Bundle Pull-out Research Articles

Growth of Cement Hydration Products on Single‐Walled Carbon Nanotubes

Single‐walled carbon nanotubes (SWCNT) were distributed on the surface of ordinary Portland cement (OPC) grains. The OPC/SWCNT composite was then hydrated at a 0.5 w/c ratio. The effects of the SWCNT on the early hydration process were studied using isothermal conduction calorimetry, high‐resolution scanning electron microscopy and thermogravimetric analysis. The observed behavior of the composite samples was compared with both OPC sonicated without SWCNT and previously published data on as‐delivered OPC. The SWCNT were found to accelerate the hydration reaction of the C3S in the OPC. The morphology of both the initial C3A and the C3S hydration products were found to be affected by the presence of the SWCNT. In particular, the nanotubes appeared to act as nucleating sites for the C3S hydration products, with the nanotubes becoming rapidly coated with C–S–H. The resulting structures remained on the surface of the cement grains while those in the sonicated and as‐delivered OPC samples grew out from the grain surfaces to form typical C–S–H clusters. Classical evidence of reinforcing behavior, in the form of fiber pullout of the SWCNT bundles, was observed by 24 h of hydration.

Fracture behavior and toughening mechanism in Zanchor reinforced composites under mode II loading

The mode II interlaminar fracture behavior and the toughening mechanism of Zanchor reinforced composite laminates were investigated by using the End Notched Flexure (ENF) and Interlaminar Shear (ILS) specimens. The ENF test results demonstrated that the Zanchor process was highly effective to improve the mode II fracture toughness of composite laminates, where the fracture toughness increased almost linearly with the Zanchor density. The R-curves of Zanchor composites were roughly divided into the transition and stable regions, where the width of the transition region became larger as the Zanchor density increased. The macroscopic fracture behavior of the Zanchor composites was still brittle under mode II loading like that of the base composite, where the crack tip process zone was estimated to be rather small regardless of the Zanchor density. The ILS test results demonstrated that the square of the normalized shear strength increased linearly with the Zanchor density and agreed quantitatively with the normalized fracture toughness. The wedge effect was supposed to be the dominant toughening mechanism against the mode II fracture, where the entangled fiber bundles partly sustained the shear stress in the vicinity of the crack tip. The entangled fiber bundles played an important role to form the mode II fracture surface, where the microscopic fracture pattern of the entangled fiber bundles was mainly the breakage of the fiber bundles rather than the pull-out or debonding of the fiber bundles.

Interfacial Shear Strength Evaluation of Jute/Poly(Lactic Acid)

In order to evaluate the interfacial shear strength between fiber bundle and matrix of jute/poly(lactic acid) (PLA), a fiber bundle pull-out test method is proposed. Shear stress distribution was calculated based on the parabolic shear-lag analysis. Fiber bundle pull-out tests were conducted to evaluate the effects of molding condition on the interfacial shear strength. The interfacial shear strength increased with increasing molding temperature up to 185°C. Then gradual decrease in the interfacial shear strength with molding temperature was observed. Similar tendency was also observed in the effect of molding time, whereas the interfacial shear strength decreased with increasing molding pressure. Comparing the result of the tensile tests in the previous study, interfacial shear strength has corelations with tensile strength.

Preparation and Mechanical Properties of Carbon Fiber Reinforced (BC x –SiC) n Multilayered Matrix Composites

A boron doped carbon materials (BCx) was prepared by chemical vapor deposition and a 3D (BCx–SiC)n multilayered matrix composite reinforced by carbon fiber, C/(BCx–SiC)n, was prepared by chemical vapor infiltration (CVI). XPS and SEM results showed that the BCx matrix had a boron content of 15 at.% and exhibited a very finely laminated structure. XRD analysis showed the BCx matrix was mainly carbon with B4C crystals in it. SEM and EDS results showed that the BCx layers and the SiC layers were deposited within the interspaces of fiber bundles, alternately arranged and paralleled to each other as designed. The fracture energy of the composite was about 16.8 KJ m−2. Flexural strength–displacement curve showed a remarkable metal-like yielding stage. Multiple fracture microstructures were induced by the multilayered matrix, such as delaminations of the multilayered matrix, deflections and propagations of cracks spread in the multilayered matrix layer by layer and long pullout of fiber bundles together with fiber clusters with multi-step pull-out structures. It was suggested that these special fracture behaviors absorbed a great deal of energy during the stress increasing and released the stress concentration, in this way, the toughness of the materials was improved.

Evaluation of Adhesion Property of UHMWPE Fibers/Nano-epoxy by a Pullout Test

Ultrahigh-molecular-weight polyethylene (UHMWPE) fibers have poor wetting and adhesion properties to polymer resins because of the inert surface of the fibers. In our previous study, a reactive nano-epoxy matrix, developed by making a modification on the matrix with reactive graphitic nanofibers (r-GNFs), showed improved wettability to UHMWPE fibers. In this work, fiber bundle pullout tests were conducted to evaluate the adhesion property between the UHMWPE fibers and the nano-epoxy matrices. Analysis of load–displacement curves from pullout tests shows that debonding initiation load and ultimate debonding load increased considerably, because of effective improvement of adhesion between the UHMWPE fibers and nano-epoxy matrix. Stress-controlled and energy-controlled models of interfacial debonding were applied for theoretical analyses. Results from ultimate IFSS, frictional shear stress, and critical energy-release rate are in good agreement with experimental results. Nano-epoxy matrix with 0.3 wt% r-GNFs shows effective improvement in terms of adhesion property between UHMWPE fiber and epoxy.

Experimental study on adhesion property of UHMWPE fiber/nano-epoxy by fiber bundle pull-out tests

In order to improve the adhesion property between ultra high molecular weight polyethylene (UHMWPE) fiber and epoxy matrix, our research has been focused on modification of the matrix with reactive graphitic nanofibers (r-GNFs). Upon previously developed nano-epoxy with r-GNFs, the adhesion property was characterized by fiber bundle pull-out tests in this study. Fiber bundle pull-out tests were performed on both single-end and double-end specimens. Comparison of the adhesion properties of single-end and double- end specimens was made to reveal the effectiveness of pull-out test method using single-end specimens. The results indicate that nano-epoxy can improve the interfacial property between UHMWPE fiber and nano-matrix effectively. It is found that, for 0.3 wt% r-GNFs nano-matrix compared to pure epoxy bundle specimens, there are about 34% and 27% increase of critical load (initial debonding load) and peak load, respectively, and about 116% and 107% increase of critical debonding energy and pull-out energy, respectively.

Effect of surface roughness on friction in fibre-bundle pull-out tests

The fracture behaviour of ceramic–matrix composites is highly influenced by frictional conditions in the interface. In the present paper the influence of interfacial roughness and geometric misfit on the clamping stress is investigated by a specific fibre bundle pull-out test: this test is performed by the superposition of an external load perpendicular to the plies of a 2D endless fibre reinforced C/C composite. The superposition is achieved by means of a specially designed load frame, which acts as a load cell. With this principle of measurement the evolution of external and internal stresses during pull-out is obsessed and the Coulomb friction coefficient μ is calculated. A distinct decrease of the Coulomb friction coefficient in the course of the pull-out test was observed. This indicates a change in the surface roughness due to interfacial wear. The friction coefficient is furthermore dependent on the pull-out velocity: its increase leads to an increase of the friction coefficient.

Microstructural characterisation of an alumina/mullite composite tested in creep

Abstract This paper presents the results of creep testing of a ceramic matrix composite (CMC) in which a matrix of mullite (Al2O3/SiO2) and SiOC (Umox) is reinforced with a cross-ply architecture [(0/90)3]s of alumina (Nextel™610) fibres. Seven specimens have been tested under different loading (50–80 MPa) and temperature (1000–1200 °C) conditions. The interfacial behaviour has been analysed through fibre push-in tests performed with a nanoindentation system. Fractographic and microstructural analyses have been performed in each specimen looking for correlations between measured parameters such as fibre and bundle pullout, crack density, crack path, oxidation, and interfacial mechanical properties.

Failure mechanism of free standing single-walled carbon nanotube thin films under tensile load

The mechanical properties of free standing films of as prepared and acid purified single-walled carbon nanotubes were studied by means of tensile stress measurements as well as electron microscopy. Films appear to fail by crack propagation involving rupture or matrix pull-out of bridging nanotube bundles.

Interface characterisation and correlation with the creep behaviour of a 2.5D SiC/C/SiC composite

Abstract The interfacial behaviour of a 2.5D woven SiC/C/SiC composite under creep conditions has been studied by means of fibre push down tests performed with a nanoindentation system. For two samples tested in creep at 1000 and 1100 °C the interface was initially cohesioned whereas for a sample tested at 1300 °C the interface is partially decohesioned. Moreover, the interface of the sample tested at 1100 °C differs from that of the sample tested at 1000 °C because only sudden debond is observed. Fractographic and microstructural analyses have been performed in each specimen in order to define possible correlations between measured parameters such as fibre and bundle pullout, oxidation, temperature, etc. and interfacial mechanical properties.

Interfacial interaction in sisal/epoxy composites and its influence on impact performance

AbstractTo obtain comprehensive knowledge of the interfacial effect on the impact performance of sisal fiber reinforced epoxy composites, the fiber surface was modified in different ways prior to compounding. By using a surface tensiometer and dynamic mechanical analyzer, interfacial interactions in the composites were characterized. The results indicated that the chemical treatments brought about strong bonding between sisal bundles and the epoxy matrix. The subsequent impact tests revealed that the microfailure mechanism involved is a function of interfacial adhesion and fiber length continuity (i.e., continuous or discontinuous fiber). In the case of unidirectional laminates, an optimum fiber treatment should be able to result in an increased affinity between fiber bundles and matrix and a decreased intercellular adhesion. In this way, extension and uncoiling of the spirally arranged microfibrils, a main energy consumption process of plant fibers, can impart significant toughness to the composites. For short fiber composites, the interfacial strength should be properly tailored so as to increase energy dissipation through debonding and pullout of fiber bundles.

Analysis of pull-out and failure of unidirectional bundles in a laminated carbon/carbon composite

The carbon/carbon composites for braking applications, processed by Messier Bugatti, Division Carbone Industrie (Villeurbanne) are laminates of [0/60/−60] n stacking, needled in the through-thickness direction. The unidirectional plies are made of adjacent meshes of square cross-section which exhibit some porosity between them because of the CVI processing route. The goal of the present paper is the study of the fracture behaviour of an individual mesh, and the analysis of the interfacial properties between the mesh and its surroundings. Tensile tests have been performed on special specimens where the mesh, embedded in the composite bulk over a given embedded length, can be loaded. For a long embedded length ( d > 3.6 mm), the mesh is broken and the ultimate stress is 260±80 MPa. For a shorter embedded length, the mesh debonds first with a mean interfacial shear stress of 18±8 MPa. The post-debonding extraction is controlled by friction, starting with an interfacial shear stress of 8±3 MPa. The pull-out curves are analysed and modelled by using the Amontons–Coulomb law.

Mechanical properties of flat braided composite with flexible interphase

Textile composites have been used extensively as industrial materials because of the excellent mechanical properties resulting from the continuously oriented fiber bundle. In a study of the mechanical properties, it is important to consider the fiber/matrix interface property as for other composite materials. In a recent study, the fiber/matrix interface is regarded as an interphase that has its own material constants and thickness; consequently, the mechanical properties of a composite can be controlled by specifically designing the interphase. In this study, we applied this concept to braided composites with flexible resin as interphase for the purpose of designing the interphase. In a static tensile test, though there were no improvements in Noncut specimens (normal braided composites), but a Cut specimen (each side of the Noncut specimen was cut) with flexible interphase was improved in fracture load and displacement. The observation of the specimen edge was carried out and it was confirmed that the progress of debonding at the fiber bundle intersection was interrupted by a flexible interphase, and a matrix crack did not occur in the Cut specimen with flexible interphase. In a fiber bundle pull-out test, it was confirmed that debonding progressed not into the fiber/resin interface but into the flexible interphase in the specimen with flexible interphase, and the interfacial property at the fiber bundle intersection was improved.

Effect of silane-based coupling agents and acrylic acid based compatibilizers on mechanical properties of oil palm empty fruit bunch filled high-density polyethylene composites

The mechanical properties of composites consisting of high-density polyethylene (HDPE) and oil palm fibrous wastes—that is, empty fruit bunch (EFB)—have been investigated. Tensile modulus showed an increase, whereas tensile strength, elongation at break, and impact strength decreased with increasing filler loading. The strong tendency of EFB to exist in the form of fiber bundles and the poor filler–matrix interaction is believed to be responsible for the poor strength displayed by the composites. Attempts to improve these properties using two types of coupling agents, that is, 3-aminopropyltrimethoxysilane (3-APM) and 3-aminopropyltriethoxysilane (3-APE) and two types of compatibilizers, poly(propylene–acrylic acid) (PPAA) and poly(propylene–ethylene–acrylic acid), (PPEAA), are described. While almost all chemical treatments increased the stiffness of the composites, limited improvement has been observed in the case of tensile strength. This have been attributed to the presence of fiber bundles that remain intact even after several types of chemical treatment have been carried out. Thus, the role of EFB as reinforcing agent is not fully realized. Scanning electron microscopy (SEM) micrographs revealed that the main energy-absorbing mechanisms contributing towards toughness enhancement is through the fiber bundle pull-out process. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 2189–2203, 1998

A New Evaluation Method of Interface between Fiber Bundles in Woven Fabric Composites

Evaluation method of interface between fiber bundles in woven fabric composites called “Fiber bundle pull-out test” was proposed. Apparent shear deformation could be applied to the fiber crossing part and the strength could be obtained. The effects of concentration of silane coupling agents on shear strength of fiber crossing part were clarified.

Polyethylene-Oil Palm Frond Composites-A Preliminary Study on Mechanical Properties

The mechanical properties of composites consisting of high density polyethylene (HDPE) and oil palm frond (OPF) have been investigated. Three sizes of OFF at different filler loadings were compounded using a single screw compounder. Modulus of rupture (MOR) of the OPF-HDPE composites decreased with increasing filler loading. Samples with smaller size particles displayed higher MOR as compared to the larger ones. The incorporation of OFF into polymer matrix has also reduced the tensile and impact properties of the composites. This has been attributed to poor filler dispersion and increasing tendency for filler-filler interactions as filler loading increases. Scanning electron microscopy (SEM) has revealed that the OPF particles embedded in the matrix were in the form of irregular shaped-fibre bundles and the failure occurred through extensive fibre bundle pull-out and debonding. This failure mechanism has provided qualitative evidence for the poor tensile and impact strengths of the composites.

Microstructure and mechanical properties of three-dimensional carbon/silicon carbide composites fabricated by chemical vapor infiltration

Three-dimensional carbon/silicon carbide composites were fabricated by chemical vapor infiltration, and the microstructure and mechanical properties were investigated. For the composites ( C SiC ) with no pyrolytic carbon interfacial layer, the mechanical properties (flexural strength, flexural elastic modulus, shear strength and fracture toughness) are increased with density of the composites. High density ( p = 2.1 g cm −3 ) C SiC composites exhibit high fracture toughness (16.5 MPa m 1 2 ) but brittle fracture behavior because of strong bonding between the fiber/matrix. Low density composites show non-catastrophic failure mode with bundle pull-out. The composites (C/PyC/SiC) with pyrolytic carbon interfacial layer exhibit good mechanical properties and a typical failure behavior involving fiber pull-out and brittle fracture of sub-bundle. Microstructural observations and theoretical analysis reveal that the tortuosity and bottleneck effect of the pores and large molar mass of reactant agent (methyltrichlorosilane) are three key issues to hinder the densification of composites. Cracks formed in the SiC matrix by thermal stress have two influences on the mechanical properties of the composites: to decrease mechanical properties and have some contribution on toughness and failure behavior by deflecting cracks.

Effects of Structure and Microcracks on the Flexure, Interlaminar Shear and Impact Properties of Three-Dimensional Composites

Three-dimensional carbon fibre/epoxy resin composites were prepared, which had either three-axis or five-axis carbon fabrics (3D-3A or 3D-5A) in four woven gauges, and Teflon® was embedded in the fabric structures to initiate various types of microcracks. The flexural, interlaminar shear, and impact properties of these 3-D composites were studied. The results indicated that the flexural properties of 3D-3A were better than those of 3D-5A. However, 3D-5A structures gave better impact strength compared to 3D-3A. The interlaminar shear strength depended on the weave gauge. The effect of microcracks on the properties of 3-D composites was generally kept within 10%, but transverse microcracks lowered the flexural properties of 3-D composites by 10–20%. The 3D-3A composites showed cracks along the interface between the Z axial bundles and the matrix, whereas the 3D-5A showed 45°-axial bundle pull-out.

Effects of Structure and Microcracks on the Flexure, Interlaminar Shear and Impact Properties of Three-Dimensional Composites

Three-dimensional carbon fibre/epoxy resin composites were prepared, which had either three-axis or five-axis carbon fabrics (3D-3A or 3D-5A) in four woven gauges, and Teflon® was embedded in the fabric structures to initiate various types of microcracks. The flexural, interlaminar shear, and impact properties of these 3-D composites were studied. The results indicated that the flexural properties of 3D-3A were better than those of 3D-5A. However, 3D-5A structures gave better impact strength compared to 3D-3A. The interlaminar shear strength depended on the weave gauge. The effect of microcracks on the properties of 3-D composites was generally kept within 10%, but transverse microcracks lowered the flexural properties of 3-D composites by 10–20%. The 3D-3A composites showed cracks along the interface between the Z axial bundles and the matrix, whereas the 3D-5A showed 45°-axial bundle pull-out.

Controlled Interfaces in Low‐temperature‐cured Phenolic Composites

The surface chemistry and interfacial adhesion of silanetreated E-glass fibers and low-power, oxygen or water plasma-treated ultrahigh-modulus polyethylene (UHMPE) fibers with acid-catalyzed, low-temperature-cured phenolic resins have been measured by X-ray photoelectron spectroscopy, (XPS) and static secondary ion mass spectrometry (SIMS), fibers bundle pullout and flexural and interlaminar shear strength properties of unidirectional composites. The most effective treatment for E-glass involved an epoxy silane rather than an amino silane owing to the protonation by the acid catalyst of the amine as well as the loss of reactive sites by the formation of carbon dioxide adducts stable at the conditions of cure. Scanning electron microscope examination of the cured phenolic resin showed phase-separated water domains; the diameter of these domains decreased towards the fiber surface in a choppedstrand mat composite owing to the lowering of the surface tension produced by the dissolution of the binder by the phenolic resin. Both water and oxygen-plasma treatments of UHMPE increased the fiber bundle pullout force by the same amount and this was attributed to direct chemical bonding to hydroxyl (and possibly epoxy) groups detected by XPS, SSIMS and derivatization. The best composite properties were obtained when oxygen plasma-treated UHMPE was used and this was attributed to the slower restructuring and higher total oxygen content enabling efficient wet-out of the fibers by the resin.