Fatigue fracture usually is defined as the failure of a part at a stress below its breaking stress due to repetitive loading conditions. It is now a well known fact that a part, designed for a maximum stress well below the yield point of the material, may be very apt to fail under cyclic loading conditions over a period of time. The metal appears to "wear out" after a time just like humans do and fatigue failure occurs. Metal fatigue may be contrasted to animal fatigue in that l) its detection before the latter stages is normally difficult if not impossible, 2) the condition is not dissipated by recovery, and 3) damage is cumulative.

Uniaxial tensile tests were performed on AISI 1018 steel specimens. Tests were conducted both in air and while the specimens were undergoing electrolytic hydrogen charging. Specimens with three different surface finishes were tested at various cathodic charging current densities. The tensile deformation was initiated only after the specimen was charged to at least 95% with hydrogen. The data presented in this study show that very low cathodic charging current densities result in larger ductility losses for specimens of all three surface finishes relative to specimens tested in air. Once this lower limit of cathodic-charging current density is reached the extent to which hydrogen induced damage is developed is primarily controlled by surface finish with cathodic charging current density playing a secondary role. Specifically, cathodic charging with hydrogen at any particular current density resulted in increased hydrogen induced damage with increased surface roughness. In addition, increased cathodic charging current density resulted in increased hydrogen induced damage within any set of specimens with a given surface roughness. Hydrogen induced damage caused the reduction in area at fracture to decrease and the extent of this damage increased as the surface roughness and the cathodic charging current density increased. The strain-to-initiate cracking decreased with increased surface roughness. Elongation to fracture was shown to be a poor measure of hydrogen induced damage and crack nucleation was shown to be easier than crack propagation. Charging of specimens to at least 95% saturation at a cathodic charging current density of 375 mA/cm² did not alter the primary fracture mode. Microvoid coalescence remained dominant although there was some evidence of quasicleavage in surface cracks. These data do not exclusively support any of the currently proposed mechanisms for hydrogen embrittlement. / Master of Science

Fatigue-crack propagation and residual static-strength data on PH15-7Mo (TH 1050) stainless steel are presented in this thesis. In addition, the capability of McEvily and Illg's crack-growth analysis and Kuhn and Figge's residual strength analysis to correlate the test data has been investigated. Axial-load fatigue-crack propagation (at R = 0 and -1) and residual static-strength tests were conducted, on 2-inch-wide sheet specimens made of PH15-7Mo (TH 1050) stainless steel. Analysis of the data showed that as individual analysis methods both analyses satisfactorily correlated the majority of the test data. However, the material constants derived in the two analyses differed significantly. This difference was attributed to the different amounts of work-hardening which occurs in the material prior to failure in the two cases. The effects of the different stress ratios on fatigue-crack growth were studied. In addition, the capability of the residual-strength analysis to predict the effects of changing buckling restraint in the vicinity of the crack.and of changing specimen width were investigated. / Master of Science

LD2668 .T4 1947 R5 / Master of Science

published_or_final_version / abstract / Civil Engineering / Doctoral / Doctor of Philosophy

by Yu, Chak Chung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (leaves 129-133). / by Yu, Chak Chung. / PREFACE --- p.i / ACKNOWLEDGMENT --- p.iv / ABSTRACT --- p.v / Chapter 1 --- INTRODUCTION --- p.1 / Chapter 1.1 --- Barkhausen effect --- p.2 / Chapter 1.2 --- Magnetoacoustic emission --- p.4 / Chapter 1.3 --- Methods of measurements --- p.5 / Chapter 1.3.1 --- Magnetization of a sample --- p.6 / Chapter 1.3.2 --- Signal detection --- p.8 / Chapter 1.3.3 --- Signal processing --- p.9 / Figures for chapter1 --- p.11 / References --- p.14 / Chapter 2 --- MAGNETIC PHENOMENA AND THEORIES --- p.17 / Chapter 2.1 --- Magnetostriction --- p.17 / Chapter 2.1.1 --- Spontaneous magnetostriction --- p.18 / Chapter 2.1.2 --- Saturation magnetostriction --- p.19 / Chapter 2.1.3 --- Field induced magnetostriction --- p.20 / Chapter 2.1.4 --- Magnetostriction at an angle θ to the magnetic field --- p.21 / Figures for section 21 --- p.24 / Chapter 2.2 --- Domain theory --- p.26 / Chapter 2.2.1 --- Magnetic domains --- p.26 / Chapter 2.2.2 --- Magnetostatic energy --- p.27 / Chapter 2.2.3 --- Magnetization process --- p.29 / Figures for section 22 --- p.30 / Chapter 2.3 --- Domain walls and domain processes --- p.33 / Chapter 2.3.1 --- Properties of domain walls --- p.33 / Chapter 2.3.2 --- "180° and non-180° domain walls, and closure domains" --- p.34 / Chapter 2.3.3 --- Domain wall motion --- p.35 / Chapter 2.3.4 --- Reversible and irreversible domain processes --- p.36 / Chapter 2.3.5 --- Barkhausen emission and magnetoacoustic emission --- p.38 / Figures for section 23 --- p.39 / Chapter 2.4 --- Hindrances to wall motion --- p.43 / Chapter 2.4.1 --- Residual stress --- p.43 / Chapter 2.4.1.1 --- Dislocation --- p.44 / Chapter 2.4.1.2 --- Magnetostriction --- p.45 / Chapter 2.4.1.3 --- Plastic deformation --- p.46 / Chapter 2.4.2 --- Inclusions --- p.47 / Chapter 2.4.3 --- "Domain nucleation, annihilation, and wall motion" --- p.48 / Figures for section 24 --- p.50 / References --- p.55 / Chapter 3 --- MEASUREMENT OF BARKHAUSEN EMISSION AND MAGNETOACOUSTIC EMISSION FROM A FRACTURED STEEL BAR --- p.57 / Chapter 3.1 --- Introduction --- p.57 / Chapter 3.2 --- Experiments --- p.58 / Chapter 3.3 --- Results and discussions --- p.60 / Chapter 3.3.1 --- BE and MAE profiles --- p.60 / Chapter 3.3.2 --- Defects --- p.61 / Chapter 3.3.3 --- Elongated grains --- p.62 / Chapter 3.3.4 --- Effect of annealing --- p.63 / Chapter 3.4 --- Conclusions --- p.64 / Figures and table for chapter3 --- p.66 / References --- p.70 / Chapter 4 --- NONDESTRUCTIVE INSPECTION OF A FRACTURED NICKEL BAR BY BARKHAUSEN AND MAGNETOACOUSTIC EMISSIONS --- p.71 / Chapter 4.1 --- Introduction --- p.71 / Chapter 4.2 --- Experiments --- p.72 / Chapter 4.3 --- Results --- p.73 / Chapter 4.4 --- Discussions --- p.74 / Chapter 4.4.1 --- Barkhausen emission --- p.74 / Chapter 4.4.2 --- Magnetoacoustic emission --- p.75 / Chapter 4.4.3 --- Comparison of nickel and mild steel --- p.77 / Chapter 4.5 --- Conclusions --- p.78 / Figures and table for chapter4 --- p.81 / References --- p.83 / Chapter 5 --- DETERMINATION OF THE ROLLING DIRECTION OF ELECTROLYTIC ZINC-COATED STEEL PLATE BY BARKHAUSEN EMISSION --- p.84 / Chapter 5.1 --- Introduction --- p.84 / Chapter 5.2 --- Experiments --- p.85 / Chapter 5.3 --- Results --- p.86 / Chapter 5.4 --- Discussions --- p.87 / Chapter 5.4.1 --- BE profiles 、 --- p.87 / Chapter 5.4.2 --- Effects of hardness and defects --- p.89 / Chapter 5.5 --- Conclusions --- p.90 / Figures for chapter5 --- p.91 / References --- p.97 / Chapter 6 --- MAGNETIC MEASUREMENTS MADE ON A NICKEL PLATE WITH HIDDEN HOLE --- p.98 / Chapter 6.1 --- Introduction --- p.98 / Chapter 6.2 --- Experiments --- p.99 / Chapter 6.3 --- Results and discussions --- p.100 / Chapter 6.3.1 --- Barkhausen emission --- p.100 / Chapter 6.3.2 --- Magnetoacoustic emission --- p.102 / Chapter 6.4 --- Conclusions --- p.103 / Figures for chapter6 --- p.105 / Chapter 7 --- CONCLUSIONS AND SUGGESTIONS FOR FURTHER STUDIES --- p.114 / APPENDIX --- p.118 / Chapter A1 --- Experimental setup for BE measurement --- p.118 / Chapter A2 --- Experimental setup for MAE measurement --- p.119 / Chapter A3 --- Specifications and models of the equipment used in the experiments --- p.120 / Chapter A4 --- List of figures --- p.121 / BIBLIOGRAPHY --- p.129

No description available.

No description available.

An investigation was conducted to determine the effect of nitrogen concentration between 0.27 percent and 1.30 percent on the internal friction peaks in 304L stainless steel. The amplitude of the internal friction peak associated with the stress-induced diffusion of interstitial nitrogen increased as a linear function of the nitrogen content. The activation energy of diffusion was found to decrease with an increase in nitrogen content. The presence of another internal friction peak was observed in the spectrum of the sar.iple containing 1.30 percent nitrogen. A metallographic investigation and a change in the magnetic properties of the specimens after testing along with the disappearance of the internal friction peak caused by nitrogen diffusion when the specimen was rerun indicated that the second peak probably resulted form a chromium-nitrogen interaction. / M.S.

This thesis presents the results of a study of the fully stressed design (FSD) of rigidly convected plane steel frames. The objective is to: (1) formulate the FSD algorithm consistent with the most recent AISC Manual of Steel Construction, (2) study the effect of some of the features of FSD on the final design, and (3) compare final designs with previously published results. Dependent section property functions are derived for the data points of available sections using a polynomial regression model with the section modulus as the independent design variable. Comparing the derived equations with two other published sets of equations demonstrates that the specific dependent functions used in an FSD solution significantly affect the structural weight of the final design. The most efficient sections are those that have the largest moment of inertia and smallest cross sectional area for a given section modulus. These functions are derived for the sections available. Finally, a procedure is suggested for automatic selection of a set of sections as the final step in the design. / Master of Science