Papers by Keyword: DMA

Abstract: Poly (ethylene 2,5-furandicarboxylate) (PEF) is a bio-based polyester that is the subject of growing interest as a potential alternative to Poly (ethylene terephthalate) (PET) for sustainable packaging. Its excellent gas-barrier properties and reduced carbon footprint make it a promising candidate, but its use at industrial scale requires a solid understanding of how temperature and thermal history affect its mechanical and viscoelastic behavior. In this study, Differential Scanning Calorimetry (DSC), Dynamic Mechanical Thermal Analysis (DMA), and optical microscopy were used to characterize the thermal transitions and crystallization behavior of PEF, compared with PET and recycled PET (rPET). DSC results show that thermal crystallization of PEF proceeds very slowly, a result confirmed by in-situ microscopy. DMA measurements provide complementary information on the evolution of both storage and loss moduli with temperature, highlighting its dependence on crystallinity and thermal history. Together, these thermal and mechanical analyses clarify how PEF’s crystallization behavior affects its thermo-mechanical response. From a processing perspective, the very slow thermal crystallization of PEF is advantageous for stretch blow molding (SBM) process of bottles, as the polymer remains essentially amorphous during heating and crystallizes predominantly under deformation during the fast forming stage.

Abstract: This article presents a comprehensive study on the damping of vibrations in a motor-pump assembly using viscoelastic and constrained layer damping treatments. The assembly's structural model, designed using SolidWorks software, is subjected to modal and harmonic analyses in ANSYS. The primary goal is to mitigate vibration amplitudes originating from the motor and pump to enhance the assembly's operational performance. Three damping treatments are investigated: Free Layer Damping (FLD), Sandwich Constrained Layer Damping (CLD), and a novel Multilayer CLD approach. The viscoelastic material is modeled using the Prony series method, and its properties are incorporated into the finite element analysis Results demonstrate that the application of damping treatments significantly reduces vibration amplitudes compared to the untreated structure. Among the treatments, the Multilayer CLD approach exhibits the highest damping efficiency, reducing the maximum amplitude by approximately 52% compared to the base structure. The study showcases the advantages of utilizing viscoelastic and constrained layer damping techniques for enhancing vibration control and operational stability in industrial assemblies. The research findings contribute to the field of structural dynamics and vibration control, offering valuable insights into the design and optimization of mechanical systems subjected to dynamic loads. This study opens avenues for further research and practical applications aimed at improving the performance and reliability of motor-pump assemblies and similar industrial equipment.

Abstract: The global scientific community for the last three decades focuses mainly on polymer-based nanocomposites due to their ease of fabrication, flexibility, and above all easiness to handle them. Among the polymer materials, polyethylene got the attraction because of its readiness to be combined with most of the filler materials available in natural form as well as newly synthesized ones. The present study focuses on the synthesis of nanocomposites of Low-density polyethylene (LDPE) with graphene oxide nanoparticles as the filler. The graphene oxide nanoparticles are synthesized using a modified Hummers method. The composites are prepared by varying the amount of graphene oxide nanoparticles in the LDPE matrix using the melt extrusion method. The nanocomposites prepared were found to have good mechanical properties compared to the virgin LDPE material. The Dynamic Mechanic Analysis (DMA) confirmed that the quantity of the graphene oxide nanoparticles has a major role in the viscoelastic behaviour of the composites.

Abstract: Carbon nanotube yarns (CNTYs) are twisted hierarchical fibers which exhibit a strong property-structure relationship. Understanding of the property-structure relationship of CNTYs will allow their use in structural and energy dissipation (damping) applications. For this reason, the morphology and structure of dry-spun CNTYs are characterized by means of Raman spectroscopy mapping, atomic force microscopy, and scanning electron microscopy and correlated to their quasi-static and dynamic mechanical properties. The continuous CNTYs present some degree of structural variability, which explains the variability measured in their dynamic mechanical response. Under tension, 42.3 μm diameter (0.71 porosity) CNTYs reach specific strengths of ~0.8 N/tex and ultimate strains ranging from 4% to 7%. Mechanical hysteresis tests under incremental cyclic strain show that the CNTYs exhibits high energy dissipation, which concur with dynamic mechanical analysis (DMA). DMA shows that CNTYs are unconventional materials with high specific stiffness (per unit weight) as well as a very high damping ratio. The damping ratio increases with temperature and reach ~0.6 at 60 °C. The mechanical response of the CNTYs under tension can be explained mainly from changes in the hierarchical structural conformation of the yarn, rather than from changes in the carbon nanotube bond distance or inherent material properties.

Abstract: The objective of this research was to investigate the influence of mixing condition on mechanical, thermal, and electrical properties of the biocomposite between poly(lactic acid) (PLA) and hybrid graphene (HG). PLA/HG composites of a fixed weight ratio (95/5 wt%) was mixed using an internal mixer, which the mixing temperatures (170, 180 and 200°C) and the rotor speeds (40, 60 and 80 rpm) were varied. It was found that the increase of E' before glass transition was attributed to the reinforcing effect of the HG. The faster the rotor speed was the higher storage modulus (E') was achieved at the lowest mixing temperature. The E' did not linearly depend on the rotor speed when mixing at higher temperature. As expected, mixing HG into PLA reduced the surface electrical resistivity. The mixing at 170°C with any rotor speed and mixing at 180°C with rotor speed of 40 or 60 rpm produced the composites in the same surface electrical resistivity, however, there was no significant difference when mixing at 200°C. From DSC analysis, there was a trend that the degree of crystallinity of the PLA/HG composites prepared at the lowest mixing temperature was higher than those prepared at the relatively higher mixing temperatures.

Abstract: A new fiber (x) reinforced Dynamic Covalent epoxy-polyurea Interface (x-DC_EPI) shows good mechanical energy transferability of impact and vibration forces. The bonding property of x-DC_EPI interface, engendered between curing, or reactive, epoxy and dynamic polyurea, is controlled by epoxy curing time (t_c). The reaction of curing epoxy, where t_c is a thermodynamic processing parameter, and fast-curing/ dynamic aliphatic polyurea, which lacks polyol in its resin chain extender, is linked to bulk mechanical energy transfer, quantified specifically via the loss modulus of x-DC_EPI. The parameter t_c effectuates designable chemical bond properties within x-DC_EPI. Using Generalized Maxwell models, viscoelastic properties of epoxy, polyurea, and x-DC_EPI are predicted, and results are verified using Dynamic Mechanical Analysis (DMA). The Maxwell models for x-DC_EPI, as a function of t_c, are used in a finite element analysis (ABAQUS) to control performance of dynamically loaded structures.

Abstract: New requests from the automotive industry suppose to apply new materials with mechanical resistance to heat and vibrations and also with low weight. In order to replace plastic materials with high damping capacity a viable solution can be the metallic materials with sufficient internal friction to transform the external mechanical energy in thermal energy without affecting the microstructure or the mechanical properties of the metallic materials. In automotive applications an important role, especially in low velocity impacts, are the bumper elements. In this article possibility of copper-based shape memory alloys to fulfill the damping necessity of metallic materials is analyzed. Dynamic - mechanical analyze of few copper based shape memory alloys is realized and the results compared to proposed a better solution of Cu-based shape memory alloy for damping materials applications. The damping capacity difference between martensite and austenite like phases is also analyzed.

Abstract: Composite materials do offer freedom to design a material fitting best to the requirements of a given application. In case of fiber reinforced polymers especially the low weight in combination with other favorable properties, e.g. high mechanical performance, are the driving force for their application. Materials from renewable resources are of high interest if sustainability is aimed. In this paper, in a holistic approach a green composite is aimed to be used in a rotor blade for wind energy production. The challenging topic for this approach is to identify a possibility to gain a thermoset resin being really green, i.e. based on renewable resources and being not critical, e.g. toxic, at any stage of the whole processing chain. For this purpose several different approaches are studied and compared with other solutions based on green resin systems from other resources and conventional petrochemical based resin systems. A hemp seed oil based epoxy resin has been tested successfully. But to be completely free of petrochemicals, bio-based hardener and catalysts are still an open topic. For manufacturing of a rotor blade an infusion process has been used and it was found, a through thickness impregnation of the natural fiber yarn based textile structure results in entrapped air. Only in-plane saturation delivered completely impregnated structures.

Abstract: In this study, vinyl ester –Jute fiber biocomposites were prepared using vacuum-assisted resin infusion (VARI) process. Woven Jute fibers were used with mass fraction 0.68. Multi-walled carbon nanotubes (MWCNTs) are added to the resin with weight ratio 0.5: 99.5 to investigate the thermo-mechanical properties of bio-composites. Storage and loss modulus of vinyl ester bio-composites were investigated in the presence MWCNTs over a range of temperature (25 to 160 ^oC) to measure the capacity of bio-composite to store and dissipate energy. Damping properties of vinyl ester bio-composites were studied in terms of tan (d). Viscoelastic test using dynamic mechanical analysis (DMA) showed that the glass transition temperature increases with the addition of MWCNTs up to 112.4 ^oC. Addition of jute fiber reinforcements improves the storage modulus value of vinyl ester more than 65% at room temperature. Significant improvement in storage modulus was found in the presence of MWCNTs.

Abstract: Trivalent iridium complexes have been recently studied due to the extent of its overlap with the solar spectrum as well as the accessibility of its ligand-ligand charge transfer (LLCT) transition in the UV region. Entrapment of the complex inside faujasitic zeolite NaY converts the dye molecule into a heterogeneous catalyst that has greater stability and usability than the free complex. Ship-in-a-bottle assemblies of trisphenanthroline iridium (III) complex unto zeolite NaY were found to produce singlet oxygen upon illumination. The possible use of these solid-state catalyst for waste water treatment was examined by using 9,10-dimethylanthracene (DMA) as a chemical trap for singlet oxygen. The degradation spectra was observed to be pseudo-first order with respect to DMA. Varying the time of illumination showed that the amount of DMA degraded was directly dependent on the length of UV irradiation.