The purpose of this lab was to implement the use of a Scanning Electron Microscope (SEM) to examine and analyze metal samples that were subject to different failure tests. These failure tests included tensile tests, impact tests, and fatigue tests. SEM’s are useful because they provide a 3D view of the surface of the material, which improves the ability to examine the failure type at a microscopic level. In addition to this, the resolving power of a SEM is much stronger than that of a standard microscope, which enables the user to obtain much more detailed images of the samples. The experiment was performed by analyzing failure tested samples that were prepared before the experiment.
From the images captured by the SEM, students were able to understand how ductile and brittle fractures occur, as well as see the effects of cyclic loading on the microstructures of materials. Ductile failures exhibited mostly rounded features with dimples present within the structures. Brittle failures exhibited a cleavage pattern that had jagged edges and no dimples. Fatigue tested samples showed a crack propagation site, crack striations, and a rupture zone where the material finally failed. The crack striations examined at a microscopic level create beach lines present at a macroscopic level.
Equipment and Procedure
The Scanning Electron
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This is because each sample needed fine adjustment of these parameters to create a good raster scan. Ideally, the working distance should be minimized to facilitate the best possible scenario for a raster scan, but, since the surface flatness of the samples varied, this distance was changed to optimize the conditions for making a good scan of the sample. Also, the magnification of the samples varied so that the defining features in each sample could be seen easier and allowed for more precise analysis of the failure