METHOD FOR MEASURING THE CONTACT AREA OF THE INDENTER WITH THE SAMPLE SURFACE Russian patent published in 2022 - IPC G01N3/42 G01N19/08 G01N23/83 

FIELD: indentation testing.

SUBSTANCE: invention relates to the field of determining the mechanical properties of materials by means of instrumental indentation. Essence: the sample is mounted rigidly on the holder of the 3D visualization device of the deformation state of the material surface in the area of elastic deformations. The indenter is installed in the holder, then with the help of a micro screw, the indenter is inserted into the material to a certain depth and fixed. The surface of the tested material is prepared in such a way that the size of the irregularities and roughness of the area of contact of the material with the indenter is much less than 1 micrometer, and the roughness control after grinding is carried out by atomic force microscopy. The device for 3D visualization of the deformation state of the material surface in the area of elastic deformations with an indenter embedded in the material is placed in an X-ray microtomograph, after which a certain number of images of the object are taken at different angles when the object rotates around the central axis of symmetry of the indenter (projections) perpendicular to the axis between the center of the source and the center of the microtomograph detector. The number of projections is selected depending on the size of the area of interest under study, the projections obtained at different angles of rotation are reconstructed into a full-fledged 3D model that captures both the contact area of the indenter with the tested material and parts of the contact-free surfaces of the material and the indenter. The indenter material is selected in such a way that its Young’s modulus and hardness are significantly higher than that of the tested material. To measure the contact area according to the obtained 3D model using the VGSTUDIO MAX 3.4 software, the 3D model is divided into a set of virtual sections necessary for analysis, then the central axis of the indenter is found, and a projection passing through this axis perpendicular to the sample surface is fixed, then this projection is visualized in 2D for further measurements, after that the tip of the indenter is allocated as a separate object, and its virtual surface is constructed. The maximum penetration depth of the indenter h is determined as a perpendicular segment from the sample surface to the point of maximum penetration, and the width of the contact area a is determined by the distance between the points of contact of the indenter surface. The sequence of actions for determining a and h is repeated at least 10 times for a set of statistics, each time rotating the projection by an angle of up to 20° through the axis of rotation of the indenter horizontally, then the values of the depth of indenter penetration and the width of the contact area measured for each rotation are averaged.

EFFECT: 3D visualization of the contact area of the indenter with the surface of the material, measurement of the width of the contact area and the depth of indenter insertion with high accuracy (less than one micrometer).

1 cl, 2 dwg, 1 tbl