Based on a combination of hexagonal honeycomb and re-entrant honeycomb cells, the concept of novel hybrid cell structures was developed. Experimental studies and numerical analyses of the behaviour of the analysed structures under in-plane compression in two compression directions were carried out. Explicit finite element analyses with an explicit integration scheme, incorporating plastic deformation and ductile damage evolution models, were employed to analyse the entire deformation process, including plastic and damage stages. Good agreement was obtained between the results of the numerical analyses and the experimental studies.

This article presents methods of planning unmanned aerial vehicle (UAV) missions in which individual platforms work together during the reconnaissance of objects located within a terrain. The planning problem concerns determining the flight routes of a swarm, where each UAV has the ability to recognize an object using a specific type of sensor. The experiments described in this article were carried out for drone formation; one drone works as a swarm information hub and exchanges information with the ground control station (GCS). Numerical models for mission planning are presented, which take into account the important constraints, simplifying the description of the mission without too much risk of losing the platforms. Several types of objective functions were used to optimize swarm flight paths. The mission models are presented in the form of mixed integer linear programming problems (MILPs). The experiments were carried out on a terrain model built on the basis of graph and network theory. The method of building a network on which the route plan of a drone swarm is determined is precisely presented. Particular attention was paid to the description of ways to minimize the size of the network on which the swarm mission is planned. The presented methods for building a terrain model allow for solving the optimization problem using integer programming tasks.

This article presents the results of dynamic tests of sandstone samples differing in strength parameters and porosity, which were carried out with the use of the split Hopkinson pressure bar (SHPB). For this study, three types of sandstones were considered: two from the region of India (Kandla Grey and Apricot Pink) and one from Central Europe (Barwald). The strength parameters of the samples were identified in static tests (UCS, BTS tests), whereas the porosity was measured using computed tomography. The performed scanning allowed the volume of the pores and their distribution in the samples to be identified. Dynamic tests involved loading the cylindrical samples with a diameter of 23 m in the range of high strain rates, i.e., ε˙ = 102 ÷ 103/s, using the SHPB (split Hopkinson pressure bar) method. Samples with three different values of slenderness were used for testing (L/D = 1, 0.75 and 0.5). Based on the dynamic characteristics of the samples, the maximum dynamic stresses, Dynamic Increase Factor (DIF) and the amount of energy absorbed by the samples were determined. The conducted research indicates a significant impact of material porosity on the amount of dissipated energy under conditions of high strain rates. The research indicates that the values of this parameter for Apricot Pink and Kandla Grey sandstones (slenderness L/D = ¾ and L/D = ½) are similar, although the uniaxial compressive strength (UCS) of Kandla Grey sandstone is approximately 60% higher than that of Apricot Pink sandstone. As a result of the sample destruction process, various forms of sample destruction were obtained. The performed grain analysis indicates a significant increase in the smallest fraction (<0.5 mm) in the case of the sandstone with the highest porosity (Apricot Pink—55% of mass outcome) in comparison to the sandstone with the lowest porosity (Kandla Grey—12% of mass outcome).

Abstract Elastomers are widely used in many industries. Their use requires thorough knowledge of their strength and stiffness parameters over a wide temperature range. However, determination of the parameters of such materials is still a challenge. Therefore, the paper presents research methodology allowing determination of the properties of rubber-like materials in a wide range of stretch and temperatures (from +50°C to −25°C) by using the example of styrene-butadiene rubber (SBR) and natural rubber (NR) elastomers. Additionally, two blends, chloroprene rubber/nitrile-butadiene rubber (CR/NBR) and NR/SBR blends, were also considered. Based on physical premises, a polynomial and Arruda–Boyce hyperelastic constitutive models parameters were determined using two different methods, namely curve-fitting and the successive response surface method.

The paper presents an elemental description and methodology of tests that take intoaccount the effect of high strain rate on materials strength parameters. The article describes suchtesting methodology as: Taylor test, split Hopkinson pressure bar method, and expanding ring test todetermine the dynamic properties of materials.Keywords: Taylor test, expanding ring test, split Hopkinson pressure bar, dynamic behaviour of materials

The experience of recent military missions clearly shows the importance of protecting vehicles and the people they carry from mines and IEDs. This protection can be achieved in many ways, using both active and passive solutions. One of the most popular solutions is using energy deflectors, which, thanks to their appropriately selected shape, can dissipate the energy from the detonation of an explosive charge, thus reducing the blast wave loading on the protected structure. The article presents the research results on two innovative groups of deflectors-double-bend and semi-spherical, characterized by a better ability to disperse energy than traditionally used V-shaped deflectors. Several possible geometric shapes differing in critical dimensions were selected, and both experimental studies and numerical analyses were carried out. A ballistic pendulum was used to measure individual deflectors' performances. The tests proved the tested solutions' increased effectiveness compared with V-shaped deflectors.

This study presents the effect of the thermo-oxidative ageing conditions on the properties of polyoxymethylene copolymer (POM-C), acrylonitrile–butadiene–styrene (ABS), and polycarbonate (PC). For this purpose, the process of accelerated aging of these materials was carried out for a period of 21 to 56 days at an elevated temperature of 140 °C. Then, the effect of this process on the thermal properties of these materials was determined using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Special attention was paid to the change in glass transition temperature. To determine the change in mechanical properties, a standard tensile test was performed. Additionally, the microstructure of the materials studied was analysed using a scanning electron microscope. Research carried out using DMA, DSC and tensile tests at different temperatures showed that generally in the case of POM-C there is no change in the material properties, however, a slight improvement can be noted. In the case of ABS, during the first 21 days of aging, there were large changes in all the material properties studied. For polycarbonate, the DMA analysis showed that there is no change in the glass transition temperature of both aged and unaged samples.

Hyperelastic materials are widely used in many industries. Their use requires thorough knowledge of their strength parameters over a wide temperature range. However, determination of the parameters of hyperelastic materials is still a challenge. Therefore, the paper presents research methodology allowing determination of the properties of hyperelastic materials in a wide range of stretch and temperatures (from +50 degrees C to -25 degrees C) on the example of NBR (nitrile butadiene rubber) and CR (chloroprene rubber) elastomers. On the basis of physical premises, a hyperelastic constitutive model was also modified through introducing an explicit dependence of strain energy on temperature, allowing an accurate reflection of the properties of the tested materials. The material parameters of the adopted strain energy functions for the NBR and CR were determined with R2 not less than 0.999.

The influence of the thermo-oxidative aging semi-crystalline polyethylene terephthalate process on the thermal and mechanical properties was analysed in the article. For this purpose, PET was aged at 140 °C for 21, 35 and 56 days. The research showed that as a result of aging, the amount of the crystalline phase increases by about 8%, which translates into the properties of the aged material. The glass transition and melt temperature of lamellar crystals formed during first and second crystallisation increase with aging. The mechanical properties of the material were analysed in the temperature range of 25 to 75 °C. The tests were showing an increase in Young’s modulus and a decrease in elongation at the break as a result of aging. This phenomenon was particularly visible during tests at 75 °C and during the morphological observation of the fracture surface, where the fracture character of the material changes from ductile to brittle. In the case of the material aged for the longest time, the temperature has a negligible influence on the elongation at break.

The mechanical properties and microstructure evolution caused by dynamic loads of 316L stainless steel, fabricated using the Laser Engineered Net Shaping (LENS) technique and hot forging method were studied. Full-density samples, without cracks made of 316L stainless steel alloy powder by using the LENS technique, are characterized by an untypical bi-modal microstructure consisting of macro-grains, which form sub-grains with a similar crystallographic orientation. Wrought stainless steel 316L has an initial equiaxed and one-phase structure, which is formed by austenite grains. The electron backscattered diffraction (EBSD) technique was used to illustrate changes in the microstructure of SS316L after it was subjected to dynamic loads, and it was revealed that for both samples, the grain refinement increases as the deformation rate increases. However, in the case of SS316L samples made by LENS, the share of low-angle boundaries (sub-grains) decreases, and the share of high-angle boundaries (grains of austenite) increases. Dynamically deformed wrought SS316L is characterized by the reverse trend: a decrease in the share of high-angle boundaries and an increase in the share of low-angle boundaries. Moreover, additively manufactured SS316L is characterized by lower plastic flow stresses compared with hot-forged steel, which is caused by the finer microstructure of wrought samples relative to that of additive samples. In the case of additively manufactured 316L steel samples subjected to a dynamic load, plastic deformation occurs predominantly through dislocation slip, in contrast to the wrought samples, in which the dominant mechanism of deformation is twinning, which is favored by a high deformation speed and low stacking fault energy (SFE) for austenite.

The effect of using a pulse shaper technique, such as rounding a striker or applying a pulse shaper on the signals recorded with the split Hopkinson pressure bar (SHPB) technique, when the striker and the input bar are in an imperfect position, was investigated. Two of the most common cases have been analyzed: an offset of the symmetry axes of the striker and the input bar; and an inclination angle between the striker and the input bar. LS-Dyna software was used to examine this problem numerically. The inclination angle imperfection has a significant impact on signal disturbances, whereas the use of a rounded striker significantly affects the limitation of the vibration flexural modes. In all considered cases, a slight imperfection causes a reduction in the high-frequency Pochhammer–Chree oscillations.

The study presents an evaluation of applicability and accuracy of Gurney equations when used in several different setups of inertial layers accelerated by exploding charges. Both solid and fragmented inertial layers were considered. The evaluation was carried out based on numerical analysis, during which it was observed that the fragmentations bears no effect on the velocity value sand neither do dimensions of symmetrical layers. However, the layer thickness has a significant effect on these values.

The split Hopkinson pressure bar method for testing the materials under high speed dynamic load, both in compressive and tensile versions, shows undesirable, interfering signals known as Pochhammer-Chree oscillations. The paper presents a numerical study in which pulse shapers made of different materials (lead, copper and rubber) were tested in order to verify their impact on the incident impulse shape in the tensile split Hopkinson pressure bar test. It was found that lead and rubber pulse shapers significantly reduced the Pochhammer-Chree oscillations, while only slightly increased the pulse rise time.

The results of experimental and numerical analysis of the influence of the non-axisymmetric pulse shaper position on recorded wave signals in the split Hopkinson pressure bar experiment are presented. The paper focuses attention on the problem of wave signal disturbances caused by a bending wave resulting from non-axisymmetric pulse shaper positions and, moreover, different shaper thickness, striker impact velocities and Wheatstone bridge configurations. The obtained results of analyses indicate that the effect of the non-axisymmetric pulse shaper position may be neglected if deviation from the bar axis does not exceed 20%.

The problem of specimen geometry imperfections for ductile materials in the split Hopkinson pressure bar (SHPB) experiments is presented in this paper. Impact of five types of imperfections most frequently encountered in experimental practice and the resulting errors in the position of the specimen in relation to the axis of the bars on the reflected and the transmitted wave profile and on the shape of the stress-strain curve was analysed. The problem was considered based on numerical analyses using a finite element method. It was found that imperfections disturb mainly the beginning and end portions of the reflected and transmitted pulses, which is reflected in the stress-strain curve profile. However, for ductile materials, influence of specimen geometrical imperfections is small, and therefore the SHPB experiments results can be considered reliable from a practical point of view. In the case of all the analysed imperfections, it can be assumed that for imperfection angles α ≤ 0.3°, errors in determination of the stress-strain curves can be omitted.

The problem of ensuring both nominal and true constant strain rate in the split Hopkinson pressure bar experiment was considered through the application of the conical striker for 316L steel specimen. The experimentally confirmed results from numerical analyses indicate that the application of a conical striker with the determined apex angle for the given experimental conditions is a good method for achieving a constant value of the strain rate. Moreover, the results of the study showed that the value of the striker apex angle has the greatest influence on the mechanical response of the specimen material. In turn, the impact velocity slightly affects the value of the striker apex angle.

The results of the experimental and numerical analysis of an influence of the non-axisymmetric pulse shaper position on the recorded wave signals in the split Hopkinson pressure bar experiment are presented. The paper focuses the attention on the problem of wave signal disturbances caused by a bending wave resulting from non-axisymmetric pulse shaper positions and, moreover, different shaper thickness, striker impact velocities and Wheatstone bridge configurations. The obtained results of analyses indicate that the effect of the non-axisymmetric pulse shaper position may be neglected if deviation from the bar axis does not exceed 20%.

Results of numerical analysis of the influence of pulse shaper geometry on wave signals in the split Hopkinson pressure bar experiment are presented. Five pulse shapers, i.e. square, ring, cross, star and disk ones have been analysed. It has been assumed that the disc pulse shaper is the reference geometry to assess the remaining types of pulse shapers. The results of numerical analyses have shown that pulse shapers with shapes different than disk are highly capable of minimizing high-frequency Pochhammer-Chree oscillations and, thus, reduce dispersion of waves propagating in the bar. The greatest damping ability has been observed while using the ring pulse shaper at both low and high impact velocities of the striker.

A significant influence of explosive charge geometry is frequently observed during experimental testing. In this paper, the effect of explosive charge shape, along with its material properties, on the generated blast waves is studied. The FEM analysis was conducted for six different explosive materials and three different cylindrical shapes, with geometrical proportions of length L to diameter D varying between 2, 1 and 0.25 and constant charge mass. We found that the blast wave generated by detonation is susceptible to shape changes. However, the different explosive materials were influenced by the charge shape in almost the same way, with only insignificant differences resulting from the material properties.

An accuracy problem of strain measurement at compression split Hopkinson compression bar experiments with a splitting-beam laser extensometer was considered. The splitting-beam laser extensometer technique was developed by Nie et al. to measure strain of a specimen during its tension under a high strain rate loading condition. This novel concept was an inspiration for the authors to develop own laser extensometer system, which allows for simultaneous and independent measurement of displacement of bar ends between which a compressed material specimen is placed. In order to assess a metrological properly of this measuring system, a wide range of high strain rate experiments were performed, including tests with various sample materials (Al 5251, Cu OFF) with different rate of strain, and with the use of two bars material. A high accuracy of the developed laser extensometer was found in measurement of specimen strain, for which uncertainty is not greater than 0.1% and, for a typical specimen dimension, the maximum permissible error is 4.5 mu m.