A Novel Algorithm for the Determination of Walker Damage in Loaded Disc Springs

In this paper, a novel algorithm for the determination of Walker damage in loaded disc springs is presented. The algorithm takes a 3D-scan of a disc spring, measured residual stresses, material parameters, and spring loads as inputs. It outputs a distribution of Walker damage over the surface area of the input disc spring. As the algorithm allows a fully automated determination of the Walker damage, it can be used by disc spring manufacturers to reduce the working time spent on this task by specialized engineers significantly. Compared to spreadsheet applications using analytical formulas and finite element models using idealized geometry, this approach offers a superior description of the stress states in disc springs

Failure behavior of modern double-layer thermal barrier coatings subjected to compression tests

Demands for reduced emissions and higher efficiency of stationary gas turbines and jet engines lead to the necessity for increased operating temperatures. Therefore, thermal barrier coating (TBC) systems deposited to high-temperature impinged parts, e.g. turbine blades and vanes, as well as combustor liners, containing an yttria-stabilized zirconia (YSZ) top layer are well established. Currently, surface temperatures of YSZ coated turbine parts are limited to approximately 1250 °C in long-term operation, due to the rapid degradation of YSZ caused by sintering and phase instability. Double-layer TBC based on gadolinium zirconate (GZO) applied on top of a 7 to 8 wt. % YSZ layer seem to be proper candidates for advanced coating architectures to withstand temperatures up to 1550 °C. The present work investigates the failure behavior and fracture process of double-layer thermal barrier coatings under uniaxial compressive loading conditions. Coating systems of type GZO and YSZ with low and high GZO porosity (LP, HP) were fabricated, to examine the influence of microstructure and spray process parameter on failure behavior and compressive strain energy. A conventional YSZ-HP single-layer coating serves as a reference. All systems were deposited via atmospheric plasma spraying (APS) on cylindrical rods made from CoNiCrAlY (LCO-22) coated, nickel-based, single crystal superalloy (PWA 1483). The total thickness of ceramic layers was about 600 µm. Effects of thermal ageing were taken into account by isothermal pre-oxidation at 1050 °C and dwell-times of 100, 500 and 1.500 hours and compared to cyclic annealed TBC systems (50 to 1050 °C, up to 500 cycles). Failure and cracking processes during compression tests were monitored by an acoustic emission (AE) system and piezo-electric, wideband sensors. Furthermore, a stereo camera system provides information about three-dimensional displacements and TBC surface strain. In as-sprayed condition, the stored volume related strain energy to failure of double-layer coatings is comparable to the referenced single-layer system. AE analysis indicates coating failure at earlier stages after thermal ageing. Consequently, pre-oxidation leads to reduced strain energies with increasing dwell-time in all investigated coating systems. Based on digital image correlations (DIC), the failure behavior of as-sprayed GZO/YSZ coatings has been identified to be similar to the YSZ single-layer system. A different behavior was observed for pre-oxidized coatings, where cracking and spallation of GZO occurs predominantly. Chair and Institute for Materials Technology, Technische Universität Darmstadt, 64283 Darmstadt, German

Additive Manufacturing of Glass Components - Exploring the Potential of Glass Connections by Fused Deposition Modeling

Glass is an indispensable material in the building industry. The combination of transparency, strength and durability makes it to an unparalleled and desirable material. The technology additive manufacturing (AM) has a potential in the building industry, based on a relatively small amount of repetitions of particular building components and the tendency of applying technology innovations for buildings. Therefore, there is an interest for additive manufacturing with glass. This paper presents and summarizes the results of the preliminary research regarding additive manufacturing of glass components for joining methods for flat glass structures. Different types of glass (borosilicate glass, quartz glass and soda lime silicate glass) are discussed. Experimental investigations of joints are intended to illustrate the performance and potential of AM glass components in case of structural use. Load bearing tests were carried out to quantify the strength and load bearing capacity level of an AM structural component. The thermal residual stresses were examined by photo-elastic tests with polarized lights and scattered light method. The investigations show in principle that load transfer via fused glass joints is possible. The performed research activity is a first step towards the Additive Manufacturing of glass structures on flat glass

November 28, 1968

https://scholarlycommons.obu.edu/arbn_65-69/1091/thumbnail.jp

Effects of full-scale substrate pretreatment with a cross-flow grinder on biogas production

The enhancement of the degradation rate of energy crops, agricultural residues and manure by different lab scale pretreatment pathways is shown in previous studies.  In general, the pretreatments resulted in higher degradation efficiencies and an increase in methane yield for lignocellulosic and fibrous biomass.  The major drawback of most of the different pretreatment methods is that either they are not feasible for application in practice or the high energy demand makes them economically inefficient.  The aim of this study was to evaluate the effects of a full-scale mechanical pretreatment with a cross-flow grinder on commonly used energy crops (maize silage, grass silage and rye grain silage) and horse manure. Furthermore, the optimal treatment intensity for the highest energy output was estimated.  A grinding time of 15 s led to a significant increase in methane yield for horse manure (+ 9.2%) and a mixture of energy crops and horse manure (+ 9.7%).  However, only lower treatment intensities proved   to have a positive energy balance.  An increase in treatment intensity resulted in a further reduction of particle size but showed no effects on the degradation efficiency.  Hence, it can be concluded that the utilization of the mechanical treatment enables the digestion of lignocellulosic and fiber-rich substrates like residuals and organic wastes and therefore increases the environmental sustainability of energy production by anaerobic digestion.Keywords: anaerobic digestion, biogas production, mechanical pretreatment, lignocellulosic materials, horse manur

Investigation of the methane potential of horse manure

During recent years the renewable energy production with agricultural biomass became more and more important.  The increased use of agricultural products instead for nutrition aroused a debate.  Therefore, the utilization of agricultural byproducts and residuals for anaerobic digestion is the essential step for the future sustainable energy production.  One available substrate would be horse manure, but literature is still lacking information about gas potential and digestibility of horse manure in biogas plants.  This work aims at investigating the suitability of horse manure with different bedding materials and to produce standard values for different horse manure samples.  Additionally the methane yields of the components of the horse manure were analyzed.  The results of the batch digestion test showed the highest specific methane yields for straw pellets with 0.247 Nm³ CH4 kg-1 VS.  Slightly lower are the values for the straw samples in range of 0.183 to 0.237 Nm³ CH4 kg-1 VS.  The digestion of alternate bedding materials like flax and woody materials leads to specific methane values beneath 0.100 Nm³ CH kg-1 VS.  Based on these results these materials should be avoided for anaerobic digestion.  The straw based horse manure produced 0.191 ± 0.02 Nm³ CH4 kg-1 VS in the batch assay.  The storage of the manure resulted in significant lower methane yields.  Hence, the anaerobic digestion of the straw based horse manure is an efficient conversion pathway and can help to avoid the utilization of acreage for energy production instead of the production of food.    Keywords: biogas, methane yield, horse manure, anaerobic digestio

Influence of LPBF-Surface Characteristics on Fatigue Properties of Scalmalloy®

Laser powder bed fusion (LPBF) has indisputable advantages when designing new components with complex geometries due to toolless manufacturing and the ability to manufacture components with undercuts. However, fatigue properties rely heavily on the surface condition. In this work, in-process surface parameters (three differing contour parameter sets) and post-process surface treatments, namely turning and shot peening, are varied to investigate the influence of each treatment on the resulting fatigue properties of LPBF-manufactured specimens of the aluminium–magnesium–scandium alloy Scalmalloy®. Therefore, metallographic analysis and surface roughness measurements, as well as residual stress measurements, computer tomography measurements, SEM-analyses, tensile and fatigue tests, along with fracture surface analysis, were performed. Despite the fact that newly developed in-process contour parameters are able to reduce the surface roughness significantly, only a minor improvement in fatigue properties could be observed: Crack initiation is caused by sharp, microscopic notches at the surface in combination with high tensile residual stresses at the surface, which are present on all in-process contour parameter specimens. Specimens using contour parameters with high line energy show keyhole pores localized in the subsurface area, which have no effect on crack initiation. Contours with low line energy have a slightly positive effect on fatigue strength because less pores can be found at the surface and subsurface area, which even more greatly promotes an early crack initiation. The post-process parameter sets, turning and shot peening, both improve fatigue behaviour significantly: Turned specimens show lowest surface roughness, while, for shot peened specimens, the tensile residual stresses of the surface radially shifted from the surface towards the centre of the specimens, which counteracts the crack initiation at the surface