Plastics. Determination of creep behaviour

1997 ◽  
Keyword(s):  
Creep Behaviour

Determination of mechanical parameters for rotating MEMS structures as a function of deposition method

2003 ◽  
Vol 795 ◽  
Author(s):  
S. Soare ◽  
S. J. Bull ◽  
A. Oila ◽  
A. G. O'Neill ◽  
N. Wright ◽  
...  
Keyword(s):  
Creep Behaviour ◽  
Peak Load ◽  
Mechanical Parameters ◽  
Deposition Method ◽  
Element Analysis ◽  
Microelectronic Devices ◽  
Micro Sensor ◽  
Geometrical Dimensions ◽  
Modelling Data

ABSTRACTThe dimensions of microelectronic devices are constantly being reduced due to the increasing operational demands imposed such as higher working frequencies, higher component density and lower power consumption. This affects the geometrical dimensions of the metallisation, i.e. its width and thickness. The mechanical properties of very thin films are considerably different from those of bulk materials and, also, the deposition method may influence the mechanical behaviour of the components. In order to obtain reliable metallisation it is therefore important to assess accurately the mechanical parameters of the interconnecting lines. As part of designing, developing and manufacturing of a stress micro-sensor there is a need to extract properties useful for performance prediction such as yield stress or creep relaxation behaviour. Part of the data may be obtained by nanoindentation but to have a more complete view, finite element analysis of the indentation cycle has to be employed. In this study nanoindentation testing was carried out at various depths on sputtered and evaporated aluminium layers with different thicknesses deposited on (100) silicon. The loading curves were then simulated by FEA and the results compared to identify the yield properties of the coating. Modelling data for thicker samples closely follows experimental data but for thinner coatings there is a considerable gradient in properties through the film thickness. By incorporating a peak load hold the creep behaviour of the metallization can also be assessed and modelling parameters developed.

Variational estimates for the creep behaviour of polycrystals

1995 ◽  
Vol 448 (1932) ◽  
pp. 121-142 ◽  
Keyword(s):  
Heterogeneous Media ◽  
Creep Behaviour ◽  
The Self ◽  
Polycrystalline Materials ◽  
Variational Procedure ◽  
Constitutive Behaviour ◽  
Effective Potentials ◽  
Self Consistent ◽  
Geometric Arrangements

A variational procedure is developed for estimating the effective constitutive behaviour of polycrystalline materials undergoing high-temperature creep. The procedure is based on a new variational principle allowing the determination of the effective potential function of a given nonlinear polycrystal in terms of the corre­sponding potential for a linear comparison polycrystal with an identical geometric arrangements of its constituent single-crystal grains. As such, it constitutes an extension, to locally anisotropic behaviour, of the variational procedure devel­oped by Ponte Castañeda (1991) for nonlinear heterogeneous media with locally isotropic behaviour. By way of an example, the procedure is applied to the de­termination of bounds of the Hashin-Shtrikman type for the effective potentials of statistically isotropic nonlinear polycrystals. The bounds are computed for the special class of untextured FCC polycrystals with isotropic pure power-law viscous behaviour, first considered by Hutchinson (1976), in the context of a calculation of the self-consistent type. The new bounds are found to be more restrictive than the corresponding classical Taylor-Bishop-Hill bounds, and also more re­strictive, if only slightly so, than related bounds of the Hashin-Shtrikman type by Dendievel et al . (1991). The new procedure has the advantage over the self-consistent procedure of Hutchinson (1976) that it may be applied, without any essential complications, to aggregates of crystals with slip systems exhibiting dif­ferent creep rules - with, for example, different power exponents - and to general loading conditions. However, the distinctive feature of the new variational proce­dure is that it may be used in conjunction with other types of known bounds and estimates for linear polycrystals to generate corresponding bounds and estimates for nonlinear polycrystals.

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