Ic Moore

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.

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.

Some Studies of the Influence of Localized and Gross Plasticity on the Monotonic and Cyclic Concentration Factors

The variation in monotonic and cyclic concentration factors (namely, Kt, Ke, Kσ) due to localized and gross plasticity is presented and discussed for two alloys of contrasting stress-strain behavior, an aluminum alloy 2024 T351 and a mild steel SAE 1015. Thin plates with circular and elliptical holes made of these alloys were subjected to monotonic and cyclic straining in a servo controlled testing machine. Predominant in the monotonic behavior of the concentration factors is the rapid increase in strain concentration factor in notched mild steel plates, attributed to the unrestrained plastic flow (Luders deformation) characteristic of this material. Such behavior is compared to the response of the continuously strain hardening aluminum alloy when subjected to a similar nominal strain history. The dominant feature of the cyclic behavior is the variation in the notch strains as influenced by the overall hardening or softening phenomenon which accompanies cyclic plastic deformation. With the aid of these results, the accuracy of the Neuber rule is checked and restrictions to its application in fatigue life predictions of notched members using smooth specimen data are presented.

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.

Atomic Absorption Analysis of Portland Cement and Raw Mix Using a Lithium Metaborate Fusion

A rapid and accurate atomic absorption method is described for the analysis of nine elements in portland cement and portland cement raw mix. These elements are aluminum, calcium, iron, magnesium, manganese, potassium, sodium, silicon, and strontium. Samples are fused with anhydrous lithium metaborate in a graphite crucible, and the molten melt is poured into a dilute acid solution. Possible interferences and “matrix” effects are minimised by calibrating the instrument with standard solutions prepared from NBS standard cements. Calcium and silicon determinations are made using a signal-averaging digital-readout device and a standard-unknown-standard bracketing technique, The precision and accuracy for all of the elements determined is sufficient for control purposes. The time required for the analysis of a single sample is approximately 1 1/2 h. When multiple samples are to be analyzed, time per sample is greatly reduced.

A Test Procedure for Determining the Resilient Properties of Granular Materials

RESULTS OF INVESTIGATION INDICATE THAT THE NUMBER OF STRESS REPETITIONS AND THE STRESS SEQUENCE HAVE LITTLE EFFECT ON THE RESILIENT BAHAVIOR OF GRANULAR MATERIALS. THERE IS NO EVIDENCE OF A CHANGE IN RESILIENT BEHAVIOR WITH CHANGES IN LOAD DURATION OR FREQUENCY. THE SIGNIFICANCE OF THESE FINDINGS IS THAT THE RESILIENT RESPONSE DETERMINED AFTER 150 TO 200 REPETITIONS WILL PROVIDE A REASONABLE INDICATION OF RESILIENT PROPERTIES FOR A MATERIAL SUBJECTED TO A COMPLEX STRESS HISTORY. FINDINGS ALSO INDICATE THAT THE RESPONSE TO STRESSES OF DIFFERENT INTENSITIES CAN BE MEASURED IN ANY SEQUENCE ON A SINGLE SAMPLE. FURTHERMORE, THE RESPONSE CAN BE DETERMINED USING EITHER STATIC OR DYNAMIC TRIAXIAL LOAD TESTS.