A10-mm drill rod was heat-treated and ground. the measured hardness he was found to be 300 brinell. estimate the endurance strength s. in mpa if the rod is used in rotating bending

The endurance strength for the rod is 434.6 MPa

Explanation:

Since the rod is used in rotating bending, we need to use Marin equation given by

Here S stands for the endurance strength for rotating  bending, is the endurance strength, and are the parameters for Marin surface modification factor.

Endurance strength.

We can start finding the endurance strength, from the directions we know that the hardness was found to be 300 Brinell, thus for such value we can find the ultimate tensile strength using

Replacing the hardness we get

Now since the ultimate tensile strength has a value less than 1400 MPa, we can find the endurance strength using

Replacing the tensile strength we get

Parameters for Marin surface modification factor.

From the directions we know that the drill rod has a ground surface finish, so then from tables we get

Thus the surface factor will be

Replacing values and the ultimate tensile strength

Then we can find the rotating shaft factor, for a diameter of 10 mm, we can use the equation

Replacing the diameter we get

Estimating endurance strength for rotating shaft.

We can replace now all values we have found in Marin equation.

Thus the endurance strength for the rod is 434.6 MPa