Structure-sensitive properties

List five different structure-sensitive properties. 

Answers Structure-sensitive properties yield strength, hardness, tensile strength, ductility, fracture toughness, fatigue strength, creep strength, corrosion resistance. 

There are, of course, many more ceramics available than those listed here alumina is available in many densities, silicon carbide in many qualities. As before, the structure-insensitive properties (density, modulus and melting point) depend little on quality -they do not vary by more than 10%. But the structure-sensitive properties (fracture toughness, modulus of rupture and some thermal properties including expansion) are much more variable. For these, it is essential to consult manufacturers data sheets or conduct your own tests. 

Physical properties of solid materials which are greatly influenced by the presence of defects of lattice order in real single crystals are called structural-sensitive properties, and are distinguished from intrinsic properties, which are determined by the elements constituting the crystal, for example the chemical bonds, the structure, etc. Color, plasticity, glide, and semiconductor properties are structural-sensitive properties, whereas density, hardness, elasticity, and optical, thermal, and magnetic properties are the intrinsic properties. Structural-sensitive... 

Owing to its single composition and pure covalent bonding, diamond is a standard solid material, and takes the role of the most appropriate sample in explaining the effects upon structure-sensitive properties when the structure of solid material deviates from the ideal state. 

More directly, solid state physics contributed to the emergence of materials science, because of one of its foci. Spencer Weart identified three pillars on which solid state physics was erected First, X-ray diffraction techniques provided precise atomic picture of solids second, quantum mechanics provided the theoretical foundations for the description of solids and the third, more subtle pillar was the attempt to discriminate between properties depending on the idealized crystal pattern and properties dependent on accidents of either the inner arrangement or the surface of the solid. [13] This focus on structure-sensitive-properties can be seen as the main investigative pathway, to resume Frederic L. Holmes s concept, which lead to materials science. 

Thus obtained results show that the polyamorphic transitions occur not only at compression (Si02, H20, etc.) but at extension as well (C) in the systems having stable or metastable crystal analogs with a different density and a different coordination number z. At the minimal z=2 (chain structures) the transitions may occurs only at compression, at the maximal z=12 (close-packed structures) - only at extension, at the intermediate z (2metastable phases can appear. Amorphization under radiation (crystal lattice extension) can be associated with a softening of phonon frequencies. The transitions in the molecular glasses consisted from the molecules with unsaturated bonds are accompanied by creation of atomic or polymeric amorphous systems. 

The mosaic structure of a crystal is one of its most profoundly structure-sensitive properties. As normally prepared, a crystal has a pronounced mosaic structure, but under conditions of more and more carefully controlled growth it is often possible to obtain crystals in which the degree of mosaic character is progressively reduced. As this process proceeds the X-ray reflexions become sharper and the mechanical strength increases. Conversely, by mechanical or thermal shock, it is often possible to reduce the degree of perfection of a carefully grown crystal. 

To understand the importance of defects in polymer crystals, one must distinguish structure-insensitive properties from structure-sensitive properties. For crystals of small molecules and rigid macromolecules (see Fig. 1.6), the structure-insensitive properties often can be derived directly from the ideal crystal structure as summarized in Fig. 5.80. The density, for example, can be calculated from the unit cell dimensions (see Sect. 5.1). The polymeric materials in form of flexible macromolecules are, in... 

Several structure-sensitive properties are listed at the bottom of Fig. 5.80. They need, in contrast to stmcture-insensitive properties, a detailed defect mechanism to be understood, as is discussed in Sects. 5.3.3-6. The structure-sensitive properties are at the center of most of the important material properties. 

For bulk materials, all techniques based on structure-insensitive properties, as described in this section and elsewhere, yield closely similar data. The crystallinity model is thus a valid defect concept to describe structure-insensitive properties of semicrystalline polymers. It breaks down for three-phase systems, consisting, for example, of a crystalline phase, a mobile amorphous phase, and a rigid-amorphous fraction (see Chap. 6). In addition, one does not expect valid answers for structure-sensitive properties. 

Important structure-sensitive properties of glasses limit the ultimate strength. A description must describe the crack-propagation, crazing, and fibrillation on fracture and plastic deformation. All of these create new external or internal surfaces, which are critically dependent on the conformation and large-amplitude motion of the macromolecules in relation to the new interfaces. Little more is discussed about this topic. The continually changing special literature on this rather empirical topic must be checked for further information. 

Another aspect of thermal analysis concerns the thermodynamic functions based on heat capacity. Obviously, the number of possible copolymers is so large, that complete measurements for all copolymers are not possible. Fortunately, the heat capacity of glassy and liquid copolymers over wide temperature ranges are not structure sensitive (for a discussion of structure-sensitive properties see Sect. 5.3.1). A simple additivity mle based on the molar composition of the components is suggested in Fig. 2.70 for the copolymers of styrene and butadiene (see also the addition scheme of heat capacities in Fig. 2.77). 

Equation (4.6) gives the resolved shear stress . The product in the equation is known as the Schmid factor and determines whether the orientation is favorable for shp. The conditions for slip are given by Schmid s Law and the value of Eq. (4.6), often represented in the literature by Tj, indicating the onset of plastic deformation and called critical resolved shear stress . CRSS is a structure-sensitive property, since it is very dependent on impurities and the way the crystal was grown and handled. 

Polymer crystals are always semicrystalline, and thus, they are far from perfect. Limited crystal sizes and complicated aggregates make the basic understanding of the structure-property relationships very difficult. To simplify, two types of properties in general exist for crystals of small molecules structure-insensitive and structure-sensitive properties. The structure-insensitive properties include... 

On the other hand, for structure-sensitive properties a knowledge of the ideal structure also is not sufficient because the structural defects play an important role in determining the properties. In the case of HTSCs, defects of an appropriate size can act as pinning... 

Inherent in mechanical testing is the variation in observations. Scatter decreases for specimens with higher ratio of minimum linear dimensions over maximum grain size for the RefC mix this ratio is about 3, which is low (too low ) for structure-insensitive properties. Structure sensitive properties require even considerably larger values to suppress experimental scatter to acceptable proportions. This is experimentally confirmed. 

---