ASSESSMENT OF THE IMPACT OF THE CONDITIONS OF THE DISK MICROSAMPLE FIXATION ON THE PUNCH TEST DIAGRAM, TAKING INTO ACCOUNT THE FRACTURE PROCESS
One of the key parameters, used for the current control of the equipment state to provide its reliable operation is mechanical characteristics of the construction materials, in particular, strength characteristics. The most correct method of their determination is distractive test for uni-axial tension of the samples, manufactured from the investigated materials. The cutting of a certain volume of the material, needed for the fabrication of the sample can be critical for the carrying capacity of the construction. That is why, the indirect methods of the mechanical characteristics determination are developed to minimize the volume of the material, used for samples manufacture. Small punch test can be refereed to these methods. As this method is not standardized, the conditions of the tests are chosen by the researchers at their discretion. The given research considers the impact of the selection of one of the parameters, namely, the clamping force, on the results of the study. Steel 45 was chosen as the model material. Numerical modeling was carried out without taking into account and taking into account sample clamping force, equaled 5, 7.5 and 10 kN. The value of the von Mises equivalent stress in the clamped zone of the sample did not exceed 264 MPa. To take into account the fracture process Gurson – Tvergaard – Needleman (GTN) model was used. The problems was simulated in the dynamic formulation, using the explicit integration scheme. Diagrams of disk microsample punching in the coordinates «load» – «deflection» at the given conditions of fixing is given. By the results of the study it was determined that the force of sample clamping does not influence greatly the punching diagram, that is why, to decrease the time, needed for the numerical calculations it can be neglected. In the course of the experimental tests it was recommended to select the clamping force of the sample so that to avoid plastic deformation of the sample in the area of the clamping.