An integrated approach for modelling the tensile behaviour of steel fibre reinforced self-compacting concrete

The present work resumes the experimental and numerical research carried out for the development of a numerical tool able of simulating the tensile behaviour of steel fibre reinforced self-compacting concrete (SFRSCC). SFRSCC is assumed as a two phase material, where the nonlinear material behaviour of SCC matrix is modelled by a 3D smeared crack model, and steel fibres are assumed as embedded short cables distributed within the SCC matrix according to a Monte Carlo method. The internal forces in the steel fibres are obtained from the stress–slip laws derived from the executed fibre pullout tests. The performance of this numerical strategy was appraised by simulating the tensile tests carried out. The numerical simulations showed a good agreement with the experimental results.     

Derivation of a crack opening deflection relationship for fibre reinforced concrete panels using a stochastic model: Application for predicting the flexural behaviour of round panels using stress crack opening diagrams

This study is aimed at proposing a simple analytical model to investigate the post-cracking behaviour of FRC panels, using an arbitrary tension softening, stress crack opening diagram, as the input. A new relationship that links the crack opening to the panel deflection is proposed. Due to the stochastic nature of material properties, the random fibre distribution, and other uncertainties that are involved in concrete mix, this relationship is developed from the analysis of beams having the same thickness using the Monte Carlo simulation (MCS) technique. The softening diagrams obtained from direct tensile tests are used as the input for the calculation, in a deterministic way, of the mean load displacement response of round panels. A good agreement is found between the model predictions and the experimental results.     

Controlled orientation of short fibre reinforcement for anisotropic performance of rubber compounds

Abstract

The potential advantages of introducing anisotropic properties into a rubber compound by replacing some particulate filler with short fibre have been investigated. The control compound (containing no fibre) was based on NR and contained 60 pphr (N330) carbon black. In the fibre filled compound, 15 pphr of the carbon black was replaced with an equivalent volume of Santoweb fibre (10 pphr). Specimens with strong fibre orientation were produced and tensile, tear, compression, and shear properties measured at different angles to the orientation. Stretching parallel to fibre orientation resulted in a stiffness at low elongations × 3·5 higher than in the control compound. However, the tensile and tear strengths were lower than the control compound, probably owing to the high stresses at the fibre surfaces leading to fibre pullout. Maximum tensile and tear strengths were obtained when fibre orientation was at angles of 20° and 45°, respectively, to the stretching direction. Stiffness at a small (5%) compression was greater when fibres were oriented parallel to the compression direction. At greater compressions, fibre buckling reduced the stiffening effect. When fibres were oriented at 45° to the plane of shearing, shear stiffness in one direction was twice the shear stiffness in the opposite direction and twice the value for the control compound. Together with greater stiffness, this orientation led to low heat loss during dynamic shearing at a particular stress amplitude (40% of the value for the control compound).     

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.     

Reorientation of short steel fibres during the flow of self-compacting concrete mix and determination of the fibre orientation factor

A simple method has been developed to assess the orientation and distribution of short steel fibres in self-compacting concrete mixes during flow. The flow of self-compacting fibre reinforced concrete has been simulated using three-dimensional Lagrangian smooth particle hydrodynamics (SPH) which is simpler and more appropriate to use to simulate the flow and to monitor the distribution of fibres and their orientation during the flow. A probability density function (PDF) has been introduced to represent the fibre orientation variables in three dimensions. Moreover, the orientation variables of each individual fibre in an arbitrary two dimensional cross-section have been calculated using the geometrical data obtained from the three dimensional simulations. From these a new definition of the fibre orientation factor has been introduced and a method proposed for its determination from the fibre orientations monitored during the simulations. It is shown that this new definition gives results that are consistent with the expected reorientation of fibres towards the principal direction of flow. A method has also been proposed for its determination from image analysis on cut sections.     

Effects of fibre content and orientation on wear properties of basalt fibre/acrylonitrile–butadiene rubber composites

Basalt fibre (BF)/acrylonitrile–butadiene rubber (NBR) composites with various BF contents and orientations were prepared, and the curing, physical and mechanical properties and wear performance under block-on-ring abrasion conditions were evaluated. The results showed that the curing time was not obviously affected by the BFs. The addition of BFs increased the hardness but had negative influence on the tensile/tear strength of the NBR composites, especially when the BFs were oriented perpendicular to the tensile/tear direction with a high content, which should be due to the weak connection between the BFs and the rubber matrix. The coefficient of friction (COF) of the composites decreased significantly when BFs were added, whereas the content (3–30 phr) and the orientation of the fibres did not mainly affect the COF. Both parallel- and perpendicular-oriented BFs were effective at improving the wear resistance of the composites, and the former showed a better effect. With the BF content increase, the wear rate initially decreased and then remained basically stable. The COF and wear rate of the composites decreased by 27% and 35% when 12 phr BFs were added in a parallel direction. The excessive BFs, especially the perpendicularly-oriented BFs, led to fracture of the worn surface due to the abrasive grain wear caused by the crushed fibres.     

Fatigue performance of an injection‐molded short E‐glass fiber‐reinforced polyamide 6,6. I. Effects of orientation,holes, and weld line

This article presents the experimental results of stress‐controlled fatigue tests of an injection‐molded 33 wt% short E‐glass fiber‐reinforced polyamide 6,6. The effects of specimen orientation with respect to the flow direction, hole stress concentration, and weld line on the fatigue life have been considered. In addition, the effect of cyclic frequency has been examined. In addition to the modulus and tensile strength, the fatigue strength of the material was significantly higher in the flow direction than normal to the flow direction, indicating inherent anisotropy of the material caused by flow‐induced orientation of fibers. The presence of weld line reduced the modulus, tensile strength, failure strain, and fatigue strength. The fatigue strength of specimens with a hole was lower than that of un‐notched specimens, but was insensitive to the hole diameter. At cyclic frequencies ≤ 2 Hz, failure was due to fatigue, and fatigue life increased with frequency. However, at cyclic frequencies > 2 Hz, the failure mode was a mixture of fatigue and thermal failures, and fatigue life decreased with increasing frequency. POLYM. COMPOS., 27:230–237, 2006. © 2006 Society of Plastics Engineers.     

Anisotropic shrinkage of injection-molded rubber

The anisotropic characteristics of injection-molded flat rubber sheets were investigated. The shrinkage and mechanical properties were measured in two directions: parallel and perpendicular to the flow direction. The results showed that (1) the shrinkage in the parallel direction is larger than that in the perpendicular direction, (2) such anisotropic shrinkage increases with the increase of vulcanization temperature and flow distance, (3) similar anisotropy was also noticed in 300% modulus, tensile strength, and elongation. Two kinds of orientation, “shear orientation” and “expanded orientation,” were observed. The former occurs by plug flow, and the latter by the expansion of the materials. The shrinkage was independent of the expanded orientation but was strongly associated with the shear orientation, while the mechanical properties were affected by the expanded orientation.     

Orientation effects on the deformation and fracture properties of high‐density polyethylene/ethylene vinyl acetate (HDPE/EVA) blends

In this paper, the tensile deformation and fracture toughness of high‐density polyethylene (HDPE)/ethylene vinyl acetate (EVA) blends, obtained by dynamic packing injection moulding, have been comprehensively investigated in different directions of rectangle samples, including longitudinal, latitudinal and oblique directions relative to the flow direction. Two kinds of EVA were used with VA content 16 wt% (16EVA) and 33 wt% (33EVA) to control the interfacial interactions. The results indicate that molecular orientation and interfacial interaction play very important roles to determine the tensile behaviour and fracture toughness. Biaxial‐reinforcement of tensile strength was seen for HDPE/16EVA blends but only uniaxial‐reinforcement was observed for HDPE/33EVA blends. The difference is caused by the different interfacial interactions as highlighted by the peel test, scanning electron microscopy (SEM) observation as well as theoretical evaluation. Very high impact strength, decreasing with increasing EVA content, was observed when the fracture propagation is perpendicular to the shear flow direction, while a low impact strength, increasing slightly increasing with EVA content, was seen when the fracture propagation is parallel to the shear flow. The fracture of oblique samples is always along the flow direction instead of along the impact direction or tensile direction. The tensile behaviour and fracture toughness are discussed on the basis of the formation of transcrystalline zones, orientation of EVA particles and matrix toughness of HDPE in different directions. Copyright © 2004 Society of Chemical Industry     

Experimental study of the hydro-mechanical behaviour of the Callovo-Oxfordian argillite

Various laboratory experiments were carried out in the framework of the MODEX-REP project on the Callovo-Oxfordian argillite core samples taken from the Meuse/Haute-Marne Underground Research Laboratory (MHM-URL) in Eastern France to provide basic data for modelling the hydro-mechanical response of the argillite to shaft sinking. The short-term mechanical behaviour of the argillite was investigated by means of uniaxial and triaxial compression tests, whereas the long-term behaviour was studied by uniaxial creep and relaxation tests. Some influence factors such as material anisotropy, scale effect, water content and sample origin were examined. Permeability of the argillite was determined on wet and dry specimens parallel and perpendicular to the bedding plane by using gas under different confining pressures. With regard to the short-term mechanical behaviour, scale and anisotropy effects were observed. The compressive strength and the failure strain of the air-dried specimens are about two times higher than those of the saturated ones. No lower creep limit, no significant scale effect and no significant anisotropy effect on the pure creep behaviour for the argillite were found. The long-term mechanical behaviour of the investigated region of the argillaceous formation is relatively homogeneous. The gas permeability parallel to the bedding plane is about one order of magnitude higher than that perpendicular to the bedding and decreases with increasing confining pressure and water content.     

Comparative evaluation of steel mesh, steel fibre and high-performance polypropylene fibre reinforced shotcrete in panel test

In this study, experimental investigations were performed on steel mesh (SM), steel fibre (SF) and high-performance polypropylene fibre (HPPF) reinforced shotcrete (HPPFRS) panels to evaluate performance characteristics such as toughness, flexural ductility, energy absorption and load capacity. The panel tests, in accordance with European specification for sprayed concrete (EFNARC), were made on 18 prismatic specimens having the same mix designs and were cured for 28 days but reinforced with various fibres. In addition, the rebound characteristics of these mixes were determined to compare the actual in situ fibre contents.Test results show that all reinforcements, including HPPFs that are low-modulus fibres, greatly improved the flexural ductility, toughness, and load-carrying capacity of the brittle matrix. It was seen that there was a positive synergy effect between steel and polypropylene fibre in hybrid fibre usage from a performance point of view. According to results, it can be concluded that a hybrid polypropylene-SF can be used alternatively instead of SM and monosteel fibre as a reinforcement in shotcrete applications to get better efficiency in mechanical properties of composite.     

Bonding of air-formed wood fibre/polypropylene fibre composites

The effectiveness of a maleated polypropylene (MAPP) as a coupling agent in wood fibre/polypropylene fibre composites made by non-woven web technology has been evaluated. The composite panels were made with 70 or 85% wood fibre, wiht the MAPP being incorporated in the panels at a level of 1 or 3% by spraying an emulsified form on the wood fibres. Both levels of MAPP significantly increased bending and tensile strength and moduli, and dynamic modulus. At the 70% wood fibre level, impact energy was increased significantly in panels with 3% MAPP. At the 85% wood fibre level, both 1% and 3% MAPP significantly increased impact energy. The MAPP also led to small improvements in water resistance for composites containing 85% wood fibre. The effectiveness of MAPP is believed to be the result of efficient incorporation at the wood/polypropylene interface, thus providing effective coupling of the polar wood component to the non-polar polymer matrix.     

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.     

Gas-dynamic resistance of a fibre layer

An equation was obtained for calculating the flow of a gas through a layer of parallel cylinders positioned perpendicular to the direction of gas flow by using the plane channel approximation. The broader applicability of the equation for calculating the gas-dynamic resistance of a layer of fibres in comparison to the published data was demonstrated for the given case of gas flow.Branch of the Institute of Energy Problems in Chemical Physics, Chernogolovka. Translated from Khimicheskie Volokna, No. 6, pp. 23–25, November–December, 1992.     

Fibre orientation distribution in turbulent fibre suspensions flowing through an axisymmetric contraction

The Reynolds averaged Navier–Stokes equation was solved numerically with the Reynolds stress model to get the mean fluid velocity and the turbulent kinetic energy in turbulent fibre suspensions flowing through an axisymmetric contraction. The fluctuating fluid velocity was represented as a Fourier series with random coefficients. Then the slender‐body theory was used to predict the fibre orientation distribution and orientation tensor. Some numerical results are compared with the experimental ones in the turbulent fibre suspensions flowing through a contraction with a rectangular cross‐section. The results show that the fibres with high aspect ratio tend to align its principal axis with the flow direction much easier. High contraction ratio makes the fibre alignment with the flow direction much easier. The contraction ratio has a strong effect on the fibre orientation distribution. Only a small part of the fibre is aligned with the flow direction in the inlet region, while most fibres are aligned with the flow direction when they approach to exit. The fibres are aligned with the flow direction rapidly in the inlet region, after that the fibre orientations change little in the most of the downstream region. The fibres with high aspect ratio are aligned with the flow direction faster when they enter the contraction. The randomising effect of the turbulence becomes significant in the downstream region because of the high turbulent intensity.     

Experimental study of the material and bond properties of frost-damaged concrete

In an extensive experimental investigation, several types of tests were conducted on a reference specimen and frost-damaged concrete. Two levels of internal frost damage were quantified by the relative dynamic modulus of elasticity and compressive strength. Test results showed a significant influence of freeze–thaw cycles on the compressive strength and even more influence on the modulus of elasticity and the compressive strain at peak stress. Reduced tensile strength and increased fracture energy were measured. From inverse analysis of wedge splitting test results, a significant effect of frost on the shape of the tensile stress–crack opening relationship was observed: tensile strength was reduced, while the post-peak behaviour was more ductile for the frost-damaged concrete. Pull-out tests showed the influence of freeze–thaw cycles on bond strength and slip. The pull-out test results are compared with similar tests available in the literature and the effect of frost on bond behaviour is discussed.     

Hot plate welding of plastics: Factors affecting weld strength

Welded joints were made under a range of conditions in polypropylene, glass fiber reinforced polypropylene and poly (methylmethacrylate) bars. Melt flow in the weld was investigated by microscopy and by contact microradiography, and weld strengths were measured by tensile tests. The fracture toughness of the weld zone was determined by tests on double edge notched specimens. The study shows that weld strength is strongly affected by hot plate temperature, heating time and melt flow during welding. Insufficient heating or melt flow results in incomplete bonding. Excessive melt flow produces strong transverse orientation. Both reduce strength, but in different ways, which can be distinguished by fracture mechanics tests.     

Influence of molecular orientation direction on the in‐plane thermal conductivity of polymer/hexagonal boron nitride composites

The effect of the molecular orientation direction of a polymer matrix on the in‐plane thermal conductivity (TC) of injection‐molded polymer/hexagonal boron nitride (h‐BN) composites is investigated. In this system, the h‐BN platelets align in the in‐plane direction owing to injection shear flow. Three molecular orientations (perpendicular, random, and parallel to the h‐BN plane) are achieved using liquid crystalline polyesters and the in‐plane TCs are compared. Although a parallel orientation of the polymer chains provides the highest TC of the matrix in the injection direction, the TC of the composites is the lowest of the three systems for this orientation. The highest in‐plane TC is found in the perpendicularly oriented system, irrespective of the in‐plane direction. These results reveal that perpendicularly oriented molecular chains serve as effective heat paths between h‐BN platelets that are arranged one above the other, and consequently, a continuous thermal network is created in the in‐plane direction. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39768.     

Non-destructive monitoring of fiber orientation using AC-IS: An industrial-scale application

A comprehensive study has been undertaken to investigate the ability of AC-impedance spectroscopy (AC-IS) to non-destructively monitor the fiber dispersion of conductive fiber-reinforced cement-based materials. Previous work showed that AC-IS effectively monitors various fiber dispersion issues in lab-scale steel fiber-reinforced specimens. In this part of the study, AC-IS was used to study fiber orientation in an industrial-scale pre-cast concrete beam. A conventional method-image analysis (IA)-was used to verify the results of AC-IS measurements. The results of AC-IS and IA were found to match very well in experimental uncertainty. Splitting tensile tests and bending tests were conducted on the parts of the beam to study the effects of fiber orientation on the mechanical performance. The results of the mechanical tests also confirmed the results of AC-IS with splitting tensile strengths increasing as the alignment of fibers increased.     

Mesoscale modelling of dynamic tensile behaviour of fibre reinforced concrete with spiral fibres

This paper performs numerical simulations of dynamic splitting tensile tests to study the dynamic properties of FRC materials. A two-dimensional mesoscale model is developed with consideration of the fibres, aggregates, and cement mortar. The FRC models with hooked-end fibres and newly developed spiral fibres are developed to investigate the effect of fibre shape on the dynamic properties of FRC material, such as the dynamic increase factor (DIF), the energy absorption capacity and the crack opening velocity. Accuracy of the numerical models for two types of FRC materials with 1% fibre content is verified with the experimental results. The effect of fibre content on the dynamic properties of the two FRC materials is also investigated. Numerical results demonstrate that the proposed mesoscale model can reliably simulate the dynamic splitting tests of FRC materials. They also demonstrate the effectiveness of the spiral FRC in resisting the dynamic tensile loads as compared to the conventional hooked-end FRC.