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## Tension & Compression Labs

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**Tension & Compression Labs**SMTL 246**These are the results from one of the tension labs**The top-left curve is for the mild steel and the bottom-right curve is for the cast iron**These are the results from one of the tension labs**The top-left curve is for the mild steel and the bottom-right curve is for the cast iron**Draw horizontal and vertical axes through the bottom end of**the mild steel curve The horizontal axis should also pass through the bottom of the cast iron curve Label the axes**Now, we add the units to the axes. The graph paper has mm**and cm markings. For the vertical load axis: For the horizontal axis, the scale is 250:1 This means that 250 cm on the paper is equal to 1 cm deformation in the sample … so 1 cm on the paper is equal to 0.004 cm in the sample … or 0.04 mm**Place units all the way up the vertical axis and a little**way along the horizontal axis. Don’t go as far as the cast-iron curve; we will need to start at 0 again there**Draw a line along the proportional part of the curve,**approximating the slope as accurately as possible**Now, find the slope by measuring the rise (change in load)**over the run (change in deformation). Make a large triangle by adding vertical and horizontal lines (a small triangle is less accurate since any error in the reading is magnified).**My (rough) measurements from the scan of the graph give me a**rise of 15.5 cm ( = 73.2 kN) and a run of 3.35 cm ( = 0.134 mm). We want to calculate E, the modulus of elasticity.**To find the yield strength, use the 0.2% offset method (this**value is for steel – use 0.05% for cast iron) Draw a line parallel to the proportional part of the curve through the point on the horizontal axis representing 0.2% strain. This line intersects the curve at the yield point. Where is the point that represents 0.2% strain?**Now, calculate the stress at the yield point based on the**load and the original cross-sectional area**Repeat the process for the cast-iron. Reset the origin to**the point where the curve crosses the horizontal axis. Do the same process for the compression test. The horizontal scale is 1000:1