by reducing the surface energy. It is observed that the second phase content is a single valued function of the ductile-brittle transition temperature.

Liquid Metal Embrittlement of 4145 Steel by Lead-Tin and Lead-Antimony Alloys

Pure lead soldered to the gage section of 200-ksi (1379-MPa) 4145 steel tensile specimens tested at temperatures ranging from room temperature to 700°F (371°C) exhibit a severe loss in ductility between 400 and 680°F (204 and 360°C). The ductility, as measured by reduction of area, recovered at 695°F (368°C), the so-called brittle-to-ductile recovery temperature. This recovery temperature was shifted to higher temperatures in a sensitive manner by relatively small amounts of either tin or antimony added to alloy the externally applied lead.

Strength and Ductility of Cr-Mo-V Steels in Creep at Elevated Temperatures

A state-of-the-art survey of literature pertaining to low alloy Cr-Mo-V steels has been completed with a view to elucidate the effects of composition, heat treatment, and microstructure on the creep strength and ductility of the steels. It appears that minor amounts of alloy additions such as boron, titanium, and cerium and impurity elements phosphorus, sulfur, tin, antimony, aluminum, and copper may affect the creep strength or ductility or both of the steels. Higher austenitizing and lower tempering temperatures lead to improved strength at the expense of rupture ductility. An upper bainite microstructure is associated with the highest creep strength and the lowest ductility, for temperatures up to 1050°F (565°C) and for times of at least up to 10,000 h. In bainite-ferrite aggregates, creep and rupture strengths increase in proportion to the amount of bainite, and the difference in strength between the various structures is maintained at least up to 10,000 h at 1070°F (575°C). Stress rupture strengths in general increase linearly with room temperature tensile strength for temperatures up to 1000°F (538°C) and times up to 10,000 h. Variation of rupture strength and minimum creep rate with temperature and time can be adequately described by the Orr-Sherby-Dorn parameter. Activation energies for both creep and for rupture are determined to be about 90 kcal/mole (375 kJ/mole). Further, it is observed that ˙e × tr ⋍ 3.3 and that tt ⋍ 0.3 tr, where ˙ϵ tt, and tr are the minimum creep rate, time for transition from second- to third-stage creep, and time to rupture, respectively.