CALCULATION OF FRACTURE STRESS FOR SADDLE CLAMP BRACKET

As noted in the previous page, the fracture toughness of 4340 steel in a 1060 MPa tensile strength condition, lies in a range of perhaps 110 MPam1/2 to about 87 MPam1/2. These values can be applied to the alloy and used to calculate the fracture stress via the following equation, which applies to a semi-elliptic crack in tension:






Values of Φ, the denominator in the K1 equation, can be found from the table below:

 

a/c

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Φ

1.00

1.016

1.051

1.097

1.151

1.211

1.277

1.345

1.418

1.493

1.571


The maximum crack length, measured from the fracture surface is 2.0 mm, and the geometry can be modelled by assuming appropriate values for a, a/c and a/B. These values can be found from the fracture surfaces where, approximately, a = 2.0 mm, c = 9.0 mm, B = 7.0 mm, W = 38.0 mm.

The interactive applet below calculates values for applied tensile stress at fracture, and can be used to assess the likely sensitivity of the result to errors in input parameters.


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