scholarly journals Experimental Study and Simulation of the Stress Relaxation Characteristics of Machine-Harvested Seed Cotton

2021 ◽  
Vol 11 (21) ◽  
pp. 9959
Author(s):  
Jun Wang ◽  
Hongwen Zhang ◽  
Lei Wang ◽  
Ximei Wei ◽  
Meng Wang ◽  
...  

Seed cotton compression molding solves the inconvenience of seed cotton transportation and storage after mechanical harvesting. Stress relaxation is closely related to the performance of the compressed seed cotton. In this study, an electronic universal testing machine with a homemade compression device was used to study the stress relaxation characteristics of machine-harvested seed cotton. The stress relaxation model of machine-harvested seed cotton was established, the influence of test factors on the response indexes was analyzed and, finally, stress relaxation characteristics of machine-harvested seed cotton were simulated. Results show that machine-harvested seed cotton stress relaxation characteristics can be described by the five-element Maxwell model. The equilibrium elastic modulus is negatively correlated with moisture content and cross-section dimensions, and the equilibrium elastic modulus is positively correlated with trash content and compression density. The rapid decay time and the residual stress ratio are negatively correlated with moisture content and compression density, but the influence of trash content and cross-section dimensions are limited. The stress relaxation process of machine-harvested seed cotton was simulated using virtual prototype technology, and the maximum error between the experimental and simulated values was obtained as 4.96%. The feasibility of the virtual prototype technique for the viscoelastic simulation of biomaterials was demonstrated.

2019 ◽  
Vol 15 (1-2) ◽  
Author(s):  
Jia-hui Chen ◽  
Nan Zhao ◽  
Nan Fu ◽  
Dong Li ◽  
Li-jun Wang ◽  
...  

AbstractMechanical properties of hulless barley stems with different moisture contents (10.23%–43.14%) were investigated by using temperature sweep, frequency sweep, stress relaxation and creep tests of dynamic mechanical analyzer (DMA) in this study. Results showed a significant dependence of storage modulus, loss modulus and tan delta on moisture content. The data from stress relaxation and creep was fitted by using generalized Maxwell model and Burgers model. 5-element Maxwell model was better for describing relaxation behaviors of hulless barely stem compared with the 3-element Maxwell model. The peak values of loss modulus and tan delta both occurred at a low temperature when moisture content increased. The dynamic mechanical properties can provide useful information for the harvesting and processing of huless barely stem.


Author(s):  
Pan Wang ◽  
Li-jun Wang ◽  
Dong Li ◽  
Zhi-gang Huang ◽  
Benu Adhikari ◽  
...  

Abstract: Stress-relaxation behavior of single rice kernel was studied using a dynamic mechanical analyzer (DMA) in compression mode. The relaxation modulus was measured in a moisture content range of 12–30 % on dry basis (d.b.) and a temperature range of 25–80°C. A constant stain value of 1 % (within the linear viscoelastic range) was selected during the stress-relaxation tests. The relaxation modulus was found to decrease as the temperature and moisture increased. A master curve of relaxation modulus as a function of temperature and moisture content was generated using the time–moisture–temperature superposition principle. Results showed that the generalized Maxwell model satisfactorily fitted the experimental data of the stress-relaxation behavior and the master curve of relaxation modulus (R2> 0.997). By shifting the temperature curves horizontally, the activation energy of the stress relaxation was obtained which significantly decreased with increase in the moisture content.


2011 ◽  
Vol 704-705 ◽  
pp. 480-485
Author(s):  
Xue Qi Li ◽  
Xi Ming Wang ◽  
Jian Fang Yu

This research aims to provide theoretical proof for the further study on the factors of stress relaxation under different conditions. In this study, use Pinus sylvestris and dynamic stress-strain test system, though change temperature and moisture to research the stress relaxation of wood. The results showed that the temperature and moisture content on the stress relaxation have a significant impact. With temperature enhancing or moisture content rising, stress dramatically relaxation and residual stress rapidly decreased. In other words, the initial stress decreased gradually and the relaxation rate was rise. It was also found that, under same conditions, compared with the tangential section of the Pinus sylvestris, the radial section has larger initial stress and smaller stress relaxation rate. Besides, the initial stress of late wood is larger than early wood but the stress relaxation rate is smaller. Key words: Pinus sylvestris, tensile stress relaxation


Alloy Digest ◽  
1981 ◽  
Vol 30 (5) ◽  

Abstract ULTRONZE is a copper alloy also known as Olin Alloy 654. It bridges the gap between standard high-performance copper alloys and beryllium-copper alloys, thus enabling the design of parts with properties previously only attainable with more expensive materials. The alloy has superior stress-relaxation characteristics, good bend performance and excellent corrosion resistance. Among its typical uses are electrical connectors, fuse clips and relay springs. This datasheet provides information on composition, physical properties, hardness, elasticity, tensile properties, and bend strength. It also includes information on corrosion resistance as well as forming, heat treating, and machining. Filing Code: Cu-417. Producer or source: Olin Brass.


2012 ◽  
Vol 8 (1) ◽  
pp. 47-49
Author(s):  
Jinghe Wang ◽  
Miao Yu ◽  
Zhichao Wu ◽  
Yingchun Liang ◽  
Shen Dong

2021 ◽  
Vol 11 (9) ◽  
pp. 4272
Author(s):  
Stefano Invernizzi ◽  
Francesco Montagnoli ◽  
Alberto Carpinteri

The present paper investigates the influence of the specimen size of EN-AW6082 wrought aluminium alloy subjected to very high cycle fatigue (VHCF) tests. The hourglass specimens were tested under fully reversed loading condition, up to 109 cycles, by means of the ultrasonic fatigue testing machine developed by Italsigma® (Italy). Three specimens groups were considered, with a diameter in the middle cross-section ranging from 3 mm up to 12 mm. The stress field in the specimens was determined numerically and by strain gauge measurements in correspondence of the cross-section surface. The dispersion of experimental results has been accounted for, and data are reported in P-S-N diagrams. The decrease in fatigue resistance with increasing specimen size is evident. Theoretical explanation for the observed specimen-size effect is provided, based on Fractal Geometry concepts, allowing to obtain scale independent P-S*-N curves. The fatigue life expectation in the VHCF regime of the EN-AW6082 aluminium alloy full-scale components is rather overestimated if it is assessed only from standard small specimens of 3 mm in diameter. Experimental tests carried out on larger specimens, and a proper extrapolation, are required to assure safe structural design.


Author(s):  
JINLAI ZHOU ◽  
YANG SONG ◽  
CHENGUANG XU ◽  
CHUNQIU ZHANG ◽  
XUE SHI

The periodontal ligament (PDL) exhibits different material mechanical properties along the long axis of the teeth. To explore the creep and the relaxation effects of dissimilar layers of PDL, this paper took the central incisors of porcine mandibular as experimental subjects and divided them perpendicular to the teeth axis into five layers. Creep experiments and relaxation experiments on five layers were conducted to obtain the creep compliance and relaxation modulus at different layers. Linear elastic model, generalized Kelvin model, and generalized Maxwell model were used to describe the major characteristics of the PDL: Instantaneous elasticity, creep and relaxation. Fitting accuracy of three-parameter, five-parameter, and seven-parameter of the model was compared, and the constitutive equations of different layers were established by the least square method. The results presented that the creep strain and the relaxation stress of PDL were exponentially correlated with time under different loading conditions. Different layers showed a significant effect on the creep strain and relaxation stress of PDL. Along the long axis of the teeth, the changing rule of the creep compliance and relaxation modulus of each layer showed quite the contrary, and the instantaneous elastic modulus first decreased to the minimum, then increased to the maximum. Higher instantaneous elastic modulus led to lower creep compliance and higher relaxation modulus. The generalized Kelvin model and the generalized Maxwell model well characterized the creep and relaxation properties of PDL. Fitting accuracy increased with the number of model parameters. The relaxation time of PDL was about one order of magnitude shorter than the creep retardation time, which indicated that the relaxation effect lasted shorter than the creep effect.


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