Papers by Keyword: Glass Transition

Abstract: This study examines the influence of the structural type of bitumen and its consistency on deformation behavior under low-temperature conditions, focusing on the glass transition temperature range, which is critical for the design of frost-resistant asphalt pavements. Motivated by the challenge of low-temperature cracking – a primary cause of asphalt pavement deterioration in cold climates – the research addresses the need to enhance bitumen’s stress relaxation capabilities to mitigate thermal cracking and extend pavement lifespan. Bitumen samples of gel, sol, and sol-gel structural types with different penetration grades (35/50, 100/150, and 160/220) were tested for creep compliance under axial tension at temperatures from -40 °C to 0 °C. The results showed that gel-type bitumen exhibit significantly higher creep compliance compared to sol-type bitumen with the same penetration, indicating better deformability. Specifically, gel-type bitumen demonstrated a plasticity index (m-value) 1.5–1.7 times higher than sol-type bitumen in the range from -40 °C to -30 °C, reflecting enhanced stress relaxation. The glass transition temperature of gel-type bitumen was found to be 4–6 °C lower than that of sol-type bitumen, further supporting its suitability for cold climates. These findings provide quantitative insights into optimizing bitumen selection for frost-resistant pavements, offering a creep compliance testing method that is simpler than traditional BBR and DSR approaches. The results are significant for improving pavement durability in regions with extreme temperature fluctuations, reducing maintenance costs, and guiding the development of performance-graded bitumen specifications.

Abstract: For the purpose of this investigation, carbon and Kevlar fiber-reinforced plastics were subjected to dynamic testing. Carbon-Kevlar fibers are included into the LY 556 resin and AR 951 hardener. Fiber makes for 40% of the study's total weight. The carbon and Kevlar composites were created by hand lay-up. The orientation considered in this research is 0/0 and 0/90 for both carbon and Kevlar composites. Advanced characterizations such as TMA and DMA has been integrated in this research. By using DMA (Dynamic Mechanical Analyzer) and the thermomechanical Analyzer (TMA), the dynamic properties were acquired. ASTM E756 was used to conduct the tests. Composite heating at room temperature to 120⁰ C was the temperature variable under investigation. The studies were conducted on TMA and DMA with a force of 0.002N, respectively. DMA uses a three-point bending loading design for its samples. Temperature affects the dimensions, storage modulus, loss modulus, and tan delta.

Abstract: The thermal and magnetic properties of the ternary Fe-B-C and quaternary Fe-B-C-Si amorphous alloys have been investigated. It has been discovered that the ternary Fe-B-C amorphous alloys with compositions close to Fe_79.3B_14.3C_6.4 exhibit a glass transition prior to crystallization on heating. The alloys also have high mass magnetization of 176–178 A m²/kg at room temperature. In addition, the glass-forming ability (GFA) of the alloys is significantly enhanced by the addition of 4 at% Si while maintaining high magnetization of approximately 170 A m²/kg at room temperature. In was found that the Fe₂₃(B, C)₆ phase (Cr₂₃C₆-type) is formed during crystallization of the quaternary Fe-B-C-Si alloys with the large GFA. It was also confirmed that the amorphous powders of Fe-Cr-B-C-Si alloys could be produced by a conventional water atomization method and exhibit the low core losses of 305–362 kW/m³ at 100 kHz and 100 mT. The quaternary Fe-B-C-Si amorphous alloys with high GFA, high magnetization and low core losses are suitable for a core material of various magnetic components.

Abstract: The paper discusses measurement problems of heat deflection and glass transition temperatures of fiber-reinforced plastics by the Martens test and thermomechanical analysis (TMA). By using the Martens test, thermomechanical profiles were obtained for an epoxy binder and glass fiber- (GFRP) and basalt fiber-reinforced (BFRP) plastics under load ranging from 5 to 75 MPa. The onset temperature of severe deformation of GFRP and BFRP was found to be 15–20°С higher than that of the epoxy binder they were made of. GFRP and BFRP were tested by TMA in the lengthwise and crosswise fiber orientations. In crosswise measurement, TMA curves showed two noticeable inflection points corresponding to two thermal transitions. This can be explained by the cured binder being present in two states in the composites. The interfacial layer contiguous to the fibers had a lower glass transition temperature (T_g) than the matrix layer located in the interfibrous space; moreover, T_g of the composites under flexural load was similar to that of the matrix.

Abstract: The properties of a resin transfer molded sheet of strand-reinforced composite for automotive applications are investigated at the microscopic level. Three components of the composite can be identified in the bright field micrograph – glass fibers, epoxy matrix and binder. The latter having been added in manufacturing process. Accelerated Nanoindentation with 64.451 single indentation experiments is performed at room temperature to generate a mechanical property map of an area containing the 3 components. The distribution of properties, mean value and standard deviation, is determined for each component. Two locations in the composite are selected for a study of the local glass transition behavior by performing dynamic indentation experiments while simultaneous variation of the temperature of the indenter tip and sample within a micro-heating chamber.

Abstract: Nanocomposite was prepared using unsaturated polyester (UP) resin as a matrix and graphene nanoparticles as a reinforcement material in six percentage weights (0, 0.1, 0.2, 0.3, 1 and 1.5%). Mechanical, calorimetric and thermal studies were performed on the (UP) resin/graphene nanocomposite. All tests showed a clear improvement of all mechanical properties examined (hardness, flexural strength (F.S), impact strength (I.S) and tensile strength (T.S)) with increasing graphene percentage. In addition, the temperature of glass transition and thermal conductivity of this composite increased with increasing graphene content.

Abstract: Re-examination of published conductivity spectra for 2Ca (NO₃)₂∙3KNO₃ (CKN) in its molten and glassy states, in terms of the MIGRATION concept, has brought to light new links between elementary processes occurring within one picosecond and their successful outcomes, i.e. those which determine the DC conductivities. The starting point of this analysis is the transition at 378 K, which arises from a change from a decoupled to a coupled transport mechanism. Remarkably, while there is a change in the shape of the conductivity dispersion and a jump in its onset frequency, there is no change in the temperature dependence of DC conductivity. What emerges from the analysis is a surprising continuity in high-frequency behaviour, with the activation energy and volume for elementary displacements, E_ed and V_ed, remaining constant from 300 K in the glass up to 500 K in the melt. The ratio, E_ed/V_ed, turns out to be equal to our previously defined DC activation moduli for CKN, given by E_DC(T)/V_DC(T) and T_g/(dT_g/dp) for charge transport in the melt and structural relaxation at T_g, respectively. It seems that, at very short times, molten CKN behaves just like an elastic solid. The importance of elastic forces for ionic transport in CKN is corroborated by the finding that the published value of the high-frequency shear modulus of glassy CKN, G_¥, matches those of E_ed/V_ed and hence of both activation moduli. The detected continuity in the picosecond behaviour of CKN across the glass transition could provide a new link between fragile liquids and glassy materials in general.

Abstract: The aim of this work was to improve the mechanical properties of polylactic acid (PLA) by natural oil polyol. Castor oil is natural oil polyol used for this work. It was directly extracted from castor seed and without chemical modification. The contents of castor oil were varied from 0 to 10 wt%. The effect of castor oil content on mechanical properties of PLA were evaluated by tensile and impact testings. Differential scanning calorimetry (DSC) and morphology analysis were used for explanation of the result. The result showed that the elongation at break and impact strength of PLA /10 wt% castor oil blend were increased about 108 and 30 % as comparing neat PLA whereas tensile strength tended to decrease about 24 %. The changes in glass transition temperature, crystallinity content and morphology of PLA corresponded well with the result of mechanical properties.

Abstract: Bearings of small turbo machines support high speed rotors rotating with the frequency over 1 [kHz]. Such bearings are often supported with O-rings made of soft materials like rubber to attenuate high frequency oscillations. Dynamic properties of rubber supporters have been measured experimentally for individual dimensions, but the universal prediction of dynamic properties for various frequencies is difficult not only because rubbers exhibit nonlinearity against its strain, but because O-ring supporters deform heterogeneously. For the precise prediction, it is necessary to investigate the viscoelasticity of rubber under various deformations and frequencies. Such properties can be measured by the standard shear vibration non-response method of ISO 6721-6 (JIS K 7244-6). However this is applicable only to low frequency range under 100 [Hz] because of the limitation of resonance frequency of the load cell. In this research, based on BERM (Base Excitation Resonant Mass) method, a new method was developed to measure the complex shear modulus at high frequencies up to 1 [kHz] of rubber sheets under homogeneous shear deformations. In the presented method, the force is calculated from the acceleration of the mass instead of the direct measurement by a load cell. Hence accurate measurement became possible even in the range beyond the resonance frequency of a load cell. The measured shear storage modulus G’ and shear loss modulus G” of deformed rubber were presented.

Abstract: Amorphous solids prepared from their melt state exhibit glass transition phenomena upon heating. Derivatives of volume like viscosity, specific heat and thermal expansion coefficient show rapid changes at the glass transition temperature (T_g). In general, application f high pressure increases the T_g (a positive dT_g/dP). This positive dTg/dP has been well understood with the Free Volume and Entropy models. However, there are few exceptions where a negative dT_g/dP has been observed. It has been proposed that the glasses which undergo negative thermal expansion can exhibit a negative dT_g/dP. In this study, electrical resistivity of semiconducting Ge₂₀Te₈₀ glass at high pressures as a function of temperature has been measured in a Bridgman anvil apparatus. Electrical resistivity showed a pronounced change at T_g. The pressure dependence of T_g (dT_g/dP) shows a decreasing trend (-dT_g/dP). Chalcogenide glasses like Se, As₂Se₃ and As₃₀Se₃₀Te₄₀ show a positive dT_g/dP in contradiction to the present observation of negative dT_g/dP. A model proposed by deNeufville and Rockstad finds a linear relationship between T_g and the optical band gap (E_g) when they are grouped according to their connectivity (Z_av).Application of high pressure decreases the interatomic distance which in turn decreases the separation between the valence and conduction bands (optical band gap). This reduction in optical band gap shifts the glass transition to lower values. It is also suggested that the sign of the pressure derivative of T_g can be negative (-dT_g/dP) if the thermal expansion coefficient is negative. Inelastic neutron diffraction studies show a negative thermal expansion coefficient for most of the Te based chalcogenide glasses. Hence, Ge₂₀Te₈₀ glass is uniquethat its pressure dependence of T_gobeys both thermodynamic and the T_g-E_g-Z_av models.