Plastic anisotropy

Shale stability is an important problem faced during drilling. Stability problems are attributed most often to the swelling of shales. It has been shown that several mechanisms can be involved [680,681]. These can be pore pressure diffusion, plasticity, anisotropy, capillary effects, osmosis, and physicochemical alterations. Three processes contributing to the instability of shales have to be considered [127] ... 

W. L. Elban and R. W. Armstrong, Plastic Anisotropy and Cracking at Hardness Impressions in Single Crystal Ammonium Perchlorate, Acta Mater., 46, 6041 (1998). 

Munoz, A., Gomez-Garcia, D., Dominguez-Rodriguez, A., and Wakai, E, High temperature plastic anisotropy of YTZ-single crystals , J. Em. Ceram. Soc, 2002, 22, 2609-13. 

Gotoh, M., (1977), A theory of plastic anisotropy based on a yield function of fourth order. Int. J. Mech. Sci., 19,505. 

Gihnan, J.J. (1959) Plastic anisotropy of LiF and other rocksalt-type crystals, Acta. Metall. 7, 608. 

The accuracy of the simulation results is given mainly by the accuracy of the material model. In the last years, the scientific research is oriented in developing of new material models able to describe the material behavior (mainly the anisotropic one) as accurate as possible (Barlat et al. 2004 Banabic 2010 Banabic et al. 2010). The computer simulation of the sheet metal forming processes needs a quantitative description of the plastic anisotropy by the yield locus. 

Accuracy of the prediction both of the yield locus and the uniaxial yield stress and uniaxial coefficient of plastic anisotropy. 

Banabic D (2000) Forming limits of sheet metal. In Banabic D, Bunge HJ, Pohlandt K, Tekkaya AE (eds) Formability of metallic materials plastic anisotropy, formability testing, forming limits. Springer, Heidelberg/Berlin... 

Arruda, E. M. and Boyce, M. C. (1993) Evolution of plastic anisotropy in amorphous polymers during straining, Int. J. Plasticity, 9, 697-720. 

The given presentation of the mechanism of the interaction of polymer molecules with turbulent flow admits a peculiar theoretical examination. The presence of polymer addition besides the increase of longitudinal viscosity is resulted in the appearance of such rheological solution properties as elastic plasticity, pseudo-plasticity, anisotropy. In [3] the influence of different rheological fluid characteristics on the wall turbulence is theoretically analyzed within the limits of monoharmonic approximation, which affords to take into account turbulent blows-out. Different variants of rheological behaviour were considered. For all that we succeded to show, that the decrease of turbulent friction arose only in mediums, possessing... 

Plastic Anisotropy, Internal Stresses, and Deformation Mechanisms... 

The MAX phases, ice and graphite, and other layered minerals such as mica, are plastically anisotropic. This plastic anisotropy, combined with the fact that they lack the five independent slip systems needed for ductility, quickly lead to a very uneven states of stress when a polycrystalline sample is loaded [129]. The glide of basal plane dislocations takes place only in favorably oriented or soft grains, which rapidly transfer the load to hard grains - that is, those not favorably oriented to the applied stress. Needless to say, this leads to high internal stresses. 

Most important - and as discussed at some length herein - the plastic anisotropy leads to kink band formation, typical micrographs of which are shown in Figure 7.10. Note that elastic anisotropy is not a necessary requirement for kinking several of the MAX phases kink, despite being elastically quite isotropic [31]. 

Early studies on BeO single crystals by Bentle and Miller [51] identified four slip systems basal slip, (0001)(1120) prismatic slip, 1100 (1120) and 1100 [0001] and pyramidal slip, Il22 (1123). Not surprisingly, significant plastic anisotropy was found. At 1000 °C, the yield stresses for these systems were as follows 35 MPa for basal slip 49 and llOMPa for prismatic slip along (1120) and [0001], respectively and >250 MPa for pyramidal slip. More recent studies on creep deformation in BeO... 

E. M. Arruda and M. C. Boyce, Evolution of Plastic Anisotropy in Amorphous Polymers during Finite Straining , Int. J. Plast. 9, 697—720 (1993). 

A specific point of attention is that the results of vane shear tests need to be corrected for plasticity, anisotropy and rate effects according to the formula c, =p- Such a correction factor is based on experience. Bjerrum (1972) has... 

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