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Improving surface integrity when drilling CFRPs and Ti-6Al-4V using sustainable lubricated liquid carbon dioxide
Full text linkIn the quest for decreasing fuel consumption and resulting gas emissions in the aeronautic sector, lightweight materials such as Carbon Fiber Reinforced Polymers (CFRPs) and Ti-6Al-4V alloys are being used. These materials, with excellent weight-to-strength ratios, are widely used for structural applications in aircraft manufacturing. To date, several studies have been published showing that the use of metalworking fluids (MWFs), special tool geometries, or advanced machining techniques is required to ensure a surface quality that meets aerospace component standards. Conventional MWFs pose a number of environmental and worker health hazards and also degrade the mechanical properties of CFRPs due to water absorption in the composite. Therefore, a transition to more environmentally friendly cooling/lubrication techniques that prevent moisture problems in the composite is needed. This research shows that lubricated LCO2 is a viable option to improve the quality of drilled CFRP and titanium aerospace components compared to dry machining, while maintaining clean work areas. The results show that the best combination of tool geometry and cooling conditions for machining both materials is drilling with Brad point drills and lubricated LCO2. Drilling under these conditions resulted in a 90 % improvement in fiber pull-out volume compared to dry machined CFRP holes. In addition, a 33 % reduction in burr height and a 15 % improvement in surface roughness were observed compared to dry drilling of titanium
Lessons, narratives, and research directions for a sustainable circular economy
Full text linkThe current enthusiasm for the circular economy (CE) offers a unique opportunity to advance the impact of research on sustainability transitions. Diverse interpretations of CE by scholars, however, produce partly opposing assessments of its potential benefits, which can hinder progress. Here, we synthesize policy-relevant lessons and research directions for a sustainable CE and identify three narratives—optimist, reformist, and skeptical—that underpin the ambiguity in CE assessments. Based on 54 key CE scholars’ insights, we identify three research needs: the articulation and discussion of ontologically distinct CE narratives; bridging of technical, managerial, socio-economic, environmental, and political CE perspectives; and critical assessment of opportunities and limits of CE science–policy interactions. Our findings offer practical guidance for scholars to engage reflexively with the rapid expansion of CE knowledge, identify and pursue high-impact research directions, and communicate more effectively with practitioners and policymakers
skrl: Modular and Flexible Library for Reinforcement Learning
Full text linkoai:ebiltegia.mondragon.edu:20.500.11984/5602skrl is an open-source modular library for reinforcement learning written in Python and designed with a focus on readability, simplicity, and transparency of algorithm implementations. Apart from supporting environments that use the traditional OpenAI Gym interface, it allows loading, con guring, and operating NVIDIA Isaac Gym environments, enabling the parallel training of several agents with adjustable scopes, which may or may not share resources, in the same execution.
The library's documentation can be found at https://skrl.readthedocs.io and its source code is available on GitHub at https://github.com/Toni-SM/skrl
Pattern selection for convective flow in a liquid bridge subjected to remote thermal action
Full text linkThe stability of thermocapillary/buoyant flows is affected by a remote thermal source. We present a nonlinear two-phase computational study of convection in a liquid bridge that develops under the action of Marangoni and buoyancy forces as well as under the influence of distant thermal disturbances. The gas phase (air) occupies a typical annular container holding a liquid bridge (n-decane, Pr = 14), and the disturbances are locally imposed in the form of hot/cold spots on the outer wall of the container. The hydrothermal wave instability and pattern selection have been explored for two temperature differences Δ���� by varying the intensity of thermal source Hf over a wide range. Not far from the critical point, in all the cases, the instability emerges in the form of a standing wave, but the azimuthal wavenumber depends on whether the external perturbation is caused by cooling (m = 2) or by heating (m = 1). Further into supercritical area, 45% above the threshold, in the region with thermal perturbations ⎯200<��������<50, the flow pattern comprises, but is not limited to, a hydrothermal traveling wave with the azimuthal wavenumber m = 2. For hotter perturbations, the instability develops either in the form of traveling or standing waves, depending on Hf, with the prevailing mode m = 1, but with a strong presence of other modes
Enhancing surface integrity of A7050-T7451 aluminium alloy by pneumatic machine hammer peening
Full text linkAerostructures withstand cyclic mechanical loads and therefore, their design must fulfil surface integrity and fatigue strength requirements. This paper studies the effect of pneumatic machine hammer peening on surface integrity of 7050-T7451 aluminium alloy. Specimens were hammer peened using two different stepover distances (0.07 and 0.35 mm) and initial offset (0.3 and 0.5 mm). A Kistler dynamometer was used to measure the forces generated by hammer peening. Then, the surface topography, residual stresses and microstructural damage of the specimens were characterised. The results demonstrate that the magnitude of residual stresses and the thickness of the affected layer increases when reducing the stepover distance, while surface roughness reduces. Additionally, none of the tested conditions produced microstructural defects. These findings suggest that pneumatic hammer peening is an additional process to manufacture thin-walled structural aluminium alloy components
UX-for Smart-PSS: Towards a Context-Aware Framework
Full text linkSmart-product service systems are a business strategy that combines product and service into one value proposition. The user experience of digital services and the smart product can be a clear differentiator among competitors to achieve economically sustainable solutions. Hence, offering a more personalized experience is an important aspect of S-PSS. This paper aims to provide a theoretical framework for a context-aware user experience in S-PSS by providing adaptive and personalized services to the users according to their needs in a given context, by exploiting the digital capabilities of smart products and referring to the use of recommendation systems. The paper presents an application scenario using a smart-wearable as an example of a product-oriented PSS to better describe the framework and each component while stating the future challenges
Goal-Conditioned Reinforcement Learning within a Human-Robot Disassembly Environment
Full text linkThe introduction of collaborative robots in industrial environments reinforces the need to provide these robots with better cognition to accomplish their tasks while fostering worker safety without entering into safety shutdowns that reduce workflow and production times. This paper presents a novel strategy that combines the execution of contact-rich tasks, namely disassembly, with real-time collision avoidance through machine learning for safe human-robot interaction. Specifically, a goal-conditioned reinforcement learning approach is proposed, in which the removal direction of a peg, of varying friction, tolerance, and orientation, is subject to the location of a human collaborator with respect to a 7-degree-of-freedom manipulator at each time step. For this purpose, the suitability of three state-of-the-art actor-critic algorithms is evaluated, and results from simulation and real-world experiments are presented. In reality, the policy’s deployment is achieved through a new scalable multi-control framework that allows a direct transfer of the control policy to the robot and reduces response times. The results show the effectiveness, generalization, and transferability of the proposed approach with two collaborative robots against static and dynamic obstacles, leveraging the set of available solutions in non-monotonic tasks to avoid a potential collision with the human worker
How-to conduct a systematic literature review: A quick guide for computer science research
Full text linkPerforming a literature review is a critical first step in research to understanding the state-of-the-art and identifying gaps and challenges in the field. A systematic literature review is a method which sets out a series of steps to methodically organize the review. In this paper, we present a guide designed for researchers and in particular early-stage researchers in the computer-science field. The contribution of the article is the following:
• Clearly defined strategies to follow for a systematic literature review in computer science research, and
• Algorithmic method to tackle a systematic literature review
Bateratzen: Empresas Competitivas y Personas Comprometidas
Full text linkLas claves para la transición hacia nuevos modelos organizativos de alta implicación: Aprendizajes de una década de investigación
Sensitivity Analysis of Various Geometries of PCD and Cemented Tungsten Carbide Cutting Tools during the Milling of GFRP Composite
Full text linkAlthough much research has been carried out in the field of the milling of GFRP (Glass Fibre Reinforced Polymer) composites, the complexity of the process is such that it is still not mastered in many industrial cases. The current work is aimed at studying the influence of three different geometries of PCD (PolyCrystalline Diamond) and cemented tungsten carbide cutting tools during the up-milling of GFRP composites at fixed cutting conditions (vc = 502 m/min and vf = 420 mm/min). Delamination, cutting forces and tool wear are compared at the fresh and worn states, and the correlation between the lifespan and the cost of the cutting tool is analysed. The main wearing phase of the tools was performed under the conditions of production in the facilities of a company (Sobelcomp, Loncin, Belgium). The results indicate that the PCD tool with the straight edge, inclined peripheral tooth shape produces the smallest total cutting force and less delamination (shortest and lowest number of delaminated fibres) at both fresh and worn states. Moreover, the grinding ability of PCD makes the cutting tool cost per part lower than for cemented carbide. The PCD tool is therefore the best option to mill GFRP parts