Fatigue Properties of Electro-Active Papers for Biomimetic Actuators

Materials ◽  
2005 ◽  
Author(s):  
John Shelton ◽  
William J. Craft ◽  
Jaehwan Kim ◽  
Jamil Grant ◽  
Jag Sankar ◽  
...  
Keyword(s):  
Elastic Properties ◽  
Low Voltage ◽  
Mechanical Strain ◽  
Low Frequency ◽  
Fatigue Loading ◽  
Load Level ◽  
Polymer Materials ◽  
Creep Model ◽  
Fatigue Properties ◽  
Strain Diagram

Cellulose-based Electro-Active Papers (EAPap) have been studied as potential actuators as a result of their low voltage operation, light weight, and low power consumption. In addition, they are bio-degradable and potentially inexpensive.1 The construction of many EAPap electromechanical actuators has been based on cellulose paper film coated with thin electrode layers. This EAPap actuator has shown a reversible and reproducible bending movement as well as longitudinal displacement under low voltage alternating current. However, the EAPap is a complex anisotropic material, which has not been extensively characterized and additional basic and design testing is required before developing EAPap application and devices. It is important to know the extended fatigue and elastic properties of EAPap materials, and this requires testing and evaluation. It has been known that the cellulose based EAPap has two distinct elastic constants connected by a bifurcation point along the stress strain diagram.2 The initial Young’s modulus of EAPap is in the range of 5-8GPa, - quite high compared to other polymer materials.3 Since these materials are anisotropic, elastic properties also differ as a function of orientation. These materials are sensitive to humidity and temperature. Fatigue tests conducted and described in this paper identify critical properties of this under-analyzed class of materials to provide a measure of its fatigue capabilities. Mechanical strain of EAPap materials has been evaluated, and it appears to follow closely a linear creep model as confirmed by low frequency cyclic (fatigue) loading. The creep parameter has also been determined to be a function of temperature and load level for all the EAPap materials tested.

scholarly journals Analysis of Shear Characteristics of Deep, Anchored Rock Mass under Creep Fatigue Loading

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Xiaofeng Li ◽  
Zhixiang Yin
Keyword(s):  
Rock Mass ◽  
Rock Strength ◽  
Low Frequency ◽  
Fatigue Loading ◽  
Load Level ◽  
Rock Masses ◽  
Sandstone Rock ◽  
Fatigue Model ◽  
Creep Fatigue ◽  
Marble Rock

To study the influence of earthquakes and engineering disturbances on the deformation of deeply buried rock masses, shear tests were carried out on anchored sandstone rock masses, anchored marble rock masses, and anchored granite rock masses under creep fatigue loading, and a new creep fatigue model was established to characterize the deformation characteristics of anchored rock masses under creep fatigue loading. The creep fatigue curves of different lithologies clearly show three stages: creep attenuation, steady-state creep, and accelerated creep. Fatigue loading can increase the creep of anchored specimens, and the lower the rock strength is, the higher the creep variable under fatigue loading is. However, for the same rock strength, with the increase in load level, the creep variable produced by creep fatigue load presents a linear downward trend. Considering the changes in the mechanical properties of the anchored rock mass under creep fatigue loading, the creep fatigue model of anchored rock masses is established by introducing a function of the fatigue shear modulus, and the accuracy and applicability of the model are verified by laboratory creep fatigue test data. The model provides a theoretical basis for the study of anchored rock mass support under low-frequency earthquakes or blasting loads.

scholarly journals Analysis of the Shear Characteristics of a Deep, Anchored Rock Mass Under Creep Fatigue Loading

2021 ◽  
Author(s):  
Xiaofeng Li ◽  
Zhixiang Yin
Keyword(s):  
Rock Mass ◽  
Rock Strength ◽  
Low Frequency ◽  
Fatigue Loading ◽  
Load Level ◽  
Rock Masses ◽  
Fatigue Model ◽  
Creep Fatigue ◽  
Accelerated Creep ◽  
Shear Characteristics

Abstract To study the influence of earthquakes and engineering disturbances on the deformation of deeply buried rock masses, shear tests were carried out on sandstone, marble and granite anchored specimens under creep fatigue loading, and a new creep fatigue model was established to characterize the deformation characteristics of anchored rock masses under creep fatigue loading. The creep fatigue curves of different lithologies clearly show three stages: creep attenuation, steady-state creep and accelerated creep. Fatigue loading can increase the creep of anchored specimens, and the lower the rock strength is, the higher the creep variable under fatigue loading. However, for the same rock strength, with the increase in load level, the creep variable produced by creep fatigue load presents a linear downward trend. Considering the changes in the mechanical properties of the anchored rock mass under creep fatigue loading, the creep fatigue model of anchored rock masses is established by introducing a function of the fatigue shear modulus, and the accuracy and applicability of the model are verified by laboratory creep fatigue test data. The model provides a theoretical basis for the study of anchored rock mass support under low-frequency earthquakes or blasting loads.

scholarly journals Effect of Fatigue Loading Mode on 718 Alloy Fatigue Properties

2018 ◽  
Vol 47 (4) ◽  
pp. 335-341
Author(s):  
Juraj Belan ◽  
Lenka Kuchariková ◽  
Eva Tillová ◽  
Denisa Závodská ◽  
Mária Chalupová
Keyword(s):  
Structural Damage ◽  
Materials Science ◽  
Low Frequency ◽  
Fatigue Loading ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Fatigue Lifetime ◽  
Loading Mode ◽  
Bending Load ◽  
Loading Modes

In materials science, fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. If the loads are above a certain threshold, microscopic cracks will begin to form at the stress concentrators such as the surface, persistent slip bands (PSBs), interfaces of constituents in the case of composites, and grain interfaces in the case of metals. Eventually a crack will reach a critical size, the crack will propagate suddenly, and the structure will fracture. The first works about fatigue phenomenon were published since 1837 and intensively was investigated by Wöhler in 1860. With needs of using the progressive materials such titanium and Ni-base superalloys become more significant to put under the various fatigue loading these sorts of alloys. Presented article deals with how the various condition of loading influenced an IN718 alloy fatigue lifetime especially. The fatigue tests provided on this kind of material was done via low frequency loading and push-pull or rotation-bending stress up to this time. Fatigue tests of experimental material was carried out at two different frequencies, 20 kHz with stress ration R = - 1 (push – pull, σm = 0 MPa) as well as the three-point bending load R ˂ 1 (σom = 526.8 MPa) at low frequency 150 Hz at room temperature. The microstructure characterization and Scanning Electron Microscopy (SEM) fractography analysis of fatigue process were done as well. The main goal of study was analyze obtained data after fatigue test and consider, if the various loading modes have influence on fatigue lifetime (initiation sites, crack propagation character, etc.).

scholarly journals Experimental and Analytical Study on Creep Characteristics of Box Section Bamboo-Steel Composite Columns under Long-Term Loading

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 983
Author(s):  
Shixu Wu ◽  
Keting Tong ◽  
Jianmin Wang ◽  
Yushun Li
Keyword(s):  
Load Level ◽  
Experimental Results ◽  
Creep Model ◽  
Composite Column ◽  
Composite Columns ◽  
Creep Coefficient ◽  
Creep Characteristics ◽  
Section Size ◽  
Steel Composite

To expand the application of bamboo as a building material, a new type of box section composite column that combined bamboo and steel was considered in this paper. The creep characteristics of eight bamboo-steel composite columns with different parameters were tested to evaluate the effects of load level, section size and interface type under long-term loading. Then, the deformation development of the composite column under long-term loading was observed and analyzed. In addition, the creep-time relationship curve and the creep coefficient were created. Furthermore, the creep model of the composite column was proposed based on the relationship between the creep of the composite column and the creep of bamboo, and the calculated value of creep was compared with the experimental value. The experimental results showed that the creep development of the composite column was fast at first, and then became stable after about 90 days. The creep characteristics were mainly affected by long-term load level and section size. The creep coefficient was between 0.160 and 0.190. Moreover, the creep model proposed in this paper was applicable to predict the creep development of bamboo-steel composite columns. The calculation results were in good agreement with the experimental results.

Study on the stiffness degradation in concrete continuous beam with externally prestressed CFRP tendons under fatigue loading

2021 ◽  
pp. 136943322199249
Author(s):  
Xing Li ◽  
Jiwen Zhang ◽  
Jun Cheng
Keyword(s):  
Fatigue Life ◽  
Fatigue Loading ◽  
Load Level ◽  
Fiber Reinforced Polymer ◽  
Stiffness Degradation ◽  
Test Results ◽  
Reinforced Polymer ◽  
Continuous Beams ◽  
Practical Engineering ◽  
Good Agreement

This paper presents fatigue behaviors and the stiffness degradation law of concrete continuous beams with external prestressed carbon fiber-reinforced polymer (CFRP) tendons. Three specimens were tested under fatigue loading, and the influence of different load levels on the stiffness degradation and fatigue life were studied, and it was found that the stiffness degradation of three test specimens exhibited a three-stage change rule, namely rapid decrease, stable degradation, and sharp decline, but there are obvious differences in the rate and amplitude of stiffness degradation. The load level has a significant influence on the fatigue life of the test specimens. An analytical model with load level considered was proposed to calculate the residual stiffness and predict the stiffness degradation, which is in good agreement with the test results. The model of stiffness degradation presents a possible solution for practical engineering applications of concrete continuous beams with externally prestressed CFRP tendons subjected to different fatigue loadings.

Fault Detection for Low-Voltage Residential Distribution Systems With Low-Frequency Measured Data

2020 ◽  
Vol 14 (4) ◽  
pp. 5265-5273
Author(s):  
Mehdi Shafiei ◽  
Faranak Golestaneh ◽  
Gerard Ledwich ◽  
Ghavameddin Nourbakhsh ◽  
Hoay Beng Gooi ◽  
...  
Keyword(s):  
Fault Detection ◽  
Distribution Systems ◽  
Low Voltage ◽  
Low Frequency ◽  
Measured Data ◽  
Residential Distribution

Low voltage and low frequency current mirror using a two-MOS subthreshold OP-Amp

1996 ◽  
Vol 32 (7) ◽  
pp. 605 ◽  
Author(s):  
K. Tanno ◽  
O. Ishizuka ◽  
Z. Tang
Keyword(s):  
Low Voltage ◽  
Low Frequency ◽  
Current Mirror ◽  
Op Amp ◽  
Frequency Current

scholarly journals Novel neuronal and astrocytic mechanisms in thalamocortical loop dynamics

2002 ◽  
Vol 357 (1428) ◽  
pp. 1675-1693 ◽  
Author(s):  
Vincenzo Crunelli ◽  
Kate L. Blethyn ◽  
David W. Cope ◽  
Stuart W. Hughes ◽  
H. Rheinallt Parri ◽  
...  
Keyword(s):  
Low Voltage ◽  
Electrical Coupling ◽  
Low Frequency ◽  
Network Activity ◽  
Thalamic Neuron ◽  
Cellular Mechanisms ◽  
Brain Areas ◽  
Sensory Stimuli ◽  
Loop Dynamics ◽  
Intracellular Ca

In this review, we summarize three sets of findings that have recently been observed in thalamic astrocytes and neurons, and discuss their significance for thalamocortical loop dynamics. (i) A physiologically relevant ‘window’ component of the low–voltage–activated, T–type Ca 2+ current ( I Twindow ) plays an essential part in the slow (less than 1 Hz) sleep oscillation in adult thalamocortical (TC) neurons, indicating that the expression of this fundamental sleep rhythm in these neurons is not a simple reflection of cortical network activity. It is also likely that I Twindow underlies one of the cellular mechanisms enabling TC neurons to produce burst firing in response to novel sensory stimuli. (ii) Both electrophysiological and dye–injection experiments support the existence of gap junction–mediated coupling among young and adult TC neurons. This finding indicates that electrical coupling–mediated synchronization might be implicated in the high and low frequency oscillatory activities expressed by this type of thalamic neuron. (iii) Spontaneous intracellular Ca 2+ ([Ca 2+ ] i ) waves propagating among thalamic astrocytes are able to elicit large and long–lasting N –methyl–D–aspartate–mediated currents in TC neurons. The peculiar developmental profile within the first two postnatal weeks of these astrocytic [Ca 2+ ] i transients and the selective activation of these glutamate receptors point to a role for this astrocyte–to–neuron signalling mechanism in the topographic wiring of the thalamocortical loop. As some of these novel cellular and intracellular properties are not restricted to thalamic astrocytes and neurons, their significance may well apply to (patho)physiological functions of glial and neuronal elements in other brain areas.

Combined effects of sulfate attack under drying–wetting cycles and loading on the fatigue behavior of concrete

2021 ◽  
pp. 136943322110427
Author(s):  
Ping Zhang ◽  
Song Ren ◽  
Yunfeng Zhao ◽  
Le Wang ◽  
Nengzeng Long ◽  
...  
Keyword(s):  
Elastic Modulus ◽  
Sodium Sulfate ◽  
Fatigue Behavior ◽  
Residual Deformation ◽  
Fatigue Loading ◽  
Damage Variable ◽  
Fatigue Properties ◽  
Sulfate Concentration ◽  
Cycle Number ◽  
Major Cycle

Concrete structures often undergo both fatigue loading and environmental impacts during their useful lifetime. This study aims to explore the fatigue properties of concrete subjected to sulfate attacks under drying–wetting cycles and loading. The coupled influences of major cycle number and sodium sulfate solution on the residual deformation, elastic modulus, and damage variable were investigated by uniaxial cyclic loading tests. Moreover, the phase composition of concrete samples was examined by X-ray diffraction. Results indicate that the concrete residual deformation and damage variable could be classified into initial and stable stages, while the elastic modulus fluctuated within a certain range. The fatigue strength of concrete was found to increase with an increase in the major cycle number and sodium sulfate concentration in the early stages, whereas the fatigue performance of concrete decreased as the major cycle number and sodium sulfate concentration increased in the later stage. The degree of influence of major cycle number and sodium sulfate concentration on the fatigue properties of concrete differed in each stage. These findings can contribute to understand the variation pattern of concrete properties in complicated environments and provide an important reference for associated construction projects.

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