Characterization and modeling of specific strain gradient modulus of epoxy

2001 ◽  
Vol 16 (2) ◽  
pp. 558-563 ◽  
Author(s):  
D. C. C. Lam ◽  
A. C. M. Chong
Keyword(s):  
Plastic Deformation ◽  
Plastic Strain ◽  
Power Law ◽  
Strain Gradient ◽  
Microelectromechanical Systems ◽  
The Body ◽  
Experimental Results ◽  
Strain Gradients ◽  
Specific Strain ◽  
Plastic Hardening

Microscale sensing and actuating components are prevalent in microelectromechanical systems. Deformations of microscale components are dependent not only on the strains in the body, but also on the strain gradients. The contribution of strain gradients to plastic hardening is characterized by the specific strain gradient modulus of the material. The specific strain gradient modulus has been predicted to vary with the plastic strain. The moduli of plastically prestrained epoxy specimens were experimentally characterized in this investigation using nanoindentation. Prestraining induced softening and an energy model are developed to separate the effect of prestrain softening from the effect of strain gradient. The results indicated that the contribution of strain gradient to hardening was initially large but diminished with increased plastic deformation. A model was developed for power law material and was shown to compare well with the experimental results.

Indentation model and strain gradient plasticity law for glassy polymers

1999 ◽  
Vol 14 (9) ◽  
pp. 3784-3788 ◽  
Author(s):  
David C. C. Lam ◽  
Arthur C. M. Chong
Keyword(s):  
Plastic Deformation ◽  
Strain Gradient ◽  
Glassy Polymer ◽  
Glassy Polymers ◽  
Strain Gradient Plasticity ◽  
Molecular Theory ◽  
Indentation Hardness ◽  
Gradient Plasticity ◽  
Strain Gradients

Plastic deformation of metals is generally a function of the strain. Recently, both phenomenological and dislocation-based strain gradient plasticity laws were proposed after strain gradients were experimentally found to affect the plastic deformation of the metal. A strain gradient plasticity law is developed on the basis of molecular theory of yield for glassy polymers. A strain gradient plasticity modulus with temperature and molecular dependence is proposed and related to indentation hardness. The physics of the strain gradient plasticity in glassy polymer is then discussed in relation to the modulus.

Inviscid hypersonic flow over plane power-law bodies

1967 ◽  
Vol 27 (2) ◽  
pp. 315-336 ◽  
Author(s):  
H. G. Hornung
Keyword(s):  
Shock Wave ◽  
Power Law ◽  
Similarity Theory ◽  
Second Order ◽  
The Body ◽  
Experimental Results ◽  
Order Effects ◽  
Normal Velocity ◽  
Wave Shapes ◽  
Good Agreement

Theoretical solutions based on the expansion scheme for large x and large M∞, as proposed by Freeman (1962), are obtained for the asymptotic inviscid flow over plane bodies of the shape y/d = (x/d)m in the range $\frac{2}{3}/\gamma < m < \frac{2}{3}$ where blast wave theory applies as a first approximation. In particular, the second-order terms, which are necessary to satisfy the body boundary conditions for the normal velocity are computed. The magnitude of the second-order terms is found to increase from zero at $m=\frac{2}{3}/\gamma $ to infinity at $m = \frac{2}{3}.$As a comparison with theory, experiments at M∞ = 8·2 were made with two plane power-law bodies in the range $\frac{2}{3}/\gamma < m < \frac{2}{3} $ and on a plane parabola with a tangent wedge nose. These consisted of the determination of shock-wave shapes, surface pressure distributions and detailed investigations of the distribution of pitot and static pressure across the shock layer.The experimental results are in good agreement with the theory in the case m =1/2, where the second-order effects are small. At m = 5/8 the region of validity of the theory is limited to much larger distances from the nose of the body and larger Mach numbers. Accordingly, the prediction for the deviation from firstorder theory, although being correct in sign, is too small. Shock-wave shapes on bodies of the same power but of different size are correlated by the similarity theory when scaled with respect to the dimension d.The experimental results obtained with the wedge-parabola are in very good agreement with a characteristics solution by C. H. Lewis (1965, unpublished).

Nanoindentation study of plasticity length scale effects in LIGA Ni microelectromechanical systems structures

2003 ◽  
Vol 18 (3) ◽  
pp. 719-728 ◽  
Author(s):  
J. Lou ◽  
P. Shrotriya ◽  
T. Buchheit ◽  
D. Yang ◽  
W. O. Soboyejo
Keyword(s):  
Plastic Deformation ◽  
Strain Gradient ◽  
Indentation Depth ◽  
Microelectromechanical Systems ◽  
Scale Parameter ◽  
Scale Effects ◽  
Length Scale Parameter ◽  
Length Scale ◽  
Gradient Plasticity ◽  
Cube Corner

This paper presents the results of a nanoindentation study of the effects of strain gradient plasticity on the elastic–plastic deformation of lithographie, galvanoformung, abformung (LIGA) Ni microelectromechanical systems (MEMS) structures plated from sulfamate baths. Both Berkovich and North Star/cube corner indenter tips were used in the study to investigate possible effects of residual indentation depth on the hardness of LIGA Ni MEMS structures between the micro- and nanoscales. A microstructural length scale parameter, , was determined for LIGA nickel films. This is shown to be consistent with a stretch gradient length-scale parameter, ls, of approximately 0.9 μm.

scholarly journals Prediction of Magnetic Properties of a Plastically Deformed Steel and One Way to Measure its Plastic Deformation

2020 ◽  
Vol 20 (2) ◽  
pp. 5-13
Author(s):  
M.J. Sablik
Keyword(s):  
Plastic Deformation ◽  
Magnetic Properties ◽  
Dislocation Density ◽  
Plastic Strain ◽  
Yield Stress ◽  
Magnetic Materials ◽  
Power Law ◽  
Phenomenological Model ◽  
Magnetic Hysteresis ◽  
Hysteresis Loss

AbstractIn this paper, we use a phenomenological model based on the Jiles-Atherton-Sablik model of stress affecting the magnetic hysteresis of magnetic materials as modified when stress goes past the yield stress We use this to show that (1) the model produces sharp shearing of hysteresis curves, as seen experimentally and that (2) it also produces a step in the hysteresis loss at small residual plastic strain. We also find that the step in the hysteresis loss can be fitted to a power law, and find that the power law can be fitted by the power m=0.270, different from the mechanical Ludwik Law exponent, and reasonably close to the experimental 0.333 and 0.202. We will also suggest a method of measuring how plastically deformed the material is by suggesting how the dislocation density can be measured.

Exponential Conductivity Increase in Strained MoS2 via MEMS Actuation

MRS Advances ◽  
2019 ◽  
Vol 4 (38-39) ◽  
pp. 2135-2142
Author(s):  
A. Vidana ◽  
S. Almeida ◽  
M. Martinez ◽  
E. Acosta ◽  
J. Mireles ◽  
...  
Keyword(s):  
Experimental Data ◽  
Electrical Properties ◽  
Microelectromechanical Systems ◽  
The Body ◽  
Experimental Results ◽  
Force Balance ◽  
Balance Model ◽  
Standard Process ◽  
Conductivity Increase ◽  
Cmos Compatible

ABSTRACTIn this work, a poly-Si0.35Ge0.65 microelectromechanical systems (MEMS)- based actuator was designed and fabricated using a CMOS compatible standard process to specifically strain a bi-layered (2L) MoS2 flake and measure its electrical properties. Experimental results of the MEMS-TMDC device show an increase of conductivity up to three orders of magnitude by means of vertical actuation using the substrate as the body terminal. A force balance model of the MEMS-TMDC was used to determine the amount of strain induced in the MoS2 flake. Strains as high as 3.3% is reported using the model fitted to the experimental data.

Numerical Simulation for Rough Contact Incorporating Plastic Deformation

2005 ◽  
Author(s):  
Fan Wang ◽  
Leon M. Keer
Keyword(s):  
Numerical Simulation ◽  
Residual Stress ◽  
Plastic Deformation ◽  
Plastic Strain ◽  
Pressure Distribution ◽  
Contact Pressure ◽  
Analytical Method ◽  
Elastic Contact ◽  
Surface Deflection ◽  
Plastic Hardening

An 3D elastic-plastic rough contact solution and code is developed using a modified semi-analytical method. It is supposed that the total surface deflection is induced by the contact pressure and plastic strain. The purely elastic contact and the influence of the plastic deformation are calculated iteratively until convergence is satisfied. The distributions of contact pressure, residual stress and plastic strain are obtained through simulation. The effects of roughness and plastic hardening upon the pressure distribution are discussed.

Analytical Modeling of Residual Stresses in Burnishing

2010 ◽  
Vol 139-141 ◽  
pp. 921-924
Author(s):  
Jing Zhao ◽  
Wei Xia ◽  
Feng Lei Li ◽  
Zhao Yao Zhou ◽  
Zheng Qiang Tang
Keyword(s):  
Plastic Deformation ◽  
Residual Stresses ◽  
Half Space ◽  
Power Law ◽  
Analytical Modeling ◽  
Normal Force ◽  
Experimental Results ◽  
Concentrated Force ◽  
Plastic Properties ◽  
Elastic Plastic

. An analytical model is developed for the prediction of residual stresses in burnishing. The model is simplified as a concentrated force pressing on elastic-plastic half-space using the solution to the Boussinesq-Flament problem. The treated material admits the elastic-plastic properties with hardening using a power law constitutive relation. Trial computation using Johnson-Cook model on AISI 1042 steel is presented and the results are verified with the experimental results given by Bouzid’s previous work. The residual stresses in the feed direction show the same trend with the experimental results while some differences still exist near the surface because of the concentrated normal force assumption and such stresses increase with the increase of burnishing force, decrease with the increase of depth and turn to zero beyond the plastic deformation boundary.

Plastic Deformation in Microtomed Sections

1971 ◽  
Vol 29 ◽  
pp. 458-459
Author(s):  
J. Temple Black
Keyword(s):  
Plastic Deformation ◽  
Plastic Strain ◽  
Applied Stress ◽  
Elastic Strain ◽  
High Strain ◽  
Tool Material ◽  
Cutting Edge ◽  
Material Structure ◽  
Geometrical Constraints

The output of the ultramicrotomy process with its high strain levels is dependent upon the input, ie., the nature of the material being machined. Apart from the geometrical constraints offered by the rake and clearance faces of the tool, each material is free to deform in whatever manner necessary to satisfy its material structure and interatomic constraints. Noncrystalline materials appear to survive the process undamaged when observed in the TEM. As has been demonstrated however microtomed plastics do in fact suffer damage to the top and bottom surfaces of the section regardless of the sharpness of the cutting edge or the tool material. The energy required to seperate the section from the block is not easily propogated through the section because the material is amorphous in nature and has no preferred crystalline planes upon which defects can move large distances to relieve the applied stress. Thus, the cutting stresses are supported elastically in the internal or bulk and plastically in the surfaces. The elastic strain can be recovered while the plastic strain is not reversible and will remain in the section after cutting is complete.

scholarly journals DESIGNING A TEMPORARY COLD PROTECTIVE GEAR CONSTRUCTED BY FOLDING NEWSPRINT PAPER CONSIDERING HEAT-RETAINING PROPERTY AND RIGIDITY

2021 ◽  
Vol 1 ◽  
pp. 1123-1132
Author(s):  
Tatsuya Oda ◽  
Shigeru Wesugi
Keyword(s):  
Natural Disaster ◽  
Cold Season ◽  
Apex Angle ◽  
The Body ◽  
Experimental Results ◽  
Protective Gear ◽  
Significant Difference ◽  
Body Shapes

AbstractDuring the cold season, the cold protective products are often short during evacuation life after a natural disaster. If evacuees can make and wear simple cold protective gears by using materials obtainable on site, it will reduce the burden on the evacuees in emergent situation. Therefore, we investigated the structure constructed by folding newsprint paper, which can improve the heat retention effect and be applied to various body shapes. Focusing on the glide reflection structure repeating a smaller chamber, the basic size was determined by experiments with reference to the accordion shape, and the experimental results indicated that the heat retention effect was significantly greater than that of a mere air layer and those of ordinary fabrics. Next, it was found that the apex angle of structure had no significant difference in the heat retention effect. Then, the dimensions of the structure were determined to maintain the air layer under the pressure of the clothes by simulation of structural analyses. Finally, we made a temporary cold protective gear that can practically cover the trunk of the body and found that the heat retention effect was significantly higher than that of unprocessed newsprint and that of accordion shape.

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