Research On The Stress Condition Of Hertz Contact And The Propagation Characteristics Of Fatigue Crack For High Carbon Steel After Laser Strengthening&Toughening Treatment

The numerical simulation analysis of the contact stress and strain field for high carbonsteel after laser strengthening&toughening treatment was carried out by use of the finiteelement ANSYS software, and the propagation characteristics of the rolling fatigue crack inthe laser strengthening zone were studied in this paper.The relationship between the friction coefficient of the contact surface and the surfacestress, the maximum shear stress and the plastic strain were analyzed by means of the finiteelement models of Hertz contact. The results show that the tensile stress and compressivestress area were significantly present respectively in the front and rear of the hertz contactarea. The friction coefficient has little influence on the transverse stress and the normalstress while it has appreciable influence on longitudinal stress. The position of maximumshear stress transfers from3mm below hertz contact area to surface, when the frictioncoefficient exceeds0.2. The plastic strain occurs in parent material of high carbon steelwhen the friction coefficient is between0.2and0.4. When the friction coefficient is0.5,plastic strain occurs inside laser hardening area.The relationship between the Hertz contact positions with Von Mises equivalent stressand plastic strain was also analyzed. The results show that it is the most dangerous whenloading position is3mm that the maximum equivalent stress occurs in laser strengtheningarea, and the maximum plastic strain occurs in parent material area.It has been found that the most evident region of variation for stress and strain lies inthe boundary of laser strengthening area and parent material area0.5mm inside and outside,and the plastic strain reduces while Von Mises equivalent stress increases after laserstrengthening&toughening treatment.The finite element model of three-dimensional crack tip has been found using singularelement method. Calculation results show that the stress intensity factor KIof crack tipwithin parent material below laser strengthening zone reduces after laser strengthening. When the maximum load of contact zone increases to1800MPa, and depth of crack withinparent material reaches1.8mm, the stress intensity factor KIof crack tip is the largest,which reaches34.6MPa·m1/2, but is still less than fracture toughness value of parentmaterial at-40℃, which is38.7MPa·m1/2.It was found that wear-resisting property of rail was improved significantly after laserstrengthening&toughening treatment.