| Autor(en) | Lippitz, Nicolas | Erdeniz, Dinc | Sharp, Keith W. | Dunand, David C. |
|---|---|
| Titel | Mechanical Behavior of Three- Dimensional Braided Nickel-Based Superalloys Synthesized via Pack Cementation |
| Herausgeber | Metallurgical and Materials Transactions A, ISSN 1073-5623, Volume 49, Issue 3, Springer US, pp817-821 |
| Erscheinungsjahr | 2018 |
| Abstract | Braided tubes of Ni-based superalloys are fabricated via three-dimensional (3-D) braiding of ductile Ni-20Cr (wt pct) wires followed by post-textile gas-phase alloying with Al and Ti to create, after homogenization and aging, γ/γ′ strengthened lightweight, porous structures. Tensile tests reveal an increase in strength by 100 MPa compared to as-braided Ni-20Cr (wt pct). An interrupted tensile test, combined with X-ray tomographic scans between each step, sheds light on the failure behavior of the braided superalloy tubes. |
| Autor(en) | Tychsen, Jörn | Lippitz, Nicolas | Rösler, Joachim |
|---|---|
| Titel | Modification of Porous Aluminum by Cold Rolling for Low-Noise Trailing Edge Applications |
| Herausgeber | Metals, ISSN 2075-4701, 8(8), MDPI, 598 |
| Erscheinungsjahr | 2018 |
| Abstract | Noise reduction of aircrafts during take-off and landing has become an important part of research in aviation. The circulation of air around the airframe is a major source of noise during landing. This includes noise generated at the trailing edge. Open porous materials, such as porous aluminum, are investigated for the reduction of this noise. In this study, cold rolling is used to enhance the structure of porous aluminum in matters of aeroacoustics and mechanical properties. An important parameter characterizing the acoustic behavior is flow resistivity which is measured using the alternating airflow method. The flow resistivity is highly dependent upon the pore structure which is analyzed using three-dimensional computer tomography (CT). Additionally, CT combined with discontinuous tensile testing is used to study the influence of cold rolling on the damage behavior of porous aluminum. Besides the damage behavior, mechanical parameters have been determined to identify reasonable degrees of deformation. A cold rolling technique to produce material with a gradient in porosity is described and experimental porous trailing edges for measurements in an acoustic wind tunnel are shown. The findings of this study show that cold rolling is a promising way to customize porous aluminum for low-noise trailing edge applications. |
| Autor(en) | Uphoff, Sonja | Krafczyk, Manfred | Kutscher, Konstantin | Rurkowska, Katherina | Langer, Sabine | Lippitz, Nicolas | Faßmann, Benjamin |
|---|---|
| Titel | A HIERARCHICAL APPROACH TO DETERMINING ACOUSTIC ABSORPTION PROPERTIES OF POROUS MEDIA COMBINING PORE-RESOLVED AND MACROSCOPIC MODELS |
| Herausgeber | Journal of Porous Media, Volume 21, Begell House, 83-100, 2018 |
| Erscheinungsjahr | 2018 |
| Abstract | Acoustic properties of porous media are very important for numerous industrial applications, the typical goal being to maximize broadband absorption to decrease the sound pressure level of the engineering system under consideration. Up to now acoustic absorption for porous media with complex inner geometry is determined experimentally, as acoustic simulations on the pore scale are computationally challenging due to the tedious geometric reconstruction of computer tomography (CT) data and the corresponding mesh generation as well as substantial computational requirements for the corresponding transient 3D solvers. The lattice Boltzmann method (LBM), which is an established computational approach to simulate pore-resolved porous media transport problems, has been used successfully for aeroacoustic setups and is utilized in this work to fill this gap. This paper presents a comparison of different experimental and numerical approaches to determine the acoustic absorption of different porous media. Experimental work with an impedance tube was carried out for comparison and CT scans were conducted to supply the detailed numerical simulation with geometry data of the porous samples. Results of LB simulations for the acoustic impedance of a microperforated plate and a felt are shown. Finally we demonstrate how microscopic parameters determined by a pore scale approach can be used to feed homogenized models to bridge the gap towards simulations of components where acoustic absorbers are applied to, e.g., wing flaps of airplanes. |
| Autor(en) | Lippitz, Nicolas | Rösler, Joachim |
|---|---|
| Titel | Analyzing the structure evolution of porous aluminum during cold rolling |
| Herausgeber | MetFoam, Barcelona, Spanien, 2015 |
| Erscheinungsjahr | 2017 |
| Abstract | In times of increasing numbers of flights and growing airports close to residential areas, noise reduction of future airplanes is of major importance. To reduce the noise, which is dominating during landing, low-noise trailing edges of porous materials are investigated. A promising material is porous aluminum, which is produced using a salt infiltration method and available with various pore shapes and porosities. However, to meet the aeroacoustic and aerodynamic requirements ideally, adjustments of the pore shape and grade of porosity are necessary. This work investigates the possibilities to influence the porosity and pore shape of porous aluminum, using a cold rolling process. First results about the forming capability and evolution of porosity and pore morphology of porous aluminum during cold rolling are presented. For this porous aluminum was characterized for different degrees of deformation, using three-dimensional X-ray tomography. |
| Autor(en) | Lippitz, Nicolas | Blech, Christopher | Rösler, Joachim | Langer, Sabine |
|---|---|
| Titel | Identification of Material Parameters for the Simulation of Acoustic Absorption of Fouled Sintered Fiber Felts |
| Herausgeber | Materials, ISSN 1996-1944, 9(8), 709, MDPI |
| Erscheinungsjahr | 2016 |
| Abstract | As a reaction to the increasing noise pollution, caused by the expansion of airports close to residential areas, porous trailing edges are investigated to reduce the aeroacoustic noise produced by flow around the airframe. Besides mechanical and acoustical investigations of porous materials, the fouling behavior of promising materials is an important aspect to estimate the performance in long-term use. For this study, two intered fiber felts were selected for a long-term fouling experiment where the development of the flow resistivity and accumulation of dirt was observed. Based on 3D structural characterizations obtained from X-ray tomography of the initial materials, acoustic models (Biot and Johnson–Champoux–Allard) in the frame of the transfer matrix method were applied to the sintered fiber felts. Flow resistivity measurements and the measurements of the absorption coefficient in an impedance tube are the basis for a fouling model for sintered fiber felts. The contribution will conclude with recommendations concerning the modeling of pollution processes of porous materials. |
| Autor(en) | Lippitz, Nicolas | Maudarbocus, Samir | Rösler, Joachim |
|---|---|
| Titel | The influence of cold rolling on the pore morphology and flow resistivity of porous aluminum |
| Herausgeber | Sixth International Conference on Porous Media and Its Applications in Science, Engineering and Industry, Waikoloa, Hawaii, USA, 2016 |
| Erscheinungsjahr | 2016 |
| Abstract | Materials with an open porosity are used in many applications, such as filters, acoustic absorbers or heat exchangers. For these applications the pore size and shape as well as the depending flow resistivity are important parameters and need to be adjusted for the specific case. The material parameters are usually defined by the manufacturing process and are therefore signature for different types of porous materials. In this study the porosity, pore shape and the depending flow resistivity of a given material are adjusted using a cold rolling process. The material chosen is a porous aluminum with a porosity of about 50% and relatively large pores, what allows to adjust pore size and porosity on large scale. To characterize the initial porous structure and describe the structural evolution during cold rolling, three dimensional X-ray scans for various degrees of deformation were taken. To analyze pore size and pore shape a line segmentation technique was applied to image stacks extracted from the 3D reconstructions parallel to the three main surfaces of the rolled plate (parallel and perpendicular to the rolled surface). Thus it is possible to examine the formation of an anisotropic porous structure and compare pore shapes and sizes for different degrees of deformation and orientations within the rolled plate. These results are then compared to the evolution of the flow resistivity, which was measured for the three main orientations. |
| Autor(en) | Lippitz, Nicolas | Rösler, Joachim |
|---|---|
| Titel | Damage Behavior of Sintered Fiber Felts |
| Herausgeber | Metals, ISSN 2075-4701, 5, MDPI AG, 591-602, Basel, Switzerland, 2015 |
| Erscheinungsjahr | 2015 |
| Abstract | The reduction of aircraft noise is important due to a rising number of flights and the growth of urban centers close to airports. During landing, a significant part of the noise is generated by flow around the airframe. To reduce that noise porous trailing edges are investigated. Ideally, the porous materials should to be structural materials as well. Therefore, the mechanical properties and damage behavior are of major interest. The aim of this study is to show the change of structure and the damage behavior of sintered fiber felts, which are promising materials for porous trailing edges, under tensile loading using a combination of tensile tests and three dimensional computed tomography scans. By stopping the tensile test after a defined stress or strain and scanning the sample, it is possible to correlate structural changes and the development of damage to certain features in the stress-strain curve and follow the damage process with a high spatial resolution. Finally, the correlation between material structure and mechanical behavior is demonstrated. |
| Autor(en) | Delfs, Jan | Faßmann, Benjamin | Lippitz, Nicolas | Mößner, Michael | Müller, Lars | Rurkowska, Katherina |
|---|---|
| Titel | SFB 880 – AEROACOUSTIC RESEARCH FOR LOW NOISE TAKE-OFF AND LANDING |
| Herausgeber | CEAS Aeronautical Journal |
| Erscheinungsjahr | 2014 |
| Abstract | This paper gives an overview about prediction capabilities and the development of noise reduction technologies appropriate to reduce high lift noise and propeller noise radiation for future low noise transport aircraft with short take-off and landing capabilities. The work is embedded in the collaborative research centre SFB880 in Braunschweig, Germany. Results are presented from all the acoustics related projects of SFB880 which cover the aeroacoustic simulation of the effect of flow permeable materials, the characterization, development, manufacturing and operation of (porous) materials especially tailored to aeroacoustics, new propeller arrangements for minimum exterior noise due to acoustic shielding as well as the prediction of vibration excitation of aircraft structures, reduced by porous materials. |
| Autor(en) | Hinze, Björn | Rösler, Joachim |
|---|---|
| Titel | Measuring and Simulating Acoustic Absorption of Open-Celled Metals |
| Herausgeber | Advanced Engineering Materials, Volume 16, WILEY-VCH Verlag |
| Erscheinungsjahr | 2014 |
| Abstract | Aircraft noise is of great importance for aircraft passengers and residents near airports. Excellent candidates as metal fiber felts or metal foams to absorb engine noise are experimentally investigated in acoustic absorption measurements. Additionally, the empirical Delany–Bazley model is applied to receive simulation results. The comparison of measured and simulated results shows good agreement. |
| Autor(en) | Rösler, Joachim | Björn Hinze, Waldemar Krause |
|---|---|
| Titel | A Concept for the Control of Pore Size in Superalloy Membranes |
| Herausgeber | Metals, ISSN 2075-4701, 4, MDPI AG, 1-7, Basel, Switzerland, 2014 |
| Erscheinungsjahr | 2014 |
| Abstract | A new method to adjust the pore size in superalloy membranes is shown, utilizing controlled cooling from solution heat treatment of the solid superalloy. Hereby, the nucleation rate and, thus, the size of the γ'-precipitates can be varied to a large extent. This leads to a corresponding variation in the pore size once the membrane material is produced by directional coarsening of the γ'-phase to an interconnected network and subsequent selective extraction of the γ-phase. Furthermore, it was found that coherent and incoherent γ'-precipitates can be used alike to fabricate superalloy membranes, and yet, result in vastly different pore morphologies. The findings widen the application range of this novel material class. |
| Autor(en) | Lippitz, Nicolas | Rösler, Joachim | Hinze, Björn |
|---|---|
| Titel | Potential of Metal Fibre Felts as Passive Absorbers in Absorption Silencers |
| Herausgeber | Metals, ISSN 2075-4701, 3, MDPI AG, 150-158, Basel, Switzerland, 2013 |
| Erscheinungsjahr | 2013 |
| Abstract | The growing noise exposure of residents, due to a rising number of flights, causes significant impacts on physical health. Therefore it is necessary to reduce the noise emission of aircrafts. During take-off, the noise generated by the jet engines is dominating. One way to lower the noise emission of jet engines is to build an absorption silencer by using porous liners. Because of the high thermic and corrosive attacks as well as high fatigue loads, conventional absorbers cannot be used. A promising material is sintered metal fibre felts. This study investigates the suitability of metal fibre felts for the use as absorption material in silencers. The influences of pore morphology, absorption coefficient, determined with perpendicular sound incidence, as well as geometric parameters of the silencer to the damping are identified. To characterise the material, the parameters fibre diameter, porosity and thickness are determined using three-dimensional computer tomography images. The damping potential of absorption silencers is measured using an impedance tube, which was modified for transmission measurements. The essential parameter to describe the acoustic characteristics of porous materials is the flow resistivity. It depends on the size, shape and number of open pores in the material. Finally a connection between pore morphology, flow resistivity of the metal fibre felts and damping potential of the absorption silencer is given. |
| Autor(en) | Hinze, Björn | Rösler, Joachim | Lippitz, Nicolas |
|---|---|
| Titel | Noise Reduction Potential of Cellular Metals |
| Herausgeber | Metals, ISSN 2075-4701, 2, MDPI AG, 195-201, Basel, Switzerland, 2012 |
| Erscheinungsjahr | 2012 |
| Abstract | Rising numbers of flights and aircrafts cause increasing aircraft noise, resulting in the development of various approaches to change this trend. One approach is the application of metallic liners in the hot gas path of aero-engines. At temperatures of up to 600 °C only metallic or ceramic structures can be used. Due to fatigue loading and the notch effect of the pores, mechanical properties of porous metals are superior to the ones of ceramic structures. Consequently, cellular metals like metallic foams, sintered metals, or sintered metal felts are most promising materials. However, acoustic absorption depends highly on pore morphology and porosity. Therefore, both parameters must be characterized precisely to analyze the correlation between morphology and noise reduction performance. The objective of this study is to analyze the relationship between pore morphology and acoustic absorption performance. The absorber materials are characterized using image processing based on two dimensional microscopy images. The sound absorption properties are measured using an impedance tube. Finally, the correlation of acoustic behavior, pore morphology, and porosity is outlined. |
| Autor(en) | Hinze, Björn | Rösler, Joachim | Schmitz, Fabian |
|---|---|
| Titel | Production of nanoporous superalloy membranes by load-free coarsening of gamma'-precipitates |
| Herausgeber | Acta Mater., ISSN 1359-6454, 59, Elsevier, 3049-3060, 2011 |
| Erscheinungsjahr | 2011 |
| Abstract | Nickel-based superalloys are predominantly used as structural materials in high-temperature applications due to their exceptional high-temperature strength based on precipitation hardening by the coherent gamma'-phase. In modern superalloys, the gamma'-phase fraction can amount to 75%, at which gamma'-precipitates align as cubes parallel to the directions of the crystal lattice. At high temperatures and under a mechanical load, e.g. during service in gas turbines, the gamma'-cubes coalesce to gamma'-rafts, generating an interpenetrating microstructure of gamma and gamma'. By extracting one phase of this interpenetrated network, nanoporous superalloy membranes containing channel-like interconnected pores are produced. So far, this can only be achieved by applying simultaneously thermal and mechanical loads during tensile creep deformation. Here, a new production process is presented. Due to internal stresses, load-free aging of single-crystalline superalloys, e.g. CMSX-4, also generates an interpenetrating microstructure of gamma and gamma'. This can be utilized to manufacture nanoporous superalloy membranes in the absence of an external mechanical load. The advantage of this process is its simplicity and the potential to fabricate larger membranes than possible by the costly tensile creep deformation process currently used. |