Compressive residual stresses are very important at fatigue life, therefore this
work has an objective to determine compressive residual stresses longitudinally,
along a surface, with three levels of deflection causing tensile prestresses on
the surface fibers, of 750 MPa, 1100 MPa and 1500 MPa, supported in one support
position on the compression side, 150 mm, equidistant from the longitudinal
center of the samples, which are made of EN 47 steel (DIN 51CrV4), with
dimensions of 15 mm thick, 70 mm width and 1500 mm long. The samples are
submitted to quenching, tempering, surface polishing and stress relief
processes, with radius of 2500 mm and concavity downwards, and after they are
immersed in a tank with mineral and conventional quenching oil compound, then
the samples are tempered and the concave surfaces are polished to remove
decarburization and took into the furnace to relieve stress caused by the
surface polishing process. Next step, the samples are peened, with deflections
of 750 MPa, 1100 MPa, 1500 MPa with support distance of 150 mm, in a machine
with controlled parameters, to introduce compressive residual stresses on
polished surfaces, this process is called stress shot peening – SSP. Specimens
are extracted to perform a tensile test for metallographic analysis and hardness
determination and residual stresses are determined by X ray diffraction, from
the surfaces of the samples longitudinally and uniaxially. The compressive
residual stress at deflections of 750 MPa, 1100 MPa and 1500 MPa are -801,67
MPa, -851,37 MPa and -914,51 MPa average, respectively. The samples are
submitted to cyclic fatigue testing to verify the influence of compressive
residual stresses developed from the three deflections. The fatigue tests
maximum results are 32877 (750 MPa), 67347 (1100 MPa) and 104952 (1500 MPa)
cycles, fracturing at contact points of the plate.