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In this paper, we propose a simple method for the modification of the unit cells in the lattice metamaterials that provides an improvement of their impact strength. The idea is based on the introduction of small mutual offsets of the interconnected struts inside the unit cells. In such way, the joints between the struts become asymmetric and the overall geometry of the unit cells can be defined as the quasi-cubic with the axis of chirality. Considering four types of cubic lattices with BCC, BCT, FCC and octahedron structures, we modified their geometry and investigated the influence of the offsets and the unit cell size on the overall performance in static and dynamic tests. From the experiments we found that the small offsets (less than the strut diameter) can allow to increase the impact strength of 3d-printed polymeric specimens in 1.5–3 times remaining almost the same density and static mechanical properties. Based on the numerical simulations, we show that the explanation of the observed phenomena can be related to the increase of plastic deformations and damage accumulation in the unit-cells with asymmetric joints leading to the transition from the quasi-brittle to the ductile type of fracture in tested specimens. [ABSTRACT FROM AUTHOR]

As of now, many investigations are performed in order to develop methods of correlation with the help of relevant algorithms. This is especially helpfull for plotting vectors of displacements in order to estimate deformation of various materials, as well as to determine correspondence between sections of two images through calculation of the cross-correlating functions and to ensure seeking of the extremum. The aim of this study was to develop relevant method to estimate mechanism of fracture of materials in accordance with the data of analysis of a photographic image in respect of the parameter of the image intensity. In addition, this method is to be used with the help of the multivariate analysis (multi-factor analysis) of the interrelationship between image intensity, surface roughness, and possibility to determination the geometrical parameters of the deformation area/deformation volume under different conditions of operation. Digital method of processing of photographs/video frames has been used in order to investigate microstructure and surface of materials in respect of criterion of the image intensity in the course of mechanical tests in accordance with deformations. Quantitative parameters of the image intensity were compared to the structure of material, as well as to the surface roughness before and after destruction of samples. The images used were obtained during mechanical testing of aluminium samples. To ensure the validity of the test results, six specimens of the same type were tested. A stress-strain diagram was drawn up for each specimen. Stress-strain diagrams from the mechanical tests were compared with those from the photo analysis using the method described above. The results correlate well with each other, but unlike the experiment, where the strain is measured only at the strain gauge location, the photo analysis provides a complete picture of the strain distribution over the entire specimen area. In addition, a multivariate analysis has been carried out to evaluate the geometric dimensions and shapes of the structure elements. [ABSTRACT FROM AUTHOR]