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  • Experimental qualification for compressive properties of unidirectional carbon-fiber reinforced composite

    Most important information about an environmental resistance (moisture, cyclic change of the temperature, ultraviolet radiation) of high strength composite material can be received at the compressive mechanical testing. The reinforcing fibers that are oriented along the specimens axis (or are oriented on the small angles relative to this axis) carry the main tencile loading. Conversely, at the compression the elastic and strength properties of the material, basically depend on the matrix properties. The specimens for mechanical testing are usually manufactured as relatively thin rectangular plates by winding or laying-up that corresponds to the ready composite parts. In order to eliminate buckling of the specimen at compressive test, its working length must be very shortened. So, this working part is unavalable for the extensometer instalaltion, and compressive strain of the specimen can be determined by the stroke of crosshead only. This stroke is a sum of very small contraction of the specimen and crosshead displacement due to elastic deformation of the testing machine. We determined the dependence of elastic deformation of the testing machine at the preliminary testing to exclude this deformation from the testing data. We present the features of the compressive testings and their numerical processing at the study of high strength GFRPs, and also the character of composite fracture studied by means of the scanning electron microscopy.

    Keywords: Polymeric composite materials, multilayered composites, environmental resistance, experimental technique, compressive testing, scanning electron microscopy

  • Comparative analysis of porous piezoceramics modelling by effective moduli and finite element methods with experimental data

    The results of computational experiments to determine the characteristics of the porous piezoelectric ceramics based on the methodology, including the effective modules method, simulations of representative volumes on a simple random method and the method of Witten-Sander, finite element method to solve static piezoelectric problems for heterogeneous composite media and the accounting of inhomogeneous polarization near the pores are presented. A comparison of the results of computer simulation with the known experimental data for the porous material PZT-4 and its analogs is realized. It is concluded that the accounting of inhomogeneous polarization in the vicinity of porous provide the better agreement between numerical results and large number of known experimental data. Thus, for most effective constants the smallest errors are obtained for a representative volume of the porous piezoelectric material, constructed by Witten-Sander method.

    Keywords: piezocomposite, porous piezoelectric ceramics, inhomogeneous polarization, mathematical modelling, models of representative volumes, finite element method, effective moduli