Plastic Phase Research Articles

Assessment of the structures contribution (crystalline and mesophases) and mechanical properties of polycaprolactone/pluronic blends

Films of biodegradable blends of polycaprolactone (PCL) and Pluronics F68 and F127 were manufactured by an industrial thermo-mechanical process to be applied as potential delivery systems. The effects of Pluronics on the structure (mesophase organization), and thermal and mechanical properties of polycaprolactone were investigated using differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), polarized optical microscopy (POM) and tensile mechanical tests. The addition of Pluronics affected the crystallization process by changing the relative amounts of crystalline, amorphous, and meso- (condis + plastic) phases. The melting transition and XRD profiles were deconvoluted to assess the individual contribution of the different crystal morphologies. Furthermore, it was found that the mechanical properties of the blends depended on the ratio and type of Pluronic. Thus, Pluronic F127 showed a larger mesophase content than its F68 counterpart with PCL and blends with enhanced ductility.

Solid state 1H, 7Li, and 13C NMR studies on new ionic plastic crystals of crown ether-Li-TFSA complexes.

This study provides the first evidence that a Li ion can form ionic plastic crystals using crown ether with a bis-(trifluoromethanesulphonyl) amide (TFSA) anion. 1H, 7Li, and 13C nuclear-magnetic-resonance (NMR) measurements of the 15-crown-5-Li-TFSA complex revealed that the constituents underwent isotropic reorientation in the plastic crystalline phase. The NMR data of the 12-crown-4-Li-TFSA salt showed that the complex is a rotator crystal (the complexes are denoted as [Li 15C5] and [Li 12C4] in this paper). The X-ray diffraction (XRD) reflection patterns of the [Li 15C5] crystal recorded in the highest-temperature solid phase (plastic phase) could be indexed to a cubic structure. Conversely, [Li 12C4] could be fitted to a trigonal structure. In this study, [M (3n)Cn] (M = Li, Na, K; n = 4-6) complexes were also prepared, and NMR, DSC, XRD, and electrical conductivity measurements were performed. Based on these results, we additionally revealed that the [Na 15C5] and [K (15C5)2] complexes are also new rotator crystals. Single-crystal XRD measurements also revealed that the [Na 15C5] compound has two stable sites in the crystal. Activation energies of molecular motions in the [M (3n)Cn] crystals were estimated using 1H NMR relaxation time (T1 and T2) measurements. The electrical conductivity measurements of [Li 12C4], [Li 15C5], and [Na 15C5] showed high ionic conductivities (∼10-2 S cm-1).

Experimental study on the mechanism of water affecting the permeability characteristics of sandstone

The permeability characteristics of sandstone are of great importance for un-conventional natural gas extraction, CO2 geological storage, coal mine gas safety, etc. Under the influence of tectonic stress and mining-induced stress, the evolution of permeability becomes exceptionally complex. A number of studies have focused on the evolution of permeability under different stress paths, ignoring the effect of water on sandstone permeability. The permeability evolution of sandstone in dry and saturated states under high and low surrounding pressures was investigated by triaxial tests. The results show that the triaxial compressive strength of the specimen significantly decreases under saturated conditions. Specifically, the triaxial compressive strength decreases by 27.12% and 10.52% under low and high confining pressure, respectively. Compared to the dry specimen, the permeability of the saturated specimen significantly decreases at all stages of loading, the initial permeability of the saturated specimen is decreased by 92.09% and 56.25% at low and high confining pressure, respectively. The S&D model was matched with the test data, an excellent goodness of fit was obtained in the elastic and plastic phase, and the mechanism of water affecting sandstone permeability was analyzed.

Pressure-freezing of dodecane: exploring the crystal structures, formation kinetics and phase diagrams for colossal barocaloric effects in n-alkanes.

Barocaloric (BC) materials provide cheaper and more energy efficient alternatives to traditional refrigerants. Some liquid alkanes were recently shown to exhibit a colossal BC effect, matching the entropy changes in commercial vapour-liquid refrigerants. Dodecane was predicted to have the largest entropy change among the studied alkanes. Using synchrotron powder and single-crystal X-ray diffraction, Raman spectroscopy, and lattice energy calculations, we investigated the BC effects of n-dodecane at high pressures and room temperature. Remarkably, a colossal entropy change |ΔS| of 778 J kg-1 K-1 at 0.15(3) GPa and 295 K was observed. Spectroscopic studies revealed that this entropy change correlates closely with the conformational transition from mixed gauche to all-trans forms during pressure-induced crystallization. Additionally, the usage of a diamond anvil cell allowed the determination of the crystal structures of in situ crystallized n-un- and dodecane, as well as evaluation of the pressure-dependent crystal growth kinetics. Furthermore, our research suggests that the entropy change (per kilogram) upon compression should be similar for all n-alkanes within the range of 9-18 carbon atoms in the molecule, based on their lattice energies. Even-numbered alkanes are predicted to exhibit superior BC properties compared to their odd-numbered counterparts due to the more symmetric crystal structures and lower propensity to form plastic phases with lower transition entropy.

Plasticity of anchors in damaged by earthquake concrete base

Most frequently used types of anchors were subjected to experimental studies to obtain valid data on post-installed anchors, such as mechanical anchors (wedge expansion anchors, undercut anchors); bonded anchors (with epoxy resin) and bent cast-in-place anchors. The authors studied the effect of an earthquake-induced damage (plastic deformation) of a concrete base and multi-cyclic dynamic loads, similar to seismic ones, on plasticity of anchors. Plastic phase deformation in case of reinforced concrete base was simulated as a system of cracks of different opening width. The results of the research show that increase in the width of the crack opening from 1.5 to 3.0 mm leads to a decrease in the values of the plasticity factors. Dynamic loading does not lead to a significant change in the plasticity factor related to static loading for all failure mechanisms, except for the bond failure. On the base of obtained results reduction factors of seismic loads may be determined for further calculation of anchor joints subjected to seismic impact.

Steel wire prestress analysis of large section jacking prestressed concrete cylinder pipe (JPCCP): Site experiment and numerical investigation

As one of the key factors of Jacking Prestressed Concrete Cylinder Pipe (JPCCP), stress condition of the steel wire has a significant influence on the safety and durability of the JPCCP. In this paper, the stress of the steel wire was analyzed in the process based on the in-situ test monitoring results and numerical investigation in the water conveyance project in Shanghai. According to test results, the stress losses during the entire process were ruled out and turned out to be quantized. The reduction rate of steel wire was quite high in the early stage of prestress, and gradually slowed down with the time. The relaxation of steel wire was the main influencing factor of prestress loss. The numerical model of JPCCP was established and verified by field test data. Mechanical properties and failure modes of JPCCP under high inner water pressure and under different prestress losses were analyzed. After the initial prestress of steel wire was reduced from 1048 MPa to 888 MPa, the prestress of concrete in pipe core was reduced by 15%, while the compressive stress of the outer concrete was reduced by 23%. The water pressure carrying capacity of the structure was reduced by 10%. The larger the prestress loss of the steel wire was, the earlier the concrete in the pipe core entered the plastic phase. The results indicate that the prestress loss of steel wire has a direct and prominent influence on the bearing capacity of the water pressure on JPCCP. To help tunnel designers incorporate the prestress requirement into their basis of design and structural analysis, an assessment method was also proposed.

Stabilization of the (C2H5)4NHSO4 High-Temperature Phase in New Silica-Based Nanocomposite Systems.

In this study, the electrotransport, thermal and structural properties of composite solid electrolytes based on (C2H5)4NHSO4 plastic phase and silica (1 - x)Et4NHSO4-xSiO2, where x = 0.3-0.9) were investigated for the first time. The composites were prepared by mechanical mixing of silica (300 m2/g, Rpore = 70Å) and salt with subsequent heating at temperatures near the Et4NHSO4 melting point. Heterogeneous doping is shown to change markedly the thermodynamic and structural parameters of the salt. It is important that, with an increase in the proportion of silica in the composites, the high-temperature disordered I41/acd phase is stabilized at room temperature, as this determines the properties of the system. Et4NHSO4 amorphization was also observed in the nanocomposites, with an increase in the matrix contents. The enthalpies of the endoeffects of salt melting and phase transitions (160 °C) changed more significantly than the Et4NHSO4 contents in the composites and completely disappeared at x = 0.9. The dependence of proton conductivity on the mole fraction reached a maximum at x = 0.8, which was three or four orders of magnitude higher than the value for pure Et4NHSO4, depending on the composition and the temperature. The maximum conductivity values were close to those for complete pore filling. The conductivity of the 0.2Et4NHSO4-0.8SiO2 composite reached 7 ∗ 10-3 S/cm at 220 °C and 10-4 S/cm at 110 °C.

A brain-wide form of presynaptic active zone plasticity orchestrates resilience to brain aging in Drosophila.

The brain as a central regulator of stress integration determines what is threatening, stores memories, and regulates physiological adaptations across the aging trajectory. While sleep homeostasis seems to be linked to brain resilience, how age-associated changes intersect to adapt brain resilience to life history remains enigmatic. We here provide evidence that a brain-wide form of presynaptic active zone plasticity ("PreScale"), characterized by increases of active zone scaffold proteins and synaptic vesicle release factors, integrates resilience by coupling sleep, longevity, and memory during early aging of Drosophila. PreScale increased over the brain until mid-age, to then decreased again, and promoted the age-typical adaption of sleep patterns as well as extended longevity, while at the same time it reduced the ability of forming new memories. Genetic induction of PreScale also mimicked early aging-associated adaption of sleep patterns and the neuronal activity/excitability of sleep control neurons. Spermidine supplementation, previously shown to suppress early aging-associated PreScale, also attenuated the age-typical sleep pattern changes. Pharmacological induction of sleep for 2 days in mid-age flies also reset PreScale, restored memory formation, and rejuvenated sleep patterns. Our data suggest that early along the aging trajectory, PreScale acts as an acute, brain-wide form of presynaptic plasticity to steer trade-offs between longevity, sleep, and memory formation in a still plastic phase of early brain aging.

Plastic deformation behavior of Pd-based binary alloys: A first-principles study

The generalized stacking fault energy is a critical parameter for plastic deformation and phase transition behavior of alloys. Here, the generalized stacking fault energies of palladium-based binary alloys (Pd 1− x M x , M = Mo, W, Re, Ru, Os, Rh, Ir, Pt; x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) in face-centered cubic (fcc) phase are systematically investigated by combining the coherent potential approximation with the exact muffin-tin orbital method within the framework of density functional theory. Analysis of the plastic behavior of Pd 1− x M x reveals that Mo, W, Re, Ru, and Os alloying elements can promote twinning, which in turn can be used to strengthen Pd alloys. When alloying reaches up to 30 at.% Mo, 40 at.% W, or 40 at.% Re, phase transition from fcc to hexagonal compact packing and stacking faults are the primary deformation of Pd 1− x M x . Contrarily, Rh, Ir, and Pt significantly suppress the twinning ability, and full slip becomes the dominant deformation mechanism. Such distinct deformation behavior of Pd-based alloys is attributed to their electron redistribution upon alloying, owing to the d - d hybridization between alloy elements and Pd atoms. This study gives valuable insight into the phase stability and provides useful guide for the design of high-strength alloys. • Alloying rich Mo, W, and Re into Pd promotes the phase transition from fcc to hcp. • Alloying elements Mo, W, Re, Ru, and Os can promote twinning mechanism of Pd 1−x M x . • Rh, Ir, and Pt alloying with Pd would facilitate full slip deformation. • Deformation of Pd 1−x M x is related to d-d hybridization between alloy atoms and Pd.

Термоактиваційний аналіз температурної залежності твердості квазікристалів системи Al—Cu—Fe

The results of thermoactivation analysis of the temperature dependence of hardness for icosahedral quasicrystals (QC) of the Al—Cu—Fe system obtained as a coating, massive compact and ingot are presented. QC as well as covalent crystals at room temperature are brittle without signs of macroplastic deformation at standard methods of mechanical testing and only the method of local indenter loading makes it possible to deform QC to significant degrees of deformation without fracture. In the studied temperature range 77—1073 K, the HV(T) hardness dependences have the same character, despite the state in which the QC was obtained. The HV(T) dependence consists from two sections: an athermal low-temperature section (77—600 K) and a section (>600 K) where the hardness decreases sharply with increasing temperature. The presence of a low-temperature athermal section on the HV(T) dependence is explained by the phase transition of the QC to a more plastic approximant phase. Phase transition of this type can be associated with a high density of phason defects, which are formed during the deformation of the QC that leads to violations of the atomic structure. Based on the experimental data of the temperature dependences of the Vickers hardness (HV) obtained by the authors and the literature data, the values of the activation energy of the dislocation motion U and the activation volume V of a number of icosahedral quasicrystals were calculated. It is shown that the value of U  0,97—1,83 eV, and V is (65—132)∙10-24cm3. Previously, the method of thermoactivation analysis of tempera¬ture dependence of a flow stress was applied to materials with different crystal structures (BCC, FCC metals, covalent crystals, refractory compounds, intermetallics, high entropy alloys). In comparison with crystalline materials, the values of thermal activation parameters of the deformation process for QC are close to refractory compounds (carbides, borides) which have a covalent component in the interatomic bond. Keywords: quasicrystals, activation energy of dislocation motion, activation volume, hardness, temperature.

FEATURES OF THE CRACKS’ FORMATION IN HETEROPHASE INCLUSIONS OF THE “EUTECTICS OF INCLUSION – MATRIX” TYPE

The purpose of the article − to study of crack nucleation features in heterophase inclusions of the “eutectic of inclusion-matrix” type during steel deformation. Methods. The research was conducted after deformation for a number of different grades steel samples in the temperature range of 20...1 200 °С on Instron-1195 and IMASH-5C with special grippers, with a gripper movement speed of 1 680 mm/min. Research methods were used: petrography, micro-X-ray spectral analysis (Cameca MS-4, Nanolab-7), optical microscopy (Neophot-21). Results. It is found that the variety of phases composing the heterophase inclusions of the "eutectic of inclusion-matrix" type leads to their different behaviour under conditions of plastic deformation. It is shown that the nucleation of brittle or viscous microcracks occurs along the internal interfacial boundaries between the metal matrix and the second phase of the eutectic. It is defined that the cracks’ nature is determined by the plasticity level of the inclusion phases and the deformation temperature. It is shown that the critical degrees of samples’ deformation, at which appreciable microcracks along the internal interphase boundaries appeared, depend on the temperature and the nature of the inclusion phase “eutectic of inclusion – matrix”. It is found that the values of deformation critical degrees determine the level of cohesive strength for internal interphase boundaries in heterophase inclusions “eutectic of inclusion – matrix”. Scientific novelty. The features of microcracks nucleation in heterophase inclusions of the “eutectic of inclusion − matrix” type are determined. It is shown that the nature of the microcracks formed along the interphase boundaries depends on the temperature, plasticity level and combination conditions of brittle and plastic phases in inclusions of the “eutectic of inclusion − matrix” type as well as on the deformation temperature. It is shown that the critical degrees of steels deformation, when microcracks appeared along the internal interphase boundaries, determine the cohesive strength of these boundaries and depend on the temperature and the nature of the inclusion phase “eutectic of inclusion − matrix” type. Practical value. The use of the obtained results will make it possible to develop technologies for producing steels with regulated types of non-metallic heterophase inclusions that will allow to increase considerably their technological and operational characteristics, and also to prevent the formation of various defects during steel pressure treatment and product operation.

FEATURES OF THE CRACKS’ FORMATION IN HETEROPHASE INCLUSIONS OF THE “DISPERSED PHASES IN A NON-METALLIC MATRIX” TYPE

The purpose of the article − to study of crack nucleation features in heterophase inclusions of the “dispersed phases in a non-metallic matrix” type under the conditions of steels’ plastic deformation. Methods. The research was conducted after deformation for a number of different grades steel samples in the temperature range of 20...1 200 °С on Instron-1195 and IMASH-5C with special grippers, with a gripper movement speed of 1 680 mm/min. Research methods were used: petrography, micro-X-ray spectral analysis (Cameca MS-4, Nanolab-7), optical microscopy (Neophot-21). Results. It is shown that the variety of phases composing the heterophase inclusions "dispersed phases in non-metallic matrix" leads to their different behaviour under plastic deformation conditions. At the same time, the nucleation of brittle or viscous microcracks occurs along the internal interphase boundaries between the "non-metallic" matrix and the dispersed particles of the second phase. The cracks’ character near the inclusions determined by the plasticity level of “matri” and dispersed phases of inclusions and the deformation temperature are revealed. The determined critical degrees of samples’ deformation, upon reaching which appreciable microcracks along the internal interphase boundaries occurred, were depend on temperature and the nature of the “dispersed phases in a non-metallic matrix” inclusions. Scientific novelty. The features of microcracks nucleation associated with heterophase inclusions of the “dispersed phases in non-metallic matrix” type with different combination of brittle and plastic phases during steels’ deformation are determined. The types of microcracks occurring in inclusions of the “dispersed phases in the non-metallic matrix” type and the locations of their formation have been determined. It is shown that the values of the deformation critical degrees determine the level of cohesive strength for internal interphase boundaries in heterophase inclusions “dispersed phases in a non-metallic matrix” at different deformation temperatures. Practical value. The use of the obtained results will make it possible to develop technologies for producing steels with regulated types of non-metallic heterophase inclusions that will allow to increase significantly their technological and operational characteristics, and also to prevent the formation of various defects in the steels' treatment by pressure and the operation of products.

Rapid homeostatic modulation of transsynaptic nanocolumn rings

Robust neural information transfer relies on a delicate molecular nano-architecture of chemical synapses. Neurotransmitter release is controlled by a specific arrangement of proteins within presynaptic active zones. How the specific presynaptic molecular architecture relates to postsynaptic organization and how synaptic nano-architecture is transsynaptically regulated to enable stable synaptic transmission remain enigmatic. Using time-gated stimulated emission-depletion microscopy at the Drosophila neuromuscular junction, we found that presynaptic nanorings formed by the active-zone scaffold Bruchpilot (Brp) align with postsynaptic glutamate receptor (GluR) rings. Individual rings harbor approximately four transsynaptically aligned Brp-GluR nanocolumns. Similar nanocolumn rings are formed by the presynaptic protein Unc13A and GluRs. Intriguingly, acute GluR impairment triggers transsynaptic nanocolumn formation on the minute timescale during homeostatic plasticity. We reveal distinct phases of structural transsynaptic homeostatic plasticity, with postsynaptic GluR reorganization preceding presynaptic Brp modulation. Finally, homeostatic control of transsynaptic nano-architecture and neurotransmitter release requires the auxiliary GluR subunit Neto. Thus, transsynaptic nanocolumn rings provide a substrate for rapid homeostatic stabilization of synaptic efficacy.

Colossal barocaloric effects in adamantane derivatives for thermal management

Plastic crystals are currently attracting interest because their solid-state caloric functionality could be used to tackle climate change in two critical areas: (i) more environmentally friendly cooling and heating driven by pressure and (ii) passive waste heat management. Here, we suggest that plastic crystals could also be used for active pressure-assisted (i.e., barocaloric) waste heat management. In contrast to the barocaloric cooling/heating cycle, for active barocaloric waste heat management, the hysteresis may not be a constraint and transition temperatures above ambient are usually desired. In contrast to passive waste heat management, the application of pressure can be an advantage to actively control the absorption and delivery of heat by the plastic crystal. Here, we have investigated the pressure-induced caloric response at the first-order phase transitions occurring above room temperature of three plastic crystals derived from adamantane: 1-adamantanol, 2-adamantanol, and 2-methyl-2-adamantanol. Colossal barocaloric effects have been found for two of them under small pressure changes of 50 MPa. This behavior occurs thanks to a colossal transition entropy change and a large transition sensitivity to pressure, which can simultaneously take place due to enormous transition volume changes. The balance between configurational and volumic entropy changes at the transition has also been discussed. For 2-adamantanol, in addition to the transition to the plastic phase, the less energetic triclinic-to-monoclinic transition at lower temperatures has also been analyzed. The transition temperatures above ambient make these compounds suitable for waste heat management and, thanks to a small hysteresis, also for industrial cooling and heat pumping.

Ionophore based optical sensors using hydrophilic polymer matrix – Ratiometric, pH independent ion-selective optodes

Classical approach for cation selective optode sensing requires high lipophilicity of receptor matrix and optical transducer dye, its application is restricted to relatively narrow pH range. We propose an alternative approach to ion-selective optodes, benefiting from rather hydrophilic polymer - plasticized polycaprolacton. This results in presence of lipophlic (plasticizer) and hydrophilic (sample/polycaprolactone) domains within the nanoprobes proposed. In consequence, this approach allows benefiting from alternative optical transducer: Nile blue dye and its unique properties and in consequence to benefit from new optical transduction mechanism allowing ratiometric sensing with no restriction for the sample pH. The response mechanism involves ionophore and ion pair composed of cation-exchanger and Nile blue cation dissolved in the plasticizer phase. Analyte incorporation to the phase occurs on expense of dye cation release to the hydrophilic phase. Ultimately a red staining of plasticizer phase is observed due to incorporation of neutral dye molecules formed in course of spontaneous hydrolysis occurring in water phase. Thus herein proposed optodes offer observable emission change at two wavelengths (increase of intensity emission as well as decrease) allowing ratiometric sensing in a broad concentration range. Moreover, herein proposed approach is applicable both in acidic and alkaline media, also in the absence of buffer, thus it mitigates significant constrain of classical optodes. As model system potassium or calcium selective nanospheres were prepared.

Coupled microscopic and micromagnetic depth-specific analysis of plastic deformation and phase transformation of metastable austenitic steel AISI 304L by flow forming

Abstract This paper presents the characterization of the microstructure evolution during flow forming of austenitic stainless steel AISI 304L. Due to plastic deformation of metastable austenitic steel, phase transformation from γ-austenite into α’-martensite occurs. This is initiated by the formation of shear bands as product of the external stresses. By means of coupled microscopic and micromagnetic investigations, a characterization of the microstructure was carried out. In particular, this study shows the distribution of the strain-induced α’-martensite and its influence on material properties like hardness at different depths. The microstructural analyses by means of electron backscattered diffraction (EBSD) technique, evidence a higher amount of α’-martensite (ca. 23 %) close to the outer specimen surface, where the plastic deformation and the direct contact with the forming tool take place. In the middle area (ca. 1.5 mm depth from the outer surface), the portion of transformed α’-martensite drops to 7 % and in the inner surface to 2 %. These results are well correlated with microhardness and micromagnetic measurements at different depths. EBSD and atomic force microscopy (AFM) were used to make a detailed characterization of the topography and degree of deformation of the shear bands. Likewise, the mechanisms of nucleation of α’-martensite were discussed. This research contributes to the development of micromagnetic sensors to monitor the evolution of properties during flow forming. This makes them more suitable for closed-loop property control, which offers possibilities for an application-oriented and more efficient production.

Deformation characteristics and permeability variations induced in the coal matrix induced by thermo-mechanical coupling

ABSTRACT To evaluate the coal deformation characteristics and explore the evolution law of coal permeability under different conditions, the MTS815 and PCI-2 acoustic emission (AE) test systems were applied to conduct the triaxial percolation test under other thermo-mechanical coupling conditions, and the fractal model of coal fractal with integrated stress and temperature was established. The results indicated that the peak stress, strength and deformation parameters of the samples were positively correlated with the confining pressure. The temperature can promote the crack propagation, derivation and new cracks of coal samples. The macrocracks and percolation channels space inside the samples increased with the increase of the thermal-mechanical coupling condition. The AE signal was mainly released in the plastic and peak phases; the growth of confining pressure intensified the aggravation of the internal damage to the coal sample and caused the frequent occurrence of AE signals. The compressive coefficient C f of coal fracture decreased with the addition of average effective stress, and the ruptured coal had the same trend with the increase in pore pressure; the calculated values of the new thermally sensitive model were consistent with the measured values. The applicability of the theoretical mechanism and the data matching were of high credibility.

Development of a compliant dashpot model with nonlinear and linear behaviors for the contact of multibody systems

A comprehensive dashpot model with hysteresis damping factors that can provide a convenient calculation approach for the elastoplastic impact behavior in multibody systems is studied in this paper. At the beginning of contact, the nonlinear hysteresis damping factor in the elastic phase is derived by approximately solving a nonlinear vibration system. When impact happens at a relatively high speed with a large load, elastoplastic deformation is inevitable, and Hertz contact stiffness cannot represent the actual contact stiffness. In order to describe the contact stiffness in the elastoplastic or plastic phase correctly, a static elastoplastic contact model is adopted to calculate the contact stiffness by approximately linearizing the relationship between load and deformation. When the contact comes into the elastoplastic phase, the impact behavior can be treated as a linear vibration system, and the linear hysteresis damping factor can be obtained from this linear system. The energy dissipation in different contact phases can be described by a nonlinear and a linear hysteresis damping factors. Such a nonlinear hysteresis damping factor can make up for the deficiency of the static elastoplastic contact model when describing the energy dissipation in the elastic contact phase. Simulation results show that the proposed dashpot model is more harmonious with the static elastoplastic contact model compared to the existing dashpot models. A slider-crank mechanism with a clearance joint and a Hopkinson incident bar are exemplified in the present work by using experimental data to validate the effectiveness of the proposed dashpot model.

Effect of Fluoride Content of Mouthwashes on Superelastic Properties of NiTi Orthodontic Archwires.

The influence of sodium fluoride (NaF) concentration in mouthwashes on the properties of superelastic NiTi orthodontic wires has been studied. In this work, 55.8%Ni and 44.2%Ti (in weight) wires were introduced in commercial mouthwashes with different NaF contents (0, 130, 200 and 380 ppm). The release of Ni2+ and Ti4+ ions was by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) at 1, 4, 7 and 14 days. Superelastic orthodontic wires present at oral temperature the austenitic phase which is transformed into a plastic phase (martensite) by cooling. The temperatures at which this occurs are influenced by the chemical composition. The release of ions from the wire will produce variations in the temperatures and stresses of the stress-induced martensitic transformation. Ms, Mf, As, Af were determined by Differential Scanning Calorimeter (DSC). The transformation stresses (austenite to stress induce martensite) were determined with a servo-hydraulic testing machine at 37 °C. The surfaces for the different times and mouthwash were observed by Scanning Electron Microscope (SEM). The release of Ni2+ in mouthwashes with 380 ppm NaF concentrations reaches 230,000 ppb in 14 days and for Ti4+ 175,000 ppb. When NaF concentrations are lower than 200 ppm the release of Ni and Ti ions is around 1500 ppb after 14 days. This variation in compositions leads to variations in Ms from 27 °C to 43.5 °C in the case of higher NaF concentration. The increasing immersion time and NaF concentrations produce a decrease of Ni in the wires, increasing Ms which exceed 37 °C with the loss of superelasticity. In the same way, the stresses (tooth position corrective) decrease from 270 MPa to 0 MPa due to the martensitic phase. The degradation can produce the growth of precipitates rich in Ti (Ti2Ni). These results are of great interest in the orthodontic clinic in order to avoid the loss of the therapeutic properties of superelastic NiTi due to long immersion in fluoride mouthwashes.

Effect of processing on microstructure and mechanical properties of pentaglycerine based solid-solid phase change materials

The present work addresses the lack of reported information about the mechanical properties of solid-solid PCMs, and how these are affected by their processing, considering that they usually incorporate fillers to increase their thermal conductivity. To this end, this work analyzes pentaglycerine (PG) based composites, which are of great interest in TES intended for 80 °C. These composites are also doped with various contents of expanded graphite (EG) with two different particle sizes. With these combinations, the effect of two typical processing methods, pressing and casting, on the microstructure of the composites is evaluated. Furthermore, the mechanical behavior of these composites in both crystal and plastic phases, as well as their thermal expansion during the transition process, is also reported in the current study. Besides demonstrating the important role that processing plays in these properties in PG/EG-based composites, it has been found that the use of EG is also beneficial for mitigating the permanent deformations experienced by these composites during thermal cycling. Finally, the exposed results give the first evidence of the interesting effect these processing methods have on the thermal properties of the composites.