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:
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.