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Lab 1: Hardness and Compression TestABSTRACTThe purpose of this lab is to test the hardness and compression properties of different materials.The Rockwell B, Rockwell C, and Brinell tests were conducted to determine hardness properties.Each of the three tests has a certain scale, meaning it will only be accurate for certain materials.Additional compressive tests were conducted to test the properties of PMMA, 1045 steel, and2024 aluminum. The elastic modulus along with yield stress/strain graphs were obtained in thisexperiment.1.INTRODUCTION1.1: Hardness testingHardness has long been a measure of durability and strength. In order to properly measure thisproperty, Friedrich Mohs developed the first standardized hardness test in 1820.1Mohs’ methodessentially compared the hardness of one material to another by observing which material is ableto scratch the other. This is also sometimes referred to as a “scratch test”. Using this test, Mohsset up a hardness scale for different materials based on how they performed in this test (Table 1).Since Mohs’ was more qualitative than quantitative, the Brinell and Rockwell scales formedafterwards and are currently much more commonly used scales to determine and measure thehardness properties of a material. In 1900, J. A. Brinell developed an indentation test, where a 10mm diameter steel ball is pressured with varying loads into the material for approximately 15seconds.1Then, by measuring the diameter of the indentation, the experimenter can calculate thehardness properties from the following formula:where P is applied load, D is diameter of indenter, and d is diameter of the indentation. Shortlyafterwards, the Rockwell test was developed to provide quicker, more accurate results regardinghardness of a material. To calculate the hardness using a Rockwell testing method, the followingformula is used:whereδis the indentation depth. HRB is used for Rockwell B testing while HRC is used forRockwell C testing.1
Table 1. Mohs Hardness Scale1.2: Compression testingCompression testing is similar to tension testing, and although it is less common, some materialsbehave differently for the two tests and therefore must be tested under both loading scenarios.During compression testing, barreling is very common among materials and it is visible as thecenter of the object expands. This occurs mostly in materials with a positive poisson’s ratio. Onecommon error during compressive testing is buckling, which is a misalignment or misplacementof the object.