A Cyclic Microbend Study on LIGA Ni Microelectromechanical Systems Thin Films

2005 ◽  
Vol 127 (1) ◽  
pp. 16-22 ◽  
Author(s):  
J. Lou ◽  
P. Shrotriya ◽  
W. O. Soboyejo
Keyword(s):  
Thin Films ◽  
Strain Gradient ◽  
Cyclic Deformation ◽  
Microelectromechanical Systems ◽  
Fatigue Behavior ◽  
Cyclic Stress ◽  
Length Scale ◽  
Gradient Plasticity ◽  
Scale Parameters ◽  
Reversed Cyclic

This paper presents the results of recent studies of cyclic microbend experiments and their consequences for plasticity length-scale phenomena in LIGA Ni microelectromechanical systems (MEMS) thin films. The strain–life fatigue behavior of LIGA Ni thin films is studied by performing fully reversed cyclic microbend experiments that provide insights into cyclic stress/strain evolution and cyclic failure phenomena. The effects of cyclic deformation on the plasticity length-scale parameters are also considered within the context of strain gradient plasticity theories. The implications of the results are then discussed for the analysis of plasticity and cyclic deformation in MEMS structures and other microscale systems.

Strain gradient plasticity length scale parameters for LIGA Ni MEMs thin films

2006 ◽  
Vol 441 (1-2) ◽  
pp. 299-307 ◽  
Author(s):  
J. Lou ◽  
P. Shrotriya ◽  
S. Allameh ◽  
T. Buchheit ◽  
W.O. Soboyejo
Keyword(s):  
Thin Films ◽  
Strain Gradient ◽  
Strain Gradient Plasticity ◽  
Length Scale ◽  
Gradient Plasticity ◽  
Scale Parameters

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.

Strain gradient plasticity to study hardness behavior of magnetite (Fe3O4) under multicyclic indentation

2009 ◽  
Vol 24 (3) ◽  
pp. 749-759 ◽  
Author(s):  
D. Chicot ◽  
F. Roudet ◽  
V. Lepingle ◽  
G. Louis
Keyword(s):  
Strain Gradient ◽  
Peak Load ◽  
Scale Factor ◽  
Strain Gradient Plasticity ◽  
Dislocation Network ◽  
Length Scale ◽  
Relevant Parameter ◽  
Characteristic Scale ◽  
Gradient Plasticity ◽  
Scale Length

The hardness of a material is generally affected by the indentation size effect. The strain gradient plasticity (SGP) theory is largely used to study this load dependence because it links the hardness to the intrinsic properties of the material. However, the characteristic scale-length is linked to the macrohardness, impeding any sound discussion. To find a relevant parameter, we suggest introducing a hardness length-scale factor that only depends on the shear modulus and the Burgers vector of the material and is easily calculable from the relation of the SGP theory. The variation of the hardness length-scale factor is thereafter used to discuss the hardness behavior of a magnetite crystal, the objective being to study the effect of the cumulative plasticity resulting from cyclic indentation. As a main result, the hardness length-scale factor is found to be constant by applying repeated cycles at a constant peak load whereas the macrohardness and the characteristic scale-length are both cycle dependent. When using incremental loads, the hardness length-scale factor monotonically decreases between two limits corresponding to those obtained at high and low loading rates, while the dwell-load duration increases. The physical meaning of such behavior is based on the modification of the dislocation network during the indentation process depending on the deformation rate.

A Study on Length Scale Effects on Indentation Delamination of Thin Films

2004 ◽  
Author(s):  
W. Li ◽  
S. Qu ◽  
T. Siegmund ◽  
Y. Huang
Keyword(s):  
Plastic Deformation ◽  
Strain Gradient ◽  
Cohesive Zone ◽  
Cohesive Zone Model ◽  
Scale Effects ◽  
Scale Dependence ◽  
Zone Model ◽  
Length Scale ◽  
Gradient Plasticity ◽  
Elastic Substrates

Simulations of indentation delamination of ductile films on elastic substrates are performed. A cohesive zone model accounts for initiation and growth of interface delaminations and a strain gradient plasticity framework for the length scale dependence of plastic deformation. With the cohesive zone model and the strain gradient formulation two length scales are introduced in to the analysis.

Length scale dependent yield strength and fatigue behavior of nanocrystalline Cu thin films

2011 ◽  
Vol 528 (25-26) ◽  
pp. 7774-7780 ◽  
Author(s):  
J.Y. Zhang ◽  
X. Zhang ◽  
G. Liu ◽  
R.H. Wang ◽  
G.J. Zhang ◽  
...  
Keyword(s):  
Thin Films ◽  
Yield Strength ◽  
Fatigue Behavior ◽  
Length Scale

Study of Small Scale Effects on the Nonlinear Vibration Response of Functionally Graded Timoshenko Microbeams Based on the Strain Gradient Theory

2012 ◽  
Vol 7 (3) ◽  
Author(s):  
R. Ansari ◽  
R. Gholami ◽  
S. Sahmani
Keyword(s):  
Strain Gradient ◽  
Beam Theory ◽  
Functionally Graded ◽  
Strain Gradient Theory ◽  
Gradient Theory ◽  
Length Scale ◽  
Scale Parameters ◽  
Linear And Nonlinear ◽  
Material Length Scale ◽  
Material Length

In the current study, the nonlinear free vibration behavior of microbeams made of functionally graded materials (FGMs) is investigated based on the strain gradient elasticity theory and von Karman geometric nonlinearity. The nonclassical beam model is developed in the context of the Timoshenko beam theory which contains material length scale parameters to take the size effect into account. The model can reduce to the beam models based on the modified couple stress theory (MCST) and the classical beam theory (CBT) if two or all material length scale parameters are taken to be zero, respectively. The power low function is considered to describe the volume fraction of the ceramic and metal phases of the FGM microbeams. On the basis of Hamilton’s principle, the higher-order governing differential equations are obtained which are discretized along with different boundary conditions using the generalized differential quadrature method. The dimensionless linear and nonlinear frequencies of microbeams with various values of material property gradient index are calculated and compared with those obtained based on the MCST and an excellent agreement is found. Moreover, comparisons between the various beam models on the basis of linear and nonlinear types of strain gradient theory (SGT) and MCST are presented and it is observed that the difference between the frequencies obtained by the SGT and MCST is more significant for lower values of dimensionless length scale parameter.

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