M. Bocian

Identification of Nonlinear Damping Using Energy Balance Method with Random Pulse Excitation

This paper presents the application of the energy balance equation to the identification of nonlinear damping in complex multi-degree-of-freedom systems subjected to excitations in the form of a random series of impulses. It is proven that the proposed procedure makes it possible to determine damping characteristics irrespective of the form of purely elastic interactions and the occurrence of the so-called mixed term. The procedure was verified experimentally, using a system with two degrees of freedom. The effect of the intensity with which impulses appear (pulse rate) on the quality of the obtained results is examined. The presented method can be applied to investigate the damping of vibrations of selected elastodamping elements in real vibrating systems.

Analysis of Material Punching Including a Rotational Speed of the Projectile

Materials used for the construction of ballistic shields are characterized by a variety of behaviours under the influence of external loads. Ballistic impact (by a bullet) in armour (ballistic shield) is an example of the phenomena that could be considered in the category of a dynamic load caused by the strike of the mass. Computer simulations are commonly used in such situations. It is especially important to adopt a proper model of the behaviour of the material. This paper presents the results obtained by simulating free 3D points and using the application developed by the authors for the purpose of this research. The made calculations include the translational motion and rotary motion of the projectile as well as the stiffness of the material, the damping of the material, friction at the points of contacting surfaces, viscous friction and plastic deformation (the material beyond the plastic yield point is perfectly plastic). The results of simulations were validated with experimental research.

Test Stand and Method for Determination of the Usefulness of the Magnetorheological Composites in Active Suspension Systems

Abstract. The paper presents test stand designed for testing magnetorheological composites (MRC) under dynamic loading, together with the method for obtaining damping characteristics of the tested material. The test stand is based on Single-Degree-Of-Freedom system excited with use of modal hammer. The MRC is stimulated with use of double circular dipolar Halbach array based on neodymium magnets. The analysis of the experimental results is performed with use of the half-power method and the circle-fit method. results presented in the paper show usefulness of the test stand and of the method for obtaining damping parameters of the MRC. The results present change in the damping character of the material under variable magnetic field.

DESIGN CONCEPT OF TEST STAND FOR DETERMINING PROPERTIES OF MAGNETORHEOLOGICAL ELASTOMERS

Abstract Magnetorheological elastomers (MRE) are “SMART” materials that change their mechanical properties under influence of magnetic field. Thanks to that ability it is possible to create adaptive vibration dampers based on the MRE. To test vibration damping abilities of this material special test stand is required. This article presents design concept for such test stand with several options of testing.

The Method of Determining Certain Parameters of Energy Absorption in Materials Under Complex Dynamic Excitations

The paper presents the method to identify the dissipative properties of the materials with a clear hysteresis loop under the quasi-static loads. Because of the fact that for low values of velocity, the resisting forces related to the speed are minimal, it is not possible to determine these forces as the functions of velocity in the quasi-static deformations. It results in the need to develop such methods for identification, which use the responses of the tested system to the cyclic loading with a high frequency. This paper presents such a method. Its application may be useful in the area of constructing the effective and modern ballistic shields.

INFULENCE OF RECRYSTALLIZATION ON DAMPING PROPERTIES OF ALLOY Fe75Zr4Ti3B17Cu1

Internal structure of metal alloys has strong influence on their mechanical properties. It can be observed even during conventional heat treatment of metals [3, 4, 6]. Nowadays advanced technologies combined with specific metal alloys allow us to obtain amorphous structure, under condition cooling rate exceeds the limits for specific alloy [1]. Such structure should poses interesting mechanical properties [5]. Paper is conAbstract:

Calculations with the Finite Element Method During the Design Ballistic Armour

For protection against projectiles with higher impact speed (up to 1000 m/s) a type of a ballistic sandwich shield can be used—which is a monolithic combination of ballistic laminates with additional materials, typically hard layers made of ceramic in the form of plates or spheres of oxides, carbides and nitrides. The authors of this paper, by using FEM to optimize defined material sets to fire the cartridge 7.62 × 54R mm, give a range of results which are compared with tests of ballistic firing on the shooting range.