Strain (elongation) (D) During the tensile testing, we took care to ensure that

Question

Strain (elongation) (D) During the tensile testing, we took care to ensure that the wedge action grips were only on the wide section of the samples. Why was that? Why would we be concerned if the grips were on the narrow section? (5 pts) 3 Problem 3 (A) Explain why the values of stress, strain and modulus for the materials in "Rivet Shear" experiment are expected to be in error (what is missing). (This is true for either rivet size.) You will need to explain (briefly- actual equations are not required) how stress, strain, and modulus are calculated for each rivet size. (6 points) am

Explanation / Answer

Answer:

D. Preventing failure in the grips is important. Additionally, grips of tensile testing machines have teeth to achieve a sufficiently strong grip that can withstand the forces required to deform the sample longitudinally. The teeth typically cause plastic deformation of the gripped portion of the sample. The plastic deformation at the grips may change the material properties and definitely changes the sample geometry. The sample geometry changes in such a way as to create stress concentrations in the gripped region. Both changes would contribute to an improper measurement if a failure occurred at the grips in a cylindrical or bar specimen without enlarged ends.

Problem 3:
A. To provide allowable stress and modulus values, some error is given to rivet shear. Plates are in shear condition, to give some tolerance, some error is given to prevent permanent failure

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