Order-disorder transitions in a sheared many body system

Motivated by experiments on sheared suspensions that show a transition between ordered and disordered phases, we here study the long-time behavior of a sheared and overdamped 2-d system of particles interacting by repulsive forces. As a function of interaction strength and shear rate we find transitions between phases with vanishing and large single-particle diffusion. In the phases with vanishing single-particle diffusion, the system evolves towards regular lattices, usually on very slow time scales. Different lattices can be approached, depending on interaction strength and forcing amplitude. The disordered state appears in parameter regions where the regular lattices are unstable. Correlation functions between the particles reveal the formation of shear bands. In contrast to single particle densities, the spatially resolved two-particle correlation functions vary with time and allow to determine the phase within a period. As in the case of the suspensions, motion in the state with low diffusivity is essentially reversible, whereas in the state with strong diffusion it is not.Comment: 12 pages, 13 figures; Supplemental Movies: https://youtu.be/oFcrWo9Vs6E, https://youtu.be/tcowb7o05JQ, https://youtu.be/GkEUwycn7V4, https://youtu.be/k-XCo8CWFU

Design of Particle Dampers for Laser Powder Bed Fusion

Additively manufactured particle dampers can significantly improve component damping. However, if designed incorrectly, the damping can be worsened. For the design of additively manufactured particle dampers, there are not yet sufficient design rules and models to describe the effect due to numerous design parameters. The research question answered in this paper describes how the effect of particle damping can be characterised as a function of excitation force and excitation frequency for different cavity sizes. To characterise the effect of particle damping, a 33 full factorial test plan is constructed, and the damping is determined experimentally. It is shown that the damping can be reliably evaluated with the circle‐fit method. The effect of particle damping is investigated for beams made of AlSi10Mg, 1.2709 and Ti6Al4V. As a result, a positive effect of the particle damping in a frequency range from 500 to 30,000 Hz and partly up to the 9th bending mode can be proven. It is shown that, for the first bending mode, there is an optimum at approx. 2000 Hz. For the optimum, the increase of the damping for the tool steel 1.2709 to 28 and for the aluminium alloy AlSi10Mg to 18 can be proven. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

Potential of additively manufactured particle damped compressor blades: A literature review

The high-cycle fatigue of compressors significantly impacts the lifetime of aircraft engines. Excitations in resonance lead to early blade fractures; therefore, vibration reduction measures for blades must be taken. Additively manufactured particle dampers are a suitable measure to suppress vibrations. The focus of this paper is to analyze the applications of additively manufactured particle dampers in compressor blades through a literature review. The design requirements, previous vibration reduction measures for compressor blades and properties of additively manufactured particle dampers are investigated in three studies. In order to evaluate the application of additively manufactured particle dampers in compressor blades, the findings are compared and research demand is derived. The main requirements on compressor blades are stiffness, vibration reduction and wear-resistance. Recent vibration reduction measures are focused on friction dampers. To optimize damping multiple vibration suppression measures shall be used. Few studies exist for additively manufactured particle dampers and some prove their damping improvement in compressor blades. Due to the complicated operation conditions, further studies are needed, which are listed to give researchers an approach for further steps

Auslegung partikelgedämpfter Strukturbauteile für die Additive Fertigung

Das kontinuierliche Streben, Strukturbauteile immer ressourcenschonender und effizienter zu gestalten, führt zu einer Reduktion der Bauteilmasse, aber auch der Dämpfung. Allerdings stellen Dämpfungsmechanismen einen entscheidenden Faktor zur Beeinflussung des Schwingungsverhaltens dynamischer Systeme dar. So können z. B. Fahrzeugschwingungen den Fahrkomfort mindern oder im schlimmsten Fall zum Bauteilversagen führen. Einen effektiven, kostengünstigen und einfach zu integrierenden Ansatz zur Schwingungsreduktion, stellt der Effekt der Partikeldämpfung dar. Insbesondere in pulverbettbasierten additiven Fertigungsverfahren wie dem PBF-LB/M, kann während des Bauprozesses unverschmolzenes Pulver in dafür vorgesehenen Bauteilkavitäten belassen und so ein hochintegrierter Partikeldämpfer gefertigt werden. Durch eine Integration der pulvergefüllten Kavitäten im Bereich der neutralen Faser kann eine hohe Dämpfung bei geringfügiger Beeinflussung der Bauteilmasse und -steifigkeit realisiert werden. Neben den zahlreichen Vorteilen ist der Einsatz laserstrahlgeschmolzener Partikeldämpfer jedoch aktuell noch stark limitiert. Die Ursachen sind vor allem die zahlreichen Auslegungsparameter, die hochgradig nichtlineare Wechselwirkungen aufweisen. Infolge dessen liegen noch keine ausreichenden Auslegungswerkzeuge wie Kennfelder, mechanische Ersatzmodelle oder Gestaltungsrichtlinien vor. Der erste Aspekt dieser Arbeit widmet sich der experimentellen Charakterisierung laserstrahlgeschmolzener Partikeldämpfer aus Aluminium AlSi10Mg und Werkzeugstahl 1.2709. Neben dem Material, werden die relevanten Einflussfaktoren Anregungskraft, Frequenz und Hohlraumvolumen analysiert. Dazu wird eine Impulshammeranregung von Biegebalken durchgeführt und die Dämpfung über das Circle-Fit Verfahren ausgewertet. Dabei konnte für ausgewählte partikelgedämpfte Balken die Dämpfung um bis zu einem Faktor von 20 gegenüber einem vollversinterten Referenzbalken gesteigert werden. Anschließend wird ein mechanisches Ersatzmodell in Form eines Zweimassenschwingers aufgebaut, welches sowohl die Stoß-, als auch die Reibvorgänge im Partikeldämpfer abbilden kann. Im Ergebnis liegt ein verifiziertes mechanisches Ersatzmodell vor, welches eine Genauigkeit von 85% verglichen zum Experiment aufweist. Darauf aufbauend werden Gestaltungsrichtlinien abgeleitet und eine Auslegungsmethode erarbeitet. Abschließend wird ein Demonstrator (Motorradgabelbrücke) unter den Gesichtspunkten einer niedrigen Masse bei gleichzeitig hoher Steifigkeit und Dämpfung ausgelegt. Die Auslegungsmethode konnte erfolgreich am Anwendungsbeispiel Gabelbrücke angewendet und die Dämpfung, verglichen zur vollversinterten Gabelbrücke, merklich gesteigert werden

Additive manufacturing of multi-material parts – Design guidelines for manufacturing of 316L/CuCrZr in laser powder bed fusion

Additive manufacturing (AM) can be used to produce multi-material parts in which the material can be varied voxel-wise in all three spatial directions. This means that the paradigm of the homogeneous material can be abandoned and local effects such as heat conduction or damping can be selectively adjusted in the part. Recently, continuous development of machine technology has allowed the production of multi-metal materials in laser powder bed fusion (PBF-LB/MM). Compared to other additive manufacturing processes for multi-material production, this allows greater design freedom and detail accuracy to be realized. However, due to the novel character of multi-material manufacturing in PBF-LB, the process knowledge for successful and reproducible fabrication is currently lacking. This paper focuses on establishing design guidelines for manufacturing the material pairing of stainless steel 316L (1.4404) and copper alloy CuCrZr (CW106C). The article is accompanied by the development of a specific process chain. As a result of this work, design guidelines for multi-material parts are available for the first time, in regard to arrangement, size, overhangs, economy, powder quality and laser scanning

Design of particle dampers for additive manufacturing

Damping mechanisms are a crucial factor for influencing the vibration behavior of dynamic systems. In many applications vibrations are undesirable and need to be reduced by appropriate measures. For instance, vibrations in vehicles can reduce driving comfort or in civil engineering resonance damage can occur in constructions. An interesting and cost-effective way of increasing damping is particle damping. In modern processes of additive manufacturing, like laser powder bed fusion (LPBF), unmelted powder can be left inside a structure on purpose after making and thus producing integrated particle dampers already. Additively manufactured particle damping has not yet reached the industrial level because there are no detailed specifications for the design process. This includes the modeling of (non-linear) dynamic properties, based on numerous design parameters. The state of the art reveals that the effect of particle damping has been convincingly demonstrated, but transferability of the obtained information is still limited. In this paper the effect of particle damping is investigated experimentally with LPBF manufactured beam structures made of AlSi10Mg. Particle damping is evaluated in terms of performance curves for different beam parameter sets. The aim is to help the designer, who needs to keep amplitudes in certain range to estimate the damping of the potential particle damper via the given performance curves. Damping is determined via experimental modal analysis by impulse excitation. The response is evaluated in the frequency domain using the Circle-Fit method with a focus on the beams first bending mode of vibration. Beyond that, a significantly increased damping could be verified up to the seventh bending mode covering a frequency range between 600 Hz and 18k Hz. Damping through particle-filled cavities shows up to 20 times higher damping compared to the same component with fused powder

Nonlinear granular damping of structures with cavities from additive manufacturing

Additively manufactured parts are often created with cavities for weight reduction or other mechanical purposes. These cavities offer the optimal base for granular damping. Unfused raw material particles can be left inside the structure or another granular material can be filled in to increase structural damping. In this paper, a simple mechanical model is developed based on measurements of a basic experiment for granular damping with only a small amount of particles

Map Management Approach for SLAM in Large-Scale Indoor and Outdoor Areas

This work presents a semantic map management approach for various environments by triggering multiple maps with different simultaneous localization and mapping (SLAM) configurations. A modular map structure allows to add, modify or delete maps without influencing other maps of different areas. The hierarchy level of our algorithm is above the utilized SLAM method. Evaluating laser scan data (e.g. the detection of passing a doorway) triggers a new map, automatically choosing the appropriate SLAM configuration from a manually predefined list. Single independent maps are connected by link-points, which are located in an overlapping zone of both maps, enabling global navigation over several maps. Loop- closures between maps are detected by an appearance-based method, using feature matching and iterative closest point (ICP) registration between point clouds. Based on the arrangement of maps and link-points, a topological graph is extracted for navigation purpose and tracking the global robot's position over several maps. Our approach is evaluated by mapping a university campus with multiple indoor and outdoor areas and abstracting a metrical-topological graph. It is compared to a single map running with different SLAM configurations. Our approach enhances the overall map quality compared to the single map approaches by automatically choosing predefined SLAM configurations for different environmental setups

Additive Manufacturing of Metallic Multi-Material Parts: Local Conductivity Adjustment through Functionally Graded Material Transitions of 316L and CuCrZr

Recently, powder bed-based additive manufacturing has made it possible to produce metallic multi-material parts where the material can be varied within the build plane voxel by voxel. This capability enables the realization of functionally graded materials for selective adjustment of local part properties, such as heat dissipation. In this study, the effect of location-dependent property adjustment using functionally graded materials is investigated for the combination of 316L and CuCrZr in terms of conductivity. Functionally graded test specimens were successfully produced with voxel sizes of 1 mm and 2 mm, demonstrating the influence of geometry-dependent material gradients on conductivity properties. Additionally, the study reveals a significant improvement in conductivity of CuCrZr by a factor of more than 4 following heat treatment. Nevertheless, the resolution of the gradient is limited by the manufacturing facility in terms of the minimum possible voxel size

Design Guidelines for Additive Manufactured Particle Dampers: A Review

Recently, additive manufacturing has been used to integrate particle dampers into structural components, particularly by means of laser powder bed fusion (LPBF), in order to significantly reduce component vibrations. The advantage over previous damping mechanisms is that these can be functionally integrated directly into the component during the additive manufacturing process by leaving unmelted powder in the component. This allows local damping effects to be adjusted and low-vibration lightweight structures to be developed and manufactured. In addition, the damping properties act over a wide frequency range and are insensitive to temperature. Despite the positive damping properties, the use of laser beam melted particle dampers is limited at the present time, since there are not yet sufficient design tools available due to the numerous non-linear influences. This is where the current contribution comes in, by developing design guidelines for laser beam melted particle dampers. The results were finally summarised in a design catalogue and support a suitable design of laser beam melted particle dampers