Optimization of the vibration isolation performance of machines using advanced materials

The precision of mechanical processing depends, among others, on the dynamic behavior of the machine used. The dynamic behavior is dictated, besides the construction characteristics, from the foundation of the machine. The foundation isolates firstly, the dynamic strain induced on the machine from the surrounding and secondly, the vibration that itself generates and spreads on the mechanical structures in its vicinity. Vibration isolation aims towards the protection of an equipment from intensive external shocks and vibrations as well as from occasional disturbances caused by the equipment itself along with the reduction of noise and vibration level in a workshop area. There is a wide set of structural components or assemblies for which vibration is directly related to performance, either by virtue of causing temporary malfunction during excessive motion or by creating disturbance or discomfort, such as stress fatigue failure, premature wear, operator discomfort, unsafe operating condition and high noise levels. For all these potential problems, it is important that the in-service or operation vibration levels that usually encountered in structures have to be predicted and brought under satisfactory control. Thus, it is vital to determine the elastic material properties and the modal parameters, i.e. damped natural frequencies of the structure to avoid resonance, damping factors and mode shapes to reinforce the most flexible points or to determine the exact points so to reduce weight or to increase damping. With respect to these dynamic aspects, nano-reinforced polymeric composites represent an excellent possibility to design components considering the requirements of the dynamic behaviour. Lately much attention has been devoted to the development of polymers in which nanomaterials are embedded in order to improve their mechanical and dynamic properties. However, for the determination of the dynamic properties of high loss factor polymers, it is imperative to apply a mathematical model fitting the experimental data of modal tests. Therefore, the objective of the current thesis is to demonstrate an efficient modal testing method for the investigation of the dynamic mechanical properties of polymeric composite materials. This method utilizes vibration tests in order to measure experimental transfer functions (TFs) as a correlation parameter to analytical-experimental determined TFs. The procedure for the identification of analytical-experimental transfer functions is carried out using a genetic algorithm (GA) by minimizing the difference between the measured data from tests and the calculated response, which is a function of the modal parameters. For the determination of the vibration isolator’s characteristics a Finite Element Model (FEM) was introduced which represents the system machine-isolator-ground. A series of experiments were conducted on a real machine with a proposed optimal set of nanocomposite mounts and the analytical-experimental transfer functions of the system machine-isolator-ground were determined. Finally, this procedure was repeated for different nanofiller concentrations in the polymeric matrix of the nanocomposite mounts, until the optimization of the dynamic characteristics was achieved and the most suitable isolator was proposed as optimal.Η δυναμική συμπεριφορά μηχανών και μηχανικών διατάξεων είναι άμεσα συνυφασμένη με την απόδοση τους. Η επίδραση του δυναμικού φαινομένου είναι πολύ σημαντική για την ασφαλή λειτουργία μιας μηχανής και για τη βελτιστοποίηση των προϊόντων της. Η επίτευξη της ακρίβειας εξαρτάται μεταξύ άλλων και από τη δυναμική συμπεριφορά της μηχανικής διάταξης. Αποτέλεσμα των ταλαντωτικών φαινομένων είναι οι διάφορες ανεπιθύμητες δονήσεις, οι οποίες επηρεάζουν την ίδια τη μηχανολογική κατασκευή αλλά και το περιβάλλον μέσα στο οποίο λειτουργεί. Συχνά προβλήματα είναι η πρόκληση προσωρινής δυσλειτουργίας λόγω υπερβολικής ταλάντωσης και η δημιουργία διαταραχών όπως αστοχία από κόπωση, πρόωρη φθορά, δυσφορία στο χειριστή, μη ασφαλείς συνθήκες εργασίας και υψηλά επίπεδα θορύβου. Για όλα τα παραπάνω πιθανά προβλήματα, είναι σημαντική η πρόβλεψη του εύρους των ταλαντώσεων μιας κατασκευής, ώστε να περιοριστούν. Η δυναμική απόκριση μιας μηχανικής διάταξης υπαγορεύεται εκτός από την κατασκευαστική της διαμόρφωση και από τις συνθήκες έδρασής της. Με την κατάλληλη έδραση επιδιώκονται αφενός ο περιορισμός της μετάδοσης των δυναμικών διεγέρσεων που προκαλεί η ίδια η μηχανή ή αυτών που δέχεται από το περιβάλλον και αφετέρου επιτυγχάνεται η απαιτούμενη ακρίβεια στην κατεργασία και στις μετρήσεις ελέγχου. Στόχος της διδακτορικής αυτής διατριβής αποτελεί η χρήση καινοτόμων νανοϋλικών για την ανάπτυξη πολύ-λειτουργικών νανοσύνθετων υλικών και την εφαρμογή τους για το βέλτιστο προσδιορισμό της έδρασης μηχανικών διατάξεων. Τα νανοσύνθετα υλικά πολυμερικής μήτρας έχουν προσελκύσει τις τελευταίες δύο δεκαετίες το ιδιαίτερο ενδιαφέρον της επιστημονικής κοινότητας, τόσο σε επίπεδο έρευνας όσο και σε σχέση με την τεχνολογική αξιοποίηση αυτών στον τομέα της βιομηχανίας. Η πρόκληση και το ενδιαφέρον στην ανάπτυξη νανοσυνθέτων υλικών πολυμερικής μήτρας είναι η εκμετάλλευση των μοναδικών μηχανικών ιδιοτήτων των νανοϋλικών για εφαρμοσμένα προβλήματα σε επίπεδο μακροδομής. Υλικά υψηλής μηχανικής απόδοσης προορίζονται για τεχνολογικά ανώτερες εφαρμογές και προσελκύουν τον ερευνητικό τομέα της σύγχρονης βιομηχανίας. Στην παρούσα διδακτορική διατριβή επιχειρείται ο αναλυτικός-πειραματικός προσδιορισμός των δυναμικών χαρακτηριστικών διάφορων νανοσύνθετων υλικών, με σκοπό την εφαρμογή των βέλτιστων για την αποφυγή μετάδοσης ταλαντώσεων μέσω της έδρασης μηχανολογικών κατασκευών. Αρχικά, τα ταλαντωτικά χαρακτηριστικά διάφορων νανοσύνθετων υλικών που χρησιμοποιούνται στην έδραση, προσδιορίζονται αναλυτικά από πειραματικά μετρημένες συναρτήσεις μετάδοσης με τη βοήθεια γενετικών αλγορίθμων. Για τον υπολογισμό των χαρακτηριστικών της έδρασης γίνεται χρήση ενός προσομοιωτικού μοντέλου πεπερασμένων στοιχείων που αντιπροσωπεύει το σύστημα μηχανή-έδραση-έδαφος. Στη συνέχεια διεξάγονται πειράματα σε πραγματική μηχανή με μία προτεινόμενη έδραση και προσδιορίζεται η συνάρτηση μετάδοσης του συστήματος μηχανή-έδραση-έδαφος. Ο βέλτιστος προσδιορισμός των ταλαντωτικών χαρακτηριστικών του προσομοιωτικού συστήματος γίνεται με τη βοήθεια ενός αναπτυγμένου γενετικού αλγόριθμου. Τέλος, παραλλάσσοντας τα δυναμικά χαρακτηριστικά της έδρασης επιτυγχάνεται η βελτιστοποίηση της γεωμετρικής της μορφής και των ταλαντωτικών χαρακτηριστικών της και προτείνεται η κατάλληλη

Vibration isolation performance of an elevator motor using Nitrile-Butadiene Rubber /Multi-Walled Carbon Nanotube composite machine mounts

The objective of this paper is to evaluate the vibration isolation performance of an elevator motor mounted on elastomeric nanocomposite mounts. A series of conventional acrylonitrile-butadiene rubber (NBR) mounts have been reinforced with 20wt% concentration of multi-walled carbon nanotubes (MWCNTs). The vibration isolation capacity of the machine mounts was calculated through the transmissibility of an elevator motor test system. A Finite Element Model (FEM) was introduced and a harmonic analysis based on the ANSYS code has been utilized to investigate the modal behavior of the nanocomposite machine mount/elevator motor system and extract a representative model of the vibrational behavior. The cyclic compression results have revealed that the stiffness and damping capacity of the conventional elastomers can be modified by adjusting the proportion of MWCNTs. Elastomers’ vibration isolation performance of the motor was ameliorated with the inclusion of MWCNTs, signifying that the enhancement of the elastomers with MWCNTs was rather effective. The vibration level of the elevator motor was decreased to 90% by incorporating the optimal concentration of MWCNTs in NBR mounts

Mechanical and FEA-Assisted Characterization of Fused Filament Fabricated Triply Periodic Minimal Surface Structures

This paper investigates the mechanical behavior of additive manufactured Triply Periodic Minimal Surface (TPMS) structures, such as Gyroid, Schwarz Diamond and Schwarz Primitive. Fused Filament Fabrication (FFF) technique was utilized in order to fabricate lattice structures with different relative densities, at 10%, 20% and 30%, using Polylactic acid (PLA). The test specimens were formed by structural TPMS unit cells and they were tested under quasi-static compression. A finite element analysis (FEA) was performed in order to predict their stress-strain behavior and compare with the experimental results. The results revealed that each architecture influences the mechanical properties of the structure differently depending on the impact of size effect. The structures were designed as sandwich structures (with a top and bottom plate) to avoid significant deterioration of the mechanical behavior, due to the size effect and this was achieved at high relative densities. The Schwarz Diamond structure demonstrated the highest mechanical strength compared with the other architectures, while the Gyroid structure also revealed a similar mechanical performance. In addition, Schwarz Primitive structure showed increased energy absorption especially during plastic deformation. The overall results revealed that the integrity of the mechanical properties of the studied TPMS FFF printed structures deteriorates, as the relative density of the structures decreases

Finite Element Analysis of Orthopedic Hip Implant with Functionally Graded Bioinspired Lattice Structures

The topology optimization (TO) process has the objective to structurally optimize products in various industries, such as in biomechanical engineering. Additive manufacturing facilitates this procedure and enables the utility of advanced structures in order to achieve the optimal product design. Currently, orthopedic implants are fabricated from metal or metal alloys with totally solid structure to withstand the applied loads; nevertheless, such a practice reduces the compatibility with human tissues and increases the manufacturing cost as more feedstock material is needed. This article investigates the possibility of applying bioinspired lattice structures (cellular materials) in order to topologically optimize an orthopedic hip implant, made of Inconel 718 superalloy. Lattice structures enable topology optimization of an object by reducing its weight and increasing its porosity without compromising its mechanical behavior. Specifically, three different bioinspired advanced lattice structures were investigated through finite element analysis (FEA) under in vivo loading. Furthermore, the regions with lattice structure were optimized through functional gradation of the cellular material. Results have shown that optimal design of hip implant geometry, in terms of stress behavior, was achieved through functionally graded lattice structures and the hip implant is capable of withstanding up to two times the in vivo loads, suggesting that this design is a suitable and effective replacement for a solid implant

The mechanical performance of 3D printed hierarchical honeycombs using carbon fiber and carbon nanotube reinforced acrylonitrile butadiene styrene filaments

The aim of this paper is to design hierarchical honeycombs as well as manufacturing such structures with a commercial 3D Printer using Fused Filament Fabrication (FFF) technique. The materials under study are commercial filaments such as acrylonitrile butadiene styrene (ABS), acrylonitrile butadiene styrene/carbon fibers (ABS/CF) and acrylonitrile butadiene styrene/carbon nanotubes (ABS/CNTs). The fabricated hierarchical honeycombs were examined by compression tests in order to evaluate the mechanical behaviour of such honeycomb 3D printed structures. The compression behaviour of the hierarchical honeycombs was assessed also with finite element analysis (FEA) and at the end there was a comparison with the experimental findings. The results reveal that the 2nd order hierarchy presented an increase both in stiffness and strength in comparison with the 0th and the 1st hierarchies which make such designs a suitable for structures require such properties. Also, the results reveal that ABS/carbon fiber constructs outperform the other materials under study

The mechanical performance of 3D printed hierarchical honeycombs using carbon fiber and carbon nanotube reinforced acrylonitrile butadiene styrene filaments

The aim of this paper is to design hierarchical honeycombs as well as manufacturing such structures with a commercial 3D Printer using Fused Filament Fabrication (FFF) technique. The materials under study are commercial filaments such as acrylonitrile butadiene styrene (ABS), acrylonitrile butadiene styrene/carbon fibers (ABS/CF) and acrylonitrile butadiene styrene/carbon nanotubes (ABS/CNTs). The fabricated hierarchical honeycombs were examined by compression tests in order to evaluate the mechanical behaviour of such honeycomb 3D printed structures. The compression behaviour of the hierarchical honeycombs was assessed also with finite element analysis (FEA) and at the end there was a comparison with the experimental findings. The results reveal that the 2nd order hierarchy presented an increase both in stiffness and strength in comparison with the 0th and the 1st hierarchies which make such designs a suitable for structures require such properties. Also, the results reveal that ABS/carbon fiber constructs outperform the other materials under study

3D Printed Hierarchical Honeycombs with Carbon Fiber and Carbon Nanotube Reinforced Acrylonitrile Butadiene Styrene

The mechanical properties of Fused Filament Fabrication (FFF) 3D printed specimens of acrylonitrile butadiene styrene (ABS), ABS reinforced with carbon fibers (ABS/CFs) and ABS reinforced with carbon nanotubes (ABS/CNTs) are investigated in this paper using various experimental tests. In particular, the mechanical performance of the fabricated specimens was determined by conducting compression and cyclic compression testing, as well as nanoindentation tests. In addition, the design and the manufacturing of hierarchical honeycomb structures are presented using the materials under study. The 3D printed honeycomb structures were examined by uniaxial compressive tests to review the mechanical behavior of such cellular structures. The compressive performance of the hierarchical honeycomb structures was also evaluated with finite element analysis (FEA) in order to extract the stress-strain response of these structures. The results revealed that the 2nd order hierarchy displayed increased stiffness and strength as compared with the 0th and the 1st hierarchies. Furthermore, the addition of carbon fibers in the ABS matrix improved the stiffness, the strength and the hardness of the FFF printed specimens as well as the compression performance of the honeycomb structures

Corn Starch-Based Sandstone Sustainable Materials: Sand Type and Water Content Effect on Their Structure and Mechanical Properties

A new biodegradable, sustainable and environmentally friendly building material is introduced and studied in this work, which can be applied to lightweight architectural structures, aiming for the reduction of the greenhouse gas emissions and mitigation of the climate change effects. The focus was to investigate the effect of water concentration and different types of sand on the mechanical properties of corn starch-based artificial sandstone. A series of cubic, cylindrical and disk specimens were prepared by varying the concentration of water and using different sources of commercial quartz sand. The quasi-static and cyclic compressive properties of starch-based artificial sandstone samples were measured as a function of water concentration and sand type, while the structure of the artificial sandstone specimens was examined by scanning electron microscopy (SEM) and optical microscopy. Moreover, the Brazilian Test was employed as the indirect method to determine the tensile strength of the samples based on the type of the commercial sand they contained. The experimental results showed that the homogeneous grading of sand grains and the latter’s chemical composition have a significant effect on the mechanical properties of the sandstone samples. The highest compression values were obtained using the microwave heating method at a water concentration of about 12 wt%, while the cyclic compression and Brazilian Tests have shown that the granulometric grading of the sand particles and the chemical composition of the sand influence the compressive and tensile strength of the material

Architected Materials for Additive Manufacturing: A Comprehensive Review

One of the main advantages of Additive Manufacturing (AM) is the ability to produce topologically optimized parts with high geometric complexity. In this context, a plethora of architected materials was investigated and utilized in order to optimize the 3D design of existing parts, reducing their mass, topology-controlling their mechanical response, and adding remarkable physical properties, such as high porosity and high surface area to volume ratio. Thus, the current re-view has been focused on providing the definition of architected materials and explaining their main physical properties. Furthermore, an up-to-date classification of cellular materials is presented containing all types of lattice structures. In addition, this research summarized the developed methods that enhance the mechanical performance of architected materials. Then, the effective mechanical behavior of the architected materials was investigated and compared through the existing literature. Moreover, commercial applications and potential uses of the architected materials are presented in various industries, such as the aeronautical, automotive, biomechanical, etc. The objectives of this comprehensive review are to provide a detailed map of the existing architected materials and their mechanical behavior, explore innovative techniques for improving them and highlight the comprehensive advantages of topology optimization in industrial applications utilizing additive manufacturing and novel architected materials