Gradient ratio test

Fannin, RJ., Vaid, Y.P., Shi, Y.C., 1994. A critical evaluation of the gradient ratio test. Geotechnical Testing Journal, GTJODJ 17, 35—42. 

Palmeira, E.M., Gardoni, M.G., Bessa da Luz, D.W., 2005. Soil-geotextile filter interaction under high stress levels in the gradient ratio test. Geosynthetics International 12,162—175. 

Void ratio versus coefficient of permeability for two similar samples tested at 22°C and 80°C. (After Silva, A.J. et al., Low-Gradient Permeability Testing of Fine-Grained Marine Sediments, In Permeability and Groundwater Contaminant Transport, STP 746, Zimmie, T.F., and Riggs, C.O., eds., American Society for Testing and Materials, Philadelphia, PA, pp. 121-136,1981. Reprinted with permission. Copyright ASTM.)... 

Many factors influence the accuracy of experimental data and each experimental run could be described by a different set of parameters n, K, Ty. Since the flow models strongly depend on input data and their evaluation, a sensitivity analysis was used to find effect of value of flow behaviour index n on accuracy of laminar and turbulent flow models. Dependency of slurry/water pressure gradient ratio i / io on mean slurry velocity V of the measured slurries for both tested turbulent models and yield power-law model is shown in Fig. 4, where also a role of parameter n is illustrated. The value of n given by best fitting of laminar data by Eq. (4) represents quite well laminar region. For turbulent data it is not valid (see dashed line). The best fitting value n for turbulent data varies not only with kind of solid material, but depends also on concentration. 

ASTM D5101. Standard Test Method for Measuring the Soil-geotextile Clogging Potential by Gradient Ratio. ASTM International, USA. 

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. 

For the WC phase, the milder composition gradients, when revealed at the surface, make smoother transitions. This produces on the average lower C/He ratios, in very good agreement with observations [1]. The abundances in WC stars are not equilibrium values, but are products of the partial He-burning, thus they are model dependent and offer a most interesting test on the quality of stellar models. 

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