13 Zentrale Universitätseinrichtungen
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/14
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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 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 Can a hand-held 3D scanner capture temperature-induced strain of mortar samples : comparison between experimental measurements and numerical simulations(2023) Haynack, Alexander; Zadran, Sekandar; Timothy, Jithender J.; Gambarelli, Serena; Kränkel, Thomas; Thiel, Charlotte; Ožbolt, Joško; Gehlen, ChristophThe expected lifespan of cement-based materials, particularly concrete, is at least 50 years. Changes in the pore structure of the material need to be considered due to external influences and associated transport processes. The expansion behaviour of concrete and mortar during freeze-thaw attacks, combined with de-icing salt agents, is crucial for both internal and external damage. It is essential to determine and simulate the expansion behaviour of these materials in the laboratory, as well as detect the slow, long-term expansion in real structures. This study measures the expansion of mortar samples during freeze-thaw loading using a high-resolution hand-held 3D laser scanner. The specimens are prepared with fully or partially saturated pore structures through water storage or drying. During freeze-thaw experiments, the specimens are exposed to pure water or a 3% sodium chloride solution (NaCl). Results show contraction during freezing and subsequent expansion during thawing. Both test solutions exhibit similar expansion behaviour, with differences primarily due to saturation levels. Further investigations are required to explore the changing expansion behaviour caused by increasing microcracking resulting from continuous freeze-thaw cycles. A numerical analysis using a 3D coupled hygro-thermo-mechanical (HTM) model is conducted to examine the freeze–thaw behaviour of the mortar. The model accurately represents the freezing deformation during the freeze–thaw cycle.Item Open Access A short-time approach for fatigue life evaluation of AISI 347 steel for nuclear power energy applications(2021) Bill, Tobias; Acosta, Ruth; Boller, Christian; Donnerbauer, Kai; Lücker, Lukas; Walther, Frank; Heckmann, Klaus; Sievers, Jürgen; Schopf, Tim; Weihe, Stefan; Starke, PeterAISI 347 austenitic steel is, as an example, used in nuclear energy piping systems. Piping filled with superheated steam or cooled water is particularly exposed to high stresses, whereupon local material properties in the pipes can change significantly, especially in the case of additional corrosive influences, leading to aging of the material. In the absence of appropriate information, such local material property variations are currently covered rather blanketly by safety factors set during the design of those components. An increase in qualified information could improve the assessment of the condition of such aged components. As part of the collaborative project “Microstructure-based assessment of the maximum service life of core materials and components subjected to corrosion and fatigue (MiBaLeB)”, the short-time procedure, StrainLife, was developed and validated by several fatigue tests. With this procedure, a complete S-N curve of a material can be determined on the basis of three fatigue tests only, which reduces the effort compared to a conventional approach significantly and is thus ideal for assessing the condition of aged material, where the material is often rare, and a cost-effective answer is often very needed. The procedure described is not just limited to traditional parameters, such as stress and strain, considered in destructive testing but rather extends into parameters derived from non-destructive testing, which may allow further insight into what may be happening within a material’s microstructure. To evaluate the non-destructive quantities measured within the StrainLife procedure and to correlate them with the aging process in a material, several fatigue tests were performed on unnotched and notched specimens under cyclic loading at room and elevated temperatures, as well as under various media conditions, such as distilled water and reactor pressure vessel boiling water (BWR) conditions.Item Open Access A novel runtime algorithm for the real-time analysis and detection of unexpected changes in a real-size SHM network with quasi-distributed FBG sensors(2021) Sakiyama, Felipe Isamu H.; Lehmann, Frank; Garrecht, HaraldThe ability to track the structural condition of existing structures is one of the main concerns of bridge owners and operators. In the context of bridge maintenance programs, visual inspection predominates nowadays as the primary source of information. Yet, visual inspections alone are insufficient to satisfy the current needs for safety assessment. From this perspective, extensive research on structural health monitoring has been developed in recent decades. However, the transfer rate from laboratory experiments to real-case applications is still unsatisfactory. This paper addresses the main limitations that slow the deployment and the acceptance of real-size structural health monitoring systems (SHM) and presents a novel real-time analysis algorithm based on random variable correlation for condition monitoring. The proposed algorithm was designed to respond automatically to detect unexpected events, such as local structural failure, within a multitude of random dynamic loads. The results are part of a project on SHM, where a high sensor-count monitoring system based on long-gauge fiber Bragg grating sensors (LGFBG) was installed on a prestressed concrete bridge in Neckarsulm, Germany. The authors also present the data management system developed to handle a large amount of data, and demonstrate the results from one of the implemented post-processing methods, the principal component analysis (PCA). The results showed that the deployed SHM system successfully translates the massive raw data into meaningful information. The proposed real-time analysis algorithm delivers a reliable notification system that allows bridge managers to track unexpected events as a basis for decision-making.Item Open Access Nano-zirconia as a protective and consolidant material for marble in architectural surfaces(2025) Urbanek, Matea; Gil-Díaz, Teba; Lützenkirchen, Johannes; Castelvetro, ValterNatural weathering of carbonate building surfaces exposed to outdoor conditions can be effectively tackled by appropriate products. The aim of this experimental study was to evaluate the effectiveness of nano-zirconia (n-ZrO2) as a consolidant for calcite surfaces. Sorption kinetics were investigated in batch experiments by applying aqueous dispersions of n-ZrO2 onto model, crushed Apuan marble samples of different bead sizes. Adsorption and desorption by the action of simulated rainwater as an environmentally relevant leaching solution were investigated. Adsorption studies revealed a good chemical affinity between n-ZrO2 and calcite, while desorption resulted in <6% release of n-ZrO2 and 100-fold lower solubility for 1 mm-sized beads compared to controls. These results suggest that n-ZrO2 may adsorb efficiently to calcite and protect the surface from dissolution. The results of further tests performed on artificially aged and consolidated samples of Apuan marble indicate that the application of n-ZrO2 only moderately affects water vapor permeability, water absorption coefficient, and drying behaviour. Therefore, no harmful effects are expected from the treatment. Micromechanical tests showed slightly increased mechanical strength after treatment. The obtained results highlight the effectiveness of n-ZrO2 as a surface consolidant and protective agent for calcite.Item Open Access Investigations of metallurgical differences in AISI 347 and their influence on deformation and transformation behaviour and resulting fatigue life(2024) Veile, Georg; Regitz, Elen; Smaga, Marek; Weihe, Stefan; Beck, TillmannDue to variations in chemical composition and production processes, homonymous austenitic stainless steels can differ significantly regarding their initial microstructure, metastability, and thus, their fatigue behavior. Microstructural investigations and fatigue tests have been performed in order to evaluate this aspect. Three different batches and production forms of nominally one type of steel AISI 347 were investigated under monotonic tensile tests and cyclic loading under total strain and stress control in low and high cycle fatigue regimes, respectively. The deformation induced α’-martensite formation was investigated globally by means of in situ magnetic measurements and locally using optical light microscopy of color etching of micrographs. The investigation showed that the chemical composition and the different production processes influence the material behavior. In fatigue tests, a higher metastability and thus a higher level of deformation induced α’-martensite pronounced cyclic hardening, resulting in significantly greater endurable stresses in total strain-controlled tests and an increase in fatigue life in stress-controlled tests. For applications of non-destructive-testing, detailed knowledge of a component’s metastability is required. In less metastable batches and for lower stress levels, α’-martensite primarily formed at the plasticization zone of a crack. Furthermore, the formation and nucleation points of α’-martensite were highly dependent on grain size and the presence of δ-ferrite. This study provides valuable insights into the different material behavior of three different batches with the same designation, i.e., AISI 347, due to different manufacturing processes and differences in the chemical composition, metastability, and microstructure.Item Open Access Anisotropy of the tribological performance of periodically oxidated laser-induced periodic surface structures(2023) Onufrijevs, Pavels; Grase, Liga; Padgurskas, Juozas; Rukanskis, Mindaugas; Durena, Ramona; Willer, Dieter; Iesalnieks, Mairis; Lungevics, Janis; Kaupuzs, Jevgenijs; Rukuiža, Raimundas; Kriūkienė, Rita; Hanesch, Yuliya; Speicher, MagdalenaLaser-induced periodic surface structures (LIPSS) enable advanced surface functionalization with broad applications in various fields such as micro- and nanoelectronics, medicine, microbiology, tribology, anti-icing systems, and more. This study demonstrates the possibility of achieving anisotropy in the tribological behavior of C45-grade steel structured by nanosecond laser radiation using the LIPSS method. The lateral surface of the steel roller was irradiated with a pulsed Nd:YAG laser at an optimum intensity I = 870 MW/cm2 for the formation of LIPSS. Two sets of samples were formed with LIPSS that were perpendicular and parallel to the roller’s rotational motion direction. The Raman intensity maps revealed that the LIPSS structure consisted of periodically arranged oxides at the top of hills. At the same time, the valleys of the LIPSS structures were almost not oxidized. These results correlated well with scanning electron microscopy energy dispersive X-ray spectroscopy mapping and atomic force microscopy measurements. A comparison of Raman and X-ray photoelectron spectroscopy spectra revealed that both the magnetite phase and traces of the hematite phase were present on the surface of the samples. Tribological tests were performed in two cycles with periodic changes in the normal clamping force and sliding speed. It was found that the LIPSS structures which were formed perpendicularly to the sliding direction on the roller had a significantly greater impact on the friction processes. Structures oriented perpendicular to the direction of motion had a positive influence on reducing the energy consumption of a friction process as well as increasing the wear resistance compared to LIPSS formed parallel to the direction of motion or ones having a non-texturized surface. Laser texturing to produce LIPSS perpendicular to the direction of motion could be recommended for friction pairs operating under low-load conditions.Item Open Access Compressive fatigue investigation on high-strength and ultra-high-strength concrete within the SPP 2020(2022) Basaldella, Marco; Jentsch, Marvin; Oneschkow, Nadja; Markert, Martin; Lohaus, LudgerThe influence of the compressive strength of concrete on fatigue resistance has not been investigated thoroughly and contradictory results can be found in the literature. To date, the focus of concrete fatigue research has been on the determination of the numbers of cycles to failure. Concerning the fatigue behaviour of high-strength concrete (HPC) and, especially, ultra-high-strength concrete (UHPC), which is described by damage indicators such as strain and stiffness development, little knowledge is available, as well as with respect to the underlying damage mechanisms. This lack of knowledge has led to uncertainties concerning the treatment of high-strength and ultra-high-strength concretes in the fatigue design rules. This paper aims to decrease the lack of knowledge concerning the fatigue behaviour of concrete compositions characterised by a very high strength. Within the priority programme SPP 2020, one HPC and one UHPC subjected to monotonically increasing and cyclic loading were investigated comparatively in terms of their numbers of cycles to failure, as well as the damage indicators strain and stiffness. The results show that the UHPC reaches a higher stiffness and a higher ultimate strain and strength than the HPC. The fatigue investigations reveal that the UHPC can resist a higher number of cycles to failure than the HPC and the damage indicators show an improved fatigue behaviour of the UHPC compared to the HPC.Item Open Access Microstructure-based lifetime assessment of austenitic steel AISI 347 in view of fatigue, environmental conditions and NDT(2021) Acosta, Ruth; Heckmann, Klaus; Sievers, Jürgen; Schopf, Tim; Bill, Tobias; Starke, Peter; Donnerbauer, Kai; Lücker, Lukas; Walther, Frank; Boller, ChristianThe assessment of metallic materials used in power plants’ piping represents a big challenge due to the thermal transients and the environmental conditions to which they are exposed. At present, a lack of information related to degradation mechanisms in structures and materials is covered by safety factors in its design, and in some cases, the replacement of components is prescribed after a determined period of time without knowledge of the true degree of degradation. In the collaborative project “Microstructure-based assessment of maximum service life of nuclear materials and components exposed to corrosion and fatigue (MibaLeb)”, a methodology for the assessment of materials’ degradation is being developed, which combines the use of NDT techniques for materials characterization, an optimized fatigue lifetime analysis using short time evaluation procedures (STEPs) and numerical simulations. In this investigation, the AISI 347 (X6CrNiNb18-10) is being analyzed at different conditions in order to validate the methodology. Besides microstructural analysis, tensile and fatigue tests, all to characterize the material, a pressurized hot water pipe exposed to a series of flow conditions will be evaluated in terms of full-scale testing as well as prognostic evaluation, where the latter will be based on the materials’ data generated, which should prognose changes in the material’s condition, specifically in a pre-cracked stage. This paper provides an overview of the program, while the more material’s related aspects are presented in the subsequent paper.