Discrete Element Simulation of Asphalt Mastics Based on Burgers Model

In order to investigate the viscoelastic performance of asphalt mastics, a micro-mechanical model for asphalt mastics was built by applying Burgers model to discrete element simulation and constructing Burgers contact model. Then the numerical simulation of creep tests was conducted, and results from the simulation were compared with the analytical solution for Burgers model. The comparision showed that the two results agreed well with each other, suggesting that discrete element model based on Burgers model could be employed in the numerical simulation for asphalt mastics.

Creep model for unsaturated soils in sliding zone of Qianjiangping landslide

The mechanical behavior of sliding zone soils plays a significant role in landslide. In general, the sliding zone soils are basically in unsaturated state due to rainfall infiltration and reservoir water level fluctuation. Meanwhile, a large number of examples show that the deformation processes of landslides always take a long period of time, indicating that landslides exhibit a time-dependent property. Therefore, the deforma- tion of unsaturated soils of landslide involves creep behaviors. In this paper, the Burgers creep model for unsaturated soils under triaxial stress state is considered based on the unsaturated soil mechanics. Then, by curve fitting using the least squares method, creep parameters in different matric suction states are obtained based on the creep test data of unsaturated soils in the sliding zones of Qianjiangping landslide. Results show that the predicted results are in good agreement with the experimental data, Finally, to fur- ther explore the creep characteristics of the unsaturated soils in sliding zones, the relationships between parameters of the model and matric suction are analyzed and a revised Burgers creep model is developed correspondingly. Simulations on another group of test data are performed by using the modified Burgers creep model and reasonable results are observed,

Generic creep behavior and creep modeling of an aged surface support liner under tension

Polymer-based materials have been motivated to be an alternative support system element in the mining/tunneling industry due to their logistic and geotechnical benefits.Thin spray-on liner(TSL),a term to define the application of the material on the rock surface with a layer ranging from 2 mm to10 mm in thickness,shows some promising results.TSLs are mainly composed of plastic,polymer,or cement-based ingredients to a certain proportion.This study intends to reveal the time-dependent response of TSL specimens,cured throughout 500 d,under four constant stress levels for stable laboratory conditions.The results were correlated using two interrelated equations to predict the material’s service life(creep-rupture envelopes).The proposed correlations offered an insight into both the effective permanent support time and the strain amount at the liner failure.The time-dependent deformation of TSL,whose performance is highly responsive to creep behavior,was obtained so that the design engineers may use the findings to avoid the severe problems of material creep.Experimental data were also used to develop a Burgers(four-element)creep model.Since the liner has a nonlinear time-dependent behavior,creep models were built for each stress level separately.Subsequently,a generic equation was obtained using the nonlinear parametric dependencies.There is a good agreement between the proposed model and the experimental results.The proposed model can be used as a basis for future numerical studies related to the support behavior of aged surface support liners.

Effects of viscoelasticity on the stability and bifurcations of nonlinear energy sinks

Due to the increasing use of passive absorbers to control unwanted vibrations,many studies have been done on energy absorbers ideally,but the lack of studies of real environmental conditions on these absorbers is felt.The present work investigates the effect of viscoelasticity on the stability and bifurcations of a system attached to a nonlinear energy sink(NES).In this paper,the Burgers model is assumed for the viscoelasticity in an NES,and a linear oscillator system is considered for investigating the instabilities and bifurcations.The equations of motion of the coupled system are solved by using the harmonic balance and pseudo-arc-length continuation methods.The results show that the viscoelasticity affects the frequency intervals of the Hopf and saddle-node branches,and by increasing the stiffness parameters of the viscoelasticity,the conditions of these branches occur in larger ranges of the external force amplitudes,and also reduce the frequency range of the branches.In addition,increasing the viscoelastic damping parameter has the potential to completely eliminate the instability of the system and gradually reduce the amplitude of the jump phenomenon.

Experimental Study on the Creep Behavior of Recombinant Bamboo

The creep behavior of bamboo due to the complicated influences of environment and stress will lead to a sustained increase in deformation,which serious effects the service performance of structures.To investigate the creep behavior of recombinant bamboo,twenty-four recombinant bamboo specimens were tested under lasting compressive and tensile loads at different load levels.The typical failure modes of recombinant bamboo under a lasting load at a high load level were buckling failure and brittle fracturing due to creep compressive creep and tensile creep development,respectively.At a high load level,the creep deformation of recombinant bamboo initially develops unsteadily and increases rapidly until failure;at a low load level,creep deformation rapidly develops in the early stage and stabilizes in the middle and late stages.The load level has notable effects on the overall creep deformation and the proportion of creep deformation.The residual deformation of creep will generally increase and the recovery of creep will decrease with increasing load level.Based on the Burgers model,predictive models that can take the load levels into account were proposed to evaluate the compressive and tensile creep behaviors of recombinant bamboo.The proposed models can be used to accurately evaluate the strain-time behavior of recombinant bamboo.

Experimental investigation of creep behavior of clastic rock in Xiangjiaba Hydropower Project

There are many fracture zones crossing the dam foundation of the Xiangjiaba Hydropower Project in southwestern China. Clastic rock is the main media of the fracture zone and has poor physical and mechanical properties. In order to investigate the creep behavior of clastic rock, triaxial creep tests were conducted using a rock servo-controlling rheological testing machine. The results show that the creep behavior of clastic rock is significant at a high level of deviatoric stress, and less time-dependent deformation occurs at high confining pressure. Based on the creep test results, the relationship between axial strain and time under different confining pressures was investigated, and the relationship between axial strain rate and deviatoric stress was also discussed. The strain rate increases rapidly, and the rock sample fails eventually under high deviatoric stress. Moreover, the creep failure mechanism under different confining pressures was analyzed. The main failure mechanism of clastic rock is plastic shear, accompanied by a significant compression and ductile dilatancy. On the other band, with the determined parameters, the Burgers creep model was used to fit the creep curves. The results indicate that the Burgers model can exactly describe the creep behavior of clastic rock in the Xiangjiaba Hydropower Project.

Nonlinear Ultra-Long Wave and Its Stability

A stability of a nonlinear ultra-long wave and its solution are discussed in this paper by employing Burger model which is subject to heat resource. It is of interest noted that the wave solution can be described by an equation of KDV or MKDV and that conditions for the existence of the solution are related to characteristic divergences. In addition, a wave velocity expression for nonlinear ultra-long waves and some diagnostic correlations among wave parameters have been obtained.

A Constitutive Model of Granite Shear Creep under Moisture

Previous constitutive models of granite shear creep have two limitations：（1） although moisture greatly affects granite shear creep behavior, currently there are no constitutive models that include this factor;（2） there are also no models that include an acceleration stage. This paper presents an improved Burgers constitutive model with the addition of a damage parameter to characterize the moisture effect and uses a nonlinear relation equation between stress and strain for inclusion as the acceleration stage. The damage parameter is determined from granite creep experiment under four different moisture contents（0%, 0.22%, 0.49%, and 0.79%）. The nonlinear relation equation is obtained by fitting a dataset of stain versus time under five different loading stages. To verify the presented model, a creep experiment was conducted on other granite samples and the results show that the model agrees well with the experimental observation data.