Papers by Keyword: Dynamic Mechanical Analysis (DMA)

Abstract: The entire simulation process for long fiber reinforced thermoplastics is examined to determine the effective mechanical properties which are influenced by the microstructural fiber orientation state. Therefore, flow and fiber orientation simulations are conducted and the obtained fiber orientation tensors are used in two-scale structural simulations. The fiber orientation distributions as well as the mechanical properties are compared with micro-computed tomography data and results from threepoint bending tests performed by dynamical mechanical analysis (DMA), respectively. The validated results show that prediction of the essential mechanical properties is possible with the applied combinated methods and that the knowledge of the fiber orientation and its gradients is of crucial importance for the entire simulation process.

Abstract: In recent years, polyurea has been successfully applied as a coating material for increasing the survivability of structures and components subjected to critical impact loading conditions. It was also shown that if a polyurea coating is reinforced with ceramic particles or short glass fibers, an enhanced benefit on the overall impact resistance due to the increased dissipation properties of the material can be observed. Notwithstanding the use of polyureas as coating materials for structures protection, other applications where control and damping of vibrations is of concern would benefit from the high dissipation characteristics of the reinforced elastomer. Nevertheless, there are well known drawbacks in the use of the reinforced elastomers which can be identified in their pronounced nonlinear behavior under cyclic loads and the softening of their mechanical properties. In order to investigate such a phenomenon, in this manuscript we present an experimental investigation conducted on the effects of different volume fractions of the same filler on the response of a polyurea elastomer at varying amplitudes of the applied strain. The characterization of the materials was conducted by using a dynamic mechanical analyzer (DMA). From our preliminary results we observed that in the case of polyurea reinforced with short glass fibers, the nonlinear response of the polymer at varying strain amplitudes becomes evident for fillers volume contents of 10%. Furthermore, the nonlinearity of the response of the material due to the Payne effect seems to be associated with the complex fibers-matrix interaction rather than the disruption of the agglomeration of the fillers under load.

Abstract: Dynamic mechanical properties of radial curtain plybamboo and its constitution unit-radial bamboo strip were studied using dynamic mechanical analysis (DMA). The results showed: experimental temperature had great effect on dynamic mechanical properties, the shape and alignment of radial bamboo strips were closely related the dynamic mechanical properties of radial curtain plybamboo.

Abstract: An aviation polysulfide sealant has been soaked in a water bath at 85 °C to study the effects of hydrothermal treatment on this material. The morphology, Shore A hardness, and mechanical properties of the sealant were measured before and after soaking. The glass transition temperature (Tg) and room temperature storage modulus (E') were measured by means of a dynamic mechanical analyzer (DMA). The results showed that the surface glossiness of the polysulfide disappeared, some bubble defects appeared on its surface, the Shore A hardness and the tensile strength increased, while the elongation at break fluctuated with aging. The Tg and E' of the sealant changed only slightly. The chemical structure of the sealant was not obviously changed, and its aggregation state was changed only slightly, thus indicating that this sealant is characterized by good hydrothermal resistance.

Abstract: Polylacticacid (PLA), produced from annually renewable, natural resources is a potential candidate for the partial replacement of petroleum based polymers and also for its biodegradability. PLA is well known for its better mechanical, thermal property but unfortunately the brittleness and rigidity limit its applicability. For a great number of applications such as packaging, fibers, films, etc., it is of high interest to formulate new PLA grades with improved flexibility and better impact properties. In order to develop PLA-based biodegradable packaging, the physico-mechanical properties of commercially available PLA should be modified using plasticizers. For this, PLA was melt-mixed with poly ethylene glycol (PEG) of 600 molecular weights by twin screw extruder. The thermal properties of plasticized PLA were characterized by utilization of dynamic mechanical analysis. The result shows that with addition of plasticizer glass transition temperature (Tg) is decreased sharply and the storage modulus was also decreased.

Abstract: Aviation polysulfide sealants have been subjected to thermo-oxidative ageing. Their morphologies, Shore A hardness, and tensile properties have been tested by means of an optical microscope, a glossiness meter, a Shore A hardness meter, and a universal testing machine. Changes in their microstructures were measured by Fourier-transform infrared spectroscopy and dynamic mechanical analysis (DMA). The results showed that glossiness was gradually reduced, and bubbles appeared on the surface of the samples during the course of ageing. The Shore A hardness of the sealant first decreased and then remained unchanged. Likewise, the tensile strength and tensile elongation percent first decreased and then remained unchanged. The infrared monitoring showed that the sealant underwent a post-cure reaction. The glass transition temperature and the room-temperature storage modulus of the sealant remained unchanged. No new functional groups were formed during ageing of the sealant. The aviation sealants did not undergo chemical degradation, showing that they have good endurance under thermo-oxidative conditions.

Abstract: In this study, temperature dependence of internal friction, tand, of ECAPed Al-Ni eutectic alloy was measured using a dynamic mechanical analysis (DMA) to discuss the recrystallization behavior of the alloy. The temperature dependence of internal friction of 8 passed samples shows a large peak at around 200 °C on heating, while this peak disappears on the subsequent cooling stage. Moreover, smaller peak was observed for 2 passed samples. Therefore, it can be concluded that the origin of the peak comes from the recrystallization of a-Al.