The possibility of using dynamic indentation method for measurement the elastic and strength properties of polymer products obtained by additive synthesis using the SLA-technology is considered. The sensitivity of the method to changes in hardness, tensile strength, and elastic modulus of products obtained by different printing modes with a thickness of the cured layer of photopolymer resin of 100, 50, and 25 microns has been estimated. A comparison is made of two main methods for calculating the physical and mechanical characteristics of a material according to the data of its impact loading diagram: an adapted classical method of mechanics of contact interaction, considering the geometric parameters of the deformed region of the material, and a method based on the energy characteristics of shock interaction. It was found that the highest sensitivity of the dynamic indentation method to changes in the properties of the additive polymer, depending on the thickness of its hardened layer, is provided when using an energy computational model for evaluating the properties of the material. The results obtained are the basis for the methods of non-destructive testing of polymer products of additive manufacturing by the method of dynamic indentation. The implementation of these techniques in portable measuring equipment is an alternative to standard destructive tests and will allow obtaining reliable data on the properties of the controlled material without the need to manufacture special witness samples.
The possibility of using the dynamic indentation method (DIM) for evaluating the elastic and strength characteristics of products made of carbon-filled SAN plastic (acrylonitrile styrene) obtained by additive synthesis using the extrusion technology of 3D printing -FDM technology (Fused deposition modeling) -in different directions is shown. An influence of surface roughness of the products tested in the range of 2.0 to 3.6 Ra on the results of measuring the dynamic hardness and dynamic elastic modulus was investigated. It is shown that the initial roughness of the specimen surface of 3.6 Ra leads to an increase in the measurement error of the physical and mechanical characteristics using DIM up to 16% and increases the coefficient of variation. The loading parameters (spherical indenter of 5-mm diameter, impact energy of 42 mJ) for the materials investigated were determined, which allow one to obtain reliable numerical data of the physical and mechanical characteristics (in the range of variation of the strength 16-33 MPa and elastic modulus 1.4-3.0 GPa) of the products inspected. The results obtained can be used for the creation of portable measuring devices that allows one to provide in-situ testing of products manufactured by 3D printing (FDM technology), without the use for standard destructive tests on the witness specimens.
Introduction. Dynamic indentation method is considered promising in testing mechanical properties of composite materials. Today, composite materials are widely used in the aviation and aerospace industries. That’s why, testing of mechanical properties of composite materials is so vital.
Method. To register the current velocity of the indenter penetration into the tested composite material, use is made of a device that enables a contactless measurement of the indenter penetration velocity after the indenter strikes the tested product.
The data obtained is digitized and sent to a PC for further processing.
Results. The experiment produced "contact force – penetration depth" diagrams for three test zones in the prepared samples. The analysis showed that the non-uniformity of mechanical properties in the rod’s butt end and side surface is stipulated by pores and microcracks, and this is confirmed by computer tomography. It is shown that dilaminations, microcracks and local non-uniformity zones in the structure tell on the elasticity modulus measurements.
Conclusions. The dynamic indentation method allows one to test composites at the micro- and macrostructural level, as well as compute their integral mechanical properties.
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