A customer has filed a warranty claim on several steel structural beams from your company, with clear evidence that the beams failed due to fatigue. Given that the customer did not exceed the rated load amplitude for the beams and that the beams were properly designed for all experienced loads to be under the fatigue limit, explain how the fatigue failure could have occurred. The fatigue crack initiated from the beam surface. Explain fatigue crack propagation and the role of surface defects in stress concentrations. Offer 3 different manufacturing surface treatment options that would prevent this problem from occurring in the future.
A customer has filed a warranty claim on several steel structural beams from your company, with clear evidence that the beams failed due to fatigue. Given that the customer did not exceed the rated load amplitude for the beams and that the beams were properly designed for all experienced loads to be under the fatigue limit, explain how the fatigue failure could have occurred. The fatigue crack initiated from the beam surface. Explain fatigue crack propagation and the role of surface defects in stress concentrations. Offer 3 different manufacturing surface treatment options that would prevent this problem from occurring in the future.
A customer has filed a warranty claim on several steel structural beams from your company, with clear evidence that the beams failed due to fatigue. Given that the customer did not exceed the rated load amplitude for the beams and that the beams were properly designed for all experienced loads to be under the fatigue limit, explain how the fatigue failure could have occurred. The fatigue crack initiated from the beam surface. Explain fatigue crack propagation and the role of surface defects in stress concentrations. Offer 3 different manufacturing surface treatment options that would prevent this problem from occurring in the future.
Since the customer did not exceed the rated load ,the beam operated with in the endurance limit. It is given that the beam is designed to withstand the experienced loads. So the fatigue failure could have occured due to some un noticed defects in the parent metal or due to some defects occured during the manufacturing process.
In unwelded metals and alloys the fatigue crack may initiate from features such as change in cross section, machining flaws etc. Which may often become vital in fatigue loading.
But here in this case since it is a structural steel there may be number welded joints. welded joints may develop defects such as blow holes, lack of penetration, slag inclusions etc. Which sometimes even NDT tests may fail to detect. These are spots of crack initiation.
The mechanism of catastrophic failure is quite fast that without any warning failure will occur.after crack initiation, the crack propagation and final failure takes place without even increasing the load.
Surface treatment processes like polishing to remove the machining flaws, shot peening, case hardening etc can improve fracture toughness of the beam to which will prevent crack propagation during fatigue loading.
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