Material selection data, evaluating

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. 

The list is far from eomplete or eomprehensive. In most instances, the data on toxieity ean be obtained by loeating an appropriate Material Safety Data Sheet for the eompound. A quiek web search can identify the toxic levels for most eompounds. The site must be evaluated with respect to the levels of compounds, their toxicity and the likelihood of deliberate or accidental contact between workers on the site and the chemicals. A suitable level of protective clothing must be selected for all workers. 

B.W. Roberts, "Survey of Superconductive Materials and Critical Evaluation of Selected Properties Physical and Chemical Reference Data, 5 581-821 (1976), contains nearly 2000 references. 

What do we usually do when we want to test or evaluate something All too often, we attempt to compare some selected data of interest for a given material or process with other presumably comparable or similar data. These data can be for materials or processes about which we think we know something, or in which we are also interested. A minimal degree of structuring is commonly employed, and there are numerous pitfalls that must be avoided if the conclusions drawn are to be worth very much. 

The variation of sensitivity between different sensors was also checked. Calibration curves with five different sensors were performed. A Relative Standard Deviation of 13, 13 and 42% of calibration slopes (sensitivity) were obtained for Cu, Pb and Cd respectively. These variations should have limited consequence on bias and precision when the standard addition method is used. However, for Cd, variations in the limit of quantification between two electrodes could be expected. Finally, the accuracy of the method was evaluated by the measurement of a SWIFT reference material used during the 2nd SWIFT-WFD Proficiency Testing exercise (Table 4.2.2). The reference value was chosen as the consensus value of the selected data population obtained after excluding the outliers. The performances of the device were estimated according to the Z-score (Z) calculation. Based on this score, results obtained with the SPEs/PalmSens method were consistent with those obtained by all methods for Pb and Cu ( Z < 2) while the result was less satisfactory for Cd (2 < Z < 3). 

Tables 22-2.1 provide some lists on the types of standard tests available. None of the lists are anywhere near inclusive of all the tests which are available. Tests are particularly useful for the comparison of materials, usually to assist the selection of a material or materials for further evaluation. The ultimate selection phase usually stems from the investigational tests in contact with the product, and is finally supported by formal stability programmes. In all these data must be adequately detailed, properly recorded and, where necessary, relevant conclusions must be drawn.

In recent years a variety of novel antifriction polymer-based materials have been developed and the known improved at different research centers and laboratories of the world. However, even a very learned expert in the field of friction is in a difficulty to evaluate truly the publicity and literary data when maJcing comparative analysis or selecting proper materials for particular friction applications. The reasons lie in the unavailability of common methods for friction testing of materials as well as evaluating criteria on the friction characteristics of materials. Explanation and selection of evaluating criteria largely depend upon the factors that influence the friction characteristics of polymers, and capabilities of the testing equipment. 

Field testing of real equipment may be conducted on small, or pilot plants, or full-scale installations. The main disadvantage of this type of testing is the expense and time required. The advantage is that the data and information more accurately reflects actual operating conditions than that obtained in the laboratory. In these pilot plant environments, materials may be evaluated to determine the type of oxides formed and the degree of protection provided. This in turn provides information to permit selection of the material that will provide the required service life. 

The procurement costs of the materials for initial construction are often the easiest cost data to obtain, and too often are used inappropriately as the sole criteria for materials selection. Materials costs based on a price per pound or other quantity usually are very misleading when used in lieu of total system costs to evaluate alternatives. Usually, in order to ensure that actual life-cycle costs are minimized, other cost factors such tis maintenance and repair must be considered. 

Rational design and materials selection must be based on an economic analysis of alternatives. In order to determine the actual costs of the alternatives, projected system life and the need for inspection, maintenance, and repair costs must be known. While there is a great deal of information available on the performance of a wide variety of materials in marine environments, these data are difficult to apply to the projection of system life. Most of the quantitative information on corrosion performance is for isolated specimens and does not address the interzone interactions and effect of design features that occur on real structures. Most of the limited amount of published information derived from the evaluation of actual structures is not quantitative and thus is difficult to use in the design of new structures. 

The literature includes additional information regarding the factors siffecting corrosion [1-3]. Also, several corrosion data summaries are avculable to assist in material selection [4-9]. Many of these include consideration of several modes of corrosion and the effects of impimties. All of the above issues must be considered when evaluating a material for service. Testing of an unstressed-annealed material when the material in service will be bent, welded, or stress-relieved may result in a service failure regardless of satisfactory test results. 

Data presented in Table 3-7 categorize gear and bearing- performance of various nonrein-forced and reinforced systems as well as TFE as an internal lubricant. The prototype test remains the best evaluation tool available to the design engineer and should be used prior to final material selection ... 

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