The aim of this project was to, based on a given idea, develop and evaluate a method for measuring residual stress in thin PVD coatings. AlCrN was deposited, by PVD, on thin circular samples of stainless steel foil and the radius of the emerged curvature was measured using an optical profilometer. From the radius data the residual stress in the coating of each sample was calculated. The foil samples examined were of two different thicknesses, 0.3 mm and 0.5 mm. With the parameters of the project the foils of 0.3 mm were found most suitable. Furthermore, the method was compared to an already established method where depositions are made on thicker substrates, which are then ground to an appropriate thickness. A correlation factor between the two methods was calculated and found to be 0.91 ± 0.28. Finally, the possibility of adapting the method in running production was investigated. Cost and time analyses were conducted and both supported the applicability of the method. / Projektets syfte var att utveckla och utvärdera en metod för att mäta restspänningar i tunna PVD-beläggningar utifrån en redan befintlig idé. Tunna cirkulära prover av rostfritt stål belades med AlCrN genom PVD och radien på den utböjning som uppstod mättes med en optisk profilometer. Restspänningen bestämdes sedan utifrån den uppmätta radien. Folier av två olika tjocklekar, 0,3 mm och 0,5 mm, utvärderades. Med de processparametrar som användes i projektet visades att folien med tjocklek 0,3 mm var den bäst lämpade. Metoden jämfördes även med en etablerad metod där tjocka substrat beläggs och sedan slipas ned till lämplig tjocklek. En korrelationsfaktor som relaterar de två metoderna bestämdes till 0,91 ± 0,28. Slutligen undersöktes möjligheterna att använda metoden i löpande produktion. Kostnads- och tidsanalyser utfördes och resultaten stödjer metodens användbarhet.

Friction Stir Welding (FSW) is a new solid-state welding process that shows great promise for use in the aerospace and transportation industries. One of the primary benefits of this process is that mechanical properties of the base material are not as severely degraded as they are with conventional fusion welding. However, fatigue crack initiation and growth properties of the resulting weld nugget are not fully understood at this time. The primary goal of this project is to characterize the fatigue crack growth properties of friction stir welds in 6061-T6 aluminum as relates to the microstructural evolution of the weld. This was accomplished by producing friction stir welds and testing fatigue crack growth response in different crack orientations with respect to the weld. In addition, residual stress measurements were conducted for all cases, using both the crack compliance and contour methods. The results from the methods were compared in order to evaluate the accuracy of each method. Being an immature technology, the potential for discovery of new applications for the FSW process exist. With this in mind, novel applications of the FSW process, including the addition of particles during welding were explored. The first step was the investigation of property changes that occur when secondary cast phases are refined using the FSW process. The FSW process successfully refined all secondary phases in A380 and A356, producing an increase in hardness. Next, methods for the creation of particle metal matrix composites using FSW will be investigated. Nano-scale alumina particles were successfully added to the matrix and homogenously distributed. Using multiple weld passes through the composite was found to increase the uniformity of particle distribution. However, the alumina particle composite failed to provide any statistically significant hardness increase over the base material. The FSW process was also evaluated for weldability of traditionally difficult alloy systems. FSW was found to show very good weldability for dissimilar cast and wrought alloys, as well as for high-pressure die castings. Lastly, the feasibility of friction stir welding/processing in repairing crack defects in complex structural members in combination with cold-spray technology was determined. Friction Stir processing was used on a cold spray 6061-T6 block, resulting in significant increases in hardness over the base material, as well as a reduction in porosity. In addition, FSP was shown to eliminate crack-type defects in cold spray materials, a finding that has important applications in part repair. The deliverables of this work include an understanding of the fatigue crack growth response of FSW/FSP 6061-T6, as well as a feasibility study exploring novel uses for the FSW/FSP process. In addition, the deliverables include CNC code, fixtures, procedures, and analytical code for the creation and analysis of FSW/FSP joints. This will be important for the continuation of FSW/FSP work at WPI.

No description available.

La méthode du contour est une technique récente pour la mesure de contraintes résiduelles dans des structures mécaniques. Elle permet d'obtenir un champ de contraintes résiduelles en 2D. Dans la méthode du contour, l'échantillon est découpé en deux parties. Les contraintes résiduelles normales aux faces découpées se détendent, ce qui cause leur déformation. Le profil de déformation des faces coupées est mesuré, puis utilisé pour le calcul de contraintes résiduelles. La méthode du contour est basée sur le principe de superposition élastique. Sa théorie assume que la détente de contraintes résiduelles est entièrement élastique. Cependant, en pratique, la détente élastique de contraintes résiduelles peut être accompagnée d'une détente plastique, ce qui induit des erreurs dans les contraintes mesurées. Ce projet se concentre sur l'étude et le contrôle des erreurs de plasticité dans la méthode du contour. Les résultats de cette recherche fournissent d'importantes informations sur la façon dont les déformations plastiques affectent les résultats de la méthode du contour. Par ailleurs une nouvelle technique de coupe pour l'atténuation des erreurs de plasticité a été développée. Des outils de calcul et des instructions sont proposés pour l'estimation des erreurs de plasticité. Enfin des instructions pour la minimisation des erreurs de plasticité sont proposées et appliquées à la mesure de contraintes résiduelles dans un échantillon. / The contour method has emerged as a promising technique for residual stress measurement in relatively large, thick and complex engineering components. The method involves making a cut in the sample of interest, measuring the subsequent relaxed deformation of the cut face and using this profile to back-calculate the original residual stress field by FE modelling. The method is based on the theory of elasticity in that the stress relaxation during test specimen cutting is assumed to be entirely elastic. However, when measuring residual stresses close to the material yield stress, plasticity can occur and affect the measurements.The main aim of this thesis was to develop methods of mitigating and estimating plasticity-induced errors in the contour method. The outcomes of this research provide a valuable insight into how accumulation of plasticity affects the performance of the contour method. A novel cutting strategy that aims at mitigating the plasticity-induced errors has been developed. Furthermore, procedures are developed to estimate the plasticity-induced errors. Finally guidelines are proposed and applied to a case study for mitigating the plasticity-induced errors in the contour method.

I detta examensarbete har undersökningar kring finfrästa ytor i härdat verktygsstål utförts i samarbete med verktygsstålsproducenten Uddeholms AB i Hagfors. Vid spånskärande bearbetning påverkas materialet ibland negativt. En försöksserie om totalt 90 finfrästa ytor i härdade varmarbetsstålen Uddeholm Orvar Supreme och Uddeholm Dievar har frästs, mätts och utvärderats för att ta reda på hur fräsprocessen inverkar på materialets egenskaper. Det visar sig att materialet påverkas olika mycket beroende på hur fräsningen utförs och med vilken typ av fräsverktyg som används. I detta arbete har endast ändradiefräsar av solid hårdmetall använts. Analysen av ytorna har gjorts med en rad mätmetoder så som optisk ytjämnhetsmätning, hårdhetsmätning med Vickersmetoden, restspänningsmätning med röntgendiffraktion och okulär inspektion av stålets mikrostruktur i ljusmikroskop. Mätningarna utfördes för att se hur materialet påverkas mekaniskt av bearbetningen.   I de mest ogynnsamma försöksfallen är den mekaniska påverkan från fräsbearbetningen av stålets ytor så stor att bearbetningen riskerar försämra tillverkade komponenters livslängd sett ur utmattningssynpunkt. Målet med arbetet är att identifiera det mest gynnsamma sätt fräsningen kan utföras på för att kunna minimera påverkan på materialets egenskaper. Detta ger möjligheten för Uddeholms AB att ge faktabaserade råd till sina kunder om vilket körsätt som ger minsta påverkan av verktygsstålet vid bearbetning. Kunderna kan nyttja då materialet till dess fulla kapacitet. / In this thesis, investigations on hardened finish milled surfaces was done in collaboration with the tool steel manufacturer Uddeholms AB in Hagfors, Sweden. The steel material is affected by machining operations, sometimes in a negative destructive manner. An experimental test series containing a total of 90 surfaces in hot work steels Uddeholm Orvar Supreme and Uddeholm Dievar were milled, measured and evaluated to clarify the milling operations effect on the steels mechanical properties. It was found that the material is affected differently according to how the milling was preformed and with which type of milling tool. In this thesis, only solid carbide end-radius milling tools were used. The surface analysis were conducted with a range of measuring techniques including optical surface roughness measurements, hardness measurements in Vickers scale, residual stress measurements with X-ray diffraction (XRD) and microstructural analysis with optical light microscope. These measurements were conducted in order to determine the milling operations mechanical affects and grade of alteration of the tool steels surfaces. In the least favorable cases, the effect from machining are so profound, that degradation of produced components can be expected in terms of fatigue wear resistance. The goal of the thesis is to identify the most favorable process parameters, in order to minimize degradation of the tooling material in customer user cases, together with the opportunity to give fact based advice to Uddeholms AB customers on the most favorable process parameters in finish milling with radius-mills of hardened hot work tool steels. In this way the customer can utilize the tooling material at its full potential.