Zbigniew Pozorski

Damage detection using thermal experiments and wavelet transformation

Damage detection using the discrete wavelet transformation (DWT) of temperature field recorded on the surface of a plate structure is discussed. Defects in the form of voids and inclusions of various magnitude are considered. Computer-simulated experiments including the ones accounting for white noise and real thermal experiments are applied. Transient heat transfer problems are analysed. The efficiency of DWT in damage detection is studied by way of a number of examples. Haar, Daubechies 4, 6 and 8 wavelets in 1D and 2D DWT are used. The usefulness of the Lipschitz exponent evaluated with the use of DWT is discussed. The issue of denoising the thermal response signals using the soft threshold shrinkage procedure is also taken up.

Damage detection using parameter dependent dynamic experiments and wavelet transformation

Abstract The paper deals with a class of problems, where localised damage is detected using static and dynamic tests. Response of a structure is analysed employing discrete wavelet transformation as a tool for signal processing. The localised damage in beam structures was modelled as bending stiffness reduction. The efficiency of static and dynamic tests is studied. The minimal number of experimental measurement data and the precision of measurements required for the successful damage localisation is discussed by several numerical examples.

Optimal Support System of Sandwich Panels

AbstractThis paper discusses self-supporting sandwich panels, which are used as wall and roof cladding. They consist of two external thin and flat facings and a thick soft core. The panels are subjected to mechanical and temperature actions. The aim of this paper was to find the optimal solution for supports of a multispan sandwich structure. The following support models were considered: rigid support and linear-elastic support, with or without an imposed limit of elastic deflection. The problem was formulated as a two-criterion optimization (i.e., the maximization of the load multiplier and the maximization of the allowable length of the span). The criteria were in mutual exclusion (i.e., the results of the optimization comprise a set of nondominated optimal solutions). It shows that the optimal choice of supporting conditions remarkably improves the capacity of thermally loaded sandwich panels used in civil engineering.

Experimental and numerical analysis of sandwich panels with hybrid core

The paper presents the experimental and numerical studies of sandwich panels with a hybrid core. The sandwich panel consists of external steel facings and a core, which is made of polyurethane foam or mineral wool or a combination of those two materials. The polyurethane foam material has a low weight and high thermal insulation properties, while the mineral wool material can provide high acoustic insulation and excellent fire resistance. Various proportions of the core materials are taken into account. It is assumed that a proper combination can provide the benefits of both materials. The structural behavior of a sandwich structure with a hybrid core is observed during laboratory tests. The failure mechanism is investigated in a four-point bending test. The material parameters of the core and facings are determined in standardized tests. The obtained parameters are used for FE simulations of the four-point bending tests. The criteria of damage initiation and propagation are defined in the interface layer of the numerical model. A satisfactory correlation between laboratory tests and numerical results is reported. Additionally, the sensitivity analysis of the numerical model response to the variation of the parameters of the interface is presented.

The comparison of numerical models of a sandwich panel in the context of the core deformations at the supports

The paper presents the problem of static structural behavior of sandwich panels at the supports. The panels have a soft core and correspond to typical structures applied in civil engineering. To analyze the problem, five different 3-D numerical models were created. The results were compared in the context of core compression and stress redistribution. The numerical solutions verify methods of evaluating the capacity of the sandwich panel that are known from the literature.

New insights into classical solutions of the local instability of the sandwich panels problem

The paper concerns the problem of local instability of thin facings of a sandwich panel. The classic analytical solutions are compared and examined. The Airy stress function is applied in the case of the state of plane stress and the state of plane strain. Wrinkling stress values are presented. The differences between the results obtained using the differential equations method and energy method are discussed. The relations between core strain energies are presented.

NUMERICAL ANALYSIS OF SANDWICH PANELS SUBJECTED TO POINT LOADS

The paper concerns the problem of static structura l behavior of sandwich panels. The panels are made of thin steel sheets and a thic k, but soft core. The effects of the impact of concentrated loads on the structural behavior of th e panels are discussed. Several different cases of concentrated loads were considered: load a cting in the plane of the panel, load perpendicular to the panel and the additional action o f c ncentrated bending moment. The loads are transferred to the panel by a small steel slab. The slab is attached to the facing of the panel. Described load cases correspond to situation s e countered in engineering practice. In order to analyze the issue, a 3-D numerical model w as used. Between the facing and the deformable core an interface layer was introduced, wh erein the criterion of damage initiation and damage propagation were defined. Different fail ure modes were taken into account. Due to the character of the problem, the geometrically nonlinear analysis and Riks’ method were applied. For each load case a failure load and extr me stresses leading to failure were determined. The differences in the obtained results w ere explained and the appropriate failure mechanisms were discussed. Analyzed sandwich panel h s fixed geometries, however, made observations are universal. The obtained results te nd to look more carefully at the problem of the impact of concentrated forces. This problem is particularly important in the case of sandwich panels, which due to its construction are very susceptible to local influence. Zbigniew Pozorski, Jolanta Pozorska

Numerical evaluation of wrinkling stress in sandwich panels

Sandwich panels have been for years used as structural and cladding elements. Characteristic feature of these structures is that important role is played by temperature actions, creep of the core and local instability of thin faces of the panel [2]. Proper estimation of these phenomena has become a challenging issue because of strong tendency to optimize technical parameters and costs.