LAB 1 written report.docx - ABSTRACT Tensile tests were...

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ABSTRACT Tensile tests were performed on gray cast iron, 1045 cold-rolled steel, 1045 normalized steel, 6061-T6 aluminum, type 304 stainless steel, and PMMA. The tension tests were performed using an Instron Model 4483 load frame. Strain measurements were taken using an extensometer. From the data collected during the experiment engineering stress-strain curves were constructed for all 6 materials. In addition, the Young’s modulus, yield strength, and ultimate strength were calculated, percent elongation, and percent reduction of area were calculated. Using the results from the experiment the ductility of each material was determined. A true stress-strain curve was constructed for the 1045 cold-rolled steel to visualize the difference between engineering and true stress-strain. 1. INTRODUCTION 1.1 Tension Test During a tension test a continuously increasing tension load is applied to a material specimen. As the load increases the specimen deforms and eventually fractures. During a tension test stress and strain data is collected to better understand the material properties of the specimen. Since the geometry of the specimens may vary we must use normalized parameters to compare the test results of different specimens. A summary of the data files used in this report can be found in table 2. The first parameter is known as engineering stress, σ. Engineering stress is defined by the equation: σ = F A [1] (1)
where F is the load applied to the specimen, and A is the cross-sectional area of the specimen. In this experiment A represents the area of the thinner middle section of the specimen. The second parameter is known as engineering strain, ε. Engineering strain is defined by the equation: ε = l i l o l o = ∆l l o Where l i is the length of the specimen at any given time, l o is the original length of the specimen, and ∆l represents the change in length. From this equation it can be seen that engineering strain is a unitless quantity. In this experiment, an extensometer is used to determine strain at any given time. 1.2 Stress-Strain Relationship Stress-strain behavior is an important tool for engineers. Whether or not a material is suitable for a certain application depends on how that material responds as the load acting on it increases. All the information needed to answer the previous questions is contained in what is known as a stress-strain curve. There are two main regions on a stress-strain curve. These two regions are known as the elastic and plastic regions. In the elastic region the load acting on the material is not enough to cause permanent deformation. Once the load is removed the material will return to its original shape. This is particularly important to structural engineers as it is not desirable for structure to permanently deform. In this region the relationship between stress and strain is linear, and spring-like. The slope of the stress-strain curve in the elastic region is defined by the Young’s Modulus of the material. Young’s Modulus is calculated using the equation E = σ ε [2] (3) (2)

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