An Apparatus Design for Multiaxial Ductile Fracture: Application to AISI1045

Metal cutting involves extensive plastic deformation as the workpiece material flows through the shear plane, promoting mechanisms of initiation, coalescence, and propagation of cracks. This the largest plastic deformation that it can withstand, above those of tensile and compression tests. Such condition ultimately leads to the onset of an ever-present crack just ahead of the cutting edge that provides the separation mechanism necessary to form the chip. However, it is neither easy nor simple to measure the fraction of the total energy involved in the material separation mechanism and its correlation with operating conditions. In this research, a new design of a multiaxial tool for determining mode II ductile fracture toughness is proposed. This testing tool is composed of several hydraulic and pneumatic actuators that allow a shearing punch to act against double-notched prismatic specimens with superimposed orthogonal load, yielding a wide range of stress triaxialities. This load can vary from the compressive to tensile yield stress of the material. Thus, allowing the influence analysis of the stress state on the mechanical response of ductile materials, like that experienced on the shear plane of metal cutting due to rake face angle variation. Experiments performed in AISI 1045 give support to the presentation and allow a better understanding of the influence of the superimposed pressure on fracture toughness of ductile metals.