Journal of Theoretical and Applied Mechanics, Sofia, vol. 53 Issue 2 (2023)

The present paper deals with delamination analysis of a multilayered inhomogeneous beam structure that exhibits non-linear viscoelastic behaviour under strains whose velocity varies step-like with time. There are two delaminations in the beam. The left-hand delamination crack arm is subjected to bending so as the velocity of angle of rotation of this crack arm varies step-like with time. A non-linear viscoelastic model with a spring and two dashpots treats the beam mechanical behaviour. Solutions of the strain energy release rate are derived for both delaminations. A parametric investigation of delamination in the beam is carried-out by using the solutions.

We analyse the spatial behaviour of diffusive microstretch thermoelasticity with microconcentrations and microtemperatures in the linear, anisotropic and non-centro-symmetric case. We define a function with a weight depending on time that characterizes the principal characteristics of the model, then study its properties and derive a differential inequality. Then we obtain an exponential spatial decay that is independent of time and is valid for unbounded bodies.

In this paper, experimental, theoretical, and numerical simulations were used to investigate the effect of adding natural fiber (Horsehair/Sheep wool) with varied weight ratios to polyester composite material on creep behavior at room temperature and constant load. A hand-layup technique was used to create polyester resin, and the test specimens were produced following the standards (ASTM). The results showed an improvement in creep behavior of polyester composites reinforced with natural fibers when compare with non-reinforced polyester, hence the amount of maximum strain was reduced to 74.64% when sheep wool was added at a weight ratio of 0.8%, and 71.114% when horsehair was added at the same weight ratio. The experimental results were verified theoretically and numerically using ANSYS Mechanical APDL software 15, the results demonstrate that they are in good agreement.

The paper considers the problem of sound scattering on a classical noise barrier and a noise barrier with a resonator. A rigorous solution is obtained. It is shown that the use of the root mean square approximation and the conjugation by points of fields in the problem of sound scattering on a classical barrier gives a good coincidence of the calculated values of fields. It is shown that for frequencies above the resonance one exists a band in which there is a dip in the frequency response of the integral criterion of the barrier. All this illustrates the advantage of the barrier with the resonator.

In this work, the thermal buckling of nano functionally graded beams is investigated using nonlocal higher order deformation shear theory with two variables. The variation of properties of FG material is made through the thickness using a power law and exponential form. Governing equations are derived using the principle of virtual work. The temperature variation is assumed to be uniform. The critical buckling temperature is calculated for various boundary conditions of the beam: simply supported and clamped-clamped beams. The nonlocal parameter, power law index, slenderness radio and boundary conditions on the critical buckling temperature of the FG nano beams are analyzed.

In this paper, a new approach for autonomous single spermatozoon tracking has been proposed. During the presented approach, there is no need to track low contrast objects (spermatozoon tail). The most important part is the motion trajectory tracking of the spermatozoon head. The effective sperm head tracking has been realized using image processing and sperm head shape recognition (as a sphere). Without following the sperm tails – moving with very high dynamics, the software application is faster working. The tracking algorithm has been realized in a square Sperm Head Region of Interest (SHROI), with a size of 100×100 pixels. The developed software application is compatible with almost all digital cameras available on the market.