Polyethylene terephthalate (PET) is used worldwide for packing, and for this reason, it is the main material in plastic waste. The paper uses granules of recycled PET (R-PET) as raw material for producing filaments for 3D printing, subsequently used for printing the test specimens in different ways: longitudinally and at angles between 10° and 40° in this direction. Both the filaments and the printed specimens experience thermally driven shape memory effect (SME) since they have been able to recover their straight shape during heating, after being bent to a certain angle, at room temperature (RT). SME could be reproduced three times, in the case of printed specimens, and was investigated by cinematographic analysis. Then, differential scanning calorimetry (DSC) was used, in R-PET granules, filaments and 3D printed specimens, to emphasize the existence of glass transition, which represents the governing mechanism of SME occurrence in thermoplastic polymers, as well as a recrystallization reaction. Subsequently, the paper investigated the 3D printed specimens by dynamic mechanical analysis (DMA) using a dual cantilever specimen holder. Temperature (DMA-TS) and isothermal scans (DMA-Izo) were performed, with the aim to discuss the variations of storage modulus and loss modulus with temperature and time, respectively.
A fragment of a Cu-15Zn-6Al (mass%) shape memory alloy (SMA), in hot rolled-water quenched condition, was subjected to thermal cycling performed by means of a differential scanning calorimetry (DSC) device. Each cycle comprised controlled heating, isothermal maintaining, and free air-cooling, repeated three times, up to maximum temperatures increased by every 10 K, between 450 and 490 K, aiming to reproduce actual functioning conditions of a SM electrical actuator with uncontrolled cooling. Both the endothermic peaks, associated with thermally induced reversion of martensite to austenite, and their derivatives were analyzed in terms of critical transformation temperatures and specific enthalpy absorptions and in terms of transformation rates, respectively, with the aim of revealing their variational tendencies with increasing heating temperature to the maximum. The progressive decay of reverse martensitic transformation was associated with the reciprocal blocking of differentially oriented populations of stabilized lath-martensite needles, observed by scanning electron microscopy.
Fe-14 Mn-6 Si-9 Cr-5 Ni (mass. %) shape memory alloys (SMAs) were produced from raw powders employed both in initial commercial state and in a mixture state of equal fractions of commercial and mechanically alloyed (MA’d) particles. After blending, pressing and sintering, powder compacts were hot rolled (HR’d) and solution treated (ST’d) before being machined into plane-parallel lamellas. Specimens with special geometry were pre-strained on a tensile testing machine. By means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) the presence of ε hexagonal close packed and α’ body center cubic stress induced martensites was revealed and their thermally induced reversion to γ face center cubic austenite was evaluated by modulated differential scanning calorimetry (MDSC). The results enabled the study of the influence of MA, HR, ST and pre-straining on phase structure and associated on shape memory effect (SME). The lamellas were hot formed into rings, which were trained in bending. Diameter reduction of trained enlarged rings, on heating, was monitored by cinematographic analysis.
Due to the pressing problems of today’s world, regarding both the finding of new, environmentally friendly materials which have the potential to replace classic ones, and the need to limit the accelerated spread of bacteria in hospitals, offices and other types of spaces, many researchers have chosen to develop their work in this field. Thus, biopolymeric materials have evolved so much that they are gradually becoming able to remove fossil-based plastics from major industries, which are harmful to the environment and implicitly to human health. The biopolymer employed in the present study, Arboblend V2 Nature with silver nanoparticle content (AgNP) meets both aspects mentioned above. The main purpose of the paper is to replace several parts and products in operation which exhibit antibacterial action, preventing the colonization and proliferation of bacteria (Streptococcus pyogenes and Staphylococcus aureus, by using the submerged cultivation method), but also the possibility of degradation in different environments. The biopolymer characterization followed the thermal behavior of the samples, their structure and morphology through specific analyses, such as TGA (thermogravimetric analysis), DSC (differential scanning calorimetry), SEM (scanning electron microscopy) and XRD (X-ray diffraction). The obtained results offer the possibility of use of said biocomposite material in the medical field because of its antibacterial characteristics that have proved to be positive, and, therefore, suitable for such applications. The thermal degradation and the structure of the material highlighted the possibility of employing it in good conditions at temperatures up to 200 °C. Two types of samples were used for thermal analysis: first, in the form of granules coated with silver nanoparticles, and second, test specimen cut from the sample obtained by injection molding from the coated granules with silver nanoparticles.
Abstract. By ingot metallurgy (IM, melting, alloying and casting), powder metallurgy (PM, using as-blended elemental powders) and mechanical alloying (MA of 50 % of particle volume), three types of FeMnSiCrNi shape memory alloy (SMA) specimens were fabricated, respectively. After specimen thickness reduction by hot rolling, solution treatments were applied, at 973 and 1273 K, to thermally induce martensite. The resulting specimens were analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), in order to reveal the presence of ε (hexagonal close-packed, hcp) and α' (body centred cubic, bcc) thermally induced martensites. The reversion of thermally induced martensites, to γ (face centred cubic, fcc) austenite, during heating, was confirmed by dynamic mechanical analysis (DMA), which emphasized marked increases of storage modulus and obvious internal friction maxima on DMA thermograms. The results proved that the increase of porosity degree, after PM processing, increased internal friction, while MA enhanced crystallinity degree.
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