Pull-out Mechanism Research Articles

Numerical investigation of pull-out capacity and failure mechanism of suction anchors with mooring line in sand

Suction anchor is a widely used anchorage foundation in taut or catenary mooring systems to fix floating structures. This paper aims to investigate the pull-out capacity and failure mechanism of suction anchors in sand using the finite element method which models the attached mooring line on the anchor padeye. The advanced critical state elastoplastic constitutive model SIMSAND is utilized which can well simulate the state-dependent peak strength and stress-dilatancy behavior of sand, and its accuracy and effectiveness are validated with centrifuge test results. A series of systematical parametric studies are then carried out to explore the effects of the mooring line, aspect ratio, padeye position and loading angle on the pull-out capacity and failure mechanism of the suction anchor. Based on the numerical results and those obtained in other researchers’ work, the optimal padeye position and the normalized V–H envelopes are explicitly discussed. Finally, a calculation framework is put forward for predicting the inclined pull-out capacity of suction anchor in sand considering the mooring line effect.

Synthesis and densification of boron carbide nanowires

One-dimensional materials have been proven to be an effective reinforcement for manufacturing high-toughness materials, but remain a great challenge in the field of B4C ceramics. In this study, B4C nanowires were synthesized and used for the preparation of B4C ceramics. The growth mechanism of the nanowires was proposed to be vapor-solid (VS) mechanism, where NaCl serves as an evaporator, porous carbon acts as a carbon source, and amorphous boron acts as a boron source. The B4C ceramics sintered at 1850 °C exhibit exceptional toughness, reaching a value of 7.13 MPa m1/2. The pull-out and bridging mechanisms play a dominant role in enhancing the toughness of the B4C ceramics. This study presents a novel approach to the synthesis of nanowires and has important implications for the production of high-performance B4C ceramics.

Numerical investigation on the pull-out capacity of suction anchors in sand considering torsional and mooring line effects

Torsional pullout of suction anchors may occur during installation due to improper positioning or deviations caused by current forces, but less attention has been paid to the effect of torsion on the pull-out capacity of suction anchor in existing literatures. This paper therefore numerically investigates the pull-out capacity and failure mechanism of suction anchors in sand considering both torsional and mooring line effects using the advanced SIMSAND constitutive model. It is found that considering torsional influence causes a significant reduction in the pull-out capacity of suction anchor in sand under horizontal and inclined loading. The case with the optimal padeye depth of 0.7L produces the largest pull-out capacity and the greatest reduction in the pull-out capacity due to torsion. The dimensionless pull-out capacity for the case without mooring line is approximately 24% higher than or almost twice that of the case with mooring line in scenarios without or with torsional condition. Based on the findings, a new framework for estimation of the pull-out capacity of the suction anchor at the optimal padeye depth in sand considering torsional and mooring line effects is finally proposed which may benefit the design of suction anchor in scenarios with torsion in the real practice.

Investigating the influence of pull-out speed on the interfacial properties and the pull-out behavior of CNT/polymer nanocomposites

Carbon nanotubes (CNTs) improve the fracture toughness of nanocomposites and composite materials by bridging the crack growth path using the pull-out mechanism. Achieving the ability to estimate the dynamic fracture toughness of these materials, the effects of pull-out speed on the pull-out behavior and the critical interfacial shear stress (CISS) between CNT and epoxy resin are investigated in this paper. Employing the molecular dynamics (MD) simulation, the optimized unit cells consisting of epoxy resin containing a single-walled CNT are prepared. Appropriate boundary conditions are applied to the ensembles and the pull-out simulation is performed for the pull-out speeds in the range of 0.0015–0.0050 Å/fs resembling medium-rate loading. The effect of the pull-out speed on the maximum pull-out force is studied. It is revealed that by increasing the pull-out speed, the maximum pull-out force decreases. The corresponding average pull-out force–displacement curves are independent of the pull-out speed and are approximately similar. Based on these simulations, the pull-out speed affects the pull-out energy in the specified speed range. The variations of the pull-out energy and the CISS relative to the changes in the CNT length and diameter are also partially affected by the pull-out speed.

Field Pull-Out Tests of Percussion Driven Earth Anchors (PDEAs)

Percussion driven earth anchors (PDEAs) are driven into soils using an installation steel hammer rod. PDEAs are relatively easy to install and have gained wide applications recently. The Texas Department of Transportation (TxDOT) planned to use these anchors for slope stability mitigation along the Clear Fork Trinity River at Interstate Highway 20 (IH-20) in Benbrook, Texas. However, there are no straightforward design and construction guidelines for these systems. In addition, the pull-out capacity and failure mechanisms of PDEAs in clayey soils have not been thoroughly studied. In this study, three PDEAs, Duckbill model 138 II (DB-138 II), were installed and tested on the proposed west channel bank slope to acquire the ultimate pull-out capacity. The anchors were embedded to an average depth of 10 feet into the slope bank, predominantly consisting of sandy lean clay (CL) soil. The slope was graded at an average 2:1 to 2.5:1 configuration. After installation, the anchors were subjected to an upward pull-out force using a hydraulic jack system to measure their pull-out capacity. The pull-out load, displacement, and strains were continuously recorded with a load cell, a linear variable differential transformer (LVDT), and a strain gauge, respectively. Pull-out load versus displacement curves were produced and analyzed to determine the behavior of the anchors. An empirical estimation method was then chosen to estimate pull-out capacity based on undrained shear strengths obtained either from laboratory tests or in situ Texas cone penetration (TCP) data. The comparison between estimated and field-obtained pull-out capacities showed that the pull capacity estimated using TCP data resulted in reasonably good agreement with the field-obtained capacity. The field experiment results help us to understand the relationship between the calculated and actual field pull-out resistance when PDEAs are used in clayey soil slopes.

The synergistic effect of hybrid nano-silica and GNP additives on the flexural strength and toughening mechanisms of adhesively bonded joints

This study intended to research the effects of nanoparticle hybridization (nano-silica and GNP) on the bending performance of adhesively bonded joints of Al-2024 sheets. For this purpose, nano-silica/GNP hybrid nanofiller reinforced single lap joints (SLJ) with total additive ratios of 0.5%, 1.0%, 1.5%, 2.0%, and 2.5% by weight were manufactured and subjected to three-point bending tests. Among hybrid nanoparticle-doped joints with a ratio of nano-silica to GNP of 1:2,1:1, 2:1, 3:1, and 3:2, the best performance was obtained in a 1.5% nano-silica +0.5% GNP doped sample with 3:1 particle ratio. The enhancement in flexural strength was 51.3% in this sample compared to the sample containing pure Araldite 2014 adhesive. In addition, it exhibited 3.1% and 30.8% better strength, respectively, compared to the samples containing single GNP and single nano-silica particles. In the SEM views which were taken from fracture surfaces of the damaged samples, it was observed that the hybridization of nano-silica and GNPs improved the particle dispersion. Nano-silica particles were attached between the GNP lamellae, forming a new three-dimensional hybrid structure. This structure improved the interfacial interaction of nanoparticles with the adhesive, and also increased the resistance of crack deviation, crack stopping, crack bridging and pull-out mechanisms against peeling and shear stresses caused by three-point bending loads.

Fabrication and compressive performance of novel lightweight C/SiC honeycomb for ultrahigh stability structures

As for high resolution satellite application field, novel C/SiC honeycomb sandwich structure is the first to propose and develop on account of such many attractive properties as excellent ultrahigh dimensional stability in thermal and moisture coupling environment, lightweight and high load-bearing. Three types of C/SiC honeycomb sandwich structures were fabricated for the first time as opto-mechanical structure in satellite. The innovative interlayer-crosslinking method to weave the continuous carbon fiber fabric of honeycomb core was proposed. The compressive properties of novel C/SiC honeycomb sandwich structures were investigated. Meanwhile, the damage mechanism for sandwich structures were analyzed by non-destructive testing. The results showed that the innovative fabrication processing possessed the capability to prepare high quality C/SiC honeycomb, which was shown from the volume and distribution of pores in the X-ray tomography. The compression modulus and strength of the C/SiC honeycomb reached 927 MPa and 10.76 MPa, and showed better rigidity and higher strength compared with classical honeycombs. Two main types of cracks wall were found in the C/SiC honeycomb, i.e., the horizontal ones in the wall with t thickness and the inclined ones in the wall with 2 t thickness. The outstanding compressive performance was attributed to the high mechanical property of ceramic-matrix composite with fiber pull-out mechanism. The exceptional lightweight capacity was inherited from the low bulk density of honeycomb structure ranged from 0.08 g/cm3 to 0.15 g/cm3. This study can help for the development of lightweight materials for opto-mechanical structure in aerospace optical remote sensing technology.

Green synthesis of graphene-hydroxyapatite nanocomposites with improved mechanical properties for bone implant materials

Herein, an in-situ synthesis of reduced graphene oxide-hydroxyapatite (RGO-HA) nanocomposites via a green reduction protocol is presented. 0.5, 1.0, and 1.5 wt% of RGO in HA are obtained by reducing the precursor solution with custard apple leaf extract. The 10x5 mm-sized discs of the RGO-HA nanocomposites are prepared and investigated for their mechanical properties. The presence of graphene in the composites is confirmed by UV–Visible, Raman spectroscopic techniques while XRD spectral analysis confirmed the α-tricalcium phosphate (TCP, JCPDS PDF No 00-009-0432) structure of HA. Nanoindentation and Vicker indentation studies revealed the enhancement in the mechanical properties of RGO-HA nanocomposites: elastic modulus, microhardness, and fracture toughness values are enhanced by 100%, 33.3%, and 64.5 %respectively for 1.5 wt% of graphene in HA matrix. The FE SEM analysis of the indentation cracks revealed that the wrapped and tucked graphene sheets in the HA matrix have hindered the propagation of the crack through pull-out, ridge growth, bridging, and deflection mechanisms. Nano scratch analysis revealed the enhanced surface roughness (120%) and coefficient of friction (102%) for 1.5 wt% composites than pure HA. The same composite showed 100% viability of HEK 293 cells at 12.5 μg/mL concentration and in vitro apatite mineralization when immersed for 7 days under SBF solution.

鎌継締結によるインターロッキング構造の力学について

In recent years, attention has focused on the excellent mechanical properties of bones, teeth, and crustaceans. In particular, interlocking tissue is strongly interested as one of the characteristics of the microscopic structure of crustaceans. The interlocking structure has sutures like puzzle pieces, and friction slip in the pull-out process occurs at the sutures by subjecting to a tensile load. As a result, it is recognized that the toughness is apparently improved. By the way, in wooden houses in Japan, iron nails are not used, but the mortise-neck joints are used to fasten timbers together. The feature is that the fastening force can be freely controlled by adjusting the angle of the suture. Therefore, in this study, we simulate the bioinspired interlocking structure by these sickle joints and develop a mechanical model based on the pull-out mechanism for this structure. In order to verify the validity of the developed model, we compared it with the finite element analysis results. Furthermore, we investigated the effect of the suture shape on the relationship between load and displacement. It was clarified that the suture shape and interfacial friction coefficient affect the maximum load and elongation at break. Finally, the relationship between the fracture energy estimated from the relationship between load and displacement and these parameters was summarized as a map.

Thermal conductivity and shear strength characterisation of hybrid GNPs and silane functionalised BN as thermal conductive adhesive

ABSTRACT The demand for high thermal conductivities and improved adhesion of thermal conductive adhesives has heighten the need for hybrid fillers with extraordinary properties, such as boron nitride (BN) and graphene nanoplatelets (GNP) especially at lower filler contents (<20 wt.%), particularly with silane-functionalised BN (fBN) and adhesion using the single lap joints approach. Thus, this study was conducted to measure the thermal conductivity and shear strength of hybrid GNP with BN or fBN at different filler sizes, GNP ratios, and silane coupling agents (KK550 and KH560). We observed that the hybrid GNP/fBN_KH560 composite at a ratio of 0.75 exhibited the highest thermal conductivity and shear strength with enhancements of 198.42% and 81.82%, respectively, attributed by the high compatibility between fBN_KH560 and the polymer matrix, proven by the lowest measured contact angle and Hansen solubility parameter difference. Despite the thermal conductivity value not surpassing that of the single-filled GNP composite, the hybrid composite at lower filler content was considered a success as it exhibited a synergetic effect when compared with single-filled BN or fBN; with the difference of 0.111. Besides, crack deflection, particle debonding and pull-out mechanism improved the shear strength and promoted cohesive failure in the hybrid composite.

Acoustic Emission Signal Characterisation of Failure Mechanisms in CFRP Composites Using Dual-Sensor Approach and Spectral Clustering Technique.

The characterisation of failure mechanisms in carbon fibre-reinforced polymer (CFRP) materials using the acoustic emission (AE) technique has been the topic of a number of publications. However, it is often challenging to obtain comprehensive and reliable information about individual failure mechanisms. This situation was the impetus for elaborating a comprehensive overview that covers all failure mechanisms within the framework of CFRP materials. Thus, we performed tensile and compact tension tests on specimens with various stacking sequences to induce specific failure modes and mechanisms. The AE activity was monitored using two different wideband AE sensors and further analysed using a hybrid AE hit detection process. The datasets received from both sensors were separately subjected to clustering analysis using the spectral clustering technique, which incorporated an unsupervised k-means clustering algorithm. The failure mechanism analysis also included a proposed filtering process based on the power distribution across the considered frequency range, with which it was possible to distinguish between the fibre pull-out and fibre breakage mechanisms. This functionality was particularly useful in cases where it was evident that the above-mentioned damage mechanisms exhibited very similar parametric characteristics. The results of the clustering analysis were compared to those of the scanning electron microscopy analysis, which confirmed the conclusions of the AE data analysis.

Bimodal microstructure toughens plasma sprayed Al2O3-8YSZ-CNT coatings

Current work pursues generating controlled bimodal microstructure by plasma spraying of micrometer-sized Al2O3 and nanostructured spray-dried agglomerate with reinforcement of 20 wt% of 8 mol % yttria stabilized zirconia (8YSZ) and 4 wt% carbon nanotube (CNT) as potential thermal barrier coating (TBC) on the Inconel 718 substrate. Composite coatings exhibit bimodal microstructure of: (i) fully melted and resolidified microstructured region (MR), and (ii) partially melted and solid state sintered nanostructured regions (NR). Reinforcement with 8YSZ has led to an increase in hardness from ∼12.8 GPa (for μ-Al2O3) to ∼13.9 GPa in MR of reinforced Al2O3-YSZ composite. Further, with the addition of CNT in Al2O3-8YSZ reinforced composite, hardness of MR has remained similar ∼13.9 GPa (8YSZ reinforced) and ∼13.5 GPa (8YSZ-CNT reinforced), which is attributed to acquiescent nature and non-metallurgical bonding of CNT with MR. Indentation fracture toughness increased from 3.4 MPam0.5 (for μ-Al2O3) to a maximum of 5.4 MPam0.5 (8YSZ- CNT reinforced) showing ∼57.7% improvement, which is due to crack termination at NR, retention of t-ZrO2 (∼3.3 vol%) crack bridging, and CNT pull-out toughening mechanisms. Modified fractal models affirmed that the introduction of bimodal microstructure (NR) i.e., nanometer-sized- Al2O3, nanostructured 8YSZ and CNTs in the μ-Al2O3 (MR) contributes ∼44.6% and ∼72% towards fracture toughness enhancement for A8Y and A8YC coatings. An enhanced contribution of nanostructured phases in toughening microstructured Al2O3 matrix (in plasma sprayed A8YC coating) is established via modified fractal model affirming crack deflection and termination for potential TBC applications.

Investigation of Failure Behaviour of Soil Nailed Excavations under Surcharge by Centrifuge Model Test

A series of centrifuge tests were performed to evaluate surcharge effects on the behavior of nailed vertical excavations. The primary purpose was to observe the mechanism of failure surface development and to compare the test results with software results based on equilibrium limit analysis. In this experiment, four different surcharges were applied to both samples with and without nails. Applying surcharge and the following excavation were performed in 40 g acceleration. At the beginning of the test, the excavation was maintained using a water-filled membrane, right next to it. At the target acceleration, the surcharge was modelled by filling the loading tank over the sample with water, and finally, with water draining from the membrane, soil excavation was simulated. Eventually, failure surfaces resulted from the experiment were compared with the ones calculated by the equilibrium limit analysis-based software. Results revealed that the shapes of failure surfaces are bilinear in all tests and that the surcharge has its effects on the development of failure surfaces. In the meantime, the pull-out mechanism was observed in the nails during failure, with no bending. The equilibrium limit analysis also estimates the width of failure wedge well and its depth conservatively.

Changes in microstructure and mechanical properties of the carbon fiber and their effects on C/SiC composites

The changes in microstructure and mechanical properties of the carbon fiber and their effects on C/SiC composites were studied. The H, N and O atoms escaped and the carbon content in the carbon fiber increased when the heat treatment temperature exceeds 1200 °C. Meanwhile, the growth of graphite crystallite leaded to stress concentration and reduced the tensile strength of carbon fiber to 2.98 GPa by 1200 °C heat treatment. The active atoms on the surface of the carbon fiber were reduced, thus weakening the bonding force between the carbon fiber and the pyrolytic carbon interface layer and improving the pullout mechanism of the carbon fiber. This result was also observed by synchrotron radiation X-ray computed tomography. The flexural strength of the C/SiC composite increased from 300 MPa without treatment to 364 MPa after 1600 °C heat treatment.

A bottom-up approach to model collagen fiber damage and failure in soft biological tissues

Understanding the damage and failure of load-carrying soft biological tissue is critical in the effectual treatment of injury and disease. The difficulty in experimentally identifying the intrinsic mechanisms by which damage initiates and accumulates, and how this ultimately leads to tissue rupture, has motivated the constitutive modeling of soft tissue failure. We present an extension of our previous microstructural continuum model (Miller and Gasser, 2021) that includes proteoglycan mediated collagen fibril sliding towards capturing the non-linear time dependent properties of collagenous tissue. We now additionally incorporate an interfibrillar failure (fibril pull-out) mechanism and showcase the resulting damage induced mechanical behavior across several length scales. Importantly, a bottom-up approach is further demonstrated, whereby the microstructural model is employed in a single-element representation of the modes of fracture. A qualitative description of soft tissue rupture is accordingly attained, to which an appropriate cohesive zone model for the equivalent fracture surface is then calibrated. In doing so, a surface-based discontinuous characterization of failure is directly derived from the upscaling of irreversible and dissipative damage mechanisms from the microscale.

Role of carbonaceous reinforcements on mechanical properties and micro-scratch behaviour of Y2O3 stabilized ZrO2

An efficient 3 mol% Y2O3 stabilized ZrO2 (3YSZ) based composite was developed for structural application. The role of graphene nanoplatelets (GNP) and multi-walled carbon nanotubes (MWNT) on evolution of phases and microstructural features in the 3YSZ-based composites that affect the mechanical and tribological properties of composites have been investigated in the present study. Here, the spark plasma sintered 3YSZ composites with 1, 2 and 4 wt% of MWNT and GNP reinforcement were synthesised. Sintered composites retained the tetragonal ZrO2 (t-ZrO2, high-temperature phase) along with the formation of ZrC with the addition of GNP/MWNT, which marginally improves the mechanical properties of the composite. The marginal enhancement in hardness and elastic modulus with GNP and MWNT reinforcement is attributed to the synergistic effect of grain refinement, densification, phases and distribution. The composite with 2 wt% of MWNT showed marginal improvement in the indentation fracture toughness (7.2 MPa m0.5) compared with monolithic 3YSZ by crack deflection, MWNT bridging & pull-out mechanism. Further, the average scratch toughness of the 3YSZ-GNP/MWNT based composite is measured as 1.99–2.15 MPa m0.5 derived from progressive load scratching. The scratch toughness with 1.5–3.3 times lower than the indentation fracture toughness is attributed to the elastic recovery during scratching and non-uniform distribution of phases in the composites. Further, the optimum value of hardness, elastic modulus, indentation fracture toughness, and scratch toughness of 2 wt% of MWNT reinforced 3YSZ composite is found suitable for structural applications.

Mode II cohesive zone law of porous sintered silver joints with nickel coated multiwall carbon nanotube additive under ENF test

Various contents of nickel coated carbon nanotube added sintered silver joints are fabricated through mechanical alloying. An analytical method is presented to compute the fracture energy of ENF tests incorporating shearing effect and thickness effect, which shows better accuracy compared with traditional method, which are closer to the solutions of compliance based beam method. Mode II fracture energy, mode II fracture toughness and mode II cohesive zone model for different contents of nickel coated carbon nanotube added sintered silver joints are presented based on the data extraction of the ENF tests. With the increase of adhesive layer thickness, the fracture energy and the mode II fracture toughness improve. However, thickness effect is less significant but not negligible comparing with the strengthening effect on the improvement of fracture toughness, which is caused by adding nickel coated multiwall carbon nanotubes. The relation between mode II fracture toughness and porosity is also discussed. For most of the conditions, the mode II fracture toughness is higher than mode I fracture toughness regardless of additive content due to the crack deflection, crack bridging and pull-out mechanisms during the crack propagation except for those high content of additive whose fracture energy is reduced because of aggregation effect.

Fabrication and performance of SiC-reinforced Cu: Role of the aspect ratio of the SiC reinforcement phase

In this study, SiC particle (SICP)- and SiC whisker (SICW)-reinforced Cu composites were prepared by pulse intermittent deposition and subsequent spark plasma sintering (SPS). After electrodeposition, the formation of Cu-coated SICP and SICW core–shell structures solved the problem of agglomeration of the second phase during the subsequent sintering. In addition, the wetting layer of Cu increased the bonding strength of the interface between Cu and the second phase. The strength of SICP-reinforced Cu was higher than that of pure Cu at the expense of elongation and thermal conductivity. Compared to SICP-reinforced Cu, SICW-reinforced Cu exhibits significantly higher strength, plasticity and thermal conductivity. The externally applied load was transferred from a soft Cu matrix to stiff SICWs, thus increasing the yield strength of the composites. Furthermore, bridge cracks, crack deflection, and whisker pull-out mechanisms improved the elongation of the composite. This work reveals the relevance of the strengthening mechanism and the aspect ratio of the reinforced phase systematically and provides an advanced pathway to fabricate high-performance metal–matrix composites by designing discontinuous second phases with tailored aspect ratios.

Study of dry sliding wear and corrosion behavior of nanocomposite Al-Si-N coated steel

The present investigation evaluates the wear and corrosion performance of Al-Si-N coated and uncoated steel substrates. The magnetron sputtering technique was used to develop the optically transparent nanocomposite Al-Si-N coating over the steel substrate. The Al-Si-N coating was the composite of a polycrystalline phase of wurtzite (hexagonal) AlN and the amorphous phase of Si3N4. The steel's surface hardness value was enhanced significantly by the Al-Si-N coating. The coated steel exhibited ~19 GPa hardness value, whereas uncoated steel has ~6 GPa. The wear performance testes of the coated and uncoated steels, examined by the ball on disc tribometer, marks 60% less wear of the coated steel than the uncoated steel at 2 N loads. The coated steel wear out by chipping and pull-out abrasive mechanism. The potentiodynamic polarization study indicates improved barrier property and adhesion of the coating than the passive film on the steel with a similar corrosion current value of ~10 nA/cm2. The corrosion performance of the uncoated steel (SS 304) did not deteriorate with the Al-Si-N coating. Our analysis-based observations conclude that the nanocomposite Al-Si-N coating exhibits a unique combination of optically transparency, high wear, and corrosion resistance, making Al-Si-N a potential protective candidate for solar panels, optoelectronic devices, automotive shields, and optical devices.

Analytical Approach for Modelling the Pull-Out Mechanism of Recycled Synthetic Fibres in Fibre-Reinforced Concrete (FRC)

This study presents a simple one-dimensional analytical model describing the pull-out process of an elastic fibre embedded in a cement matrix, which captures the ductile behaviour of Fibre Reinforced Concrete (FRC) elements.The shear stress arising at the frictional interface between fibre and matrix during the pull-out is assumed to increase with the slippage distance, as a consequence of the growing abrasion of the fibre surface.The equilibrium conditions between the external axial load and the interfacial shear stress are imposed with reference to the undeformed configuration.The model is validated through comparison with both experimental data obtained by testing partially recycled polymeric fibres embedded in a cement matrix, and several datasets available in the literature comprising polypropylene fibres with and without silica coatings.The proposed model can properly describe the response of synthetic fibres that exhibit considerable axial elongation and slip-hardening interface behaviour.However, it may also predict the non-linear relation between the tensile load and the fibre displacement for different kinds of fibre, by setting adequately the constitutive parameters.