Calculating of dumps stability laying on weak gently dipping interface

Relevance of the research. Stable parameters of dumps are critical in mining operations ensuring their safety and economic efficiency. This problem is particularly acute for mining enterprises engaged in surface mining and for coal open pit mines, in particular. One of the main problems of this issue is related to the substantiation of rigorous methods for assessing stability and determining the limiting parameters of external and internal dumps filling an embankment on weak gently dipping interface. In the technical and regulatory literature, this issue has been considered for a long time. However, there are no specific recommendations for finding the most dangerous sliding surfaces on slopes, as well as methods for calculating shearing and restraining forces along these surfaces. All the signs are that the reason for the stability loss of operated dumps is the absence of theoretically substantiated design schemes, respectively, there are errors in the design of dumping. Purpose of the work is to develop reliable methods for calculating the limiting parameters of dumps on weak gently dipping interface. The main idea of the work is to apply a new, not previously used scheme for calculating the stability of dumps on weak gently dipping interface. Research methods. The work deals with the apparatus of flow mechanics and more specifically, the rigid-plastic model (the method of limit equilibrium), and the variational, integral and differential branches of calculus act as a mathematical apparatus. Results and conclusions. Based on the results of previous studies, a new scheme for calculating the stability of the dump during its destruction along weak interface was proposed, which implies the absence of a curved section of the sliding surface under the slope and the convex shape of the sliding surface under the berm. In contrast to the existing calculation schemes, such a calculation scheme predicts significantly lower values of the critical parameters of dumps. It means that the use of the proposed scheme will prevent the destruction of dumps by landslides along the dumpbasement interface and increase the economic efficiency of enterprises. Because a sufficiently large overestimation of the critical parameters of dumps at weak interface limited by current regulatory documents has been determined, it is recommended to revise these parameters for the designed and operated dumps using the proposed schemes for calculating their stability.

Examining The Mechanical and Durability Properties of Concrete Containing Recycled Fine Aggregates Possessing Different Contamination Levels

Three types of recycled fine aggregates (RFA) possessing different contamination levels (washed – unwashed) were used in the present study. RFAs were used instead of natural fine aggregate (NFA) at the concentrations of 10%, 20%, 40%, and 80%. No significant negative characteristics were observed in green and hardened characteristics of concrete when using RFA at up to 80% concentration. However, using less-washed or unwashed RFA at 10% or 20% concentration is generally appropriate. The use of less-washed or unwashed RFAs at the concentration of 40% or more negatively affects the slump values of concrete. Especially the use of unwashed RFA at 80% concentration yielded more significant damages. The non-hydrated cement particles in the RFA show insemination or hardening acceleration behavior and affected the 7-day pressure strength of concrete at a higher level. However, together with the use of RA having a weak interface transition zone, the splitting tensile strength values of concretes more significantly decreased. In conclusion, it was determined that RFAs can be used up to 80% concentration after an appropriate washing procedure. From the aspect of costs, in order to prevent durability problems, it should not be used at any concentration higher than 20% without a washing procedure. From the aspect of protecting the sustainable environment and natural sources, it is very important to increase the use of RFAs in concrete production.

Tensile and fatigue properties of fiber-reinforced metal matrix composites Cf/5056Al

Fiber-reinforced metal matrix composites have mechanical properties highly dependent on directions, possessing high strength and fatigue resistance in fiber longitudinal direction achieved by weak interface bonding. However, the disadvantage of weak interface combination is the reduction of transversal performances. In this article, tensile and fatigue properties of carbon fiber-reinforced 5056 aluminum alloy matrix (Cf/5056Al) composite under the condition of medium-strength interface combination are carried out. The fatigue damage mechanisms of Cf/5056Al composite under tension–tension and tension–compression loads are not the same, but the fatigue life curves are close, which may be the result of the medium-strength interface combination.

A Potential High-Throughput Route to Collagen-Mimicked Carbon Nanotube Fiber via Domino Pushing and Ion Bombardment

Carbon nanotubes (CNTs) have been shown owning extraordinary mechanical properties for decades, but to date, their wide application as load-bearing structural materials has not been realized mainly due to the critical obstacles of weak interface, poor distribution and alignment, and lack of economic technology for mass production and processing. In order to overcome these obstacles, we proposed a potential route from as-grown CNT forest to collagen-mimicked CNT films with covalently crosslinked CNTs arranged in a staggered alignment. To consolidate the foundation of the route, its critical step of ion bombardment to construct the intertube crosslinks in CNT films was simulated using molecular dynamics simulations. Results show that the ion bombardment can efficiently construct the intertube crosslinks and greatly improve the elastic modulus and strength of CNT films by as much as 24% and 660%, respectively, with comparison to the nonbombarded ones. The influences of the number and the kinetic energy of the incident particles were systematically investigated and the corresponding contours were presented, suggesting the optimal energy and number of the incident particles for the elastic modulus and strength of collagen-mimicked CNT films. The work not only provides a novel route to mass fabrication of high-performance CNT fibers but also gives useful guidelines on the optimization of processing design.

Micro- and Macromechanical Properties of a Composite with a Ternary PLA–PCL–TPS Matrix Reinforced with Short Fique Fibers

Biocomposites were prepared from a ternary matrix of polylactic acid (PLA), polycaprolactone (PCL), and thermoplastic starch (TPS) and reinforced with native fique fibers from southwestern Colombia. The influence of surface modification by alkalization of fique fibers on the interfacial properties of the biocomposite was studied using pull-out tests. Additionally, the effect of short fique fibers in three proportions (10%, 20%, and 30% (w/w)) on the tensile mechanical properties of the composite was evaluated. The experimental results indicated that the interfacial shear strength (IFSS) of the ternary matrix was predominantly influenced by PCL and characterized by the development of a weak interface that failed due to matrix yielding. Furthermore, the incorporation of short fique fibers increased the elastic modulus of the composite to values similar to those estimated with the Tsai–Pagano model. The alkalization treatment of the fique fibers improved the interface with the composite matrix, and this phenomenon was evidenced by the results of the micromechanical and tensile characterizations of the composite.

An Investigation into the Effects of Weak Interfaces on Fracture Height Containment in Hydraulic Fracturing

Hydraulic fracturing is an effective method for developing unconventional reservoirs. The fracture height is a critical geometric parameter for fracturing design but will be limited by a weak interface. Fracture containment occurs when fracture propagation terminates at layer interfaces that are weaker than the surrounding rock. It always occurs in multilayer formation. Therefore, the mechanism of fracture height containment guides fracture height control in hydraulic fracturing. In order to study the fracture containment mechanism, this paper first calculates the propagation behaviour of the fracture in 3D under the influence of a weak interface through a block discrete element method and analyzes the geometric characteristics of the fracture after it meets the weak interface. Then, the induced stress of the hydraulic fracture on the weak interface is calculated by fracture mechanics theory, and the mechanism of blunting at the fracture tip is explained. Then, two kinds of interface slippage that can lead to blunting of the fracture tip are discussed. Based on the behavior of shear slippage at the interface, a control method for multilayer fracturing in thin sand-mud interbed and pay zone fracturing in shale is proposed. The results show that the fracture height is still limited by the weak interface in the formation without the difference of in-situ stress and rock properties. Interface slippage is the main factor impeding fracture propagation. Fracture height containment can be adjusted and controlled by changing the angle between the hydraulic fracture, the interface, and the stress state to strengthen and stiffen the interface. This study has a certain guiding significance for fracture height control in the design of hydraulic fracturing of shale or thin sand-mud interbed reservoirs.

Harnessing the interface mechanics of hard films and soft substrates for 3D assembly by controlled buckling

Techniques for forming sophisticated, 3D mesostructures in advanced, functional materials are of rapidly growing interest, owing to their potential uses across a broad range of fundamental and applied areas of application. Recently developed approaches to 3D assembly that rely on controlled buckling mechanics serve as versatile routes to 3D mesostructures in a diverse range of high-quality materials and length scales of relevance for 3D microsystems with unusual function and/or enhanced performance. Nonlinear buckling and delamination behaviors in materials that combine both weak and strong interfaces are foundational to the assembly process, but they can be difficult to control, especially for complex geometries. This paper presents theoretical and experimental studies of the fundamental aspects of adhesion and delamination in this context. By quantifying the effects of various essential parameters on these processes, we establish general design diagrams for different material systems, taking into account 4 dominant delamination states (wrinkling, partial delamination of the weak interface, full delamination of the weak interface, and partial delamination of the strong interface). These diagrams provide guidelines for the selection of engineering parameters that avoid interface-related failure, as demonstrated by a series of examples in 3D helical mesostructures and mesostructures that are reconfigurable based on the control of loading-path trajectories. Three-dimensional micromechanical resonators with frequencies that can be selected between 2 distinct values serve as demonstrative examples.