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

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 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.

The correlation between the internal material length scale and the microstructure in nanoindentation experiments and simulations using the conventional mechanism-based strain gradient plasticity theory

2009 ◽  
Vol 24 (3) ◽  
pp. 1197-1207 ◽  
Author(s):  
B. Backes ◽  
Y.Y. Huang ◽  
M. Göken ◽  
K. Durst
Keyword(s):  
Yield Stress ◽  
Strain Gradient ◽  
Plasticity Theory ◽  
Strain Gradient Plasticity ◽  
Length Scale ◽  
Gradient Plasticity ◽  
Hardening Behavior ◽  
Material Length Scale ◽  
Material Length ◽  
Strain Gradient Plasticity Theory

In the present work a new equation to determine the internal material length scale for strain gradient plasticity theories from two independent experiments (uniaxial and nanoindentation tests) is introduced. The applicability of the presented equation is verified for conventional grained as well as for ultrafine-grained copper and brass with different amounts of prestraining. A significant decrease of the experimentally determined internal material length scale is found for increasing dislocation densities due to prestraining. Conventional mechanism strain gradient plasticity theory is used for simulating the indentation response, using experimentally determined material input data as the yield stress, the work-hardening behavior and the internal material length scale. The work-hardening behavior and the yield stress were taken from the uniaxial experiments, whereas the internal material length scale was calculated using the yield stress from the uniaxial experiment, the macroscopic hardness H0 and the length scale parameter h* following from the nanoindentation experiment. A good agreement between the measured and calculated load–displacement curve and the hardness is found independent of the material and the microstructure.

Length Scale in Solder Joints Materials

2006 ◽  
Author(s):  
Juan Gomez ◽  
Cemal Basaran
Keyword(s):  
Strain Gradient ◽  
Constitutive Models ◽  
Strain Gradient Plasticity ◽  
Length Scale ◽  
Gradient Plasticity ◽  
Additional Material ◽  
Size Dependent ◽  
Dependent Behavior ◽  
Material Length Scale ◽  
Material Length

Strain gradient plasticity theories that have emerged during recent years to provide an explanation for size dependent behavior exhibited by some materials have also created a need for additional material parameters. In this study on Pb/Sn solder alloys the material length scale, which is needed for use in strain gradient plasticity type constitutive models, is determined. The value of length scale is in agreement with values available in the literature for different materials like copper, nickel and aluminum.

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