Inelastic Deformation And Fatigue Damage In Metals At High Homologous Temperatures

From concept to application, this book describes the method of strain-range partitioning for analyzing time-dependent fatigue. Creep (time-dependent) deformation is first introduced for monotonic and cyclic loading. Multiple chapters then discuss strain-range partitioning in details for multi-axial loading conditions and how different loading permutations can lead to different micro-mechanistic effects. Notably, the total-strain method of strain-range partitioning (SRP) is described, which is a methodology that sees use in several industries. Examples from aerospace illustrate applications, and methods for predicting time-dependent metal fatigue are critiqued.

Combined experimental and theoretical investigations into the inelastic deformation and damage behavior of engineering alloys at elevated temperatures are being pursued. The analysis of previously performed strain rate change and relaxation tests on modified 9Cr-1Mo steel showed the need for inclusion of a recovery of state term in the growth laws for the state variables of the viscoplasticity theory based on overstress (VBO). Recovery of state terms were introduced and the experimental results were satisfactorily simulated. The finite deformation theory of VBO has been developed further to include a convected derivative rationale for the choice of the objective stress rate. The reversing direct current voltage drop measurements during low cycle fatigue at elevated temperature were improved. A passive filter bank and new positioning devices for the coils were installed. Tests at 650°C and lasting several days showed excessive, uncontrollable temperature changes. It was decided to drop the test temperature to 538°C which is close to the operating temperature of Type 304 Stainless Steel. The temperature fluctuations in torsion tests were within {plus minus}3°C which was considered satisfactory. Testing will continue at 538°C.

Combined experimental and theoretical investigations into the inelastic deformation and damage behavior of engineering alloys at elevated temperatures are being pursued. The analysis of previously performed strain rate change and relaxation tests on modified 9Cr-1Mo steel showed the need for inclusion of a recovery of state term in the growth laws for the state variables of the viscoplasticity theory based on overstress (VBO). Recovery of state terms were introduced and the experimental results were satisfactorily simulated. The finite deformation theory of VBO has been developed further to include a convected derivative rationale for the choice of the objective stress rate. The reversing direct current voltage drop measurements during low cycle fatigue at elevated temperature were improved. A passive filter bank and new positioning devices for the coils were installed. Tests at 650°C and lasting several days showed excessive, uncontrollable temperature changes. It was decided to drop the test temperature to 538°C which is close to the operating temperature of Type 304 Stainless Steel. The temperature fluctuations in torsion tests were within ±3°C which was considered satisfactory. Testing will continue at 538°C.

In several industrial fields (such as automotive, steelmaking, aerospace, and fire protection systems) metals need to withstand a combination of cyclic loadings and high temperatures. In this condition, they usually exhibit an amount—more or less pronounced—of plastic deformation, often accompanied by creep or stress-relaxation phenomena. Plastic deformation under the action of cyclic loadings may cause fatigue cracks to appear, eventually leading to failures after a few cycles. In estimating the material strength under such loading conditions, the high-temperature material behavior needs to be considered against cyclic loading and creep, the experimental strength to isothermal/non-isothermal cyclic loadings and, not least of all, the choice and experimental calibration of numerical material models and the selection of the most comprehensive design approach. This book is a series of recent scientific contributions addressing several topics in the field of experimental characterization and physical-based modeling of material behavior and design methods against high-temperature loadings, with emphasis on the correlation between microstructure and strength. Several material types are considered, from stainless steel, aluminum alloys, Ni-based superalloys, spheroidal graphite iron, and copper alloys. The quality of scientific contributions in this book can assist scholars and scientists with their research in the field of metal plasticity, creep, and low-cycle fatigue.

An integral review is given in this book on the fatigue phenomenon covering the fundamentals of fatigue damage initiation, relevant factors influencing fatigue crack propagation and fatigue life, random load analysis, and simulation for theoretical and experimental fatigue life assessment. The entire chain of problems related to fatigue of metals and structural components is covered. Specifically, it describes the low-cycle plastic properties and statistically interprets the material stress reaction, examining original results of investigations on inelastic deformations under high cycle cyclic loading and correlating them with a number of use parameters. The limit states of bodies with primary defects and their resistance to fatigue crack propagation are discussed. Measurements, analysis and real-time modelling of operating loads for experimental fatigue life verification are reviewed as well as introducing some new fatigue damage accumulation hypotheses based on dissipated energy.

Combined experimental and theoretical investigations into the inelastic deformation and damage behavior of engineering alloys at elevated temperatures are being pursued. Modeling of effects of recovery of state observed in modified 9Cr-lMo steel has been completed. Finite deformation formulations of viscoplasticity theory based on overstress (VBO) include a modified growth law for the equilibrium stress and a rationale for choosing objective derivatives of stress-like state variables. Numerical simulations are in progress. Seven biaxial low-cycle fatigue tests at 538C have been completed with the reversing DC potential drop apparatus attached. A new method of data analysis and smoothing was developed which showed a significant increase in voltage drop in the area of crack formation. Correlation with solutions of Laplace's Equation for a semi-elliptical crack showed similar shapes for the voltage drop.

This volume presents a collection of contributions on materials modeling, which were written to celebrate the 65th birthday of Prof. Nobutada Ohno. The book follows Prof. Ohno’s scientific topics, starting with creep damage problems and ending with homogenization methods.