Papers by Keyword: Rate Dependence

Abstract: Combined with the research of dynamic mechanical properties of concrete under earthquake action by lots of scholars home and abroad, research status of rate-dependent test within the scope of the Earthquake strain rate (10^-4/s~10^-1/s) on common concrete materials is reviewed, including the dynamic uniaxial compressive properties, dynamic uniaxial tensile properties, as well as multi-axis dynamic performance. The influence of the Earthquake strain rate on concrete strength, energy absorption capability and deformation capacity such as the elastic modulus, Poisson's ratio, peak strain, and ultimate strain are discussed intensively. Results show that the tensile strength, compressive strength and energy absorption capability of concrete increase with the increase of strain rate, while the results of the various parameters of the deformation ability are not consistent, the reason is that different test results caused by different test conditions. In this paper, the reference for the further study on rate-dependent of concrete in the future is provided.

Abstract: In this paper, the static and dynamic mechanical viscoelastic behavior of NEPE propellant are studied. Under static conditions, five samples were subjected to constant-strain-rate monotonic loading with five different loading rates at room temperature. The dynamic mechanical analysis was employed for measurements of temperature and frequency dependence of the NEPE propellant by mean of BOSE-DMA-ELF3200 in frequency range from 1Hz to 16Hz. And get the dynamic mechanics temperature spectrum In the low temperature region, a single relaxation is observed in loss modulus-temperature Curves, which is glass transition relaxation. The results showed that NEPE propellant showed rate dependence and the same mechanical properties in the lower temperature and higher frequency.

Abstract: The micromechanical investigation of fiber cross-section shape effect on the rate sensitive nonlinear behavior of a glass/epoxy was performed at 10^-5/s and 1/s, which considering four shapes, square, cross, circle and ellipse. With the strain of different rate loadings measured by Fibre Bragg gratings (FBGs) sensors, the rate-dependent inelastic constitutive relationship of epoxy is built by using an internal state variables viscoplasticity model. Then, through homogenizing the properties of unit cells, the responses of resin and its composites at 30° and 60° off-axis loadings are predicted by a micromechanical model compared with the experiments data. The effect of fiber cross-section fiber on the 30° and 90° off-axis responses are discussed with respect to the viscoplastic parameters of the resin determined. The results indicate that the micromechanical model accurately calculates the behavior of the PMCs employed. The square fiber causes the largest flow stress and plastic strain in the four cases. And the influences on overall responses for the four fiber shapes are enhanced with raising off-axis angles but weaken with the rate increase. However, the elliptical fiber yields the highest modulus in linear elastic stage. The square fiber is the most effective and the elliptical fiber is the least effective in the nonlinear deformation stage. Besides, the elastic properties are unaffected by loading rates when it is less than 1/s.

Abstract: High damping capacity is one of the prominent properties of NiTi shape memory alloy (SMA), having applications in many engineering devices to reduce unwanted vibrations. Recent experiments demonstrated that, the hysteresis loop of the stress-strain curve of a NiTi strip/wire under a tensile loading-unloading cycle changed non-monotonically with the loading rate, i.e., a maximum damping capacity was obtained at an intermediate strain rate (ε^._critical). This rate dependence is due to the coupling between the temperature dependence of material’s transformation stresses, latent-heat release/absorption in the forward/reverse phase transition and the associated heat exchange between the specimen and the environment. In this paper, a simple analytical model was developed to quantify these thermo-mechanical coupling effects on the damping capacity of the NiTi strips/wires under the tensile loading-unloading cycle. We found that, besides the material thermal/mechanical properties and specimen geometry, environmental condition also affects the damping capacity; and the critical strain rate ε^._critical for achieving a maximum damping capacity can be changed by varying the environmental condition. The theoretical predictions agree quantitatively with the experiments.

Abstract: In order to investigate the effect of loading rate on the tensile performance, the uniaxial tensile experiments were conducted on universal testing machine under different loading rates (5 mm/min, 10mm/min, 50 mm/min, 100 mm/min and 150 mm/min), and a constant gage length equal to 200mm, resulting in loading strain rate of 4.17×10-4, 8.33×10-4/s, 4.17×10-3/s, 8.33×10-3/s,1.25×10-2/s, and the tensile stress-strain curves were obtained. The experimental results show that the tensile properties of the conveyor belt exhibit obvious rate-dependent behavior. In this paper, the rate sensitivity coefficient varied with loading rate, was calculated, and the nonlinear rate-dependent behavior was also investigated.

Abstract: In the current paper, a macroscopic differential model is constructed on the basis of the Landau theory of the first order phase transformation. Hysteresis loops and butterfly-shaped behaviors are modeled as a consequence of polarizations and orientation switchings. A non-convex free energy function is constructed to characterize different polarization orientations in the materials. Polarizations and orientation switchings are modeled by formulating the system state switching from one equilibrium state to another, as differential equations. The hysteresis loops and butterfly-shaped behaviors are successfully modeled. Comparison of the model results with the experimental counterpart is also presented.