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Reference Point Indentation (RPI) refers to a specialized form of indentation testing. RPI utilizes a unique method of measurement by establishing a relative reference point ''at the location of measurement.'' This unique capability makes it possible to measure materials that are in motion, oddly shaped, visco-elastic, or that may be coated or covered by another, softer material. Unlike traditional indentation testing, RPI testing uses the location of measurement as the relative displacement reference position. Indentation itself is perhaps the most commonly applied means of testing the mechanical properties of materials. The technique has its origins in the Mohs scale of mineral hardness, in which materials are ranked according to what they can scratch and are, in turn, scratched by. The characterization of solids in this way takes place on an essentially discrete scale, so much effort has been expended in order to develop techniques for evaluating material hardness over a continuous range. Hence, the adoption of the Meyer, Knoop, Brinell, Rockwell, and Vickers hardness tests. More recently (ca. 1975), nanoindentation〔Poon, B; Rittel, D; Ravichandran, G (2008). ("An analysis of nanoindentation in linearly elastic solids" ). ("International Journal of Solids and Structures" ) 45 (24): 6018. doi:10.1016/j.ijsolstr.2008.07.021〕 techniques have been established as the primary tool for investigating the hardness of small volumes of material. However, even more recently (ca. 2006),〔Paul K. Hansma, Patricia J. Turner, Georg E. Fantner ("Bone Diagnostic Instrument" ) ("Review of Scientific Instruments" ) 77, 075105 (2006)〕 interest in measuring functional roles of biomaterials drove the development of the Reference Point Indentation technique. New research in field such as biomaterials has led scientists to begin considering materials as complex systems that behave differently than the constituent parts. For example, materials like bone are hierarchical and made of many components including calcium, collagen, water, and non-collagenous proteins. Each of these components has unique material properties. When combined to form bone, the function of the tissue is different than any one constituent. Understanding this mechanical system is becoming a new field of research called Materiomics.〔Buehler, M.J., ("Materiomics: Materials Science of Biological Protein Materials, from Nano to Macro. The A to Z of Materials" ). (February, 2010).〕 RPI specifically aims to aid materiomics researchers understand the functional capabilities of these types of materials at a relevant length-scale. ==Background== In a traditional indentation test (macro or micro indentation), a hard tip whose mechanical properties are known (frequently made of a very hard material like diamond) is pressed into a sample whose properties are unknown. The load placed on the indenter tip is increased as the tip penetrates further into the specimen and soon reaches a user-defined value. At this point, the load may be held constant for a period or removed. The area of the residual indentation in the sample is measured and the hardness, , is defined as the maximum load, , divided by the residual indentation area, , or . For most non-Reference Point Indentation techniques, the projected area may be measured directly using light microscopy. As can be seen from this equation, a given load will make a smaller indent in a "hard" material than a "soft" one. This technique is limited due to large and varied tip shapes, with indenter rigs which do not have very good spatial resolution (the location of the area to be indented is very hard to specify accurately). Comparison across experiments, typically done in different laboratories, is difficult and often meaningless. Reference Point Indentation improves on these macro and micro indentation tests by indenting on the microscale with a very precise tip shape, high spatial resolutions to place the indents, and by providing real-time load-displacement (into the surface) data while the indentation is in progress. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Reference Point Indentation (RPI)」の詳細全文を読む スポンサード リンク
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