The designers of heavy, off-road vehicle suspension systems face unique challenges. The ride comfort versus handling compromise in these vehicles has been frequently investigated using mathematical optimisation. Further challenges exist due to the large variations in vehicle sprung mass. The suspension system must provide adequate isolation from road load inputs throughout its payload operating range. This is imperative if good vehicle structural life is to be ensured. A passive suspension system can only provide optimal isolation at a single payload. The designer of such a suspension system must therefore make a compromise between designing for a fully-laden or unladen payload state. This work deals with suspension optimisation for vehicle structural life. The work mainly addresses two questions: 1) What are the suspension characteristics required to ensure optimal isolation of the vehicle structure from road loads? and 2) If such optimal suspension characteristics can be found, how sensitive are they to changes in vehicle payload? The study aims to answer these questions by examining a Land Rover Defender 110 as case study. An experimentally validated mathematical model of the test vehicle is constructed for the use in sensitivity studies. Mathematical optimisation is performed using the model in order to find the suspension characteristics for optimal structural life of the vehicle under consideration. Sensitivity studies are conducted to determine the robustness of the optimal characteristics and their sensitivity to vehicle payload variation. Recommendations are made for suspension characteristic selection for optimal structural life. AFRIKAANS : Ontwerpers van swaar, veldvoertuig suspensie stelsels staar unieke uitdagings in die gesig. Die ritgemak teenoor hantering kompromie in hierdie voertuie is reeds telkemale ondersoek, ook met wiskundige optimering. Verdere uitdagings bestaan as gevolg van die groot veranderinge in geveerde massa by hierdie voertuie. Die suspensiestelsel moet gepaste isolasie van pad insette oor `n wye reeks van bedryfstoestande lewer. Dit is veral belangrik indien daar verseker wil word dat die voertuig goeie struktuurleeftyd het. `n Passiewe suspensiestelsel kan egter slegs optimale isolasie by `n enkele vragtoestand lewer. Die ontwerper van `n passiewe suspensie stelsel moet dus `n kompromie aangaan tussen ontwerp vir `n vol of leë vragtoestand. Hierdie studie handel oor suspensie optimering vir struktuur leeftyd. Die werk spreek hoofsaaklik twee vraagstukke aan: 1) Watter suspensie karakteristieke word benodig om die voertuig struktuur optimaal van padinsette te isoleer? en 2) Indien sulke optimale karakteristieke gevind kan word, wat is hulle sensitiwiteit vir veranderinge in voertuig vrag? Die studie mik om hierdie vraagstukke aan te spreek deur ondersoeke op `n Land Rover Defender 110 toetsvoertuig. `n Eksperimenteel gevalideerde, wiskundige model van die toetsvoertuig word saamgestel met die oog op sensitiwiteitstudies. Wiskundige optimering word met die model uitgevoer om sodoende die suspensie karakteristieke vir optimale struktuurleeftyd vir die betrokke toetsvoertuig te bepaal. Sensitiwiteitsanalises word gedoen om die robuustheid van die optimale karakteristieke, met betrekking tot veranderinge in voertuig vrag, vas te stel. Aanbevelings word gemaak oor die keuse van suspensie karakteristieke vir optimale struktuur leeftyd. Copyright / Dissertation (MEng)--University of Pretoria, 2010. / Mechanical and Aeronautical Engineering / unrestricted

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Thread rolling is a unique metal forming process which is commonly used to form screw threads on threaded fasteners and precision leadscrews at relatively high rates of speed. Threads are formed on a cylindrical blank by flat or cylindrical dies having the reverse form on them, which rotate and penetrate the blank simultaneously, to plastically deform it into a precise geometry. Thread rolling dies are exposed to a complex state of cyclical contact stresses that eventually cause the dies to fail by fatigue and wear. The stress state is not easily ascertained through standard analytical models due to complex geometry and process conditions. This research seeks to better understand the state of contact stresses present in cylindrical thread rolling dies as they form material, to aid in identifying and testing economical methods of improving thread rolling die fatigue life. Some work has been published on using FEA simulation software to model the thread rolling process, but no work has been published on using FEA software to analyze the stresses in thread rolling dies. DEFORM®-3D Forming Simulation Software by Scientific Forming Technologies Corporation in Columbus, Ohio was used to simulate the throughfeed thread rolling process and model the state of stresses in the dies. The results were compared to the Hertzian contact stress model and the Smith Liu equations for rolling and sliding friction. Fatigue life prediction methods involving S-N curves, surface fatigue strength, and Weibull probability distributions were tested using the simulation data against field results. An optimized die design was generated from a design of experiments simulating different die design geometry. Findings show that field failures correlate well to the DEFORM® simulation results. The Hertz model with Smith Liu equations improved correlation with the simulation. Fatigue life prediction models correlated reasonably well to field results using the simulation data for inputs. These findings can aid in selecting appropriate die materials, design parameters, and fatigue life treatments.

This thesis has been conducted at Cargotec Sweden AB as a case study on the loader body of the HIAB XS 144 crane. The loader body is the innermost part in the cranes arm-system and its fatigue life is critical to the operational life of the whole crane. Welding is the main joining process in Cargotec’s cranes and are often a limiting factor when it comes to fatigue life. The weld joining the column to the loader body is carrying the whole crane moment. Previous testing has shown that this weld often limits the fatigue life of the loader body, it has thus been evaluated. Weld fatigue life is affected by a large amount of parameters. To pinpoint the parameters mainly affecting the weld fatigue life and to understand their influence, calculations have been organized using factorial design. The evaluation has been carried out using 3D finite element calculations utilizing sub-modelling to calculate local stresses in the weld notches. Different parameters have been evaluated based on their influence on the local notch stresses. To estimate stresses from the evaluated parameters, regression equations have been fitted. The effective notch method has been used to estimate weld fatigue life. The evaluation has shown that a butt-weld design with root-support, only being welded from the outside of the loader body, as used on some other crane models, could not provide a robust design for the XS 144 crane. The evaluation could also point out several critical parameters that need to be considered when using such design. Apart from the local weld geometry, plate thickness, plate angle, material offset and thickness in the casted column were mainly affecting the weld notch stresses.

The thesis deals with the fatigue resistance of material MAR-M 247 at temperatures of 650 °C, 800 °C and 900 °C. Based on the results obtained, curves of durability ("S/N curves") were drawn and the effect of temperature on the fatigue behaviour of nickel-based superalloys MAR-M 247 and IN713 LC was evaluated. Fractographic analysis was used to examine the failure mechanism and the effect of casting defects on the fatigue crack initiation.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19184号 / 工博第4061号 / 新制||工||1626(附属図書館) / 32176 / 京都大学大学院工学研究科マイクロエンジニアリング専攻 / (主査)教授 田畑 修, 教授 琵琶 志朗, 准教授 土屋 智由, 教授 松原 厚 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Yes / Super-fine stainless wires (SSWs) with micron diameter and large specific surface area can simultaneously strengthen and toughen reactive powder concrete (RPC) at low volume fraction, so SSW reinforced RPC composites have potential for developing infrastructures bearing fatigue load or with aseismic requirements. In this paper, the uniaxial compressive fatigue characteristics of such composites under high stress levels were investigated, and the modification mechanisms of SSWs to RPC were revealed through failure state and microstructure analyses. The results showed that incorporating only 0.5 vol.% SSWs into RPC enables the fatigue life and energy dissipation capacity to increase by 252.0% and 262.3%, meanwhile, the fatigue limit strength of composites at the failure probability of 50% reaches up to 76.6% of static uniaxial compressive strength, due to the improvement effect on microstructure compactness, inhibiting effect on flaw initiation, and the ability to convert single main crack into radial multiple micro cracks centered on SSWs. Furthermore, the average maximum fatigue strain and residual strain of composites are improved by 73.7% and 87.2%, respectively, which can be ascribed to the bridging, debonding and being pulled-off effect of SSWs. It can be therefore concluded that the incorporation of SSWs endows RPC with excellent fatigue performance, thus further enlarging the application of composites. / The authors would like to thank the National Science Foundation of China (51908103 and 51978127), and the China Postdoctoral Science Foundation (2019M651116) for providing funding to carry out this investigation.

When designing an engineering part, better decisions are made by exploring the entire space of design variations. This design space exploration (DSE) may be accomplished manually or via optimization. In engineering, evaluating a design during DSE often consists of running expensive simulations, such as finite element analysis (FEA) in order to understand the structural response to design changes. The computational cost of these simulations can make thorough DSE infeasible, and only a relatively small subset of the designs are explored. Surrogate models have been used to make cheap predictions of certain simulation results. Commonly, these models only predict single values (SV) that are meant to represent an entire part's response, such as a maximum stress or average displacement. However, these single values cannot return a complete prediction of the detailed nodal results of these simulations. Recently, surrogate models have been developed that can predict the full field (FF) of nodal responses. These FF surrogate models have the potential to make thorough and detailed DSE much more feasible and introduce further design benefits. However, these FF surrogate models have not yet been applied to real engineering activities or been demonstrated in DSE contexts, nor have they been directly compared with SV surrogate models in terms of accuracy and benefits.This thesis seeks to build confidence in FF surrogate models for engineering work by applying FF surrogate models to real DSE and engineering activities and exploring their comparative benefits with SV surrogate models. A user experiment which explores the effects of FF surrogate models in simple DSE activities helps to validate previous claims that FF surrogate models can enable interactive DSE. FF surrogate models are used to create Goodman diagrams for fatigue analysis, and found to be more accurate than SV surrogate models in predicting fatigue risk. Mode shapes are predicted and the accuracy of mode comparison predictions are found to require a larger amount of training samples when the data is highly nonlinear than do SV surrogate models. Finally, FF surrogate models enable spatially-defined objectives and constraints in optimization routines that efficiently search a design space and improve designs.The studies in this work present many unique FF-enabled design benefits for real engineering work. These include predicting a complete (rather than a summary) response, enabling interactive DSE of complex simulations, new three-dimensional visualizations of analysis results, and increased accuracy.

Additive manufacturing methods has been prevailing for several decades and the recent technological advancements brings in the flexibility and consideration for large-scale production in the industries. The components manufactured with these methods have wide variety of applications and therefore, it is crucial to investigate the mechanical performance of the printed parts. There have been many researches done to investigate the mechanical behaviour of polymer material but the studies are limited when it comes to the fatigue performance of the polymer parts printed using multi-jet fusion technology. The aim of the master thesis is to investigate the fatigue behaviour of polyamide12 (PA12) material with the components manufactured using HP’s multi-jet fusion 3D printing machine. Fatigue life is influenced by several factors such as the loading condition, the topology of the specimen, material properties, print quality and the environmental conditions. It is therefore essential to consider all these factors when developing the experiments for fatigue life prediction. The master thesis work can be divided into three sections. The first section focuses on evaluating the mechanical properties of polyamide12. This includes the quasi-static test for determining the tensile properties of specimens with the geometrical influence, the difference in properties in relation to the print directions, the influence of humidity and porosity over the mechanical performance of the material and finally the effect of internal heat generation and the surrounding temperature. The results show that the temperature and the quality of the specimens are the two major factors affecting the mechanical and fatigue performance of PA12. That being said, the next section focuses on setting up the fatigue experiments based on the data obtained from the static tests. When carrying out the experiment, both the test frequency and the surrounding temperature were foundto have a greater impact over the fatigue results. High test frequency showed a dramatic increase in the temperature of the specimen which caused an early failure. Hence, the experiments were developed in such a way that the influence of the thermal fatigue can be ignored by controlling the temperature of the specimen through a compressed air cooling system. The final section presents the findings, the conclusions about the material behaviour and the development of a finite element model to predict the fatigue life of a topology optimised demonstrator part using the data gathered from the experiments. / Additiva tillverkningsmetoder har använts i flera decennier och de senaste tekniska framstegen möjliggör flexibilitet och storskaliga produktionsprocesser. Komponenter tillverkade med dessa metoder har många olika tillämpningar inom industrin och därför är det avgörande att undersöka de tillverkade materialens mekaniska prestanda. Det har gjorts många undersökningar av det mekaniska beteendet hosmaterial som metaller och polymerer, men studierna är begränsade när det gäller utmattnings prestandan hos detaljer som tillverkats med multi-jet fusionsteknik.  Syftet med examensarbetet är att undersöka utmattnings beteendet hos polyamid-12 (PA12) tillverkat med hjälp av HP multi-jet fusion 3D-utskriftsteknik. Utmattnings livslängden påverkas av flera parametrar såsom belastnings tillståndet, provets topologi, materialegenskaper, utskrifts kvalitet och miljöförhållanden. Det är därför viktigt att ta hänsyn till alla dessa faktorer när man utvecklar experimenten för utmattnings karakterisering. Examensarbetet kan delas in i tre avsnitt. Det första avsnittet fokuserar på att utvärdera de mekaniska egenskaperna hos PA12. Detta inkluderar kvasi statisk provning för att bestämma drag egenskaperna hos prover med olika geometrier, skillnaden i egenskaper i förhållande till utskrifts riktningarna, inverkan av fukt och porositet på materialets mekaniska prestanda och slutligen effekten av yttre temperatur. Resultaten visar att temperaturen och kvaliteten på proverna är de faktorer som har störst inverkan på den mekaniska prestandan hos PA12. Med detta som utgångspunkt fokuserar nästa avsnitt på att sätta upp utmattnings experimenten baserat på data som erhållits från de statiska testerna. Under utformningen av experimenten visade sig test frekvensen och den omgivande temperaturen ha en stor inverkan på utmattnings resultaten. Hög test frekvens bidrog till en dramatisk ökning av temperaturen hos provet vilket resulterade i tidigt brott. Experimenten utformades därför på ett sätt så att termisk inverkan kan undvikas, genom att kontrollera provets yttre temperatur med ett trycklufts kylsystem. Det sista avsnittet presenterar resultaten, slutsatser om materialets beteende och utvecklingen av en finita element modell för att förutsäga utmattnings livslängden för en topologioptimerad demonstratören med hjälp av data som samlats in från experimenten.

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