Microscopic level, strength

What causes the phenomenon of stress and strain reduction and why is the reduction in impact and work properties so visible at small or negligible changes in elastic modulus and ultimate strengths As discussed previously, mechanical properties deal with stress and strain relationships that are simply functions of chemical bond strength. At the molecular level, strength is related to both covalent and hydrogen intrapolymer bonds. At the microscopic level, strength... 

The expert tried to optimise the design of unbreakable crockery. First he wanted to find reasons for using ceramic as the main material in terms of desired properties. From this first step, he concluded that ceramic had some advantages over metals or composites. The expert made a sharp distinction between intrinsic and extrinsic properties. The choice of type of ceramics was not relevant becanse the desired properties are extrinsically determined. Thns relevant properties cannot be much influenced by the difference in bonding strength due to the different types of ions of the material. Consequently, the properties of ceramic crockery are not mnch inflnenced by the actual choice of ceramic material. Because of this, the expert did not inclnde the ionic stmcture in his reasoning. When he was asked why he did not nse this snb-microscopic level, he explained it was not necessary becanse this [the desired properly] is not imdeigoing influences at atomic level at all . 

Hardness is determined by hardness tests which involve the measurement of a material s resistance to surface penetration by an indentor with a force applied to it The indentation process occurs by plastic deformation of metals and alloys. Hardness is therefore inherently related to plastic flow resistance of these materials. Brittle materials, such as glass and ceramics at room temperature, can also be subjected to hardness testing by indentation. This implies that these materials are capable of plastic flow, at least at the microscopic level. However, hardness testing of brittle materials is frequently accompanied by unicrack formation, and this fact makes the relationship between hardness and flow strength less direct than it is for metals. 

Recently, microscopic-level research has developed very small carbon networks called nanotubes. As you can see in Figure 4.19D, nanotubes are like a fullerene network that has been stretched into a cylinder shape. Nanotubes of C400 and higher may have applications in the manufacture of high-strength fibres. In the year 2000, researchers built a nanotube with a diameter of 4 x 10 m. Up to that time, this nanotube was the smallest structure assembled. 

Blends of polymers can pose their own unique problems as well. An example is where colorants exhibit preferential dispersion to one of the polymer phases. The other polymer phase remains virtually uncolored. Macroscopically, this may not be a problem as the molded part appears uniformly colored. But even at this level, if wall thickness is very thin, color striations may become apparent. Other performance measures may be adversely affected as well. At the microscopic level, since all of the colorant is dispersed in one phase, impact strength and other properties may be reduced at pigment concentrations that are much lower than expected. This would primarily occur in blends where the colorant prefers the resin phase that provides the toughness to the blend. 

Polymer-polymer interfaces are an important area of study since the interfacial behaviour is fundamental to the bulk properties of the system. This is particularly true when two or more polymers are mixed to form a blend, but the interface also plays a dominant role in areas such as adhesion, welding, surface wetting and mechanical strength. To understand fully polymer behaviour in such applications, the interface must be characterised at a microscopic level. Through deuterium labelling the interface between otherwise indistinguishable polymers can be studied, and neutron reflectivity provides unprecedented detail on interfacial width and shape. In addition to the inherent interdiffusion between polymers at a polymer-polymer interface, the interface is further broadened by thermally driven capillary waves. Capillary waves... 

A theory of strength of metals at high temperatures has to be based on experimental data. An experimental technique was developed for in situ X-ray investigations of metals and alloys directly during creep process [79]. The structural peculiarities of the high-temperature strained metals were also studied by transmission electron microscopy (TEM). Our goal was to obtain data that enable us to observe the events on atomic and microscopic levels. 

Two methods are used for determining the fabric-damaging properties of bleach systems tensile strength loss, on a macroscopic level, and the decrease in the degree of polymerization, on a microscopic level. Recently it was shown that there is only poor correlation between the resnlts of both test methods. To obtain reliable data, measnranent of tensile strength loss after 20 or 50 wash... 

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