A 10-mm steel drill rod was heat-treated and ground. The measured hardness was found to be 290 Brinell. Estimate the endurance strength, Se, in MPa if the rod is used in rotating bending.

the endurance strength   = 421.24  MPa

Explanation:

From the given information; The objective is to estimate the endurance strength, Se, in MPa .

To do that; let's for see the expression that shows the relationship between the ultimate tensile strength and Brinell hardness number .

It is expressed as:

where;

= Brinell hardness number

=  Ultimate tensile strength

From ;

; replace 290 for ; we have

988.9 MPa

We can see that the derived value for the ultimate tensile strength when the Brinell harness number = 290 is less than 1400 MPa ( i.e it is 988.9 MPa)

So; we can say

The Endurance limit can be represented by the formula:

= 494.45 MPa

Using Table 6.2 for parameter for Marin Surface modification factor. The value for a and b are derived; which are :

a = 1.58

b =  -0.085

The value of the surface factor can be calculate by using the equation

The formula that is used to determine the value of   for the rotating shaft of size factor d = 10 mm is as follows:

Finally; the the endurance strength, Se, in MPa if the rod is used in rotating bending is determined by using the expression;

= 0.8792×0.969×494.45

= 421.24  MPa

Thus; the endurance strength   = 421.24  MPa

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