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The air transport markets affected by global economic climate and regional demand characteristics are evolving fairly dynamically. To cope with the evolving demand and to penetrate desired market segments, operators' usage of aircraft has been getting more and more dynamic with increased deviation from the originally designed mission objectives. The objective of this research is to investigate the effects of in-service rrusslon variation on aircraft structural performance so as to provide airlines with a more realistic approach toward better fleet management. During the research, the scenarios and phenomena causing fleet in-service mission variations were investigated. A survey on the utilisation of world-wide aircraft fleets was conducted and presented. The in-service missions of aircraft fleets were found to vary significantly in terms of mission profile. Furthermore, the utilisation patterns of individual aircraft in the same fleet of a major airline are also being thoroughly analysed. Tremendous variations of mission mixes are found among individual aircraft. In order to analyse the effects of the in-service mission variation, methodologies and models based on fatigue test results have been developed by the author. Actual service data are being input for the effect analysis. It is found that the mission variation has a considerable engineering influence on the aircraft's structural performance either in terms of mission airworthiness or fatigue life span. Finally, a conceptual model, the 'Integrated Airline Fleet Management Model' (IAFM), has been developed as a blueprint for practical application. By implementing the IAFM, airline will be able to obtain a realistic picture of the health of its aircraft. With a more reliable basis for maintenance planning, improved inspection accuracy, reduced maintenance cost and better structural airworthiness can be achieved.

Low pressure steam turbine last stage blade behaviour was investigated and researched over duration of this PhD project period. The aim of the research was to enhance the life of last stage blades by investigation and mitigation of the accumulative damage throughout the life of the turbine blade. The research was mainly broken down in to three main themes covering erosion, High Cycle Fatigue in industrial service and High Cycle Fatigue under laboratory conditions. The three themes were then further analysed during the research analysis for correlation and the extent of accumulative damage contribution during each stage. An accumulative damage model was constructed together with mathematical expressions for each stage of accumulative damage. The erosion damage model was constructed first and separately, followed by a separate damage model for crack initiation and propagation. After this a combined damage model was constructed to represent accumulative damage throughout the turbine blade lifecycle. After the damage mechanisms were researched and understood, a damage mitigation model was constructed consisting of primary damage mechanisms and secondary damage mechanisms. The primary damage mechanisms were then investigated further and a life extension technique developed to increase turbine blade life by reducing damage rates per turbine start, giving more starts life capability to the last stage blades. The secondary mitigation mechanisms was not covered in this project and regarded as future work under the low pressure turbine life extension possibilities. The research work also gave a spin off which allowed the author to conduct and finish a separate piece of work of designing the problem out through redesigning the turbine blade and condenser space in conjunction with leading experts from the industry.

Moisture damage in asphalt mixes can be defined as loss of strength and durability due to the presence of moisture at the binder-aggregate interface (adhesive failure) or within the binder (cohesive failure). This research focuses on the evaluation of the susceptibility of aggregates and asphalts to moisture damage through understanding the micro-mechanisms that influence the adhesive bond between aggregates and asphalt and the cohesive strength and durability of the binder. Moisture damage susceptibility is assessed using surface energy measurements and dynamic mechanical analysis (DMA). Surface energy is defined as the energy needed to create a new unit surface area of material in vacuum condition. Surface energy measurements are used to compute the adhesive bond strength between the aggregates and asphalt and cohesive bond strength in the binder. DMA testing is used to evaluate the rate of damage accumulation in asphalt binders and mastics. The DMA applies a cyclic, torsional strain controlled loading to cylindrical asphalt mastics until failure. The DMA results are analyzed using continuum damage mechanics that focuses on separating the energy expended in damaging the material from that associated with viscoelastic deformation. A new approach is developed to analyze the DMA results and calculate the rate of damage. The developed approach is used to evaluate six asphalt mixtures which have performed either well or poorly in the field. The resistance of the field mixes to moisture damage is shown to be related to the calculations of bind energies and the accumulated damage in the DMA.

Primary goal of this thesis is to present proposed method for fatigue life evaluation applicable to light composite aircraft. The first chapter of this thesis is focused on certification specifications and requirements for fatigue life proof of structure. Significant part of this thesis is dedicated to fatigue life evaluation and guideline how to proceed in evaluation of fatigue data. Thesis also points out on possible methods of statistical fatigue data analysis and critical parts of structure in means of fatigue life. The last part of thesis is focused on design of experimental evaluation of structure including test rig and load sequence. This chapter also provides inside into possible means of introducing artificial defects into the structure.

<div>High temperature alloys have been extensively used in many applications, such as furnace muffles, fuel nozzles, heat treating fixtures and fuel nozzles. Due to such conditions these materials should have resistance to cyclic loading, oxidation and high heat. Although there are numerous prior experimental and theoretical studies, there is insufficient understanding of application of the unified viscoplasticity theory to finite element software for fatigue life</div><div>prediction.</div><div><br></div><div>Therefore, the goal of this research is to develop a procedure to implement unified viscoplasticity</div><div>theory in finite element (FE) model to model the complex material deformation pertaining to thermomechanical load and implement an incremental damage lifetime rule to</div><div>predict thermomechanical fatigue life of high temperature alloys.</div><div><br></div><div>The objectives of the thesis are:</div><div>1. Develop a simplified integrated approach to model the fatigue creep deformation</div><div>under the framework of ‘unified viscoplasticity theory’</div><div><br></div><div>2. Implement a physics - based crack growth damage model into the framework</div><div><br></div><div>3. Predict the deformation using the unified viscoplastic material model for ferritic</div><div>cast iron (Fe-3.2C-4.0Si-0.6Mo) SiMo4.06</div><div><br></div><div>4. Predict the isothermal low cycle fatigue (LCF) and LCF Creep life using the damage model</div><div><br></div><div>In this work, a unified viscoplastic material model is applied in a FE model with a combination of Chaboche non-linear kinematic hardening, Perzyna rate model and static recovery</div><div>model to model rate dependent plasticity, stress relaxation, and creep-fatigue interaction.</div><div><br></div><div>Also, an incremental damage rule has been successfully implemented in a FE model. The calibrated viscoplastic model is able to correlate deformations pertaining to isothermal LCF, LCF-Creep and thermal-mechanical fatigue (TMF) experimental deformations. The life predictions</div><div>from the FE model have been fairly good at room temperature (20°C), 400°C and 550°C under Isothermal LCF (0.00001/s and 0.003/s) and LCF-Creep tests.</div><div><div><br></div><div>The material calibration techniques proposed for calibrating the model parameters resulted in a fairly good correlation of FE model derived hysteresis loops with experimental hysteresis, pertaining to Isothermal LCF (ranging from 0.00001/s to 0.003/s), Isothermal LCF-Creep tests (with hold time) and TMF responses. In summary, the method and models developed in this work are capable of simulating material deformation dependency on temperature, strain-rates, hold time, therefore, they are capable to modeling creep-stress relaxation and fatigue interaction in high-temperature alloy design.</div></div>

The paper presents a computer-based guide of the effect of layout and loading (tension and torque) on the timing belt life and uses it to show the sensitivity of life to changed conditions in an automotive camshaft drive. The predictions are in line with experience. The guide requires belt property information, such as the tooth and tension member stiffness, the friction coefficient between the belt lands and pulleys and the pitch difference from the pulley, in order to calculate the tooth deflections caused by the belt loadings on the various pulleys in the layout. It also requires information on how the belt life depends on the tooth deflections. Experimental data are presented on the life±deflection relations of a commercial automotive timing belt tested between 100 and 140 8C, although the bulk of the data has been obtained at 120 8C. Four different life laws have been found, depending on whether the failure-initiating deflection occurred on a driver or a driven pulley, and whether at entry to or exit from the pulley. Theoretical analysis of the tooth loading in the partial meshing state shows that, in three cases out of the four, the different life±deflection laws transform to a single relation between the life and the tooth root strain. The exception is failure caused by driven entry conditions; work is continuing to understand better the causes of failure in this circumstance

This study aims to investigate the effect of a 96 I/O Film-BGA package of surface mounted components on the thermal induced nonlinear viscoplastic deformation of solder balls during temperature cyclic loading between -40¢J to 125¢J. Specifically, it aims to study the trend effect of the joint fatigue life with respect to four control factors of the PI (Polyimide) thickness, die size, die thickness, and the upper copper trace thickness. Then, two different package types of Fan-in and Fan-out design in terms of the joint fatigue life are discussed. Due to the structure/loading symmetry, a three-dimension octant finite element structure was modeled to capture the entire package structural behaviors and a formulation of Modified Coffin-Manson was used to predict the joint fatigue life. Under temperature cyclic loading, the study results show that the die size, die thickness, and PI thickness had significant impact on the solder joint fatigue life, especially the effect of applying die size to the joint, but the upper copper trace thickness had little effect on the joint fatigue life. The study results also show that the package type of Fan-out design had higher joint fatigue life than that the package type of Fan-in design did for this Film-BGA package. In addition, by using the Taguchi method, the research could find the intensity of affected fatigue life due to the selected four control factors, and determine the optimized design by means of the optimized dimensions of the control factors. Then, the use of the ANOVA (analysis of variance) method helped the researcher predict the optimized joint fatigue life in comparison with the study results by using ANSYS finite element software analysis.

As bridges continue to age and budgets reduce, transportation officials often need quantitative data to distinguish between bridges that can be kept safely in service and those that need to be replaced or retrofitted. One of the critical types of structural deterioration for steel bridges is fatigue-induced fracture, and evaluating the daily fatigue damage through field measurements is one means of providing quantitative data to transportation officials. When analyzing data obtained through field measurements, methods are needed to properly evaluate fatigue damage. Five techniques for evaluating strain data were formalized in this dissertation. Simplified rainflow counting, which converts a stress history into a histogram of stress cycles, is an algorithm standardized by ASTM and the first step of a fatigue analysis. Two methods, effective stress range and index stress range, for determining the total amount of fatigue damage during a monitoring period are presented. The effective stress range is the traditional approach for determining the amount of damage, whereas the index stress range is a new method that was developed to facilitate comparisons of fatigue damage between sensors and/or bridges. Two additional techniques, contribution to damage and cumulative damage, for visualizing the data were conceived to allow an engineer to characterize the spectrum of stress ranges. Using those two techniques, an engineer can evaluate whether lower stress cycles (concern due to electromechanical noise from data acquisition system) and higher stress ranges (concern due to possible spike from data acquisition system) contribute significantly to the accumulation of damage in the bridge. Data from field measurements can be used to improve the estimate of the remaining fatigue life. Deterministic and probabilistic approaches for calculating the remaining fatigue life were considered, and three methods are presented in this dissertation. For deterministic approaches, the output of the equations is the year when the fatigue life has been exceeded for a specific probability of failure, whereas for probabilistic approaches, the probability of failure for a given year is calculated. Four different steel bridges were instrumented and analyzed according to the techniques outlined in this dissertation. / text