# chem and engineering question

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1. Looking back to mechanical testing for practice: A tension test was performed on a metal specimen having an original diameter of 12.5 mm and a gauge length of 50mm. Plot the stress-strain curve and determine the modulus of elasticity (Youngâ€™s modulus), yield strength, the UTS, ductility, fracture stress and toughness of the material.

2. For some viscoelastic polymers that are subjected to stress relaxation tests, the stress decays according to the following equation:

Ïƒ(t)=Ïƒ0exp(âˆ’tÏ„)



$\text{}$

Suppose that you have a sample with these properties and you subject it to a measured strain of 0.5 m/m and you measure the stress needed to hold this strain. Determine the relaxation modulus of the material at 10 sec. if the initial stress level was 3.5 MPa and the stress dropped to 0.5 MPa after 30 sec. Using excel (or another program such as Matlab) make a plot of this behavior out to 100 sec. At what time does this sample reach equilibrium? Indicate that value on your plot.