Material properties range

In the previous section we noted that, in the abstract, A1 (or any other material) may be characterized by a series of numbers, its material parameters, to be found in a databook. However, as we already hinted at, because of the history dependence of material properties, the description of such properties is entirely more subtle. There is no one aluminum, nor one steel, nor one zirconia. Depending upon the thermomechanical history of a material, properties ranging from the yield strength to the thermal and electrical conductivity can be completely altered. The simplest explanation for this variability is the fact that different thermomechanical histories result in different internal structures. 

PolyhydroxyaUcanoates (PHAs) are the biopolymers possessing the material properties ranging from rigid and highly crystalline to flexible, amorphous, and elastomeric. Because of such properties and inherent biodegradability, PHAs have attracted the world-wide attention of scientists and researchers as environment-friendly alternative to the conventional petroleum-based polymers. Polyhydroxybutyrate (PHB) and polyhydroxyoctanoate (PHO) have been found to possess biocompatibility in mammalian systems. Such biomaterials have got great potential as medical implantation devices [78-81]. 

Piezoelectric and Electrostrictive Device Applications. Devices made from ferroelectric materials utilizing their piezoelectric or electrostrictive properties range from gas igniters to ultrasonic cleaners (or welders) (72). 

Because shear and compressive strengths s andp depend in a similar way on material properties such as lattice stmcture and bond strength,yis often in a rather narrow range of about 0.20—0.35 for a wide variety of materials. The following are typical data for sliding on steel with bearing materials varying several hundredfold in yield pressure ... 

Copolymers extend the number and range of available materials, enabling the polymer scientist to achieve combinations of material properties (eg, tensile strength, solubiHty, solvent resistance, low temperature flexibiHty, etc) unattainable from the simple constituent homopolymers. As a result, a large number of copolymers have become commercially important. Table 1 Hsts some of them. 

These price and property ranges do not include fine retardant grades or highly filled materials for sound deadening. Shore A or D as indicated. 

The early 1980s saw considerable interest in a new form of silicone materials, namely the liquid silicone mbbers. These may be considered as a development from the addition-cured RTV silicone rubbers but with a better pot life and improved physical properties, including heat stability similar to that of conventional peroxide-cured elastomers. The ability to process such liquid raw materials leads to a number of economic benefits such as lower production costs, increased ouput and reduced capital investment compared with more conventional rubbers. Liquid silicone rubbers are low-viscosity materials which range from a flow consistency to a paste consistency. They are usually supplied as a two-pack system which requires simple blending before use. The materials cure rapidly above 110°C and when injection moulded at high temperatures (200-250°C) cure times as low as a few seconds are possible for small parts. Because of the rapid mould filling, scorch is rarely a problem and, furthermore, post-curing is usually unnecessary. 

Ashby has taken his approach a stage further with the introduction of physically based estimates of material properties where these have not been measured (Ashby 1998. Bassett et al. 1998), where an independent check on values is thought desirable or where property ranges of categories of materials would be useful. Figure 5.5(c) is one example of the kind of estimates which his approach makes possible. A still more recent development of Ashby s approach to materials selection is an analysis in depth of the total financial cost of using alternative materials (for different number of identical items manufactured). Thus, an expanded metallic foam beam offers the... 

The contrast in knowledge is a result of the degree of complexity of materials properties elastic piezoelectric solids have perhaps the least complex behaviors, whereas ferroelectric solids have perhaps the most complex mechanical and electrical behaviors of any solid under shock compression. This complexity is further compounded by the strong coupling between electrical and mechanical states. Unfortunately, much of the work studying ferroelectrics appears to have underestimated the difficulty, and it has not been possible to carry out careful, long range, systematic efforts required to develop an improved picture. 

The toughness of a material is a design driver in many structures subjected to impact loading. For those materials that must function under a wide range of temperatures, the temperature dependence of the various material properties is often of primary concern. Other structures are subjected to wear or corrosion, so the resistance of a material to those attacks is an important part of the material choice. Thermal and electrical conductivity can be design drivers for some applications, so materials with proper ranges of behavior for those factors must be chosen. Similarly, the acoustical and thermal insulation characteristics of materials often dictate the choice of materials. 

Include plastics with coefficient of friction, chemical resistance, and others. Many plastic materials inherently have a low coefficient of friction. Other plastic materials can incorporate this property by compounding a suitable ingredient such as graphite powder into the base material. It is an important feature for moving products, which provides for selflubrication. Chemical resistance is another characteristic that is inherent in most plastic materials the range of this resistance varies among materials. 

Materia] Selector Access to (1) GE Select, a comprehensive database in Microsoft Windows format of the family of GE polymers which allows users to sort for the GE product families and grades of materials that will best meet the specified property ranges, and (2) CAMPUS, a worldwide database for plastic materials with uniform global protocol for acquiring and comparing data on competitive plastic materials. 

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