Microplasticity

The annealing curves for several copper alloys are compared to copper in Figure 4. Solute additions affect the annealing response, as they do for cold working, by interaction with microplastic processes that account for softening as dislocations and subgrains are eliminated during the anneal. 

Stress relaxation, while aUied to creep, is different (20—23). Stress relaxation is the time-dependent decrease in load (stress) at the contact displacement resulting from connector mating. Here, the initial elastic strain in the spring contact is replaced by time-dependent microplastic flow. Creep, on the other hand, relates to time-dependent geometry change (strain or displacement) under fixed load, which is a condition that does not apply to coimectors. 

Duysen, J. C. van, Doukhan, J. C. (1984). Room temperature microplasticity of a-spodumene LiAlSi206. Phys. Chem. Minerals, 10, 125-32. 

The special atomic structure of quasicrystals is responsible for a number of unique physical and chemical properties in particular, a very high hardness (up to 10 GPa) with some microplasticity for indentation at room temperature. The majority of studied quasicrystals are Al-base intermetallic phases. 

Ievlev, V.M., Kostyuchenko, A.V., Darinskii, B.M., and Barinov, S.M. (2014) Hardness and microplasticity of nanocrystalline and amorphous calcium phosphate coatings. Phys. Solid State, 56 (2), 321-329. 

Recent work has characterized the microparticles and identified their sotrrces other than those from the degradation of materials. For example, textile fibers, sometimes coming directly from the water of washing machines [BRO 11], are clearly identified as a source constituting a significant contribution to the sea. UNESCO also assesses that purification sludge stations are also an important sotrrce of microplastics. 

The proportion of polymers in these objects is important. Their use has been widespread in recent years for the manufacture of nets, ropes and lines. In France, 36% of stranded individuals of the species Caretta caretta contain litter in their stomachs of which 80% is plastic mistaken for jellyfish. In the estuary of the Rio de la Plata, a veiy urban area, 37% of catfish contain litter principally constituted of plastics. In the case of the fulmars of the North Sea, [FRA 11] evaluates the average weight of ingested microplastics to be 0.38 g per individual, with 92% of individuals being affected and with an average of 37 pieces per individual. This value is not... 

LES 11] Leslie H.A., van der Meulen M.D., Kleissen F.M., et al. Microplastic litter in the Dutch marine environment, Deltares report, final report, 1203772-000,2011. 

McKee, M. (2004). Rising tide of micro-plastics plaguing the seas. New Scientist, 6 May 2004 [online]. Available from http //www.newscientist.com/article/dn4966-rising-tide-of-microplastics-plaguing-the-seas.html [Accessed 7 March 2007]. 

Fukami, A. and Adachi, D. (1965). A new method of preparation of a self perforated microplastic grid and its application. J. Electron Microsc. 14, 112-118. 

Therefore, the development of new hard materials requires the preparation of phases with small microplastic deformability of the crystal lattice, and reduced grain sizes in the sintered polycrystals, and highly perfect microstructures. For example, sintered alumina ceramics which have a submicrometer microstructure and associate this small grain size with a macrohardness of 20-24 GPa (compared with 17-19 GPa in conventionally sintered corundum) were obtained only when new processing approaches became available, which could reduce the flaw population [1]. 

Table 1. Comparison of critical stresses for microplastic deformation of the crystal lattice and for...

To simplify the mathematical procedure, a characteristic area A = (2/ pi) is introduced. At some load P, the microplastic deformability 8 can be defined as... 

With Eq. (3/3a), this deereasing influence of the load in more fine-grained microstructures is expressed by smaller values of the ratio (5e/5i)o- Table 2 displays fitting parameters for the experimental data of Fig. 4 for smaller grain sizes, increasing asymptotic hardness values H o are associated with decreasing parameters ( e/ i)o- la submicrometer alumina microstructures, the increase of the microplastic deformability (the decrease of the hardness) becomes smaller and smaller and approaches zero already at small indent sizes of 10-20 pm (see Fig. 4), and which characterizes the extension of the plastic zone approaches the initial deformability at rather small loads of about 1N. 

Therefore, the most probable reason for the different hardness in ground and in polished ceramics is that a high density of grinding-induced dislocation and twin networks in the machined surfaces reduces the microplastic deformability (increase the hardness) at an indentation site, in a similar way to small grain sizes. 

Within the framework of the understanding outlined above it is clear that after grinding, a subsequent further microplastic deformation (on indentation) must be the more difficult the less mobile the grinding-induced dislocations are, that is the closer the spacing of grain boundaries, the smaller the grain size is. As a... 

Concerning the cutting mechanism, there are differences between processing ductile, metallic materials and brittle hard materials such as glass or ceramics. In case of ductile materials, microplastic deformations of surfaces, hardening, and embrittlement as well as breakaways of particles... 

Microplastically deformed zone Lapping disc surface... 

The initial study on the ductile-mode machining of brittle materials was done by Yoshikawa and Taniguchi who have developed the general description for the behavior of briffle materials in the plastic flow zone, by generalizing the microplasticity" of Mcmahon, and the elastic/plastic theory of Hill and Hertz. 

---