Characterising the time-dependant behaviour on the single fibre level of SHCC: Part 1: Mechanism of fibre pull-out creep

SHCC (Strain Hardening Cement-based Composite) has been designed and optimised to overcome the main weaknesses of ordinary concrete, which is its brittleness. SHCC shows a high tensile ductility and can resist the full load at a tensile strain of more than 4%. An in depth investigation into the time-dependant behaviour is still lacking for SHCC. This paper is the first part of a two paper series about the time-dependant behaviour on the single fibre level. In this paper, the tensile creep behaviour of SHCC is studied to distinguish mechanisms of creep. Tensile creep and shrinkage test results are reported for dumbbell type SHCC specimens. The specimens are pre-cracked to simulate in-service conditions, with subsequent sustained load at various levels, here chosen as 30%, 50%, 70% and 80% of the ultimate resistance. To distinguish the sources of significant creep deformation under these sustained loads, single fibre pull-out tests are performed under sustained load. It is shown that the time-dependent fibre pull-out is a significant source of time-dependent deformation, along with the formation of new cracks in SHCC under sustained load.     

A comparative investigation of interfacial adhesion behaviour of polyamide based self-reinforced polymer composites by single fibre and multiple fibre pull-out tests

Abstract

Interfacial adhesion of composite materials plays an important role in their mechanical properties and performance. In the present investigation, analysis of the interfacial properties of self-reinforced polyamide composites by using microbond multiple fibre pull-out test is emphasised. Microbond specimens prepared through thermal processing are tested for their interfacial properties by multiple fibre bundle pull-out tests and compared with that of traditional single fibre pull-out test specimens. Multiple fibre pull-out addresses the volume fraction as well as eliminates the possibility of fibre breakage before matrix shear. Higher scatter in the data in the samples is addressed in the present studies. FTIR and Fractographic studies are carried out for deep understanding of the post pull-out interfacial adhesion.     

Wetting kinetics and adhesion strength between polypropylene melt and glass fibre: influence of chemical reactivity and fibre roughness

A systematic experimental investigation with the purpose of quantifying the effect of the interactions between non-polar (unmodified) and polar (modified) polypropylene melts and treated fibre surfaces during wetting has been performed. The glass fibres were sized by aminosilane (γ-APS), γ-APS/polyurethane film former (γ-APS/PU) and γ-APS/polypropylene film former (γ-APS/ PP). Unsized fibres were used for comparison and were also coated with an azidosilane layer. Zeta potential and contact angle measurements were employed to investigate the surface properties of the treated glass fibres. The surface roughness was characterised using both atomic force microscopy and scanning electron microscopy. A method based on axisymmetric drop shape analysis was employed to determine the surface tension of the polymer melt. The wetting of the fibres by the polymer melt was investigated using the Wilhelmy balance technique. The wetting kinetics was different for different fibre surface treatments. The chemically reactive system based on azidosilane showed a better wetting than the other systems. The aminosilane/polypropylene film former (γ-APS/PP) treated fibre was also characterised by a fast wetting, most probably due to the physical similarity between the polymer and the fibre sizing and, thus, probable compatibility. In the receding case the differences between the reactive systems were smaller than they were for the advancing case. Higher adhesion tension calculated from the wetting measurements correlated well with higher adhesion strength determined from single fibre pull-out tests.     

Effect of silane treatment on the Curaua fibre/polyester interface

ABSTRACT

Good adhesion at fibre/matrix interface of lignocellulosic fibres is crucial when substituting synthetic fibres in polymer composites. The great variability presented by those fibres requires diverse characterisation studies for better insights on fibre surface treatments and resin systems interactions. In this work, Curaua fibres were treated using silane coupling agents to improve their interfacial properties with polyester. The fibres were pre-treated using 4?wt% solution of NaOH and then treated with 5?wt% solution of (3-aminopropyl) trimethoxysilane (AMPTS) or triethoxymethylsilane (TEMS). Characterisation of the treated fibres was carried out using infrared spectroscopy, X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. Fibre wettability and adhesion towards polyester was investigated using contact angle measurements and pull-out tests, respectively. The AMPTS treatment yielded a significant result of 20.2?MPa in interfacial shear strength (≈2.5 times that of the untreated fibre), attributed to the increase in availability of binding sites with polyester.     

Carbon fibre cloth as an electrode material: electrical conductivity and mass transfer

The paper deals with carbon fibre cloth electrodes, employed in the fabrication of composite materials. The electrical conductivity of single bundles, groups of bundles and cloth is studied. Ohm's law applies to the electrical conduction in the direction of the fibre length, but bundle conductivity decreases with the number of fibres in the bundle. Electrochemical mass transfer between a flowing electrolyte and a cloth arranged as a flow-through or a flow-by porous electrode indicates the existence of double porosity in the material. Due to double porosity, only the external surface of the cloth works as an electrode. This finding shows that the material is not suitable for such an application.     

The influence of zirconia fibre on ablative composite materials

ABSTRACT

Zirconia fibres have excellent high temperature ablation resistance and have been widely used in ablative materials. In this paper, zirconia fibre was used for reinforcing the ablative composite materials to study the influence of zirconia fibre had upon the mechanical properties and the high temperature ablation properties of such composites. The results showed that the bending strength of the material was also good and reached a maximum of 13.05?MPa. After sintering at 1400°C, the bending strength was also great which could reach 13.05?MPa. In addition, the corrosion resistance of the composites was excellent and the oxygen-acetylene line ablation rate was 0.03?mm?s^?1 when the fibre content was 30?wt-%.     

Experimental results of a pull-out test performed with single- and multi-fiber samples

Widely-used methods for characterising the fibre/matrix interface in polymeric composites are the fragmentation test and the droplet test as a special kind of the single-fibre pull-out test. A severe disadvantage of these tests is that non-realistic model samples are investigated which contain only one fibre in the matrix. In order to obtain data about the effect of the different residual stress situations for fibres in such samples and in composites, pull-out tests of E-glass fibres in polystyrene and polycarbonate are performed using samples, where the investigated fibre is surrounded by 0 to 3 other near fibres. Neighbouring fibres can increase the pull-out forces by a factor of three and the interfacial toughness by a factor of four. This has to be taken into account, if the tests are performed not only for comparison reasons but for measuring interface properties.     

EXPERIMENTAL RESULTS OF A PULL-OUT TEST PERFORMED WITH SINGLE- AND MULTI-FIBER SAMPLES

Widely-used methods for characterising the fibre/matrix interface in polymeric composites are the fragmentation test and the droplet test as a special kind of the single-fibre pull-out test. A severe disadvantage of these tests is that non-realistic model samples are investigated which contain only one fibre in the matrix. In order to obtain data about the effect of the different residual stress situations for fibres in such samples and in composites, pull-out tests of E-glass fibres in polystyrene and polycarbonate are performed using samples, where the investigated fibre is surrounded by 0 to 3 other near fibres. Neighbouring fibres can increase the pull-out forces by a factor of three and the interfacial toughness by a factor of four. This has to be taken into account, if the tests are performed not only for comparison reasons but for measuring interface properties.     

The effect of matrix composition on fibre/matrix interfacial bond shear strength in fibre-reinforced mortar

The effects of factors associated with the composition of the matrix, i.e. curing conditions and time and mix proportions, on the shear strength of the interfacial bond between steel fibres and a cementitious mortar matrix have been examined experimentally using a single-fibre pull-out test technique. The experimental results indicate that bond shear strength increases significantly with an increase in matrix curing time and, for specimens with the fibre axis perpendicular to the direction of casting and compaction of the matrix, with a decrease in the proportion of water by weight in the matrix mortar. This latter effect is attributed to bleed water gain under the embedded fibre, as it is not observed in specimens with the fibre axis parallel to the direction of casting and compaction of the matrix. Furthermore, the results indicate that there is no correlation between interfacial bond shear strength and matrix mortar compressive strength.     

Polyester fibre with high dyeability and pilling

Polyester fibre based on poly(ethylene terephthalate) modified by addition of 3 wt. % sulfoisophthalic acid Na salt dimethyl ester, has high resistance to the pilling effect and elevated dyeability with disperse dyes. Sorption of the dye by the modified fibre at 100°C is several times higher (and in the case of a disperse dye, more than one order of magnitude higher) than sorption of dyes by mass-produced polyester fibre. The fastness of dyeing the modified and mass-produced fibres in different kinds of treatment is almost the same. The high sorption capacity of the modified fibre not only allows dyeing it with disperse dyes at normal pressure in a wide range of deep and medium shades, but also reducing the amount of unused dye in the baths and thus decreasing the effect on the environment. Translated fromKhimicheskie Volokna, No. 1, pp. 35–39, January–February, 2000.     

Operational properties of the chemisorptive fibre VION AN-1

Conclusions Boundary conditions have been determined for the regeneration of VION AN-1 fibre which ensure retention of its sorptive properties on repeated use.The rate of sorption of acid vapors depends on the original fibre structure only at a low relative humidity of the gas stream.On sorption of acid vapor by the moistened fibre, hydration of the ionogenic groups of the polymer takes place; this leads to a change in its structure. In this case, the rate of sorption does not depend on the porosity of the original fibre.Translated from Khimicheskie Volokna, No. 3, pp. 37–38, May–June, 1987.     

Effect of PAN-based and pitch-based carbon fibres on microstructure and properties of continuous Cf/ZrB2-SiC UHTCMCs

In this paper the microstructure and mechanical properties of two different C_f/ZrB₂-SiC composites reinforced with continuous PyC coated PAN-derived fibres or uncoated pitch-derived fibres were compared.Pitch-derived carbon fibres showed a lower degree of reaction with the matrix phase during sintering compared to PyC/PAN-derived fibres. The reason lies in the different microstructure of the carbon. The presence of a coating for PAN-derived fibres was found to be essential to limit the reaction at the fibre/matrix interface during SPS. However, coated bundles were more difficult to infiltrate, resulting in a less homogeneous microstructure.As far as the mechanical properties are concerned, specimens reinforced with coated PAN-derived fibres provided higher strengths and damage tolerance than uncoated pitch-derived fibres, due to the higher degree of fibre pull-out. On the other hand, the weaker fibre/matrix interface resulted in lower interlaminar shear, off-axis strength and ablation resistance.     

Characterization of fibre/resin bonding in composites using a pull-out test

From the early use of glass fibres in an organic matrix to that of high strength and high modulus fibres such as carbon and Kevlar, the subject of fibre/matrix bonding has received considerable attention. This paper gives details of a pull-out test has been used to measure the adhesion between fibres and matrix. A summary of results obtained with the test technique, over a period of some ten years, is also given. Despite operational difficulties the method gave interesting results regarding the mechanical aspects of the interaction between fibres and matrix.     

Compression behaviour of a fibre bundle with grafted carbon nanotubes

When carbon nanotubes (CNTs) are grown on carbon fibres, with the goal to increase toughness of a carbon fibre reinforced composite, the compressibility of the carbon fibre bundle or a fabric decreases significantly. The pressure, necessary to achieve the desired fibre volume fraction in a composite, should be increased by several bars. The paper proposes modelling approaches for calculation of the change of compression resistance of the CNT-grafted fibre bundle and fabric. The models use a previously developed algorithm for calculation of the compression resistance of a random assembly of CNTs. Two possible scenarios for the CNT-growth positioning are considered: a CNT assembly that homogeneously fills the free space between the fibres and a CNT assembly that is localised on the surface of the fibres. The model is validated against measurements of the compression resistance of carbon fibre bundles and fabrics with CNTs grown using the CVD method.     

Scale factor in the electrophysical properties of Lanom fibre

Conclusions The distribution of the specific electrical resistance of Lanom fibre is satisfactorily described by the sum of several distributions, wherein the mean value is displaced from the low-ohm region to the high-ohm one as the length of the measured section is increased.The function dependence of the critical content of parallel-included elementary fibres on length of the measured section can serve as a quantity which characterizes the scale factor in electrophysical properties of Lanom fibre. An increase in content of fibres indicates a rise in the exponential scatter of the specific electrical conductivity of elementary sections in the tow and a higher nonuniformity in its electrophysical properties, which is apparently one of the main indices in any method of preparing electrically conducting fibres.Mathematical models which describe the electrophysical properties of Lanom fibre have been examined. It has been found that the scale factor for specific electrical resistance depends on the exponential scatter in electrophysical properties in single sections of elementary fibres.Translated from Khimicheskie Volokna, No. 2, pp. 26–28, March–April, 1989.     

A simple kinetic approach to fibre failure: 2. Lifetime distributions

A simple kinetic theory of fibre failure has been developed that predicts not only the median lifetimes of fibre samples under constant load but also the distribution in these lifetimes based upon the distribution in the static breaking load of the fibre samples. The theory is applied to Kevlar fibres where data for lifetime under various loads are known.     

Modelling method based on idealised fibre bundles

Abstract

In the fibrous structures such as textiles and composites there are fibre assemblies exhibiting statistical bundle like behaviour. This paper presents a modelling method and software FibreSpace, based on a system of structuralised statistical fibre bundles, so called fibre bundle cells. These fibre bundle cells introduced before represent different idealised and typified fibre properties such as fibre shape, state of deformation, gripping as a connection with the vicinity, and the characteristic of force-transmitting and damage. With the help of the weighted parallel connection of the fibre bundle cells the mechanical behaviour and the damage process of real fibrous systems can be modelled as well as some structural properties or the strength data of single fibres can be determined by a fibre bundle cells model identified on the basis of measurements. The applicability of the fibre bundle cells method and modelling program developed is demonstrated by modelling the load and damage process of real textile structures and unidirectional composites during tensile or flexural test.     

Heterogeneity of carbon fibre

A range of polyacrylonitrile (PAN) and pitch based carbon fibre types (high, standard and intermediate modulus fibres) have been characterised using both physical and chemical techniques, the results highlighting the heterogeneity of the fibre. Nano-indentation showed variation in stiffness between different fibres of the same type as well as variation along a 20 μm length of a single fibre. Tensile tests showed variance of approximately 25% in tenacity for three different carbon fibre types but less variability in modulus with values from 8% to 19%. Raman spectroscopy showed variation in the graphitic content both between fibres of different origin as well as variation, with 0.5 μm spatial resolution, along the length of a single fibre. Inverse gas chromatography surface energy measurements of larger samples of fibres were carried out using the novel approach of incremental surface coverage by varying the probe molecule concentration and revealed different levels of energetic heterogeneity for PAN based fibres collected at different stages of carbon fibre production. The heterogeneity of the unoxidised fibres (collected after carbonisation) was restricted to about 15% of the fibre surface whereas the surface oxidised fibre sample (collected after the electrolytic oxidation bath) was heterogeneous over more than 30% and the sized fibres were shown to be quite homogeneous.     

Ultrasonic testing of natural fibre polymer composites: effect of fibre content, humidity, stress on sound speed and comparison to glass fibre polymer composites

This work investigates the application of ultrasonic testing UT in evaluating natural fibre thermoplastic composites NFTC. The characterisation of sound propagation speed in the composite is intended to be a tool for evaluating the NFTC namely fibre content, fibre distribution and external factors’ effects like relative humidity and stress. The quality of fibre distribution homogeneity can be assessed by mapping the returning signals of the emitted longitudinal ultrasonic wave. This study presents the measured sound speeds for a composite system of flax and polypropylene (PP). Flax fibre loadings rang from 0 to 60 wt%. Humidity factor is studied at 10, 50 and 95 % relative humidity RH levels. Different stress levels of 0, 10 and 20 MPa are applied on composite samples in an orthogonal direction to the longitudinal wave propagation direction. Using non-immersion: contact UT; an increasing linear trend of calculated longitudinal sound speed by 1 % is indicated per every 11 wt% increase of the applied flax fibres. This rate increased with more RH levels. More stress decreases the sound speed but in a trend parallel to the non-stressed samples. Finally, the distribution quality of the fibre is assessed using the ultrasonic technique. Results are compared with the reference corresponding PP–glass fibre composite. The high E-modulus and the density of glass fibres are opposite factors. Thus, the sound speeds for the both cases of 30 wt% flax and glass fibres are close and not more than 0.6 % different.     

Grinding characteristics and removal mechanisms of unidirectional carbon fibre reinforced silicon carbide ceramic matrix composites

The grinding performance of unidirectional carbon fibre reinforced silicon carbide ceramic matrix composites (C_f/SiC) was investigated in this paper. The effects of the fibre orientation and grinding depth on the surface integrity and grinding forces and an understanding of the grinding mechanisms are the primary concerns of this article. This problem is relatively unexplored; therefore, the main value of this research is to improve the processing quality and reduce the production cost. In the C_f/SiC grinding procedure, cracks, fibre wear, interfacial debonding, fibre pull-out and outcrop can be detected on the ground surface. The grinding depth and deflection angle have been shown to have a notable influence on the surface quality in different datum planes. A suitable grinding depth and deflection angle should be carefully chosen to achieve good surface quality in different machined surfaces. Specifically, the surface quality decreases and the grinding forces increase with increasing grinding depth. In addition, greater grinding surface quality is observed at β?=?90°, i.e., γ?=?0°, but poorer machined surfaces are obtained at α?=?0°, i.e., γ?=?90°. The surface topography, roughness and grinding forces of unidirectional C_f/SiC could be forecasted according to the analysis conclusions. This research is expected to offer guidelines for increasing the machining quality of C_f/SiC.