The study of the stress-strain state of steel rolled on helical rolling mills and the reasons for the premature opening of the axial internal cavity in the semifinished product during the rolling operation have been subjects of considerable interest and debate among scientists for decades. However, until recently there has not been any agreement on the reasons that axial fracture develops in such products during rolling. The proponents of the different theories on this subject can be divided into two camps: those supporting the theory based on shear stresses, and those adhering to the theory based on normal stresses.Advocates of the shear stress theory argue that the axial fractures are caused by residual stresses created by the application of external forces and that the subsequent development of fracture in the axial cavity occurs as a result of shear stresses. These researchers believe that the shear stresses are formed at a 45 deg angle to the direction of the acting external loads and that shear takes place under the influence of those loads. Since the semifinished product is turned during the rolling operation, the direction of shear also continuously changes. As a result, the central (axial) zone of the product is continually undergoing plastic deformation in shear. The proponents of the shear stress theory assert that fracture of the axial zone occurs because of the action of intensive alternating loads.
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