Search results for "Critical resolved shear stress"
showing 7 items of 7 documents
Transient response in nonlinear region of molten polymers subjected to a sudden imposition of constant shear stress or constant electric field
1980
Experimental transient results in the nonlinear region are reported for a commercial polyisobutylene subjected to sudden imposition of either a constant shear stress or a constant electric field. Some steady-state results, eventually obtained in different types of experiments, are also considered. In both cases, a model analysis is presented that accounts for the nonlinear effects through changes in the free volume depending upon the applied stress. The good comparison between theoretical predictions and experimental results seems to indicate that the phenomenological approach advanced here is very promising.
Variable-charge method applied to study coupled grain boundary migration in the presence of oxygen
2009
International audience; One of the important differences between simulation and experiments in grain boundary (GB)-dominated metallic structures is the lack of impurities such as oxygen in computational samples. A modified variable-charge method [Elsener A, Politano O, Derlet PM, Van Swygenhoven H. Modell Simul Mater Sci Eng 2008;16:025006] based on the Streitz and Mintmire approach [Streitz FH, Mintmire JW. Phys Rev B 1994;50:11996] is used to study coupled GB motion in an Al bicrystal with a [1 1 2] symmetrical tilt GB in the presence of substitutional O, and compared with the stick–slip process identified by Cahn and Mishin [Cahn JW, Mishin Y, Suzuki A. Acta Mater 2006;54:4953]. It is found…
Predicting the equilibrium bed slope in natural streams using a stochastic model for incipient sediment motion
2011
In this paper, a method to predict the equilibrium bed slope in natural streams based on the incipient motion criterion is proposed. The method is based on the criterion suggested by Gessler to simulate the grain size distribution of the armour coat using the concept of critical shear stress of a sediment mixture. In particular, a different expression of the probability for a single particle size to be part of the armour coat is firstly proposed; then, a simple two-steps criterion is suggested to estimate the safety factor required by the proposed approach. The method is applied in three different Italian regions (Calabria, Basilicata, and Tuscany) and required several field campaigns invol…
Development of branching brittle and ductile shear zones: A numerical study
2017
Continental collision zones are usually associated with large-scale strike-slip shear zones. In most cases these shear zones are complex and consist of multiple strands, varying in width, length, and total displacement. Here we present 2-D numerical models to simulate the formation of such shear zones at different depth levels within the crust, under either brittle (frictional/plastic) or ductile conditions. Localization of shear zones is initiated by a material contrast (heterogeneity) of the material parameters. We systematically test the rate of strain-weakening in brittle and in ductile regimes to understand its influence on the development of shear zone networks. Our simulations sugges…
Linear Viscoelasticity of Liquid-Crystalline Polymers
2004
A linear (small-amplitude) periodic shear deformation of anisotropic viscoelastic liquids obeying the Akay–Leslie rheological model is considered. The frequency dependences of the real and imaginary components of the complex shear modulus and complex normal-stress coefficient are determined. A comparison between calculation results and test data on the shear flow of poly(γ-benzylglutamate) in m-cresol is carried out. It is stated that, if the material is characterized by some initial orientation, both components of the complex shear modulus contain a multiplier which depends on the degree of the initial orientation and increases the values of the components compared with those for an initia…
Monoclinic model shear zones
1998
Abstract Although many ductile shear zones are supposed to have developed by approximately simple shear flow, some must have formed under different conditions. A few types of such ‘non-simple shear zones’ have been proposed in the literature such as transpression-, transtension- and stretching-shear zones. This paper presents a full three-dimensional kinematic model of shear zones with monoclinic flow geometry. Monoclinic shear zone types can be classified according to flow parameters, and according to the geometry and orientation of accumulating finite strain. Modelling of finite strain accumulation shows that a number of unusual and potentially problematic structural features may develop …
Flow-induced structures in magnetorheological suspensions
1999
We have measured the yield stress of a magnetic suspension as a function of the external field. To explain the existence of this yield stress, we report a comparison between two models, one based on isolated chains of particles and the other taking into account that the structure is formed by aggregates of particles.