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The improvement of computing power provides a support for finite element simulation analysis, which can solve more complex structures and nonlinear problems more efficiently. In this study, based on the finite element simulation analysis technology, the complex mechanical properties of Mn-Cu alloy are simulated. Prony series constitutive model and parallel rheological constitutive model are respectively adopted to simulate the stress relaxation test of Mn-Cu alloy under different deformation conditions. The stress relaxation experimental data are extracted and converted into the corresponding model parameters and the finite element simulation calculation is carried out. The simulation model parameters which can accurately describe the nonlinear mechanical properties of Mn-Cu alloy are obtained. By comparing the simulation and experimental results, it is concluded that the parallel rheological framework can more accurately characterize the stress relaxation behavior of Mn-Cu alloy. Under different initial strain conditions, the relative error of the simulation results and the test results under corresponding working conditions is less than 1%. Compared with Prony series constitutive model, parallel rheological framework is more suitable for the simulation of Mn-Cu alloy under complex working conditions. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology & Engineering Geology / Shuiwendizhi Gongchengdizhi is the property of Hydrogeology & Engineering Geology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

BACKGROUND: With the rapid development of 3D printing technology in tissue engineering, a variety of scaffold materials prepared by 3D printing are widely used in mandibular defect repair. 3D printing technology brings new possibilities for mandibular defect repair. OBJECTIVE: The 3D bionic bone scaffold material was constructed by low-temperature 3D printing technology, and the internal structure of the scaffold was precisely controlled, and the mechanical properties of the scaffold were analyzed. METHODS: Under the same volume, by changing the interlacing angle of the printed scaffold wire harness and the wire harness, low-temperature 3D printing technology was used to print silk fibroin/type I collagen/hydroxyapatite scaffolds with different angles (30°, 45°, 90°) and polycaprolactone/hydroxyapatite scaffolds (a total of 6 sets of scaffolds). The uniaxial compression mechanics experiment was loaded to 6 groups of scaffolds at a compression rate of 0.5%/s, compressed to 30% strain to observe the relationship between stress and strain. The stress relaxation experiment was applied to the three printing angles of silk fibroin/collagen I/hydroxyapatite scaffolds at a compression rate of 0.5%/s at 10%, 20%, and 30% strain, and the relaxation retention time was 3 hours to observe the relationship between stress and time. In the creep experiment, the silk fibroin/collagen I/hydroxyapatite scaffold with an angle of 90° was compressed and printed at a constant pressure of 2.5, 3.75, and 5 kPa, and the creep retention time was 3 hours to observe the relationship between strain and time. RESULTS AND CONCLUSION: (1) Uniaxial compression mechanics experiment: The mechanical properties of 3D printed silk fibroin/type I collagen/ hydroxyapatite scaffold and polycaprolactone/hydroxyapatite scaffold compression showed that the 90° scaffold had higher Young’s modulus than the 30° and 45° scaffolds under the same compression strain. (2) Stress relaxation experiment: When the compression rate, compression strain and compression angle were constant, the stress of silk fibroin/type I collagen/hydroxyapatite scaffold decreased rapidly with the extension of relaxation time, then slowly decreased. With the extension of relaxation time, the stress of the scaffold decreased rapidly in the beginning time (within 1 600 seconds), and in the later period (3 700 seconds). When the compression rate and compression strain were kept constant, the initial and stable stress values of silk fibroin/type I collagen/hydroxyapatite scaffolds with 90° printing angle were higher than those of scaffolds with 30° and 45° printing angle. When the compression rate and compression angle were constant, the initial and stable stress values of silk fibroin/type I collagen/hydroxyapatite scaffolds increased with the increase of compression strain. (3) Creep test: With the extension of creep time, the strain of 90° silk fibroin/type I collagen / hydroxyapatite scaffolds increased rapidly in the initial stage (within 500 seconds), then increased slowly, and finally leveled off. The strain range of the scaffolds was 35% to 55% at 2.5 kPa, and 43% to 57% at 3.75 kPa. The strain of the scaffold ranged from 45% to 57% under 5 kPa. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Beijing University of Technology is the property of Journal of Beijing University of Technology, Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The principle of cotton fiber creep recovery and stress relaxation based on viscoelasticity was studied. The constitutive model for cotton fiber creep and stress relaxation was established. The creep value and variation of cotton fibers were tested under different compressive load. The results showed that the creep and stress relaxation of cotton fibers represented nonlinear viscoelasticity. The mechanical behaviors like creep recovery and stress relaxation for cotton fibers were well evaluated by nonlinear viscoelasticity model. In the scope of the study, by adding more load, the creep recovery value of cotton fibers was increased and the creep recovery mechanical index was enlarged. As the strain value of cotton fibers increase, the mechanical index of stress relaxation was enlarged. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Axial stress and strain of sandstone with different moisture content were measured by self-designed stress relaxation-dynamic disturbance testing apparatus. It is showed that there exists stress decline and strain increase after the dynamic disturbance was applied on the sandstone specimen. Effects of moisture content on the stress relaxation magnitude and level were analyzed. According to the constitutive law of rock subjected to accumulated deformation disturbance， the disturbance factors range from 2 to 6 at different moisture content conditions.The results show that ①During the stress relaxation process， the magnitude and level of stress relaxation at different time are increased due to the effect of water.The stress reduction can be enhanced by water. ②Under the same impact energy， both the strain increase and stress decrease are observed in sandstone specimen under higher moisture level. The disturbance factor increases with the increase of moisture content. [ABSTRACT FROM AUTHOR]

In recent years, rice straw as a kind of renewable material is being used widely in China. The rheologic characteristics of crop straw have great effect on the power consumption, productivity and compression process of compressing equipment, as well as on the bale durability. At present, a lot of researches have been done by many domestic and foreign scholars on the compression rheologic characteristics, but the researches have been aimed at the rectangular baler instead of the steel-roll round baler, and the test materials are mainly concentrated on corn straw, wheat straw and alfalfa, which limit the development and application of the round baler for crop straw in China. Stress relaxation is an important phenomenon in the rheologic characteristics of straw. In order to deeply research stress relaxation phenomenon of intact rice straw during rotary compression under the round baler, a steel-roll round baler was used for rotary compression test in this paper. To timely monitor the force during rotary compression, the force testing device was developed. In experiments, moisture content of rice straw (12%-68%), dry material quantity of bale (15-23 kg), steel roll speed (222-318 r/min) and feeding speed of rice straw (0.4-1.6 kg/s) were chosen as experimental factors, which were at 5 levels. Stress relaxation time and balance elastic modulus were decided as the evaluation indices, and quadratic orthogonal rotatory combination design was used to analyze the effect of different factors. Through analyzing experimental data by Matlab 8.0, the stress relaxation model of intact rice straw during rotary compression could be expressed by three-element equation which was available through the parallel connection of one Maxwell unit and one spring. The regression equations of stress relaxation time and balance elastic modulus had been established respectively by using Design Expert software. Through variance analysis of regression equations for stress relaxation time and balance elastic modulus, the coefficients of determination (R²) for the models were 0.96 and 0.97 respectively, which indicated that the proposed model was agreeable with the practical condition, thus the proposed model could be used to predict the change of the stress relaxation time and balance elastic modulus during rotary compression. In addition, the relations between evaluation index and each single factor were shown in response surface. The results showed that: with the increase of moisture content of rice straw, both of stress relaxation time and balance elastic modulus decreased; with the increase of dry material quantity of bale, stress relaxation time decreased and balance elastic modulus increased; with the increase of steel roll speed, stress relaxation time and balance elastic modulus decreased and then increased; and with the increase of feeding speed of rice straw, stress relaxation time decreased and balance elastic modulus increased gradually. The contribution rate of each factor on stress relaxation time was as follows: moisture content of rice straw > dry material quantity of bale > feeding speed of rice straw > steel roll speed. The contribution rate of each factor on balance elastic modulus was as follows: dry material quantity of bale > moisture content of rice straw > feeding speed of rice straw > steel roll speed. When moisture content of rice straw was 65%, dry material quantity of bale was 17 kg, steel roll speed was 257 r/min and feeding speed of rice straw was 1.6 kg/s, stress relaxation time was 17.08 s and the balance elastic modulus was 4.01 kPa, which were the best results. The research provides theoretical and technical support for the process optimization of round baler, as well as the analysis of its compression mechanism. [ABSTRACT FROM AUTHOR]

A total of 25 reinforced concrete ( RC ) beams strengthened with pre-tensioned carbon fiber reinforced polymer ( CFRP) were conducted to investigate the prestress losses. Through monitoring the stains on CFRP, the total prestress losses were 14. 38% and 15. 36% relative to the original prestress respectively when the levels of prestressing were 20% and 30% . Over tensioning and twice-tensioning technology were carried out to reduce successfully the prestress loss in the study. Based on existing design specification for prestressed reinforced concrete structures, the prestress loss during the reinforced period contained three parts; prestress loss caused by the relative slip between CFRP and anchorage device; prestress loss caused by the elastic compression deformation of concrete; prestress loss caused by the stress relaxation of CFRP. The formula to calculate the prestress loss was proposed based on the experimental results, which would provide reference value for the design of prestressing FRP strengthening technology. [ABSTRACT FROM AUTHOR]

The rapid development of space technology has put forward higher requirements for electrical connector reliability. The reliability issues of electrical connectors under thermal cycling conditions are presented. A thermal cycling test scheme combined with the accelerated life test theory is proposed for electrical connectors. The accelerated thermal cycling test is carried out. It is found that the value of contact resistance increases slowly with the number of thermal cycles. The extrapolated value of thermal cycling life is calculated by gray model. Finally, the failure analysis on the jack of typical samples is illustrated. It is indicated that the crystal size rises, the fragmentation degree of the sub structure and the dislocation density increase, and there is more β'phase appearing in the jack of samples after test. The result shows that the change of microstructure is the fundamental reason for the stress relaxation phenomenon of jacks and the contact reliability degradation of electrical connectors. [ABSTRACT FROM AUTHOR]

Strain-induced crystallization of cross-linked rubber significantly affects its strength and mechanical properties. To date, theories on the thermodynamic equilibrium of strain-induced crystallization have been proposed. However, the effects of the crosslinking density from these theories are not consistent with the experimental results. Recent experiments using synchrotron radiation led to a better temporal and spatial resolution. Time constants of strain-induced crystallization could be estimated and a quantitative discussion about the relationship between strain and crystallization rate became possible. At the same time, the stress relaxation of cross-linked rubber at a fixed length was found to be mainly due to strain-induced crystallization. These new experimental results are also inconsistent with the thermodynamic theories. In order to explain the experimentally obtained data of the strain-induced crystallization, a heterogeneity of the network structure must be considered. As a result of the recent studies, a more detailed understanding of the reinforcing effect by strain-induce crystallization is becoming possible. [ABSTRACT FROM AUTHOR]

In order to investigate the stability of salt caverns in long term operation, three different shapes of salt cavern models were analyzed with respect to the stress distribution of cavern wall and volume change of cavern under various running pressures. The simulation results showed that stress on the wall is at the highest level in the initial operation period of the cavern storage, and stress concentration occurs mainly in parts with higher curvature on the cavity wall. The stress relaxation is also noticeable under fluctuating operation pressure, and the stress in different parts becomes evenly distribution along the cavern wall with stress gradually declining. There is no obvious fluctuation in changing of cavern stress and cavern volume when the operation pressure varies from 4 to 14.5 MPa annually. After a time span of ten years simulation, volumes of pear-shaped cavern, ellipsoid-shaped cavern and cone-shaped cavern reduces 27%, 22% and 37% respectively, and the decrease rate of cavern volume becomes smaller and smaller. [ABSTRACT FROM AUTHOR]

The theory of the blind-hole method used to measure surface residual stresses in plate was applied to measure surface residual stresses in forged barrel accurately. A kind of FEA software ABAQUS was used to calculate the relaxation coefficients of the blind-hole, and the applicable range of the blind-hole method to measure the surface residual stresses in forged barrel was confirmed by comparing the relaxation coefficients of the blind-hole in the plate and in the forged barrel under the same material, the same force and the same drilling condition. A new method to minimize the off-center error was proposed. The surface residual stresses in a forged barrel were measured by using this method. [ABSTRACT FROM AUTHOR]

To relieve the internal stress in SU-8 photoresist by using ultrasonic stress relief technology, the theory of the stress relief is discussed. Based on the wafer curvature measurement, a profile method was used to calculate the internal stress in SU-8 layers. The effect of ultrasonic stress relief to SU-8 layers was studied by experiments. The experimental values of internal stress before and after the ultrasonic stress relief process were compared. The experimental results show that the internal stress in SU-8 layers can be reduced for 2 MPa, and the relief rate is about 23. 17% after 10 min of ultrasonic stress relief. It is proved that the internal stress in SU-8 layers can be effectively reduced when the proper parameters of ultrasonic stress relief are chosen. [ABSTRACT FROM AUTHOR]

We investigated the effects of Alphabics training on a group of elderly individuals who were certified by the municipal government to be in need of special care at a senior care center. Alphabics was designed as part of a stress management program in 1990 and it utilizes a unique breathing method, relaxation techniques, accompanying alpha music and an elastic band called an Alphabics Band, which is used as a support gear for elderly individuals interested in participating in this exercise. The Alphabic band is used not only for concentric exercise but also for moderate eccentric exercise. The study group consisted of 20 elderly individuals, 12 out of 20 in the group, average age of 77 (±3.3 yrs) participated in 10-week Alphabics training and the remaining 8, average age of 78.3 (±3.3 yrs), did not participate. The test for physical activity and ADL consisted of grip strength (right/left), single-leg balance with eyes open, 10m walk and ADL (Ability of Daily Living) a standard measure by the Ministry of Education, Culture, Sports, Science and Technology. The results were as follows: The first group showed improvement in grip strength (right/left), 10m walk and score of ADL (p<0.05). Therefore, Alphabics training is recommended for older individuals in search of higher physical ability and more activity in their daily life. [ABSTRACT FROM AUTHOR]