Present study deals with the prediction of crack initiation angle for mixed mode (I/II) fracture using finite element techniques and J-Integral based approach. The FE code ANSYS is used to estimate the stress intensity factor numerically. The estimated values of SIF were incorporated into six different crack initiation angle criteria to predict the crack initiation angle. Single edge crack specimens of Araldite-Hardener were used for the present analysis. Load was applied up to critical limit of the specimens containing crack at different angles of inclination. The crack initiation angle obtained using stress intensity factor and J-integral based approach were found close to each other and also found to be in good agreement with the available experimental results in literature. It is also investigated that as crack inclination angle increases material was found to behave in a brittle manner.

Roller compacted concrete pavement (RCCP) is a zero-slump and stiff-dry mixture which is usually placed with an asphalt paver and compacted by conventional vibratory roller compactors to achieve the required density. RCCP consistently has a slightly lower cement content than conventional concretes of similar strength. Nowadays, RCCP is used for any type of industrial or heavy-duty pavement and has advantages including cost saving as a result of the construction method and the increased placement speed of the pavement. Therefore, the use of RCCP pavement has become more and more popular in recent years. There are numerous studies on the mechanical properties of fibre reinforced focused on cement paste and normal concrete. However, our understanding of what exactly happens when hybrid fibres used to reinforce RCCP mixes with respect to fracture toughness is quite limited. Accordingly, in this study, three point bending test was carried out on mono and hybrid fibre-reinforced RCCP based on modified two-parameter model to determine the value of Mode I plane-strain fracture toughness of fibre-reinforced RCCP by considering possibility of crack deflection during its propagation through modified two-parameter fracture model. Finally, it can be observed that, for great amount of fracture angle, the application of Two-parameter fracture model instead of modified Two-parameter fracture model cause to an overestimation of the fracture toughness values.

The critical crack Tip Opening angle ( ) is considered as a convenient parameter to characterize the crack arrest toughness of natural gas pipeline. Load-displacement curve is a comprehensive reflection of geometry, mechanical property and fracture behavior of a loaded specimen, so it would be highly advantageous to deduce from load-displacement curve directly. From force-displacement curves, maximum force of 209kN and 207kN were obtained for experimental and numerical data, respectively. In this article, a combination of load-displacement and deformation of the drop weight tear test specimen was used to calculate the critical crack tip opening angle. For this purpose, the simplified single-specimen test method was used. The is dependent on the slope of the steady-state crack growth region and the plastic rotation factor. Firstly, based on the fact that load decreases linearly with the increment of displacement during steady-state crack growth, the slope of the experimental load-displacement curve of API X65 steel in the steady-state crack growth region was obtained as 21. 583. Secondly, by modeling the drop weight tear test in Abaqus software and using two methods of mises stress and neutral axis, the plastic rotation factor was obtained as 0. 5688 and 0. 5651, respectively. Finally, these parameters were used and the critical crack tip opening angle was determined as 12. 00 and 12. 08 degrees.

Oscillations in various structures of the solar atmosphere, such as transverse (kink) oscillations of coronal loops, can be used in seismology. Transvers kink oscillations of coronal loops are often accompanied by solar flares. Despite the intensive study of kink oscillations of coronal loops in recent years, the excitation mechanism of these oscillations are still not known. In this paper, we aim to clarify the excitation mechanisms of transverse oscillations of coronal loops. For this purpose, first 458 oscillation events were identified by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) during its first ten years (2010–2019) with the use of the Helioviewer, JHelioviewer and Heliophysics Events Knowledgebase (HEK). Then, the association of these oscillation events with probable mechanism for exciting the kink oscillations such as flares, lower coronal eruptions and plasma ejections, and coronal mass ejections bursts were listed. Finally, about 138 suitable kink oscillations out of 485 oscillations with high-amplitude, long oscillation period and visible through the naked eye that were accompanied with other probable excitation mechanism of kink oscillations, were selected. This statistical analysis of the transverse oscillation coronal loops showed that that 102 of these 138 oscillation events (74 %) were associated with lower coronal eruptions or plasma ejections. About 38 oscillations out of 138 transverse oscillations (27.5%) were associated with coronal mass ejections/eruption. Also, 65 events (47 %) were associated with flares. The required speed of hypothetical drivers of transverse oscillations were calculated. The magnitude values of calculated speeds for shock wave of flares were found to be lower than 500±100 km/s in 87% of the cases. Also, the magnitude values of speeds for lower coronal mass eruption/ejection were obtained to be lower than 500±125 km/s in 94% of the cases. The magnitude values of these speeds are acceptable for lower coronal mass eruption/ejection. But, such low speeds do not favor the association of the oscillation excitation with a shock wave of flares, as usually assumed. Also, statistical analysis of start time and time difference of hypothetical drivers of transverse oscillations showed that there is no clear correlation between them. The results of this study indicated that shock wave of flares cannot be the main cause of transverse oscillations of coronal loops. So, this analysis shows that the most probable excitation mechanism of the kink oscillations of coronal loops are eruptions or plasma ejections rather than the blast shock waves ignited by flares. ‎

The flow of binary granular mixture made of fine sand and sugar into a vertical Hele-Shaw cell gives rise to heaps exhibiting segregation and stratification. Our experimental study shows that the ratio of flow rate and wall separation decides which of these two will occur. We find the phase diagram of heap morphologies classified as a function of the ratio of flow rate and wall separation. We find that the wavelength of the stratification is scaled by this ratio. We observed that in every flow rate the product of wavelength, and wall separation remains constant, so the wavelength varies with wall separation by a monotonic function (I/d). Granular stratification is found to occur only in a confined region of the parameter space. We present an interpretation for the existence of this region in phase space.

The temperature increase of the solar corona compared to the lower layers solar atmosphere, such as the photosphere  and chromosphere, and the solar wind, are still two unsolved issues in solar physics. Due to the higher magnetic pressure of the corona compared to the thermal pressure of the corona, solar loops have magnetic structures that can play a role in the transfer of thermal energy in the upper solar atmosphere. Therefore, measuring the magnetic field in these structures is special importance. A seismological method based on MHD waves has recently been developed to measure the coronal magnetic field based on wave signatures observed in the solar atmosphere. Due to the presence of MHD waves, coronal waves can be generated in the vicinity of magnetic reconnections, or disturbances that can reach the solar corona through the photosphere-coupled magnetic field. The basis of this method is similar to the seismology of the sun. In this way, by observing and then considering the appropriate model for the corona structure, wave characteristics and physical parameters of the environment such as amplitude, temporal and spatial spectrum, temperature and density structures can be obtained and the observed properties with physical parameters compared. But the source of these waves has not been determined definitively, although p-states in the photosphere have been introduced as a clear candidate for the source of these waves. In this research, using the images observed with the Hinode X-ray telescope (Hinode/xrt) taken on 11 September, 2017 in the global time interval 06:20:16 to 17:56:25, the physical parameters such as loop length, period, phase speed, Alfven speed and the magnetic field related to them are determined by image processing and seismology. After receiving the images and preparing time slices from them, these transverse fluctuations are analyzed using the wavelet method. The length of three loops was determined by approximating half a loop as 113.0±1.1, 80.0 ±0.8, and 63.0±0.6 Mm. Considering the approximate values ​​of the plasma density in the rings and the average molecular weight in the corona as well as the average number density in the corona, the average time of oscillations was obtained in the range of 3.0-16.0, 3.0-4.0 and 3.0-8.0 minutes, respectively. The maximum phase speed of these oscillations was calculated in the range of 1250±628, 890±445 and 700±350 km s-1 for three loops. Also, maximum Alfven speed in each loop was determined as 904±452, 640±320, and 504±252 km s-1 respectively. The maximum magnetic field related to these oscillations was calculated by the seismological method with the approximation of the thin cylindrical model for three loops in the range of 16.0±8.0, 11.0±5.5, and 8.2 ±4.1 Gauss respectively. Also, the correlation of oscillations in the largest loop was analyzed by the wavelet method and the results showed that for certain frequencies, the basic kink mode and the first excited mode of the kink appear in the oscillating tube. According to the results of this research, these fluctuations can be interpreted as transverse kink oscillations.

SummaryGeomechanical properties of some sedimentary and metamorphic rocks are important because they are anisotropic.  These properties affect on stability of rock construction. In this research, the changes in the stress intensity factor in anisotropic rock have been investigated based on the changes in the crack angle with the loading axis and anisotropy ratio. In this research, the finite element method and ABAQUS software are used because of their ability to simulate anisotropic rock. The CCNBD disc sample was used according to the standards of ISRM. It concluded that the stress intensity factor is dependent on the anisotropy ratio, layering angle, and crack length and pure tension (mode one) does not necessarily occur at a zero-crack angle with the loading axis (β=0), and this angle is completely affected by the layering angles (Ѱ).Introduction Investigating the behavior of rock under load and determining its mechanical properties are important to designing rock structures. The importance increases when the rock is anisotropic. In the design two mechanical properties; the first rock strength and the second deformation should be considered. The anisotropy rocks require the simultaneous investigation of the resistance behavior and the failure mechanism [1]. A rock is called anisotropic when the value of mechanical properties is different in two different directions. Fracture toughness is the critical stress intensity factor of a sharp crack where propagation of the crack suddenly becomes rapid and unlimited [2].For materials that have linear elastic behavior, this property is usually expressed in terms of a quantity called the critical value of the stress intensity factor. This parameter is indicated by the symbol K [3] In this research, the main question is to investigate the changes in the stress intensity factor in anisotropic rocks by changing the angle of the crack with the loading axis, anisotropy ratio, crack length, and layering angle.Methodology and ApproachesFor investigation of research question numerical method was considered. The software used Abaqus finite element(FEM) [4]. Abaqus is a set of powerful engineering simulation programs based on the FEM and can solve a wide range of problems from a relatively simple linear analysis to very complex nonlinear analysis. The rock sample was an anisotropic Phyllite belonging to the abutment of the Azad Dam in Kurdistan and the mechanical properties of the sample were taken from Abadat (2013) [5]. CCNBD disk numerical models (D=54 mm and t=30 mm) of Phyllite according to the standard of the International Society of Rock Mechanics (ISRM) with anisotropy ratio (E/E'=1.8 and E/E'=4) in different layering angles (ψ=0-30°-45°-60°-75°-90°) and in different crack angles with loading extension (β) and in different crack lengths (a=12-24-36 mm) were built and executed by Abaqus. After execution, the Abacus determined the stress intensity factor of each model, and data were collected and analyzed.Results and ConclusionsSensitivity analysis by variation of four parameters which were anisotropy ratio, different layering angles, different crack angles with loading extension, and different crack lengths was carried out. 180 models were built and executed by Abacus software. Three parameters were kept constant the last was changed and the stress intensity factor was evaluated. Figures 2, 3, and 4 show the effect of the anisotropy ratio variation on the angle of the crack with the loading axis in the pure tensile (mode one), pure shear (mode two), and mixed-mode in the crack length of 12 mm respectively.1- Variations of layer angle (ψ), crack angle with loading axis (β), crack length(a), and change of anisotropy ratio have a noticeable effect on the values of the stress intensity factor.2- In different crack lengths and in different anisotropy ratios, for a constant layering angle, the stress intensity factor of tensile mode is maximum at β=0 and minimum at β=90° and the stress intensity factor of shear mode is minimum at β=0 and β=90̊ and maximum at β between 30̊-40̊.3- Mode one(pure tensile) in different angles of layering does not necessarily occur at a zero-degree angle with the loading axis (β=0) and this angle is completely affected by the angles of layering (Ѱ).4- According to the results in different layering angles and in different anisotropy ratios, the β angle is different, so that the pure tensile in the layering angle of 30° and the anisotropy ratio equal to 4 occur in β =6°. However, this value is equal to 2° for the anisotropy ratio equal to 1.8

We have studied quark matter coupled with string cloud and domain walls in the context of general relativity. For this purpose, we solved Einstein's field equations for quark matter coupled to the string cloud and domain walls in spherical symmetric kink space-time. It is found that cosmic strings and domain walls do not survive in this space-time. Hence, the space-time in both the cases reduces to Minkowskian and the space-time is flat.