Tham khảo tài liệu 'volume 18 - friction, lubrication, and wear technology part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Fig. 2 Nanoindentation instrument with CDR xyz three-dimensional specimen micromanipulator H removable specimen holder s specimen D diamond indenter W balance weight for indenter assembly E electromagnet load application C capacitor depth transducer . Courtesy of Micro Materials Limited With hard machines Ref 10 16 17 the indentation depth is controlled for example by means of a piezoelectric actuator. Force transducers used in existing designs include a load cell with a range from a few tens of N to 2 N Ref 17 18 a digital electrobalance with a resolution of . - N and a maximum of N Ref 16 and a linear spring whose extension is measured by polarization interferometry Ref 10 . As noted in Table 2 it should be possible to vary the load or in hard machines the displacement either in ramp mode or with a discontinuous increment step mode . The important effects of varying the ramp speed that is the loading rate will be discussed in the section Choosing to Measure Deformation or Flow in this article. The ramp function needs to be smooth as well as linear and there is evidence Ref 19 that if the ramp is digitally controlled the data will vary for the same mean loading rate according to the size of the digitally produced load increments unless these are very small. The basic requirements include a system for data logging and processing. Scatter in nanoindentation data tends to be greater than with microindentation partly as a result of unavoidable surface roughness but principally because the specimen volume being sampled in a single indentation is often small compared with inhomogeneities in the specimen such as grain size or mean separation between inclusions . Thus unless such indent is to be located at a particular site it is usually necessary to make perhaps five ten or more tests and to average the data. The spacing between indents must be large enough for each set of data to be unaffected by deformation resulting from nearby indents and the total span .
