—The formation of a crystal structure and properties of a welded joint between a porous stainless steel plate and a solid plate of greater thickness with the use of nanomodifying additives has been ...experimentally investigated. To obtain a high-quality butt joint of the plates, the end layer of the solid plate was found to have been penetrated. The laser beam axis is shifted from the boundary of the plate joint by some distance, which is necessary to compensate the (material of) metal during the melting of the porous plate. The application of nanomodifying additives reduces the grain size of the weld structure, which, in turn, has a positive effect on the mechanical properties of the resulting joint. The results of tensile strength tests have shown that the failure of nanomodified samples, unlike unmodified ones, occurred only in the main porous metal. The average value of the tensile strength is 89.5 MPa.
The system for monitoring acoustic emission (AE) parameters in mechanical testing of materials built up from electronic equipment and corresponding software is described. The electronic equipment ...based on a high-speed data storage module with a USB interface provides conversion of AE signals, their amplification, filtering, and digital input to a personal computer. The AEMonitor software performs continuous analog-digital conversion of AE signals, evaluation of their spectral distribution (fast Fourier transform), online display, accumulation, and storage of experimental data with load parameters for their further analysis. The software features an online automatic display of the spectral distribution of signals and corresponding stresses against the number of AE pulses from tested materials. The functional potentials of the system were verified in bending tests of corundum refractory and glass fiber plastic specimens with recording AE parameters. The relations between major AE parameters, form, and spectral distribution of pulses under loading of those materials were greatly different due to varied fracture mechanisms.
One of the most common ways to assess the activity of acoustic emission (AE) sources and their hazard under mechanical loading of materials and structures is to use the local-dynamic criterion. To ...verify the latter, specimens of various materials, namely fiberglass, corundum refractory, and steel, were tested under static loading during three-point bending. A special software AE-Criterion was developed to determine the AE parameters, including the current parameters of source activity, based on the local dynamic criterion using both the force factor and the time since the beginning of the test. Taking into account the multiplicity and stochastic nature of AE events during the loading of materials, it is proposed to determine the average values of
M
S
,
M
T
, and the values of the indices
I
AS
and
I
AT
of the activity degree of AE sources when applying the force parameter and time, respectively. The analysis of the data obtained during the bending tests of the above-mentioned specimens and, accordingly, the calculation of the parameters of source activity showed that the value of the index I
AS
, when using the force factor, satisfactorily reflects the deformation and fracture processes of these materials. The study’s results indicate the suitability of the local dynamic criterion for diagnosing the deformation and fracture processes of the above materials.
The results of tests and determination of mechanical properties of unidirectional polymer composite reinforced with T800 carbon fiber under tension and compression in the longitudinal and transversal ...directions in the temperature range from room to 315°C are presented. The typical type of fracture of specimens under tension in the longitudinal direction and compression in both directions at room temperature and 315°C is shown. It is established that with increasing temperature, all investigated properties of the material decrease, but least of all the elastic modulus and ultimate strength in longitudinal tensile tests. When the glass transition temperature of the epoxy matrix is reached and exceeded, a sharp degradation of such properties of the material in the longitudinal direction as the ultimate strength and the elastic modulus under compression is observed. An almost uniform degradation of the strength and elastic characteristics of the composite in the transversal direction with increasing temperature is noted. The strength and elastic modulus of the polymer composite reinforced with T800 carbon fiber under longitudinal tension have been calculated based on the known values of the ultimate strength and the elastic modulus of the fiber. It is found that the values of the elastic modulus defined during the tests are consistent with the calculated value, while the experimentally obtained value of the ultimate strength of the composite is significantly lower than the calculated one.
The paper presents the results of the calculated estimate of the critical pressure level in the oxidant tank of the launch vehicle using generalized diagrams of elastic-plastic deformation of the ...aluminum alloy AMg6. These diagrams consider the anisotropy of the physical and mechanical properties of the material. The calculation of the stress-strain state is performed using the simplified calculation scheme for the specified structural element of the tank depending on the internal pressure in the axisymmetric statement considering the elastic-plastic deformations. The calculation analysis is based on the mixed scheme of the finite element method, which provides the continuous approximation of displacements and stresses. It allows one to determine the stress-strain state of the tank element with high accuracy. It is implied that the maximum values of stresses and strains occur in the area of the fillet region connecting the ring with the cylindrical shell of the tank. Complying with the obtained data, the calculation of the stress-strain state of the tank element using generalized deformation diagrams, taking into account the anisotropy of physical and mechanical properties and the nature of the load of aluminum alloy AMg6, leads to a more conservative estimate of the critical pressure level as compared with the standard calculation based on the uniaxial tensile diagram.
Experimental investigations were carried out to study permanent connection between porous and compact titanium and stainless steel plates of various thicknesses attained with the use of continuous CO
...2
laser radiation. It has been established that in order to obtain a high-quality butt joint of plates, it is necessary that the end layer of a compact plate be penetrated through when the axis of the laser beam is shifted from the interface of the parts by a certain distance, which is necessary for the impregnation of the welded zone of the porous part with molten metal. The use of modifying additives increases the dispersiveness and uniformity of the weld structure, which has a positive effect on its mechanical characteristics.
The effect of thermal regimes and some technological methods (the application of intermediate compact metal inserts and nanomodifying additives) on the quality of laser-welded permanent joints of ...porous titanium or stainless steel plates has been experimentally studied in this work. It has been established that the formation of a high-quality defectless seam requires the use of an intermediate compact (nonporous) metal insert placed butt to butt between the edges of welded plates. In this case, the position of a focal spot should be installed at a depth equal to the thickness of a plate, i.e., on its lower surface. To form a bead joint or a joint flush to the plates to be welded together, the height of an insert must exceed the thickness of the plates. The application of nanomodifying titanium nitride based additives increases the structural dispersity and uniformity of a seam, thus producing a positive effect on the mechanical characteristics of a welded joint.
Experimental-and-informational technology for studying tubular structures of rocket-and-space equipment made of carbon plastic under the action of internal overpressure was developed in this study. A ...comparative assessment of the tightness and strength of structures made of six types of polymer composite materials, in particular, modified by treatment with high-energy plasma flows of dielectric barrier discharge fibers in acrylic acid (C
3
H
4
O
2
) and allylamine (C
3
H
7
N) media was performed. The applicability of modification treatment of composite polymeric materials was proved, which allows an increase in their strength characteristics by up to 25% compared with the original material.
Using a combination of MOC-hydride epitaxy and pulsed laser deposition, InGaAs/GaAs heteronanostructures with a (Ga,Mn)As layer on the surface are obtained, and the influence of the action of a ...pulsed excimer laser (with a wavelength of 248 nm, pulse duration of ~30 ns, and energy density in the range of 200–360 mJ/cm
2
) on their radiative, structural, and galvanomagnetic properties is studied. The study is carried out using photoluminescence spectroscopy complemented by the possibility of analyzing radiation polarization characteristics of the structures. The crystalline perfection of the initial and laser-irradiated samples was studied with the use of Raman scattering spectroscopy. The elementary composition of the structures and its distribution over the depth were studied by secondary ion mass spectrometry. The influence of pulsed laser annealing on ferromagnetic properties of heteronanostructures is characterized by the behavior of magnetic field dependences of the Hall resistance and magnetoresistance at temperatures of 10–300 K within the range of magnetic fields of ±3600 Oe. At room temperature, the study was carried out in magnetic fields reaching ±28 000 Oe. The calculated temperature distributions along the sample thickness and in time using the laser annealing model based on solving the problem about heat propagation in a one-dimensional GaAs system with allowance for the (Ga,Mn)As layer on the surface are obtained using original data on the thermal conductivity of structures with a (Ga,Mn)As layer. The data were obtained by the modified frequency division technique (the 3ω method).
