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On data-driven nonlinear uncertainty modeling: Methods and application for control-oriented surface condition prediction in hard turning
(2020-10-16)
In this article, two data-driven modeling approaches are investigated, which allow an explicit modeling of uncertainty. For this purpose, parametric Takagi-Sugeno multi-models with bounded-error parameter estimation and nonparametric Gaussian process regression are applied and compared. These models can for instance be used for robust model-based control design. As an application, the prediction of residual stresses during hard turning depending on the machining parameters and the initial hardness is considered.
Aufsatz
Influence of the Miniaturisation Effect on the Effective Stiffness of Lattice Structures in Additive Manufacturing
(2020-10-29)
Thin-walled and cellular structures are characterised by superior lightweight potential due to their advantageous stiffness to weight ratio. They find particular interest in the field of additive manufacturing due to robust and reproducible manufacturability. However, the mechanical performance of such structures strongly depends on the manufacturing process and resultant geometrical imperfections such as porosity, deviations in strut thickness or surface roughness, for which an understanding of their influence is ...
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Damage Tolerance Evaluation of E-PBF-Manufactured Inconel 718 Strut Geometries by Advanced Characterization Techniques
(2020-01-06)
By means of electron beam powder bed fusion (E-PBF), highly complex lightweight structures can be manufactured within short process times. Due to the increasing complexity of producible components and the entangled interplay of damage mechanisms, common bulk material properties such as ultimate tensile or fatigue strength are not sufficient to guarantee safe and reliable use in demanding applications. Within this work, the damage tolerance of E-PBF-manufactured Ni-based alloy Inconel 718 (IN 718) strut geometries ...
Aufsatz
Determination and Validation of Residual Stresses in CFRP/Metal Hybrid Components Using the Incremental Hole Drilling Method
(2020-09-21)
Lightweight materials contribute to an efficient decrease in fuel consumption in the automotive and aircraft industries. Hybrid components made of metal and carbon fiber-reinforced plastics (CFRP) have a high potential in lightweight applications due to their high strength-to-weight ratio. For cost-effective processing of hybrid materials, advanced manufacturing processes such as the prepreg-press-technology have been developed, in which the bonding between a metallic component and a fiber compound is exclusively ...
Aufsatz
The politics of energy landscapes: the influence of local anti-wind initiatives on state policies in Saxony, Germany
(2020-01-23)
Background
In recent years, landscapes in many countries have been transformed by efforts to fight global warming, specifically the shift towards renewable energies such as wind power. This development has been met by growing opposition from local citizens and their initiatives. There is an ongoing debate about whether and how such protests have a real impact on the development of energy landscapes.
Methods
Drawing on the rare case of a state government scaling back ambitious targets for the expansion of renewables, ...
Aufsatz
Access to the learning material enhances learning by means of generating questions: Comparing open- and closed-book conditions
(2020)
Generating questions referring to the learning material is a powerful learning strategy. The present study investigated potential mechanisms behind this effect. Students (N=231) read a text and then generated questions referring to the text in three conditions: (1) open-book (i.e., text accessible), (2) closed-book (i.e., text inaccessible), and (3) cued closed-book (i.e., text inaccessible but keywords provided). After one week, students’ knowledge gain was larger in the open-book and cued closed-book conditions ...
Aufsatz
Occurrence, distribution and alternative hosts of Wheat streak mosaic virus infecting ginger in Kaduna State, Nigeria
(2020-06-29)
A field survey was conducted during the 2018 rainy season (June – October) in three major ginger producing Local Government Areas (LGAs) of Kaduna State, Nigeria to determine the occurrence and spread of wheat streak mosaic virus (WSMV) infecting ginger. Symptomatic and asymptomatic ginger leaf samples (n=180) and weed samples (n=45) were collected from the surveyed fields and indexed against WSMV using Double Antibody Sandwich Enzyme-linked Immunosorbent Assay (DAS-ELISA). The results obtained showed that WSMV ...
Aufsatz
Typology of smallholder’s pig production systems in South Kivu, Democratic Republic of Congo: Challenges and opportunities
(2020-06-30)
Pig farming plays an important role in farmers’ livelihoods in many tropical countries. It contributes to food security of the poorest as well as the development of rural economy through multiplier effects. In the South Kivu province, pig farms are almost exclusively owned by smallholders. A few studies have attempted to describe thoroughly pig farming systems in this province. This study was undertaken to characterise pig production systems, in order to better understand their current situation, namely constraints ...
Aufsatz
On the structural integrity of Fe-36Ni Invar alloy processed by selective laser melting
(2020)
Specimens made from pre-alloyed Invar (Fe-36Ni) powder were fabricated by selective laser melting and stress-relief heat treated afterwards. A relative density of the fabricated parts of 99.6 % was determined by computed tomography. The microstructure and mechanical behavior under monotonic and particularly cyclic loading at ambient temperature were investigated. Results reveal a bimodal microstructure containing columnar and equiaxed grains with an average grain size of 75 μm and pronounced texture 〈001〉 || BD. The ...
Aufsatz
Dynamic Tensile Deformation of High Strength Aluminum Alloys Processed Following Novel Thermomechanical Treatment Strategies
(2020-05-14)
Herein, the effects of a very recently introduced novel thermomechanical process route on the microstructural evolution and dynamic tensile deformation behavior of two different precipitation hardenable aluminum alloys, i.e., AA6082 and AA7075, are studied. The investigated materials are hot formed and quenched in differently tempered tools to reveal the influence of cooling rate. Microstructure analysis is conducted to study the influences of different cooling strategies on the microstructure evolution and prevailing ...