CREEP PROPERTIES AND PREDICTION MODEL OF PADDY SOIL UNDER COMPRESSION

In order to study the compressive creep properties and laws of paddy soil, multi-stress creep experiments of paddy soil with different moisture content were carried out. The results show that the creep deformation of paddy soil, subjected to compressive loads effect, develops stably and the paddy soil is not destructed under the yield strength when the stress is low. When the stress level is higher than the yield strength, the internal damage of paddy soil would be caused at the moment of loading. With the extension of creep time, the cracks would gradually expand, resulting in the soil to yield, break and disintegrate. According to the analysis of the deformation properties of paddy soil under compression and the change trend of creep curve, the nonlinear viscoelastic-plastic model was composed of the nonlinear viscoplastic model and Burgers model in series. The creep test curve was introduced into the model for fitting, and the coefficient of determination reached more than 0.96. Based on the model, the strain composition, strain proportion, and strain rate of paddy soil were studied. Finally, the nonlinear model was compared with Burgers model by verification test. The fitting accuracy of the nonlinear model was better than Burgers model, and the coefficient of determination and relative error were 0.997 and 0.437%, respectively, which proved the rationality and correctness of the nonlinear viscoelastic-plastic model. This study can provide a theoretical basis for the optimization of tillage machinery structure and the simulation analysis of soil tillage and compaction.

Temperature and Stress Effects on the Compressive Creep Behavior of Parallel Strand Bamboo

Parallel strand bamboo (PSB) is an engineered bamboo product fabricated using crushed bamboo fiber bundles. Recently, this product finds applications in the civil engineering field. It is expected that the use of this composite will continue to grow because of its excellent mechanical performance, relatively low variability in material properties, and shape standardization. Modern bamboo structures made from PSB composites may be subjected to temperature variations during service. So far, however, there has been little discussion about the temperature-dependent creep. In this study, an investigation was carried out on the short-term behavior of the compressive property of PSB. A stress range of 8 to 64 MPa over a temperature range of 25°C to 75°C was considered in the 24-hour creep tests. In addition, Burgers model was adopted to describe the short-term creep behavior of PSB. Temperature and stress effects on the creep compliance of the Burgers model were also discussed.

Comparative Analysis of Viscoelastic Properties of Open Graded Friction Course under Dynamic and Static Loads

The viscoelastic properties of open graded friction course (OGFC) are closely related to anti-permanent deformation ability, noise reduction ability and durability. To study the viscoelastic parameters of OGFC under dynamic and static loads and to establish the functional relationship between them, uniaxial compression creep tests and dynamic modulus tests were performed to obtain the creep compliance and the dynamic modulus of OGFC. In addition, the Burgers model, modified Burgers model, second-order extensive Maxwell model, Scott-Blair model and modified Sigmoid model were employed to quantitatively analyze the dynamic and static viscoelastic properties of OGFC. Subsequently, the relaxation modulus of OGFC was deduced by the viscoelastic theory. Then, the dynamic modulus of OGFC was calculated according to the deduced relaxation modulus. Based on the calculated values and the measured values of dynamic modulus, the functional relationship of viscoelastic parameters of OGFC under dynamic and static loads was established. The results show that the increase in test temperature has adverse effects on the viscoelastic indexes of OGFC, such as creep compliance, relaxation modulus, and dynamic modulus; the dynamic modulus derived from static creep compliance has a good linear correlation with that obtained by dynamic modulus tests, but the correlation of the phase angle is poor.

Determination and verification of the calculated model parameters of salt rocks taking into account softening and plastic flow

The article suggests using a combination of the modified Burgers model and the Mohr – Coulomb model with the degradation of the adhesion coefficient and the increase in the friction coefficient to determine the parameters of salt rocks. A comparative analysis of long-term laboratory tests and field observations in underground mine workings with the results obtained using a calculated model with certain parameters is carried out. The parameters of the Mohr – Coulomb model with the degradation of the adhesion coefficient and the increase in the friction coefficient were obtained from the statistically processed data of laboratory tests, and the parameters of the modified Burgers model were determined. Using numerical methods, virtual (computer) axisymmetric triaxial tests, both instantaneous and long-term, were performed on the basis of the proposed model with selected parameters. A model problem is solved for comparing the behavior of the model with the data of observation stations in underground mine workings obtained from borehole rod extensometers and contour deformation marks. The analytically obtained coefficients of the nonlinear viscous element of the modified Burgers model for all the analyzed salt rocks did not need to be corrected based on the monitoring results. At the same time, optimization was required for the viscoelastic element coefficients for all the considered rocks. The analysis of the model studies showed a satisfactory convergence with the data on the observation stations. The comparative analysis carried out on the models based on laboratory tests and observations in the workings indicates the correct determination of the parameters for salt rocks and the verification of the model in general.

Study on Mechanical and Viscoelastic Properties of Asphalt Mixture Modified by Diatomite and Crumb Rubber Particles

To optimize the properties of asphalt mixtures and make full use of waste rubber tires, diatomite and crumb rubber particles were applied to reinforce the asphalt mixtures in this study. The rutting tests, the three-point bending tests, the freeze-thaw splitting tests, and the uniaxial compression creep tests were performed to analyze the effects of asphalt types and aggregate gradation on the pavement properties of diatomite and crumb rubber particles reinforced asphalt mixtures (DRPAM). Subsequently, the creep and relaxation characteristics of DRPAM were analyzed by the Burgers model, the modified Burgers model, the second-order extensive Maxwell model, and the Scott–Blair model. The results show that rubber particles and diatomite can reinforce the high temperature, low temperature, and viscoelastic properties of asphalt mixtures, although the improvement effect is weaker than styrene-butadiene-styrene (SBS). Consequently, it is concluded that rubber particle and diatomite compound modified asphalt mixture with suspension dense gradation and SBS binder will have better performance.

Experimental Investigation and Constitutive Modeling of the Uncured Rubber Compound Based on the DMA Strain Scanning Method

Existing research tends to focus on the performance of cured rubber. This is due to a lack of suitable testing methods for the mechanical properties of uncured rubber, in particular, tensile properties. Without crosslinking by sulfur, the tensile strength of uncured rubber compounds is too low to be accurately tested by general tensile testing machines. Firstly, a new tensile stress testing method for uncured rubber was established by using dynamic thermomechanical analysis (DMA) tensile strain scanning. The strain amplitude was increased under a set frequency and constant temperature. The corresponding dynamic force needed to maintain the amplitude was then measured to obtain the dynamic force-amplitude curve observed at this temperature and frequency. Secondly, the Burgers model is usually difficult to calculate and analyze in differential form, so it was reduced to its arithmetic form under creep conditions and material relaxation. Tensile deformation at a constant strain rate was proposed, so the Burgers model could be modified to a more concise form without any strain terms, making mathematical processing and simulating much more convenient. Thirdly, the rate of the modified Burgers model under constant strain was in good agreement with the test data, demonstrating that the elastic stiffness was 1–2 orders of magnitude less than the tensile viscosity. In the end, it was concluded that large data dispersion caused by the universal tensile test can be overcome by choosing this model, and it may become an effective way to study the tensile modeling of uncured rubber compound.

DETONATION PROPAGATIONIN PERIODIC NONUNIFORM MEDIA: RESONANCE AND MODE LOCKING PHENOMENA

In recent work [1], the analog Burgers model of detonation [2] was used in order to explore how detonation propagates in a medium with periodically varying reactivity.