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

An analytical treatment of the fatigue performance of a cam-roller followler system as influenced by residual stresses induced by grinding, is developed. An approach based on an extended Hertzian analysis is used to determine the 3-D contact stress fields, which are then combined by elastic superposition with the residual stress fields. These residual stresses were measured previously by the x-ray diffraction technique and represent a range of grinding protocols from mild to abusive. The maximum cyclic component, generally occurring subsurface, is then identified in terms of an effective stress amplitude and mean which are used with a fatigue damage model to predict fatigue crack initiation. Results, pending experimental confirmation, appear reasonable and provide a useful basis for optimizing cam performance in terms of manufacturing and design parameters. / Master of Science

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

This thesis presents the application of topology to machining at the micro and macro levels through an experimental study, modeling and analysis. Uncoated carbide tools of four different cutting edge radii and four different feed rates are used to perform orthogonal machining on AISI 1045 steel disks. The study analyzes the cutting forces, changing grain boundary parameters, micro-hardness, temperature and correlates them to the residual stresses that hold a key to the product life. This analysis helps to understand and evaluate the aspects of grain boundary engineering that influence the fatigue life of a component. The two components of residual stresses (axial and circumferential) are measured, and are correlated with the different cutting edge radii and feed conditions. A topology-based modeling approach is applied to study and understand various outputs in the machining process. The various micro and macro topological parameters that influence the machining process are studied to develop a model to establish the effects of topological parameters in machining using Maple program.

GKN Aerospace in Trollhättan don’t use the latest ANSYS version and need to upgrade their life analysis models. The aim with this thesis is to do a study of the new models and investigate the times required for the calculations. A flight mission were chosen and this mission together with different life analysis models were run in the GKN in house program Life Analysis System. The results were analyzed and depending on the results additional runs were made or the problem were sent to the life management group at GKN Aerospace. Strain levels versus time were also plotted for the runs with the new models to get a perception where any problems occurs. The results from the model 4.10.149 had no variations between equal runs for the high pressure turbine and the low pressure turbine but there was a variation between the results when equal runs was made with the high pressure compressor. The results from model 4.10.157 and 4.10.124 and 4.10.160 and 4.10.173 had variations in the fatigue life for equal runs. The variations can depend on that the calculations converges to different solutions, the reason for this can depend on the non-linear contact elements. The variation in the results between equal runs occurs when the model uses two or more cores. The time required for the calculation becomes faster with the use of more cores. The longest duration had model 4.10.173 because of the many requirements for the calculations in this model. The problem with the variation in the results is sent to ANSYS.

Indiana University-Purdue University Indianapolis (IUPUI) / Additive manufacturing (AM) or 3D printing has gained significant advancement in recent years. However the potential of 3D printed metals still has not been fully explored. A main reason is the lack of accurate knowledge of the load capacity of 3D printed metals, such as fatigue behavior under cyclic load conditions, which is still poorly understood as compared with the conventional wrought counterpart. The goal of the thesis is to advance the knowledge of fatigue behavior of 15-5 PH stainless steel manufactured through laser powder bed fusion process. To achieve the goal, a combined numerical and experimental study is carried out. First, using a rotary fatigue testing experiment, the fatigue life of the 15-5 PH stainless steel is measured. The strain life curve shows that the numbers of the reversals to failure increase from 13,403 to 46,760 as the applied strain magnitudes decrease from 0.214\% from 0.132\%, respectively. The micro-structure analysis shows that predominantly brittle fracture is presented on the fractured surface. Second, a finite element model based on cyclic plasticity including the damage model is developed to predict the fatigue life. The model is calibrated with two cases: one is the fatigue life of 3D printed 17-4 stainless steel under constant amplitude strain load using the direct cyclic method, and the other one is the cyclic behavior of Alloy 617 under multi-amplitude strain loads using the static analysis method. Both validation models show a good correlation with the literature experimental data. Finally, after the validation, the finite element model is applied to the 15-5 PH stainless steel. Using the direct cyclic method, the model predicts the fatigue life of 15-5 PH stainless steel under constant amplitude strain. The extension of the prediction curve matches well with the previously measured experimental results, following the combined Coffin-Manson Basquin Law. Under multi-amplitude strain, the kinematic hardening evolution parameter is incorporated into the model. The model is capable to capture the stresses at varied strain amplitudes. Higher stresses are predicted when strain amplitudes are increased. The model presented in the work can be used to design reliable 3D printed metals under cyclic loading conditions.

The doctoral thesis deals with fatigue life evaluation of composites structures. The thesis pro-vides complex review of problematic and it is based on recent situation assessment. The main ob-jective of the thesis is to design the methodology of fatigue life evaluation of composites struc-tures. The designed methodology is applied to fatigue life evaluation of sailplane wing and propel-ler blades. One part of the thesis deals with laboratory fatigue tests of composite specimens which are intended for comparison of the effect of manufacturing technology and environment condition.

No description available.

Doctor of Philosophy / Department of Civil Engineering / Hayder Rasheed / Most state highway agencies do not perform routine fatigue inspections on highway signs, luminaires, and traffic signals, thereby increasing the potential for unnoticed fatigue cracking. The Kansas Highway System utilizes over 450 sign trusses, most of which have been in service for 30-45 years. In addition, to aging support structures, the structural designs these signs and signals sometimes result in significant cyclical loading due to wind gust. This study conducted fatigue evaluations using nominal axial member-specific stress ranges corresponding to a wind speed database for a 45-year period, as well as, hundreds of structural analysis simulations. Potential fatigue failure was assessed for each member of the support structure by evaluating the ratio of consumed fatigue cycles to ultimate fatigue cycles using Miner’s rule to estimate finite life. If the ratio was close to zero after 45 years or any number of actual service years, the member was expected to have a practically infinite life. If the ratio was close to 1 after the service years, the member was expected to be at the end of its life. This information can help inspectors identify for critical spots that may have developed fatigue cracks that otherwise would be difficult to detect. Two approaches were hypothesized to account for fatigue life deterministically and probabilistically. Fatigue Life Simulator Software (FLSS) was developed to manage hundreds of simulations and determine the fatigue life of all members in a structure in specific areas of Kansas. FLSS is compatible and works simultaneously with STAAD Pro Software and Sign Truss Interface provided by KDOT, to generate results. Users apply the results to study the behavior of overhead structures and identify critical spots that should be physically inspected and potentially replaced. Results in Kanas indicated a range of structural fatigue life varying by city. Modifications were made to the output files of Sign Truss Interface to incorporate American Association of State Highway and Transportation Officials (AASHTO) load cases 1 and 2 and simulate wind speed into wind pressure using the effect of the two load cases. The modification also automatically incorporated 45-years of wind speed data into the Sign Truss Interface to simulate and generate structural models to determine corresponding stresses to the wind effect.