Triple correlation for detection of damage-related nonlinearities in composite structures

Nonlinear effects in vibration responses are investigated for the undamaged composite plate and the composite plate with a delamination. The analysis is focused on higher harmonic generation in vibration responses for various excitation amplitude levels. This effect is investigated using the triple correlation technique. The dynamics of composite plate was modelled using two-dimensional finite elements and the classical lamination theory. The doubled-node approach was used to model delamination area. Mode shapes and natural frequencies were estimated based on numerical models. Next, the delamination divergence analysis was used to obtain relative displacements for delaminated plies. Experimental modal analysis test was carried out to verify the numerical models. The two strongest vibration modes as well as two vibration modes with the smallest and largest motion level of delaminated plies were selected for nonlinear vibration test. The Fisher criterion was employed to verify the effectiveness and confidence level of the proposed technique. The results show that the method can be used not only to reveal nonlinearities, but also to reliably detect impact damage in composites. These results are confirmed using the statistical analysis

Study of ultrathin Pt/Co/Pt trilayers modified by nanosecond XUV pulses from laser-driven plasma source

We have studied the structural mechanisms responsible for the magnetic reorientation between in-plane and out-of-plane magnetization in the (25 nm Pt)/(3 and 10 nm Co)/(3 nm Pt) trilayer systems irradiated with nanosecond XUV pulses generated with laser-driven gas-puff target plasma source of a narrow continuous spectrum peaked at wavelength of 11 nm. The thickness of individual layers, their density, chemical composition and irradiation-induced lateral strain were deduced from symmetric and asymmetric X-ray diffraction (XRD) patterns, grazing-incidence X-ray reflectometry (GIXR), grazing incidence X-ray fluorescence (GIXRF), extended X-ray absorption fine structure (EXAFS) and transmission electron microscopy (TEM) measurements. In the as grown samples we found, that the Pt buffer layers are relaxed and that the layer interfaces are sharp. As a result of a quasi-uniform irradiation of the samples, the XRD, EXAFS, GIXR and GIXRF data reveal the formation of two distinct layers composed of Pt1-xCox alloys with different Co concentrations, dependent on the thickness of the as grown magnetic Co film but with similar ∼1% lateral tensile residual strain. For smaller exposure dose (lower number of accumulated pulses) only partial interdiffusion at the interfaces takes place with the formation of a tri-layer composed of Co-Pt alloy sandwiched between thinned Pt layers, as revealed by TEM. The structural modifications are accompanied by magnetization changes, evidenced by means of magneto-optical microscopy. The difference in magnetic properties of the irradiated samples can be related to their modification in Pt1-xCox alloy composition, as the other parameters (lateral strain and alloy thickness) remain almost unchanged. The out-of-plane magnetization observed for the sample with initially 3 nm Co layer can be due to a significant reduction of demagnetization factor resulting from a lower Co concentration

Effect of flax fibers addition on the mechanical properties and biodegradability of biocomposites based on thermoplastic starch

The research was intended to develop a biocomposite as an alternative biodegradable material, for the production of, e.g., disposable utensils. The author’s tested thermoplastic maize starch, both without additives and with the addition of crumbled flax fiber in the share of 10, 20 and 30 wt%. The plasticizer added was technical glycerin and the samples were produced by a single-screw extruder. The mechanical strength tests were performed, including the impact tensile test and three-point bending flexural test. Afterwards, the samples were tested for biodegradability under anaerobic conditions. The methane fermentation process was carried in a laboratory bioreactor under thermophilic conditions with constant mixing of the batch. All samples proved to be highly susceptible to biodegradation during the experiment, regardless of the flax fiber share. The biogas potential was about 600 ml·g-1, and the methane concentration in biogas ranged from 66.8 to 69.6%. It was found, that the biocomposites can be almost completely utilized in bioreactors during the biodegradation process. The energy recovery in the decomposition process with the generation of significant amount of methane constitutes an additional benefit

Analysis of strength properties of the extruded product of a two-layer polyethylene-elastomer

Intensywne poszukiwania nowych polimerowych materiałów konstrukcyjnych wynikają z potrzeby wytwarzania wytworów o polepszonych właściwościach. Właściwości te mogą być analizowane w odniesieniu do gotowego wytworu lub dla określonych właściwości poszczególnych jego komponentów. Podczas użytkowania wytworów z tworzyw polimerowych, wraz ze wzrostem temperatury otoczenia mogą zmieniać się znacznie właściwości fizyczne, zwłaszcza mechaniczne, a w skrajnych przypadkach może nastąpić przemiana stanu skupienia tworzywa i utrata określonego kształtu lub wymiarów. W artykule przedstawiono analizę cech wytrzymałościowych opartą na wynikach badań eksperymentalnych, obejmujących badania wytłoczyn otrzymanych podczas wytłaczania jednoskładnikowej taśmy, jak także współwytłaczania wytłoczyny dwutworzywowej w postaci rury o przekroju pierścieniowym.The intensive search for new polymeric materials of construction based on the need for preparing the products of enhanced properties. These properties can be analyzed in relation to the finished product or of the specific properties of its individual components. During use of the products of polymeric materials with an increase in ambient temperature can vary greatly physical, especially mechanical, and in extreme cases can occur transition of state material, and loss of a particular shape or dimensions. The article presents an analysis of the characteristics of strength, based on the results of experimental research, including research residue obtained during the extrusion of mono tape, as well as co-extrusion of extrudate double plastic in the form of a tube of annular cross-section