1,720,978 research outputs found
GREEN TRIBOLOGY: WEAR EVALUATION METHODS FOR SUSTAINABILITY PURPOSES
No full textA sustainable development of machines, mechanisms and processes is one of the main goals of the 2030 agenda for Sustainable Development Goals (SDG). Currently, approximately 23% of the global energy consumption depends on inefficient performance of the tribological contacts. Particularly, about 20% of the energy loss is due to friction issues, and the remaining part is employed to remake and replace worn parts or to fix other wear-related failures. Green tribology is a crucial discipline for enhancing sustainability, because it is oriented at minimizing friction and wear phenomena. Therefore, wear evaluation is a fundamental starting point for designing new production or diagnostic techniques oriented to sustainability. In the industrial field this allows the optimization of design and processes, leading to reduction of pollution, minimization of energy dissipation and costs (SDG9, SDG12). In the field of human life, this can give a strong contribution to prevent damages, extending resistance and useful life of natural or prosthetic biocomponents, with an improvement of health and better life generation (SDG3). This paper presents and discusses various wear evaluation methods and related workflows with different purposes and benefits for sustainability. Some case studies demonstrate that wear evaluation substantially contributes at creating sustainable products and applications
A numerical procedure based on orowan's theory for predicting the behavior of the cold rolling mill process in full film lubrication
No full textIn this paper, a numerical model for predicting the working parameters of the cold rolling
mill process in full film lubrication is presented. The model is useful from an industrial point
of view, because it can forecast the thickness reduction of the metal sheet and the pressure trend,
so that the rolling mill process parameters can be regulated to obtain a specific output thickness.
Experimental tests were performed, and results are compared to the theoretical ones resulting from
the model. The novelty of the proposed model is that it combines Orowan’s theory for the plastic
deformation analysis with the Reynolds equation in full film lubrication and the continuity conditions.
The lubricant flow and viscosity are studied, taking in account their dependence on pressure and
temperature. The proposed model describing the full film regime is also compared to another one,
previously proposed by the authors, based on the well-known slab analysis and sharing with it the
representation of the lubrication regime, the mathematical procedure, and the boundary conditions.
The results show that the proposed model provides a better prediction of the working parameters
with respect to the model based on the slab analysi
Sustainable Design of Machine Guards
No full textPromoting sustainable industrialization by fostering safety of machinery is a fundamental and ethical approach. Working in safe conditions is essential to comply with the UN’s Sustainable Development Goals (SDG) and, in particular, with SDG3 and SDG8, therefore making machines safer during their operation becomes a basic aim for a more sustainable society. From this perspective, the influence of certain design or/and physical parameters on machine safety must be necessarily analyzed even if standards do not consider them, with obvious advantages also in terms of industrial innovation, complying with SDG9. The present work refers to the study of machine protection panels to characterize their ability to resist ballistic penetration. In ISO 14120-Annex B, the methodologies and standards for the design and validation of machine guards are described, but the influence of many characteristics and parameters has not been considered to characterize the protection performance. This paper presents some results in the terms of withstanding capacity of polycarbonate panels to ballistic penetration considering the size of the guards and their ageing condition due to solar radiation. The analyses for the inspection of the through-hole cracks and deformation of the panels have been performed with an innovative method by using a metrology grade 3D optical scanner and 3D inspection techniques
Metal transfer evaluation on ceramic biocomponents: A protocol based on 3D scanners
No full textTitanium signs frequently appear on femoral heads coupled with metal back acetabular components, after dislocation or repositioning of total hip arthroplasties. These metallic deposits, called metal transfer, are a significant clinical phenomenon because they can affect the resistance and tribological performance of the prosthesis. The quantification and the study of position of the metal transfer extent over a prosthesis surface is a scientific problem to be addressed to design more effective replacements. This paper proposes a new protocol to evaluate the metal transfer amount, employing 3D optical scanners, and reverse engineering software. The technique allows the assessment of metal transfer rates, absolute areal coverage, and position of the metal deposits by acquiring the 3D digital colored model of the hip ball surfaces with high-precision 3D scanners, and separating the regions with metallic depositions by 3D mesh processing. Results permit to evaluate effects on the tribological behavior of the synovial biobearing
Contact mechanics analysis of a soft robotic fingerpad
Full text linkThe precision grasping capabilities of robotic hands is a key feature which is more and more required in the manipulation of objects in several unstructured fields, as for instance industrial, medical, agriculture and food industry. For this purpose, the realization of soft robotic fingers is crucial to reproduce the human finger skills. From this point of view the fingerpad is the part which is mostly involved in the contact. Particular attention must be paid to the knowledge of the mechanical contact behavior of soft artificial fingerpads. In this paper, artificial silicone fingerpads are applied to the last phalanx of robotic fingers actuated by tendons. The mechanical interaction between the fingerpad and a flat surface is analyzed in terms of deformations, contact areas and indentations. A reliable model of fingertip deformation properties provides important information for understanding robotic hand performance, that can be useful both in the design phase and for defining control strategies. The approach is based on theoretical, experimental, and numerical methods. The results will be exploited for the design of more effective robotic fingers for precision grasping of soft or fragile objects avoiding damages
Roughness digital characterization and influence on wear of retrieved knee components
No full textTribological performance of knee components are strongly related to the surface character-istics. Primarily, the roughness and its 3D distribution on the surfaces affect the joint performance. One of the main limitations related to the tribological study of knee prostheses is that most of the research studies report in vitro or in silico results, as knee retrievals are difficult to find or are too damaged to be analyzed. This paper is focused on the roughness characterization of retrieved metal femoral components of total knee replacements (TKR) by means of a rugosimeter and involving digital methods to reconstruct the 3D topography of the studied surfaces. The aim of this study is to investigate how changes and distribution of roughness are correlated between the medial vs. the lateral part and how the resulting digital topography can give insights about the wear behavior
Does metal transfer differ on retrieved Biolox®Delta composites femoral heads? Surface investigation on three Biolox®generations from a biotribological point of view
No full textBackground: Currently, little is known about the effects that metal transfer affecting hip implants may have on roughness. The main aim of this study is to propose a metrological technique in order to better characterize this phenomenon on the surface of composite ceramic femoral heads, discussing its influence on the biotribological behaviour of the coupling. In addition, through the acquired data, we investigate whether the metal transfer extension and roughness alterations on a femoral head is correlated to the material, the follow-up of the implant and whether metal transfer is associated with changes in the roughness of alumina surface, considering different follow-ups.Methods: Three generations of femoral heads manufactured in ceramic (Biolox (R), Biolox (R) Forte, and Biolox (R) Delta) were retrieved from patients after different implantation periods (mean follow up = 6.9 years) and they were analysed using a roughness tester and an optical non-contact 3D scanner, in order to characterize the metal transfer on the bearing surface.Results: Surface area where the metal transfer was observed ranged between 29.6 mm(2) and 573.6 mm(2). The mean values of Sa (average roughness) were different between the Affected Zone (0.3 +/- 0.1 mu m) and Unaffected Zone (0.03 +/- 0.1 mu m). In particular, regions of metal transfer were rougher than the non-metal transfer regions of the articular surface and this is demonstrated by both the areal roughness parameters considered: Sa (arithmetic mean height) and St (maximum height of the surface) parameters (p = 0.002, Wilcoxon paired-test). St parameter acquired on the Biolox (R) Delta femoral heads showed the lowest mean value (11.92 mu m).Conclusion: We found no correlation between follow-up vs. roughness and total surface area of metal transfer. Furthermore, we found that the amount of areal coverage of metal transfer is correlated with the surface roughness. Finally, MT effect on composite ceramic implants caused lower height of peaks and valleys when compared to common ceramic. (C) 2017 Elsevier Ltd. All rights reserved
An Educational Test Rig for Kinesthetic Learning of Mechanisms for Underactuated Robotic Hands
No full textTeaching robotics requires interdisciplinary skills and a good creativity, providing instructions and hands-on experiences, exploiting different kinds of learning. Two kinds of learning methods are commonly used: the ‘visual learning’ and the ‘auditory learning’, recognizable by the preference of an approach for images, rather than for texts, or oral explanations. A third possible learning style is the ‘kinesthetic learning’, based on tactile activities, which is generally least exploited, both by teachers in the classroom and by students during individual study. In this perspective, the use of educational test rigs is a good practice and adds an opportunity to share a passion for robotics. The paper focuses on the realization and application of an educational test rig aimed at explaining how a differential mechanism works and how it can be applied to robotic underactuated soft grippers to move multiple robotic fingers independently of each other using just a single actuator. The differential test bench was realized by 3D printing and mounted with the help of students in high school seminaries oriented to encourage students towards robotic or mechatronic studies. This activity was very thrilling for the students and helped them to approach robotics in a natural way, exploiting kinesthetic learning as it is demonstrated by test results
Intraoral scanners in dentistry: A review of the current literature
No full textBackground: Intraoral scanners (IOS) are devices for capturing direct optical impressions in dentistry. The purpose of this narrative review on the use of IOS was to: (1) identify the advantages/disadvantages of using optical impressions compared to conventional impressions; (2) investigate if optical impressions are as accurate as conventional impressions; (3) evaluate the differences between the IOS currently available commercially; (4) determine the current clinical applications/limitations in the use of IOS.Methods: Electronic database searches were performed using specific keywords and MeSH terms. The searches were confined to full-text articles written in English and published in peer-reviewed journals between January 2007 and June 2017.Results: One hundred thirty-two studies were included in the present review; among them, 20 were previous literature reviews, 78 were in vivo clinical studies (6 randomized controlled/crossover trials, 31 controlled/comparative studies; 24 cohort studies/case series; 17 case reports) and 34 were in vitro comparative studies.Conclusions: Optical impressions reduce patient discomfort; IOS are time-efficient and simplify clinical procedures for the dentist, eliminating plaster models and allowing better communication with the dental technician and with patients; however, with IOS, it can be difficult to detect deep margin lines in prepared teeth and/or in case of bleeding, there is a learning curve, and there are purchasing and managing costs. The current IOS are sufficiently accurate for capturing impressions for fabricating a whole series of prosthetic restorations (inlays/onlays, copings and frameworks, single crowns and fixed partial dentures) on both natural teeth and implants; in addition, they can be used for smile design, and to fabricate posts and cores, removable partial prostheses and obturators. The literature to date does not support the use of IOS in long-span restorations with natural teeth or implants. Finally, IOS can be integrated in implant dentistry for guided surgery and in orthodontics for fabricating aligners and custom-made devices
Knee Wear Assessment: 3D Scanners Used as a Consolidated Procedure
No full textIt is well known that wear occurring in polyethylene menisci is a significant clinical problem. At this regard, wear tests on biomaterials medical devices are performed in order to assess their pre-clinical performance in terms of wear, durability, resistance to fatigue, etc. The objective of this study was to assess the wear of mobile total knee polyethylene inserts after an in vitro wear test. In particular, the wear behavior of mobile bearing polyethylene knee configurations was investigated using a knee joint wear simulator. After the completion of the wear test, the polyethylene mobile menisci were analyzed through a consolidated procedure by using 3D optical scanners, in order to evaluate the 3D wear distribution on the prosthesis surface, wear depths, wear rates, amount of material loss and contact areas. The results in terms of wear rates and wear volumes were compared with results of gravimetric tests, finding equivalent achievements
- …
