Issue 3

JTAM, Sofia, vol. 47 Issue 3 (2017)

Regular Mechanical Transformation of Rotations into Translations: Part 2. Kinematic Synthesis of the Elements of High Kinematic Joints, Realizing the Process of Motions Transformation

Emilia Abadjieva1, Valentin Abadjiev2
1Graduate School of Engineering and Resource Science, Faculty of Engineering and Resource Science, Akita University, Tegatagakuen-machi 1-1, Akita, Japan
2Institute of Mechanics, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., bl. 4, 1113 Sofia, Bulgaria

This work is developed on the basis of the illustrated main parts of the kinematic theory (theory of gearing) of the spatial rack drives in Part 1 of this study. The applied theoretical approach to their synthesis, based on the T. Olivier's second principle is defined. A study of the geometric nature of the surface of action (mesh region, respectively) of these class transmissions is shown. Research software programs for synthesis and visualization of these transmissions and their specific elements are elaborated, on the basis of the given algorithms to the synthesis of the elements of high kinematic joints (active tooth surfaces), with which the movable links of the studied gear systems are equipped.

JTAM, Sofia, vol. 47 Issue 3 pp. 03-24 (2017), [Full Article]

Heat and Mass Transfer of Unsteady Hydromagnetic Free Convection Flow through Porous Medium Past a Vertical Plate with Uniform Surface Heat Flux

Mohamed Abd El-Aziz1,2, Aishah S. Yahya2
1King Khalid University, Faculty of Science, Mathematics Department, Abha 9004, Saudi Arabia
2Helwan University,Faculty of Science, Mathematics Department, P.O.Box, 11795, Cairo, Egypt

Simultaneous effects of thermal and concentration diffusions in unsteady magnetohydrodynamic free convection flow past a moving plate maintained at constant heat flux and embedded in a viscous fluid saturated porous medium is presented. The transport model employed includes the effects of thermal radiation, heat sink, Soret and chemical reaction. The fluid is considered as a gray absorbing-emitting but non-scattering medium and the Rosseland approximation in the energy equations is used to describe the radiative heat flux for optically thick fluid. The dimensionless coupled linear partial differential equations are solved by using Laplace transform technique. Numerical results for the velocity, temperature, concentration as well as the skin friction coefficient and the rates of heat and mass transfer are shown graphically for different values of physical parameters involved.

JTAM, Sofia, vol. 47 Issue 3 pp. 25-58 (2017), [Full Article]

Failure Mechanisms of Brittle Rocks Under Uniaxial Compression

Taoying Liu1,2, Ping Cao1
1School of Resources & Safety Engineering, Central South University, Changsha, Hunan, 410083, China
2Ma’anshan Institute of Mining Research, Ma’anshan, Anhui, 243004, China

The behaviour of a rock mass is determined not only by the properties of the rock matrix, but mostly by the presence and properties of discontinuities or fractures within the mass. The compression test on rock-like specimens with two prefabricated transfixion fissures, made by pulling out the embedded metal inserts in the pre-cured period was carried out on the servo control uniaxial loading tester. The influence of the geometry of pre-existing cracks on the cracking processes was analysed with reference to the experimental observation of crack initiation and propagation from pre-existing flaws. Based on the rock fracture mechanics and the stress-strain curves, the evolution failure mechanism of the fissure body was also analyzed on the basis of exploring the law of the compression-shear crack initiation, wing crack growth and rock bridge connection. Meanwhile, damage fracture mechanical models of a compression-shear rock mass are established when the rock bridge axial transfixion failure, tension-shear combined failure, or wing crack shear connection failure occurs on the specimen under axial compression. This research was of significance in studying the failure mechanism of fractured rock mass.

JTAM, Sofia, vol. 47 Issue 3 pp. 59-80 (2017), [Full Article]

Analytical Solution of Displacements Around Circular Openings in Generalized Hoek-Brown Rocks

Houxu Huang1, Jie Li1, Jiuqi Wei2
1State Key Laboratory of Disaster Prevention and Mitigation of Explosion and Impact, PLA University of Science and Technology, Nanjing, China
261489 Army Unit, Luoyang, China

The rock in plastic region is divided into numbers of elements by the slip lines, resulted from shear localization. During the deformation process, the elements will slip along the slip lines and the displacement field is discontinuous. Slip lines around circular opening in isotropic rock, subjected to hydrostatic stress are described by the logarithmic spirals. Deformation of the plastic region is mainly attributed to the slippage. Relationship between the shear stresses and slippage on slip lines is presented, based on the study of Revuzhenko and Shemyakin. Relations between slippage and rock failure are described, based on the elastic-brittle-plastic model. An analytical solution is presented for the plane strain analysis of displacements around circular openings in the Generalized Hoek-Brown rock. With properly choosing of slippage parameters, results obtained by using the proposed solution agree well with those presented in published sources.

JTAM, Sofia, vol. 47 Issue 3 pp. 81-95 (2017), [Full Article]