University of Siegen
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Publication Access status: Open Access , Brittle fracture of notched components fabricated by stereolithographySince additive manufacturing (AM, i.e., 3D printing) has been widely used for production of end-used products, the mechanical strength of parts fabricated by this technology have gained considerable significance. The current study presents fracture load assessment of 3D-printed components fabricated by the stereolithography (SLA) technique using UV sensitive resin material. In this context, dumbbell-shaped specimens were printed and tested to determine basic mechanical properties. Moreover, V-notched semi-circular bending test coupons with various notch opening angles (i.e., 15°, 30°, 45°, 60°, 75°, and 90°) were printed and examined. Parallel to the experimental tests, we developed a finite element model to simulate the load carrying performance of 3D-printed parts. Moreover, we used the digital image correlation technique to determine displacement and strain field on the surface of the examined specimens. Since the mechanical strength and fracture behavior of 3D-printed parts are investigated in the current study, the presented outcomes can be utilized for innovative designs of parts fabricated by SLA with a higher mechanical strength, and improved load-carrying capacity.Source Type:Article7 11 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Static and dynamic characterization of 3D-printed polymer structural elementsConsidering wide applications of Additive Manufacturing (AM), profound knowledge on the mechanical performance of AMed components is a necessity. In the present study, the mechanical behavior of AMed polymer parts under static and dynamic tests has been investigated. To this end, cantilever beams with three different mesostructure cells were designed and fabricated via ABS Carbon material based on the fused deposition modeling process. The specimens were subjected to a series of static bending tests and free vibration experiments. In addition, numerical models have been presented for both static bending and the dynamic tests. In the current study, digital image correlation technique has been employed to determine strain field and validate the numerical results. The experimental findings and numerical outcomes have been compared and the convergence has been investigated. Based on the applications of AM in fabrication of structural elements with complex geometries, the results of the current study are useful for new designs of AMed parts with customized mechanical strength and enhanced structural performance.Source Type:Article4 106 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Mixed mode brittle fracture of stereolithographic 3D-printed partsTechnical advances in additive manufacturing (AM), also known as three-dimensional (3D) printing, have led to applications of this technology in creation of end-use items. Consequently, performance and the mechanical strength of AMed parts have become of significant importance. In this research, fracture behavior and crack propagation of AMed cracked plates are investigated. To this aim, the stereolithography (SLA) technique is used to fabricate square plate specimens with a hole in the center and radial cracks that started at the perimeter of the central hole. Here, full range of mixed-mode fracture (from pure mode I to pure mode II) are obtained by altering the angle between the crack and the applied load. We used the finite element method to determine stress intensity factors. This study deals with a series of experiments on 3D-printed cracked plates to study mixed-mode fracture and crack propagation in brittle fracture of SLA 3D-printed components. Additionally, the digital image correlation technique was used to determine strain field on the surface of the specimens. As SLA is one of the most commonly used concepts in polymer 3D printing and has garnered significant attention for fabrication of complex structural elements, the outcomes of this study are useful for next developments and innovative designs of 3D-printed polymeric components.Source Type:Article1 7 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Historische Grundlagen der mobilen Gesellschaft(2023)Der Band versammelt in interdisziplinärer Perspektive verschiedene aktuelle Ansätze zur Erforschung der Geschichte von Verkehrsinformationssystemen. Er fragt dabei nach Entwicklungsverläufen, Gestaltungen und Gestalter:innen vom analogen Verkehrsfunk bis hin zur digitalen Navigation und Verkehrssteuerung.Source Type:Book5 10 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Effects of steps on the load bearing capacity of 3D-printed single lap jointsDamage in adhesively bonded joints typically initiates in the overlap area due to high level of bonding (peel) stress. Different approaches are being considered to decrease the peel stress and improve the overall strength of the joint. One possible approach is to shape the over lap area into a stepped form configuration and enhance the performance of the joint. In the current study, we investigate effects of stepped-shape overlap area on the load bearing capacity of additively manufactured single-lap joints. To this aim, stepped-lap adhesively bonded joints with different designs and geometries in the overlap (bonding) area are considered with 3D-printed polylactic acid (PLA) adherends using the fused deposition modeling (FDM) process. Three configurations with different step sizes are considered to manufactured a set of adhesively bonded single-lap joints and to investigate the optimum length of the steps. The results are compared with our previous experimental findings on 3D-printed conventional single-lap joints. The obtained outcomes reveal that creating steps in the overlap area has a significant influence on the structural integrity and fracture load of 3D-printed adhesive-bonded joints and the bonded structures with identical step size in boding area reveal a better performance in load carrying capacity and shows a higher fracture load. Parallel to the experimental practices, a finite element model also developed to simulate the load carrying performance of the adhesively bonded singlelap joints with equal step size and 3D-printed PLA adherends. The FE model confirms the experimental outcomes and reveals the details of the cohesive failure and damage evolution mechanism in this bonded structures with PLA printed adherends. The proposed technique has a great potential to be a competitive alternative to conventional single-lap joints made by 3D printing. The presented results can be used for further fabrication of 3D-printed joints with a better structural performance.Source Type:Article4 20 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Methods to enhance the automation of operational modal analysisThe vibration-based damage detection and the monitoring of modal data are currently based on different Operational Modal Analysis (OMA) approaches. For the continuous monitoring of modal quantities, different techniques for automated feature extraction are known. Especially in recent years several research groups and companies have been working on the automatic interpretation of stability plots. Nevertheless, many questions regarding data pre-processing for OMA in time or frequency domain are still unanswered. The present paper deals with issues regarding effective pre-processing methods for OMA based on Covariance-Stochastic Subspace Identification. In this context, the orthogonality of matrices after model order reduction, etc. are referred. This includes, for example, a comparison between the classical calculation of the reduced-order matrices and a procedure that preserves the orthogonality of these matrices. A method known from the signal denoising and image processing is also successful used to extract and select the modes. The mode extraction method is validated with an innovative three-dimensional stability plot. This paper does not claim to solve all tasks of an automated OMA, but it contributes the calculation of clean, easy to interpret, stability plots, which should facilitate the automatic evaluation in the future. The effectiveness of the algorithms is demonstrated by means of simulated (3DOF-StateSpace) and measured data of a laboratory structure described in [1]. Afterwards the results and the future works on the topic are discussed.Source Type:Article6 13 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Automated set-up parameter estimation and result evaluation for SSI-Cov-OMATraditionally, modal analysis and the extraction of modal parameters from vibration data is a process that requires a more or less extensive amount of manual interaction from setting input parameters up until finding the eigenfrequencies. The growing interest in continuously monitoring mechanical structures e.g. for automated damage detection methods has led to the development of many approaches to automate different aspects of modal analysis. In this context, the Covariance-driven Stochastic subspace identification (Cov-SSI) is a widely used method. The present paper provides an automated Cov-SSI algorithm combined with a peak-picking approach for the automatic determination of input parameters. In this regard, using the Prominence-parameter allows to examine the PSD by finding the most relevant peaks. The herein shown algorithm is currently suitable for systems with a limited number of sensors. Cov-SSI results are arranged in stability plots and interpreted using the hierarchical clustering method. By creating stability plots for a wide range of block rows a sensitivity analysis is used to find the optimal result based on the averaged standard deviation of damping of the clusters in every stability plot. A second aspect of this paper is comparing the common method for order reduction with a modified method described in [1], which preserves the orthogonality of the , and matrix of the singular value decomposition. Exemplary results on both methods are provided using simulated data (state-space, 3 DoF)Source Type:Article6 12 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Performance optimization of a Kirsten–Boeing turbine by a metamodel based on neural networks coupled with CFDThe supply of energy is sustainable only if it is predominantly based on renewable or regenerative energies. For this reason, the use of micro-hydropower plants on rivers and streams is considered recently. This is a particular challenge for the preservation of ecologically permeable streams, so that no dams or similar structures can be considered. While the axial turbine design has prevailed in wind power, there is still no consensus for the generation of energy in free water flow conditions. In this work, an existing prototype of an unusual vertical axis Kirsten–Boeing turbine was investigated. A multivariate optimization process was created, in which all important machine parameters were checked and improved. By using neural networks as a metamodel coupled with flow simulations in ANSYS CFX, a broadly applicable optimization strategy is presented that yielded a blade design that is 36% more efficient than its predecessor in experiments. During the process, it was shown how to set up a complex sliding mesh problem with ANSYS expressions while evaluating a free surface problem.Source Type:Article3 8 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Data on the current state of problem solving and improvement during physical product development within complex (manufacturing) systems(2019); ; Due to the exponential increase of failure cost during the product development process, problems have to be effectively remedied as early as possible and with shortened innovation cycles, increasingly efficient. For the manufacturing of complex products at low maturity levels (referred to as physical product development), nonconformance problem solving constitutes a major difficulty in this regard (Camarillo et al., 2017; Walter et al., 2010). The data presented in this article was collected from German companies, differing in size and industry sector, manufacturing highly complex products at low maturity. Selected and consulted companies therefore operate in (or comparable to) the automotive prototyping, air and space, shipbuilding, special machinery or electronics domain. The survey comprises the answers of 46 participants, gathered via online questionnaire. It subdivides into 18 questions covering the companies’ characteristics, knowledge management and documentation systems within the product development process, as well as the appraisal of technological potentials. The obtained data gives an insight into the industrial status quo of nonconformance problem solving. The data allows to derive existing deficits and dedicated research on solutions.Source Type:Article1 24 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , The response of nonlinearly loaded antennas to repetitive HPEM excitations as obtained from equivalent circuit modelsIn this contribution the effects of repetitive pulse excitations on linearly and nonlinearly loaded antennas are studied on the basis of equivalent circuit models. In the known linear case, repetitive pulses can lead to an increase of the amplitudes of oscillations. These oscillations decay, if realistic quality factors are assumed, comparatively quickly. In the considered nonlinear case the effects of repetitive pulses can add up and persist along much larger time scales. This remarkable effect has no equivalent in the linear case.Source Type:Article2 12
