From materiality to plasticity

Typical stress-time profiles for the various materials (28.5-at. % Ni, fee and bcc) and various stress regions are shown in Fig. 5.12. The leading part of the profile results from the transition from elastic to plastic deformation. The extraordinarily sharp rise in stress for the second wave in Fig. 5.12(a) and the faster arrival time compared with that in Fig. 5.12(b) is that expected if the input stress is above the transition, whereas the slower rise in Fig. 5.12(b) is that expected if the stress input to the sample is below the transition. The profile in Fig. 5.12(c) for the bcc alloy was obtained for an input particle velocity approximately equal to that in Fig. 5.12(a) for the fee alloy. The bcc alloy shows a poorly defined precursor region, but, in any event, much faster arrival times are observed for all stress amplitudes, as is indicative of lower compressibility. 

The chemical uses for ethylene prior to World War II were limited, for the most part, to ethylene glycol and ethyl alcohol. After the war, the demand for styrene and polyethylene took off, stimulating ethylene production and olefin plant construction. Todays list of chemical applications for ethylene reads like the WTiat s What of petrochemicals polyethylene, ethylbenzene (a precursor to styrene), ethylene dichloride, vinyl chloride, ethylene oxide, ethylene glycol, ethyl alcohol, vinyl acetate, alpha olefins, and linear alcohols are some of the more commercial derivatives of ethylene. The consumer products derived from these chemicals are found everywhere, from soap to construction materials to plastic products to synthetic motor oils. 

Figure 1.6 FALLO approach includes going from material to fabricated product (courtesy of Plastics FALLO)...

Complex fluids are amazingly diverse, ranging from foodstuffs, to biological materials, to plastic coatings. Nevertheless, such substances have shared characteristics, including... 

Plasticizers are one of the most important classes of additives. These are the additives that give the plastics flexibility and durability. Most of these additives are used in PVC, which is in turn used in a wide variety of compounds ranging from plumbing and construction materials to plastic bottles. Unfortunately, since the additives are not reacted into the polymer, they can migrate to the surface of the finished plastic product and then evaporate or leach into the surrounding environment. This disadvantage for use is an advantage for analysis, because these plasticizers are easily desorbed from the base polymer. 

Phenol is the raw material for the production of many substances, ranging from aspirin to plastics. 

Softening point Temperature or (usually) temperature range, characterizes the transition from solid to plastic/paste-like and then liquid state of a material, for example, glasses, thermoplastics (q.v. glass transition temperature). 

The yield strength (a load) or yield stress (a stress value) is the point at which plastic deformation occurs (point A, Figure 10.1 la). For most materials, the transition from elastic to plastic behaviour is rarely abrupt, and a single point does not mark the boundary between elastic and plastic deformation. In order to obtain a guide as to when a stress value passes that required for plastic deformation to occur, it is usual to select a value of the stress that leads to 0.2 % plastic strain (0.002 strain). This is also called the 0.2 % offset yield strength. [This value is arbi-... 

Fine-grained soil which contains clay minerals in the presence of water can be remolded. As the amount of water in the soil increases the material moves through various physical states. These states are solid to semisolid to plastic and finally to a liquid state. The Atterberg limits describe the firmness (i.e., consistency) of this remolded soil with varying moisture contents. The transition from semisolid to plastic state is defined as the plastic limit. The point of transition from plastic to liquid state is defined as the liquid limit. Both of these limits are defined in terms of water contents using simple mechanical tests. A third limit defined as the plasticity index is the difference in percent water content between the liquid limit and the plastic limit. The test procedure has been described in detail in ASTM (D4318). 

The brackets that hold the lighting systems in place have also gone from steel to plastic. Typical materials for this application include glass-filled nylon, PC, glass-filled PET, and sheet molding compound (SMC). The plastic brackets are much lighter in weight than the metal part they replaced. 

Special attention is required when selecting the correct indenter tip. Sharp indenters such as the Berkovich tip indenter have been used by most researchers to measure the hardness and Young s modulus. However, the assumption of the transition from elastic to plastic behavior of the material is not permissible with a sharp-tipped indenter because these indenters create a nominally constant plastic strain impression. With a spherical tip, on the other hand, the depth of penetration increases as the contact stress increases therefore, the response of the elastic to plastic transition and the contact stress—strain property of a material can be determined (He and Swain, 2007). 

Fourth, molded-in metal parts should be avoided whenever alternate methods will accomplish the desired objectives. If it is essential to incorporate such inserts, they should be shaped so that they will present no sharp inside comers to the plastic. The effect of the sharp edges of a metal insert would be the same as explained in the first point above, namely, brittleness and stress concentration. The cross-section that surrounds a metal insert should be heavy enough that it will not crack upon cooling. A method of minimizing cracking around the insert is to heat the metal insert prior to mold insertion to a temperature of 250 to SOOT so that it will tend to thermoform the plastic into its finished shape. The thickness of the plastic enclosure will vary from material to material. A reasonable guide is to have the thickness 1.75 to 2 times the size of the insert diameter. 

The behavigur noted with chalk, which was chosen because it produces thick traces. was also obtained with other materials which ranged from metals to plastics. Continuous and oscillating tests were run (17). The conclusions reached proved to be quite general and will therefore be presented as such. They indicate that ... 

Transportation per functional unit from raw materials to plastics conversion operations,... 

The first LCA study, from Boustead Consulting and Associates, compares the LCA of single-use plastic bags with single-use paper. The cradle-to-gate analysis includes the environmental impacts of plastic bags from the creation of the plastic from raw materials to plastic pellets. 

Sharps containers are made from a variety of materials from cardboard to plastic. As long as they meet the definition of a sharps container (i.e., containers must be closable, puncture-resistant, leakproof on sides and bottom, and labeled or color-coded), OSHA would consider them to be acceptable. 

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