The paper presents part of the results of larger research aimed at evaluating the possibility of improving the characteristics of the FFF printed product by using hybrid heating sources. The results presented aim at the influence of the cooling rate on the characteristics of parts manufactured by 3D FFF printing from Polylactic acid (PLA), with a focus on the structural, thermal and mechanical properties, when the additional heat source is represented by a hot air jet. Microscopic analysis showed that rapid cooling generates a more irregular texture, poor interlayer adhesion and a rougher surface, while slow cooling ensures a uniform texture, improved interlayer adhesion and fewer defects. From a thermal point of view, the glass transition temperature (T_g) was slightly higher for the slowly cooled samples, due to the relaxation of internal stresses. The crystallization temperature (T_c) increased progressively with the reduction of the cooling rate, indicating a higher initial crystallinity, and the energy associated with the crystallization reaction decreased. The melting temperature (T_m) showed minimal variations, but the melting enthalpy was higher for the slowly cooled samples, reflecting better organized crystals. Mechanical properties revealed that the rapidly cooled parts have higher stiffness at low temperatures, due to internal stresses, but brittle behaviour. The slowly cooled parts showed higher stiffness at high temperatures and ductile behaviour, with progressive deformations before fracture, due to the relaxation of internal stresses and the formation of partial crystals. The results emphasize the importance of controlling the cooling rate in the FFF process to optimize the interlayer adhesion, mechanical properties and thermal stability of the printed parts, allowing to adapt their performance to specific application requirements.
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The manufacture of composite materials with hybrid matrix and reinforcements from agricultural waste, which have properties/structure corresponding to the field where they will to be used, is a challenge both in terms of environmental protection and low production costs. Based on this premise, in this article, composite materials reinforced with crushed sunflower seed shells or chopped wheat straw were fabricated, and a hybrid resin matrix based on rosin was used. The chemical structure was studied, along with the influence of the reinforcement addition on the morphology of the materials and their behaviour under various mechanical solicitations: tension and compression.
Wooden resistance elements, such as beams and pillars, are often used in construction. They must be designed and made so as to withstand the loads to which they are subjected during use. The predominant stress of the beams is bending, the maximum values of normal stresses due to the loads that solicitate the beams being important to know for ensuring its bearing capacity. In this paper an experimental study is presented regarding the resistance elements of the beams type. The beams are made of two types of wood, namely beech wood and poplar wood, having a rectangular section. These beams were reinforced with composite materials based on carbon fiber such as plates and fabric that were applied to the beams with the help of an epoxy resin, in order to study their behavior when subjected to bending stress. Bending tests were made until the beams were damaged, measuring, in this sense, the applied forces and the related displacements. The strength of wooden beams reinforced with composite materials was compared with the strength of wooden beams without the addition of composite material, thus establishing which is the better constructive reinforcement solution, for the two essences of wood, to ensure safety in operation, in construction field.
Nowadays, Manufacturing and automotive industries have begun to employ renewable resources as a result of public awareness and rigorous legal requirements relating to the usage of polymers. This study has focused on employing Snake Grass (SG) fiber as reinforcement in Aegle Marmelos with Epoxy blended hybrid matrix (AME), since natural fiber reinforced composites provide a significant role in the development of lightweight structural components. The primary study investigated the effects of fibre length and fibre volume percentage on the mechanical properties of snake grass fibre. Based on the test results, the composite with a 15 mm fibre length and a volume percentage of 20% SG fiber has better mechanical qualities. Finally, mechanical and dynamic mechanical properties are used to assess the impact of Aegle marmelos with Epoxy blended hybrid matrix addition into the snake grass fibre composite. The inclusion of natural fiber with epoxy matrix and natural (Aegle marmelos) filler increased composite characteristics due to their synergistic effect. This enhances the adhesion and stress transmission uniformity between the reinforcements. The morphology of the fiber surface is assessed using micrographs acquired with a scanning electron microscope.
A new bicomponent hybrid material was obtained by encapsulating quercetin in PLGA using solvent evaporation method. The morphological aspects of the samples were established by scanning electron microscopy (SEM). Particle size distribution was determined by dynamic light scattering (DLS), numerical distribution showing that the particles are micrometric, with two granulometric intervals: [385-479] nm and [662-918] nm. Morphology was typical for PLGA, spherical one; the obtained particles are porous with micrometric pores. Zeta potential (ZP, -4.84mV) showed that the particles have electronegative surface charge. The loading efficiency was determined spectrophotometric and it was 18.3% in the mentioned synthesis conditions.
This study aimed to compare the impact of thermal cycling on the flexural strength (σfs) of 3-dimensional (3D) printer resins and polymethyl methacrylate (PMMA). It also aimed to evaluate different surface treatment protocols and surface sealant applications on the surface roughness (Ra) and surface hardness (VHN) of the resins used. Rectangular (25×2×2 mm) and disc (Ø10×2-mm) specimens were fabricated from auto-polymerized PMMA, and 3D-printed resins were tested for mechanical properties (ISO 10477) using thermal cycling (n=10). Disc specimens were separated into three groups (n=10) based on the surface treatments: conventional sanding (C), disk polishing (P), and surface sealant coating (O). Ra and VHN values were statistically analyzed with the Kolmogorov Smirnov, Shapiro Wilk, Independent Samples t-test, Mann-Whitney test, one-way ANOVA test and Kruskal Wallis test (α =.05). A significant main effect was found on the flexural strength analysis for each of the two factors: thermal cycling procedure (p[0.001) and materials (p 0.001). A significant main effect was found on the surface roughness and hardness analysis for each of the two factors: surface treatment protocols (p[0.001) and materials (p[0.001). Based on the results; interim materials produced with 3D-printed resins have better mechanical properties than conventionally polymerized materials. Coated materials had lower surface roughness values than polished ones, and adding a surface sealant agent increased their hardness significantly.
The study investigates the effects of aggressive factors environments commonly found in industrial environments on the elastomeric material TPU 95 A, which is integrated into a multitude of soft robotics applications. Specimens made of TPU 95 A were subjected to aggressive liquid media - cooling oil, distilled water, and ultraviolet radiation (UV-C) to evaluate changes in their mechanical and elastic properties following uniaxial tensile tests. The research, carried out using additive manufacturing technology, highlights the importance of monitoring how the external factors impact elastic and mechanical characteristics of TPU 95 A material. The results obtained after the experimental tests proves to us that the aggressive media analyzed had a greater or lesser influence on the material. By uniaxial tensile tests, it was found that the liquid absorption had a very important impact on the tensile strength of the material. For example, at 1.02% absorption in distilled water, the maximum value of the ultimate strain decreased by 0.257 mm/mm, and at 3.06% absorption in cooling oil, the maximum value of the strain decreased by 0.672 mm/mm.
Using propylene-ethylene block copolymer (PPB) and metallocene polypropylene random (mPPR) as matrix, olefin block copolymer (OBC) and metallocene polyethylene (mPE) as reinforcement, trimethylolpropane trimethacrylate as sensitizer, antioxidant 1010 and dioctadecyl 3,3-Thio-dipropionate as antioxidant, the radiation-crosslinked polypropylene with excellent high-temperature performance was prepared by one-step process and it was used to produce the heat shrinkable tape with three layers structure further. The effect of the formula, the orientation, the crosslinking, the heat treatment and shrink on the crosslinked-polypropylene were studied. The results show that the crosslinked-polypropylene has optimum overall property when the amounts of PPB, mPPR, OBC, and mPE were 50, 10, 15, and 15 phr, respectively. After the orientation in one-step process and the radiation crosslinking with the irradiation dose of 6 Mrad, the tensile strength, the elongation at break, the shrinkage ration, the gel content of the crosslinked-polypropylene reached 33 MPa, 390%, 30%, 51%, respectively. After heat treatment, its mechanical properties further improved and the decrease of its tensile strength and elongation at break did not exceed 15% after thermal ageing at 130 oC for 100 days. Moreover, the corresponding heat shrinkable tapes show outstanding peel strength, impact strength and cathodic disbondment properties in various conditions.
Bone substitutes are found in natural or synthetic form. Different types of bone substitutes are used, including alloplasts or xenografts. These materials should be biocompatible, and have adequate mechanical properties. Bone substitute materials have become a clinical procedure in the treatment of periodontitis. In current practice, various bone substitutes are used, including alloplasts (β-tricalcium phosphate) and xenografts with good results. The aim of this study was to evaluate the efficacy of alloplasts (β-tricalcium phosphate) and xenografts in the preprosthodontic periodontal therapy of intrabony defects. The study was carried out on a group of patients with severe periodontitis treated by periodontal surgery, in which these materials were used as bone substitutes. Patients presented or not performed fixed prosthetic restorations. These biomaterials function as osteoconductive scaffolds. Both materials ensure the filling of bone defects in periodontal intrabony defects through their own capabilities. Alloplasts (β-tricalcium phosphate) and xenografts are effective in periodontal regeneration. The evaluation of periodontal parameters after the surgical interventions with bone substitutes indicates the favorable prognosis over time of the two types of materials used.
The study aims to present the results obtained following the burned patients micrografting, from the perspective of analyzing the physical and chemical properties of polyamide as a support for skin micrografts. To carry out the project, the data was obtained from the use of 100 micrografting kits with polyamide support which were analyzed and the results were interpreted in order to obtain relevant information regarding the effect of polyamide in accelerating the healing process, the rate of postoperative complications, as well as the acceleration in integration of the skin grafts.The comparative analysis was performed with a control group consisting of 108 free split skin grafts covered with classic cotton tulle. The conclusions of the study show that the use of polyamide in the therapeutic protocol of micrografting accelerates the process of grafts integration, while reducing the rate of postoperative complications, as well as decreasing the lenght of hospitalization.