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BACKGROUND: Patellar tendon is an important structure to maintain the stability of the knee joint and exhibits unique nonlinear mechanical properties under tension, but the effect of elastin on the mechanical behavior of the patellar tendon under tensile loading is still unclear. OBJECTIVE: To study the effect of elastin on the mechanical properties of patellar tendon through targeted enzyme treatment of elastin. METHODS: (1) Thirty fresh porcine patellar tendons, weighing 40–50 mg, were evenly divided into five different elastase concentrations (0, 1, 5, 10, 20 U/mL) or incubated in elastase solutions for five different times (0, 1, 4, 6, 12 hours), and finally the elastin content was detected. (2) Patellar tendon was treated in PBS or 5 U/mL elastase for 8 hours, then Verhoeff Van Gieson (VVG) staining and Masson staining were performed. (3) Twenty fresh porcine patellar tendons were randomly divided into PBS control group and elastase-treated group. After 9 points were marked on the sample surface, the longitudinal tensile test and stress relaxation test were carried out. The displacement of the marked points was calculated by optical non-contact method for subsequent strain analysis and stress calculation. The samples were incubated in PBS or 5 U/mL elastase for 8 hours, and the same mechanical test was performed again. RESULTS AND CONCLUSION: (1) Incubating in 5 U/mL elastase for 8 hours could meet the requirements of this experiment. (2) Compared with pre-treatment, tissue tensile stress was significantly reduced in the PBS and elastase-treated groups, which were both decreased by about 40% (P < 0.001, P < 0.01). Compared with pre-treatment, the relaxation percentage after treatment increased significantly, with a difference of about 12% (P < 0.05). On the normalized average stress-time curve, the stress of elastase-treated treatment group decreased more than that of PBS group, with a difference of about 16% (P < 0.0001). (3) The above results showed that elastin played an important role in the tensile mechanical properties and viscoelastic properties of patellar tendon, further supplementing the understanding of the multiscale tendon structure-function relationships, which would be beneficial to the development and improvement of microstructure constitutive model in the future to simulate patellar tendon lesions and surgical intervention. [ABSTRACT FROM AUTHOR]

Aiming at the problem that cationic surfactant fracturing fluid adsorbs in the formation and causes secondary damage to the reservoir, a long-chain tertiary amine（hereinafter referred to as OADA） was synthesized in the laboratory using oil diamine as raw material and Eschweiler-Clarke reaction.OADA was used as thickening agent and acetic acid as assistant.The effects of the amount of potassium chloride and the molar ratio of the main agent to acetic acid on the viscosity of the system were studied.The performance indexes of OADA clean fracturing fluid system, such as temperature resistance, shear resistance, viscoelasticity and suspended sand, were investigated.By scanning the frequency and stress of the system at room temperature, it is found that the system is mainly elastic.The system still has a viscosity of more than 25 mPa·s when it is continuously sheared at 100 ℃ and 170 s-1 for 1 h.The gel breaker has low viscosity and surface interfacial tension, and the damage rate to the core is only 5.82%,it has low damage characteristics and good compatibility with formation water. [ABSTRACT FROM AUTHOR]

A chemically cross-linkable molecular self-conjugated polymer, HCG-2， was synthesized from acrylamide， acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, functional monomers containing cross-linking sites, and cetyl dimethyl allyl ammonium chloride， and its synthesis conditions were optimized. The thixotropy and viscoelasticity of HCG-2 were investigated, and it was found that a dynamic structure could be formed between HCG-2 molecules in aqueous solution， and the surfactant sodium dodecyl sulfate could improve the strength of this structure; the relationship between temperature and the thixotropy and viscoelasticity of the system was investigated, and it was found that the interaction between HCG-2 molecular chains under the influence of the surfactant was weak and could not withstand too high temperature However, after using chemical cross-linking agents to form chemical bonds between the molecular chains, the temperature and shear resistance of the system at 180℃ could meet the requirements of the industry standard. [ABSTRACT FROM AUTHOR]

Objective Aiming at the problems of poor shear resistance of polymer and the influence of deep formation viscosity retention in conventional chemical flooding system, wormlike micelle oil displacement technology was studied. Methods Using betaine surfactant monomer (PSM), N, N-dimethylpropylene diamine and other raw materials, by two-step reaction of amidation and quaternization, the wormlike micellar surfactant for oil displacement with viscoelasticity and interfacial activity was synthesized under the conditon of reduced pressure spin drying. The molecular structure, theological properties, microstructure, shear resistance, salt resistance, interfacial tension and oil displacement characteristics of wormlike micelle were investigated. Results The structure obtained by NMR was consistent with the target product. Wormlike micelle has good viscosity increasing (mass fraction O. 30% —O. 50%, apparent viscosity 10 — 50 mPa • s, 7. 34 s-1), salt resistance (<100 000 mg/L) and the ability to reduce oil-water interfacial tension (10-2 mN/m). The core displacement experiment results showed that the wormlike micelle has stronger oil displacement ability than conventional polymer, and the FOR was increased by 11. 7%. Field well group test increased oil by 2 700 m3. Conclusions Wormlike micelle oil displacement technology can be used as an efficient oil displacement agent in offshore high water-cut reservoirs to effectively increase oil rate and reduce water production. Keywords: wormlike micelle; oil displacement; viscoelasticity; surfactant; interfacial tension [ABSTRACT FROM AUTHOR]

The rapid development of nanotechnology has increased the possibility of nanoparticles coming into contact with humans and the environment, bringing risks to biological and environmental safety. Nanoparticles can reach the alveolar surface through respiration, so it is necessary to explore the interaction between nanoparticles and phospholipid molecules in the pulmonary surfactant. The surface pressure-mean molecular area ((π-A) isotherms, surface pressure-time (Δπ-t) curves, compression-expansion curves and oscillation curves of oleic acid covered Fe;, magnetic nanoparticles (OA-Fe3O4 MNPs) and phosphatidylglycerole (DPPG) at the air-water interface were measured by Langmuir technique. and the surface morphology characteristics of DPPG mono- layers were monitored by Brewster angle microscope (BAM). The results showed that the π-A isotherms moved to the direction of the increase of the molecular area with the increase of the content of OA-Fe3O4 MNPs. OA-Fe3O4 MNPs formed complex with DPPG molecules, resulting in a significant increase in the surface pressure and a decrease in the compression modulus (Cs-1) of the monolayer. Compared with pure DPPG monolayer. the surface pressure of monolayer decreased obviously within one hour due to the existence of OA-Fe3O4 MNPs. The expansion curve of DPPG monolayer showed obvious hysteresis with the increase of OA-Fe3O4 MNPs. When the surface pressure is 25 mN/m, DPPG monolayers showed nonlinear response to sinusoidal strain disturbance of 5% of molecular area. OA-Fe3O4 MNPs did not change the viscoelastic characteristics and the time scale of relaxation process of DPPG monolayers. BAM images supported the above results. [ABSTRACT FROM AUTHOR]

As a new fracturing fluid system with good sand-carrying performance and imbibition displacement, nano variableviscosity slickwater has been successfully applied to shale oil volume fracturing in Changqing Oilfield. The field test results show that it has good sand-carrying performance and stimulation effect. Under the condition of 40 % sand ratio, the pressure of sand adding process is stable, and the daily oil production of a single well can reach 11.31 tons after fracturing construction, but its sandcarrying mechanism and imbibition performance are not clear. In this paper, the laboratory experimental study on the field concentration of nano variable-viscosity slickwater and the conventional EM30S crosslinkable slickwater system is carried out. Through the experimental methods of dynamic sand-carrying migration, transmission electron microscope (TEM), rheological property evaluation, and pressurized imbibition under the condition of reservoir temperature and pressure, the sand-carrying mechanism of nano variable-viscosity slickwater is revealed and its imbibition performance is evaluated. The experimental results show that the intersection value of elastic modulus and viscous modulus of slickwater reflects the sand-carrying capacity of slickwater solution. The smaller the intersection value is, the stronger the elastic sand-carrying capacity is; Under the same viscosity, the intersection value of viscoelastic modulus of nano variable-viscosity slickwater CNI system is only 0.0741 Hz, which is far lower than 0.181 Hz of field slickwater EM30S, resulting in its static and dynamic elastic sand-carrying performance much higher than EM30S; TEM results show that the strengthening association structure between nano emulsion and variable-viscosity slickwater is the main reason for the enhancement of elastic sand-carrying performance of slickwater. In addition, the results of pressure imbibition experiment show that the nano variable-viscosity slickwater has good imbibition displacement performance, and can replace the crude oil in the nano pores of shale, and the overall recovery can reach 36%. Among them, the order of recovery efficiency of different pore types is: mesopore > micropore > macropore. [ABSTRACT FROM AUTHOR]

To get a further insight into the corresponding relationship between ultrasonic attenuation characteristics in concrete and the concrete random inhomogeneity, firstly, based on digital image processing technology, the digital model of concrete structure was established by taking the content and particle size of aggregate as variable. Secondly, Kelvin-Voigt constitutive relation was introduced to characterize the viscoelasticity of concrete during ultrasonic wave propagation. Thirdly, the quality factors of aggregate and cement mortar measured by spectral ratio method and other measured parameters were fed into the ultrasonic control equation. Finally, the propagation of ultrasonic wave in concrete was simulated by staggered grid finite difference method. The influences of random parameters such as aggregate particle size, aggregate content, cement mortar wave velocity and quality factors on ultrasonic wave propagation in concrete were analyzed from the perspectives of energy and frequency. The results show that ultrasonic scattering attenuation is most sensitive to the randomness of concrete and is the main contribution of ultrasonic energy attenuation. Although the effect of viscoelasticity can be ignored, it will cause further attenuation compared with the scattering energy. The recommended incidence frequency for ultrasonic nondestructive testing of concrete structures is 50 ~ 100 kHz. The research provides a useful reference for establishing the mapping relationship between concrete properties and ultrasonic propagation parameters. [ABSTRACT FROM AUTHOR]

With zirconium oxychloride as the main body and glycerol/cocamidopropyl dimethylamine ethyl lactone as the ligand, a functional cross-linking agent CL・24 w 让h surface activity was obtained, and the synthesis of the product was proved by infrared spectroscopy・ The obtained CL-24 and hydrophobic associating polyacrylamide polymer GS25 form polymer gel, and it is found that it can realize "secondary crosslinking" in the process of crosslinking・ The microstructure and rheological properties of jelly were characterized by scanning electron microscope and rotary rheometer・ The results showed that the functional surfactant CL-24 and associative polymer formed a spatial network structure ・ After shearing for 1 h at 130 °C and 170 s 1, the viscosity in clear water 101 mPa • s, and that in 20 000 mg/L sodium chloride solution was 113 mPa • s,让 was found that the functional crosslinking agent CL-24 promoted the polymer gel to show excellent temperature and salt resistance. Through dynamic rheological frequency scanning and stress scanning, it was found that the polymer gel fluid formed showed elastic characteristics and obvious u secondary crosslinking" phenomenon. [ABSTRACT FROM AUTHOR]

In order to reveal the influence mechanism of wood chemical composition on longitudinal static and dynamic viscoelasticity of cell wall from the perspective of micromechanics, enrich the research content of mechanical properties of wood cell wall and provide reference for selective fiber utilization, wood cell wall at 2/3 of the cross section of Pinus massoniana wood was taken as the research object. Hemicellulose and lignin in cell wall were removed step by step by chemical method, and the contents of cellulose, hemicellulose and lignin were measured by NREL’S LAPS. The changes of chemical composition of wood cell wall were analyzed by Fourier transform infrared spectroscopy. The mechanical properties such as creep compliance, storage modules and loss modulus of wood cell wall were measured by nano indentation technology. Then, the relationship between the static viscoelastic properties of wood cell wall and chemical components was studied using Burgers model. The results showed that cellulose played a leading role in the static viscoelastic properties of wood cell walls. Wood extract had little effect on the viscoelasticity of cell wall. The effects of hemicellulose and lignin on the dynamic viscoelasticity of cell wall were significant. After removing hemicellulose and lignin, the storage modulus of cell wall was reduced by 17.4% and 49.4%, respectively, while the loss modulus was increased. [ABSTRACT FROM AUTHOR]

Mechanical stability of soil structure determined the scour resistance, erodibility, collapsibility, slope stability, and foundation stability of the soil, even the large-scale agricultural instruments, as well as irrigation and water conservancy projects. Alternatively, rheology has widely been one part of soil physical characterization under deformation. The rheological parameters can be utilized to clarify the highly complex soil process, including the most significant soil aggregation factors, such as soil bulk density and water content. In this study, the widely distributed Lou soil and loessal soil on the Loess Plateau were selected as the research objects. An amplitude scanning test was selected to simulate the oscillation load process. An investigation was made on the effect of soil bulk density and water content on the mechanical stability of soil structure under the oscillation load. The results show that: 1) The soil density increased the contact point between soil particles, leading to the increasing cohesion and friction between particles. The shear strength parameters were all increased, including the shear stress at the linear viscoelastic region, the shear stress at yield point, the maximum shear stress, and the storage modulus at the yield point, as the increase of soil bulk density, indicating the increase in the stability of soil structure. In terms of viscoelastic parameters, the shear strain at the linear viscoelasticity region and the maximum shear stress decreased, whereas, the shear strain at yield points and integral zone increased first and then decreased, with the increase of soil bulk density. Soil particles were under the most stable way of organization and combination (1.3 g/cm3 ). Shear strength parameters with the change of soil bulk density were more sensitive than viscoelastic parameters. 2) As the increase of soil water content, the shear strength parameters presented the decreasing trends, including the shear stress at the linear viscoelastic region, the shear stress at yield point, the maximum shear stress, and the storage modulus at the yield point, indicating the decreased stability of soil structure. In viscoelastic parameters, the shear strain at the linear viscoelasticity region increased with the increase of water content, but the shear strain at yield point and integral zone decreased. It indicated that the cohesion and friction between soil particles decreased, with the increase of soil water content. The higher water content of soil particles decreased the relative sliding resistance between particles, leading to the deterioration of soil structural stability. 3) The elasticity and shear strength of Lou soil was higher than that of Loessal soil. This was mainly because Lou soil contained a higher content of clay, organic matter, cation exchange capacity, and specific surface area than those of Loessal soil, indicating the improved cementation strength between soil particles. Consequently, the rheological parameters from the amplitude scanning test in the rheometer can be used to quantitatively characterize the mechanical stability of soil structure, providing for rich evaluation parameters to further understand the micromechanical properties of soil. The finding can provide a shred of strong scientific evidence for agricultural water and soil engineering design, as well as the prevention and control of landslide and geological disasters in the Loess Plateau. [ABSTRACT FROM AUTHOR]

The viscoelastic nature of the microenvironment around a cell is critical to cell mechanobiology, and modulates the mechanical feedback between cells and extracellular matrix. However, the mechanisms underlying the ways that cells actively sense and respond to the viscoelastic microenvironment remain elusive. There? fore a molecular clutch model was developed for cell traction to predict the effects of substrate viscoelasticity on the dynamics of focal adhesions connecting the intracellular actin cytoskeleton to the viscoelastic substrate. The model predicts that certain levels of viscoelastic dampings can increase cell tractions on relatively compliant substrates, and this damping reduces cell tractions on relatively stiff substrates. The model predictions are qualitatively consistent well with reported experimental observations. The model offers physical insights into the role of substrate viscoelasticity on cell tractions and cell spreading. [ABSTRACT FROM AUTHOR]

Because the actuator composed of the dielectric elastomer has a viscoelastic effect during the driving process of the soft robot, which makes it difficult to accurately control the robot, a kind of beetle antennae search (BAS) algorithm optimization PID was proposed. The control algorithm was used for precise control of the soft robot. Firstly, the rheological model was used to build the dynamic model of the dielectric elastomer actuator (DEA). Secondly, the use of the BAS algorithm had a strong global optimization ability and a single optimization strategy to convert the PID controller parameters into BAS algorithm in the three-dimensional space. Finally, the PID parameters in the iterative process were optimized. The experimental results show that the maximum tracking error of sine triangle wave is 0.95 mm and 1.08 mm. Compared with other control methods the proposed method has better control accuracy of the actuator. [ABSTRACT FROM AUTHOR]

In order to solve the problem of rutting on the cold recycled foamed asphalt pavement under the action of high temperature and heavy load, and to understand the dynamic response of the road surface when the recycled mixture was used as the lower layer and the upper base layer respectively, a high - shear and dense foamed asphalt cold recycling mixture (F - B) was designed, combined with regional climate characteristics and viscoelastic theory, obtained the temperature field of different structural layers and the strain changes under moving axle load through the finite element method, and compared with the conventional gradation. The results showed that the pavement temperature field had obvious non - linear characteristics, and the shear resistance of the material could be improved by improving the gradation. There was about 10% residual strain of the pavement after unloading, and the viscoelastic model could obtain the residual deformation of the pavement, which could better reflect the formation of ruts. The longitudinal strain of the foamed asphalt layer was alternating between positive and negative, which was easy to cause road fatigue damage. Under low speed and heavy load, the use of high shear density grading could reduce the maximum shear stress of the surface layer and the generation of flow rutting. When foamed asphalt was used as the lower layer, the road surlace had better resistance to vertical deformation under heavy load. [ABSTRACT FROM AUTHOR]

In order to study the mechanism of the formation of micelle system by the combination of propylene bis (octadecyl dime thylammonium chloride) (abbreviated as 18-3-18),potassium chloride and sodium salicy-late,and to find the viscosity The best ratio of elastic surfactant (VES) fracturing fluid system. In this paper, scanning electron microscope (SEM) is used to observe the microstructure of different components mixed with viscoelastic surfactant, and the viscosity is measured with a viscometer. Find the best ratio, a nd add polyoxyethylen e to hope to further improve its viscoelasticity. The results show that when the concentration of 18-3-18 is fixed at 2 wt %,the potassium chloride content is adjusted to 7 wt %, the sodium salicylate content is at 0. 6 wt %, the formed VES fracturing fluid has the best viscoelasticity, and after adding 0. 1 wt% polyoxyethylene, the viscosity of the system has increased significantly, and the effect is better at high shear rate. [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]

In order to investigate the effect of load, speed and material on the numerical solution of viscoelastic rotating beam displacement, a mathematical modeling method was used to derive a fractional-order model of the viscoelastic rotating beam based on the constitutive relationship, strain displacement relationship, and Hamilton principle of viscoelastic materials. Numerical simulation was performed using Legendre wavelet as the basis function. The displacement solutions are given under uniform and linear loads. The results show that the difference in load, speed and material will affect the numerical solution of the viscoelastic rotating beam displacement. The preliminary conclusion of the research is to establish and solve the fractional-order model of fractional-order viscoelastic rotating beam in the time domain, which is helpful for the research on the vibration of rotating beam. [ABSTRACT FROM AUTHOR]

Objective · To examine the carotid viscoelasticityusing ultrasonic shear wave dispersion (USWD) technique, and to preliminarily analyze its correlation with blood flow shear rate. Methods · Forty-five patients of General Surgery Department of Shanghai General Hospital, Shanghai Jiao Tong University School of Medicine December 2018 to January 2019 were recruited, and divided into the elder group (≥ 50 years old) and the younger group (R), shear wave dispersion (SWDR), blood flow maximum shear rate (SRmax) and mean shear rate (SRmean). The correlations between SWER, SWDR and blood flow shear rate were analyzedPearson correlation, respectively. Results · ①Compared with the younger group, the carotid artery SWER, SWDR, SRmax and SRmean of the patients in the elder group were lower (all PR and SWDR of carotid artery of all patients were positively correlated with SRmax and SRmean, respectively (all PConclusion · Carotid arterial viscoelastic index based on USWD technique is closely related to the blood flow shear rate, which is expected to provide a new perspective for the study of carotid arterial diseases. [ABSTRACT FROM AUTHOR]

BACKGROUND: Cartilage tissue engineering repair is an important method to repair cartilage defects. Silk fibroin/type II collagen scaffolds are viscoelastic materials that have excellent biocompatibility and exhibit solid and liquid characteristics, but the micro-mechanical properties between different layers are still a problem worthy of attention. OBJECTIVE: To obtain the relationship between macro-loading force of scaffold and micro-force between layers, so as to obtain the macro-force under the micro-force of optimal cell proliferation. METHODS: The compression stress relaxation experiment of the blank scaffold was designed, and the finite element model of the scaffold was constructed after fitting viscoelastic constitutive equation with experimental data. The stress relaxation of the model was simulated to obtain the mechanical state between the scaffold layers. RESULTS AND DISCUSSION: The force of each layer of the scaffold was distributed at 1.185-3.305 N, and the stress of each layer gradually decreased with time until it converged. The total displacement of the scaffold increased with the number of layers. The strain values between the layers of the scaffold ranged from 1.82x10-2-4.47x10-2 to 4.47x10-2-4.47x10-2. This value indicates that this is the best state for culturing cells. The finite element analysis results show that when 10% strain occurred macroscopically in the scaffold, the strain value of each layer was distributed in the numerical range of 2%-7%. When the macro strain of the stent was 5%, the strain value of each layer was distributed between 1% and 2%. When 20% strain occurred on the scaffold macroscopically, the strain value of each layer was distributed between 8% and 18%. Comparison results revealed the optimal strain value for cell proliferation was 4%-7%. [ABSTRACT FROM AUTHOR]

Ｔｈｅ ｌｏｎｇｉｔｕｄｉｎａｌ ｄｙｎａｍｉｃｓ ｏｆ ｖｉｓｃｏｅｌａｓｔｉｃ ｎａｎｏｒｏｄｓ ｗａｓ ｉｎｖｅｓｔｉｇａｔｅｄ ｂａｓｅｄ ｏｎ ｔｈｅ ｎｏｎｌｏｃａｌ ｔｈｅｏｒｙ ａｎｄ ｔｈｅ Ｋｅｌｖｉｎ ｖｉｓｃｏｅｌａｓｔｉｃ ｔｈｅｏｒｙ， ｉｎｃｌｕｄｉｎｇ ａｘｉａｌ ｆｒｅｅ ｖｉｂｒａｔｉｏｎ ａｎｄ ｗａｖｅ ｐｒｏｐ⁃ ａｇａｔｉｏｎ． Ｆｉｒｓｔｌｙ， ｔｈｅ ｐａｒｔｉａｌ ｄｉｆｆｅｒｅｎｔｉａｌ ｇｏｖｅｒｎｉｎｇ ｅｑｕａｔｉｏｎｓ ｗｅｒｅ ｄｅｒｉｖｅｄ ａｎｄ ｔｈｅｎ ｔｈｅ １ｓｔ ３ ｖｉ⁃ ｂｒａｔｉｏｎ ｐｒｏｐｅｒｔｉｅｓ ｗｅｒｅ ｄｉｓｃｕｓｓｅｄ ｕｎｄｅｒ ３ ｋｉｎｄｓ ｏｆ ｔｙｐｉｃａｌ ｂｏｕｎｄａｒｙ ｃｏｎｄｉｔｉｏｎｓ ｗｉｔｈ ｔｈｅ ｄｉｍｅｎ⁃ ｓｉｏｎｌｅｓｓ ｍｅｔｈｏｄ． Ｆｉｎａｌｌｙ， ｔｈｅ ｒｅｌａｔｉｏｎｓｈｉｐｓ ｂｅｔｗｅｅｎ ｔｈｅ ｃｉｒｃｕｌａｒ ｆｒｅｑｕｅｎｃｙ， ｔｈｅ ｗａｖｅ ｓｐｅｅｄ ａｎｄ ｔｈｅ ｗａｖｅ ｎｕｍｂｅｒ ｗｅｒｅ ｏｂｔａｉｎｅｄ ｉｎ ｔｈｅ ｐｒｏｂｌｅｍ ｏｆ ｗａｖｅ ｐｒｏｐａｇａｔｉｏｎ． Ｔｈｅ ｎｕｍｅｒｉｃａｌ ｒｅｓｕｌｔｓ ｓｈｏｗ ｔｈａｔ， ｔｈｅ ｓｍａｌｌ⁃ｓｃａｌｅ ｅｆｆｅｃｔ ｍａｋｅｓ ｔｈｅ １ｓｔ ａｎｄ ２ｎｄ ｆｒｅｑｕｅｎｃｉｅｓ ｄｅｃｒｅａｓｅ ｐｅｒｓｉｓｔｅｎｔｌｙ ａｎｄ ｔｈｅ ３ｒｄ ｆｒｅｑｕｅｎｃｙ ｉｎｃｒｅａｓｅ ｆｉｒｓｔ ａｎｄ ｄｅｃｒｅａｓｅ ｌａｔｅｒ， ｗｈｉｃｈ ｉｎｄｉｃａｔｅｓ ｔｈａｔ ｔｈｅ ｎａｎｏｓｔｒｕｃｔｕｒａｌ ｓｔｉｆｆ⁃ ｎｅｓｓ ｉｓ ｗｅａｋｅｎｅｄ ｏｒ ｓｔｒｅｎｇｔｈｅｎｅｄ． Ｉｎ ｐａｒｔｉｃｕｌａｒ， ｆｏｒ ａ ｃｏｎｃｅｎｔｒａｔｅｄ ｍａｓｓ ａｔ ｔｈｅ ｆｒｅｅ ｅｎｄ ｏｆ ｔｈｅ ｎａｎｏｒｏｄ， ｔｈｅ ２ｎｄ ｆｒｅｑｕｅｎｃｙ ｈａｓ ｍｕｌｔｉｐｌｅ ｖａｌｕｅｓ ｗｈｅｎ ｔｈｅ ｖｉｓｃｏｅｌａｓｔｉｃ ｃｏｅｆｆｉｃｉｅｎｔ ｉｎｃｒｅａｓｅｓ， ｗｈｉｃｈ ｍａｙ ｃａｕｓｅ ｉｎｓｔａｂｉｌｉｔｙ． Ｔｈｅ ｎｕｍｅｒｉｃａｌ ｅｘａｍｐｌｅｓ ａｌｓｏ ｐｒｏｖｅ ｔｈａｔ ｓｔｒｏｎｇｅｒ ｎｏｎｌｏｃａｌ ｅｆｆｅｃｔ ｂｒｉｎｇｓ ｌｏｗｅｒ ｄａｍｐｉｎｇ ｅｆｆｅｃｔ ｏｆ ｖｉｓｃｏｅｌａｓｔｉｃ ｍａｔｅｒｉａｌｓ． Ｔｈｅ ｌｏｎｇｉｔｕｄｉｎａｌ ｗａｖｅ ｃａｎ ｐｒｏｐａｇａｔｅ ａｔ ｈｉｇｈ ｗａｖｅ ｎｕｍｂｅｒｓ ｄｕｅ ｔｏ ｏｃｃｕｒｒｅｎｃｅ ｏｆ ｔｈｅ ｅｓｃａｐｅ ｆｒｅｑｕｅｎｃｙ． Ｔｈｅ ｅｆｆｅｃｔｓ ｏｆ ｖｉｓｃｏｅｌａｓｔｉｃ ｃｏｅｆ⁃ ｆｉｃｉｅｎｔｓ ｏｎ ｔｈｅ ｄａｍｐｉｎｇ ｒａｔｉｏ ｍａｙ ｂｅ ｉｇｎｏｒｅｄ ａｔ ｌｏｗ ｗａｖｅ ｎｕｍｂｅｒｓ， ｈｏｗｅｖｅｒ， ｂｅ ｓｉｇｎｉｆｉｃａｎｔ ａｔ ｈｉｇｈ ｗａｖｅ ｎｕｍｂｅｒｓ． [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]

In the feed industry, through crushing, mixing and conditioning, feedstuffs are pelleted by mechanical equipment to obtain pellet products. In this compression process, the feed material particles are overlapped and staggered with each other, and the granular system is changed from the loose state into the curing bond with squeeze flow and the gap flow occurs synchronously. The mechanism for the pelleting process appears to be a regular relationship of stress and strain and other mechanical properties. Therefore, it is necessary to learn the stress-strain relationship and rheology properties of the feedstuffs during the compression process, and it is of theoretical significance to analyze the forming rules of granules and optimize the pelleting process and equipment. In this paper, based on characteristics and nonlinear properties of wheat as a feedstuff, a nonlinear visco-elasto-plastic constitutive model for characterization of rheological properties was constructed. Based on the experiment, and establishment and verification of the numerical model, the rheological properties such as viscoelasticity and plasticity of the feedstuff were analyzed by the model coefficients, and the influence of material properties and processing parameters on the rheological properties is studied. Also, the relationship between the rheological coefficients of the materials and the quality of the pellet is learned, which provides a new methodology for the study on the compression process of pellet feed. According to the process of pelleting, the factors in compression trials were selected including moisture, particle size (i.e., mesh size) and forming temperature, compression load. During the initial stage of the compression process, air between the particles was extruded by pressure and relative positions of particles are rearranged under the action of the inertial force. With the process progressing, the gap gradually decreases to infinitely small and the relative positions of the particles cease to change significantly, after which the deformation of the material can be considered as caused by its own viscoelastic properties, and therefore the compression process is divided into inertial deformation stage and visco-elasto-plastic compression stage for better description. According to the theory of rheology, the feedstuffs properties exhibited during the compression process are summarized as elastic-plastic, viscous and particle-wall friction, and represented by the strain hardening spring element, Newton viscous dashpot element, and Coulomb friction element, respectively. The elastic modulus shows the flexibility of the elastic element or the difficulty of compression. It turns out that the larger the coefficient, the more difficult the deformation and the stronger the stiffness of the material, which can stand for the strength and deformation properties. The improvement of the plastic strain showed by combined plastic exponent, which is coupled by plastic modulus and strain hardening exponent, indicates that the deformation can be maintained after the removal of the compressive stress, which has a special meaning on the quality control of the pellet feed. The viscous coefficient is mainly characterized by the ability of the particles to be bonded in the process of pelleting, thus reflecting the capacity of the formed pellet to stay stable under external force without significant damage in the current state. Meantime, the frictional loss factor can reflect the characteristics of energy dissipation, which mainly includes the friction and adhesion between the particles or the particles and the die wall. The compression stage was divided into 5 even ranges in order to study the various material properties along with the process. The numerical results of the constitutive model of wheat were obtained under 15% material moisture content, 2. 0 mm mesh size, 80 °C forming temperature and 3 kN compression load, which showed that the determination coefficients (R2) in all stress ranges were beyond 0.99 and the mean relative error values were 3.883%, 1.798%, 2.992%, 1.496%, and 6.721% in the ranges of 1-5, respectively. The comparative curve showed a good fit between the actual test value and model value; besides, the χ2 examination showed that the χ2 values of the data in each range were much smaller than the standard values in the degree of freedom of 130 and the significance of 0.001. Based on the above criteria, this constitutive model possesses a good performance that can be used to characterize the rheological properties of wheat. The constitutive model coefficients and the rheological properties of the feedstuff were characterized by regular changes, which showed obvious stress function: The elastic modulus increased with the increase of stress, indicating the deformation performance of the material was gradually weakened and the overall compressibility of the material decreased step by step to reach the end of forming, and the stiffness increased significantly. The increases of combined plastic exponent showed that the plastic deformation of the material increased gradually with a sudden downside in the last range. The absolute value of the viscosity coefficient increased gradually, which means that the bonding force among the material particles is enhanced with the progress of the forming, and the connection between the particles is strengthened therewith. For the influence of various forming factors, results were showed as follows: The increase in forming temperature can improve the elastic modulus, which means a better compression deformation capacity; with preferable softening, and bonding effect on the compressibility, higher moisture content can improve the combined plastic exponent and viscosity coefficient at the same time; the decrease of the particle size increases the absolute value of the viscosity coefficient, indicating its significant positive effect on the particle bonding force. The correlation relations between the pellet quality index and the constitutive model coefficients show that the pellet density, the pellet forming ratio and the pellet hardness were correlated with the viscous coefficient, plastic modulus, and elastic modulus respectively (P<0.001), which owned the highest correlation coefficients that were all above 0.80, illustrating the close relationship between pellet product quality and feedstuff rheological properties. The nonlinear visco-elasto-plastic constitutive model constructed in this paper can provide a new methodology and perspective for the research of the process of feed pelleting, and provide theoretical basis for analyzing the particle forming characteristics, and product quality from the view of material rheology, which give contribution to the efficient and low-cost pellet production and the improvement of product quality. [ABSTRACT FROM AUTHOR]

Based on the meshless natural element method, a new algorithm was proposed to solve 2D viscoelastic problems. According to the elastic-viscoelastic correspondence principle and the Laplace transform technique, the viscoelastic problem was transformed into an elastic problem in the Laplace space and then the basic formula of the natural element method for the analysis of viscoelastic problems were derived. As a recently developed meshless method, the natural element method (NEM) is essentially a Galerkin method based on natural neighbour interpolation. Compared to most other meshless methods, the shape function employed in the NEM has interpolation property and its support domain is anisotropic. Some numerical examples verify the effectiveness of the developed method. [ABSTRACT FROM AUTHOR]

High pulsed electric field (HPEF) pretreatment is helpful to induce breakdown and displacement effect in cell of fruits and vegetables, which is useful to improve drying speed. We should study the effect of HPEF on the physical properties of fruits and vegetables, which puts the base for optimizing the parameters and mechanism analysis. In this study, 2 kinds of fruits and 2 kinds of vegetables, apple, pear, potato and radish were chosen as raw material. The moisture contents of apple, pear, potato and radish were approximately 86.89%, 89.46%, 78.35% and 93.61%, respectively. Immediately before measuring, the fruits and vegetables were washed and peeled by hand, and then cut into 13 mm diameter and 5 mm thickness using a cork borer. High pulsed electric field generator was used for the HPEF pretreatment of the fruits and vegetables, and the parameters were set as follows: 1) 1 000 V/cm pulse strength, 60 ?s pulse length, pulse number of 15, 2) 1 250 V/cm pulse strength, 90 ?s pulse length, pulse number of 30, and 3) 1 500 V/cm pulse strength, 120 ?s pulse length, pulse number of 45. After HPEF pretreatment, the dynamic viscoelasticity behavior was performed with DMA testing machine using compression platen (diameter of 15 mm). The linear viscoelastic range (LVR) was determined through stress sweeps. A constant amplitude of 10 μm was then chosen (common to the LVR of all samples) to obtain the mechanical spectra as frequency sweeps from 1 to 100 Hz at 25 ℃ and temperature sweeps from 25 to 90 ℃ at 10 Hz. The test and analysis of dynamic viscoelastic of fruits and vegetables were performed by TA Universal Analysis software. Analysis of variance was applied to the data. In order to study the differences among samples, all the data were analyzed with the use of SAS (statistical analysis system) software (version of 9.2). The microstructure analysis was performed by scanning electron microscopy (SEM) on apple samples with the 3 sets of pretreatment parameters, and untreated samples. The storage modulus, loss modulus and loss tangent on different HPEF pretreatment parameters and different oscillation frequency were plotted to characterize the viscoelastic behavior. The theoretical analysis about dynamic viscoelastic mechanics was presented. Results showed that all samples showed a slight linear increase in storage modulus, loss modulus and loss tangent as frequency diminished. A statistically significant difference in storage modulus, loss modulus and loss tangent between different varieties was confirmed. For apple samples, the HPEF pretreatment led to the decrease of storage modulus and loss modulus by 72.36% and 78.09%, respectively. It was primarily attributed to the changes of the cell structure and the intracellular space of the cell as revealed by the SEM. The same decreasing tendency of storage modulus and loss modulus with the increasing of HPEF parameters was observed for potatoes. However, the radish showed a contrary tendency that the storage modulus and loss modulus of radish tissue increased with the increasing of HPEF parameters. High cell turgor pressure may be the main reason for the increase in radish dynamic viscoelasticity after HPEF pretreatment. To pears, as HPEF pretreatment parameters were 1 000 V/cm pulse strength, 60 ?s pulse length, and pulse number of 15, the storage modulus and loss modulus of pear tissue reached the maximum. The reason may be the changes in pear cell turgor pressure caused by low HPEF pretreatment, and then with the further increasing of the HPEF parameters, pear cell membrane could be damaged and the dynamic viscoelasticity of pear tissue decreased. With the temperature increasing, the storage modulus of apple, pear, potato, and radish decreased by 34.44%±3.47%, 49.04%±10.64%, 28.12%±10%, and 55.25%±5.61%, respectively. The loss modulus of them decreased by 66.49%±8.05%, 82.12%±15.12%, 44.66%±7.79%, and 67.84%±2.54%, respectively. These results can provide useful information for the optimization of drying process parameters and the improvement of the industrial pretreatment technique in vacuum freeze-drying processing. [ABSTRACT FROM AUTHOR]

The coal-rock interface recognition is a key technology of autonomous control of unmanned mining equipment in deep dangerous coal seam. The method of coal-rock interface recognition using ultrasonic waves was proposed based on the differences in acoustic impedance between coal and rock. The medium model of coal seam was established by generalizing the first-order wave equation to Kelvin-Voight viscoelastic model and anisotropic medium. With the staggered-gird finite difference method,the propagation of ultrasonic waves was simulated in the model. The medium model of coal seam was verified by experimental and simulation results. The research shows that the viscoelastic VTI medium model and the staggered-grid finite difference method can be used to numerically simulate the propagation of ultrasonic waves in coal seam. Thus, it provides a theoretical basis for the coal-rock interface recognition using ultrasonic waves. [ABSTRACT FROM AUTHOR]

In order to develop a natural, safe improver of steamed bread and nutrition fortifier, as well as increase the added value of wheat bran, phenolic xylans from wheat bran with different addition level (0.25%, 0.5%, 1.0%, 2.0%) and molecular weight (82°, 581kD) were chosen and their effects on fermented dough properties and qualities of steamed bread were investigated. Low molecular weight phenolic xylans were obtained by ultrasonic degradation of phenolic xylans. The rheometer and low-field nuclear resonance (NMR) were used to observe the changes of fermented dough properties with phenolic xylans. The texture profile analyzer was used to observe the changes of qualities of steamed bread with phenolic xylans. The viscoelasticity, water distribution and mobility of fermented dough, color, texture, sensory evaluation score of steamed bread were evaluated in the experiment. The results showed that along with the increase of phenolic xylans from wheat bran, the elastic modulus and proton density A22 increased then decreased, viscous modulus and proton density A23 increased, relaxation time T22 of fermented dough decreased. The lightness and adhesiveness decreased, redness and yellowness increased, specific volume, cohesiveness, resilience and sensory score of steamed bread increased and then decreased, hardness and chewiness of steamed bread decreased and then increased with increasing addition level of phenolic xylans from wheat bran. The higher molecular weight of wheat bran phenolic xylans was, the larger quantitative change of the elastic modulus and viscous modulus would be. The high molecular weight wheat bran phenolic xylans had long relaxation time T22 and small proton density A21 of fermented dough. When the molecular weight of wheat bran phenolic xylans was low, the specific volume and springiness of steamed bread were large, but the hardness and chewiness of steamed bread were relatively large. Compared with the control group, the addition of phenolic xylans from wheat bran could improve the rheological properties and water properties of fermented dough and quality of steamed bread. When the content of wheat bran phenolic xylans was 0.5%, the improvement effect of fermented dough and steamed bread qualities was best. When the addition level of wheat bran phenolic xylans was lower than 1.0%, the properties of fermented dough and qualities of steamed bread were improved. However, the properties of fermented dough and qualities of steamed bread deteriorated when phenolic xylans content was 2.0%. The improvement effect of properties of fermented dough and qualities of steamed bread with high molecular weight wheat bran phenolic xylans was better than low molecular weight wheat bran phenolic xylans. The method and data stated in this study were useful and valuable to the industry and can provide the theoretical basis for phenolic xylans widely application to the flour products. [ABSTRACT FROM AUTHOR]

Viscoelastic suspension is a newly applicable suspension for a large power and heavy crawler vehicle. The viscoelastic suspension can support a heavy load efficiently when walking and working on the off road, raise the adhesion property of a vehicle, and decrease the impact vibration level of the vehicle. The suspension consists of a metal part and viscoelastic material which are spaced and arranged to notably control vibration by transforming vibration energy into thermal energy to dissipate it into the air due to the hysteretic characteristic of viscoelastic materials. To predict and accurately study the dynamic behavior of viscoelastic suspension and evaluate its vibration damping capability, fractional calculus was introduced because of the facts that the fractional calculus exhibits global correlation and data-fitting well when describing rheological phenomenon. In this context, a fractional order Kelvin-Voigt model considering the geometric factors i.e. A radius-thickness ratio incorporated into a dynamic model of viscoelastic suspension for crawler vehicle was established. In this model, the viscoelastic part was represented by a parallel-combination of a spring whose stress is in direct proportion to the strain and a spring pot whose stress is in direct proportion to the fractional derivative of the strain differentiating from the conventional damping pot with stress being proportional to the first derivative of the strain. A numerical solution was obtained by adoption of a Grumwald-Letnikov fractional derivative definition and a matrix function theory and its calculating codes were programming in Matlab. A history correlation coefficient was achieved to embody the afore-history influence of the viscoelastic suspension on its dynamic behavior. Parameters of a fractional model was acquired by fitting data using a least-square method based on a viscoelastic material tensile test carried out on a Testometric M350-10kN according to GB/T 528-1998 and GB/T 9865.1. For a pragmatic study case, a heavy crawler tractor installed with 8 viscoelastic suspensions was considered to analyze its vibration control effect by establishing its fractional model. Also the parameter influence on the vibration control effect, including exciting frequency, fractional order, and ratio of radius to thickness, was examined. The results showed that, compared with rigid suspension, the viscoelastic suspension exhibited remarkable vibration control capability, especially at the resonant frequency of about 4.5 Hz by reducing the response magnitude of the vehicle body by 64.10% in max value and 66.40% in RMS, thus satisfying the supporting and stable demands of the crawler tractor walking and working on the off road. Radius-thickness has a negative influence on the response magnitude of viscoelastic suspension, that is to say there is an effective way to reduce the vibration by introducing a geometry-modified viscoelastic suspension with higher thickness and lower action aero. Fractional order, however, exhibits a positive correlation to the behavior of the response magnitude, which inspires another valid method of altering the viscoelastic material parameter to perfect the vibration of the crawler tractor. The history-dependent factor gives evidence of the long range correlation of the fractional model, i.e., the system response at current time relates to the whole history whose influence increases with time closer to the current time. This research provides an essential theoretical basis for multi-objective optimization and dynamic design of a viscoelastic suspension for a higher power and heavy load crawler vehicle. Experiment study is an essential procedure as a further study. So our future work will stress the indoor test of a dynamic mechanical analysis (DMA) of viscoelasitc materials, deriving a fractional constitutive model considering the temperature-frequency effect of viscoelastic material, and carrying out an in-situ test of a real crawler vehicle establishing a different-parameter viscoelastic suspension to investigate stable/dynamic stiffness, fatigue features, and vibration control capability under working conditions of cutting, pulling, digging, and crossing over an obstacle. [ABSTRACT FROM AUTHOR]

Considering the spherical visco-elastic structure, the post-seismic deformation inversion mode had been constructed based on the visco-elastic earth model. We developed the inversion mode and inversion software package based on the post-seismic fault dislocation model considering the crust-stratified structure. Using the genetic algorithm to invert the different fault dislocation parameters due to strike slip fault, dip slip fault respectively and comparing to the result inverted from the homogenous dislocation model, the result shows that the inversion algorithm used here could invert the dislocation parameters from the large region using the genetic algorithm and the inversion result is better to use. The inversion mode proposed here could better invert the seismic source parameters to different types fault. There is also a important find to suggest us that we could not use the minimum of VTPV as the only rule to judge the inversion result whether good or not when the model mode is not obvious. We should find other ways to make a supplement judge. [ABSTRACT FROM AUTHOR]

Nonlinear vibration of a hinged-hinged viscoelastic buckled beam subjected to primary resonance in the presence of internal resonance was investigated. The governing integro-partial differential equation was derived via introduction of coordinate transform for the non-trivial equilibrium configuration, with the viscoelastic constitutive relation taken into account. Based on the Galerkin method, the governing equation was truncated to a set of infinite ordinary differential equations and the condition for internal resonance was obtained. The multiple scales method was applied to derive the modulation-phase equations. Steady-state periodic solutions to the system as well as their stability were determined. The numerical examples were focused on the nonlinear phenomena, such as double-jump and hysteresis. The generation and vanishing of a double-jumping phenomenon on the amplitude-frequency curves were discussed in detail. The Runge-Kutta method was developed to verify the accuracy of results from the multiple scales method. [ABSTRACT FROM AUTHOR]

Based on the 3-dimensional (3D) fractional order constitutive equation of viscoelastic body waves, the frequency dispersion characteristics of viscoelastic P- and S-waves were analyzed. Also, the isolation effects of the discontinuous rigid pile barrier and the elastic pile barrier in soft clay on viscoelastic SH waves were comparatively studied. With the finite difference method (FDM), an array of vibration amplitude reduction factors for different pile spacing-to-diameter ratios, different fractional orders and different frequencies of incident waves were obtained, and the isolation effect of the elastic pile isolation system in comparison with the rigid was analyzed. The results exhibit that the smaller pile spacing-to-diameter ratio is, or the larger the fractional order is, the better isolation effect of the rigid barrier will be. In contrast, the elastic barrier has better isolation effect in some special target area when the fractional order becomes smaller. [ABSTRACT FROM AUTHOR]

The constant rate uniaxial tension tests and tension-recover tests are conducted to obtain the accurate mechanical property of the EPDM insulation material. A visco-hyperelastic constitutive model is developed based on the mechanical behavior characteristics of EPDM. The method is established by applying the hyperelastic theory which was established under finite deformation condition in combination with linear viscoelastic theory. Then the way to obtain the model parameters is proposed, which is simple and easy to be generalized. The results show that EPDM has the typical hyperelastic mechanical characteristics, and presents a rate-dependent effect. The visco-hyperelastic constitutive model proposed can describe the uniaxial mechanical property of EPDM accurately. The model can provide a theoretical reference for structural integrity analysis of solid rocket motor made of EPDM insulation material. [ABSTRACT FROM AUTHOR]

In order to investigated dissipation characteristics and control effect of a kind of viscoelastic (VE) damper with new elestomeric material during earthquakes, a shaking table test on a steel frame structure added with VE dampers was designed and conducted. Six dampers were installed in pairs at each story of the structure and connected to the upper and lower beam vertically. The structure with additional VE dampers and that without additional VE damper were subjected to three ground motions whose peak ground accelerations (PGAs) vary from 0.1 g to 0.6g. The dynamic properties and structural responses of the two structures were compared. The experimental results indicate that the control effect on acceleration and displacement is remarkable, while the effect on the shear force is limited. The frequency dependence of VE damper is not obvious. The additional stiffness decreases along with the increase of damper deformation, while the additional damping ratio initially increases and then declines. The structural frequency varies from 2.81 Hz to 1.19 Hz, and the maximum additional damping ratio is 18.21%. The adverse effect caused by initial stiffness of VE damper must not be ignored. The maximum deformation of VE dampers is remarkable, and the maximum shear strain in this test reaches 336%. [ABSTRACT FROM AUTHOR]

Affected by environment elements, the degeneration of mechanical property for carbon fiber reinforced polymer (CFRP) composites under hygrothermal environments is an important engineering problem, and the key segment on solving this problem is how to reappear the aging effect of natural environment on CFRP by taking accelerated aging experiments under laboratory condition. Based on time-temperature-humidity superposition principle (TTHSP), the change of viscoelasticity for CFRP is considered as damage measure for Hygrothermal aging. The equivalent conversion relationship between different Hygrothermal environments is determined, and the calculating method of equivalent conversion coefficient is provided. Taking a typical CFRP used in warcraft structure for example, equivalent conversion coefficients under different hygrothermal environments are calculated, the accelerated aging environment spectrum are programmed according to the conversion of ground parking environment spectrum, and the accelerating result is acceptable . Finally, the influences of temperature and humidity on equivalent conversion coefficient are checked, and the result shows that the influence of temperature change on equivalent conversion coefficient is more remarkable than that of humidity change. [ABSTRACT FROM AUTHOR]

To obtain the simulation of early concrete thermal stress, based on the ABAQUS secondary development platform, subroutines that are used to calculate the temperature field and the viscoelastic stress field were written by considering the effect of degree of hydration and maturity, separately. And the validity and rationality of the subroutines were proved by comparing with the theoretical solution. Using sequential coupling method of temperature field and stress field, the user subroutine was used to study the early temperature and stress variation of a mass concrete pile cap. The result shows that with and without consideration of the impact of degree of hydration, the change rules of temperature field are the same. When considering the degree of hydration the peak temperature is lower than that when not taking into account of the degree of hydration. Considering and not considering the influence of early concrete creep, the stress values at the surface points and the center point decrease at the early age after casting, indicating that the creep characteristics of concrete has a certain weakening effect on both tensile and compressive stress at the early age. And due to the low tensile strength of early age concrete, thermal cracks that are perpendicular to the edge of the surface is easier to appear, which means enough attention should be paid to this in practical engineering. [ABSTRACT FROM AUTHOR]