17.) What is the Yield Strength of Rockalite? (5 points)

The yield strength marks the transition from elastic (linear portion of the stress-strain curve) to plastic deformation (non-linear portion of the stress-strength curve). For Rockalite it is 70 MPa.

18.) What is the Rupture Strength of Rockalite? (5 points)

The rupture strength is recognized by the vertical stress drop without an increase in strain. Rockalite failed at 77 MPA.

19.) Does Rockalite deform in a brittle, semi-brittle, or ductile manner. Support your choice with a quantitative value that describes this materials response to stress. (5 points)

Rockalite is a semi-brittle material as the amount of shortening for  prior to failure by rupturing  is between 5 and 10 %. (Rupture occurs after the dashed blue line)

20.) What is the Young's Modulus for Rockalite?  (5 points)

The value for the Young's Modulus is determined from the slope of the elastic portion of the stress-strain curve of the material.

(70 MPa / ^-2) = ^-35 MPa.    I will accept (70 MPa / ^- 0.02) = ^-3500 MPa