Paweł Bogusz

Experimental investigations of double multi - leaf spring subjected to impact load

The article deals with experimental investigations of a prototype double multi-leaf spring, compound of a fourleaf main spring and a double-leaf supporting spring subjected to an impact test. In real conditions of car movement (e.g. curb, bump), dynamic oscillating loads, which generate dynamic stress in a car suspension affecting other elements of the car, occur. Consequently, effects of coupled oscillations having a great impact on comfort of a driver and passengers can be observed. The research was conducted in the Laboratory of Material and Construction Strength Department of Mechanics and Applied Computer Science (DMACS) in the Faculty of Mechanical Engineering of Military University of Technology. The experiment was carried out on an original construction of a spring impact hammer developed in DMACS. Energy of the impact was set up by changing mass of a beam with beater and beam dropping height. The results were presented in the form of table summaries, time-dependent load and displacement graphs. The methodology of the research presented in the paper and a set of measuring equipment can be utilized to evaluate load and vibrations of any multi-leaf spring under impact load with given energy. The experimental results obtained from the test are supposed to be used to verify and develop FEM model describing a spring under impact load and oscillations.

EVALUATION OF TRUE STRESS IN ENGINEERING MATERIALS USING OPTICAL DEFORMATION MEASUREMENT METHODS

The aim of the paper is to evaluate a method of determining true stress in the steel sample subjected to static axial tensile on a universal testing machine. The tensile specimens were made of steel ST3, which was chosen because of its relatively high plastic deformations. Strain measurement was performed using traditional extensometers and additionally a non-contact optical deformation measuring system. Material properties were obtain by the extensometer measurements. The optical equipment registered the investigated sample through the optical system composed of two cameras and calculated a three-dimensional model of the material deformation in time. Displacement fields in axial and radial directions were determined with Digital Image Correlation method (DIC). Then the logarithmic axial strain map and radius shrinkage map in the area of the neck were obtained. Characteristic dimensions of the neck: curvature and width were also measured. It allowed determination of cross-section area changes in the real time, and in the result, calculation of actual true stress in the material during failure process. In this case Bridgman’s and other scientists’ formulas of stress distribution in the neck were applied. A numerical model, where material properties of finite elements were described by the Johnson-Cooke material model, was developed in LS-PrePost software. The FEM model was computed in LS-DYNA solver. The output tensile curve and neck curvature radius were compared with relevant data obtained from the optical measuring system.

Proving Ground Tests of Selected Energy Absorbing Structure Variants Under a Shock Wave Load

Military actions conducted in the XXI century in Iraq and Afghanistan have shown that the tactical and technical solutions applied so far are not sufficiently effective in wars, in which one side of the conflict has a significant advantage over the other. The most effective weapon employed in the strategy of combat engagements are Improvised Explosive Devices, so called IEDs. They are most frequently placed on roads travelled by allied forces vehicle convoys. According to the statistics, they were the cause of death of approximately 40% of all soldiers killed when fighting in Afghanistan and Iraq between 2003 and 2011. In order to increase the safety of a vehicle’s crew against the shock wave of a mine and IED explosion, An additional layer in the form of a protective panel will be aimed at decreasing the inertial force affecting the vehicle’s passenger during an AT mine or IED explosion, which is the primary cause of injuries sustained by vehicle personnel.

Crushing Behaviour of the PVC Foam Loaded with Beaters of Various Shapes

Abstract Statistically, at least 50% of all injuries experienced by police officers in the line of duty are due to assaults with blunt objects. Therefore, vests used by the police should provide not only good ballistic resistance, but also good protection against such threats. Foamed materials are possible to be used for body protectors or inserts of protective clothes. The effects of dynamic impact with beaters of different shapes onto behaviour of polymeric foamed material were determined. There were used four types of beaters: flat, cylindrical, edgy and cornered. Strikes with blunt objects such as a flat board, baseball bat, edgy brick, pavement brick or a sharp stone, to which a protective ware can be subjected, were simulated. The impact load was applied to the rectangular specimens, made of polyvinyl chloride foam, with a usage of a drop hammer. Plots of force versus compression for all the tested samples were obtained and analysed. The effects of impacts with beaters of different shapes onto foamed material samples were presented. A shape of the blunt object significantly influences crushing behaviour of the foamed material. The impact energy of a flat beater is absorbed effectively on a short distance, since it is spread on a relatively large surface. The cylindrical and edgy beaters did not cause fragmentation of the samples, however, on the upper surfaces of the samples, permanent deformations mapping the beaters shapes as well as some cracks occurred. An impact with a sharp object, for example, a cornered beater is very difficult to be neutralized by the foam material, because it is cumulated on a small area.

Experimental and numerical investigation of energy absorption elastomer panel with honeycomb structure

The paper presents a prototype design of elastomer energy absorbing panel made in a shape of honeycomb structure. The proposed panel was installed in a protected plate and tested on a specially designed test stand, where a shock wave from a small explosive charge was applied. The elastomer honeycomb structure was compared with a version of the panel made of solid elastomer materials, the same as used in the honeycomb structure and also with a protected plate without any panels. During the research, acceleration in the middle part of each investigated protected plate was recorded. The protected plates were scanned after the tests in order to measure their maximum deformation. Acceleration graphs and maximum deflections of all three considered structures were compared. The obtained results were used to validate numerical models of the designed structures and the test stand. A discreet model of the test stand and models of elastomer panels were developed with HyperMesh FEM software using shell and solid elements. The materials were described using a tabulated Johnson-Cook model and constitutive model for the rubber parts; all available in the material library of Ls-Dyna software. The blast loading was simulated using the CONWEP method. This model generates a boundary condition, based on the experimental data and TNT equivalent mass, which substitutes the wave propagation with a pressure. Finally, the experimental results of acceleration and deformation of the plates were compared with the corresponding results of the numerical analyses carried out using finite element method. The numerical models can be utilised in the future research as a virtual range stand. The developed elastomer honeycomb structure can be modified to meet various requirements of ballistic protection levels, by applying elastomer of different stiffness or optimizing shape and dimensions of the honeycomb structure.

Experimental evaluation of energy absorbing properties of selected elastomer materials

The paper presents identifying studies of mechanical properties of the selected materials from the group of elastomers including Asmathane (65 ShA), Easyprene FPS (30 ShA), Biresin (U1305). The tests were carried out at the Laboratory of Strength of Materials, the Department of Mechanics and Applied Computer Science, with the use of an especially designed stand for testing the energy absorption of materials. The research aims were to determine the basic properties and characteristics of the selected materials as well as to compare them and identify the material with the best energy-absorbing characteristics. For a single load-unload cycle, applied dynamically, the hysteresis loops were recorded. Energy-absorption of individual materials and maximum strength were determined. During the experimental test, a fast speed camera was used for accurately register the progress performance of the test. The pictures of the dynamic tests of materials behaviour are shown. The curves of the tested materials are compared in the graphs. The resulting data will help to create constitutive models of the tested materials, which in the next stages of the project will be used in numerical studies on the impact of detonation on the designed protective panel.

Experimental and numerical tests of separated side lock of intermodal wagon

The object of the paper is to investigate the strenght of a separated subsystem of a wagon for transport of trucks semitrailers. The wagon designed in the Department of Mechanics and Applied Computer Science, Military University of Technology, allows easy and independent loading, transport and unloading without any special equipment or additional platform infrastructure. It is possible to utilize it for transport of various vehicles types such as tractors, cars, semitrailers, containers, heavy equipment. The tests presented in the paper concern a wagon separated construction element – a side lock. It is a key subsystem of the platform allowing transfer of its loads generated in the transport position (a wagon ready to go) to the form of longitudinal forces operating in the sides of the structure. The locks are simultaneously the most strained parts of the wagon. There were carried out the numerical analyses and experimental studies of a single lock were carried out. Owing to the application of Aramis non-contact optical system of strains measurement, the lock deformations as well as the areas of the minimum and maximum main deformations were defined.