What type of failure is shown below Please label A B and C I

What type of failure is shown below Please label \"A, B, and C\". If the Tensile Strength of the material is 200 KSI, what would you estimate the load on the member was at failure? The Director of Engineering has asked you to investigate a machine frame made from a weldment, that is experiencing excessive deflection in service. Loads on the frame are in the 20 KSI range. The frame is currently made from 1020 CRS with a yield strength of 36 KSI. Your manager suggests replacing the 1020 steel with an 4340 alloy with a yield strength of 90 KSI. Do you support that recommendation? If this design change is implemented what impact will it have on the manufacturing process?

Solution

9. Fracture at C is a brittle fracture possibly caused by a crack propagation due to repeated loading (fatigue). There is no sign of ductile elongation and grains are visible. The fracture is sudden and the load which caused was about the endurance limit which is roughly half of the tensile strength. (200/2 = 100ksi).

10. Changing over to AISI4340 steel will provide higher strength and rigidity to the frame but costs will go up. It has to be studied from the economy point of view. Alternative frame design may also be contemplated to overcome the deflection problem.There may be some impact on the manufacturing process as the new material is harder and tougher, hence more difficult to cut.