1,720,972 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
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
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
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
Design of soft grippers with modular actuated embedded constraints
No full textUnderactuated, modular and compliant hands and grippers are interesting solutions in grasping and manipulation tasks due to their robustness, versatility, and adaptability to uncertainties. However, this type of robotic hand does not usually have enough dexterity in grasping. The implementation of some specific features that can be represented as “embedded constraints” allows to reduce uncertainty and to exploit the role of the environment during the grasp. An example that has these characteristics is the Soft ScoopGripper a gripper that has a rigid flat surface in addition to a pair of modular fingers. In this paper, we propose an upgraded version of the Soft ScoopGripper, developed starting from the limits shown by the starting device. The new design exploits a modular structure to increase the adaptability to the shape of the objects that have to be grasped. In the proposed device the embedded constraint is no rigid neither unactuated and is composed of an alternation of rigid and soft modules, which increase versatility. Moreover, the use of soft material such as thermoplastic polyurethane (TPU) reduces the risk of damage to the object being grasped. In the paper, the main design choices have been exploited and a finite element method (FEM) analysis through static simulation supports a characterization of the proposed solution. A complete prototype and some preliminary tests have been presented
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
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
Three-Dimensional Experimental Analysis of Wear in Retrieved Hip Implants
No full textWear is recognized as one of the main causes of hip replacement failure, as it can lead to instability, pain, and revision surgeries. Consequently, numerical and experimental wear investigations on hip implants are highly relevant in biomedical and orthopedic research. This study is focused on the application of advanced experimental analyses for wear characterization of hip replacements and presents an innovative and dedicated experimental wear assessment protocol based on 3D scanners. The method was tested on retrieved metal-on-plastic hip implants and provided 3D wear maps of the damaged surfaces of both the cup and head. Some preliminary results obtained on a plastic cup are here presented and discussed. The primary goal of these analyses is to understand the causes and mechanisms of wear so that prosthetic materials and designs can be improved, implant reliability, and patients’ quality of life enhanced. The research activity presented in this paper promotes more responsible production and consumption, making the biomedical sector more sustainable and resilient over time. Therefore, it contributes directly to the goals of sustainable development by improving health and well-being (SDG3), promoting technological innovation and reducing environmental impact (SDG9 and SDG12) with a reduction of material wastage and favoring recycling and waste management, improving collaboration between universities, research centers, biomedical industries, and hospitals (SDG17)
Development and validation of wear models by using innovative three-dimensional laser scanners
No full textOne of the main problems in railway and tramway systems, both dynamically (safety, comfort etc.) and economically (planning of maintenance interventions, reduction of wheel and rail lifetime etc.), is represented by the wear of wheel and rail profiles, due to the wheel–rail interaction. The profile’s shape variation caused by wear influences the dynamic behaviour of the vehicle and, in particular, the wheel–rail contact conditions. Hence, nowadays, one of the most important topics in the railway field is the development of reliable wear models to predict profiles evolution, together with the use of more efficient and accurate measuring instruments for the model validation and the rolling components inspection. In this context, the aim of this research work is the development and the validation of wear models, using experimental data acquired through an innovative measuring instrument based on noncontact three-dimensional laser scanning technology. The tramway line of the city of Florence, characterized by very narrow curves and critical in terms of wear, has been chosen as a reference test case. Moreover, the inspection procedures currently adopted on this line for the maintenance plan are based only on classical two-dimensional contact measurement systems, not so accurate for a complete wear assessment. Therefore, the introduction of a new three-dimensional laser scanning technology may have a great impact on the maintenance management of the line
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