A nanoindentation hardness testing system, including an atomic-force microscope (AFM)-based nanoindentation tester and a calibration method using electrolytically polished single-crystal metals as references, was proposed. This was applied to a study of the mechanical properties of fine-grained ferritic steel (grain size of 1.2 m) and coarse-grained ferritic steel (30 m). An empirical function giving the macroscopic hardness for all four reference metals from the nanoindentation force curves was established. The converted Vickers hardness (HV*) of the coarse-grained steel is almost independent of the indent size. The fine-grained steel shows only HV* 130 with an indent of only 100 nm, compared with a macroscopic hardness of HV 210. The difference, HV 80, is considered to reflect the amount of grain-boundary strengthening. The critical indent size for the hardness transition seems to be around 1 m, comparable to the grain size of the specimen. This result supports the explanation of grainboundary strengthening. It is also consistent with Pickering's work on low-carbon steel, as the estimated locking parameter (k of 2.6 ϫ 10 5 N/m 3/2 ) in the Hall-Petch relationship is in good agreement with his value of 2.4 ϫ 10 5 N/m 3/2 .
The effect of microstructural factors on hardness was investigated in normalized, tempered, aged and crept materials for Mod.9Cr-1Mo steel, using nanoindentation and microhardness tests. Nanohardness and microhardness decreased during tempering, aging and creep exposure. Dislocation spacing, lath width, high angle boundary (block and packet boundary) spacing and inter-particle spacing increased during tempering, aging and creep exposure. A converted Vickers hardness was introduced to compare directly nanohardness and microhardness to Vickers hardness. The converted Vickers hardness increased with indent size in all the materials tested. Hardness at an indent size less than 1 mm mainly consists of dislocations inside lath grains. Hardness at an indent size larger than 1 mm originates from not only dislocation but precipitates and high angle boundaries such as block and packet boundaries. Comparing the converted Vickers hardness with lath width and high angle boundary spacing in normalized material with no precipitates, it was found that the lath boundary does not contribute to hardness. The difference in converted Vickers hardness between tempered and aged material was obviously large at the indent size, greater than inter-particle spacing. The decrease in hardness during aging is caused by increase in inter-particle spacing due to coarsening and coalescence of precipitates. On the other hand, not only changes in precipitates but also increase in high angle boundary spacing and dislocation spacing contribute to decrease in hardness during creep exposure.
Objective: We assessed the effectiveness and appropriateness of our original off-the-job training (Off JT) system using data acquired from recruited medical students and doctors.Materials and Methods: We presented our original homebuilt Off JT system, which is simple and inexpensive. In our unique system, we performed anastomosis at the bottom of a plastic pot, which mimics the actual open surgical procedure at a deep site. There were four evaluation points: (A) operating time, (B) performance of anastomosis by semi-automatically analyzing the image with the coefficient of variation (standard deviation/length) of the “bite” and the “pitch,” (C) scoring of the total surgical skill evaluated by the trainers according to the Operative Performance Rating System (OPRS), and (D) the relationship of these three factors (A, B, and C).Results: The procedural time and coefficient of variation of the bite and pitch decreased and the OPRS score increased after training. There was a strong correlation between procedural time, anastomotic performance, and OPRS score.Conclusion: The effectiveness of our original homebuilt system was shown by reduced procedural time, improved anastomotic quality, and increased OPRS score.
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