Failure Criteria for Brittle Notched Specimens

Recently, new failure criteria were proposed for brittle materials to predict their failure loads regardless of the shapes of a notch or a crack in the material. This paper is to further evaluate the failure criteria for different shapes of notches and different materials. A circular hole, elliptical hole or crack-like slit with a different angle with respect to the loading direction was considered. Double circular holes were also studied. The materials studied were an isotropic material like polymethyl methacrylate (PMMA) as well as laminated carbon fiber composites. Both cross-ply and quasi-isotropic layup orientations were examined. The lamination theory was used for the composite materials so that they can be modelled as an anisotropic and homogeneous material. The test results were compared to the theoretical predictions using the finite element analysis with 2-D plane stress models. Both theoretical failure stresses agreed well with the experimental data for the materials and notch geometries studied herein.

Mechanical Properties of Polyester Toughened with Nano-Silica

The fabrication of nanocomposites has played role to the development of the nanotechnology and the technology of advanced composite materials. Thermoset polymers are used in engineering applications widely. Their mechanical properties can be change with adding particles. The mechanism of toughening polymers has been suggested recently by reinforcing well dispersed particles to the plain polymer. Nano-silica particles were added to thermoset polymer of polyester to evaluate their influence on the mechanical properties of the toughened polymer using both experimental and numerical methods. The Representative Volume Element (RVE) approach, which employs finite element models, has been developed to achieve that aim numerically for various types of nano-particle reinforcement ratios. In each case, the stiffness has been calculated with using the equivalent homogeneous material concept. Experimentally, toughened thermoset polymers of polyester reinforced with nano-silica were prepared with different particle content ratio. Several tests were conducted on the nanocomposite, and it was observed increasing nano-silica ratio caused increase in Young’s modulus and decrease in ductility.

Simulation of the Vibrations Produced to the Human Body During Operation of the Bucket Wheel Excavators. A Case Study of ERc 1400-30/7 Type Excavator

The paper deals with the analysis of the dynamic response over time of the excavator boom during operation. For a start, we determined the variation in time of the forces acting on the rotor shaft, due to the excavation. These forces have high values and a slow variation over time, which depends on the rotation speed of the bucket wheel and the number of buckets installed on it. A virtual model of the BWE boom was proposed, for which the dynamic response in time due to the excavation forces was determined, for a point in the main cabin of the BWE. A virtual sensor has been attached to this point corresponding to seat of the operator. The simulation of the dynamic response over time was performed taking into account a global damping of 2% of the critical damping. The simulation was performed both for the excavation of a homogeneous material and for the case of a shock (a sudden appearance of an inclusion of hard material during the cutting of the homogeneous material).

EVALUATION OF MINERALIZED PLASMATIC MATRIX DURING SINUS LIFT WITH THE SIMULTANEOUS PLACEMENT OF DENTAL IMPLANTS

Objectives:Mineralized plasmatic matrix is reported to improve the quality of the bone/fibrin mixture, creating a stable and easy to handle homogeneous material. However, few studies evaluate the use of the mineralized plasmatic matrix during sinus lift with the simultaneous placement of dental implants. Purpose: This study evaluated the efficiency or not of MPM compared to the xenograft bone grafting in the maxillary sinus lift. Patients and methods:This study was conducted randomly on patients selected for treatment with a total of sixteen lateral windows sinus lift with simultaneous implant placement. Their ages ranged between 20 and 60 years old. Participating patients were divided into two groups equally and randomly The control group: eightsinus floor elevation was performed using simultaneous implant placement. As a grafting material, Xenograft was used. The study group: eight Sinus floor elevation was achieved with simultaneous implant placement. Xenograft has been used in the form of MPM as a grafting material. CBCT taken before and after sinus augmentation to measure bone volume and height after 1 week of baseline (T0), after 6 months (T1), and after 12 months of baseline (T0) (T2). The Osstell(PT) was used for assessment implant stability at implant insertion (PT0) as well as for loading visit (PT1). Result:A significant difference was observed between the two groups in bone volume (p=0.049). No significant difference was observed between the two groups (p=0.129) in height of graft. Conclusion:MPM eliminated the need for barrier membranes when a guided bone regeneration procedure is considered.The useofMPM as a grafting bone offered greater graft stability and handling.

Geometry optimization for tunable band gap and wave guiding in periodic grid structures

A proper lattice structure consisting of homogeneous material is designed in this paper to investigate the maximum bandwidth of perfect lattice structures and tunable property of waveguide with linear geometric defect by means of selecting optimal geometric lattice cell. A simulation model based on finite element method is used to calculate dispersion curves and transmission spectrums of lattice structures with different geometric parameters. Meanwhile, a simplified theoretical model of unit cell, which considers the mass of grid bar and stiffness of node area, is applied to validate the accuracy of simulation result and may provide an effective approach for prediction of band gap lower boundary. Then, the validated numerical results show different orders of widest band gap that can be realized by different optimal geometric structures. Moreover, waveguide property can be effectively controlled and manipulated by changing defect parameters. The present study may establish theoretical and simulation foundation to control and manipulate band structures and other acoustic propagation characteristics of waveguide devices.

Algorithms for thermal diffusivity measurement of heterogeneous 1D materials based on Infrared Microscopy Enhanced Angstrom Method

An infrared microscopy enhanced Angstrom method has been develpoed to measure the thermal diffusivity. Infrared microscopy technique can acquire temperatures of multiple points at one shot. Two algorithms for calculating thermal diffusivity were proposed and compared in practice. One is based on global temperature data and the other is based on local temperature data. The according calculated thermal diffusivities are denoted as α n G and α n L . Three 1D materials of different heterogeneity (Cu wire, Ni-Cu wire and PVA-CNT fiber) were measured on the experimental platform. The calculated α n G and α n L values show that for homogeneous material such as Cu, these two algorithms give similar results, while for heterogeneous ones (Ni-Cu and PVA-CNT), they come to be discrepant. The data fluctuation analysis of f n L zooms in the discrepancy and verifies that α n L is more sensitive to local property change and more competent in revealing heterogeneous properties.

Rational design of hybrid polymetallic structures taking into account mass loads

Рассмотрена проблема рационального (оптимального) проектирования высотных или административно-управленческих сооружений при активном использовании гибридных полиметаллических стандартизированных элементов, создаваемых на основе различных надежно разработанных технологий. Целью решения проблемы является подбор и перераспределение материалов, при которых с обеспечением требуемых комфортных и безопасных условий существования будут значительно улучшены экономические показатели создаваемого проекта. В качестве гарантированных требований комфортного существования использованы разработанные автором три различия критерия деформативности фазовых материалов в условиях заданных типов и полей внешних нагрузок. Первый критерий: «предельно допустимое упругое состояние» - когда ни один из фазовых материалов не будет деформироваться за пределом упругости. Второй критерий: «предельно допустимые деформации упрочнения» - когда фазовые материалы не переходят в состояние разупрочнения. Третий критерий: «предельно допустимые деформации разрушения» - когда какой-либо из фазовых материалов будет «локально» разрушаться. При расчетах учитывается, что ряд физических характеристик материалов в широких пределах технологических переработок довольно устойчиво сохраняют свои значения и используются как заранее известные данные из справочной литературы. К ним относятся пределы упругости и прочности, модули Юнга, удельные плотности и стоимости фазовых материалов. Такая малочувствительная технологическая устойчивость позволила для всех фазовых материалов при аппроксимации диаграммы деформирования различных металлических материалов использовать единообразную зависимость в виде кубической параболы, коэффициенты которой и упомянутые три предельно допустимые деформации выражаются через устойчивые характеристики - пределы упругости, прочности и модуль Юнга. На основе известных кинематических и статических гипотез описания неупругого деформирования стержневых систем для всех типов предельно-допустимых деформаций, получены единообразные системы уравнений, которые позволяют для заданных условий внешнего воздействия определить геометрические параметры и топологическую структуру распределения всех фазовых материалов по конструкции. В качестве внешних воздействий на конструкцию высотного сооружения рассматриваются традиционные ветровые нагрузки с заданным законом изменения вдоль вертикальной оси, заданные моменты и силы на верхнем вертикальном срезе и изменяемые при топологических перераспределениях массовые нагрузки. Степень усовершенствования проекта оценивается на основе анализа изменения введенных относительных характеристик несущей способности, податливости и стоимости проекта. Для сравнения используется эталонный проект из однородного материала. The problem of rational (optimal) design of high-rise or administrative and management structures with the active use of hybrid polymetallic standardized elements, created on the basis of various reliably developed technologies, is considered. The purpose of solving the problem is the selection and redistribution of materials, in which, with the provision of the required comfortable and safe conditions of existence, the economic indicators of the project being created will be significantly improved. Three differences in the deformability criterion of phase materials under conditions of specified types and fields of external loads, developed by the author, were used as guaranteed requirements for comfortable existence. The first criterion: "maximum permissible elastic state when none of the phase materials will deform beyond the elastic limit. The second criterion: "maximum permissible hardening deformations when phase materials do not pass into a softening state. The third criterion: "maximum permissible fracture strains when any of the phase materials will "locally"fail. The calculations take into account that a number of physical characteristics of materials in a wide range of technological processing rather stably retain their values and are used as data known in advance from the reference literature. These include the limits of elasticity and strength, Young’s moduli, specific densities and costs of phase materials. Such a low-sensitivity technological stability made it possible for all phase materials to use a uniform dependence in the form of a cubic parabola for approximating the deformation diagram of various metallic materials, the coefficients of which and the above three maximum permissible deformations are expressed in terms of stable characteristics - the limits of elasticity, strength and Young’s modulus. On the basis of the known kinematic and static hypotheses of the description of inelastic deformation of rod systems for all types of maximum permissible deformations, uniform systems of equations are obtained that allow for the given conditions of external action to determine the geometric parameters and the topological structure of the distribution of all phase materials over the structure. Traditional wind loads with a given law of variation along the vertical axis, given moments and forces on the upper vertical cut, and mass loads varying during topological redistributions are considered as external influences on the structure of a high-rise structure. The degree of improvement of the project is estimated based on the analysis of changes in the entered relative characteristics of bearing capacity, flexibility and cost of the project. For comparison, a reference design from a homogeneous material is used.

In-situ-grown silver–polymer framework with coordination complexes for functional artificial tissues

Sensorized actuators are critical to imitate proprio-/exteroception properties of biological neuromuscular systems. Existing add-on approaches, which physically blend heterogeneous sensor/actuator components, fall short of yielding satisfactory solutions, considering their suboptimal interfaces, poor adhesion, and electronic/mechanical property mismatch. Here, we report a single homogeneous material comprising seamless sensing-actuation unification properties at nano-/molecule levels, in which built-in sensing functions originate from the actuator architecture itself. In-situ-grown silver nanoparticles and metal-ligand complexes cooperatively create a silver–polymer framework (SPF) that is stretchable (1200%), conductive (0.076 S/m), and strong (0.76 MPa in-strength). SPF displays concomitant multimodal sensing (mechanical and thermal cues) and sensorized actuation capabilities, which include proprio-deformation and external stimuli perceptions (simultaneous with load-lifting ability up to 3700× of own weight). In view of its human somatosensitive muscular systems imitative functionality, the reported SPFs bode well for use with next generation functional tissues including artificial skins, human-machine interfaces, self-sensing robots, and otherwise dynamic materials.

Characterization of Ternary CuNiCo Metallic Nanoparticles Produced by Hydrogen Reduction

Different methods of producing nanostructured materials at the laboratory scale have been studied using a variety of physical and chemical techniques, though the challenge here is the homogeneous distribution of the elements which also depends on the precursor elements. This work thus focused on the micro-analytical characterization of Cu–Ni–Co metallic nanoparticles produced by an alternative chemical route aiming to produce solid solution nanoparticles. This method was based on two steps: the co-formation of oxides by nitrates’ decomposition followed by their hydrogen reduction. Based on the initial composition of precursor nitrates, three homogeneous ternaries of the Ni, Cu and Co final alloy products were pre-established. Thus, the compositions in %wt of the synthesized alloy particles studied in this work are 24Cu–64Ni–12Co, 12Cu–64Ni–24Co and 10Cu–80Ni–10Co. Both precursor oxides and metallic powders were characterized by means of X-ray powder diffraction (XRD), scanning electron microscopy (SEM/EDS) and transmission electron microscopy (TEM). The results show that the synthesis procedure was successful since it produced a homogeneous material distributed in different particle sizes depending on the temperature applied in the reducing process. The final composition of the metallic product was consistent with what was theoretically expected. Resulting from reduction at the lower temperature of 300 ∘C, the main powder product consisted of particles with a spheroidal and eventually facetted morphology of 50 nm on average, which shared the same FCC crystal structure. Particles smaller than 100 nm in the Cu–Ni–Co alloy agglomerates were also observed. At a higher reduction temperature, the ternary powder developed robust particles of 1 micron in size, which are, in fact, the result of the coarsening of several nanoparticles.

The effect of model material properties on thermal imaging measurements

The temperature distributions arising on the surface of the solid model are investigated. A flow with a shock wave and laminar boundary layer interaction is considered as the main flow. Calculations of the conjugate problem are performed based on RANS approach. The investigated cases correspond to homogeneous material of the solid model and the model consisting of two materials with different thermal conductivity. In this study, the model designs are found to obtain a temperature distribution suitable for thermal imaging measurements. In addition, in the calculations, the effect of forced heating of the model wall on the temperature distribution is investigated.