Residual stress effects and damage tolerance behaviour of integral lightweight structures manufactured by FSW and HSM

Estágio realizado na empresa Airbus Operations GmbH, orientado pelo Mr. Marco PacchioneTese de Programa Doutoral. Engenharia Mecânica. Universidade do Porto. Faculdade de Engenharia. 201

The contour method for residual stress determination applied to an AA6082-T6 friction stir butt weld

Residual stresses parallel to the welding direction on a cross-section of a 3 mm thick friction stir butt-welded aluminium alloy AA6082-T6 plate were determined using the contour method. This is a destructive relaxation based measurement technique capable of determining the full- eld residual stresses perpendicular to a plane of interest. A wire electro discharge machining cut was performed revealing the plane of interest. The residual stresses present before the straight cut lead to a deformed cutting plane. Then, a coordinate measuring machine was used to acquire the cutting plane shape of both plate halves after the cut. A data reduction scheme for noise and error elimination was used. The measured deformation was applied to a linear elastic nite elements model considering the real specimen geometry. A full contour map of longitudinal residual stresses on a weld cross section was determined in this way, revealing detailed information on the residual stress distribution in the inside of a friction stir weld, especially in the nugget zone. A typical M-shape, usually described for the residual stress distribution in friction stir welds, was found. The maximum residual stresses are below the yield strength of the material in the shoulder region and, outside of the welding region, low tensile and compressive residual stresses are responsible for the necessary stress equilibrium on the plane of interest. A comparison was made with the established incremental hole drilling technique on an equivalent plate for validation and good agreement of both techniques was obtained. The distribution, as well as the magnitude of the residual stresses measured by both techniques, is very similar, thus validating both the experimental and numerical procedures used for the contour method application, which is presented and discussed in the paper.The present work was partially funded by the project PTDC/EME-TME/66362/2006 and PhD scholarship SFRH / BD / 41061 / 2007 of the Portuguese Fundação para a Ciência e Tecnologia. Dr. P. Moreira acknowledges POPH - QREN-Tipologia 4.2 - Promotion of scientific employment funded by the ESF and MCTES. The help of José Fernando Rocha Almeida is also acknowledged

Examining Stress Relaxation in a Dissimilar Metal Weld Subjected to Postweld Heat Treatment

Dissimilar metal welds are often required in nuclear power plants to join components made from austenitic steels to those from ferritic steels, particularly in fast breeder reactor plants, in order to join the intermediate heat exchanger to the steam generator. The process of welding alters the microstructure of the base materials and causes residual stresses to form, both because of the change in the microstructure and the differing thermal histories in various regions. Postweld heat treatment (PWHT) is required to relieve the residual stresses and achieve preferable microstructural gradients across the weld joint. Therefore, in order to arrive at the optimal PWHT process, it is necessary to investigate the effects of heat treatment on the joint integrity, microstructure, and residual stress relaxation in the welds. To investigate the effect of PWHT on the residual stress relaxation and corresponding alteration of microstructure across a welded joint, a dissimilar weld between modified 9Cr-1Mo steel and austenitic stainless steel AISI 316LN was made using autogenous electron beam welding. To achieve this, the welding process was first modeled numerically using finite element analysis, and the residual stress predictions were validated by experimental investigation using neutron diffraction. The validated model was then used to study the residual stress relaxation through the simulation of PWHT. The predicted stress relaxation was compared with contour method measurement of residual stresses in the actual welded plate subjected to PWHT. The results indicate that, although some relaxation of residual stresses occurred during PWHT, there is still a significant portion of highly localized residual stresses left in the specimen

Analysis of the crack growth behavior in a double cantilever beam adhesive fracture test using digital image processing techniques

Digital image processing (DIP) techniques offer interesting possibilities in various fields of science.Automated analyses may significantly reduce the necessary manpower for certain cumbersometasks. The analysis of large series of images may be done in less time, since automatedimage processing techniques are able to work efficiently and with constant quality 24h per day.In this work, a series of images obtained by a high-speed camera is analyzed in order to determinethe crack growth behavior during a double cantilever beam (DCB) test [1]. The presentwork represents a contribution to the effort of automatizing the crack growth measurement,comparing various different techniques which may later be optimized for a specific task.Detecting cracks automatically from test images obtained by a digital camera is a difficult task,since the quality of crack images depends on the test conditions. The roughness of the specimensurface, luminance condition, and the camera itself may influence the detection quality.The specimens tested in this work where painted with white colour since this was found to leadto the best contrast for crack detection. High accuracy may only be expected if a sufficientlyhigh resolution is acquired by the camera and if the available lens setup is optimized for thespecific task.The DCB test is performed in order to obtain the experimental compliance-crack length curveof a polymeric adhesive. Accurate and reliable crack length measurement is indispensable forthe generation of the previously mentioned compliance-crack length curves. It should be notedthat due to the lenses used, unlike shown by Ryu [2], the distance to the specimen is higher than800 mm. This distance has to be reduced by the use of a different lens setup in order to get abetter accuracy of the results. Nevertheless a comparison between different DIP methods is possible.Four different algorithms were developed using The MathWorks MatLab, Massachusetts[3] in order to automatically measure the crack length and a comparison of the obtained resultsis made.Algorithm A is based on thresholding [4] each image of the sequence in order to detect thewhite painted region around the crack. In algorithm B, the image sequence is processed by afilter which reinforces horizontal lines such as the crack, and then isolated pixels are removedfrom the images using morphological cleaning [4]. In algorithm C, the first of two consecutiveimages is subtracted from the second one in order to detect the crack as a difference betweenboth images. Algorithm D is based on the optical flow concept developed by Horn [5]. Thebasic idea is to determine the velocity of each pixel in the image when this changes its positionfrom one image to the next in the analyzed sequence, and relate this information to the growing crack

Characterisation of short-length scale residual stress variations within an electron beam welded P91 Ferritic–Martensitic steel plate

In this research, an electron beam (EB) butt-welded P91 steel plate (~9 mm thick) is selected to measure longitudinal residual stresses (acting in the welding direction) using a promising residual stress measurement technique - the contour method. The EB weld causes short length scale residual stresses within the narrow width of the fusion zone with steep stress gradients lateral to the weld line, which presents a new challenge for the residual stress measurements. The special measures were taken for all main steps of the technique to improve its the spatial resolution, thereby the short length scale residual stresses were captured. The success of the measurement is assessed by comparing the contour method result to the neutron diffraction result, and a good agreement were found in the results of both the techniques. These results also shows that the contour measurement results successfully captured the steep stress gradient on both sides of the weld centre-line (0 mm) with tensile stress peaks situated just 2.8 mm apart. It is one of the best resolutions in residual stress length-scale in this component achieved in contour measurements

Demographic, clinical and antibody characteristics of patients with digital ulcers in systemic sclerosis: data from the DUO Registry

OBJECTIVES: The Digital Ulcers Outcome (DUO) Registry was designed to describe the clinical and antibody characteristics, disease course and outcomes of patients with digital ulcers associated with systemic sclerosis (SSc). METHODS: The DUO Registry is a European, prospective, multicentre, observational, registry of SSc patients with ongoing digital ulcer disease, irrespective of treatment regimen. Data collected included demographics, SSc duration, SSc subset, internal organ manifestations, autoantibodies, previous and ongoing interventions and complications related to digital ulcers. RESULTS: Up to 19 November 2010 a total of 2439 patients had enrolled into the registry. Most were classified as either limited cutaneous SSc (lcSSc; 52.2%) or diffuse cutaneous SSc (dcSSc; 36.9%). Digital ulcers developed earlier in patients with dcSSc compared with lcSSc. Almost all patients (95.7%) tested positive for antinuclear antibodies, 45.2% for anti-scleroderma-70 and 43.6% for anticentromere antibodies (ACA). The first digital ulcer in the anti-scleroderma-70-positive patient cohort occurred approximately 5 years earlier than the ACA-positive patient group. CONCLUSIONS: This study provides data from a large cohort of SSc patients with a history of digital ulcers. The early occurrence and high frequency of digital ulcer complications are especially seen in patients with dcSSc and/or anti-scleroderma-70 antibodies

Characterization of different aluminium alloys of the series 6000 and of their joining processes

Tese de mestrado integrado. Engenharia Mecânica. Faculdade de Engenharia. Universidade do Porto. 200

Standortpotenzial der Steiermark für die Gründung einer Kapitalanlagegesellschaft

Im Rahmen dieser Masterarbeit wird untersucht, wie geeignet die Steiermark als Standort für die Gründung einer Kapitalanlagegesellschaft ist. Hierzu werden die Anforderungen von Kapitalanlagegesellschaften ermittelt und mit den Standortfaktoren in der Steiermark verglichen. Das Arbeitskräftepotenzial, die Marktnähe und die Belastung durch Steuern und Abgaben wurden als die drei wichtigsten Standortfaktoren für Kapitalanlagegesellschaften identifiziert. Grundsätzlich kann die Steiermark als durchaus geeigneter Standort gesehen werden. Die Grundvoraussetzungen sind gegeben und die Steiermark besitzt Stärken bei wichtigen Standortfaktoren. Die Schwächen in einigen entscheidenden Bereichen schränken die Attraktivität der Steiermark im Vergleich zu anderen Regionen allerdings deutlich ein. Im Zusammenhang mit der Analyse des Standortpotenzials beschäftigt sich diese Arbeit auch mit den Auswirkungen der Standortwahl auf das Marketing. Regionalität als mögliches Verkaufsargument wird kritisch untersucht und mit anderen relevanten Einflussgrößen wie Vertrauen in Verbindung gesetzt. Ein leichter ?Country-of-Origin? Effekt ist auch im Kontext von Kapitalanlagegesellschaften zu beobachten. Dennoch stellt der Standort ein eher unwichtiges Entscheidungskriterium für Kunden dar. Zum Einsatz als Verkaufsargument scheint Regionalität dennoch geeignet, da der Standort eine positive Auswirkung auf das Kundenvertrauen haben kann.This master thesis analyzes the potential of Styria as a business location for a new investment company. As part of the analysis, the needs of investment companies are identified and compared to the site-related factors in Styria. The supply of skilled labor, the marketability and the tax burden are identified as the three most important site-relevant factors for investment companies. In general, Styria can be viewed as suitable business location. The basic prerequisites are met and Styria has strengths concerning important site-related factors. The weaknesses in some critical areas are clearly limiting the attractiveness of Styria, when compared to other regions. In the context of the analysis of the site-related factors, this thesis also studies the effects of the site selection on marketing. Regionalism as a potential selling point is critically analyzed and linked to other relevant factors of influence, such as trust. A weak ?Country-of-Origin? effect can also be observed in the context of investment companies. The business location, however, still remains of rather low importance in the decision making process of customers. That notwithstanding, the use of regionalism as a selling point seems applicable, since the business location can have a positive impact on the trust customers put in an investment company.Paul Richter-TrummerAbweichender Titel laut Übersetzung der Verfasserin/des VerfassersZsfassungen in dt. und engl. SpracheGraz, Univ., Masterarb., 2014(VLID)25207