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This experiment primarily examines the tensile characteristics of different materials, including two polymers and two metals. The findings from these tests help differentiate each material and provide a foundation for designing safe structures. The tensile properties were evaluated by applying a pulling force that stretches each specimen from both ends at a controlled speed until failure occurs. Data collection involved measuring parameters such as applied load, cross-sectional dimensions, and elongation of each sample.

The tested specimens included steel, aluminum, low-density polyethylene (LDPE), and high-density polyethylene (HDPE). Prior to testing, their thickness and width were measured, and the samples were secured in a tensile testing machine. The machine, operated via DOS, was calibrated to ensure accurate results for each material. During the test, the machine simultaneously pulled the samples at a predetermined rate, recording data on elongation and applied force. The data was saved on a 2MB floppy disk and later transferred into digital spreadsheets for analysis of stress and strain.

Upon analyzing the initial measurements and the resulting data, the samples underwent tensile testing where the machine produced two main outputs: percentage strain and load. These values were used to calculate and plot the engineering stress and strain for each material. Notably, the experimental results significantly deviated from standard reference values. For example, the typical elastic modulus for steel is approximately 30 million psi, but the experiment yielded about 21.487 ksi. Similarly, aluminum's known elastic modulus is around 10.6 million psi, whereas the test produced only 3.826 ksi. For LDPE, the expected tensile strength was about 30 ksi, but only 0.265 ksi was observed, and for HDPE, the reference value of 200 ksi contrasted with an experimental value of 0.601 ksi.

These discrepancies suggest possible human errors throughout the experimental process, which may have affected measurements from initial dimensions to data entry and analysis stages. Although such errors seem extensive, the shape and form of the resulting stress-strain graphs appear correct. The true stress versus strain graphs, which account for instantaneous cross-sectional area reduction during necking, showed higher stress values compared to the engineering stress plots, as expected. Necking occurs when the material transitions from elastic to plastic deformation, resulting in permanent changes in shape and a decrease in cross-sectional area.

The ultimate tensile strengths for aluminum and HDPE matched anticipated high values consistent with their material properties. However, the reported ultimate tensile strength for steel was surprisingly lower than that of aluminum, indicating an error likely caused by human mistake. Overall, the experiment aimed to compare the tensile behaviors of different materials under specific conditions. Despite some errors, the resulting graphs effectively depicted the main characteristics and responses of the materials when subjected to tensile forces.

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