Slip Systems in Metals

2 Relationship between Lattice Type and Ductility 9.2.1 Slip Systems in Metals 

The ductility of a metal depends on the number and type of slip systems. The slip systems for the various lattice types are shown in Table 9.2. Note that in the 111 family there are four different planes (111), (111), (111)/ and (111). (Other permutations of the indices are planes parallel to these four distinct planes.) The slip directions for the (111) must lie in the plane, hence their dot product with the vector normal to the plane must be zero. Thus the three slip directions in the (111) plane will be [110], [101], and [Oil]. (Remember this only works only for cubic systems.) Again, other permutations of these indices are directions parallel to these three directions. 

The basal plane in the hep system is the only high-density plane in that system. The other planes are usually not active at room temperature and are not even mentioned in some texts. Dislocations that become blocked from moving in one plane can move in an intersecting plane, a process known as cross slip. But since the primary hep slip planes are parallel to each other, cross slip cannot occur in hep structures. Consequently, hep metals tend to be more brittle than fee or bcc metals. 

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Methods for mechanical testing of materials are briefly introduced along with various strengthening mechanisms. The number and siu-face area of the slip systems in metals and in ceramics are shown to be responsible for the ductility (or the lack of it) and for ductile-to-brittle transitions. Griffith s theory of brittle fracture is used to introduce fracture mechanics and to develop the concept of fracture toughness. The viscoelastic behavior of polymers is briefly discussed. 

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