Papers by Keyword: Dynamic Mechanical Property

Abstract: For the sake of studying the influence of loading frequency on the hydroxyl-terminated polybutadiene (HTPB) coating’s dynamic mechanical properties during aging, the one month’s thermal accelerated aging test was carried out at 70°C. The dynamic mechanical properties of the aged HTPB coatings were tested through dynamic mechanical analysis (DMA) Q800 with the loading frequency range of 0~100Hz, the dynamic strain amplitude of 0.1% and the test temperature of 25°C. The change models of the dynamic modulus with the loading frequency were established. The results showed that with the extension of the aging time, the storage modulus and the loss modulus both rose, which were related with the change of the crosslinking network structure. The storage modulus increased exponentially with the loading frequency, and the correlation coefficients fitted by the exponential models were all greater than 0.96. The loss modulus changed in sections. When the loading frequency was less than 70 Hz, the loss modulus showed a cubic function growth relationship with the loading frequency, and the correlation coefficients were larger than 0.98; when the loading frequency was between 70 Hz and 100 Hz, the loss modulus showed a quadratic function relationship with the loading frequency that first decreased and then increased, and the correlation coefficients were all larger than 0.97.

Abstract: As a new material, the microstructure of β20C titanium alloy can match well with property by forging process. However, the microstructure of billet is inhomogeneous in actual forging. For ensuring microstructures homogenization, two forging processes are designed. Process 1 is large deformation above the phase transition (T=1050°C, 70% deformation) and small deformation in two-phase region (T=860°C~890°C, ≤40% deformation). Process 2 is small deformation above the phase transition (T=1050°C, 40% deformation) and large deformation in two-phase region (T=860°C~890°C, 50%~60% deformation). Then microstructures are observed and dynamic compressive strength and the critical fracture strain of samples are test after solid-solution treatment. It turns out that the homogeneity of microstructure of process 2 is improved by heat treatment. The microstructure is lamellar microstructure with 1650MPa dynamic strength and 15% critical fracture strain through “Process 1 + 840°C 1h/FC” while the microstructure is equiaxed microstructure with 1650MPa dynamic strength and 20% critical fracture strain through “Process 2 + 840°C 1h/FC”. In conclusion, the microstructure of large deformation in two-phase region can accumulate more deformation energy which is beneficial for dynamic recrystallization.

Abstract: Ti-5553(Ti-5Al-5Mo-5V-3Cr-1Fe) is a new near-β Titanium alloy with some applications as structural components in aircrafts. In this paper, Ti-5553 alloy was heat treated at four different solid solution temperatures: 770°C, 790°C, 830°C and 850°C, followed by the same aging treatment. Quasi-static compressive and tensile experiments as well as Split Hopkinson Pressure Bar (SHPB) compression experiment were carried out to investigate the mechanical properties of Ti-5553 alloy. The microstructure evolutions were characterized using Optical Microscope (OM) and Scanning Electron Microscopy (SEM). The experimental results demonstrated that different microstructures of Ti-5553 alloy were obtained through four different heat treatment procedures. The main microstructures are aα+βb with different volume fractions. Ti-5553 alloy treated at 770°C, with secondary α precipitates embedded in β matrix, behaves the best combination of strength and toughness. In dynamic compression, strain rate hardening effect occurs exclusively in the samples with the Widmanstatten structure and not occurs in other samples.

Abstract: A series of vinylidenefluoride (VDF) and chlorotrifluoroethylene (CTFE) copolymers were prepared by radical copolymerization, the chain elements structures of the copolymers were gain with the elemental analysis, and the crystal regions with X-ray diffraction spectrum. The effect of chain elements structure on the crystallinity and dynamic mechanical properties was discussed with the DMA analysis. The result shows: the increasing of the CTFE content decreases the chain elements structure of VDF-VDF, the random distribution of VDF-CTFE structure has a great effect on the crystallization properties and the dynamic mechanical properties. The increasing of CTFE content improves the storage modulus and the damping of copolymers in the amorphous copolymers, while the distribution of chain segments’ length gets narrower.

Abstract: The paper aims a comparison with respect to the dynamic mechanical properties of few hybrid polymer based composite architectures based on experimental data against micro-mechanical models based numerical predictions. The hybrid polymer based composites considered were particle-fiber combinations reinforced within an unsaturated polyester resin to provide different architectures. Variations in storage modulus (E’), loss modulus (E’’) and damping factor (tan δ) with temperature increase and different particle volume fraction were investigated. Data comparison reveals the herein composite architectures’ performances over the benchmark and enables further insight into the material development and characterization issues.

Abstract: The high strain rate deformation behavior of as-annealed and as-cold rolled pure titanium was inspected by Split Hopkinson Pressure Bar (SHPB). The effect of deformation structure on adiabatic shear behavior in pure titanium was analyzed from the aspect of dynamic mechanical response and microstructural evolution. It was found that the strong {0001} basal texture was formed in as-cold rolled pure titanium. There were Geometrically Necessary Boundaries (GNBs) with spacing of 0.6μm and Incidental Dislocation Boundaries (IDBs) with size of 80nm in one grain. The enhancement of adiabatic shear sensitivity in as-cold rolled titanium was attributed to the deformation induced dislocation boundaries. The core of adiabatic shear band (ASB) was full of fine equiaxed grains with average size of 0.4μm, which was induced by dynamic recrystallization.

Abstract: The dynamic mechanical property and microstructure evolution of commercial pure titanium with initial lamellar dislocation boundary structures were studied at different strain rate compression. The experiments were conducted to the cylindrical specimens using Gleeble-3500 thermal mechanical simulation machine at room temperature. With increasing of the strain rate, strain rate strengthening effect was found in the material. New dislocation boundary structures along impact direction were generated which perpendicular to initial dislocation boundary. Then the S bands boundary structure was formed by interaction between new and initial dislocations. It can be supposed that initial dislocation boundary are sheared and kinked by new dislocation slipping.

Abstract: In this article, the damping mechanism of organic hybrids consisting of Nitrile Butadiene Rubber (NBR) and phenolic oligomer 4-methyl-pheno reaction products of both dicyclopentadiene and isobutylene (MPDI) were investigated by dynamic mechanical analysis (DMA). It was shown that NBR/MPDI blends exhibit only one damping peak, which shifted to higher temperature with the increase of MPDI content, and the maximum of tan δ peak decreased slightly when the ratio of NBR/MPDI was no more than 100/20, and then increased when the ratio rised from 100/20 to 100/80. Fourier transform infrared spectrum (FT-IR) showed that the hydrogen bond were formed between -OH of MPDI and a-H of NBR. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) measurements indicated that MPDI exhibit amorphous features, which was compatible with the blends. These may imply that much more stable damping material with both higher tan δ peak and controllable damping peak position can be achieved.

Abstract: The Composite based on CIIR and variable sulfur/accelerator ratio were prepared by compounding and vulcanizing process. Tensile properties and dynamic mechanical properties of CIIR were studied. The results indicate that tensile strength and loss factor are influenced by sulfur/ accelerator ratio. Tensile strength and modulus are improved with increasing sulfur/accelerator ratio while loss factor decrease with increasing sulfur/ accelerator ratio.

Abstract: Two-step casting method was developed for preparing quasi constrained layer damping structural polymeric composite. Quasi constrained layer structural piezoelectric ceramic P82/carbon black(CB)/epoxy resin(EP) composites were successfully prepared when the ceramic content was less than 30% in volume. Dynamic mechanical analysis(DMA) showed that the composites with quasi constrained layer structure exhibited perfect damping properties. When the piezoelectric ceramic P82 volume fraction was 10%, the composite showed the highest loss factor peak value of 1.182, the widest damping temperature range of 44.2°C, and the largest loss area of 32.17. The storage moduli of composites with quasi constrained layer structures were higher than that with non quasi constrained layer structure.