Question

Kıc = Yovta A part has been designed in the form of a thick steel plate to support a load in tension. The design stress on the part is 1200 MPa. While in service the part will be routinely inspected with an X-ray non-destructive testing device. This X-ray inspection device will detect any interior cracks larger than 0.5mm. During the initial design of the part, the required Klc for the steel was determined to be 38MPa.m .5. This Kic value was calculated using the above equation, assuming the geometry parameter (Y) for the plate is 1.12 and while taking into account of the sensitivity of the X-ray inspection device (to provide a value for a). Due to concerns about the dangers posed by brittle fracture, it has been decided that a factor of safety in fracture toughness of 2 should now be used when selecting the type of steel for this part. Assuming no changes in part geometry are possible and the objective is to prevent part failure, what one type of steel from the three options in the table below is now suitable for this part? Briefly justify your choice. Material Fracture Toughness, Kic Yield Strength, (MPa.m05) Oy (MPa) Option A 90 1150 Option B Steel alloy 4140 (Tempered @ 482°C) Steel alloy 4340 (Tempered @ 260°C) Steel alloy 4340 (Tempered @ 425°C) 50 1640 Option C 87 1420 [NOTE: This question does not ask you perform a calculation using the provided Kic equation. Instead it gives you the numerical answer from a Kic equation and asks you to interpret what that answer means in this context]

Answer 1

Given] Kic= 38 m pa mo.5 fos=2 to min. Required Kies (kic) ver a fosx Kıc = 2238=76 MPamos Nows from ttable we should choose material for which KIC? 76MPamuis ... Material A (kicago mpamis, & Material c (kec=87) are suitable for this application. But Material 'Ć has higher yield strength so, most suitable choice is material C,

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