Abstracts:The paper presents studies on the application of the boundary integral equation method for investigation of dynamic stresses in Cosserat continuum with constrained microrotations. For the solution of the non-stationary problem, the Fourier transform for time variable was used. The fundamental functions for the two-dimensional case of Cosserat continuum with constrained micro-rotations are built. Thus, the fundamental functions for the time-domain problem are derived as the functions of the two-dimensional isotropic continuum and the functions, which are responsible for the effect of shear-rotation deformations. The method of mechanical quadrature and collocation technique are applied for numerical calculations. Several numerical examples show the comparison of distribution of dynamic stresses in the foam medium with the cavity under the action of impulse loads accounting for the shear-rotation deformations effect and without accounting for this effect.

Abstracts:Due to the fact that anisotropic medium model is much common in earthquake engineering, dynamic response of a circular cavity and a crack in anisotropically elastic half-space under incident out-plane waves is examined in present work by using the methods of complex variable and Green's function. Based on the theory of Green's function, the method of complex variable is firstly developed to derive the corresponding Green's functions of half-space containing a circular cavity applied by an out-plane source load. Combined with “Crack-division”, a series of forces (the same in magnitude but opposite in direction to the stresses produced by incident SH-waves) are applied along the region where the crack will be constructed. Consequently, the total stresses will be zero, i.e., a crack can be created. Then, the displacement field while the crack coexists can be further derived. Finally, a mass of numerical examples are given to investigate the influence of different parameters on the dynamic stress concentration factors (DSCF) around the cavity and dynamic stress intensity factors (DSIF) at the crack tip.

Abstracts:The statistical energy analysis (SEA) is applied to predict the transient energy response of structures with time-varying parameters for the first time. With the energy governing equations derived by considering time-varying SEA parameters and energy flow item caused by time-varying damping loss factor, SEA method is firstly applied to predict transient energy response of time-varying systems. Then, numerical examples of a time-varying two-oscillator system, a time-varying L-shaped fold plate and a complex time-varying vibro-acoustic structure are investigated to demonstrate the effectiveness and accuracy of SEA method for time-varying system. The Newmark-beta method and finite element method are used to verify the accuracy of predicted transient energy response. Results show that SEA method for time-varying system is capable of predicting transient energy response of time-varying structures with sufficient accuracy and also applicable for transient analysis of complex time-varying structures with a small computational cost.

Abstracts:In this paper we assess, using finite element calculations performed with ABAQUS/Explicit, the influence of porosity in the development of necking instabilities in flat metallic samples subjected to dynamic tension. The mechanical behaviour of the material is described with the Gurson–Tvergaard–Needleman [6, 22, 23] constitutive model pre-implemented in the finite element code. The novelty of our methodology is that we have included in the gauge of the specimen various non-uniform distributions of initial porosity which, in all cases, keep constant the average porosity in the whole sample. This has been carried out assigning random values of initial porosity (within specified bounds) to some nodes and zero to the others. Therefore, the larger the percentage of nodes with non-zero initial porosity, the smaller their initial value of porosity. The goal is to provide an idealized modelling of the distributions of void nucleating particles which in many structural metals nucleate early in the deformation process and lead to material porosity. The key point of this paper is that, following this methodology, we reproduce the experimentally-observed asymmetric-growth of the pair of necking bands which define the localization process in flat tensile samples subjected to dynamic loading [25].

Abstracts:This paper concerns the study of vibroacoustic problems. By considering a displacement-pressure formulation, a non-symmetric eigenvalue problem is obtained. In order to solve it, three numerical schemes are compared: the classical ARPACK solver, an indicator method (initially proposed in [4]) which has the property to be null at the eigenvalues, and an original method based on the analysis of Taylor series expansions near a singularity. Numerical results show all the evaluated numerical methods give accurate results but the indicator method requires the lowest computational times. Nevertheless, the original method based on the behavior of the perturbation method close to eigenvalues seems to be a very promising technique.

Abstracts:A micromorphic theory of electromagnetic non-conducting materials is outlined accounting for microdensities of mass and bound charges. Electromagneto-elastic coupling is then described by connecting microstrain measures with electric dipoles and quadrupoles. Application of this approach to granular materials is realized by exploiting well established constitutive models of grain interactions. A set of general equations is derived from a variational approach and its linearized form is discussed under the quasi-static assumption. Electromagnetic effects, which are expected under the action of an electric field, arise due to induced polarization, assuming grains are endowed with an intrinsic electric dipole and/or quadrupole.

Abstracts:This work presents a theoretical law to predict the mean Nusselt number for a laminar pipe flow of a magnetic fluid subjected to an uniform magnetic field. The intensity of the field, the magnetic susceptibility of the fluid and the orientation angle formed between the magnet and the direction of the flow appear explicitly in the final expression obtained in this work. The theory developed here considers the superparamagnetism hypothesis, so it can not be applied for magneto-rheological suspensions of large (micrometric) particles. However, it could be used for the vast majority of commercial ferrofluids in conceptual designs of more efficient heat exchangers, specially in microfluidic applications. The limitations of our theory are also discussed. We provide a curve with combinations of operational parameters for which the Nusselt number of the flow may be intentionally controlled in order to increase or decrease the convective heat transfer rates inside the pipe. The breakthroughs and limitations of our theory are also discussed in details as well as some suggestions for future works.

Abstracts:The effect of crack position and length on the fracture behavior in the superconductor/ferromagnetic (SC/FM) bilayer strip is investigated with finite element method. Owing to the composite structure of the SC/FM hybrids, the electromagnetic body force acting on the SC/FM bilayer strip will lead to complicated mechanical deformation during magnetization. The crack is prone to propagate even in the field ascent stage when the crack gets close to the sample bottom, which is quite different from the feature in a single SC sample. Moreover, the crack length and position leads to two inverse variations of stress intensity factor (SIF). SIF is positive and has peak value in the intermediate stage of field reduction when crack is close to superconducting layer. By contrast, SIF is positive except the intermediate stage and has maximum value at the beginning of the descent stage. Such novel behavior of SIF versus applied field can be explained by the strain distribution along the thickness direction for various crack positions. Generally, the maximum SIF at the maximum applied field is much larger than that in the field descent stage. The fracture behavior at the upper tip and lower tip exhibits significantly different characteristics. The maximum SIF at the lower tip is much larger than that at the upper tip as the crack is sufficiently close to the bottom surface.

Abstracts:This paper presents a finite element formulation for the analysis of softening in plane problems. The model is not based on the non-local or gradient-dependent approaches. It is an extension of lumped damage mechanics. Lumped damage mechanics, or LDM, is a formulation that introduces ideas of fracture and damage mechanics into the concept of plastic hinge. So far, LDM was limited to the analysis of frames and arches, but within this limited framework it represents also a regularization scheme. A finite element in LDM is the assemblage of an elastic beam-column with two inelastic hinges at the ends of the element.

Abstracts:We model an artery with perivascular soft tissue as a uniform cylindrical membrane tube surrounded by a flexible substrate with distributed stiffness. We derive the equations of motion of the arterial model, and obtain evolution equation derived in the long wavelength limit from the general equations of motion. We analyze the stability of axisymmetric perturbations at the bifurcation state taking into the consideration of surrounding soft tissue stiffness and constant axial stretch. We observe that the surrounding soft tissues progressively reduce the domain of real valued solutions with increasing constant axial stretch. The results suggest that the stationary solitary wave solution is unstable.