tool_design_Ashby_chart - Strength, hardness and wear...

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Abrasive Cloths Ceramics are ideally suited to this task being extremely hard and available in the form of fine grit. Typically glass and silicon carbide of varying grit sizes are available. Strength, hardness and wear resistance. The strength of a material is the load it can take (per unit area) before permanently deforming. For metals this is normally by yielding, which gives the values shown on the chart below. Ceramics have high failure strengths in compression and these are the values shown on the chart. In tension, ceramics fail by fracture and the strength is much lower (typically 10%). The hardness of a material is related to its strength – hard materials are also strong materials. This is because hardness is really another measure of the resistance to permanent deformation, but for a small indent rather than the whole specimen. The resistance to wear of a material is a difficult property to define. In practice it is found that harder materials have better wear resistance. We can therefore use the chart below to select materials which will have good wear resistance (they lie towards the top). Cast iron is hard and brittle, but easy to machine (because it contains flakes of graphite). Why is it used for tools such as vices, marking-out tables, and V-blocks?
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This note was uploaded on 07/24/2011 for the course EMA 4714 taught by Professor Staff during the Spring '08 term at University of Florida.

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tool_design_Ashby_chart - Strength, hardness and wear...

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