01E45 Mechanical Properties Lab Report

01E45 Mechanical Properties Lab Report - Mechanical Image...

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Image 1: Rubber sheet Image 2: Photoelastic sheets Mechanical Properties Lab Report Norbert Wang Engineering 45 Mechanical Properties of Materials Abstract Exploring mechanical properties of materials was the primary focus of this experiment. Samples for observation included slabs of copper (4 slabs with varying thickness), stainless steel, mild steel, aluminum, brass, and a thick rubber sheet. The metal slabs were tested for hardness using Brinell and Rockwell standards. The rubber sheet was tested for stress concentration in continuous and discontinuous regions (a hole in the material). As a supplement, photoelastic stress analyzing equipment was also examined to see the stress concentrations of various discontinuous region shapes by use of color changes. Introduction All materials deform elastically and/or plastically when given enough stress. Stress is defined as pressing in to a material (force over area) whereas strain is defined as stretching or squeezing a material (length change over original length). If a material is elastic, its shape will be renewed once the stress/strain has subsided. If a material is plastic, deforming it will cause a permanent change in its shape. Hardness is a mechanical property that describes how resistant a material is against deformation. It can be best described as how easily scratched or dented the material is by other materials. To measure hardness, Brinell and Rockwell machines can be used. They basically dent the material of examination with a known force (500-3000kg for Brinell and 60kg for Rockwell) and measure how large (for Brinell) or deep (for Rockwell) the indentation is under a microscope (for Brinell) or on a readable meter (for Rockwell). Stress concentration is the other aspect of this lab. Continuous elastic material, like a sheet of tough rubber will increase in length in the direction of applied force, and decrease in width. If a discontinuous region, like a hole or crack, exists, the concentration of stress is unevenly divided throughout the material.
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It can be measured that the stress around the discontinuous region is significantly higher than that in a continuous region. Procedure This lab was broken up into 4 parts, each exploring a specific mechanical property of a material or series of materials. Part 1: Brinell Hardness Measurement Copper 0.250, aluminum, brass, mild steel, and stainless steel participated in this part. By applying either 500kg (for Cu, Al, and brass) or 3000kg (for both steels) an indentation was made by a blunt 10mm diameter indenter on the surface of the metal. This indent was observed under a microscope and its diameter was measured very accurately in mm. From this the Brinell hardness number can be calculated (see Figure 1) with indentation area and projected indentation area. Part 2: Rockwell Hardness Measurement
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01E45 Mechanical Properties Lab Report - Mechanical Image...

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