Investigation of the Physical and Mechanical Properties of ABS Plastic for the Additive FDM Process in the Manufacture of Models for Experiments in Wind Tunnels

Work has been carried out to determine the physical and mechanical properties of ABS plastics for the manufacture of aerodynamic models using the additive technology of layer-by-layer synthesis FDM for testing in wind tunnels. The samples were tested at normal and negative temperatures. The features of the structure of the samples and the features of their destruction are revealed. The possibility of using ABS plastic for the manufacture of various models used in experiments in wind tunnels is evaluated.

A Study on the Dynamic Strength Deterioration Mechanism of Frozen Red Sandstone at Low Temperatures

In this study, the dynamic mechanical properties of red sandstone at low temperatures were studied by performing SHPB dynamic impact tests. According to damage and energy theories, the influences of different low temperatures on the dynamic strength, damage variable, and energy dissipation of red sandstone were analyzed. Combined with a fracture morphology analysis, the deterioration mechanism of the dynamic mechanical strength of red sandstone was deduced at lower negative temperatures. The research results showed that lower negative temperatures (<−30 °C) caused “frostbite” in red sandstone, which resulted in a sharp reduction in the macroscopic, dynamic mechanical strength of rock under high strain. Transient engineering disasters can easily occur under such a dynamic disturbance. According to the fracture morphology analysis, low temperatures generated a large number of cracks at the interface between the components of red sandstone. The plastic deformation ability of the crack tip was poor, and stability loss and expansion under high strain rate were readily achieved, resulting in low-stress brittle failure. However, due to the complex mineral composition of the cementitious materials, they were more susceptible to low temperature. Therefore, under the double action of dynamic load and low temperatures, it was found that damage occurred in the cementitious materials first, and then fracture of the red sandstone as a whole resulted.

Using interpolation and correlation to evaluate the quality of cement composites exposed to a thermally aggressive environment

Introduction. The article addresses the quality evaluation of cement composites after their exposure to the atmospheric environment that features a rapid change in positive and negative temperatures. The article has a numerical assessment of the quality of cement composites. The quality assessment method encompasses the Spearman’s rank correlation, the coefficient of determination, and the adjustment ratio. Materials and methods. Testable cement composites are the compositions numbered from one to eight. They differ in the concentration of various additives, including superplasticizers and aggregates. Testable compositions were exposed to cyclic changes in positive and negative temperatures, and four of their properties were checked in the points of control on Day 0, Day 15, and Day 45. Linear interpolation was used to expand the data array. Changes in the properties of composites were compared with the benchmark values; the Spearman’s rank correlation and the coefficient of determination were calculated. Moreover, arrays of interpolated values were reduced to relative units to calculate the adjustment ratios. Entry values were employed to develop the evaluation metrics and assess the quality of cement composites. Results. The proposed numerical metrics is used to rank the testable samples and identify the best compositions. Library functions and transformations, available in the MATLAB system, are applied to each action, which can be implemented in nearly any software programming language. Conclusions. The proposed method of heuristic quality evaluation of cement composites may be applied to the cases when testable samples are exposed to versatile adverse and aggressive operating conditions.

Study of the influence of negative temperatures on biomass accumulation and cell viability of callus and cell aggregates of Rhodiola rosea L.

As a result of determining the resistance to the action of different negative temperatures of callus cells and cellular aggregates of Rhodiola rosea, it was shown that after exposure of callus to -8oC, only 52% of the cells survived. In the case of exposing the experimental variant of R. rosea cell aggregates to -8oC, the value of cell viability was 68%. This suggests that the frost tolerance of cell aggregates is higher than that of callus cells, which indicates that the stress factor to be tolerated is higher, the lower the de-gree of organization of the biological system.

Epigenetic in heritance and selection of heat and frost resistant wheat (Triticum aestivum L.) Genotypes

The primary resistance and plasticity of the response to shock with negative temperatures (SNT) or heat shock (HS) of different winter wheat genotypes grown in Ukraine and then reproduced in Moldo-va are determined. The values of the mentioned parameters specifically varied depended on the genotype specificity and conditions of seeds reproduction. Thus, data support the hypothesis about the specificity of trans-generational inheritance of wheat genotypes adaptations to extreme temperatures. Furthermore, the correlation coefficient between the resistance SNT value to HS and inversed value (HS/SNT) ratio may indicate the epigenetically inherited effects.

Activitatea proceselor FS II şi REDOX la frunzele de cimişir de vârste diferite ca indicatori ai rezistenţei lor la şocul сu temperaturi negative

The resistance of annual and biennial leaves of boxwood to the effects of negative temperatures has been studied. The parameters of PS II activity and the parameters of the redox potential were deter-mined in different periods after exposure to shock at temperatures of -5°C, -10°C , -15°C and -20°C. It was shown that the stability and ability to recover from damage caused by shock at different temperatures, were higher in annual leaves compared to biennial leaves.