Cezary Ajdukiewicz

Verification of Plasticity Theory with Isotropic Hardening and Additive Decomposition of Left Deformation Tensor Using Digital Image Correlation System

The development of measurement methods, and in particular digital image correlation (DIC) systems, which are designed to measure of entire displacements and deformations fields, opens up new areas of research. In general, the materials constitutive relations are formulated in such a way that material parameters could be determined with relatively simple experimental tests carried out on samples with uniform (approximately) stress and strain fields. Then it is possible to apply them to complex boundary value problems formulated e.g. in the small or large deformation theories. The application of DIC allows to verify the accuracy of their predictions by comparing the results of the experiment with solutions to boundary value problems obtained using the finite element method (FEM).

Experimental Study on Mechanical Properties of Polyethylene HDPE in Conditions of Hydraulic Impact Simulation

Experimental research on mechanical properties of hardened polyethylene HDPE, is developed in the paper. The conditions of hydraulic impact simulation, caused by sudden opening or closing of the valve or by working pomp were adopted in the model. The created in such conditions shock wave moves at a high speed causing additional dangerous dynamic loadings, which lead to faster pipe wear process. The aim of this study is to determine Youngs modulus of the pipe material in the cyclic load conditions. The assumed amplitude and frequency of the applied load relates to variation of the impact wave pressure also the speed of the disturbances propagation are taken from experimental measurement of the real water hammer. The measured Youngs modulus is higher than that obtained from a static tensile test. The presented study arises from the need to verify the actual value of pipe material mechanical properties, i.e. longitudinal stiffness, for designing of hydraulic pipes under conditions of water hammer.