Search

In the present study, the capacity of two commercial NiTi and NiTiCu shape memory alloy (SMA) wires to develop work-generating (WG) and constrained-recovery (CR) shape memory effects (SMEs), as well as the capacity of a commercial NiTiFe super-elastic wire to act as cold-shape restoring element, have been investigated. Using differential scanning calorimetry (DSC), the reversible martensitic transformation to austenite of the three NiTi-based wires under study was emphasized by means of an endothermic minimum of the heat flow variation with temperature. NiTi and NiTiCu wire fragments were further tested for both WG-SME and CR-SME developed during the heating, from room temperature (RT) to different maximum temperatures selected from the DSC thermograms. The former tests revealed the capacity to repetitively lift various loads during repetitive heating, while the latter tests disclosed the repetitive development of shrinkage stresses during the repetitive heating of elongated wires. The tensile behavior of the three NiTi-based SMA wires was analyzed by failure and loading–unloading tests. The study disclosed the actuation capacity of NiTi and NiTiCu shape memory wires, which were able to develop work while being heated, as well as the resetting capacity of NiTiFe super-elastic wires, which can restore the initial undeformed shape of shape memory wires which soften while being cooled down. These features enable the design of a robotic gripper based on the development of NiTi-based actuators with repetitive action. [ABSTRACT FROM AUTHOR]

One of the useful features of 3D-printed specimens of recycled polyethylene terephthalate glycol (R-PETG) is the ability to repetitively develop free recovery as well as the work-generating, shape-memory effect. This behavior is enabled by the R-PETG's capacity to stiffen during cooling, thus allowing for a new temporary shape to be induced. Aiming to devise an explanation for the polymer's stiffening, in this study, the variation in some of the R-PETG's parameters during cooling are emphasized and discussed. The evolution of an R-PETG filament's shape was monitored during room-temperature-bending heating–cooling cycles. Straight-shape recovery and the complete loss of stiffness were observed at the start and the end of heating, respectively, followed by the forced straightening of the filament, performed by the operator, around 40 °C, during cooling. The tests performed by dynamic mechanical analysis disclosed the rise of the storage modulus (E') after 100 °C heating followed by either liquid-nitrogen- or air-cooling to room temperature, in such a way that E' was always larger after cooling than initially. Static tests emphasized a peculiar stress variation during a heating–cooling cycle applied in air, within the heating chamber of the tensile testing machine. Tensile-failure tests were performed at −10 °C at a rate of 100 mm/min, with specimens printed at various deposition directions between 10 and 40° to the transversal direction. The specimens printed at 40°, which had the largest ultimate strains, were broken with tensile rates between 100 and 500 mm/min. Deformation rate increase favored the shift from crazing to delamination failure modes. The correlation between the structural changes, the sharp E' increase on heating, and the stiffening induced by cooling represents a novel approach that enables the use of 3D-printed R-PETG for the fabrication of the active parts of low-priced lightweight resettable actuators. [ABSTRACT FROM AUTHOR]

Pain is one of the main reason that compels patients to visit dentists. Poorly managed pain following treatment in the dental office can lead to patients lack of trust in the dentist, postponing or even avoiding dental treatments. The physiopathology of pain is a complex process involving both the central nervous system and the peripheral nervous system, so the use of analgesics with different modes of action can lead to improved, faster and longer-lasting pain relief. This article provides an overview of the mode of action, effectiveness and results obtained from studies in the literature related to the combination of ibuprofen and paracetamol in a single tablet. [ABSTRACT FROM AUTHOR]

NiTi based shape memory alloys are one of the most intensely studied alloys from its class. Therefore, diverse commercial applications have been developed due to certain properties such as: shape memory effect, superelasticity and corrosion resistance. Currently, the main applications of NiTi alloys are automotive manufacturing and aerospace actuators, biomedical devices or pipe couplings. In recent years, NiTi shape memory alloys have been alloyed with a third element in order to improve the above-mentioned properties. In order to investigate the influence of the alloying elements on the thermal behavior of NiTi alloys, the addition of the third alloying element (Ta and Nb) is under investigation in the present study. The thermal behavior of the three alloys (NiTi, NiTiNb and NiTiTa) was studied by differential scanning calorimetry. Following the experiments, it was observed that the addition of the third alloying element influences the critical transformation temperatures.

SAE 430B is a Cu-based alloy, which, due to good properties qualify the alloy in special bronzes category. In this paper, the influence of the casting parameters on the properties of the SAE 430B cast in two types of moulds: (i) temporary (based on quartos sand) and (ii) permanent (metallic mould). Samples in as-cast condition were cut and prepared for chemical and microstructural analysis. The chemical composition was determined via spectroscopic analysis, the structural characterization was carried out by optical and electronic microscopy. EDS chemical analysis was used to identify the compositions of phases and compounds in the material. The corrosion behaviour was analysed in seawater by a linear potentiodynamic polarization test. The microstructure of as-cast samples presents a ß phase structure with intermetallic precipitates with various morphologies. With the increase in cooling rate, corrosion potential values become more negative and current density increases. [ABSTRACT FROM AUTHOR]

A flare-up is defined as a pain and/or swelling of the soft tissues that occurs within a few hous or a few days following the root canal treatment. In some cases, the flare-ups can apear after the finishing of the root canal treatment, due to the penetration or development of the microorganisms into the root canal. The pain felt by the patient depends on the extent of the periradicular tissue injury, its severity and intensity of the inflammatory imune response. The article discusses the microbial irritation of apical periodontal tissue caused by insufficient instrumentation and filling of the root canals, factors that lead to failure of the outcome of root canals treatment. [ABSTRACT FROM AUTHOR]

Active elements made of Ti50Ni45Cu5 shape memory alloy (SMA) were martensitic at room temperature (RT) after hot rolling with instant water quenching. These pristine specimens were subjected to two thermomechanical training procedures consisting of (i) free recovery shape memory effect (FR-SME) and (ii) work generating shape memory effect (WG-SME) under constant stress as well as dynamic bending and RT static tensile testing (TENS). The structural-functional changes, caused by the two training procedures as well as TENS were investigated by various experimental techniques, including differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), X-ray diffraction (XRD), and atomic force microscopy (AFM). Fragments cut from the active regions of trained specimens or from the elongated gauges of TENS specimens were analyzed by DSC, XRD, and AFM. The DSC thermograms revealed the shift in critical transformation temperatures and a diminution in specific absorbed enthalpy as an effect of training cycles. The DMA thermograms of pristine specimens emphasized a change of storage modulus variation during heating after the application of isothermal dynamical bending at RT. The XRD patterns and AMF micrographs disclosed the different evolution of martensite plate variants as an effect of FR-SME cycling and of being elongated upon convex surfaces or compressed upon concave surfaces of bent specimens. For illustrative reasons, the evolution of unit cell parameters of B19′ martensite, as a function of the number of cycles of FR-SME training, upon concave regions was discussed. AFM micrographs emphasized wider and shallower martensite plates on the convex region as compared to the concave one. With increasing the number of FR-SME training cycles, plates' heights decreased by 84–87%. The results suggest that FR-SME training caused marked decreases in martensite plate dimensions, which engendered a decrease in specific absorbed enthalpy during martensite reversion. [ABSTRACT FROM AUTHOR]

Fe-14Mn-6Si-9Cr-5Ni (mass. %) shape memory alloy (SMA) has been developed as a commercial grade of Fe-Mn-Si based SMAs with excellent formability and corrosion resistance. Producing FeMnSiCrNi SMAs by powder metallurgy enables a better control of chemical composition and grain size. This paper discusses the variation of bending creep deformation, as a function of time, temperature and force, in the case of a powder metallurgy (PM) Fe-14Mn-6Si-9Cr-5Ni SMA with 50 % mechanically alloyed powder volume. Creep test temperatures were selected based on phase transitions determined by dynamic mechanical analysis (DMA), during heating. The results suggested the tendency of martensite plate variants to reorient along a common direction, after creep. [ABSTRACT FROM AUTHOR]

Fe-14Mn-6Si-9Cr-5Ni (mass %) shape memory alloy (SMA) specimens were obtained by powder metallurgy in as-blended state (0_MA) and with particle volume fractions of 10 and 20 % MA’d powders, respectively. After hot rolling and solution treatment, between 973 and 1373 K, the specimens were pre-strained up to 4 %, on a tensile testing machine. The influences of: (i) MA’d fractions, (ii) solution treatment temperature and (iii) pre-straining degree were analysed by X-ray diffraction (XRD), optical (OM) and scanning electron (SEM) microscopy. In this purpose, the gauges of pre-strained specimens were cut and metallographically prepared. Dynamic mechanical analysis (DMA) was employed to emphasize the reverse transformation, during heating, of thermally induced martensite, obtained after solution treatment. The results proved that, as an effect of PM-MA processing, mechanical properties were improved, the amount of stress induced martensite increased and the reverse martensitic transformation was enhanced.

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.

The thermally induced reversible diffusionless martensitic transformation, that governs the mechanism of shape memory alloys (SMAs), can be conveniently illustrated, on differential scanning calorimetry (DSC) curves, by a close variation loop of heat flow with temperature. Cooling-induced direct (forward) martensitic formation causes an exothermic maximum, while martensite reversion, on heating, is associated with an endothermic peak. The occurrence of diffusion-controlled phenomena is emphasized by discontinuities of heat flow variations, such as those observed in the case of Cu-Zn-Al SMAs, experiencing thermoelastic martensitic transformation. When heating such a martensitic Cu-Zn-Al SMA, four solid-state transitions were observed on DSC curves, under the form of: (1) an endothermic minimum ascribed to martensite reversion to parent phase; (2) an endothermic minimum associated with transitory formation of bainite; (3) an exothermic maximum corresponding to the precipitation of equilibrium α-phase and (4) an endothermic peak representing the order-disorder transition of parent phase. The first transition is diffusionless, while the other three are diffusion-controlled. The DSC equipment was used to investigate the effects of: (1) heat treatment temperature, (2) number of cycles of thermomechanical treatment and (3) thermal cycling within the temperature range where diffusion-controlled solid-state transitions occur in a Cu-Zn-Al SMA, the results being corroborated with that obtained by optical (OM) and transmission (TEM) electron microscopy. [ABSTRACT FROM AUTHOR]