In the metal sheet-forming process, localised thinning immediately before failure is a rapid and intensive process. This paper discusses such intensive thinning and elaborates on the importance of the hardening behaviour at large plastic strains. In particular, for the reliable prediction of intensive sheet-thinning evolution, an accurate determination of the hardening behaviour is important; however, the identification cannot be performed using classical uniaxial tests owing to necking. Therefore, this paper describes the development of a new shear specimen that provides enough data for hardening curve characterisation up to an equivalent plastic strain value that is twice that in a tensile test. After characterisation, based on the inverse identification procedure, two verification cases confirmed the identified data. Both cases are typically considered stochastic processes, and they exhibit a large scatter in the experimental testing: Necking evolution in a uniaxial case and localisation evolution of a notched specimen. However, the verification analyses confirm that both processes are deterministic, and a good prediction could be reached exclusively by a precise identification of the hardening behaviour at large plastic strains.

By the computer-aided method of material characterization many complex identification cases, where classic experimental–analytical methods of physical properties identification fail, can be successfully solved. Such an example is the standard tensile test of a flat steel sample, where the yield curve cannot be identified after the occurrence of the necking phenomenon. Yet, in deep drawing of metal sheets, strains and stresses beyond the limits derived by classic analytic expressions upon the tensile test measurements are often met. In order to enable physically objective numerical simulations of those processes, reliable material properties data must be provided. To cope with the problem of the extended yield curve identification, a special combined experimental/numerical technique has been developed. The technique relies on the comparison between the real material response, measured by the standard tensile test, and the response, obtained from a numerical simulation of the same test under assumption of a prescribed material behaviour. By proper tuning of some characteristic parameters of this tentative material behaviour law, the numerical response can be drawn close to the measured one. For this purpose a special numerical approach, based on mathematical optimization methods is employed.

Summary An inverse identification method for characterization of wood sorptive properties is presented. The method relies on a computer simulation of a real experiment, in our case a desorption experiment, where spruce heartwood samples were dried from 27% to 8% moisture content. Three samples, distinguished by the respective moisture flow pattern through the specimen, were investigated. A computer aided material characterization using the so-called inverse problem identification method was performed on the measurements. The solution of the specified inverse problem enabled us to estimate the moisture diffusion coefficients of wood and to determine the moisture content field in the sample simultaneously. The method is first verified on two simple cases of uniaxial moisture flow, and then is used to characterize the diffusion coefficients on a biaxial moisture flow sample. In the latter case some salient features of the proposed method are exhibited.

This paper focuses on transverse moisture transport in spruce wood caused by changing climate conditions. Aiming to determine the space and time dependent moisture content (MC) field in the cross section of the sample during the drying process, at first a series of measurements on small clear specimens of spruce wood were carried out and secondly a computer simulation of the drying experiment was done. The MC was measured by the destructive gravimetric method. The measurement was repeated several times for consecutive time intervals during the drying period. In a computer aided material characterization, a so-called inverse problem identification method is used. The solution of the inverse problem enabled us to estimate the moisture diffusion coefficients and to simultaneously determine the MC field.

The mechano-sorptive effect (MSE) can be classified as a veryinteresting, but not yet completely explained phenomenon of woodbehaviour. We therefore decided to try to discover its most relevantmechanisms, by conducting two independent series of measurements:accurate measurements of bending deflections on small, clear specimensof spruce wood in changeable climate conditions; and average moisturecontent (MC) in three parts of the cross-section of unloaded dummysamples. The paper emphasises on the sorptive part of MSE. A computersimulation of the wetting experiment is done to determine the space andtime-dependent MC field in the cross-section of the sample. Using aso-called inverse problem identification method, where the equivalenceof the computed and measured responses of the numerical model and realsample is imposed, we identified unknown material properties. Thesolution of the inverse problem enabled us simultaneously to estimatethe moisture diffusion coefficients and to determine the MC field. Twokinds of boundary conditions were used in simulations. To estimate themagnitude of sorption stresses a numerical analysis using Finite ElementMethod (FEM) was done. The sorptive stresses resulting from thenonhomogeneous MC distribution in the sample were obtained. The decisivefactor is the gradient of moisture content and resulting sorptivestresses must be taken into account because their magnitude is of thesame order as the load induced bending stresses. Our experiments and thecalculations following enabled us to conclude that the reason for MSbehaviour could be the simultaneous action of permanent load stressesand the transient triaxial sorptive stress state.

Wood is a natural product of biological origin. It is a low density, cellular polymer composite with quite complex structure. Unlike most materials used in engineering wood possesses strong anisotropy that must be recognised at several levels of material organisation. Particular types of anisotropy can be identified within a layer of the woody cell, in the cell wall as a whole, in the entire cell, in an aggregate of cells, and finally in an aggregation of several types of woody tissue. For deeper understanding of the mechanical behaviour of wood a good knowledge of each constituent in a particular level of material organisation as well as relations between the levels is required. In numerical model, which is based on Finite Element method, two structural levels are used. On the first level a cell wall is taken into consideration, on the second one a typical softwood structure is presented as a assemblage of early- and latewood cells.

The modem material science is largely engaged in processing of advanced materials. Since the behaviour of such materials is usually characterized by complex relationships an efficient material characterization is demanded, along with the material processing. Accordingly, special experimental techniques and material identification methods are developed. This paper considers the characterization of thermal properties of an anisotropic solid, as determined by a numerical solution of the corresponding inverse problem. In particular, a transient heat transfer in an orthotropic cylindrical specimen is considered.