Hardness measurements nondestructive

Many Investigators of hydrolytic stability of polymers utilize hardness measurements since the readings are very easy to take and the tests are essentially nondestructive, thus obviating the need for many test specimens. This work emphasizes that high retention of hardness does not prove that the material has displayed a good retention of other physical properties or withstood extensive degradation. 

Treatments of deteriorated wood, which are often indispensable, especially for waterlogged wood, must be tailored to the particular properties and state of deterioration of each object (44). Therefore, it becomes highly desirable to find appropriate methods of nondestructive evaluation. Some preliminary experiments with ultrasonic pulse measurements appeared to be sensitive to the loss in degree of anisotropy accompanying loss of crystalline structure in cellulose (45), However, most published efforts appear to have been focused entirely on hardness measurements 41, 46-48),... 

Hardness measurements are not always truly nondestructive, and much depends on the particular method chosen. A special method that does not cause any damage has been reported but not described in detail (48), but other methods may leave some dents or needle holes (47), The latter, although quite unacceptable in some cases, might be considered virtually nondestructive in particular situations, especially with larger objects. An example is the survey conducted on timbers of the Mary Rose using a needle impact hardness tester (Pilodyn instrument) (41). 

Hardness is a measurement of material resistance to plastic deformation in most cases. It is a simple nondestructive technique to test material indentation resistance, scratch resistance, wear resistance, or machinability. Hardness testing can be conducted by various methods, and it has long been used in analyzing part mechanical properties. In reverse engineering, this test is also widely used to check the material heat treatment condition and strength, particularly for a noncritical part, to save costs. The hardness of a material is usually quantitatively represented by a hardness number in various scales. The most utilized scales are Brinell, Rockwell, and Vickers for bulk hardness measurements. Knoop, Vickers microhardness, and other microhardness scales are used for very small area hardness measurements. Rockwell superficial and Shore scleroscope tests are used for surface hardness measurements. Surface hardness can also be measured on a nanoscale today. 

As well as being a good way of measuring the yield strengths of materials like ceramics, as we mentioned above, the hardness test is also a very simple and cheap nondestructive test for (Ty. There is no need to go to the expense of making tensile specimens, and the hardness indenter is so small that it scarcely damages the material. So it can be used for routine batch tests on materials to see if they are up to specification on without damaging them. 

Much more information can be obtained by examining the mechanical properties of a viscoelastic material over an extensive temperature range. A convenient nondestructive method is the measurement of torsional modulus. A number of instruments are available (13—18). Afore details on use and interpretation of these measurements may be found in references 8 and 19—25. An increase in modulus value means an increase in polymer hardness or stiffness. The various regions of elastic behavior are shown in Figure 1. Curve A of Figure 1 is that of a soft polymer, curve B of a hard polymer. To a close approximation both are transpositions of each other on the temperature scale. A copolymer curve would fall between those of the homopolymers, with the displacement depending on the amount of hard monomer in the copolymer (26—28). 

Hardness testing, in the past, has been mainly used as a simple, rapid, nondestructive production control test, as an indication of cure of some thermosetting materials, and as a measure of mechanical properties affected by changes in chemical composition, microstructure and ageing. 

Results published by Kirsch and Drennen in 1995 [87] suggest that valuable information about the tablet core can be obtained through the film coat, permitting nondestructive analysis of coated dosage forms for potency, hardness, and other parameters. Likewise, the NIR method provided an accurate measure of coating levels. 

Due to its simplicity, its nondestructive nature, and the fact that minimal machining is required to prepare the sample, the use of the Vickers hardness indentations to measure Ki. has become quite popular. In this method, a diamond indenter is applied to the surface of the specimen to be tested. Upon removal, the sizes of the cracks that emanate (sometimes) from the edges of the indent are measured, and the Vickers hardness H in GPa of the material is calculated. A number of empirical and semiempirical relationships have been proposed relating Ki., c, Y, and //, and in general the expressions take the form... 

Hardness of a material may be determined in several ways (1) resistance to indentation, (2) rebound efficiency, and (3) resistance to scratching. The first method is the most commonly used technique for plastics. Numerous test methods are available for measuring the resistance of a material to indentation, but they differ only in detail. Basically they all use the size of an indent produced by a hardened steel or diamond indentor in the material as an indication of its hardness—the smaller the indent produced, the harder the material, and so the greater the hardness number. Hardness tests are simple, quick, and nondestructive, which account for their wide use for quality control purposes. 

To confirm the hypothesis of the presence of BSA on the pore wall, measurements of the SP through the pores of both the ZIOOS and ZIOOS+BSA membranes were performed with a 0.001 M NaCl solution at different pHs (de Lara and Benavente 2009) Figure 2.12b shows a comparison of the results obtained with both membranes. Positive -potential values were obtained for the ZIOOS membrane in agreement with the electropositive character of both AI2O3 and Zr02, but the -potential/ pH dependence found for the ZlOOS+BSA-fouled membrane is completely different, with a zero -potential value at a pH of 5, that is, the isoelectric point obtained for the fouled membrane hardly differs from that for the protein (BSA isoelectric point -4.9 Nystrom and Jarvinen 1991), which is a clear indication of protein deposition on the membrane pore wall and a confirmation of the EIS results. These results further confirm the use of EIS, a nondestructive technique, to study membrane modifications caused by fouling. 

An objective evaluation of the methods on the basis of literature data is hardly possible, because of differences in experimental conditions, sample, amount of sample available, and measurement time. Therefore, the detection limit values stated in the literature given in Tables 1-4 should be considered, at best, approximate. But it is clear that there is no single instrumental technique that meets all the analytical requirements. For example, some methods may be applicable over only a limited concentration range, may be subject to matrix effects or spectral interferences, or have a limited availability. Also, sometimes nondestructive fast methods are needed. The choice of an instrumental method depends on the material to be analyzed and the type of analysis required. 

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