Despite a large demand from industry, a realistic chatter modeling for hard turning has not been available due to the complexity of the problem, which is mainly caused by flank wear and nonlinearity in hard turning. This thesis attempts to develop chatter models for predicting chatter stability conditions in hard turning with the considerations of the effects of flank wear and nonlinearity. First, a linear model is developed by introducing non-uniform load distribution on a tool tip to account for the flank wear effect. Second, a nonlinear model is developed by further incorporating nonlinearity in the structure and cutting force. Third, stability analysis based on the root locus method and the describing function approach is conducted to determine a critical stability parameter. Fourth, to validate the models, a series of experiment is carried out to determine the stability limits as well as certain characteristic parameters for facing and straight turning. From these, it is shown that the nonlinear model provides more accurate predictions than the linear model, especially in the high-speed range. Furthermore, the stabilizing effect due to flank wear is confirmed through a series of experiments. Fifth, to fully account for the validity of linear and nonlinear models, an empirical model is proposed to fit in with the experimental stability limits in the full range of cutting speed. The proposed linear and nonlinear chatter models will help to improve the productivity in many manufacturing processes. In addition, chatter experimental data will be useful to develop other chatter models in hard turning.

Hard turning is a machining process where a single point cutting tool removes material harder than 45 HRC from a rotating workpiece. Due to the advent of polycrystalline cubic boron nitride (PCBN) cutting tools and improved machine tool designs, hard turning is an attractive alternative to grinding for steel parts within the range of 58-68 HRC, such as bearings. There is reluctance in industry to adopt hard turning because of a defect called white layer. White layer is a hard, 1-5 쭠deep layer on the surface of the specimen that resists etching and therefore appears white on a micrograph. When aggressive cutting parameters are used, even using a new tool, white layer is expected. If more conservative parameters are selected, one does not expect white layer. There is some debate if white layer actually decreases the strength or fatigue life of a part, but nevertheless it is not well understood and therefore is avoided. This research examines the use of two different non-destructive evaluation (NDE) sensors to detect white layer in hard turned components. The first, called a Barkhausen sensor, is an NDE instrument that works by applying a magnetic field to a ferromagnetic metal and observing the induced electrical field. The amplitude of the signal produced by the induced electrical field is affected by the hardness of the material and surface residual stresses. This work also examines the electrochemical properties of white layer defects using electrochemical impedance spectroscopy. This idea is verified by measuring the electrochemical potential of surfaces with white layer and comparing to surfaces without any. Further corrosion tests using the electrochemical impedance spectroscopy method indicate that parts with white layer have a higher corrosion rate. The goal of this study is to determine if it is possible to infer white layer thickness reliably using either the Barkhausen sensor or electrochemical impedance spectroscopy (EIS). Measurements from both sensors are compared with direct observation of the microstructure in order to determine if either sensor can reliably detect the presence of white layer.

Residual stresses play an important role in the performance of machined components. Component characteristics that are influenced by residual stress include fatigue life, corrosion resistance, and part distortion. The functional behavior of machined components can be enhanced or impaired by residual stresses. Because of this, understanding the residual stress imparted by machining is an important aspect of understanding machining and overall part quality. Machining-induced residual stress prediction has been a topic of research since the 1950s. Research efforts have been primarily composed of experimental findings, analytical modeling, finite element modeling, and various combinations of those efforts. Although there has been significant research in the area, there are still opportunities for advancing predictive residual stress methods. The objectives of the current research are as follows: (1) develop a method of predicting residual stress based on an analytical description of the machining process and (2) validate the model with experimental data. The research focuses on predicting residual stresses in machining based on first principles. Machining process output parameters such as cutting forces and cutting temperatures are predicted as part of the overall modeling effort. These output parameters serve as the basis for determining the loads which generate residual stresses due to machining. The modeling techniques are applied to a range of machining operations including orthogonal cutting, broaching, milling, and turning. The strengths and weaknesses of the model are discussed as well as opportunities for future work.

Tekinimas yra vienas iš svarbiausių metalo apdirbimo būdų detalių gamyboje. Tekinimo įrankis turi ypač didelę reikšmę šiame procese, jis pjaunamąsias savybes praranda dėl pjaunančiųjų briaunų ištrupėjimo, pjaunančiojo pleišto plastinės deformacijos ir ypač dėl peilio darbinio paviršių dilimo. Norint parinkti optimalius pjovimo rėžimus ir įrankius, reikia nustatyti pagrindinius veiksnius, turinčius įtakos tam procesui. Tad gamybinėje įmonėje atlikti aliumininių detalių apdirbimo, smulkiagrūdžio karbido tekinimo plokštelėmis stebėjimai, norint išsiaiškinti pagrindinius veiksnius turinčius įtakos plokštelių nusidėvėjimui. Buvo pasirinktos trys plokštelės, kurios dirbo skirtingais režimais. Užfiksuoti plokštelių išdirbiai, bei nudilimo tipai pagal plokštelių viršūnių pakitimus. Iš gautų duomenų nustatyta, kad daugiausia įtakos plokštelių nusidėvėjimui turi abrazyvinis, difuzinis ir adhezinis dilimai. / Turning is the most popular in metal working and cutting tool has big dispose in this work. The durability of the cutting tool depends of the tool accuracy, quality, of the setting parameters, of the cutting regime and the formation of motion. The cutting tool loses its quality for the following reasons: cracking of the cutting edges; plastic deformation of the cutting tool and most important cutting tool working edge attrition. In the production facility was during the observation after aluminum parts production, where they were processed fine grain carbide turning plates. For research the main factors for affecting the plates wear. Three plates were chosen, which worked in different operating modes. Was recorded plates output and types of wear, by geometry changing of plates head. From the data obtained revealed that the main influencing the wear plate wear is abrasive, diffuse, and adhesive wear.

Gas turbine blade/vane cooling is obtained by circulating the high pressure air from compressor to the internal cooling passage of the blade/vane. Heat transfer and cooling effect in the rotating blade is highly affected by rotation. The typical rotation number for the aircraft engine is in the range of 0~0.25 and for the land based power generation turbine in the range of 0~05. Currently, the heat transfer data at high rotation numbers are limited. Besides, the investigation of heat transfer phenomena in the turn region, especially near hub portion is rare. This dissertation is to study the heat transfer in rectangular channels with turns in the tip or the hub portion respectively at high rotation numbers close to the engine condition. The dissertation experimentally investigates the heat transfer phenomena in a two-pass rectangular channel (AR=W/H=2:1) with a 180 degree sharp turn in the tip portion. The flow in the first passage is radial outward and after the turn in the second passage, the flow direction is radial inward. The hydraulic diameter (Dh) of the channel is 16.9 mm. Parallel square ribs with an attack angle (alpha) of 45 degrees are used on leading and trailing surfaces to enhance the heat transfer. The rib height-to-hydraulic diameter ratio (e/Dh) is 0.094. For the baseline smooth case and the case with rib pitch-to-height ratio (P/e) 10, channel orientation angles (beta) of 90 degrees and 135 degrees were tried to model the cooling passage in the mid and rear portion of the blade respectively. Two other P/e ratios of 5 and 7.5 were studied at beta=135 degrees to investigate their effect on heat transfer. The data are presented under high rotation numbers and buoyancy parameters by varying the Reynolds number (Re=10,000~40,000) and rotation speed (rpm=0~400). Corresponding rotation number and buoyancy parameter are ranged as 0~0.45 and 0~0.8 respectively. The dissertation also studies the heat transfer in a two-pass channel (AR=2:1) connected by a 180 degree U bend in the hub portion. The flow in the first passage is radial inward and after the U bend, the flow in the second passage is radial outward. The cross-section dimension of this channel is the same as the previous one. To increase heat transfer, staggered square ribs (e/Dh=0.094) are pasted on leading and trailing walls with an attack angle (alpha) of 45 degrees and pitch-to-height ratio (P/e) of 8. A turning vane in the shape of half circle (R=18.5 mm, t=1.6 mm) is used in the turn region to guide the flow for both smooth and ribbed cases. Channel orientation angles (beta) of 90 degrees and 135 degrees were taken for both smooth and ribbed cases. The heat transfer data were taken at high rotation numbers close to previous test section.

Uppsatsen undersöker behovet av och tillgången till studie- och yrkesvägledning i vändpunkter och utgår från karriärvalsteorin Careerships definition av dessa. Alla individer ställs inför flera vändpunkter under sitt liv och vissa är mer tydliga än andra. Tidigare forskning visar att individer med fler valmöjligheter inom sin vändpunkt upplever ett större behov av studie- och yrkesvägledning än individer med få valmöjligheter. Ofta upplever exempelvis arbetssökande ett litet handlingsutrymme och lågt förtroende för myndighetsutövare. Undersökningens resultat visar att behovet men också tillfredsställelsen av studie- och yrkesvägledning är störst inom grundskolan och lägst för gruppen arbetssökande. I uppsatsen diskuteras om intresset för studie- och yrkesvägledning skulle öka i vuxengrupper om fler gavs möjlighet att ingå i en kontinuerlig studie- och yrkesvägledningsprocess. / This essay examines the need for career counselling when reaching a turning point based on the career selection theory, Careership. All individuals are recurrently faced with turning points during their career, some clearer than others. Previous research indicates that individuals with more options in their turning point feel a greater need for career counselling than individuals with fewer choices. For example jobseekers often experience that they have little room for manoeuvres and a low confidence in authorities. The result from this study shows that the need for and also the satisfaction with career counselling are biggest in elementary school and the lowest for jobseekers. In the essay we discuss whether the interest in seeking for career counselling would increase if grown ups were given the opportunity to be a part of a continuous career counsellingprocess.

Denna studie vill ge större inblick och förståelse för individen bakom den kriminella stämpeln, samt bringa insyn i dessa individers egna tankar om sina kriminella handlingar och kampen ut ur kriminaliteten. Avsaknaden av tron på att personliga livshändelser sker utifrån egna handlanden, där personen istället agerar passivt offer i sitt liv är något som återfinns hos interner. Motsatsen till detta är personer som tror på sitt eget handlande, det vill säga internal locus of control. Denna uppsats belyser kriminellas bakgrundshistoria till uppbrottet ur den kriminella livsstilen med fokus på locus of control, vändpunkter och framtidsperspektiv. Tio personer deltog, varav åtta män och två kvinnor i enskilda semistrukturerade intervjuer. Resultatet visade att majoriteten förklarade sin kriminalitet med yttre faktorer. De nådde vändpunkten när rädslan för att förlora sitt liv eller sina närstående blev för stor. Nio av tio ser nu långsiktigt på sin framtid till skillnad från förr.

隨著科技的進步與資訊科學的發展，大量的資訊處理自動化逐漸取代傳統人工技術，然而不恰當地使用自動化技術，卻可能危害人類的權益與空間。為避免過度濫用機器自動化對人類所造成的災害，本研究根據不同的適用情境，分別提出以靜態及動態圖型為基礎的人機區分方法，透過簡單的影像處理技術，產生機器難以分析但人類能夠易於判別的人機辨識影像。並且由認知的角度，設計實驗進一步探討人類視覺優勢以及接受度，作為影像產生時的標準。最後，提出人機區分技術與應用情境整合實作的方法，以觀實效。 / The idea of using a computer program to distinguish humans from machines, sometimes referred to as the “Reverse Turing Test”, has emerged only quite recently. The term CAPTCHA, which stands for “Completely Automated Public Turing Test to Tell Computers and Humans Apart", is defined as: “a program that can generate and grade tests that: □ Most human can pass but □ Current computer program can’t pass! “ In this thesis, a texture-image based approach is developed to encode text information in such a way that machine vision algorithms will experience significant difficulties while human can extract the embedded text effortlessly. Both static images and dynamic sequences will be explored. It is anticipated that the cost of storing, and subsequently decoding information from such visual patterns will be prohibitedly high, both in terms of time and space complexity. To validate the postulation, fundamental principles of the human cognitive process will be examined. Experiments will also be carried out to gather user feedback and investigate the limitations of human visual systems. Finally, several application scenarios that call for the integration of a CAPTCHA will be identified and discussed.

This thesis presents a method for the prediction of final peak-to-valley (PTV) surface profile variation for face turning of rings of non-uniform cross section. An analytical method relates initial part form, part deflection during workholding and machining, and part elastic recovery to final PTV surface profile variation. Finite element method is used to supplement the analytical model, and experiments are conducted to validate both the analytical and finite element approaches. Analytical and finite element results correspond well with experimental observations, with average relative errors of 11.6 and 7.2 percent, respectively.

Excessive vibrations continue to be a major hurdle in improving machining efficiency and achieving stable high speed cutting. To overcome detrimental vibrations, an enhanced understanding of the underlying nonlinear dynamics is required. Cutting instability is commonly studied through modeling and analysis which incorporates linearization that obscures the true nonlinear characteristics of the system which are prominent at high speeds. Thus to enhance cutting dynamics knowledge, a comprehensive nonlinear turning model that includes tool-workpiece interaction is experimentally validated using a commercial laser vibrometer to capture tool and workpiece vibrations. A procedure is developed to use instantaneous frequency for experimental time-frequency analysis and is shown to thoroughly characterize the underlying dynamics and identify chatter. For the tests performed, chatter is associated with changing spectral components and bifurcations which provides a view of the underlying dynamics not experimentally observed before. Validation of the turning model revealed that the underlying dynamics observed experimentally are accurately captured, and the coupled tool-workpiece chatter vibrations are simulated. The stability diagram shows an increase in the chatter-free limit as the spindle speed increases until 1500rpm where it begins to level out. At high speeds the workpiece dominates the dynamics, and excessive workpiece vibrations create another stability limit to consider. Thus, workpiece dynamics should not be neglected in analyses for the design of machine tools and robust control laws. The chip formation mechanisms and high speeds make micro-milling highly non-linear and capable of producing broadband frequencies that negatively affect the tool. A nonlinear dynamic micro-milling model is developed to study the effect of parameters on tool performance through spectral analysis using instantaneous frequency. A lumped mass-spring-damper system is assumed for modeling the tool, and a slip-line force mechanism is adopted. The effective rake angle, helical angle, and instantaneous chip thickness are accounted for. The model produced the high frequency force components seen experimentally in literature. It is found that increasing the helical angle decreased the forces, and an increase in system stiffness improved the dynamic response. Also, dynamic instability had the largest effect on tool performance with the spindle speed being the most critical parameter.