Data requirements, plastics mechanical

Comparison between the results obtained in air and in detergent shows that aggressive environment affects the crack resistance only below a certain "critical" value, K ic. This is probably to be attributed to a diffusion-controlled plasticization mechanism, which requires times larger than a certain "critical" time (for crack initiation) or crack speeds lower than a certain "critical" speed (for crack propagation) to be activated. This assumption is confirmed by literature data. 

The recent AFM experimental data concerning plastic flow place severe restrictions on possible theoretical accounts of plastic deformation in crystalline solids due to shock or impact. The high spatial resolution of the AFM, = 2 x lO " m, reveals substantial plastic deformation in shocked or impacted crystal lattices and molecules. Understanding how this occurs and its effect on plastic flow requires a quantum mechanical description. The semi-permanent lattice deformation has necessitated the development of a deformed lattice potential which, when combined with a quantum mechanical theory of plastic deformation, makes it possible to describe many of the features found in the AFM records. Both theory and the AFM observations indicate that shock and impact are similar shear driven processes that occur at different shear stress levels and time durations. The role of pressure is to provide an applied shear stress sufficient to cause initiation. 

The first interactive electronic encyclopedia for users of plastics, materials selection is carried out using 3 search routines. The Chemical Resistance Search eliminates materials that cannot meet user specified chemical resistance requirements. The other search routines ( Elimination and Combined Weighting ) eliminate candidate materials based on 72 properties, falling within one of the following groups General and Electrical, Mechanical, Cost Factors, Production Methods and Post Processing. All data is evaluated and based on independent tests conducted in RAPRA s laboratories. 

When the experimentalist set an ambitious objective to evaluate micromechanical properties quantitatively, he will predictably encounter a few fundamental problems. At first, the continuum description which is usually used in contact mechanics might be not applicable for contact areas as small as 1 -10 nm [116,117]. Secondly, since most of the polymers demonstrate a combination of elastic and viscous behaviour, an appropriate model is required to derive the contact area and the stress field upon indentation a viscoelastic and adhesive sample [116,120]. In this case, the duration of the contact and the scanning rate are not unimportant parameters. Moreover, bending of the cantilever results in a complicated motion of the tip including compression, shear and friction effects [131,132]. Third, plastic or inelastic deformation has to be taken into account in data interpretation. Concerning experimental conditions, the most important is to perform a set of calibrations procedures which includes the (x,y,z) calibration of the piezoelectric transducers, the determination of the spring constants of the cantilever, and the evaluation of the tip shape. The experimentalist has to eliminate surface contamination s and be certain about the chemical composition of the tip and the sample. 

As a matter of fact, an E(T) curve provides much more information than the singlepoint tests on softening temperatures however, due to the time dependency of the mechanical properties, not even enough to provide a basis for construction purposes. For the use of plastics under load at elevated temperatures creep data are required ... 

While Heckel plots are able to distinguish between plastic and fragmenting mechanisms, they do not readily distinguish between plastic and elastic deformation. The data presented in Table 11.4 would suggest that microcrystalline cellulose and starch 1500 have very similar properties, yet the elastic nature of starch and its derivative products is well documented in the literature. Additional methods are, therefore, required to measure elasticity. 

With the practical approach, most plastics are required to withstand only short-term static mechanical loads—that is, no dynamic loads. Thus, conventional short-term static tests generally suffice. The engineering approach recognizes that many plastic products have been used since their inception to take long-term dynamic or static loads. Thus, they consider fatigue, torsion, creep, and other data that include plastic s viscoelastic properties. See kiss plastic processing. 

Simultaneously, processes of plastic deformation, fracture and interactions with the environment, and counterbody can occur. The latter ones have been studied by mechanical engineers and tribologists, but the processes of phase transformations at the sharp contact have been investigated for only a few materials (primarily, semiconductors) and the data obtained so far can only be considered preliminary. One of the reasons for the lack of information may be the fact that the problem is at the interface between at least three scientific fields, that is, materials science, mechanics, and solid state physics. Thus, an interdisciplinary approach is required to solve this problem and understand how and why a nonhydrostatic (shear) stress in the two-body contact can drive phase transformations in materials. 

The generation of failure and deformation of molded clay are the undesirable problems requiring quality control during ceramic production. The mechanical properties of wet clay are important parameters to understand the mechanism of the drying phenomena. Many experimental data are available for a variety of clays [22-26]. The mechanical behavior of clay is generally described by the viscoelasticity or plasticity, which is dependent on the moisture content. In addition to... 

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