Application of the continuum damage mechanics model in the three point bending test of Ti-6Al-4V titanium alloy specimens

One of the most important and challenging activities in the simulation of the mechanical behaviour of materials is the prediction of the failure phenomena. If well calibrated, damage models can simulate and predict the failure of materials in a generalized way allowing the replication of not only the calibration tests themselves but also of different loading cases. Generally damage models can be categorized into three different groups including phenomenological models, porosity models and continuum damage mechanics (CDM) models. Different CDM models have been proposed by researchers and these models have been applied in diverse loading conditions, geometries and materials. However the limitations and advantages of the CDM models are still not completely explored in the application areas. In this paper, a CDM model, (previously calibrated with round smooth specimen) has been applied in a three-point bending test model in order to simulate the correlated experiment. Specifically, the CDM framework has been applied in a finite element model and the obtained results have been compared with the experimental data. The tested material is Ti-6Al-4V titanium alloy, which is a widely used material in the aerospace industry because of its high strength and low density. Load-displacement data in the experiments and numerical simulations are the main results, which have been compared. Therefore, the ability of the CDM model to simulate the three point bending test has been investigated and the results are discussed

Extremal Charged Rotating Dilaton Black Holes in Odd Dimensions

Employing higher order perturbation theory, we find a new class of charged rotating black hole solutions of Einstein-Maxwell-dilaton theory with general dilaton coupling constant. Starting from the Myers-Perry solutions, we use the electric charge as the perturbative parameter, and focus on extremal black holes with equal-magnitude angular momenta in odd dimensions. We perform the perturbations up to 4th order for black holes in 5 dimensions and up to 3rd order in higher odd dimensions. We calculate the physical properties of these black holes and study their dependence on the charge and the dilaton coupling constant.Comment: 20 pages, 3 figure

Higher dimensional slowly rotating dilaton black holes in AdS spacetime

In this paper, with an appropriate combination of three Liouville-type dilaton potentials, we obtain the higher dimensional charged slowly rotating dilaton black hole solution for asymptotically anti-de Sitter spacetime. The angular momentum and the gyromagnetic ratio of such a black hole are determined for the arbitrary values of the dilaton coupling constant. It is shown that the dilaton field modifies the gyromagnetic ratio of the rotating dilaton black holes.Comment: 11 pages, 1 figure, the version to appear in Phys. Rev.

A Case Study on Influence of Utilizing Hill-type Muscles on Mechanical Efficiency of Biped Running Gait

The presence of compliant elements in biped running mechanisms generates a smoother motion and decreases impact forces. Biological creatures that have a complicated actuation system with parallel and series elastic elements in their muscles demonstrate very efficient and robust bipedal gaits. The main difficulty of implementing these systems is duplicating their complicated dynamics and control. This paper studies the effects of an actuation system, including Hill-type muscles on the running efficiency of a kneed biped robot model with point feet. In this research, we implement arbitrary trajectories compatible with the initial condition of the robot, and we calculate the necessary muscle forces using an analytical inverse dynamics model. To verify the results, we execute the direct dynamics of the robot with the calculated control inputs to generate the robot’s trajectory. Finally, we calculate the contractile element force of the muscles and its cost of transport, and we investigate the effects of the muscles’ elements on reducing or increasing the cost of transport of the gait and maximum actuating forces.Наявність податливих елементів у механізмах виконання двоногої ходи породжує плавність руху і зменшує сили удару. Біологічні істоти, які мають складну систему спрацьовування з паралельними і серіями еластичних елементів в м'язах, демонструють дуже ефективну і надійну двоногу ходу. Основними труднощами реалізації цих систем є дублювання їх складної динаміки і контролю. Вивчаються наслідки спрацьовування системи, в тому числі м'язів типу Хілла на ефективність роботи коліна у моделі двоногої ходи. У цьому дослідженні введено довільні траєкторії, сумісні з початковим станом робота, і розраховано необхідні сили м'язів за допомогою аналітичної зворотної моделі динаміки. Для перевірки результатів виконано пряму динаміку робота з обчисленням імпульсів управління для генерації траєкторії робота. Розраховано скорочувальну силу елемента м'язів і вартість його передачі для робота, і досліджено вплив елементів м'язів на зменшення або збільшення витрат на ходу і максимальні виконавчі сили

Asymptotically flat charged rotating dilaton black holes in higher dimensions

We find a class of asymptotically flat slowly rotating charged black hole solutions of Einstein-Maxwell-dilaton theory with arbitrary dilaton coupling constant in higher dimensions. Our solution is the correct one generalizing the four-dimensional case of Horne and Horowitz \cite{Hor1}. In the absence of a dilaton field, our solution reduces to the higher dimensional slowly rotating Kerr-Newman black hole solution. The angular momentum and the gyromagnetic ratio of these rotating dilaton black holes are computed. It is shown that the dilaton field modifies the gyromagnetic ratio of the black holes.Comment: 9 pages, 1 figur

Black ringoids: spinning balanced black objects in d >= 5 dimensions - the codimension-two case

We propose a general framework for the study of asymptotically flat black objects with k+1 equal magnitude angular momenta in d >= 5 spacetime dimensions (with 0 0 are dubbed black ringoids. Based on the nonperturbative numerical results found for several values of (n, k), we propose a general picture for the properties and the phase diagram of these solutions and the associated black holes with spherical horizon topology: n = 1 black ringoids repeat the k = 0 pattern of black rings and Myers-Perry black holes in 5 dimensions, whereas n > 1 black ringoids follow the pattern of higher dimensional black rings associated with 'pinched' black holes and Myers-Perry black holes

Hawking emission from quantum gravity black holes

We address the issue of modelling quantum gravity effects in the evaporation of higher dimensional black holes in order to go beyond the usual semi-classical approximation. After reviewing the existing six families of quantum gravity corrected black hole geometries, we focus our work on non-commutative geometry inspired black holes, which encode model independent characteristics, are unaffected by the quantum back reaction and have an analytical form compact enough for numerical simulations. We consider the higher dimensional, spherically symmetric case and we proceed with a complete analysis of the brane/bulk emission for scalar fields. The key feature which makes the evaporation of non-commutative black holes so peculiar is the possibility of having a maximum temperature. Contrary to what happens with classical Schwarzschild black holes, the emission is dominated by low frequency field modes on the brane. This is a distinctive and potentially testable signature which might disclose further features about the nature of quantum gravity.Comment: 36 pages, 18 figures, v2: updated reference list, minor corrections, version matching that published on JHE

Higher Dimensional Charged Rotating Dilaton Black Holes

In this paper, we present the metric for the $n$-dimensional charged slowly rotating dilaton black hole with $N = [(n -1)/2]$ independent rotation parameters, associated with $N$ orthogonal planes of rotation in the background of asymptotically flat and asymptotically (anti)-de Sitter spacetime. The mass, angular momentum and the gyromagnetic ratio of such a black hole are determined for the arbitrary values of the dilaton coupling constant. We find that the gyromagnetic ratio crucially depends on the dilaton coupling constant, $\alpha$, and decreases with increasing $\alpha$ in any dimension.Comment: 15 pages, 1 figur