Length Scale Dependent Deformation in Polymers

2012 ◽  
Author(s):  
F. Alisafaei ◽  
Seyed Hamid Reza Sanei ◽  
Chung-Souk Han
Keyword(s):  
Liquid Crystal ◽  
Size Effects ◽  
Liquid Crystal Polymers ◽  
Length Scale ◽  
Indentation Testing ◽  
Indentation Size ◽  
Length Scales ◽  
Indentation Tests ◽  
Length Scale Dependent Deformation ◽  
Beam Bending

Length scale dependent deformation of polymers has been observed in different experiments including micro-beam bending and indentation tests. Here the length scale dependent deformation of polydimethylsiloxane is examined in indentation testing at length scales from microns down to hundreds of nanometers. Strong indentation size effects have been observed in these experiments which are rationalized with rotation gradients that can be related to Frank elasticity type molecular energies known from liquid crystal polymers. To support this notion additional experiments have been conducted where Berkovich and spherical indenter tips results have been compared with each other.

A micromechanics-based constitutive model for nanocrystalline shape memory alloys incorporating grain size effects

2021 ◽  
pp. 1045389X2110282
Author(s):  
Xiang Zhu ◽  
Guansuo Dui ◽  
Yicong Zheng
Keyword(s):  
Grain Size ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Size Effects ◽  
Boundary Phase ◽  
Length Scale ◽  
Internal Length ◽  
Length Scales ◽  
Size Dependent ◽  
Grain Size Effects

A micromechanics-based model is developed to capture the grain-size dependent superelasticity of nanocrystalline shape memory alloys (SMAs). Grain-size effects are incorporated in the proposed model through definition of dissipative length scale and energetic length scale parameters. In this paper, nanocrystalline SMAs are considered as two-phase composites consisting of the grain-core phase and the grain-boundary phase. Based on the Gibbs free energy including the spatial gradient of the martensite volume fraction, a new transformation function determining the evolution law for transformation strain is derived. Using micromechanical averaging techniques, the grain-size-dependent superelastic behavior of nanocrystalline SMAs can be described. The internal length scales are calibrated using experimental results from published literature. In addition, model validation is performed by comparing the model predictions with the corresponding experimental data on nanostructured NiTi polycrystalline SMA. Finally, effects of the internal length scales on the critical stresses for forward and reverse transformations, the hysteresis loop area (transformation dissipation energy), and the strain hardening are investigated.

An Investigation of Film Thickness Effect on Mechanical Properties of Au Films Using Nanoindentation Techniques

2005 ◽  
Vol 875 ◽  
Author(s):  
Yifang Cao ◽  
Zong Zong ◽  
Wole Soboyejo
Keyword(s):  
Thin Films ◽  
Mechanical Properties ◽  
Electron Beam ◽  
Film Thickness ◽  
Size Effects ◽  
Experimental Studies ◽  
Thickness Effect ◽  
Length Scale ◽  
Indentation Size ◽  
Au Thin Films

AbstractThis paper presents the results of nanoindentation experimental studies of Au thin films with different thicknesses. The effects of film thickness and microstructure on the hardnesses of electron-beam deposited Au films were studied in terms of Hall-Petch relationship. The effects of different thicknesses on indentation size effects (ISE) are explained within the framework of mechanism-based strain gradient (MSG) theory using the concept of microstructural length scale.

Modelling of Liquid Crystal Polymers at Different Length Scales

1998 ◽  
Vol 21 (2-3) ◽  
pp. 143-160 ◽  
Author(s):  
G. Goldbeck-Wood ◽  
P. Coulter ◽  
J. R. Hobdell ◽  
M. S. Lavine ◽  
K. Yonetake ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystal Polymers ◽  
Length Scales

The Identation Size Effect and Hall-Petch Behaviour of Annealed Polycrystalline Copper

2006 ◽  
Vol 976 ◽  
Author(s):  
XiaoDong Hou ◽  
T.T. Zhu ◽  
N. M. Jennett ◽  
A. J. Bushby
Keyword(s):  
Grain Size ◽  
Size Effect ◽  
Size Effects ◽  
Indentation Size Effect ◽  
Indentation Test ◽  
Small Radius ◽  
Contact Radius ◽  
Length Scale ◽  
Indentation Size ◽  
Non Destructive

AbstractMethods to obtain tensile stress-strain properties of materials from a practically non-destructive indentation test are of great industrial interest. However, to do this successfully, indentation size effects must be accounted for. Many indentation size effects, such as strain gradient plasticity and micro-pillar experiments [1], show a size dependence proportional to the inverse square root of a length scale, in common with Hall-Petch behavior. Recently, however, the indentation size effect from small radius spherical indenters has been shown, for a range of fcc metals, not to follow a Hall-Petch-like relationship but to be proportional to the inverse cube root of indenter radius [2]. Here, we investigate these differences further and present results for the indentation size effect with spherical indenters on Cu samples that have been engineered to have different grain sizes. The important experimental control parameter of the relative size of the indentation compared to the grain size is also explored since the cross over from grains significantly smaller than the contact radius to grains significantly larger than the contact radius occurs at different length scales in each sample. A thorough understanding of the various length-scale effects in the different test methods (e.g. the indentation size effect and grain size effect in indentation), is essential if a relationship, robust enough for industrial application, is to be defined to obtain tensile properties from an essentially non-destructive indentation test.

Plasticity size effects in nanoindentation

2004 ◽  
Vol 19 (1) ◽  
pp. 137-142 ◽  
Author(s):  
A.J. Bushby ◽  
D.J. Dunstan
Keyword(s):  
Phase Transition ◽  
Plastic Deformation ◽  
Size Effect ◽  
Finite Volume ◽  
Continuum Mechanics ◽  
Size Effects ◽  
Fused Silica ◽  
Length Scale ◽  
Indentation Size ◽  
Yield Behavior

In conventional continuum mechanics, the yield behavior of a material is size independent. However, in nanoindentation, plasticity size effects have been observed for many years, where a higher hardness is measured for smaller indentation size. In this paper we show that there was a size effect in the initiation of plasticity, by using spherical indenters with different radii, and that the length scale at which the size effect became significant depended on the mechanism of plastic deformation. For yield by densification (fused silica), there was no size effect in the nanoindentation regime. For phase transition (silicon), the length scale was of the order tens of nanometers. For materials that deform by dislocations (InGaAs/InP), the length scale was of the order a micrometer, to provide the space required for a dislocation to operate. We show that these size effects are the result of yield initiating over a finite volume and predict the length scale over which each mechanism should become significant.

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