GENERAL MICKOSCOPY 





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Fig. 4. Photomicrographs of replicas of an area 

 on a cylinder liner showing progressive damage 

 during a wear test. Top, Step 1; Center, Step 5; 

 Bottom, Step 6. 



of interest to note that when replicas are 

 metal shadowed, there is a lack of contrast 

 in structure within the shadows. This arti- 

 fact may be avoided, if necessary, by 

 shadowing from opposite directions. 



The most widespread application for repli- 

 cas is in the study of surfaces of opaque 

 specimens; however, they are also useful in 

 confining observation to the surface struc- 

 ture of transparent materials. Surfaces of 

 curved objects, large objects which cannot 

 be removed for examination, or parts of an 

 intact mechanical device can be studied by 

 the replica method. Replicas from curved 

 surfaces, especially from cylinders, can be 

 flattened without seriously distorting the 

 structure rendered. An example of the repli- 

 cation of a curved surface in a mechanical 

 device, which was not dismantled, is the 

 study of scuffing and wxar on the cylinder 

 liners in a diesel engine (24). The progress 

 of the wear was followed by replication. An 

 engine test run was interrupted at certain 

 intervals and replicas were taken of the 

 cylinder-liner walls. Because it could not be 

 anticipated precisely w^here the most sig- 

 nificant scuffing would appear, the entire 

 w^all was replicated. These replicas were 

 compared after the test w^as completed, and 

 areas of interest were selected and studied 

 more critically. Figure 4 illustrates that 

 most of the wear in one of these selected 

 areas took place catastrophically between 

 Steps 5 and 6 and very little occurred be- 

 tween Steps 1 and 5. This type of retrospec- 

 tive study offers many advantages. 



Specimen Preparation for Transmitted 

 Light. Objects viewed by transmitted il- 

 lumination are usually transparent and are 

 studied by means of a biological-type micro- 

 scope. The specimen preparation is or- 

 dinarily held on a microscope slide and 

 covered with a cover-glass. In fact, as was 

 previously mentioned, the objectives of the 

 microscope employing transmitted light are 

 corrected for use with a cover-glass, ^^ery 



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