A Heuristic Approach to Predict the Tensile Strength of a Non-Persistent Jointed Brazilian Disc under Diametral Loading

The mechanical response of rock bridges plays a key role in the stability of concrete and rock structures. In particular, the tensile failure of non-persistent discontinuities can result in their coalescence and the failure of rock or concrete engineering structures. The effect of non-persistent joint parameters on rock structures\u27 failure under tensile mode has not been investigated by many researchers yet. Many non-persistent jointed Brazilian concrete discs are tested under diametral loading in this work, to study the influence of joint spacing, joint continuity factor, loading direction with regard to joint angle, and bridge angle on their tensile behavior. Heuristic methods like artificial neural network (ANN), adaptive neuro-fuzzy inference system (ANFIS) and a combination of ANFIS with particle swarm optimization (ANN-PSO) and genetic algorithm (ANFIS-GA) were adopted to explore the relationship between tensile strength and stiffness as the response and non-persistent joint parameters as input parameters. The results revealed that all the applied intelligent methods have the ability to predict tensile strength of non-persistent jointed discs, and their outputs are consistent with laboratory results; however, the ANN approach had the best performance with R2 = 0.966, RMSE = 0.176. In addition, parametric analysis of the proposed model showed that the model is highly sensitive to joint continuity factor and loading direction, while it is sensitive to joint spacing and bridge angle

Dentoskeletal effects of class II malocclusion treatment with the modified Twin Block appliance

The purpose of this study was to prospectively assess the dentoskeletal effect of a modified Twin Block appliance for treatment of class II malocclusions. Lateral cephalograms of 25 Class II malocclusion patients were compared to evaluate skeletal, dentoalveolar and soft tissue changes pre- and post-treatment with a modified Twin Block appliance. A total of 33 angular and linear variables were used for analysis. The differences were calculated at the start and end of treatment. The paired T test was performed to compare the cephalometric measurements before and after treatment. Compared the pre- and post- treatment measurements, there was a significant increase in SNB (P<0.001), CO-Gn (P<0.001), ANS-Me (P=0.001), Mandibular base (P<0.001), Lower 1 to NB (°) (P=0.004), Lower 1 to NB (mm) (P<0.001), and Z-angle (P=0.001) following functional therapy with modified Twin Block appliance. On the other hand, a significant decrease was observed in ANB (P<0.001), NA-Pog (P<0.001), overjet (P<0.001), and overbite (P=0.007), Upper 1 to palatal plane (P=0.007), UL-E-line (P<0.001), LL-E-line (P=0.001), and H-angle (P=0.002) after treatment with modified Twin Block appliance. The modified Twin-Block improves facial esthetics in Class II malocclusion by a combination of changes in skeletal as well as dentoalveolar structures. The increase of mandibular unit length was observed to be due to a true mandibular growth not just a repositioning of the mandible. The modified appliance, however, did not show any superior effects in terms of less dental compensation compared to the conventional Twin?Block appliance

Tensile Behavior of Layered Rock Disks under Diametral Loading: Experimental and Numerical Investigations

The Tensile Strength and Cracking Behavior of Layered Rocks in a Tensile Stress Field Are One of the Most Significant Characteristics of Rock Masses, Which May Strongly Affect the Stability of Rock Structures. the Study Presented Here Investigated the Effect of Layer Spacing and Inclination Angle on the Indirect Tensile Strength, Crack Development, Failure Pattern, and Contact Force Chain of Layered Disks under Diametral Loading using Experimental and Numerical Investigations. Numerous Experimental Models Made from Plaster Were Examined under Diametral Loading, and a Two-Dimensional Particle Flow Code (PFC2D) Was Adopted for in Depth Simulation of the Failure Process. Both Numerical and Experimental Results Were Found to Be in Great Agreement and Showed that the Increase in the Layer Orientation Up to 15° Results in the Peak in the Tensile Strength Followed by a Decrease. Specimens with the Spacing Ratio (SR) of 0.5 and 0.1 Showed the Highest and Lowest Tensile and Compressive Stresses at the Disk Center, respectively. Moreover, the Numerical Analysis Indicated the Formation of Three Failure Pattern Types: TL, PB, and TL-PB. Tensile Cracks Mainly Formed in the Direction of Diametral Loading, and their Maximum Number Formed at 15° and SR = 0.5. Additionally, the Shear Ones Formed in a Conjugate System and Had Negligible Numbers. the Analysis of the Contact Force Chain Showed that the Layers Do Not Affect the Compressive Force Chain at Α \u3c 45° But at Higher Angles, the Stronger Layers Transfer Compressive Force. However, when Α Ranges from 0° to 30°, Tensile Forces Are Distributed in Stronger Layers, and with an Increase in Α, the Concentration of These Forces in These Layers Diminishes and the Forces Are Reoriented in the Direction of Diametral Loading

Critical Reynolds number for nonlinear flow through rough-walled fractures: The role of shear processes

This paper experimentally investigates the role of shear processes on the variation of critical Reynolds number and nonlinear flow through rough-walled rock fractures. A quantitative criterion was developed to quantify the onset of nonlinear flow by comprehensive combination of Forchheimer's law and Reynolds number. At each shear displacement, several high-precision water flow tests were carried out with different hydraulic gradients then the critical Reynolds number was determined based on the developed criterion. The results show that (i) the Forchheimer's law was fitted very well to experimental results of nonlinear fluid flow through rough-walled fractures, (ii) the coefficients of viscous and inertial pressure drops experience 4 and 7 orders of magnitude reduction during shear displacement, respectively, and (iii) the critical Reynolds number varies from 0.001 to 25 and experiences 4 orders of magnitude enlargement by increasing shear displacement from 0 to 20 mm. These findings may prove useful in proper understanding of fluid flow through rock fractures, or inclusions in computational studies of large-scale nonlinear flow in fractured rocks

Three-Dimensional Geostatistical Analysis of Rock Fracture Roughness and Its Degradation with Shearing

Three-dimensional surface geometry of rock discontinuities and its evolution with shearing are of great importance in understanding the deformability and hydro-mechanical behavior of rock masses. In the present research, surfaces of three natural rock fractures were digitized and studied before and after the direct shear test. The variography analysis of the surfaces indicated a strong non-linear trend in the data. Therefore, the spatial variability of rock fracture surfaces was decomposed to one deterministic component characterized by a base polynomial function, and one stochastic component described by the variogram of residuals. By using an image-processing technique, 343 damaged zones with different sizes, shapes, initial roughness characteristics, local stress fields, and asperity strength values were spatially located and clustered. In order to characterize the overall spatial structure of the degraded zones, the concept of ‘pseudo-zonal variogram’ was introduced. The results showed that the spatial continuity at the damage locations increased due to asperity degradation. The increase in the variogram range was anisotropic and tended to be higher in the shear direction; thus, the direction of maximum continuity rotated towards the shear direction. Finally, the regression-kriging method was used to reconstruct the morphology of the intact surfaces and degraded areas. The cross-validation error of interpolation for the damaged zones was found smaller than that obtained for the intact surface

Study on failure mechanism of room and pillar with different shapes and configurations under uniaxial compression using experimental test and numerical simulation

Experimental and discrete element methods were used to investigate the failure behavior of room and pillar with different configurations under uniaxial loading. Concrete samples with dimension of 15 cm × 15 cm × 5 cm were prepared. Within the specimens, rooms and pillars with different configurations were provided. The room dimension was 1 cm × 1 cm, and the pillar dimension was according to the room configuration. Twelve different configurations were chosen for rooms and pillars. The axial load was applied to the model by rate of 0.05 mm/min. The results show that the failure process was mostly governed by both the non-persistent joint angle and joint number. The compressive strength of the specimens was related to the fracture pattern and failure mechanism of the pillars. It was shown that the shear behaviour of pillars was related to the number of the induced tensile cracks, which increased by increasing the room angle. The compressive strength of samples increased with the increase of the room angle. The failure pattern and failure strength are similar in both methods, i.e., the experimental testing and the numerical simulation

Correction To: A Heuristic Approach to Predict the Tensile Strength of a Non-Persistent Jointed Brazilian Disc under Diametral Loading (Bulletin of Engineering Geology and the Environment, (2022), 81, 9, (364), 10.1007/s10064-022-02869-8)

Originally, there is a mistake in the affiliation of the third author. Taghi sherizadeh has just one affiliation as follows: Department of Mining and Nuclear Engineering, Missouri, University of Science and Technology, Rolla, MO 65409, USA The original article has been corrected

Impact of nanohydroxyapatite on enamel surface roughness and color change after orthodontic debonding

Abstract Background The aim of this prospective in vitro study was to evaluate the effect of nanohydroxyapatite (nanoHAP) serum on the enamel surface roughness and tooth color stability after orthodontic debonding procedure. Methods The crowns of 30 premolars were embedded in acrylic blocks with a 4 mm × 5-mm-sized window on the middle third of buccal surfaces. Primary roughness values were evaluated by an atomic force microscope (AFM). After bracket debonding, and polishing procedures, the second roughness parameters were recorded. Specimens were then randomly assigned to two equal groups. NanoHAP serum and HAP toothpaste were applied for 10 days in the first and second groups, respectively. Then, after the third AFM, initial color parameters were measured. Following 1-week immersion in the coffee solution, second color assessment was performed. The fourth AFM was registered after 2 months of aging process. Results All roughness parameters were elevated following debonding procedure. There was no statistically significant reduction in roughness parameters after 10 days of nanoHAP serum or HAP toothpaste application. Both groups showed significant color change after immersion in the coffee solution. Conclusions NanoHAP serum with the protocols used in this study could not restore enamel surfaces to their original condition

Sustained antibacterial activity of orthodontic elastomeric ligature ties coated with a novel kombucha-derived bacterial nanocellulose: An in-vitro study.

Incipient carious lesions, the most common complication in orthodontic patients with fixed appliances, call for the development of novel preventive dental materials that do not rely on patient adherence. The present study aimed to assess the ability of elastomeric ligatures coated with bacterial nanocellulose (BNC) to deliver sustained antibacterial activity, during the standard 28-day interval between orthodontic appointments, without compromising their mechanical properties. Kombucha membrane was used to produce cellulose as a secondary product from the fermentation of tea broth with symbiotic bacteria and yeast culture. Characterization of BNC-coated elastomeric ligatures was performed using Fourier Transform Infrared Spectroscopy and Energy Dispersive Spectroscopy analysis. The samples were pre-treated by immersion first in isopropyl alcohol, then in 8 mL nanocellulose solution for 7 days. Tensile strain and strength of the BNC-coated and conventional ligatures were evaluated using a tensile testing machine. Direct contact and agar diffusion tests were performed to assess the antibacterial activity of nanocellulose. In addition, the release profile of BNC was evaluated. Data analysis was performed by one-way analysis of variance (ANOVA) followed by post-hoc Tukey's test and Wilcoxon signed-rank test. P values less than 0.05 was regarded as significant. There was no statistically significant difference in tensile strain and strength between the BNC-coated and conventional ligatures. The coated ligatures provided sustained antibacterial activity during the required 28 days. The use of BNC-coated elastomeric ligatures in patients with fixed orthodontic appliances might be a promising solution to plaque formation and subsequent enamel decalcification