Compressive Stress Effect on the Radial Elastic Modulus of Oxidized Si Nanowires

Nano Letters ◽  
2010 ◽  
Vol 10 (6) ◽  
pp. 2031-2037 ◽  
Author(s):  
G. Stan ◽  
S. Krylyuk ◽  
A. V. Davydov ◽  
R. F. Cook
Keyword(s):  
Elastic Modulus ◽  
Compressive Stress ◽  
Stress Effect ◽  
Si Nanowires

Gap Test of Crack-Parallel Stress Effect on Quasibrittle Fracture and Its Consequences

2020 ◽  
Vol 87 (7) ◽  
Author(s):  
Hoang Thai Nguyen ◽  
Madura Pathirage ◽  
Gianluca Cusatis ◽  
Zdeněk P. Bažant
Keyword(s):  
Compressive Stress ◽  
Process Zone ◽  
Main Idea ◽  
Stress Effect ◽  
Test Beam ◽  
Simple Modification ◽  
Out Of Plane ◽  
Three Point Bend Test ◽  
Strength Models ◽  
Gap Test

Abstract In the standard fracture test specimens, the crack-parallel normal stress is negligible. However, its effect can be strong, as revealed by a new type of experiment, briefly named the gap test. It consists of a simple modification of the standard three-point-bend test whose main idea is to use plastic pads with a near-perfect yield plateau to generate a constant crack-parallel compression and install the end supports with a gap that closes only when the pads yield. This way, the test beam transits from one statically determinate loading configuration to another, making evaluation unambiguous. For concrete, the gap test showed that moderate crack-parallel compressive stress can increase up to 1.8 times the Mode I (opening) fracture energy of concrete, and reduce it to almost zero on approach to the compressive stress limit. To model it, the fracture process zone must be characterized tensorially. We use computer simulations with crack-band microplane model, considering both in-plane and out-of-plane crack-parallel stresses for plain and fiber-reinforced concretes, and anisotropic shale. The results have broad implications for all quasibrittle materials, including shale, fiber composites, coarse ceramics, sea ice, foams, and fone. Except for negligible crack-parallel stress, the line crack models are shown to be inapplicable. Nevertheless, as an approximation ignoring stress tensor history, the crack-parallel stress effect may be introduced parametrically, by a formula. Finally we show that the standard tensorial strength models such as Drucker–Prager cannot reproduce these effects realistically.

scholarly journals Distinct Roles of Tensile and Compressive Stresses in Graphitizing and Properties of Carbon Nanofibers

Micromachines ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1096
Author(s):  
Yujia Liu ◽  
Edmund Lau ◽  
Dario Mager ◽  
Marc J. Madou ◽  
Maziar Ghazinejad
Keyword(s):  
Electron Microscopy ◽  
Tensile Strength ◽  
Elastic Modulus ◽  
Compressive Stress ◽  
Pyrolytic Carbon ◽  
Building Blocks ◽  
Mechanical Stresses ◽  
Mems Devices ◽  
Carbon Mems ◽  
Treated Carbon

It is generally accepted that inducing molecular alignment in a polymer precursor via mechanical stresses influences its graphitization during pyrolysis. However, our understanding of how variations of the imposed mechanics can influence pyrolytic carbon microstructure and functionality is inadequate. Developing such insight is consequential for different aspects of carbon MEMS manufacturing and applicability, as pyrolytic carbons are the main building blocks of MEMS devices. Herein, we study the outcomes of contrasting routes of stress-induced graphitization by providing a comparative analysis of the effects of compressive stress versus standard tensile treatment of PAN-based carbon precursors. The results of different materials characterizations (including scanning electron microscopy, Raman and X-ray photoelectron spectroscopies, as well as high-resolution transmission electron microscopy) reveal that while subjecting precursor molecules to both types of mechanical stresses will induce graphitization in the resulting pyrolytic carbon, this effect is more pronounced in the case of compressive stress. We also evaluated the mechanical behavior of three carbon types, namely compression-induced (CIPC), tension-induced (TIPC), and untreated pyrolytic carbon (PC) by Dynamic Mechanical Analysis (DMA) of carbon samples in their as-synthesized mat format. Using DMA, the elastic modulus, ultimate tensile strength, and ductility of CIPC and TIPC films are determined and compared with untreated pyrolytic carbon. Both stress-induced carbons exhibit enhanced stiffness and strength properties over untreated carbons. The compression-induced films reveal remarkably larger mechanical enhancement with the elastic modulus 26 times higher and tensile strength 2.85 times higher for CIPC compared to untreated pyrolytic carbon. However, these improvements come at the expense of lowered ductility for compression-treated carbon, while tension-treated carbon does not show any loss of ductility. The results provided by this report point to the ways that the carbon MEMS industry can improve and revise the current standard strategies for manufacturing and implementing carbon-based micro-devices.

scholarly journals The Damage of Fly Ash-Slag Concrete under Sustained Loading in Marine Environments

2018 ◽  
Vol 206 ◽  
pp. 02003
Author(s):  
J Gong ◽  
J Cao ◽  
Y F Wang
Keyword(s):  
Elastic Modulus ◽  
Fly Ash ◽  
Compressive Stress ◽  
Damage Model ◽  
Sulfate Solution ◽  
Solution Concentration ◽  
Sulfate Attack ◽  
Multiple Factors ◽  
Sustained Loading ◽  
Engineering Environment

The durability damage of concrete structures in the actual engineering environment is often the result of the interaction of the load and the environment, climate and other multiple factors. In this paper, the test researches were carried out on the concrete mass and dynamic elastic modulus under the effects of sustained loading, sulfate attack and dry-wet circulation, and the test phenomenon and results were discussed and analyzed. Then this paper proposed the durability damage model of the concrete under the effects of sustained loading, sulfate attack and dry-wet circulation considering the compressive stress level, the sulfate solution concentration and the age of corrosion as test factors, and the rationality of the model was discussed.

scholarly journals Numerical Simulation of Strength, Deformation, and Failure Characteristics of Rock with Fissure Hole Defect

2020 ◽  
Vol 2020 ◽  
pp. 1-15 ◽  
Author(s):  
Shaojie Chen ◽  
Zhiguo Xia ◽  
Fan Feng
Keyword(s):  
Elastic Modulus ◽  
Stress Concentration ◽  
Compressive Stress ◽  
Failure Modes ◽  
Elliptical Hole ◽  
Major Axis ◽  
Minor Axis ◽  
Peak Strain ◽  
Secondary Cracks ◽  
The Right

Using discrete element software, namely, particle flow code as two-dimensional program (PFC2D), two types of models were established: vertical fissure hole combination and horizontal fissure hole combination with ratios of major and minor axis of ellipse being 1, 1.2, 1.5, 2, and 3, which corresponded to a total of ten samples. The failure mode, mechanical behavior, and stress state before and after crack generation in elliptical hole crack combination models with different ratios of major and minor axis were analyzed. The crack development, stress field evolution, and acoustic emission characteristics of the vertical fissure model and horizontal fissure model were studied at the optimized ratio of major and minor axis of ellipse being 1.5. The results showed that elliptical hole fissure with different ratios of major and minor axis resulted in the decrease in the strength and elastic modulus of rock and increase in the peak strain of rock. The effect of the horizontal fissure model on the peak strength, peak strain, and elastic modulus of rock was found to be greater than that of the vertical fissure hole model. Ellipses with different ratios of major and minor axis in various models slightly influenced the rock failure modes, and their failure modes corresponded to tensile shear failure and tensile failure. Before crack formation, the tensile stress concentration areas of each model were, respectively, distributed at the upper and lower ends of the vertical fissure and the major axis of ellipse, and the compressive stress concentration areas were distributed at both ends of the major axis of ellipse and the fissure in the horizontal direction. After the model failed, the compressive stress concentration areas of the vertical fissure model and the horizontal fissure model transferred to the left upper part and the right upper part of the model along the left end of the hole and the right end of the fissure, respectively. When the ratio of major and minor axis of ellipse was 1.5, cracks in the vertical model and the horizontal model of fissure developed along the axial direction at the ends of cracks and holes, respectively, and then secondary cracks were generated at the ends of left and right sides. The maximum compressive stress in each stage of the vertical fissure model was greater than that of the horizontal fissure model, and when the model was damaged, its stress release was more.

Research on Compressive Deformation Characters of Mortar-Free Grouted Concrete Masonry

2014 ◽  
Vol 1004-1005 ◽  
pp. 1531-1536 ◽  
Author(s):  
Xi Xi He ◽  
Ye Lin
Keyword(s):  
Elastic Modulus ◽  
Compressive Stress ◽  
Test Data ◽  
Strain Curve ◽  
Compressive Deformation ◽  
Filling Rate ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Concrete Masonry

Compressive experiments on mortar-free grouted concrete masonry composed with hollow blocks were studies in this essay. Characteristics of compressive stress-strain curve were analyzed by utilizing test data of 15 specimens with 100% filling rate of grouted concrete. Further more, elastic modulus formula was proposed according to results of previous and present work.

Effect of Temperature on Punchthrough in Electrical Characteristics of the Plasmalemma of Chara coralinna

1976 ◽  
Vol 3 (6) ◽  
pp. 819
Author(s):  
M.J Beilby ◽  
H.G.L Coster
Keyword(s):  
Steady State ◽  
Elastic Modulus ◽  
Electric Field ◽  
Compressive Stress ◽  
Potential Difference ◽  
Effect Of Temperature ◽  
Electrical Characteristics ◽  
Absolute Value ◽  
A Value ◽  
Increasing Temperature

At the punchthrough, the current required to maintain the hyperpolarized potential difference (p.d.) of the plasmalemma increases very rapidly with increasing hyperpolarization so that, in the steady state, the membrane cannot be hyperpolarized beyond a certain level. It was found that punchthrough in the plasmalemma of C. corallina occurred at more negative (i.e. at greater hyperpolarizing) potentials as the temperature was decreased, from a value of ~ -310mV at T = 32�C to ~ -420 mV at T = 5�C. Some considerations are given to the compressive stress induced in the plasmalemma due to the electric field. These stresses at the p.d. values required for punchthrough are very considerable (~ 3 x 10*6 Nm*-�), and could lead to significant strains in the membrane. The degree of electromechanical compression of the membrane would increase with increasing temperature if, as the evidence cited suggests, the elastic modulus of the membrane decreases with increasing temperature. This would account for the decrease in the absolute value of the p.d. required for punchthrough with increasing temperature.

Predicting compressive stress‒strain curves of structural adobe cubes based on Acoustic Emission (AE) hits and Weibull distribution

2019 ◽  
Vol 10 (6) ◽  
pp. 766-791 ◽  
Author(s):  
Fatemeh FaghihKhorasani ◽  
Mohammad Zaman Kabir ◽  
Mehdi AhmadiNajafabad ◽  
Khosrow Ghavami
Keyword(s):  
Elastic Modulus ◽  
Weibull Distribution ◽  
Compressive Stress ◽  
Failure Probability ◽  
Compressive Strain ◽  
Strain Curve ◽  
Short Fibers ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Content Type

Purpose The purpose of this paper is to provide a method to predict the situation of a loaded element in the compressive stress curve to prevent failure of crucial elements in load-bearing masonry walls and to propose a material model to simulate a compressive element successfully in Abaqus software to study the structural safety by using non-linear finite element analysis. Design/methodology/approach A Weibull distribution function was rewritten to relate between failure probability function and axial strain during uniaxial compressive loading. Weibull distribution parameters (shape and scale parameters) were defined by detected acoustic emission (AE) events with a linear regression. It was shown that the shape parameter of Weibull distribution was able to illustrate the effects of the added fibers on increasing or decreasing the specimens’ brittleness. Since both Weibull function and compressive stress are functions of compressive strain, a relation between compressive stress and normalized cumulative AE hits was calculated when the compressive strain was available. By suggested procedures, it was possible to monitor pretested plain or random distributed short fibers reinforced adobe elements (with AE sensor and strain detector) in a masonry building under uniaxial compression loading to predict the situation of element in the compressive stress‒strain curve, hence predicting the time to element collapse by an AE sensor and a strain detector. In the predicted compressive stress‒strain curve, the peak stress and its corresponding strain, the stress and strain point with maximum elastic modulus and the maximum elastic modulus were predicted successfully. With a proposed material model, it was illustrated that the needed parameters for simulating a specimen in Abaqus software with concrete damage plasticity were peak stress and its corresponding strain, the stress and strain point with maximum elastic modulus and the maximum elastic modulus. Findings The AE cumulative hits versus strain plots corresponding to the stress‒strain curves can be divided into four stages: inactivity period, discontinuous growth period, continuous growth period and constant period, which can predict the densifying, linear, non-linear and residual stress part of the stress‒strain relationship. By supposing that the relation between cumulative AE hits and compressive strain complies with a Weibull distribution function, a linear analysis was conducted to calibrate the parameters of Weibull distribution by AE cumulative hits for predicting the failure probability as a function of compressive strain. Parameters of m and θ were able to predict the brittleness of the plain and tire fibers reinforced adobe elements successfully. The calibrated failure probability function showed sufficient representation of the cumulative AE hit curve. A mathematical model for the stress–strain relationship prediction of the specimens after detecting the first AE hit was developed by the relationship between compressive stress versus the Weibull failure probability function, which was validated against the experimental data and gave good predictions for both plain and short fibers reinforced adobe specimens. Then, the authors were able to monitor and predict the situation of an element in the compressive stress‒strain curve, hence predicting the time to its collapse for pretested plain or random distributed short fibers reinforced adobe (with AE sensor and strain detector) in a masonry building under uniaxial compression loading by an AE sensor and a strain detector. The proposed model was successfully able to predict the main mechanical properties of different adobe specimens which are necessary for material modeling with concrete damage plasticity in Abaqus. These properties include peak compressive strength and its corresponding axial strain, the compressive strength and its corresponding axial strain at the point with maximum compressive Young’s modulus and the maximum compressive Young’s modulus. Research limitations/implications The authors were not able to decide about the effects of the specimens’ shape, as only cubic specimens were chosen; by testing different shape and different size specimens, the authors would be able to generalize the results. Practical implications The paper includes implications for monitoring techniques and predicting the time to the collapse of pretested elements (with AE sensor and strain detector) in a masonry structure. Originality/value This paper proposes a new method to monitor and predict the situation of a loaded element in the compressive stress‒strain curve, hence predicting the time to its collapse for pretested plain or random distributed short fibers reinforced adobe (with AE sensor and strain detector) in a masonry building under uniaxial compression load by an AE sensor and a strain detector.

Compressive stress effect on the loss mechanism in a soft piezoelectric Pb(Zr,Ti)O3

2019 ◽  
Vol 90 (7) ◽  
pp. 075001 ◽  
Author(s):  
H. Daneshpajooh ◽  
M. Choi ◽  
Y. Park ◽  
T. Scholehwar ◽  
E. Hennig ◽  
...  
Keyword(s):  
Compressive Stress ◽  
Stress Effect ◽  
Loss Mechanism
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