Characterization techniques mechanical properties

In order to realize the potential of these ceramics they must be fabricated, and with such a low decomposition temperature sintering to high strength is proving a problem. Hardness determinations will prove useful in characterizing the mechanical properties of these and other ceramic superconductors, but as yet little has been reported. Table 6.21 contains hardness values obtained for the YBa2Cu307 superconductor at room temperature and at liquid Nj temperatures (77 K). As expected, the Vickers hardness rises to 3.1 GPa at 77 K and some success with sinter additives is achieved because the standard material hardness is raised from 2.2 to 2.5 GPa after sintering in their presence. Indentation hardness techniques have been used to establish the Kic value of 1.1 MPam. ... 

In any given material, the relaxation modulus will reflect the response of the material on different timescales. To make a measurement, materials are deformed under a periodic load with frequency w. Then, G and G are measured across a wide range of frequencies (typically three to four decades). Measurements of G and G" can be used to characterize the mechanical properties of soft materials, including polymer networks and colloidal systems. The technique is also known as mechanical spectroscopy. In a viscoelastic material, the elastic modulus will cross over the viscous modulus at the transition point from viscous to elastic bulk behavior and indicates a possible sol-gel transition or the onset of rubbery behavior in a polymer network. 

Nanoindentation is nowadays one of the most used methods to measure the mechanical properties of polymers, attracting great attention as a technique to mechanically characterize polymer nanocomposites [137-142]. This technique uses the same principle as microindentation, but with much smaller probe areas and very low loads (on the order of nanonewtons), so as to produce indentations from less than a hundred nanometers to a few micrometers in size and depth [143]. Although it has been vastly used to characterize the mechanical properties, particularly hardness, elastic modulus, yield stress, and fracture toughness, of several polymers [144—152] and shown to be mainly influenced by the testing procedure, penetration depths, and holding time, limited work has been dedicated to the characterization of the mechanical behavior of polymer nanocomposites using this technique. 

The ability to probe surface mechanical properties with nanometer-scale lateral and vertical resolutions is critical for many emerging applications. For nanomechanical prohing experiments, one usually exploits either AFM or microindentation techniques. AFM enables characterization of mechanical properties of the sample through probe indentation and shear. Mechanical tests include indentation, wear, and force-distance curves measured upon normal and shear loading. ... 

Mechanical Properties. The performance of various polyester resin compositions can be distinguished by comparing the mechanical properties of thin castings (3 mm) of the neat resin defined in ASTM testing procedures (15). This technique is used widely to characterize subtle changes in flexural, tensile, and compressive properties that are generally overshadowed in highly filled or reinforced laminates. 

The present review shows how the microhardness technique can be used to elucidate the dependence of a variety of local deformational processes upon polymer texture and morphology. Microhardness is a rather elusive quantity, that is really a combination of other mechanical properties. It is most suitably defined in terms of the pyramid indentation test. Hardness is primarily taken as a measure of the irreversible deformation mechanisms which characterize a polymeric material, though it also involves elastic and time dependent effects which depend on microstructural details. In isotropic lamellar polymers a hardness depression from ideal values, due to the finite crystal thickness, occurs. The interlamellar non-crystalline layer introduces an additional weak component which contributes further to a lowering of the hardness value. Annealing effects and chemical etching are shown to produce, on the contrary, a significant hardening of the material. The prevalent mechanisms for plastic deformation are proposed. Anisotropy behaviour for several oriented materials is critically discussed. 

These include cold drawn, high pressure oriented chain-extended, solid slate extruded, die-drawn, and injection moulded polymers. Correlation of hardness to macroscopic properties is also examined. In summary, microhardness is shown to be a useful complementary technique of polymer characterization providing information on microscopic mechanical properties. 

In Section 2.4, the main aspects of the nitrogen-induced structural changes are presented, by the discussion of the most important characterization techniques. This presentation is complemented by an overview of a-C(N) H structure. Finally, in Sections 2.5 and 2.6, respectively, results concerning the mechanical properties, and the electrical and optical properties of a-C(N) H films are presented. As long as possible, they will be correlated with the observed structure changes. 

Some small-angle X-ray scattering (SAXS) techniques have also been applied to elastomers. Examples are the characterization of fillers precipitated into elastomers, and the corresponding incorporation of elastomers into ceramic matrices, in both cases to improve mechanical properties [4,85,213]. 

The solvent evaporation method resulted in the production of LS characterized by a smaller size (20 pm mean diameter) but poor mechanical properties in respect to particles with the same composition that were obtained by the melt dispersion technique (170 pm mean diameter). The use of a combination of lipids and a methacrylic polymer (Eudragit RSI00) overcame this problem, resulting in the production of spherical particles with a narrower size distribution and good mechanical properties [53,56],... 

TMA has mainly been used in the study of polymers. The mechanical properties study may be used to characterize a polymer as well as to assess its mechanical utility. There is an obvious application to quality control. The ability to study small specimens gives the technique a distinct advantage over more traditional methods of mechanical testing if sample size is limited. A typical TMA study has already been exemplified in Figure 11.19. 

This chapter provides a concise summary of the most important concepts and characteristics of CNTs including structural aspects (i.e. chirality, defects, doping), properties (i.e. mechanical, electronic, thermal), synthesis and characterization techniques and post-processing strategies (i.e. purification, separation, functionalization), and is thus intended as an introduction for newcomers. 

Proper characterization of composite interfaces, whether it is for chemical, physical or mechanical properties, is extremely difficult because most interfaces with which we are concerned are buried inside the material. Furthermore, the microscopic and often nanoscopic nature of interfaces in most useful advanced fiber composites requires the characterization and measurement techniques to be of ultrahigh magnification and resolution for sensible and accurate solutions. In addition, experiments have to be carried out in a well-controlled environment using sophisticated testing conditions (e.g. in a high vacuum chamber). There are many difficulties often encountered in the physico-chemical analyses of surfaces. 

The mechanical properties of PLA rely on the stereochemistry of insertion of the lactide monomer into the PLA chain, and the process can be controlled by the catalyst used. Therefore, PLAs with desired microstructures (isotactic, heterotactic, and S3mdiotactic) can be derived from the rac- and W50-Iactide depending on the stereoselectivity of the metal catalysts in the course of the polymerization (Scheme 15) [66]. Fundamentally, two different polymerization mechanisms can be distinguished (1) chain-end control (depending on stereochemistry of the monomer), and (2) enantiomorphic site control (depending on chirality of the catalyst). In reality, stereocontrolled lactide polymerization can be achieved with a catalyst containing sterically encumbered active sites however, both chain-end and site control mechanisms may contribute to the overall stereocontrol [154]. Homonuclear decoupled NMR analysis is considered to be the most conclusive characterization technique to identify the PLA tacticity [155]. Homonuclear... 

The purpose of the second dwell is to allow crosslinking of the matrix to take place. It is during the second dwell when the strength and related mechanical properties of the composite are developed. To characterize the exothermic crosslinking reaction of a thermosetting polymer matrix, a thermal cure monitor technique such as Differential Scanning Calorimetry... 

Molecular Orientation Characterization of molecular orientation is important as many physical and mechanical properties of polymers depend on the extent and uniformity of the orientation [2,4,25]. Orientation can be measured by using a variety of techniques [2,4,25,33,34]. IR spectroscopy not only allows the characterization of amorphous and crystalline phases separately, it also provides morphological data and can be used to map orientation with high spatial resolution [35]. 

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