Absorptivity measurements during laser powder bed fusion of pure copper with a 1 kW cw green laser
Publisher : Elsevier Ltd
A 1 kW CW green laser source operating at 515 nm was used to investigate the absorptivity of pure copper powder beds and pure copper substrates. Various interaction regimes were considered, ranging from the solid and/or powder layers, to the liquid state and up to the deep penetration keyhole regime. Reflectance measurements were carried out using an Ulbricht integrating sphere during static tests and single L-PBF tracks. For each experiment, absorptivity values were discussed using the real penetration depth observed on cross-section. Absorptivity values were found to be in relatively good agreement with analytical models of the powder bed and the keyhole regime absorptivity. Such results provide useful insight on the use of green wavelengths for the optimization of the L-PBF process on highly reflective and conductive materials like copper.
Which typical floor movements of men’s artistic gymnastics result in the most extreme lumbar lordosis and ground reaction forces?
Publisher : Taylor & Francis Online
Back pain is prevalent among gymnast populations and extreme flexion or extension of the lumbar spine along with high ground reaction forces (GRFs) are known to increase intervertebral stress. The aim of this study was to determine which postures and dynamic conditions among common floor movements provide the greatest risk of injury in men’s artistic gymnastics (MAG). For this purpose, lumbar spine curvatures, obtained through a full-body subject-specific kinematic model fed by motion capture data, and GRFs on feet and hands were compared between typical floor movements of MAG (pike jump, round off back handspring, front handspring, forward and backward tucked somersaults) performed by six adolescent gymnasts. The round off back handspring and the pike jump resulted respectively in the largest lumbar extension and flexion, and the forward tucked somersault take-off in the highest GRF. At ground impacts, the largest lumbar flexion was during the backward tucked somersault landing and only the back handspring hands ground contact phase led to lumbar extension. Such identification of high-risk conditions should enable better back pain management in gymnastics through more tailored training adaptations, particularly in case of pathologies or musculoskeletal specificities.
Analyzing Intra-Cycle Velocity Profile and Trunk Inclination during Wheelchair Racing Propulsion
Publisher : MDPI AG
The analysis of intra-cycle velocity profile of manual wheelchair (MWC) users has been used to highlight the significant role of trunk inertia in propulsion biomechanics. Maximal wheelchair linear velocity has previously been observed to be reached after the release of the handrims both during sports activities and daily life propulsion. This paper provides a combined analysis of linear velocity and trunk kinematics in elite wheelchair racing athletes during straight-line propulsion at stabilized speeds. MWC and trunk kinematics of eight athletes (level: 7 elite, 1 intermediate; classification: T54 (5), T53 (2) and T52 (1)) were monitored during 400 m races using inertial measurement units. An average propulsion cycle was computed for each athlete. The main finding of this article is the difference in propulsion patterns among the athletes, exhibiting either 1, 2 or 3 peaks in their velocity profile. A second peak in velocity is usually assumed to be caused by the inertia of the trunk. However, the presence of a second velocity peak among more severely impaired athletes with little to no trunk motion can either be associated to the inertia of the athletes’ arms or to their propulsion technique.
Miniature laser powder bed fusion system for in situ synchrotron x-ray micro-computed tomography experiments at the European Synchrotron Radiation Facility
Publisher : AIP Publishing
We describe our miniature laser powder bed fusion (L-PBF) system for in situ synchrotron x-ray micro-computed tomography (XCT) at the European Synchrotron Radiation Facility. This replicator was designed to extend the characterization of L-PBF to 3D. This instrument fills in a technical gap because the existing replicators were mostly designed to shed light on the dynamic mechanisms involved in molten pool formation but, therefore, suffered from a lack of 3D information. Technical details regarding the setup and beamline integration are given. Experimental validations via post-mortem XCT scans and in situ scans acquired during experiments conducted at the BM05 beamline of the European Synchrotron Radiation Facility are provided. Based on a few illustrative examples, we show that such a replicator opens the path to collect key 3D information that to date could not be available. Our miniature instrument complements the other replicators developed in the world by other research groups that enable operando x-ray imaging (radiography) and operando x-ray diffraction.
Finite element mesh generation for nano-scale modeling of tilted columnar thin films for numerical simulation
Glancing Angle Deposition (GLAD) is a technique used in Physical Vapor Deposition (PVD) to prepare thin films with specific properties. During the deposition process, a tilt is introduced between the sputtered atoms flux and the normal of the substrate surface. By shadowing effect, this induces tilted nano-columns that affect the properties of the coating. To predict these properties, several existing tools simulate the different steps of the PVD deposition. First, a simulation of the sputtering of atoms from a metallic target is made, followed by the computation of the atoms transportation from the target to the substrate. Finally, the growth of the film is computed. All these simulations use point based representation to represent the deposited atoms. However, such representation is not suited for classical finite elements analysis (FEA).
In this paper, a methodology for generating FEA meshes from the points produced by film growth simulation is presented. Two major scientific challenges are overcome. Firstly, how to segment the ”film” point cloud into a collection of individual “columns” and secondly, how to generate the meshes of the columns that are approximately represented by points. The point cloud segmentation is computed through neighbourhood notion. The mesh is obtained as an implicit surface by the marching cubes algorithm and smoothed by a Humphrey’s class Laplacian algorithm. Numerical simulations based on the generated FEA meshes will be conducted using Abaqus FEA software.
Intent Detection for Virtual Reality Architectural Design
In the context of optimization and reduction of cycles of product design in indus-try, digital collaborative tools have a major impact allowing an early-stage integra-tion of multidisciplinary challenges and oftentimes the search of global optimum rather than domain specific improvements. This paper presents a methodology for improving participants’ implication and performance during collaborative design sessions through virtual reality (VR) tools thanks to intention detection through body language interpretation and thus, reduction of cognitive workload. A proto-type of the methodology is being implemented based on an existing VR aided de-sign tool called DragonFly developed by Airbus. We will first discuss the choice of the different biological inputs to choose for our purpose, and how to merge these multimodal inputs in a meaningful way in order to ease further evolution and maintenance of our solution. Then, we will focus on the extraction of these inputs, their preprocessing, and the inference of intent and associated parameters. Finally, we will show the beginning of the application of this methodology to our specific use case of aircraft system installation.
On the Use of Quality Metrics to Characterize Structured Light-based Point Cloud Acquisitions
Even if 3D acquisition systems are nowadays more and more efficient, the resulting
point clouds nevertheless contain quality defects that must be taken into account
beforehand, in order to better anticipate and control their effects. Assessing the quality of
3D acquisitions has therefore become a major issue for scan planning. This paper presents
several quality metrics that are then studied to identify those that could be used to optimize
the acquisition positions to perform an automatic scan. From the experiments, it appears
that, when considering multiple acquisition positions, the coverage ratio and score indicator
have significant changes and can be used to evaluate the quality of the measurements. Differently,
other indicators such as efficacy ratio, registration error and metrological characteristics
are insensitive to some acquisition positions
General framework of geometric simplification for mitigating cybersickness
Publisher : IEEE
Virtual reality have advanced rapidly and are spreading in much of the world for huge numbers of application domains. However the cybersickness appears for many VR users and it is still a significant issue preventing them to feel free to use VR technology. In most of VR experience, the immersive display system can provoking much more self-motion perceived by eyes than the one given by vestibular systems. Through the sensory conflict theory, the mismatch in visual and vestibular sense causes sickness. In this paper a general framework for applying geometric simplification on the virtual scene is proposed with the aim of lowering the visually induced self-motion that can be quantified by optic flow analyzed on the rendered images. The synthetized image that includes original scene at central part and simplified scene at peripheral part, are rendered to VR users. The analyzed optic flow on the synthetized images is much less than the one given by the original images.
Influence of Anodized Titanium Surfaces on the Behavior of Gingival Cells in Contact with: A Systematic Review of In Vitro Studies
Publisher : MDPI AG
Electrochemically anodized (EA) surfaces promise enhanced biological properties and may be a solution to ensure a seal between peri-implant soft tissues and dental transmucosal components. However, the interaction between the modified nano-structured surface and the gingival cells needs further investigation. The aim of this systematic review is to analyze the biological response of gingival cells to EA titanium surfaces in in vitro studies with a score-based reliability assessment. A protocol aimed at answering the following focused question was developed: “How does the surface integrity (e.g., topography and chemistry) of EA titanium influence gingival cell response in in vitro studies?”. A search in three computer databases was performed using keywords. A quality assessment of the studies selected was performed using the SciRAP method. A total of 14 articles were selected from the 216 eligible papers. The mean reporting and the mean methodologic quality SciRAP scores were 87.7 ± 7.7/100 and 77.8 ± 7.8/100, respectively. Within the limitation of this review based on in vitro studies, it can be safely speculated that EA surfaces with optimal chemical and morphological characteristics enhance gingival fibroblast response compared to conventional titanium surfaces. When EA is combined with functionalization, it also positively influences gingival epithelial cell behavior.
Contribution to the design of reconfigurable multi-product assembly systems by architecture solutions generation through a new locating-driven approach
Publisher : Elsevier BV
Production companies are today faced with increasing product varieties, shortened development times and product life cycles, and decreasing lot sizes. Reconfigurable manufacturing and assembly have been developed as new manufacturing paradigm to face this challenging market environment. However, the aspects of enabling multi-product assembly and operational reconfiguration are rarely addressed. This article presents a new approach, aiming at this research potential: the use of component locating in the center of a new assembly system design method around component locating modules. It is detailed how the use of component locating allows the generation of a system architectures solution space. To support the application
of locating strategies, a new model, the precedence-locating graph, is introduced. The approach is described with an illustrative example and the new concept has been tested on an industrial case study in the automotive industry which can only be mentioned partially due to confidentiality issues.