Pull-out Process Research Articles

A New Laboratory Short Encapsulation Pull Test for Investigating Load Transfer Behavior of Fully Grouted Cable Bolts

A new laboratory short-encapsulation pull test was developed to better understand load transfer behavior of fully grouted cable bolts that are commonly used in underground mines. Within the embedment section, a series of tests was performed to examine the effect of confining medium diameter on the maximum bearing capacity of cable bolts. A bearing plate appropriate for the investigation of bond failure at both cable/grout and grout/rock interfaces was designed. To prevent a cable bolt from rotating during the pull-out process, a system of locking keys and nuts was integrated into the design to couple together the holder tube, anchor tube, and bearing plate while still allowing axial movement of the cable bolt. Three experiments were conducted. First, different termination methods were used and compared to evaluate the effect of termination instruments on the performance of cable bolts. Then, the confining medium was subjected to a range of preconfinement pressures to determine its effect on cable bolt performance. And finally, the effect of borehole roughness on the pull-out behavior of plain and modified cable bolts was investigated. Once the testing environment was determined, pull-out tests were undertaken on plain and modified cable bolts in a medium-strength material.

Study of the interaction of the rupture zones of contiguous anchor plates in analogical medium

Knowing what occurs above anchor plates is certainly instructive. In this general vision of the interaction soil-anchor plates that our work was directed. An experimental study which required the design and implantation of a model containing plastic granules powder to similate a natural environment, is presented. The latter is subjected to the removal of anchor paltes. For each test, digital photographs are taken to materialize different deformed configurations during the pullout process. These photos processed in couples by the 7D software (image correlation) giving the evolution of the displacement field and plane strain analogical environment. Particular attention is paid to the discussion of the interference of rupture zones of contiguous anchors by reducing the distance between plates.

Experimental and Numerical Study of the Interfacial Shear Strength in Carbon Fiber/Epoxy Resin Composite under Thermal Loads

This study examined the influence mechanism of temperature on the interfacial shear strength (IFSS) between carbon fiber (CF) and epoxy resin (EP) matrices under various thermal loads using experimental and numerical simulation methods. To evaluate the change in IFSS as a function of the increase in temperature, a microbond test was performed under controlled temperature environment from 23°C to 150°C. The experimental results showed that IFSS values of CF/EP reduce significantly when the temperature reaches near glass transition temperature. To interpret the effect of thermal loads on IFSS, a thermal-mechanical coupling finite element model was used to simulate the process of fiber pull-out from EP. The results revealed that temperature dependence of IFSS is linked to modulus of the matrix as well as to the coefficients of thermal expansion of the fiber and matrix.

Study on Single-yarn Pullout Test of Ballistic Resistant Fabric under Different Preloads

During bullet penetrating fabric, the pull-out force of yarn in fabric is related to the impact resistance of fabric when the yarn is pulled out from the fabric. The complex uncrimping and friction slip behavior occur during the yarn pullout process, which is critical to learn the impact resistance of fabric. Based on digital image correlation technique, the deformation behavior of Kevlar 49 fabric subjected to preload during the single-yarn pullout process was studied in this paper. The pullout force and displacement curve shows a straight rise and an oscillated decrease. In the linear rise stage, the yarn uncrimping causes a static friction effect. The maximum of the pullout force is not linearly increased with the preload. In the oscillating descending stage, the local descent of the pullout force indicates that the yarn end is gradually withdrawn from the fabric, and the local rise indicates that the yarn end moves to the next weft/warp interaction until the yarn is completely pulled out. The shear deformation of fabric corresponds to the single-yarn pullout process.

Experimental investigation of compaction-grouted soil nails

An innovative compaction-grouted soil nail was designed by injecting grout into a special latex balloon (grouting bag) to avoid bleeding and penetration of grout into the surrounding soil. A series of large-scale model tests was performed to study the surrounding soil responses due to grouting and the subsequent pull-out resistance of the soil nail. The experimental results show that grouting pressure plays an important role in the enhancement of the density and (or) strength of the surrounding soil. In addition, during the pull-out process, the compaction-grouted soil nail exhibits a strain-hardening behaviour without a yield point. This is a significant advantage of this new soil nail, indicating that it can enable soil masses to remain stable against a relatively large deformation before ultimate failure. The main factors behind the improvement of the pull-out resistance of the new soil nail are, first, the compaction–densification of the soil near the grouting bag due to grouting, resulting in the enhancement of the shear strength of the soil, and, second, the enlargement of the grouting bag, causing the increase of the interface shear and end resistance to the pull-out of the soil nail.

Mechanically robust TiAlSiN coatings prepared by pulsed-DC magnetron sputtering system: Scratch response and tribological performance

In this study, scratch tests and wear tests were performed on a series of magnetron sputtered TiAlSiN coatings. These coatings varied from coarse columnar grains to fine fibrous grains in microstructure, accompanied by a gradual increase in hardness and modulus values. The analysis of the scratch results showed that the critical loads (Lc1 and Lc2) were related to the H/E* and H3/E*2 values, where higher H/E* and H3/E*2 led to higher critical loads. The improvement in scratch toughness might benefit from the complex cracking patterns in fine-grained coatings before coating spallation occurred. The wear performance of these TiAlSiN coatings against a ruby ball revealed that coatings with coarse columnar grains possessed better wear resistance than fine-grained coatings despite the fact that fine-grained coatings had higher H/E* and H3/E*2 values. It is believed that coatings with coarse columnar grains could restrain the grain pull-out process during abrasive dry sliding. In some cases, the compact layer of wear debris on the wear track, which can provide additional load bearing capacity, is beneficial to the wear resistance of the coating.

A comparison study on mechanical properties of polymer composites reinforced by carbon nanotubes and graphene sheet

To compare enhancements of mechanical properties of polymer composites reinforced by carbon nanotubes and graphene sheet, molecular models of polymer matrix reinforced by the same weight percentage of carbon nanotubes and graphene sheet are developed. Pull-out process and strain constant method are applied to find mechanical properties of the nano-composites by examining the interfacial interactions between nano-reinforcements and polymer matrices. The results show that about 18% higher in Young's modulus, 8.7% higher in tensile strength, and 5% higher in surface crack energy are obtained for the composites by incorporation of graphene sheet than those by incorporation of carbon nanotubes. Graphene sheet is found to play a better role in delaying the propagations of cracks. To explore the mechanisms on the enhanced tensile and fracture properties, the interfacial interaction energy and shear forces between the nano-reinforcements and polymer matrices, and total van der Waals energy of the polymer composites are examined and interpreted accordingly.

Analytical analysis of dynamic stress distribution of fiber reinforced polymer rod based on realistic boundary shear stress

Abstract A closed-form analytical solution of the dynamic stress distribution of the fiber reinforced polymer (FRP) rod is presented in this paper. It is derived based on a trilinear model from a boundary shear stress of the FRP rod. The dynamic stress distribution of the FRP rod during the pull-out process can be modelled by this analytical solution, which is correlated against experimental data. Especially, the stress distributions of the rod at six evolution points are studied. This analytical solution offers a new approach for predicting the ultimate load bearing capacity of the FRP rod.

Synergistic Reinforcing Mechanisms in Cellulose Nanofibrils Composite Hydrogels: Interfacial Dynamics, Energy Dissipation, and Damage Resistance.

Engineering reversible cross-links between nanoparticles and polymer matrix is a promising avenue to reinforce the mechanical properties of elastomers and in particular soft hydrogels. In this work, we study a model system of composite hydrogel reinforced with cellulose nanofibrils (CNFs), where the integration of reversible hydrogen bonds into a lightly covalently cross-linked polyacrylamide (PAAm) matrix. This approach yields the dual cross-linked networks with synergistically improved strength, modulus, and toughness. The reversible nature of the hydrogen-bonded cross-links manifests a strong strain rate (έ) dependent dynamics properties. The CNF-PAAm interaction among physically adsorbed chains on the surface of CNF is examined as a function of CNF fraction by sum frequency generation spectroscopy. The results indicate a decrease of the number of free -OH groups on the CNF surface. Moreover, the deformation-resting experiments show a unique interface stiffening mechanism where the polymer chains desorbed from the CNF surface under oscillatory shear become entangled during resting time. The bending micromechanics test reveals that the CNF interfacial slip imparts the capability to strengthen the composites during deformation. The fibril pull-out process activates a series of dissipation mechanisms that increase the crack propagation resistance. These findings advance our understanding the role of interfacial layer in microscopic reinforcement mechanism and provide a constitutive foundation for exploring the deformation behaviors of the cellulosic hydrogels.

Nature of the pull-out system of carbon nanorope/polyethylene composite and twisting effect on interfacial behavior

The nature of the pull-out system of carbon nanorope/polyethylene (CNRP/PE) composite is studied by using molecular dynamics approach. The deformation of the CNRP/PE composites in pull-out process is exhibited. The influence of twisting deformation on the interfacial interaction of the composites is investigated. The results show that the energy of the pull-out system is conserved; and the interfacial bonding is weak resulting in a sliding failure of the CNRP inside PE matrix.

Loading, support and geometry effects for pin-reinforced hybrid metal-composite joints

Reliable joining technologies are increasingly required for multi-material lightweight structures. For metal-composite joints, there is significant potential to integrate through-thickness pins onto the metal surface to improve bond strength. We investigated Selective Laser Melting manufactured Ti-64 adherends with integrated pins bonded to carbon fibre-reinforced polymer composite, and characterised joint performance from pure tension to shear-dominated pin loading. Both single pin and multi-pin double cantilever beam specimens were examined and correlated using experimental and finite element methods. Adherend support conditions affected the single pin pull-out process and related energy absorption up to 35% for all pin offset angles. The pin alignment with respect to the crack direction and fibre angle had little effect on joint performance. Pins with grooved surface features further increased energy absorption by 60% compared to smooth cylindrical pins. This work adds significant insight into pin-reinforced hybrid metal-composite joints and their performance and optimisation in realistic structural scenarios.

Enhancement of tribological properties of polymer composites reinforced by functionalized graphene

Abstract Polymer composites reinforced by pristine and functionalized graphene are investigated to identify the improvement of tribological properties of polymer composites. A pull-out process is conducted to study the interfacial interactions between polymer matrices and graphene reinforcements using molecular dynamics simulations. Molecular layer models containing Fe atoms as the top nano-layer are built to study the enhancement of tribological properties of the polymer composites by sliding the top Fe nano-layer on the surface of the polymer matrix. The simulation results show that decreases of about 13% and 42.3% in the average friction coefficient and abrasion rate of the functionalized graphene/polymer composites can be achieved. In order to provide the understandings of the findings, the interfacial interaction energy, RDF values between graphene and polymer matrix are particularly calculated and discussed.

Failure Mode and Pullout Capacity of Anchor Piles in Clay

Anchor piles are wildly adopted in mooring systems. However, there are still challenges in predicting the failure mode and pullout capacity of the pile. Previous Finite Element (FE) analysis was all based on the traditional small strain FE analysis. The whole pullout process of the pile cannot be simulated. Hence, the failure mode of the pile is hard to be understood, especially under small loading angles to the horizontal. In addition, theoretical analysis received limited attention in analyzing the failure mode and pullout capacity of anchor piles under inclined loading. In the present work, both Large Deformation Finite Element (LDFE) and theoretical analyses are performed to investigate the failure mode and pullout capacity of anchor piles. The effectiveness of the LDFE analysis is at first verified by model test data. Then, a theoretical method is proposed to predict the Optimal Loading Point (OLP), failure mode and pullout capacity of the pile under inclined loading. Comparative study is also performed between LDFE and theoretical analyses. It is concluded: (1) the proposed theoretical method is effective in predicting the OLP, failure mode and pullout capacity of anchor piles; (2) the OLP is not affected by the length-to-diameter ratio and the failure direction of β>5°, while very sensitive to the soil strength and the loading angle; (3) there is a critical loading angle, below which the pile will be pulled out vertically; and (4) the lateral capacity at the OLP could be more than twice that at the top of the pile.

A controllable way to measure the interfacial strength between carbon nanotube and polymer using a nanobridge structure

The interfacial strength between an embedded carbon nanotube (CNT) and a polymer matrix is a direct indicator of the interfacial load transfer which significantly impacts the effective mechanical properties of CNT/polymer nanocomposites. However, unavoidable kinks or entanglement of the CNTs in the polymer may complicate the characterization of the interface as measured through nanopullout experiments. In the current work a CNT/polymer nanobridge structure in a suspended polymer film is developed to allow the observation of the embedded portion of the CNT after the pullout process. The nanobridge structure was created on the basis of phase separation of a polymer blend, self-assembly of the CNTs in liquid flow, and ductile fracture of the polymer under thermal and solvent treatment. This structure accommodates a nanomechanical interfacial characterization method where a transverse force applied on the suspended CNT using an atomic force microscope results in an axial pullout force, which is obtained by the force-distance curves and a force balance relation. The high resolution of the AFM in the loading process and the ability to observe the embedded portion of the CNT eliminate uncertainties of the nanopullout process and provide a more controllable approach for measuring the interfacial strength in CNT/polymer nanocomposite systems.

Enhanced interfacial strength of carbon nanotube/copper nanocomposites via Ni-coating: Molecular-dynamics insights

The molecular bridging between carbon nanotube (CNT) within the meta matrix is hopeful for enhancing nanocomposite's mechanical performance. One of the main problems for nanocomposites is the inadequate bonding between nonstructural reinforcement and meta matrix. Ni-coating on CNT is an effective method to overcome the drawback of the inadequate strength, but the enhancing mechanism has not well interpreted yet. In this paper, the enhancing mechanism will be interpreted from the molecular-dynamics insights. The pullout process of CNT and Ni-coated CNT against copper matrix is investigated. The effects of geometric parameters, including CNT length and diameter, are taken into considerations and discussed. Results show that the interfacial strength is significantly improved after the Ni-coated CNT, which shows a good agreement with the experimental results available in the open literature. Besides, the sliding mechanism of Ni-coated CNTs against copper matrix is much more like a kind of friction sliding and directly related to the embedded zone. However, the pullout force of the CNT without Ni-coating is nearly proportional to its diameter, but independent of embedded length.

Research on the Strength Variation of Root-Clay Systems under Freeze-Thaw Action

The aim of this paper is to study the influence of an effective root system of rhizome plants on the reinforcement of slope soil under freeze-thaw conditions. This study focused on the mechanical properties between roots and clay in the root system of four plant species from different regions of China (northeast, northern, central, and southern areas): Setaria viridis, Eleusine indica, Zoysia japonica, and Carex leucochlora. Based on the interfacial friction effects between the plant roots and the soil, pull-out tests and unconfined compressive strength tests were conducted on the reinforced soil system for varying numbers of freeze-thaw cycles. Several stages of the pull-out process of the root system in clay are explicitly proposed based on the interfacial friction test results. The results showed that the friction effect between Zoysia japonica roots and the soil was the most significant and that these roots had the best reinforcement effect. In contrast, the friction and reinforcement effects between Setaria viridis roots and the soil were the worst, and the resulting unconfined compressive strength was the smallest. However, the freeze-thaw resistance ability of the Setaria viridis and soil system was stronger than that of the Zoysia japonica system.

Effect of polymer matrix and nanofiller on non-bonding interfacial properties of nanocomposites

To investigate the effect of polymer matrix and nanofiller on interfacial mechanical properties of their resulting nanoreinforced composites, pull-out tests of different nanofillers, such as graphene (GE), graphane (GA) and carbon nanotube (CNT), from various polymer matrix including polyethylene (PE), poly(methyl methacrylate) (PMMA), polytetrafluoroethylene (PTFE) and poly(vinylidene chloride) (PVDC), are simulated using molecular dynamics method (MD). The velocity-load model is applied in MD simulations, and the variation of non-bonding energy (van der Waals interaction), pull force and the average interfacial shear strength (ISS) in the pull-out process are obtained and presented graphically. Under the same mass density, when PE is used as polymer matrix for GE and CNT nanofillers, the resulting nanoreinforced composite possesses the highest non-bonding interfacial energy and the strongest ISS, and the pull force required for pulling out the nanofiller is the largest. For GA nanofiller, the GA-PMMA produces the highest non-bonding interfacial energy and the ISS. With the increase of diameter of CNT, the effect of its reinforcement becomes weak gradually. The chirality of GE does not influence the interfacial mechanical property of GE-reinforced nanocomposite. The (3, 3) CNT nanofiller produces the almost identical interfacial characteristic compared with GE nanofiller. However, when the GA nanofiller is used, the non-bonding energy, pull force and the average ISS of nanocomposite increases by nearly 100%.

Inclined Fiber Pullout from a Cementitious Matrix: A Numerical Study.

It is well known that fibers improve the performance of cementitious composites by acting as bridging ligaments in cracks. Such bridging behavior is often studied through fiber pullout tests. The relation between the pullout force vs. slip end displacement is characteristic of the fiber-matrix interface. However, such a relation varies significantly with the fiber inclination angle. In the current work, we establish a numerical model to simulate the entire pullout process by explicitly representing the fiber, matrix and the interface for arbitrary fiber orientations. Cohesive elements endorsed with mixed-mode fracture capacities are implemented to represent the bond-slip behavior at the interface. Contact elements with Coulomb’s friction are placed at the interface to simulate frictional contact. The bond-slip behavior is first calibrated through pull-out curves for fibers aligned with the loading direction, then validated against experimental results for steel fibers oriented at 30 and 60. Parametric studies are then performed to explore the influences of both material properties (fiber yield strength, matrix tensile strength, interfacial bond) and geometric factors (fiber diameter, embedment length and inclination angle) on the overall pullout behavior, in particular on the maximum pullout load. The proposed methodology provides the necessary pull-out curves for a fiber oriented at a given angle for multi-scale models to study fracture in fiber-reinforced cementitious materials. The novelty lies in its capacity to capture the entire pullout process for a fiber with an arbitrary inclination angle.

Effect of the yarn pull-out velocity of shear thickening fluid-impregnated Kevlar fabric on the coefficient of friction

This study explains the yarn pull-out process behavior of woven fabrics in relation to their mechanical properties. Empirical research on the relationship between the yarn pull-out behavior and fabric properties are evaluated, along with a detailed comparison of friction between the fabric fibers in static and dynamic modes. Samples are tested in three modes, namely, neat, dissolved liquid, and silica particle- based Shear thickening fluid (STF)-treated fabric. Accordingly, the presence of STF increases friction between the fabrics and the warp and weft yarns, as well as prevents the displacement of the yarns. Increased friction also leads to an increase in the energy absorption of the yarn pull-out process. In this research, the pull-out test has been performed at three different velocities: 50, 250 and 500 mm/min. Results show that increases in the pull-out velocity increase the pull-out force of the neat and dissolved liquid samples. By contrast, the behavior is completely opposite in the STF-treated sample. Comparing the yarn pull-out values indicates that the STF-treated samples have the highest value, which is approximately three times higher than that of the neat sample.

Functionalization enhancement on interfacial shear strength between graphene and polyethylene

Pull-out processes were simulated to investigate the interfacial mechanical properties between the functionalized graphene sheet (FGS) and polyethylene (PE) matrix by using molecular dynamics simulation with ReaxFF reactive force field. The interfacial structure of polymer and the interfacial interaction in the equilibrium FGS/PE systems were also analyzed to reveal the enhancement mechanism of interfacial shear strength. We observed the insertion of functional groups into polymer layer in the equilibrium FGS/PE systems. During the pull-out process, some interfacial chains were attached on the FGS and pulled out from the polymer matrix. The behavior of these pulled out chains was further analyzed to clarify the different traction action of functional groups applied on them. The results show that the traction effect of functional groups on the pulled-out chains is agreement with their enhancement influence on the interfacial shear strength of the FGS/PE systems. They both are basically dominated by the size of functional groups, suggesting the enhancement mechanism of mechanical interlocking. However, interfacial binding strength also exhibits an obvious influence on the interfacial shear properties of the hybrid system. Our simulation show that geometric constrains at the interface is the principal contributor to the enhancement of interfacial shear strength in the FGS/PE systems, which could be further strengthened by the wrinkled morphology of graphene in experiments.