MSL_LAB3 Stress and Strain - MANE-4040 MECHANICAL SYSTEMNS...

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MANE-4040 MECHANICAL SYSTEMNS LABORATORY (MSL) Lab Report Cover Sheet Title of Lab: _Stress and Strain Measurement ________________ Section Tu, W(am), W(pm), Th : _4 ________________________________________ Group ID (A, B, C, D, E ): _E ________________________________________ Submitted by Group Leader: _Adam Larouche ____________________________ Group Member: 1 _Dan Garr ________________________________ Group Member: 2 _Carl Hansen _____________________________ Group Member: 3 _Sam Harrington __________________________ Group Member: 4 _Adam Larouche __________________________ Group Member: 5 _Matt Wilcox _____________________________ Lab Scheduled Date: _2/21/2008 _________________________________ Lab Report Due Date: _3/6/2008 __________________________________ Lab report Received Date (by TA): __________________________________________ Late Penalty Points (by TA): __________________________________________ Section Possible Points Points Given Abstract 10 10 Introduction 10 9 Experimental Procedures 15 14 Results 25 24 Discussion of Results 25 22 Conclusions 15 15 Total 100 94
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Abstract: In this report, the results of polycarbonate and aluminum tensile tests were used to understand how loading conditions affect material properties such as the Young’s modulus, yield strength, ultimate strength and strain to failure. The report details the procedure of using an Instron machine to perform the test and LABView software to record the data. From the recorded data, engineering stress vs. engineering strain plots were created for each test. This report includes a presentation and in-depth analysis of these plots as they relate to each other and previously determined results. Also included is a brief empirical analysis of relaxation mechanics. A discussion of results concludes the report. Introduction: This experiment involved testing the tensile strengths of polymer and aluminum samples. To do this, a load was applied by the Instron machine, and the deformation of the sample bar was measured accordingly. There were two ways to measure the deformation: to measure the deflection of the machine as it is applying the load, and to attach an instrument (an extensometer) to measure the strain in the specific region where the deformation takes place. The extensometer measures the deformation more accurately because it measures only a specific region of the specimen that has been pre-measured while the Instron machine measures the deformation of the machine itself, as well as the deformation of the whole specimen. It is important to relate the load applied and the deformation of the specimen. Engineering strain, ε , is the deformation, L divided by the original length of the specimen, 0 L . 0 L L = ε However, engineering strain does not take into account the reduction in cross-sectional area as the sample is deformed. Logarithmic strain, which is defined as ε , is the deformation of the specimen taking into account the reduction of cross-sectional area as the specimen is deformed. Logarithmic strain can be calculated by: ) 1 ln( + = tr True stress, σ , is the stress that relates to the logarithmic strain: E P tr tr σ = = i A where P is the load applied, E is the elastic modulus of the material, and A i is the cross-sectional area at an instant of time. The elastic modulus, E, is of interest, and it is desired to calculate it. However, we don’t know what A i and σ are, so we need to use engineering stress, s, which can be calculated by: E A P = = where A is the initial cross-sectional area.
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MSL_LAB3 Stress and Strain - MANE-4040 MECHANICAL SYSTEMNS...

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