Long test methods

The Knoop test is a microhardness test. In microhardness testing the indentation dimensions are comparable to microstructural ones. Thus, this testing method becomes useful for assessing the relative hardnesses of various phases or microconstituents in two phase or multiphase alloys. It can also be used to monitor hardness gradients that may exist in a solid, e.g., in a surface hardened part. The Knoop test employs a skewed diamond indentor shaped so that the long and short diagonals of the indentation are approximately in the ratio 7 1. The Knoop hardness number (KHN) is calculated as the force divided by the projected indentation area. The test uses low loads to provide small indentations required for microhardness studies. Since the indentations are very small their dimensions have to be measured under an optical microscope. This implies that the surface of the material is prepared approximately. For those reasons, microhardness assessments are not as often used industrially as are other hardness tests. However, the use of microhardness testing is undisputed in research and development situations. 

Very light and weather resistant systems require very long outdoor exposure times. In order to accelerate the testing of pigmented systems, test methods have been developed which simulate outdoor conditions. The evaluation of such a test is not only conveniently accelerated, but the resulting data are easy to reproduce and independent of location, climate, date, and time. 

The uncertainty of a measurement is always a very important consideration but it is especially so with durability tests. In addition to the basic physical test methods, there are the complications of exposure conditions, tests spanning long times and the process of extrapolating results to make predictions. The combination of these factors will inevitably lead to large uncertainties that can very easily be of such a magnitude that any conclusions are meaningless. Terms used to describe precision include repeatability, which refers to within laboratory variation and reproducibility, which refers to variation between laboratories. 

This test method has been demonstrated to be effective for use in predicting the long-term storage stability of distillate fuel. The results obtained closely approximate those obtained after fuel storage at ambient temperature. For example, fuel storage at 110°F (43°C) for 12 to 13 weeks has been shown to correlate well with one year of storage at ambient temperature. 

This test method is commonly utilized throughout the world to rapidly determine the oxidative stability of distillate fuel. Although not as effective at predicting the long-term stability of distillate fuel as ASTM D-4625, this method is useful for measuring the resistance of fuel to rapid degradation by oxidation. Metal catalysts such as copper and iron are sometimes added to the fuel to further accelerate... 

Better test methods should be developed to evaluate, model, and monitor the potential long-term environmental impacts of single compounds emitted as a result of new products or processes. 

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