The Image-Based Finite Element Evaluation of the Deformed State

The article presents one of the possible approaches to modeling objects with anisotropic properties based on images of the study area. Data from such images are taken into account when building a numerical model. In this case, material inhomogeneity can be included by integrating the local stiffness matrix of each finite element with a certain weight function. The purpose of the presented work is to develop a finite element for the formation of a computational ensemble and simulation of mechanical behavior taking into account the data of two-dimensional medical images. To implement the proposed approach, we used the assumption that there is a correlation between the values in the image pixels and the elastic properties of the material. Meshing was based on a four-node plane finite element. This approach allows using the quantitative phase or scanning electronic images, as well as computed tomography data. A number of test problems for compression of elementary geometry samples were calculated. The distal part of the rat femur was considered as a model problem. A computed tomography scan of the sample was used to construct a numerical model taking into account the inhomogeneity of the material distribution inside the organ. The distribution field of the nodal displacements based on data obtained from the images of the study area is presented. Within the framework of a model problem, we considered how a computer tomograph resolution influences the quality of the obtained results. For this purpose, calculations were carried out based on compressed input medical images.

Assessment of the Homogeneity of Polymeric Materials Using Hounsfield Units

The X-ray transparency of various polymers and plastics is one of the most important factors in the choice of material in the design of new medical robotic and mechatronic systems and complexes. Along with the radiolucency, such a parameter as material inhomogeneity is also one of the main ones. The inhomogeneity of the material can not only affect the radiolucency of individual areas of the product but also impose restrictions on the use of polymeric materials by changing the physical and mechanical properties of the products. In this work, a technique was proposed for determining the location of regions of interest with reliable values on a CT image. Data were obtained for the values of the parameter HU and standard deviation for various polymer materials. A technique was proposed for determining the degree of heterogeneity of polymeric materials. The values of the degree of heterogeneity were obtained for all investigated materials.

Influence of Creep on Longitudinal Fracture of Inhomogeneous Rod Loaded in Torsion and Bending

The present paper analyzes the influence of creep on longitudinal fracture in continuously inhomogeneous rod of circular cross-section loaded in torsion and bending. The rod exhibits continuous material inhomogeneity in both radial and longitudinal directions. The creep is described by using non-linear time-dependent relations between the principle stresses and strains. A time-dependent solution to the strain energy release rate is derived by analyzing the complementary strain energy. The time-dependent strain energy release rate is found also by considering the energy balance for verification. The solutions are applied to perform a parametric study of the strain energy release rate under creep.

Interpretation of Nondestructive Magnetic Measurements on Irradiated Reactor Steel Material

Neutron irradiation-generated embrittlement of nuclear pressure vessel steel was inspected by a nondestructive magnetic method, called magnetic adaptive testing (MAT). This method is based on systematic measurement and evaluation of minor magnetic hysteresis loops. Result of MAT measurement was compared with the result of the traditional Charpy measurement. Good correlation was found between these parameters. One of the main findings of the present work is that the considerable part of scatter of points obtained by magnetic measurement can be attributed to local material inhomogeneity. Another important conclusion is that the embrittlement highly depends on the initial local material conditions, i.e., the initial microstructure, which are very different even within the same block of reactor steel material. By taking this into account, the magnetic descriptors obtain more precise determination of the local embrittlement than the traditionally used destructive mechanical parameters from Charpy data.

Piezo-phototronic Effect in Centro-symmetric BiVO4 Epitaxial Films

With exciting functionality, topological defects in ferroic system have attracted much attention. Under proper design, the emergence of polar domain walls in non-polar ferroelastics enables piezo-phototronic effect. In this study, we revealed ferroelastic twin texture with localized piezoelectric effect in epitaxial BiVO4 film by piezoresponse force microscopy. Supported by the strain field analysis, we found the piezoresponse confined at domain wall area is attributed to the flexoelectric effect induced by the presence of ferroelastic twin domains during the paraelastic to ferroelastic phase transition. The piezo-phototronic phenomenon was further supported the experimental evidence of dye-degradation and generation of reactive radicals. This work not only provides new insights into the introduction of piezo-phototronic effects in non-polar materials, but also sheds light on a new concept to use material inhomogeneity for acquiring multifunctionality.

Deformation and Failure Characteristics of Sandstone Subjected to True-Triaxial Unloading: An Experimental and Numerical Study

The influence of maximum principal stress level on true-triaxial unloading behaviors and the failure mechanism of sandstone samples were comprehensively investigated by laboratory tests and discrete element simulations. The results show that the level of σ1 at unloading point significantly affects the deformation and failure characteristics of sandstone samples under true-triaxial unloading conditions. As the level of σ1 at unloading point increases, the ultimate bearing capacity of sandstone sample is increasingly strengthened, while the sample collapses more easily during the unloading process, and the failure mode of sandstone sample changes from mixed tensile-shear failure to shear failure. With the increase in the level of σ1 at unloading point, the accumulative micro-cracks at the unloading point and micro-crack generation rate during the unloading phase exhibit an increasing trend, while the sum of micro-cracks at the unloading phase and the ratio between the amount of tensile micro-cracks and shear micro-cracks roughly show a downward trend. The formation of macro fracture in sandstone sample is closely related to the stress conditions and material inhomogeneity. The tensile fracture in the upper right part of sample when the level of σ1 is relatively low should be attributed to the superiority in tensile contacts between particles in terms of contact number and corresponding tensile force.

On the question of determining the deformed state of an anisotropic nonlinear inhomogeneous pipe

Рассматривается деформированное состояние анизотропной нелинейно-неоднородной трубы. Примем неоднородность материала как зависимость предела текучести от координат. На неоднородность материала способны влиять различные факторы, такие как: ударные воздействия, температура, радиационное облучение и другие. Вдоль эллиптических кривых предел текучести считается неизменным. Результаты, учитывающие влияние анизотропии на напряженно-деформированное состояние различных конструкций и тел являются востребованными в современном мире. The deformed state of an anisotropic nonlinear inhomogeneous pipe is considered. Let us take the material inhomogeneity as the dependence of the yield stress on coordinates. For material heterogeneity are capable of influencing factors such as: shock effects, temperature, radiation exposure and others. Along the elliptical curves, the yield stress is assumed to be constant. Results taking into account the effect of anisotropy on stress-strain state of various structures and physicality in demand in the modern world.

VIBRATION OF 2D-FGSW TIMOSHENKO BEAMS UNDER A MOVING HARMONIC LOAD

Vibration of two-directional functionally graded sandwich (2D-FGSW) Timoshenko beams under a moving harmonic load is investigated. The beams consist of three layers, a homogeneous core and two functionally graded skin layers with the material properties continuously varying in both the thickness and length directions by power functions. A finite element formulation is derived and employed to compute the vibration characteristics of the beams. The obtained numerical result reveals that the material inhomogeneity and the layer thickness ratio play an important role on the natural frequencies and dynamic response of the beams. A parametric study is carried out to highlight the effects of the power-law indexes, the moving load speed and excitation frequency on the vibration characteristics of the beams. The influence of the beam aspect ratio on the vibration of the beams is also examined and discussed.