MATERIALE PLASTICE

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Polymer plasma laser ablation has been investigated theoretically. An elegant mathematical tool using the fractal structure of space-time was developed. The model was verified with good accuracy on the existing experimental results.
 
The thermal properties of nanofilled and microfilled restorative composites (Filtek Supreme XT and Filtek Z250) are studied in comparison with the ones of teeth. Our results show slightly decreased values of the thermal constants of Filtek Supreme XT with respect of Filtek Z250, due to the smaller filler particle size. Both analyzed composite materials have the values of the thermal conductivity and diffusivity very close to the one of enamel, with the better fitting in the case of Filtek Supreme XT Comparing with the values for dentin, the thermal conductivity is about two times higher, while the thermal diffusivity is three times higher.
 
Common skeleton of 1,2,4-triazole
Synthesis of PU chains 
Antibacterial gels offer an efficient hygiene in the absence of soap and water. The most part of these products are based on mixtures of different antibacterial and fungicide substances dissolved in an alcohol. Unfortunately, all cosmetic products containing alcohols wash the sebum and dry the skin. In the present study, alcohol-free antibacterial hydrogels were obtained through the synthesis of polyurethane (PU) microstructures with an increased amount of surfactant; 5-mercapto-1,2,4-triazole derivatives were used as active compounds inside the PU microstructures as antibacterial agents. There were studied: the pH of samples, the size and stability of PU microstructures, the skin irritation, sebum level and the hydration of stratum corneum using the mouse model and their efficiency against Escherichia coli. The results indicate that were obtained hydrogels with a slightly acid pH, PU microstructures with sizes between 185 and 265 nm and with a medium stability. It was found that these new antibacterial hydrogels do not produce an important modification of skin parameters (erythema, melanin, sebum and hydration of stratum corneum) and are efficient against E. coli.
 
The aim of this study was to evaluate the role of local administration of vitamin D in influencing the rate of orthodontic tooth movement. Six dental arches were included in this study. Every arch was divided intro two hemiarches: experimental hemiarch and control hemiarch. The canines were included in this study. Control canines received orthodontic therapy compared with experimental canines which received orthodontic therapy associated with local administration of calcitriol (1,25 dihydroxycholecalciferol). The rate of tooth movement was measured in both hemiarches. We noticed a difference between the rates of orthodontic treatment in experimental and control hemiarches respectively. This might be attributed to local administration of calcitriol (1,25 dihydroxycholecalciferol).
 
A series of aromatic polysaccharides were synthesized by dihydrazides polycondensation with acid dichlorides, containing imide cycles and hexafluoraisopropylidene group. The thermal cyclization of these polyhydrazides to poly-1,3,4-oxadiazols was studied by IR spectroscopy, thermogravimetric and differential calorymetry analyses. The hydrazide gropups are cyclized in the 1,3,4 oxadiazol structure by heating at 280 degrees C, for 24 h, under vacuum. The cyclization reaction activation energy groups with the increase of the hydrazide groups conversion rate in oxadiazol cycles.
 
A series of aromatic polysaccharides were synthesized by dihydrazides polycondensation with acid dichlorides, containing imide cycles and hexafluoraisopropylidene group. The thermal cyclization of these polyhydrazides to poly-1,3,4-oxadiazols was studied by IR spectroscopy, thermogravimetric and differential calorymetry analyses. The hydrazide gropups are cyclized in the 1,3,4 oxadiazol structure by heating at 280°C, for 24 h, under vacuum. The cyclization reaction activation energy groups with the increase of the hydrazide groups conversion race in oxadiazol cycles.
 
A series of five new aromatic polyhydrazid.es containing pendent acetyloxybenzamide groups has been synthesized by low-temperature solution polycondensation of 5-(4-acetyloxybenzamido)-isophthaloyl chloride with dihydrazides of terephthalic, isophthalic, 2,5- or 2,6-pyridin dicarboxylic acids, or with p-aminobenzhydrazide in N-methyl-2-pyrrolidinone (NMP). These polyhydrazides were gradually thermally treated up to 280°C in order to be converted in corresponding poly(1,3,4-oxadiazole)s. The inherent viscosity of polyhydrazides is in the range of 0.31-0.69 dL/g. The polymer structures were confirmed by infrared spectra. The polymers were characterized from solubility and thermal properties point of view.
 
Thin films, in the range of tens of micrometers thickness, have been prepared by casting onto glass plates the chloroform or N-methylpyrrolidone solutions of poly(1,3,4-oxadiazole-ether)s. The polymers have been prepared by nucleophyilic substitution polymerization technique of 2,5-bis(p-fluorophenyl)- 1,3,4-oxadiazole with various aromatic bisphenols, such as 4,4′- isopropylidenediphenol, 4,4′-(1,4-phenylene-diisopropylidene)bisphenol or 4,4′-(hexafluoroiso-propylidene)diphenol. They showed high thermal stability with decomposition temperature above 410°C and glass transition temperature in the range of 187-211°C. The polymer films exhibited good mechanical properties with tensile strengths in the range of 36.92-44.50 MPa, tensile modulus in the range of 1.42-1.74 GPa and elongation at break in the range of 3-91%. Electrical insulating properties of polymer films were evaluated on the basis of dielectric constant. The values of the dielectric constant at 10 kHz were in the range of 2.98-3.18.
 
In this study, a new organic nucleating agent N, N -bis(stearic acid)-1,4-dicarboxybenzene dihydrazide (PASH) to improve crystallization behavior of poly(L-lactic acid) (PLLA) along with the effect of PASH on melting behavior, thermal stability of PASH-nucleated PLLA was holistically reported. The melt-crystallization process illustrated that PASH as an effective heterogeneous nucleating agent could boost PLLA�s crystallization rate, but increasing PASH concentration and cooling rate conversely inhibited melt-crystallization process of PLLA in this study. With respect to melt-crystallization process, a larger amount of PASH leaded to a shift of cold-crystallization peak to lower temperature level. Isothermal crystallization revealed, in comparison to pure PLLA, that the half time of overall crystallization of PLLA/PASH was significantly decreased with PLLA containing 3 wt% PASH having the minimum t1/2= 67.3 s at 105şC. The different melting behaviors of PLLA/PASH under different conditions were attributed to the nucleating effect of PASH within PLLA. In particular, the melting behavior at a heating rate of 10�C/min after isothermal crystallization depended primarily on the crystallization temperature. Whereas, the impact of crystallization time on melting behavior was negligible. Nonetheless, the melting behavior was influenced by the heating rate after non-isothermal crystallization. The thermal stability of PLLA was detrimental with the addition of PASH owing to a typical drop in onset thermal decomposition temperature.
 
In this work, biodegradable Poly(L-lactide) (PLLA) was modified through adding a new organic additive N, N -bis(benzoyl) 1, 4-naphthalenedicarboxylic acid dihydrazide (NABH). A comparison on crystallization of the pure PLLA and PLLA/NABH revealed that the NABH as effective heterogeneous nucleation sites enhanced PLLA𠏋 crystallization, and an increase of NABH loading was able to further accelerate crystallization rate of PLLA; whereas a faster cooling rate was not conducive to PLLA𠏋 crystallization, but the appearance of obvious crystallization peak upon cooling at 30şC/min confirmed the advanced enhancing role of NABH for PLLA crystallization again. The investigation on influence of the final melting temperature on the crystallization behavior of PLLA showed that the 170 şC was optimum final melting temperature for enhancing crystallization, even the onset crystallization temperature of PLLA/NABH were higher than 150şC. The melting processes of PLLA/NABH after different crystallization not only could reflect the previous crystallization, but also depended on crystallization temperature and heating rate. Thermal decomposition results showed that the existence of NABH slightly weakened thermal stability of PLLA, and the maximum difference in onset thermal decomposition temperature was only 9.4şC comparing with the pure PLLA. However, the presence of NABH in PLLA matrix seriously weakened optical property.
 
High resolution mass spectra, as well as fragmentation processes under electron impact for bis(2,4-dimethyl-5-amino-benzo[b] [1,8]-naphthyridines) 1 and bis(benzo[b] [1,8]naphthyridones) 2 linked by methylene linear chain are presented.
 
This paper presents and discusses research conducted with the purpose of developing the use of solar energy in the heat treatment of steels. For this, a vertical axis solar furnace called at Plataforma Solar de Almeria was adapted such as to allow control of the heating and cooling processes of samples made from 1.1730 steel. Thus temperature variation in pre-set points of the heated samples could be monitored in correlation with the working parameters: the level of solar radiation and implicitly the energy used the conditions of sample exposed to solar radiation, and the various protections and cooling mediums.The recorded data allowed establishing the types of treatments applied for certain working conditions. The distribution of hardness, as the representative feature resulting from heat treatment, was analysed on all sides of the treated samples. In correlation with the time-temperature-transformation diagram of 1.1730 steel, the measured values confirmed the possibility of using solar energy in all types of heat treatment applied to this steel. In parallel the efficiency of using solar energy was analysed in comparison to the energy obtained by burning methane gas for the heat treatment for the same set of samples. The analysis considered energy consumption, productivity and the impact on the environment. Thanks to various data obtained through developed experiences, which cover a wide range of thermic treatments applied steels 1.1730 model, we can certainly state that this can be a solid base in using solar energy in applications of thermic treatment at a high industrial level.
 
This paper presents the synthesis of complex nanostructures of the Fe 3O4-n[SiO1.5γ-(CH2) 3(NH2)](NH2)nδ-(GL) nεtype [Fe3O4 = magnetic core; n[SiO 1.5γ-(CH2)3(NH2)] = coated layer; (NH2)nδ-NH2 = surface and deep amino groups which play an important role in biochemical interfacing; (GL) nε = exterior superficial glutaraldehyde layer}. These nanostructures have several interesting physical and chemical characteristics, such as: biochemical fixing without destructing the microorganisms on the Fe3O4-n[SiO1.5γ-(CH2) 3(NH2)](NH2)nδ-(GL) nε surface and the ability to differentiate the microorganisms in magnetic field, according to the mass ana volume. In order to obtain superior biochemical fixing performances we have analysed and determined the chemical and physical distributional mechanisms of(NH2)nδ- NH2, groups on the surface and in the depth of the above-mentioned nanostructure. For this purpose we have deduced the control equations according to the synthesis parameters, which triggers the growth of the silicone polymer layer and the distribution of the amino groups in its structure.
 
As a result of the requirement to achieve the implementation of the European Water Framework Directive (WFD) in all the member states by 2015, Romanian's water management policies need to carefully look and consider water quality issues. All waters will achieve a good ecological status, therefore simulation of the existing status of the water bodies and analysis of proper adaptation measures for improving water quality is an important part of the implementation process Water quality models play an essential role in support of the water management decisions. Present paper presents an application of the DHI tool, Mike 11, for the simulation of water quantity and quality of Bega River. The evolution of a pollutant source is traced both in time and space on a segment of the Bega River, from Topolovat to Otelec. The obtained results show that model is able to capture the water quality of the river, as per the observed values, and it is possible to be used in the future to predict the impact of a certain pollutant on the Bega River. The results the possibility to develop what-if analyses, which can help decision makers to choose the best adaptation strategy.
 
The purpose of our study was to analyze the influence of Ti-6Al-4V and Ti-15Zr dental implants, with complex implant designs, on the cortical and trabecular mandibular bone in regards to the stress value and its distribution using finite element analysis. A total of four 3D implant assemblies were modeled, each consisting of implant, abutment, abutment screw, cement layer, and ceramic crown. Implants were modeled with different macrostructure designs with focus on the main thread and microthread design as well as complex geometry details. All implants were inserted in the second molar position in the mandible bone section, consisting of two macro-structures, a 2 mm thick cortical bone and an internal cancellous bone. Results revealed that small variations in the implant design led to a great difference in the stress values and distribution in both cortical and cancellous bone. Our results suggest no major difference between Ti-6Al-4V and Ti-15Zr in regards to the material�s ability to decrease stress in the periimplant bone. However, within the same material, results revealed important differences between thread design and implant geometry concerning the stress values and stress concentration in cortical and cancellous bone in the mandibular model.
 
The current trend in screening against cervical cancer is to improve the sensitivity of screening method and p16/Ki-67 dual-stained cytology, represents a promising approach. We performed a study to investigate the correlation between the p16/Ki-67 co-expression and HPV type on a group of patients with ASCUS and LSIL on Pap smear. On all patients, dual stain test and HPV genotyping were performed. In the group of patients with positive dual stain p16/ki-67 test, the number of patients with HPV type 16 was significantly higher than the number of patients with any other type of HPV. Also, all patients with CIN3 or above (cervical cancer) were positive for p16/Ki-67. Our study shows the potential use of those two tests to identify patients with high risk for severe dysplasia.
 
Scientific literature surve
Selected articles (sterilization of 3D printed products)
PLA and PETG properties [12, 13]
Thermal properties of ASA [23]
In the context of the COVID-19 pandemic and the lack of protective equipment worldwide, we aimed to study the literature for finding guidelines in the 3D manufacture of respiratory masks. We have searched for papers in CI-EXPANDED, SSCI, A & HCI, CPCI-S, CPCI-SSH, BKCI-S, BKCI-SSH, ESCI, CCR-EXPANDED, IC, using 3D printing materials sterilization and 3D printing materials disinfection keywords. From 80 results in databases, after refining, we selected six papers. We have also searched for manufacturers information regarding 3D printing materials sterilization or disinfection. We have found seven materials that are suitable for 3D printing and sterilization, with regards to multiple utilizations. Analyzing the properties and recommendations for sterilization of elements obtained by 3D printing, a thorough filaments structures/behavior research for most of the 3D models for printing is needed regarding synthetic polymers suitable for 3D printing; also, to establish the physical and chemical properties resulted after the reactions with sterilizing substances. In the context of the COVID-19 pandemic, the authors want to help and find guidelines in the 3D manufacture for producing respiratory masks.
 
The crystal structure of tetrakis(2,2'-bithiophene-5-yl)silane, C16H10S4Si0.5, has been determined at 293K in the Monoclinic (I2) symmetry. The Si atom has quasi-perfect tetrahedral geometry and bithiophene unit are quasi-planar. Comparison of Si-C bond lengths with literature data indicates an electron donating effect of the terminal thienyl ring on the first C linked to the Si central atom. The study of C-C bond lengths reveals a much more aromatic character for the four thienyl rings directly linked to the Si atom. The molecular packing arrangement shows that each molecule presents eight intermolecular contacts.
 
We analyze polymer dynamics in a fractal paradigm. Then, it is shown that polymer dynamics in the form of Schrödinger - type regimes imply synchronization processes of the polymers� structural units, through joint invariant function of two simultaneous isomorphic groups of SL(2R) - type, as solutions of Stoka equations. In this context, period doubling, damped oscillations, self - modulation and chaotic regimes emerge as natural behaviors in the polymer dynamics. The present model can also be applied to a large class of materials, such as biomaterials, biocomposites and other advanced materials.
 
New aromatic polyimides have been synthesized by polycondensation reaction of 3,3′-dimethyl-4,4′-diaminodiphenylmethane with benzophenontetracarboxylic dianhydride or hexafluoroisopropylidene diphthalic anhydride in N-methylpyrrolidinone as a solvent, followed by chemical imidization in the presence of acetic anhydride and pyridine at 100°C for 4 h. The obtained polyimides presented excellent solubility, high thermal stability and good film forming ability. The degree of polyimides cure has been observed to have a profound influence on the films fluorescence.
 
In this work, the corrosion resistance of hybrid coatings obtained from plastic materials was evaluated and compared with the corrosion resistance of Zn coatings. Zinc and hybrid coatings were obtained by electrodeposition from zinc sulphate electrolyte. For obtained hybrid coatings it was used as disperse phase two type of plastic materials: phenol-formaldehyde resin and epoxy resin. Polarization was used to measure the corrosion rate and behaviour of zinc and hybrid coatings in 3.5% NaCl solution. Tafel curves show that the including particles of plastic materials in zinc matrix disturbs the cathodic reactions and reduces anodic reaction leading to decrease of corrosion current and increase the corrosion resistance of hybrid coatings obtained at the same electrodeposition parameters as zinc coatings. Smallest values of corrosion rate were evaluated for hybrid coatings obtained with phenol-formaldehyde resin as disperse phase that indicates a good corrosion resistance in 3.5% NaCl solution.
 
Despite important progress in the field of the thin flexible transistor (TFT)-based electronics, a major challenge still exist for organic TFTs to decrease the operating voltage, which is related to the properties of the dielectric and semiconductor layers from the OTFTs structure. In this paper, we present the electrical behavior of two biocompatible polymers, polyvinylpyrrolidone (PVP 360) and polyvinyl alcohol (PVA), regarding the application as insulating layer in thin-film transistors. The PVA and PVP 360 thin films were deposited onto epoxy resin copper double-sided layer and polyethylene tere-phthalate/Indium tin oxide (PET/ITO) substrates by sol-gel method, spin-coating technique. Two sol concentrations (1 and 5 wt. %) were prepared and the contact angle onto the used substrates was measured using a digital microscope camera. The obtained films have been characterized by scanning electron microscopy (SEM) and dielectrical behaviour. For electrical measurements, the metal-insulating-metal (MIM) structure was realized by cooper electrodes deposition at room temperature, onto the top of thin films, by magnetron sputtering method. The current (I) - applied voltage (from -5 to +5 V) curves were measured in air at room temperature (RT), using the Picoammeter homemade device. PVA and PVP 360 thin films showed low leakage currents with values within � 2 nA for �5 V range.
 
The aim of this study was to achieve a polymeric scaffold, ex-vivo, using 3D printing technology and then subjecting it to various tests to check its optimal property. Initially there was selected a lower jaw with a bone defect that would have prevented any treatment based prosthetic implant. The mandible was first scanned using an optical scanner (MAESTRO DENTAL SCANNER MDS400). The scanning parameters using optical scanning system are: 10 micron accuracy, resolution 0.07 mm, 2 rooms with High-Resolution LED structured light, two axes. The scan time of the mandible was 4-5 min. Later the same mandible was scanned using CBCT's CRANEX 3DX. The images obtained using CBCT's were correlated with those obtained by optical scanning. Further on, there was achieved the digital design of the future scaffold with the conventional technique of wax addition directly on the mandibular bone defect. After that, this was again scanned using scanning system MAESTRO DENTAL SCANNER MDS400, and using CBCT's CRANEX 3DX. The images obtained were correlated with all the scanned images of original mandible bone defects. There were made two polymeric scaffolds using 3D printing system an (D20 Digital Wax System 3D Printer). After printing, scaffold sites were introduced for 30 minutes in an oven curing. Later the pieces obtained were processed to remove small excesses of work. There were obtained 3 blocks of polymers that have a good adaptation to the bone profile. Often, in oral implantology and maxillofacial surgery appear bone defects. They prevent an optimal treatment of bio-functional and aesthetic restoration. Using 3D printing technology one can achieve scaffold sites of different biocompatible materials that have optimal properties to replace bone defect and restore the defective area. These scaffold sites have an intimate adaptation to the defect. 3D printing techniques used to restore bone defects can quickly and efficiently give the possibility to have a successful implantology prosthetics treatment.
 
UV curing is a photochemical process in which high-intensity ultraviolet light is used to instantly cure or ��dry�� coatings, inks, adhesives and thin film technology. It has been around as a coating for wood, paper and as a clear coating via photolithography process on printed circuit boards PCBs or integrated circuit boards ICBs for years. It is fast becoming one of the most popular techniques in the paint and coatings industry. Most of the formulation use multifunctional acrylate monomers or oligomers or a mixture of them that crosslink under exposure to UV/EB radiations in a free radical process. We briefly present the advantages of EB vs. UV. A new type of formulation based on multifuctional monomer of dicyclopentadiene epoxy derivative with additional diluent as co-reactive solvent will be described and evaluated. This formulation differs from the acrylate one by the use of a cationic photoinitiator. The final product presents all the advantages of epoxy resins viz. better adherence, mechanical and thermal properties, compared to acrylate systems. Formulation has been optimized thanks to the differential scanning photocalorimetry DPC. This type of formulation is developed for additive digital manufacturing - 3D Printing (building layer by layer).
 
This work are made for determine the possibility of generating the specific parts of a threaded assembly. If aspects of CAD generating specific elements was analysed over time in several works, the technological aspects of making components by printing processes 3D through optical polymerization process is less studied. Generating the threaded appeared as a necessity for the reconditioning technology or made components of the processing machines. To determine the technological aspects of 3D printing are arranged to achieve specific factors of the technological process, but also from the specific elements of a trapezoidal thread or spiral for translate granular material in supply process are determined experimentally. In the first part analyses the constructive generation process of a spiral element. In the second part are identified the specific aspects that can generation influence on the process of realization by 3D DLP printing of the two studied elements. The third part is affected to printing and determining the dimensions of the analysed components. We will determine the specific value that can influence the process of making them in rapport with printing process. The last part is affected by the conclusions. It can be noticed that both the orientation and the precision of generating solid models have a great influence on the made parts.
 
The torus or toroidal surfaces are geometries that can be easily found in various industrial applications, from containers, devices, cartwheels, design objects and even machine parts, being also a geometric primitive often used in solid constructive geometry. For a better understanding of the torus-type surface mechanical behavior, this paper aims to study the toroidal geometry manufactured from ABS material by using the FDM 3D printing method and subjecting each sample to compression tests to identify the influence of the sample filling percentage in the case of triangular pattern.
 
3D printed pneumatic gripper: a) 3D CAD model of pneumatic gripper; b) section view of the pneumatic gripper showing clearances; c) FDM printing process; d) finished pneumatic gripper prototype
Rotational pneumatic mechanism: a) 3D model of pneumatic rotational mechanism; b) section view of the mechanism showing part clearances; c) manufacturing the mechanism through FDM; 3D printed prototype of a pneumatic rotational mechanism
3D printed pneumatic chuck mechanism: a) 3D model of 3-jawed chuck mechanism; b) section view of the mechanism showing part clearance and internal air ducts; c) manufacturing the mechanism through FDM; d) top view of the 3D printed prototype; e) actuated chuck mechanism gripping a cylindrical surface
3D printed pneumatic latching mechanism: a) 3D model of pneumatic latching mechanism; b) section view of model which shows part clearances; c) latching mechanism with pins in locked position; d) latching mechanism with retained shaft.
Various applications in industry and medicine require the transmission of movement using systems that do not influence magnetic or electromagnetic fields. These components include systems which transmit linear or rotational motion, change position (switches), attach or detach to objects (latches), grip objects, etc. This paper looks into the possibility of producing such mechanisms using FDM 3D-printed parts from thermoplastic materials with embedded moving parts, which can be pneumatically actuated. In order to make the parts suitable for use in pressurized air systems, different sets of printing parameters have been investigated. PLA annealing is used in the attempt to minimize play and increase air-tightness of 3D-printed parts.
 
The article presents the process by which, with the help of 3D printing technology, the piston of the differential injection device was produced using ABS material. It was made with fused filament fabrication (FFF) technology, and the smoothing process was used to improve the surface quality. The piston is part of a complex equipment for underground fertilization of agricultural crops.
 
3D printing process
Since the development of 3D printing, over the past decades, the domain of application has evolved significantly! Concerning the orthosis and prosthesis manufacturing, the 3D printing offers many possibilities for developing new medical devices for people with disabilities. Our paper wish to synthetize the main 3D printing methods and the biomaterial properties which can be used in orthosis and prosthesis manufacturing, like polylactic acid or acrylonitrile butadiene styrene. Fused Deposition Modeling and Stereo lithography are most used for medical devices manufacturing and usually using polylactic acid, considering the properties of this polymer and de organic componence.
 
The extension of 3D printing processes for parts made of polymeric materials highlighted the possibility of manufacturing threaded surfaces through such processes. In principle, the operation of a threaded joint involves tensile forces in the threaded rod. The dimensional characteristics of the threaded surface and some input factors in the 3D printing process can influence the tensile strength of threaded rods made of polymeric materials. An experimental research aimed at the tensile behavior of a threaded joint was designed, using a plastic screw and a special steel nut. A factorial experiment was designed and implemented to identify an empirical mathematical model capable of highlighting the influence of the dimensional characteristics of the threaded surface and some of the input factors in the 3D printing process on tensile strength. The test samples from polymeric materials were manufactured by 3D printing, then subjected to tensile tests. The mathematical processing of the experimental results allowed the determination of a mathematical model that allows the inclusion of the ordering of the factors taken into account in terms of the intensity of the influence that these factors exert on the tensile strength of the threaded rods. It was found that the diameter of the threaded rod exerts the strongest influence on the tensile strength of the threaded rod obtained by 3D printing, increasing the diameter of the threaded rod causing an increase in the maximum deformation of the rod. Increasing the thread pitch leads to a decrease in the maximum deformation of the threaded rod.
 
The purpose of this research is to establish the technology of 3D printable production on the principle of FDM of gears made of PLA, ABS and PETG mainly. In the paper we present first the dimensional generation and specific aspects that need to be considered to produce gears with internal or external teeth of the cylindrical type with vertical or inclined teeth. Generating the gears appeared as a necessity for the reconditioning of the components of the processing machines and of the electric machines made both in the process of elaboration of the bachelor’s and the laboratory works, with reduced energy resource consumption and low pollution as low as possible. After the construction, we past to identify the dimension that have implications for both mechanical and kinematic resistance to achieve a product with good cinematic and functional characteristics. After that are made an analysis of the layers generated, both from the computer simulation and from the point of view of the analysis of layers physically generated on a gear tooth with external teeth.
 
The paper is part of a series in which the influence of the manufacturing defects on the functional behavior in biodegradation medium of some items obtained, both by 3D printing and by classical procedure (pressing), from an originaly renwable matrials based on polylatic acid will be presented. The first results regarding the correlation of the defects appeared at manufacturing into plates with the biodegradation behavior in an Aspergillus Niger(A.niger) medium, studied by SEM microscopy, are presented. These results demonstrated that the development of the A. Niger microorganism is related manly to the defects appeared at the melt processing of renewable polymeric material into finished product. A notable role in controlling the appearance of the manufacturing defects belongs both to the melt rheological properties which are responsible for the continuous or discontinuous flow and to the technical performance of the used equipement, 3D printer or classic hydraulic press. If the polymeric material melt has too high viscosity than the continuous flow is not possible and so the overlapped melt fronts are created which generate the voids formation, sometimes joined by small nano and/or micrometric channels. The rheological properties of the melts depend both on the material formulation and the seleted melt processing conditions.
 
Treatment of impacted teeth often implies placing a bonded attachment and using orthodontic forces to move the tooth into occlusion. The aim of the paper is to describe a novel methodology of manufacturing orthodontic attachments for impacted teeth using the latest CAD software and 3D printing technology. A biocompatible acrylic based resin was used to print a custom made attachment designed based on the volumetric data aquired through cone bean computer tomography. Custom design of the attachment simplified clinical insertion and treatment planning and 3D printing made its manufacturing easier. Being a first trial, more reasearch is needed to improve the methodology and materials used.
 
Low-volume production components represent a possibility to create prototypes from the same process and materials that someone use for the final product and to bring new products to market instead of waiting for final components to arrive from the machine shop. Additive FDM create geometrical products through the deposition of ABS (Acrylonitrile-Butadiene-Styrene) filaments layer by layer satisfying this necessity. Since the specialized literature offers little information on the properties of such plastic materials, in this paper the authors present some experimental procedures in order to evaluate the elastic and mechanical properties of such a plastic material. The specimens have been printed on a 3D "ULTIMAKER-2" printer.
 
Fused Filament Fabrication (FFF) is the most popular and widely used additive manufacturing process for printing polymer and composite products. Various production factors influenced the strength and stiffness of the part manufactured by 3D printing. A comprehensive experimental analysis was conducted in this study to examine the effect of FFF process parameters (infill density, pattern, and layer thickness) on mechanical properties and failure mechanism. The tensile, flexural, and impact test specimens were printed using ABS and carbon fibre reinforced ABS filaments in accordance with ASTM standards. Furthermore, dynamic properties are studied using dynamic mechanical analysis to estimate the loss factor and glass transition temperature under the impact of temperature and frequency in addition to static properties. Further, the results showed the addition of carbon fiber in ABS increases the mechanical properties. The failure modes are studied using optical microscopy and Scanning Electron Microscopy images and it has been visualized that due to improper layer deposition, poor bonding between the previous layer and low infill density creates a void in the specimen which results in poor mechanical properties. The Dynamic Mechanical Analysis showed that at higher frequency the molecular movement decreases which in turn stabilizes the composite behavior and reduces the loss factor.
 
The paper presents the study on the static mechanical properties of PLA (Polylactic Acid) produced with entry-level additive technologies using three printing directions. During the experimental work were tested a total of 15 �dog bone� ASTM D638-14 standard specimens made from additively manufactured polymer (PLA) through FDM (Fused Deposition Modelling) technique, where the material and rectilinear pattern infill geometry and infill percentage of 100% were constant and the printing orientation was varied. Usually technical data sheets that are delivered by filament materials producers include the most satisfactory data which are valid for only one specific printing direction. The printing direction is deliberately selected, in such way that the best material characteristics are achieved. In addition to this matter, as the additive manufacturing market grew significantly in the past couple of years, the filament production market showed a consequential growth. The aftermath of this expansion had a direct impact towards the quality and costs of the filaments used for 3D printing, in order to satisfy both the low-end and high-end users. Therefore, in this frame, the present research provides entry-level additively manufactured PLA performances showing significant changes depending on the different printing directions and determine the build orientation influence on the mechanical properties, in the aim of providing aid for both mechanical designer and product manufacturer at the stage of the printed product mechanical properties.
 
Facial epistasis represent facial prosthetic components made of acrylic or silicone plastics, which have no other function than to rebuild the lost region of the face in order to partially restore the physiognomy. A mandatory step in the manufacturing process of epistasis is represented by fingerprinting the tissue defect and the entire facial region and making a study model as basis for designing the epistasis .
 
The didactic platform (a) and the prehension system used for testing the jaws (b)
Printing of jaws vertical position -a horizontal position -b
Thickness of the jaws' wall, a -of the virtual geometric model [9], b -made after printing
Plastically deformed jaws a -PLA, b -ABS, c -PET
Damaged ABS jaw
The studies presented in this article are based on the variation of some constructive parameters on various types of materials for a prehension system jaws. The pneumatic actuation prehension system is part of the structure of a manipulator integrated within a teaching platform for installation. In the tests, the varied parameters were the following: the type of plastic material, the way of printing on the 3D printer bed, the degree of fill (the density) and the geometric shape. The experimental tests have resulted in an optimal version of the prehension system jaws.
 
In this research are establish the technology of 3D printable parts by the principle of FDM 3D printed for threaded made by PLA, ABS, Nylon or PETG. In the paper are present first the dimensional generation and specific aspects that need to be considered to produce threaded with internal teeth of the metric, round or trapezoidal type. Generating the threaded appeared as a necessity for the reconditioning or made of the components of the processing machines made both in the process of elaboration of the bachelor�s and the laboratory works, with reduced energy resource consumption and low pollution as low as possible. After the construction, it is identify the dimension that have implications for both mechanical and kinematic resistance to make a product with good cinematic and functional characteristics. After that are made an analysis of the layers generated, both from the computer simulation and from the point of view of the analysis of layers physically generated for a threaded with internal teeth. At the end are presented which are necessary for operations to obtain a product with good features starting from two types of thread generated 8x2 and 10x2 moments.
 
The developments in the biocompatible materials and additive manufacturing technologies gave birth to new possibilities in reconstructive surgery. In addition to revolutionizing the diagnostic possibilities, the modern medical imaging has led to the development of surgical planning software. Using these state-ofthe- art technologies, a new standard of care is rising with the spread of patient specific implants. Our view in studying and using these materials and technologies goes beyond their biocompatibility, focusing on the functional and esthetic impact of these restorations. Our aim is to show their potential benefits and pitfalls presenting a couple of posttraumatic and oncological application possibilities, focusing on the new presurgical planning, choice of materials and manufacturing technologies.
 
The aim of the work is conduct to highlight how the technological parameters has influence of 3D printed DLP on the generation of wheel, made from resin type material. In the first part of the paper is presents how to generate in terms of dimensional aspects specific design cylindrical gears, conical and worm gear. Generating elements intended to reduce the cost of manufacturing of these elements. Also are achieve the specific components of this work are put to test with a laboratory test stand which is presented in the paper in the third part of the paper. The tested gears generated by 3D-printed technique made with 3D printed with FDM or DLP technique. After the constructive aspects, proceed to the identification of conserved quantities, which have an impact both in terms of mechanical strength, but his cinematic, in order to achieve a product with kinematic features and good functional domain specific had in mind. The next part is carried out an analysis of the layers are generated using the DLP and FDM method using an optical microscope with magnification up to 500 times, specially adapted in order to achieve both visualization and measurement of specific elements. In the end part, it will highlight the main issues and the specific recommendations made to obtain such constructive mechanical elements.
 
The FDM printer Leapfrog Bolt Pro
Hexagonal 3D printed part with specimens cut out of it
Designing a sample to be made by FDM 3D printing is a fundamental problem in further studies related to such printed structures as material properties vary depending on filament orientation and G-code particularities. Samples designed to simulate wall structures inside 3D printed parts have been tested to allow separate evaluation of key components in such parts. Results show a very long plastic region in filaments without imperfections. As filament strands break steps of similar values appear in the reaction force measured by the machine.
 
Hirrus 3D model of the drone and the paylaod components [17].
Side view of the payload compartment door assembly. In point "A" is a steel shaft that rests in a curved seat that can slide along it, in point B there is a geometric configuration that allows this end to hang on the side of a closed toothed belt, mounted between two belt wheels.
Meshing with tetrahedral elements. Detail of the mesh in the contact area In "Figure 16" is presented the field of total deformations and in "Figure 17" the field of equivalent stresses in the contact area between the steel bolt and the curved seat of the ABS structure.
Contact area detail for ABS parts: representation of Von Mises equivalent stresses.
With the development of unmanned aerial vehicle (UAV) systems for a multitude of real-time applications, 3D printing technologies have been developed to make thermoplastic structures by fusing filament Fused Deposition Modeling (FDM) or Fused Filament Fabrication (FFF). However, we consider that the realization of new technologies of experimental models / technological demonstrators / prototypes becomes profitable by using 3D printing technologies. The main aim of the paper is to highlight how the use of three types of materials, which are processed differently, influences the Von Mises stresses of the payload used for a UAV, with the mission of photographing and filming from high altitude.
 
In order to improve thermal behavior and dimensional strability of polylactic acid (PLA) designed both for 3D and 4D printing technology-fused deposition modeling (FDM) using a scalable procedure, the polymer was melt compounded with additives which control the morphology by crystallization and/or reinforcing. Using the formulations which provide polylactic acid (PLA) improved thermo-mechanical properties and desired dimensional stability, the new materials were shaped, on a laboratory line, as filaments for printing technology. The selected compounds were than scaled up on a 50 kg/h compounding line into granules which prove to have good shapability as filaments for printing technology (1.85 +/- 0.05 mm diameter, required ovality, good appearance and smooth surface) and performed properly at 3D printing. The obtained results proved that functional properties of PLA can be improved by various methods so that, depending on the reached performances, the new material can be converted through printing technology into items for performance applications. The novelty of the article is related to the fact that it identifies a modifying solution for controlling the morphology of a type of PLA designed for 3D printing that already has an advanced crystallinity.
 
Initial conditions of testing the spherical parts under compression efforts
Expected elastic behavior of a spherical hollow part under the action of an axial compression force Fa In order to better characterize the theoretical behavior of the plastic spherical hollow parts under the action of the axial compression efforts, a simulation utilizing the finite element method was developed. Generally, this method offers the possibility to formulate some remarks about the material behavior before developing the experimental research and it could be used inclusively to define the values of the process input factors. Subsequently, the method could be used to compare its results with the results experimentally obtained. The analysis allows also a certain prediction concerning the risk of crack generation.
Position of the plastic spherical hollow part on the testing equipment before applying the axial compression force
Experimental conditions and results
The form of the outer and inner surfaces of hollow spherical parts determines the developments of some particular categories of efforts during the compression tests. The overall purpose of the research presented in this paper was to study the behaviour of the hollow spherical parts under axial compression. The PLA hollow spherical parts were obtained by 3D printing and using distinct values for certain process input factors. The finite element method was used to theoretically investigate the behaviour of the parts and it highlighted the total plastic deformation of the test pieces. To experimentally verify the theoretical considerations, an L9 Taguchi orthogonal design was performed. The empirical mathematical model thus determined highlighted the stronger influence exerted by the printing plate temperature, printing speed, and part wall thickness.
 
The aim of this experimental study is to compare the biointegration and tissue response to different surgical mesh types, inserted in various layers of the abdominal wall of Wistar rats. After 30 days, the rats were sacrificed and the meshes were removed en bloc with the subcutaneous tissue, muscular layer and peritoneum. Tissue response (fibrosis, inflammation) was measured using quantitative and semi-quantitative morphometry. We observed that polyethylene terephthalate 3D mesh induces significantly more fibrosis compared to polypropylene mesh and the fibrosis is absent or minimal in case of the control group. Tissue reaction, including fibrosis, is reduced around the polypropylene mesh. We also observed that fibrosis is more intense towards aponeurosis and peritoneum. We can conclude that the 3D mesh shows better biointegration if it is used in proper circumstances. It’s well tolerated by the organism if sutured to the aponeurosis and preferable with monofilament stitches.
 
3D printing paired with CBCT imaging technology could provide a more individualised approach to orthodontic diagnosis and tratment. The aim of the present study is to asses dimensional differences between the CBCT image and 2 types of 3D printed replicas of an impacted maxillary canine, and to determine whether this method could be used in the future development of customised orthodontic attachments. Ten replicas were printed using the STL file of the impacted canine using two types of resin- five of each, with the same printer. Linear measurements of maximum height, length and width, were made. Mean dimensional erorrs were 0.184 mm and 0.068 mm. The largest discrepancy was in lenght - 0.362 mm. More reasearch is needed, but in this study we obtained printed resin replicas that provide sufficient dimensional accuracy to be used in orthodontics.
 
With technology becoming more and more advanced, the medical system is being consistently improved. From intraoral scanners that started to replace conventionally impressions technique to printed surgical guides that directs the drilling systems of implants, dentistry is one of the beneficiars of new and advanced treatments that are ergonomic, safe and put both the medical team and the patient in a more pleasant experience. The purpose of our article is to summarize the application of acrylic and metacrylic resin in 3D printing of surgical guides used in orthodontics.
 
In this paper, the authors show a part of research works performed on the use of 3D scanners and 3D printers to execute plastic parts with complex surfaces. 3D scanning allows copying of certain surfaces in our environment, based on existing models. Scanned models may represent various objects, made of a wide range of materials: metals, ceramics, fabrics, plastics, leather, organic materials etc. [1]. This paper shows the results achieved using a scanner and a common and affordable - low-price - printer. 3D scanners and printers allow execution of clones of certain parts with irregular surfaces.
 
By the extrusion and injection technique, polymer-based composite samples (polypropylene and thermoplastic polyurethane) were obtained with BaTiO3 filler in concentrations between 0 and 35 %. Following the preliminary characterizations performed by coupled thermal analysis techniques, it was found that the composite samples obtained have thermal stability up to a temperature of about 250 oC and can be processed by extrusion at temperatures between 180 and 240oC. Above this temperature, a series of degradation processes take place by successive thermooxidation with the formation of volatile products.The electrical characterization of the composite samples was performed by the dielectric spectroscopy technique, which showed that the A tga dielectric losses increase as the BaTiO3 content of the composite increases. The maximum increase being recorded at 50 Hz (the slope A tga /% BaTiO3 about 0.003 /% BaTiO3). It was also found, that the electrical conductivity (o) of the composite increases with the increase of content in BaTiO3 so that o at 100 kHz for the composite with 35 % BaTiO3 is about 50 times higher than for the reference sample M 0 (without filler).
 
Top-cited authors
Andrei Victor Sandu
  • Gheorghe Asachi Technical University of Iasi
Anton Hadar
  • Polytechnic University of Bucharest
Ioan Curtu
  • Universitatea Transilvania Brasov
Horia Iovu
  • Polytechnic University of Bucharest
Mohd Mustafa Al Bakri Abdullah
  • Universiti Malaysia Perlis