13 Zentrale Universitätseinrichtungen
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/14
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Item Open Access Investigation of oxide layer development of X6CrNiNb18-10 stainless steel exposed to high-temperature water(2024) Veile, Georg; Hirpara, Radhika; Lackmann, Simon; Weihe, StefanThe oxide layer development of X6CrNiNb18-10 (AISI 347) during exposure to high-temperature water has been investigated. Stainless steels are known to form a dual oxide layer in corrosive environments. The secondary Fe-rich oxide layer has no significant protective effect. In contrast, the primary Cr-rich oxide layer is known to reach a stabilized state, protecting the base metal from further oxidation. This study’s purpose was to determine the development of oxide layer dimensions over exposure time using SEM, TEM and EDX line scans. While a parabolic development of Cr in the protective primary layer and Fe in the secondary layer was observed, the dimensions of the Ni layer remained constant. Ni required the presence of a pronounced Fe-rich secondary layer before being able to reside on the outer secondary layer. With increasing immersion time, the Ni element fraction surpassed the Cr element fraction in the secondary layer. Oxide growth on the secondary layer could be observed. After 480 h, nearly the entire surface was covered by the outer oxide layer. In the metal matrix, no depletion of Cr or Ni could be observed over time; however, an increased presence of Cr and Ni in the primary layer was found at the expense of Fe content. The Nb-stabilized stainless steel was subject to the formation of Niobium pentoxide (Nb2O5), with the quantity and magnitude of element fraction increasing over exposure time.Item Open Access Expanded measurement uncertainty concept for the calibration of Charpy pendulum impact machines(2025) Gerber, SiegfriedWith this approach, it is for the first time possible to map all for the direct calibration relevant influences on the impact energy that are to be tested according the standard and to determine complete the respective deviation and measurement uncertainty component. Therefore it is necessary to transfer the tested parameters in influences on the indicated absorbed energy. Based on the numerical example of a presented specific calibration, it has been shown that many influences that have not yet been considered must also be considered, whereas some components can be neglected.Item Open Access Experimental study on mechanical properties of European oak and Norway spruce clear wood(2025) Gambarelli, Serena; Bošnjak, Josipa; Fararoni Platas, Rey Noé; Jin, KexinThe trends in the building industry related to sustainability and environmental footprint make timber structures more appealing than ever. Many challenges in understanding the behaviour of structural timber can be addressed by combining experimental and numerical methods. However, sophisticated numerical tools require a complete description of the behaviour at the material level. Even though there are vast databases on the properties of different species, there are only limited studies on the mechanical response with complete stress–strain curves for all relevant directions. In order to bridge this gap, the present study investigates the mechanical response of European oak (hardwood) and Norway spruce (softwood). Uniaxial tensile and compressive tests were performed on small clear wood specimens. The behaviour was investigated for the direction parallel (longitudinal) and perpendicular to the grain (radial and tangential). Both species exhibit brittle tensile behaviour in all material directions, in contrast to the ductile performance under compression. The tensile strength lies at 70 MPa and 80 MPa for spruce and oak, respectively, whereas both species exhibit a compressive strength of approximately 50 MPa in the longitudinal direction. Due to the narrow range of the investigated density, growth-ring angle and growth-ring width, only a limited effect of these parameters was observed on the tensile behaviour in the longitudinal direction.Item Open Access Innovative approach to conceptual design of enterprise risk management software(2024) Stanojević, Petar; Misita, Mirjana; Đurić, Goran; Kuzmanović, Bogdan; Milošević, Mladen; Balos, DanielThe paper shows the integration of the theoretical and practical aspects of designing an ERM software tool. The basic idea of the designed ERM is conceived in the form of an algorithm using the integration of ISO 3100, the COSO framework, the risk matrix designed according to the risk appetite of the observed company, quantitative and qualitative models for risk assessment, and the generation of consequences and mitigating measures for each identified risk. Methodologies for risk assessment in the presented ERM include the following: For business risks, questionnaires were generated for different business areas (from knowledge bases) and the assessment was conducted according to risk matrices. Workplace risk is assessed according to the Kinney method, while technical risks are assessed according to the API 580, 581 standard. Software is created to outbalance problems of all types of risk that may arise regardless of the complexity of the business and the risk itself. The algorithm, model and software were developed and successfully tested in two Serbian companies.Item Open Access Effect of weld length on strength, fatigue behaviour and microstructure of intersecting stitch-friction stir welded AA 6016-T4 sheets(2023) Walz, Dominik; Göbel, Robin; Werz, Martin; Weihe, StefanFriction stir welding is a promising joining process for boosting lightweight construction in the industrial and automotive sector by enabling the weldability of high-strength aluminum alloys. However, the high process forces usually result in large and heavy equipment for this joining method, which conflicts with flexible application. In order to circumvent this issue, a friction stir welding gun has been developed which is capable of producing short stitch welds-either stand-alone as an alternative to spot welds or merging into each other appearing like a conventional friction stir weld. In this study, the influence of the stitch seam length on the strength properties of intersecting friction stir welds is investigated, and the weld is characterized. For this purpose, EN AW-6016 T4 sheets were welded in butt joint configuration with varying stitch lengths between 2 and 15 mm. Both the static and dynamic strength properties were investigated, and hardness and temperature measurements were carried out. The results show a scalability of the tensile strength as well as the fatigue strength over the stitch seam length, while the substitute proof strength is not affected. Hereby, the tensile strength reached up 80% of the base materials tensile strength with the chosen parameter setup. Likewise, the stitch weld length influences the hardness characteristics of the welds in the transition area.Item Open Access Development and evaluation of a robot guided friction stir welding gun(2025) Walz, Dominik; Sommer, Korbinian; Werz, Martin; Weihe, StefanFriction stir welding (FSW) generally involves considerable process forces that require the use of heavy and cost-intensive machines like heavy-duty robots with massive clamping and anvil structures, which limits the flexibility of the application. To address this challenge, the Steppwelder FSW gun was developed at the MPA University of Stuttgart. This innovative welding gun enables the production of short stitch welds that can function as stand-alone alternatives to spot welds or merge seamlessly into continuous welds. The C-shaped frame design enables a closed flux of force within the gun, making it suitable for the attachment to industry standard robots used in automotive body construction processes such as clinching, riveting, or resistance spot welding (RSW). This paper presents the overall design of the welding gun, featuring a spindle and a C-frame optimized for FSW, and examines two design iterations with a focus on their stiffness characteristics. The first design, version 1.5, is an early prototype developed to demonstrate the feasibility of the process. The second version 2.0 incorporates enhancements aimed at increasing stiffness and projection while reducing the installation space to prepare it for broader application. Both frame designs are modeled as digital twins (DT) in the ABAQUS simulation software, incorporating a force-time profile of up to 14 kN based on physical models. The elastic deformation behavior and precise deflection values were then qualitatively and quantitatively analyzed at defined measuring points. These DTs were validated and calibrated by using digital image correlation on their physical counterparts under applied force. The optimized design of the welding gun offers a robust system capable of delivering consistent and reliable results for friction stir stitch welding, addressing the growing demand for flexible joining solutions in lightweight materials and mega-casting applications.Item Open Access Rationalisierung der Bewehrungstechnik - ein unerschöpfliches Forschungsthema oder eine Möglichkeit zur Kostensenkung und Qualitätssteigerung im Stahlbetonbau?(1982) Rehm, Gallus; Eligehausen, Rolf; Neubert, Bernd; Lehmann, RolfVon Flächentragwerken abgesehen, dominiert immer noch die "konventionelle" Bewehrung aus Einzelstäben und Einzelbügeln. Dies ist sowohl im Hinblick auf die Wirtschaftlichkeit als auch auf die Dauerhaftigkeit keineswegs optimal. Daher werden im folgenden am Beispiel stabförmiger Bauteile Maßnahmen zur Verbesserung aufgezeigt und die wirtschaftlichen Vorteile anhand einer praktischen Erprobung erläutert sowie die mögliche Verbesserung der Ausführungsqualität diskutiert.Item Open Access Enhancement of microstructure, tensile and fatigue performance of EN AW-1050 by wire-based friction stir additive manufacturing(2026) Donaubauer, Stefan; Schmid, Raphael; Weihe, Stefan; Werz, MartinAdditive manufacturing (AM) of aluminium by solid-state routes offers a promising pathway to overcome the limitations of fusion-based processes, such as porosity and hot cracking. This study investigates the potential of wire-based friction stir additive manufacturing (W-FSAM) as an innovative solid-state process. A test specimen made of EN AW-1050 was fabricated and characterised using mechanical testing as well as optical and electron microscopy. Microstructural characterisation revealed a fully consolidated, pore-free build with fine equiaxed grains and partial dynamic recrystallisation (DRX). The average grain size decreased from 13.4 µm near the substrate to 9.7 µm at the top, reflecting the variation in cumulative thermal exposure along the build height. A homogeneous hardness distribution (21.2 HV) and smooth interlayer interfaces were observed. Tensile tests in the travel direction yielded an ultimate tensile strength of approximately 85 MPa and an elongation exceeding 60%, while high-cycle fatigue tests demonstrated a fatigue strength of about 30 MPa at 2×106cycles ( R=0.1) with ductile fracture features. The results confirm that W-FSAM enables the production of fine-grained, defect-free CP-Al structures whose mechanical properties, in terms of strength and ductility, exceed those of the reference material. Thus, W-FSAM represents a promising solid-state additive manufacturing route for the production of high-performance CP-Al components.Item Open Access Fire rating of post-installed anchors and rebars(2020) Mahrenholtz, Philipp; Sharma, AkanshuFire safety is a critical performance aspect of construction products, and post-installed anchors and rebars are no exemption in that regard. During their service life, anchors and rebars are subjected to different kinds of load actions, so they have to be qualified and designed for critical safety performance. While the qualification guidelines for static and seismic loading have matured to conclusive requirements over the past two decades, the requirements for determining the resistance to fire are just about to consolidate. This contribution strives to provide clarity on the fire rating of post-installed anchors and rebars. For this, the current status of the regulations, as well as the underlying background, is reviewed after a brief introduction. Typical examples of fire ratings in the field of post-installed anchors and rebars are given, and recent research undertaken to close the last regulative gaps is briefly presented.Item Open Access Oxygen diffusion in a functionally graded material with cracks using a novel probability distribution for varying parameters(2025) Lammert, Robert; Petrova, Vera E.; Weihe, StefanThe elastic modulus profile of a functionally graded material (FGM) is additionally affected by oxygen diffusion. In contrast to earlier work, the reacting material is decreasing in concentration toward the oxygen‐exposed surface, so the rule used to model the elastic modulus is adjusted accordingly. Furthermore, the original distribution function is replaced by a smoother one with similar properties. The resulting oxidation model, including an appropriate fracture toughness rule, is used to calculate critical loads for a set of three parallel edge cracks in the half plane. These loads are then checked against the model without oxygen diffusion.