Mechanical properties stress concentration

The microstmcture and imperfection content of coatings produced by atomistic deposition processes can be varied over a very wide range to produce stmctures and properties similar to or totally different from bulk processed materials. In the latter case, the deposited materials may have high intrinsic stress, high point-defect concentration, extremely fine grain size, oriented microstmcture, metastable phases, incorporated impurities, and macro-and microporosity. AH of these may affect the physical, chemical, and mechanical properties of the coating. 

Large differences in microstructure between parent metal, heat-affected zone and weld bead. Sharp changes in mechanical properties give local stress concentrations. 

Higher extent of silica generation with high TEOS concentration improves the mechanical properties severalfolds as illustrated by the tensile stress-strain plots on ACM-sdica hybrid nanocomposites on increasing TEOS concentrations in Figure 3.6. 

The most common mechanical property of cements that has been measured routinely is compressive strength (Polakowski Kipling, 1966). Measurement is easy to carry out but there are several reasons to consider that the results from the technique are unsatisfactory. Interpretation of results is uncertain because of the complexities in the mode of failure. Minor imperfections in the material lead to localized stress concentrations which affect the magnitude of the result. 

Owing to hydrogen embrittlement, the mechanical properties of metallic and nonmetal-lic materials of containment systems may degrade and fail resulting in leaks. Hydrogen embrittlement depends on many factors such as environmental temperature and pressure, purity of metal, concentration and exposure time to hydrogen, stress state, physical and mechanical properties, microstructure, surface conditions, and the nature of the crack front of material [23]. 

The mechanical properties are good with medium to low elongations at break and more limited strains at yield. Moduli and hardnesses are in a high range but notched impact strengths are in a medium range. Polyetherimide displays notch sensitivity and stress concentrators must be avoided when designing. 

The behaviour at low temperatures is good, depending on the mechanical constraints undergone. Mechanical properties vary little between room temperature and -70°C. Suitably designed parts are usable at cryogenic temperatures, -160°C for example. Notched Izod impact strengths are weak and parts must be designed to avoid stress concentrators. 

The mechanical properties are good but notched Izod impact strengths are weak and parts must be conveniently designed to avoid stress concentrators. 

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