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The nonlinear viscous element was introduced to study the creep process of recycled aggregate concrete. It was combined in series with the classic Burgers model to form a five-element six-parameter nonlinear creep model. Tensile creep tests were conducted on the recycled aggregate concrete with different fiber volume fractions and different replacement rates of recycled aggregate to investigate the variation of tensile creep compliance with loading time. Referring to the relationship between creep compliance and time in the creep model, the six mechanical parameters of the concrete's nonlinear creep model were identified through the optimization algorithm based on Levenberg-Marquardt. The fitting results of the model are consistent with the experimental results, indicating that the model can well reflect the creep characteristics of recycled aggregate concrete. It also shows that concrete with 0. 12% volume fraction of recycled polypropylene fiber and 50% replacement rate of recycled aggregate has good economic practical value [ABSTRACT FROM AUTHOR]

In order to study the creep viscoelastic-plastic mechanical behavior of asphalt mixture, the Maxwell model is used as the basic model, and the fractional order calculus operator theory is used to construct the fractional order viscous body to replace the Newton body in the basic model. The nonlinear viscous damper is introduced and connected in series with the foundation model. The damage variable is defined, the damage evolution is carried out according to the Lemaitre equivalent strain principle, and the fractional creep model of asphalt mixture considering aging damage is obtained. The model parameters are solved, the parameter sensitivity is analyzed, and the damage evolution is carried out. The creep data of asphalt mixture are identified by using the model, and compared with the empirical model to verify the feasibility and rationality of the model. [ABSTRACT FROM AUTHOR]

Based on rheological mechanics and viscoelastic mechanics, a theoretical model for the coupling of prestress loss of anchor and creep of rock was established. Considering the influence of prestress loss when the prestressed anchor was used to reinforce rock mass, the creep equations of stable creep rock and unstable creep rock were derived, and the formula for calculating prestress of anchor with time was obtained. The results showed that the anchor prestress loss was faster in the period of completion of anchor tension; then the rate of prestress loss was gradually reduced and finally stabilized, and the creep of rock also became stable. By comparing the calculated results with the experimental results in existing literature, the curves of the two were consistent, which verified the correctness of the model. The comparison between the variation of anchor cable prestress at Jinping Hydropower Station and the calculation results of the theoretical model proves the accuracy of this research model applied to engineering examples. The theoretical analysis results established in this paper considering the coupling of anchor cable prestress loss and rock mass creep have a wider application range than previous coupling models, which is not only applicable to stable creep rock, but also to unstable creep rock. The warning of abnormal changes in anchor cable anchoring force and the long-term safe operation of slope engineering have extensive engineering application value. [ABSTRACT FROM AUTHOR]

The geological disasters such as collapse, landslides, and ground subsidence caused by major engineering projects in the loess area are often closely related to the creep properties of loess. The current research of loess creep is summarized from the aspects of research stages, research methods, constitutive models, and engineering disasters, which are caused by creep of loess; the existing problems and the future trends in the research of loess creep are discussed. Specifically, ① based on a systematic review of domestic and foreign literature, the research of loess creep is divided into three stages, including the basic properties research stage, the engineering disaster research stage, and the major engineering project research stage; ② starting from the research methods of loess creep, various methods used in the research of loess creep and various factors affecting loess creep, especially the influence of water content, dry density and load on creep properties of loess, are analyzed and discussed; ③ the research characteristics of loess creep constitutive models are summarized, and the advantages and disadvantages of three models, including element theory constitutive model, empirical constitutive model, and semi-empirical and semi-theoretical constitutive model are evaluated; ④ the creep failure characteristics of common engineering types, such as slopes, roadbeds and tunnels in the loess area are summarized; ⑤ establishing a loess creep constitutive model that considers the influence of multiple factors, systematically studying the dynamic evolution and microscopic constitutive models of loess creep, and studying the creep properties under dynamic load, are the future trends of loess creep research. [ABSTRACT FROM AUTHOR]

In thermal power units, superheater, reheater and other parts need to be applied to dissimilar steel welded joints to meet the needs of different environments, which requires the material to have higher high temperature corrosion resistance, yield limit and tensile strength, and service caused by aging will greatly affect the performance of the welding parts, and then affect their life. In order to study the effect of service on the mechanical properties of dissimilar steel welded joint T92 / Super304H. Tensile tests were carried out on welded joints in service and out of service with different loading rates at 610 ℃ . The stress-strain curves and fitting curves were obtained, and the fracture morphology was analyzed by scanning electron microscope( SEM. ) The constitutive equation and creep life prediction model of welded joints were obtained by creep tests under different stresses at the same temperature, and the fracture causes were analyzed. The results show that the fracture occurs on the T92 side (heat-affected zone of T92) of both the in-service and out-ofservice welded joints during high temperature tensile, and the specimen has obvious neck shrinkage. The larger the initial stress is, the shorter the creep life is. With the increase of the initial stress level, the creep strain rate changes rapidly. The fitted curve of life prediction is consistent with the actual creep test. [ABSTRACT FROM AUTHOR]

In order to explore the creep rupture evolution law of rocks with weak interlayers under different working conditions, based on the continuous-discontinuous element method (CDEM), the creep rupture evolution law of rocks with weak interlayers under constant load was studied by theoretical analysis and numerical simulation. The creep evolution process of rocks with weak interlayers with different dip angles, different thickness and different mechanical properties of weak interlayers was simulated. The results show that the rock mass creep is controlled by the dip angle of the weak interlayer. With the increase of the dip angle of the weak interlayer, the faster the rock creep rate, the shorter the time to enter the accelerated creep stage. For the same dip angle, the larger the thickness of the weak layer, the slower the creep rate and the smaller the axial strain during creep failure. The creep rate of rock containing soft interlayer is inversely proportional to the elastic modulus of soft interlayer. The smaller the elastic modulus of soft interlayer material, the smaller the overall strength of rock mass, and the faster the creep rate of rock. [ABSTRACT FROM AUTHOR]

BACKGROUND: Collagen type II, silk fibroin and hyaluronic acid, which can provide an ideal microenvironment for cells, have become ideal scaffold materials for cartilage repair. OBJECTIVE: To evaluate physicochemical properties and biomechanical properties of cartilage tissue engineering scaffolds prepared from collagen type II, silk fibroin and hyaluronic acid. METHODS: Collagen type II-silk fibroin-hyaluronic acid composite scaffolds were prepared by low-temperature 3D printing technology. The microstructure, porosity and water absorption of scaffold were detected. Different strain rates were used to compress the scaffold, and the rate dependent properties of the scaffold were investigated. Constant stress level or constant strain was applied on the surface of scaffold for 3 600 s, and the creep behavior and stress relaxation behavior were investigated. RESULTS AND CONCLUSION: (1) The prepared scaffolds had three-dimensional porous structure, uniform pore size and good connectivity. The porosity was (85.1±1.6)%. The water absorption expansion rate was (1 071.7±131.6)%. (2) Under different strain rates, the compressive stress-strain curves of cartilage scaffolds did not coincide, which indicated that the compressive mechanical properties of cartilage scaffolds were rate dependent. With the increase of strain rate, the Young’s modulus increased. (3) When the stress level was constant, the creep strain first increased rapidly and then increased slowly. When the stress level increased, the creep strain also increased. (4) When the compression strain was constant, the stress of scaffold decreased rapidly at first and then slowly with the relaxation time. With the increase of the compression strain, the stress at different times increased. (5) The mechanical properties of the collagen type II-silk fibroin-hyaluronic acid composite scaffolds are similar to those of host cartilage, which means that the prepared scaffold is a kind of nonlinear viscoelastic material. [ABSTRACT FROM AUTHOR]

Soft interlayer is an important thin layer that affects the stability of rock mass and is one of the causes of engineering disasters, and the study of its characteristics has important engineering significance. In order to investigate the influence of water-bearing soft interlayer on the stability of underground cavern chamber, a multi-conditions control model test was conducted by the self-researched lever-type plane stress model test system, taking the water-bearing state of interlayer, interlayer location and interlayer thickness as factors, and the change law of stress and surface convergence deformation of each measurement point around the cavern in the excavation and creep test stages under different working conditions was analyzed. The test results show these follows. When excavation is carried out, the vertical stress at the measurement point directly above the excavation profile decreases, and the stress at the measurement point near the shoulder of the hole increases, and the further away from the cavern, the smaller the influence of excavation. After the end of excavation, the stress tends to increase, and the dynamic adjustment magnitude decreases and finally stabilizes. When the cavern is excavated, the measurement points around the cavern on the model surface mainly show vertical convergence deformation, and after the excavation is completed, the vertical convergence deformation is still dominant. During the excavation in the test phase and creep test phase, the degree of influence of weak interlayer characteristics on the stability of underground cavern chamber is: water content state of weak interlayer > location of weak interlayer > thickness of weak interlayer. In the underground cavern project with weak interlayer, especially when the weak interlayer contains water, measures such as dredging and drainage should be taken to control the influence of the weak interlayer on the stability of the underground cavern. [ABSTRACT FROM AUTHOR]

Due to the indispensable application of foundation pile in high backfill site, considering the influence of creep characteristics of high backfill soil on the mechanical properties of foundation pile during its use process, the finite difference software FLAC3D and the time effect were used to calculate the filling thickness of 10 m and pile diameter of 1 m. The foundation pile with rock-socketed depth of 3 m was subjected to numerical simulation analysis with pile top loads of 0, 0. 5, 1, 2, 3, 5 MPa respectively, and the stress and deformation characteristics of foundation pile under different pile top loads were obtained. The results show that the settlement increases at first and then tends to balance with time, and the rate of pile top displacement changes with time under different pile top loads lags behind the settlement and deformation rate of pile top filling. At the initial stage of creep, the maximum internal force of pile accelerates, but the resistance of pile tip does not increase at this stage. As the creep of fill enters the middle and later stage, the pile tip resistance develops rapidly, and the lateral friction resistance transfers to the pile tip resistance. After the creep stability of the surrounding fill, the maximum axial force of pile is positively correlated with pile top load, but the added value of axial force of pile decreases with the increase of pile top load. Pile tip resistance and its added value also increase with the increase of pile tip load. The study can provide reference for the design and construction of pile foundation in high fill site. [ABSTRACT FROM AUTHOR]

The creep behaviors of zirconium base (Zr based) metallic glass proposed serving in the space environment were studied by macro scale creep test method. The results showed that no significant creep in compression indicated in 200 °C，and the long term deformation ratio indicated the same value to its excess free volume，which indicates that free volume plays an important role in the creep deformation of amorphous alloys as the initial structural unit for the formation of shear bands. In below the yield strength and glass transition temperature of Zr based the metallic glass? respectively? the compressive and tensile creep behavior significantly changed in 300 PC. In this study，the experimental results of Zr based metallic in creep further define the serving thermal and mechanical limits in space, Ifs service temperature should not exceed 200 °C and the load can't exceed 1 000 MPa. [ABSTRACT FROM AUTHOR]

Winter wheat is the primary cropping system in grain production in the North China Plain. In this study, two planting patterns were applied, including the precision planting pattern (W) and conventional cultivation planting pattern (C), in order to clarify the effect of different planting pattern on lodging resistance of winter wheat with delaying irrigation at the jointing stage. In each planting pattern, the winter wheat was irrigated with 60 mm at the jointing stage (I1), and delaying irrigation 60 mm for 10 d at the jointing stage (I2). The main physical indexes of winter wheat stalk were measured, including the plant height, gravity center height, and fresh weight, as well as the diameter, fresh density, and the wall thickness of the basic secondary internode. A systematic investigation was made on the internode mechanical indexes, such as the bending resistance and bending rigidity of basic secondary internode, lodging resistance index, the creep deformation in the basic secondary internode of winter wheat at heading, filling and dough growth stage. The planting pattern and irrigation schedule were explored for comprehensive optimization on the lodging resistance of winter wheat. The results showed that there was a significant trend to improve the bending resistance strength in the basic secondary internode, and the bending rigidity significantly increased at the heading stage under the wide precision planting pattern with delaying irrigation at the jointing stage. However, the bending resistance strength and bending rigidity in the basic secondary internode, and the fresh weight were significantly reduced at the dough stage in this treatment. The wide precision planting pattern with delaying irrigation at the jointing stage significantly increased the lodging resistance index at the heading stage, and thereby improved the lodging resistance index at the dough stage, where the average lodging resistance index at the heading, filling, and waxing stage were 2.03, 1.58 and 1.87 N/(m·g), respectively. The basic secondary internode of winter wheat had creep characteristics under the proportional load less than its ultimate bending resistance strength. Specifically, the average maximum of creep strain was the highest at the heading stage, and it was still large at the filling stage under the wide precision planting pattern with delaying irrigation at the jointing stage. All of mechanical behavior was in the transition from the deceleration to stable creep stage, where the maximum creep strain ranged from 0.6%-3.7%, and the average maximum of creep strain ranged from 0.7%-2.5%. Combined with the lodging resistance index and creep test, the lodging resistance of winter wheat was the best under the condition of wide precision planting pattern with delaying irrigation for 10 d at the jointing stage. The findings can provide a promising theoretical basis and technical support for water saving and high yield of winter wheat in North China Plain. [ABSTRACT FROM AUTHOR]

Creep is one of the important mechanical properties for straw plastic composite. The creep performance is closely related to stress, temperature and time. Tn order to study the creep properties of SPC, creep experiments were carried out under different stresses and temperature. Rased on the principle of time temperature stress equivalence and Burgers model, the master curve of creep and their expressions of SPC under reference temperature and reference stress were obtained, and the creep compliance of the composite under low temperature or low stress was deduced by WLF equation according to the principle of time temperature stress equivalence. Therefore, the long-term creep behavior of SPC at low temperature or low stress level could be predicted by the short-term creep behavior at high temperature or high stress level. [ABSTRACT FROM AUTHOR]

Aiming at the deformation of the end face of the mounted mechanical seals during long-term storage, an ANSYS finite element model was established to study the eccentric defects of the mounted mechanical seals and investigate the effect of accelerating the deformation of the end face of the mounted mechanical seals by the thermal cycling acceleration method. The Bailey-Norton creep equation was used to numerically analyze the normal and eccentric defects of the mounted mechanical seals, and the relationship between the end face deformation and the eccentric defect of the mounted mechanical seals under natural storage conditions was obtained. Based on the creep equation, the thermal cycling acceleration process was simulated, and the relationship between the end face deformation of the mounted mechanical seals and the thermal cycling interval was obtained. The results indicate that the saddle-shaped deformation of the end face of the mounted mechanical seals with eccentric defects is more obvious than normal, and the difference of peak-to-valley is greater than that of a normal mounted mechanical seal. During the process of the thermal cycling acceleration, the deformation of the end face of the mounted mechanical seals has increased, and the deformation is greater than that under natural storage conditions, indicating that the acceleration effect of the thermal cycling acceleration method is obvious. [ABSTRACT FROM AUTHOR]

BACKGROUND: Most of studies on the mechanical properties of modified glass ionomer cement mainly focus on the compression and bending experiment，but there are few reports on the stress relaxation and creep experimen1s of glass ionomer cement after adding strontium hydroxyapatite. OBJECTIVE: To compare the stress relaxation and creep characteristics of traditional glass ionomer cement, composite resin enamel adhesive and modified glass ionomer cement. METHODS: Strontium doped hydroxyapatite was added into glass ionomer cement according to the mass ratio of 15%, and then the modified glass ionomer cement was prepared. Samples of modified glass ionomer cement, composite resin enamel adhesive and traditional glass ionomer cement were maded. Ten samples from each group were taken for stress relaxation test and another 10 samples for creep test. RESULTS AND CONCLUSION: (1) At 7 200 sin the stress relaxation test, the stress in the traditional group was decreased by 1.18 MPa, decreased by 1.39 MPa in the composite group, and decreased by 1.38 MPa in the modified group. The decreased value in the traditional group was significantly less than that in the composite and modified groups (P < 0.05). There was no significant difference between composite and modified groups (P > 0.05). (2) At 7 200 s in the creep test, the stress in the traditional group was increased by 0.24%, increased by 0.33% in the composite group, and increased by 0.32% in the modified group. The increased value in the traditional group was significantly less than that in the composite and modified groups (P < 0.05). There was no significant difference between composite and modified groups (P > 0.05). (3) The viscoelastic properties of glass ionomer cement are improved by compounding 15% strontium-doped hydroxyapatite with glass ionomer cement. The increase of viscoelasticity is beneficial to the adhesion and bulk bond strength of glass ionomer cement. [ABSTRACT FROM AUTHOR]

Under the action of overburden pressure, the coal pillars retained by strip mining underground are prone to creep over time, showing obvious viscoelastic-plastic characteristics and causing different degrees of damage. Based on the disturbance state concept theory and the deformation characteristics of coal in creep process, Kelvin model is used to describe the relative integrity of materials, and the clay pot in Burgers model is replaced by a non-linear clay pot to describe the fully adjusted state of the material. By introducing Weibull distribution function, the perturbation factor function with time as the independent variable is selected and the constitutive model of the whole creep process of coal is established with perturbation factor as weight function. The parameters of the creep model of coal based on the disturbance state concept are identified by the indoor creep test data, which verifies the rationality of the model. Compared with the traditional model, this model has better compatibility and can well describe the initial, stable and accelerated creep stages of coal. [ABSTRACT FROM AUTHOR]

In this paper, the elastic modulus and creep degree of RCC gravity damwere calculated based on the measured displacement and strain. Using Fortran language and numerical calculation software Flac3D, a creep numerical calculation program was developed to realize the simulation calculation of the whole process during construction and operation. The displacement and strain measurements during the sudden rise of water level were used to invert the stable elastic modulus of the dam body and dam foundation. Based on the orthogonal experiment design and the creep numerical calculation program, a sample of the correspondence between the parameters to be inverted and the calculated strain values at the monitoring points was obtained. With the help of intelligent algorithm support vector machine (SVM) and genetic algorithm (GA), the calculated strain values and GA-SVM prediction model for inverse parameter relationship was established. During the inversion calculation, the measured strain value at the monitoring point was true, and the calculated strain value was directly calculated by the GA-SVM prediction model, eliminating the need for numerical calculation. The strain values calculated according to the feedback of the inversion parameters were in good agreement with the measured values. The research results show that the inversion calculation method of the creep variant in this paper is reasonable and effective, which greatly reduces the numerical calculation of the entire process of the creep variant and its parameter inversion time required. [ABSTRACT FROM AUTHOR]

BACKGROUND: Once the articular cartilage has a crack defect, its mechanical properties will change. In previous studies, the investigation of damaged articular cartilage mostly focused on compression, and there were few studies on tensile properties. OBJECTIVE: To measure the uniaxial quasi-static tensile properties by preparing crack defects on the cartilage layer samples. METHODS: The articular cartilage of the fresh adult pig knee joint was selected to prepare a cartilage specimen containing a crack defect. The tensile properties were tested at different stress rates (0.001, 0.01 and 0.1 MPa/s) and the creep properties were tested under different constant stresses (1, 2 and 3 MPa). RESULTS AND CONCLUSION: (1) In the tensile test at different stress rates, as the stress rate increases, the stress required to reach the same strain increased gradually, and the Young's modulus of the test piece increases with the increase of the stress rate. (2) The tensile stress-strain curves of the articular cartilage with cracks at different stress rates did not coincide, indicating that the tensile properties of the articular cartilage with crack defects are rate-dependent. (3) In the creep experiment under different constant tensile stress levels, the creep strain increased with the increase of the tensile stress level, the creep compliance decreased with the increase of the tensile stress level, and with the creep time. The creep strain increased rapidly and then increased slowly. (4) To conclude, different stress rates and different constant stresses have great influence on the tensile mechanical properties of articular cartilage with crack defects. The experimental results provide a mechanical reference for the repair of defective articular cartilage. [ABSTRACT FROM AUTHOR]

According to the concept of harmonious development between human and nature, an environment - friendly composite slab of cold - formed thin - wall steel and bamboo plywood is proposed. In order to investigate its mechanical properties under long - term load, the specimens are produced and tested with fasteners or no fasteners as experimental parameters, analysis of the deflection development of steel - bamboo composite slabs with time and the strain development of steel and bamboo with time are obtained, moreover the second bending test of specimens after unloading is carried out to be compared with the bending test of short - term specimens. The results show that the creep of steel - bamboo composite slabs is small under long - term load, the strain development trend of steel and bamboo are consistent, the bearing capacity of composite slabs decay by about 7% , which prove steel - bamboo composite slabs can give available play to the mechanical properties of two kinds of materials, and have good overall performance and bearing capacity. Through theoretical derivation, the short - term stiffness formula of steel - bamboo composite slabs is deduced, and the proposed formulas of long - term stiffness and deflection are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

The creep behavior of 316L austenitic stainless steel at 600 ℃ was studied by multi-section creep test. Based on the experimental results, the creep constitutive model of 316L austenitic stainless steel was established by considering the combined time hardening creep constitutive model, the inverse finite element method and the neural network method. The creep curves predicted by the creep constitutive model agree with the ones obtained from the standard creep test method. Therefore, the multi-section creep test can obtain the creep results under multiple loads through a single specimen and get higher creep experimental efficiency. [ABSTRACT FROM AUTHOR]

To obtain fire resistance capacity of high strength Q690 steel columns, fire tests on full-scale H-shaped welded Q690 steel columns were carried out by using furnace subjected to ISO 834 fire curve. The relationships between temperature of Q690 column, axial displacement, lateral displacement and fire duration were measured under different load ratio. Critical temperature and limited fire resistance were obtained based on the test data. Fire resistance analysis model was established by employing ABAQUS software by taking the effect of high temperature creep in steel and residual stresses variation into consideration. Fire response of steel columns were simulated and good agreement was found between simulation and test. The effect of load ratio, slenderness ratio and heating rate on mechanical behavior of steel columns were analyzed by the validated finite element model. The study shows that bear steel columns only survive about 20 min in fire and the failure mode is overall buckling. Load ratio has great influence on fire resistance of Q690 steel columns. However, slenderness ratio and heating rate have minor effect. The critical temperature of Q690 steel columns is about 60℃ lower than those predicted by Chinese code GB 51249—2017 and Eurocode EN 1993-1-2. Finally, a simple approach for fire resistance design of Q690 steel columns was proposed. [ABSTRACT FROM AUTHOR]

In order to ensure the long-term stability of Jinping Underground Laboratory (CJPL) caverns, the creep characteristics of 2 400 m deep-buried marble were studied. The multi-stage loading creep tests were conducted on the basis of convention triaxial compression tests to analyze the law of axial and circumferential deformation of marble during the creep process and the difference of creep characteristics of marble under different confining pressures (5 and 64 MPa). Then the long-term strength of marble was discussed by using the isochronous stress-strain curve method and a creep model based on fractional derivative was proposed to describe the process of creep deformation. The results show that under the confining pressures of 13 MPa and 27 MPa, the axial stress-strain curves of marble drop rapidly after reaching the peak stress and under confining pressures of 40, 53 and 64 MPa, the strain curves near the peak stress show obvious plateau section, which indicates that the deformation behavior of deep marble in CJPL tends to change from brittleness to ductility with the increase of confining pressures. Compared with low stress level, the marble under high stress level is more prone to creep, the circumferential creep phenomenon is more significant and the dilatancy phenomenon during creep process is more obvious. The volume creep deformation of specimens under 64 MPa confining pressure is 16. 3 times of that under 5 MPa confining pressure. During the creep loading process, the deformation modulus of marble increases first and then decreases. In the stage of increasing modulus of deformation, the increasing range under high confining pressure is smaller than that under low confining pressure. The increase of deformation modulus under 64 MPa confining pressure is 1. 8 GPa, less than 3. 6 GPa under 5 MPa confining pressure, which indicates that the specimen has been partially compacted under high confining pressure. With the increase of stress level, the modulus of deformation decreases and the decrease range under high confining pressure is greater than that under low confining pressure. The decrease of deformation modulus of specimens under confining pressure of 64 MPa is 9. 4 GPa, which is about 22% of the peak deformation modulus. The decrease of specimen under confining pressure of 5 MPa is only 1. 8 GPa, which is about 4% of the peak deformation modulus. These indicates that the crack initiation and propagation of specimens under high confining pressure are more intense and the rock deterioration is more serious before failure. Under the same deviating stress condition, the creep rate of specimens with larger confining pressure is smaller, but the deformation is larger and the dilatancy phenomenon is remarkable when the failure occurs. It shows that under the same external load condition, when the environmental stress level of deep surrounding rock is higher, the deformation of surrounding rock is difficult to converge, and it is prone to aging large deformation failure. When the confining pressure is 5 and 64 MPa, the long-term strength of marble is 170 and 290 MPa, respectively, which are 82% and 73% of the corresponding triaxial compressive strength. Based on the fractional derivative, a new viscous-elastic-plastic damage creep model of marble was established and it was proved that the model is simple in form and can well describe the characteristics of non-linear acceleration in marble creep process. [ABSTRACT FROM AUTHOR]

Gussasphalt concrete is the main impervious material of core wall in hydraulic projects. A series of experiments of creep characteristics of asphalt concrete with three kinds of asphalt contents under different temperatures and different deviatoric stress state was conducted by using the high-pressure triaxial apparatus. The effects of asphalt contents and temperature on the creep characteristics of guss asphalt concrete under different deviatoric stress statements were studied. Test results indicate that the creep of specimen increases with deviatoric stress decreases under the same asphalt content and the growth is affected by the temperature and asphalt content. The relationships between the creep and deviatoric stress of the specimen gradually change from linear to nonlinear with the temperature increases. The creep of the specimen nonlinearly increases with the asphalt content increases under the same deviatoric stress state and the growth rate increases with the increase of asphalt content. The creep of the specimen increases with the temperature increases under the same loading time and the creep rate increases with the increase of asphalt content. In the three-dimensional space, the LogisticCum formula is used to process experimental data and the three-dimensional curved surface is obtained. The creep model of the guss asphalt concrete was established by considering the influence to the creep by many factors such as temperature, asphalt content and deviatoric stress. The predict surface of the creep model compared with the test surface has a very high fitting degree. [ABSTRACT FROM AUTHOR]

In order to improve the utilization rate of bamboo and enhance the comprehensive utilization of waste plasties, the bamboo flour ( BK) /waste polyethylene ( PK) composites were prepared by injection molding. The effect of the different BF contents on the composites bending properties, the notched impact strength, bending creep performance, and the accelerated aging performance were studied. Results showed that the bending properties and creep performance showed a trend of increase with the increase of BK content, but the notched impact strength gradually declined and the xenon lamp accelerated aging resistance slightly decreased for the composites containing (), 15%, 30% and 45% BK. The optimum content of the BK was 30%. The bending strength and bending modulus of 30% BK/waste PK composite were 22.36 MPa and 1 033.61 MPa, respectively, enhanced by 18.4% and 92.2% respectively; the notched impact strength was 12.41 kj · in--, fell by 39.3%, compared to the composite without adding BF. At the 75% stress level, after 3 6(H) s creep test, the caused deflection of the 30% BK/waste PK composite was 0.59 mm, while the brittle fracture occurred after 527 s and the deflection was 1.68 mm for the control sample. After 480 h xenon lamp accelerated aging, the bending strength and bending modulus retention of the 30%' BK/waste PK composite were 85% and 80% respectively, and the color difference value was 38.1. [ABSTRACT FROM AUTHOR]

In order to study the creep characteristics of landslide slip zone soil, the ZLB-1 triad direct shear creep instrument is used to do the experiment of creep behavior of landslide slip zone soil in open pit mine under graded loading. Fractional damage creep constitutive model is established on the base of fractional calculus and damage mechanics theory. The result shows that shear creep deformation increases with the growth of shear load at the same time; attenuated creep occurs when shear load is lower than long-term strength; isovelocity creep and accelerated creep occur when shear load is higher than long-term strength; and the nonlinearity of creep of sliding zone soil increases with the growth of time. The determination coefficient of the fitting curve is between 0.951 6 and 0.999 1, so that the fitting precision of the new type creep constitutive model is relatively high and the three stages of creep can be well described. [ABSTRACT FROM AUTHOR]

In order to study the creep damage characteristics of sandstone, the TAW-2000 electro-hydraulic servo controlled rock triaxial was used to carry out the graded loading creep test of sandstone samples. By introducing the Xiyuan and the Kachanov damage model, the damage creep model was established to describe the accelerated creep stage. Test results show that the under low stress loading, there are dense and closure of the phenomenon; creep properties of rock exists from low strain of strain hardening gradually turned into high stress strain softening phenomenon of fissures in the rock pressure; under the same confining pressure, rock under pressure in the steady creep stage of creep rate is higher than the low stress creep rate. The parameters of creep damage model are identified by Origin software using the Levenberg Marquardt algorithm. The test curve has a high degree of coincidence, which verifies the rationality of the established creep damage model and makes up for the shortcomings of the Xiyuan body that is difficult to describe the accelerated creep. [ABSTRACT FROM AUTHOR]

On the basis of elasto-viscoplastic theory of Perzyna, a mesoscopic coupled elasto-viscoplastic damage model, describing the whole creep process of rock from initial creep, stable creep to nonlinear acceleration creep, is constructed by introducing a mesoscopic unit strength damage model based on the strain energy theory. The characteristics of the creep rate change with time in the creep process of rock can be taken into consideration, and can be integrated into the EPCA3D. The model was verified by the experimental data and then applied to the numerical experiments of single and triaxial compression creep process under different axial stresses, confining the pressures and homogeneity coefficients. The results showed that, on one hand, the increased axial stress can speed up the creep rate, which reducesthe creep failure time. On the other hand, the increased confining pressure and homogeneity coefficient can reduce the creep rate and lead to the increase of creep failure time.This study can better reproduce the typical experimental phenomena. It can be used to explain the mechanical mechanism of creep-induced rock burst in coal mines, and also better reflect the accumulation of elastic strain energy after the excavation of coal mine roadway and the damage process of surrounding rock undergoing stable creep and accelerating creep. This study can provide an analytical tool for the long-term stability of rock mass engineering. [ABSTRACT FROM AUTHOR]

Nanoindentation tests were conducted on titanium alloys to investigate the strain rate sensitivity at room temperature. The indenter was loaded to a fixed maximum load with different loading strain rate. The strain rate sensitivity of hardness and modulus was investigated based on continuous stiffness measurement, and the influence of strain rate on creep displacement was further studied. Results show that the titanium alloys exhibit great dependence on loading strain rate in terms of hardness while no obvious relationship can be observed between modulus and strain rate. In addition, dislocation motion is the main creep mechanism at holding stage, and creep stress exponent decreases with the increase of loading strain rate. [ABSTRACT FROM AUTHOR]

In order to investigate the relationship between stability and time, and the failure characteristics and damage development rule of rich-water packing material under load, the rich-water packing material with a certain water-solid ratio was prepared in this study. The creep property of rich-water packing material in different stress levels was studied by creep experiment. The deformation characteristics of stain change with time during the creep process which could be divided into three stages, attenuation, steady and acceleration were analyzed. The critical load of packing body instability was presented. The creep damage model for rich-water packing material was established by introducing damage variable based creep test data. The relationships of mechanic parameters among stress, stain, time, damage factor and so on were deduced. The results show that the failure critical load of rich-water packing material with water-solid ratio 2． 0 is 90% of its compressive strength. The improved Burgers model considered the influence of time and stress on creep parameters and reflected the weakening of parameters with time. The study shows that the model could be used to describe the damage deterioration rule of rich-water packing material before failure by fitting. [ABSTRACT FROM AUTHOR]

In order to understand the mechanical property of rice seedlings stem raised in cell tray in the stretching process, the general tensile, creep and stress relaxation property of rice seedlings stem were tested with JK-100KE micro-control electronic universal testing machine (UTM) and analyzed. The test variety of rice was Huahang No.31, planting in plastic cell tray in the field in Qilin North of South China Agricultural University. After growing for 25 days in the field, the seedlings had 3 to 5 leaves, and the seedlings with straight stalks and good growth were selected for the experiment. In experiment process, two ends of seedling stem samples were fixed in upper and lower clamps of the UTM respectively, and the original distance between 2 clamps was 20 mm. The frequency of data acquisition was 1/s. In the general tensile test, the loading rates were 2, 4, 6, 8, 10 and 12 mm/min, respectively, and 20 repetitions were carried out under each loading rate. In the creep test, the loading speed was 0.1 N/s. When the stress reached about 1.5 MPa, the stress began to be maintained, the test was ended after being maintained for 1 200 s, and the tensile creep curve of the seedling stem was obtained. The creep test was repeated 20 times. In the stress relaxation test, the loading speed was 0.6 mm/min. When the strain reached about 2.5%, the strain began to be maintained. The test was ended after being maintained for 1 200 s, and the tensile stress relaxation curve of the seedling stem was obtained. The stress relaxation test was repeated 20 times. The results of general tensile test showed that the seedling stalks usually ruptured 2 times due to the structural features of the covering leaf sheath. And before the first rupture, the stress-strain curve was linear. The fracture strain was 5.2%-9.6%, the fracture stress was 3.1-7.3 MPa, and the modulus of elasticity was 0.46-0.93 MPa. And the average fracture stress increased linearly with the increase of loading rate. In this study, the tension creep and stress relaxation process were described by the Burgers 4-element model and the Maxwell 5-element model, respectively. The tensile creep and stress relaxation testing data were fitted with MATLAB curve fitting tool, and the relevant rheological parameters were obtained, and the constitutive equations of creep and stress relaxation of rice seedling stems raised in cell trays were established. The creep model fitting parameters were that: delay elastic modulus Ek was 2.8-6.2 MPa, delay viscosity coefficient ηk was 308-817 MPa·s, delay time Tk was 106-175 s, instant elastic modulus Ek0 was 0.5-1.0 MPa, viscosity coefficient ηkv was 5 329-13 750 MPa. The stress relaxation model fitting parameters were that: decay elastic modulus Em1 and Em2 were respectively 0.06-0.15 MPa and 0.05-0.12 MPa, decay viscosity coefficients ηm1 and ηm2 were 1.7-5.2 MPa·s and 16.2-63.9 MPa·s respectively, relaxation time Tm1 and Tm2 were 26-42 s and 260-535 s respectively, instant elastic modulus Em0 was 0.34-0.61 MPa. Based on the selected rheological models and constitutive equations, and considering biological characteristics of the seedling stems, the parameters, including the creep rate, creep compliance, stress relaxation rate, stress relaxation time, were analyzed. The results showed that there are 2 kinds of tissue structure in seedling stem, that is, tender and strong, which could be reflected by the Maxwell bodies with 2 different stress relaxation times. And the processes of creep and stress relaxation were both the process of the transition from unbalanced structure and matter structure to the balance state in rice seedling stem, and also the process of mutual containment of elastic dynamic force and viscous resistance to achieve the equilibrium state. In the creep process, the unrecoverable plastic strain was generated, and under the same conditions, it was increased with the increase of initial stress and creep time, and the proportion of the plastic strain with the total strain increased with creep time, which had no relationship with the initial stress size. What’s more, the stress relaxation process resulted in microscopic damage, including the broken or extended macromolecular chains, increased or decreased bond angle and so on. This research provide a reference for damage assessment and simulation analysis of seedlings pulled up from plastic cell trays. In the future, the relationship between the rheological properties of rice seedlings stem and the levels of stress and strain should be further studied. [ABSTRACT FROM AUTHOR]

A viscoelasticity-viscoplasticity-viscodamage constitutive model is derived to characterize the complicated mechanical properties of composite modified double base (CMDB) propellant. The model parameters are obtained by a series of creep-recovery tests. Creep-recovery tests under different stress levels and loading times as well as some constant loading rate-recovery tests are done to verify the model. The test results show that the viscoelasticity-viscoplasticity-viscodamage constitutive model is capable of predicting the creep-recovery response and constant loading rate-recovery response of CMDB propellant. Compared with viscoelasticity-viscoplasticity constitutive model, the viscoelasticity-viscoplasticity-viscodamage model has a significant improvement in predicting the mechanical properties of CMDB propellant. The damage variable becomes steady gradually after it slowly increases first and then rapidly increases with strain. When the strain changes more slowly, the damage variable is larger, and the difference between the predicted results of the viscoelasticity-viscoplasticity-viscodamage model and the viscoelasticity-viscoplasticity model is greater. [ABSTRACT FROM AUTHOR]

Ｔｈｅ ｌａｕｎｃｈｉｎｇ ｔｕｂｅ ｉｓ ａｎ ｉｍｐｏｒｔａｎｔ ｐａｒｔ ｏｆ ｔｈｅ ｒｏｃｋｅｔ ｓｙｓｔｅｍ． Ｉｎ ｔｈｅ ｐｒｏｃｅｓｓ ｏｆ ｌｏｎｇ⁃ ｔｅｒｍ ｓｔｏｒａｇｅ， ａｇｉｎｇ ｐｈｅｎｏｍｅｎａ ｉｎｅｖｉｔａｂｌｙ ｏｃｃｕｒ ｕｎｄｅｒ ｖａｒｉｏｕｓ ｓｔｒｅｓｓ ａｎｄ ｅｎｖｉｒｏｎｍｅｎｔ ｆａｃｔｏｒｓ， ｗｉｔｈ ｉｍｐｏｒｔａｎｔ ｉｎｆｌｕｅｎｃｅｓ ｏｎ ｔｈｅ ｓｙｓｔｅｍ ｒｅｌｉａｂｉｌｉｔｙ． Ｔｈｅ ｇｌａｓｓ ｆｉｂｒｅ ｒｅｉｎｆｏｒｃｅｄ ｐｌａｓｔｉｃ （ＧＦＲＰ） ｌａｕｎｃｈｉｎｇ ｔｕｂｅ ｗａｓ ｓｔｕｄｉｅｄ ｔｈｒｏｕｇｈ ｔｈｅｒｍｏｍｅｃｈａｎｉｃａｌ ｔｅｓｔｓ ｏｆ ｔｈｅ ｏｎｅ⁃ｗａｙ ＧＦＲＰｓｌａｂｓ． Ｔｈｅ ｔｅｓｔｓ ａｎｄ ｍｅａｓｕｒｅｍｅｎｔｓ ｇａｖｅ ｔｈｅ ｂａｓｉｃ ｔｈｅｒｍｏｄｙｎａｍｉｃ ｐｅｒｆｏｒｍａｎｃｅｓ ｏｆ ｔｈｅ ｏｎｅ⁃ｗａｙ ＧＦＲＰ ｓｌａｂ ｍａｔｅｒｉａｌｓ， ｉｎｃｌｕｄｉｎｇ ｔｈｅ ｂａｓｉｃ ｍｅｃｈａｎｉｃａｌ ｐｒｏｐｅｒｔｉｅｓ ａｆｔｅｒ ａｃｃｅｌｅｒａｔｅｄ ａｇｉｎｇ． Ｔｈｅ ｍｅｃｈａｎｉｃａｌ ｍｏｄｅｌ ｆｏｒ ｔｈｅ ＧＦＲＰ ｌａｕｎｃｈｉｎｇ ｔｕｂｅ ｗａｓ ｃｏｎｓｔｒｕｃｔｅｄ ａｎｄ ｔｈｅ ｔｈｅｒｍｏｄｙｎａｍｉｃ ｃｈａｒａｃｔｅｒｉｓｔｉｃｓ ｏｆ ｔｈｅ ＧＦＲＰ ｌａｕｎｃｈｉｎｇ ｔｕｂｅ ｕｎｄｅｒ ｌｏａｄｓ ｗｅｒｅ ａｎａｌｙｚｅｄ． Ｔｈｅｎ ｔｈｅ ｃｒｅｅｐ ｍｏｄｅｌｓ ｆｏｒ ｔｈｅ ＧＦＲＰ ｌａｕｎｃｈｉｎｇ ｔｕｂｅｓ ｗｅｒｅ ｅｓｔａｂｌｉｓｈｅｄ， ｔｈａｔ ｉｓ， ｔｈｅ ｃｏｍｐｏｓｉｔｅ ｌａｍｉｎａｔｅ ｍｏｄｅｌ ａｎｄ ｔｈｅ ａｎｉｓｏｔｒｏｐｉｃ ｍｏｄｅｌ． Ｗｉｔｈ ｔｈｅ ｓｔｒｕｃｔｕｒａｌ ｍｏｄｅｌ， ｔｈｅ ｍａｔｅｒｉａｌ ｐａｒａｍｅｔｅｒｓ ｆｏｒ ｔｈｅ ｌｏｎｇ⁃ｔｅｒｍ ｐｅｒｆｏｒｍａｎｃｅ ａｎａｌｙｓｉｓ ｏｆ ｎｏｎ⁃ｍｅｔａｌｌｉｃ ｄｉｒｅｃｔｉｏｎａｌ ｔｕｂｅｓ ｗｅｒｅ ｐｒｏｖｉｄｅｄ． [ABSTRACT FROM AUTHOR]

Aiming at the failure mode of combined support of roadways between rock bolt and cable bolt,the constitutive model of surrounding rock and the constitutive model of anchorage body,which can reflect the accelerated creep of surrounding rock and the working characteristics of rock bolt respectively,are established based on the deformation characteristics of surrounding rock.The control effect of anchorage foundation location on the deformation of surrounding rock is analyzed by solving the creep equation of anchorage body.The result shows that the creep control mechanism of bolt support to surrounding rock can be summarized in two aspects:the first is to share the load of surrounding rock,the second is to increase the stiffness of surrounding rock and enhance the resistance to the deformation of surrounding rock.Giving a full play to the supporting performance of rock bolt,lengthening the supporting time of rock bolt and maintaining the stable working state of roadway need to meet two criteria:the load of rock bolt does not exceed the critical breaking load of rod,meanwhile,the anchorage foundation should be located beyond the plastic zone.It can maximize the bearing capacity of support system when the anchorage foundation of end-anchored form is located in the elastic surrounding rock.Under this circumstance,the end-anchored form,whose stress foundation locates in elastic rock mass and whose anchoring effect can occur rapidly after the deformation of surrounding rock,is better than a full-length anchoring form.The butt long bolt has the advantages of large elongation and flexible anchor length,and it can solve the problems that the rock bolt of roadway,in the centralized transportation roadway of 3rd panel in western of Puhe coal-mine,is often pulled out and its cable bolt breaks easily. [ABSTRACT FROM AUTHOR]

TiO2 particles were synthesized with precipitation method. The SEM results showed that the particles are rounded spheres with average diameter of 660 nm. The polyurethane composites were prepared by dispersing the TiO2 particles in the matrix, and the structure were observed by SEM. The results indicate that 0-3 type composites with particles dispersing in the matrix were prepared without applied electric field, and the 1-3 typelike composites with particles arranging oriented were prepared upon applied electric field. The dynamic viscoelasticity and creep properties of the two kinds of polyurethane composites were tested and compared. The results indicate that the 1-3 type-like polyurethane composites containing TiO2 particles have higher storage modulus and much stronger creep resistance than 0-3 type composites. [ABSTRACT FROM AUTHOR]

In order to investigate the statistical characteristics of acoustic emission (AE) of sandstone during uniaxial creep，the AE signals have been captured both in long-time and step loading creep tests. Histogram analysis and maximum likelihood method were used to study the statistical characteristics of AE absolute energy respectively. The results show that the AE jerks of long-time and step loading creep tests have similar shape，but the AE rate of step loading was higher than that of long-time test；Both the probability density functions (PDF) of long-time and step loading creep tests satisfied the power law well，and the exponents came from histogram analysis and maximum likelihood method were very similar. These exponents were much closer to the earthquake results than to the exponent of uniaxial compression. Unlike the smooth fracture surfaces of sandstone sample in uniaxial compression，the fracture surfaces induced by creep were much coarser and with stepped fractures. These results agreed with the assumptions and results of fiber bundle model with time dependence fiber elements. [ABSTRACT FROM AUTHOR]

Two full-size timber beams were designed to investigate long-term behavior for 1200 days, including a reference unstrengthened beam and a timber beam strengthened with steel plate. Experimental results indicate that the primary creep stage and stable creep stage are clearly observed both in the reference beam and the strengthened beam, but the increments of the deflection and curvature at the mid-span section of the strengthened beam are smaller than those of the reference beam, which reflects the restraint effect of steel plate on the long-term performance of timber beam. The strain of the wood was observed to increase with the increase of the temperature and moisture content. Aging theory, Burgurs model and the five-parameter model were fitted to predict the mid-span deflection to time curves of the reference beam. Comparison between the prediction and experimental results shows that the five-parameter model has satisfactory accuracy at both the primary stage and the stable creep stage, and could provide fairly accurate prediction. Finally, a numerical model was developed using the creep equation bulit-in ANSYS to simulate the long-term deflection, while the coefficient in the creep equation was defined as constant at each time step and calculated by linearization technique. The predicted results are in good agreement with the test results. [ABSTRACT FROM AUTHOR]

For the low strength and poor stability of water-high filling materials improves the property of it. The unstable failure characteristics of water-high filling materials was studied by stress-strain and creep test. The microstructure of water-high filling materials and the improvement mechanism of it were analyzed by using scanning electron microscopy (SEM) and different thermal analysis-thermal gravimetry (DTA-TG). It is found that the creep curve has decelerating and stable stage when stress level is low and it increase accelerating stage when stress level reach critical load. The stress-strain curve has initial deformation, elastic, plastic deformation and disruption four stages. The gel time shortened, compressive strength improved, elastic modulus increased, unstable failure critical load raised and deformation decreased of water-high filling materials after improvement. Owing to more ettringite crystals and alumina gel in the water-high filling materials after improvement, the microstructure of hardening body become more densification and bearing capacity improved. [ABSTRACT FROM AUTHOR]

In the arid-semiarid area of northwest China, the shallow water such as the water of rivers and lakes, valley runoff water, the phreatic water of Quaternary in sand-layer and so on are precious water resources which maintain regional ecological geological environment and the body of water resource protection in coal mining. According to the regional geological structure of the shallow water aquifer-aquifuge, the N2 laterite,distributed widely above coal seam in northwest coal field of China, as the direct aquifuge bottom of regional shallow water or valleys runoff cushion, playing a crucial role to the coal mining with water protection and ecological environment protection, is the key aquifuge soil. In this paper, based on the analysis of regional distribution features, the basic physical, hydro-physical and the mechanical properties of N2 laterite, the impermeability of post-mining stress recovery creep, before mining crack and post mining was deeply studied and analyzed by the water pressure test before and after mining, the test of creep permeability and the experiment of soil-water interaction and so on. The results show that the N2 laterite has a good capacity of self-recovery after the impermeability was broken by mining crack. The mechanism of impermeability self-recovery was explained from the perspective of geological structure, soil-water interaction and rheological properties；and according to this finding, the reconstruction of aquifuge and major engineering geological properties included was proposed. [ABSTRACT FROM AUTHOR]

An experimental study to examine the validity of this assumption was presented. Two groups of concrete specimens with two different cross-section shapes were cast under the premise of the same effective thickness. The shrinkage and creep deformation was monitored during a period of 181 days. Experimental results show that effective thickness employed in current prediction models can not totally represent the size and shape effect on time-dependent deformation. For early age concrete under the condition of the same effective thickness, the time-dependent deformation of plate type components has higher development speed relative to the square column type components. In the later period, when there is a moisture balance between the internal concrete and the outside environment, the influence of the cross-section shape on the time-dependent deformation abates. At last, under the condition of the same stress ratio, the time-dependent deformation of concrete specimens with different cross-section shapes is almost identical. Therefore, emphasis should be laid on the influence of cross-section shape on vertical deformation difference in the construction process of high-rise buildings. [ABSTRACT FROM AUTHOR]

Based on the one-dimensional compression creeping and step-loading test on the soft soil subjected to the vacuum preloading treatment in Tianjin Binhai New Area, the modified Singh-Mitchell empirical creep model was used to improve the Terzaghi consolidation theory, and a new one-dimensional consolidation equation was obtained. The new equation used the soft soil mechanics indexes, obtained from the one-dimensional compression and creep tests, as the calculation parameters, and considered the creep deformation generated after primary consolidation. The results obtained from the new equation on different depths of specimens with different stress levels are very close to the test results,which indicates that the new equation can reflect the stress-strain-time relationship of soft soil and is applicable for the soft soil foundation in Tianjin Binhai New Area. [ABSTRACT FROM AUTHOR]

In order to study the viscoelastic constitutive relations of PTFE coated fabrics, the creep tests and stress relaxation tests of PTFE ( polytetrafluoroethylene) coated fabric were carried out, in which the effects of initial stress and initial tensile rate are considered. Several viscoelastic constitutive relations are used to fit the experiment data and the relationship between creep and stress-relaxation is discussed. Results show that PTFE coated fabrics are typically viscoelastic, which should be considered in the design and analysis. The effect of initial stress level on the material viscoelasticity is significant. With initial stress increasing, the material viscoelasticity becomes more obvious. The effect of initial tensile rate on the material viscoelasticity is not significant. The five-component generalized Kelvin model, Burgers model and fractional exponential model can be used to simulate the creep behaviors of PTFE coated fabrics, which is related to the components of constitutive relations. The transformation relationship between creep and stress relaxations based on the metals can not be directly used in the analysis of PTFE coated fabrics. [ABSTRACT FROM AUTHOR]

According to the deformation monitoring data of surrounding rock at soft rock roadway，it is found that the creep capability of surrounding rock of soft rock roadway is gradually weakened with the decrease of soft rock thickness. Thus, the “hesitation effect” of creep of surrounding rock of soft rock roadway was put forward. Based on the effect of friction between hard and soft rock and surrounding rock mass displacement constraint stress, this paper investigated the mechanical mechanism of “hesitation effect” occurred. Using dynamic simulation technology, the corresponding critical condition of the “completely hesitation effect” of surrounding rock occurred was obtained, and also the calculation method of critical thickness was presented. On the basis of the research above, the essence of “yield” was analyzed, the applicability of the principle of “yield” was provided, and the meaning of “secondary supporting” was introduced and improved. Finally, with the industrial test, the significance of the “hesitation effect” on the design of roadway support was proved. [ABSTRACT FROM AUTHOR]

A tri-axial creep-seepage-adsorption and desorption experimental device has been developed to study seepage law and gas adsorption and desorption characteristics in the process of loaded gas bearing coal rheology. It is composed of testing main machine, servo-controlled loading system, triaxial compression chamber, pore pressure control system, adsorption and desorption system, temperature control system, deformation monitoring system and safe guard system. The maximum axial pressure is 500 kN, and the maximum confining pressure is 50 MPa. The heating temperature can reach as high as 90 ℃; and the dimensions of tested cylinder samples are φ50 mm×100 mm. The advantages of the device are as follows:① It can be used to test the porosity and mechanical parameters of coal and to carry out the gas adsorption desorption and creep-seepage experiments of loaded gas-bearing coal and other experiments as well. The device,in addition, is powerful in function, stable in performance and accurate in testing.② It can also be fitted to conduct creep-seepage experiments for long time because of adopting the ball screw loading mode. And the maximum loading time can be more than two months.③ The device is equiped with high and low temperature control system. And it can be used to keep the constant temperature at the gas inlet, gas outlet and the triaxial compression chamber, which can effectively avoid the messurement error caused by temperature variation. Experiments of coal porosity testing, gas desorption characteristics and creep-seepage law of loaded coal are conducted using this device. These conclusions validate the functional diversity, accuracy and reliability in testing on the device. [ABSTRACT FROM AUTHOR]

To analyze how creep interacts with shear lag effect in concrete box girders, the calculation formulae for the creep secondary internal force and stress were derived with the energy variation method. With a simply supported-to-continuous box girder for example, the creep bending moment and stress were calculated under the shear lag effect, and the shear lag coefficients were obtained under the influence of creep. The results show that the shear lag effect increases the creep stress significantly. Under the shear lag effect, the creep variation at the intermediate bearing section is the maximum, where the secondary bending moment increases by 42.56% and the flange normal stress above the web plate decreases by 8.5%. [ABSTRACT FROM AUTHOR]

The rock specimen from the roof of a mine was experimented using self-developed RLM-2000M，and the rock specimen's viscoelasticity characteristics was derived under the influence of mining stress.In this paper，Burgers model was implemented for the theoretical analysis of coal creep damage and fracture law under mining influence，and the overlying rock's creep damage and fracture model under mining influence was built. Therefore，the failure law of roof and floor under mining influence was studied. The FLAC3D and borehole imaging technology were applied in this study. The results show that the model developed can better reflect the rock creep failure. The results reveal the creep failure characteristics of roof and floor rock at E9-10 seam of Tenth Mine，Pingdingshan. The study can provide a theoretical evidence for the study of roof and floor's creep failure. [ABSTRACT FROM AUTHOR]

The traditional phenomenological creep models，which ignore the physical mechanisms of time-dependent fracturing in rocks，are not adequate to replicate the realistic creep behavior of rocks under complex loadings. In this study，a dual-scale model was proposed to represent the realistic rock medium in the framework of continuum mechanics. In addition，based on the mechanisms of time-independent and time-dependent growth of microcracks，the theories of damage mechanics and fracture mechanics were employed to develop the micro-crack based damage constitutive equations and failure criterion at the micro-scale. The obtained governing equations were programmed with Matlab and Comsol，which are capable of capturing the time-dependent damage and failure process of rocks. Furthermore，a bi-axial compressive creep test was performed and the numerical results show that the proposed model replicates the typical tri-modal creep behavior and the time-dependent fracturing in rocks. The proposed model provides a useful approach to further investigate the long-term stability of rock engineering and to predict the geological disasters. [ABSTRACT FROM AUTHOR]

This paper intends to propose the creep model for recycled aggregate concrete filled tube (RACFST), which is based on the concrete model with the capability of well predicting the time-dependent behavior of recycled aggregate concrete (RAC) . Existing concrete models for RAC only consider the influence of the amount of residual cement mortar attached on the recycled aggregate on the creep of concrete, without considering the effect of the water-cement ratio of the origin concrete. Based on the analytical results, the important factor which influences time effects of RAC was specified to propose a modified model considering the water-cement ratio of the original concrete. All the concrete models for RAC were benchmarked against 39 available creep tests to evaluate the reliability of those models in predicting the creep of RAC. It is indicated that the modified model proposed in this paper has the best performance in estimating the creep of RAC members whose water-cement ratios are different from those of original concrete. In order to verify the reliability of the proposed model in predicting the long-term responses of RACFST, the creep models were benchmarked against the long-term tests on eight RACFST stub columns under axial loading with different loading ages. The strength of RAC core in the experiments was higher than that of original concrete. When predicting the test results, the age-adjusted effective modulus method was employed by adopting an infinite notional size for the concrete component to eliminate the effects of relative humidity. It can be noted that the modified model proposed in this paper also has the best accuracy in predicting the creep of RACFST with the maximum deviation within 8%, which can be applied in the analysis of long-term responses for such member in the practical engineering. [ABSTRACT FROM AUTHOR]

In order to analyze the creep properties of cemented body used in backfilling mining, triaxial creep experiments were conducted. Based on these, the damage evolution equation considering time and stress was deduced, and damage variable was brought in modified Nishihara model, and the new constitutive model was established and the 3D creep equation of backfilling cemented body was deduced. The creep model parameters were integrated based on the experiment data, and the comparative analysis of creep curves in theory and on experiment was conducted. The findings show that backfilling cemented body is viscosity elastic-plastic material and has obvious rheological characteristics, there are only decay creep and steady-state creep when deviatoric stress is small, when it is big, there is accelerated creep. Creep amount increases with the increasing of stress, but increase rate is weakened. It shows that the modified Nishihara model considering damage can better reflect the creep law of backfilling cemented body. [ABSTRACT FROM AUTHOR]

The differential viscoelastic plasticity constitutive equation with the creational rheological elements in humidity field of rock which considers the influence of humidity was finished based on the Nishihara theological model. The model equation considering humidity effect of creep, unloading and relaxation were deduced. When the stress is less than yield stress, the model is a stable creep model; and the unloading curve contains instantaneous elasticity, elastic after-effect and viscosity flow induced by humidity. When the stress is greater than yield stress, the model is an unstable creep :and the curve of unloading includes instantaneous elasticity, elastic after-effect and the viscosity flow induces by the stress and humidity. The multiaxial creep equation was also established according to equivalent effective strain and stress theory. This model reflects the rheological properties of rock, and can be used for analysis of stability of rocks. [ABSTRACT FROM AUTHOR]