Modelling Triaxial Tests on Fibre-Reinforced Sands with Different Fibre Orientations Using the Discrete Element Method

Linxian Gong,Lei Nie,Chang Liu,Yan Xu 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.8

Fibre-reinforced soil has been widely applied as a composite fill material in geotechnical engineering. In this study, triaxial tests of fibre-reinforced specimens with different fibre orientations were performed employing the discrete element method. The approach enables an investigation of some significant micromechanical properties, including the contact orientation distribution, coordination number, particle displacement field, and contact sliding fraction. From the discrete element method (DEM) perspective, fibre orientation affects the contact force distributions and the load-bearing mechanism for this mixture system. More horizontal fibre particles participate in supporting the strong force chains compared with the vertical and random fibres. Fibre orientation also affects the pattern of displacement fields, which shows that horizontal fibres can limit the formation of localised shear bands. Horizontal fibres also cause the largest increase in the normal contact force acting on the fibre–sand interface and the coordination number of the sand–fibre contact type, which leads to an increase of sliding friction between fibres and the sand matrix. The majority of horizontal fibres could also produce tension during triaxial compression, leading to a more effective reinforcement. The results from this study could contribute to improving our knowledge of mechanical behaviours of sand–fibre composites.

Evaluation and Analysis of Fracture Modes in Single Composite Basalt/Epoxy Fibres by Photoelastic Method and Single Fibre Fragmentation Test

Eoghan Thornton,Pouyan Ghabezi,Calvin Ralph,Findhan Strain,Noel M Harrison 한국섬유공학회 2022 Fibers and polymers Vol.23 No.5

In this work, the suitability of basalt fibres for uni-directional composite material applications, and adhesionbetween the fibres and the matrix they are embedded in have been investigated. A single fibre fragmentation test was carriedout on 13 μm diameter basalt fibres embedded in a dog-bone epoxy matrix. Photoelastic analysis was used to observedifferent fracture mechanisms in a single fibre composite sample and fibre breaks during testing. A theoretical model basedon a Griffith’s fracture mechanics approach was used to determine the fibre-matrix interfacial shear strength, which is ameasurement of the level of adhesion between the fibre and the matrix. It was also used to predict the fibre fragment axialstress and the fragment interfacial shear stress, both as functions of axial position on the fibre. A finite element model wasdeveloped to simulate the fibre fracture process, and the redistribution of stresses in the fibre and the local region surroundinga fibre break. The developed experimental procedure was successful in that stress-induced birefringence was observed in thetested samples, as well as the characteristic shear stress light fringes that occur in the regions surrounding fibre fractures. Also, there were some similarities between the finite element model results and the theoretical predictions. The critical fibrelength, lc was measured as 0.752 mm, whereas this value was calculated 0.6708 mm from finite element predicted interfacialshear stress distribution for fibre fragment. A combination of all three types of failure modes was recorded across the samplesthat were tested, while only a single failure mode was observed in the finite element model. According to the theoreticalmodel, for a given set of parameters and constant stress with only the fibre length varying, the axial stress in the fibre reducesas the fibre gets smaller.

Relations between the Characteristics of Angora Rabbit Fibre

Onal, Levent,Korkmaz, Mahmut,Tutak, Mustafa The Korean Fiber Society 2007 Fibers and polymers Vol.8 No.2

Angora rabbit fibre is one of the finest specialty animal fibres with its well-known reputation for fineness, lightness and softness. This study evaluated the Angora fibre shape and morphology in comparison with Cashmere fibre and wool as well as the relation between characteristics of Angora fibre. Unlike other keratinous textile fibres, single Angora fibre composes of two sections named as body and head, each of which has individual surface characteristics. Differences between the scale shapes, scale length and scale frequency of Angora hair types were explained in details. Medullation in Angora fibre was explained for different types of Angora hairs defined as down, awn, and bristle. This classification was done according to the fibre fineness starting from the finer one. Relation between fibre shape and comfort factor was also analyzed. The relation between mean fibre diameter (MFD), fibre curvature (FC) and percentage of medullation by volume (MEDV) for Angora rabbit fibre was not as strong as wool and Cashmere fibre. Accordingly, when Angora hair types were analyzed individually, it was observed that relation between FC and MEDV for Angora fibre was stronger than wool and Cashmere fibre. Multiple regression analysis was also performed. Diameter distribution along the snippet length (about $200\;{\mu}m$) of Angora fibre is uneven compared to Cashmere fibre and wool.

Experimental Study on Shear Behaviour of Hybrid Fibre Reinforced Concrete Beams

M. P. Karthik,D. Maruthachalam 대한토목학회 2015 KSCE JOURNAL OF CIVIL ENGINEERING Vol.19 No.1

In general Fibre Reinforced Concrete (FRC) can improve the strength properties of hardened concrete; likewise this experimentalinvestigation is to clarify Shear cracking behaviour of Hybrid Fibre Reinforced Concrete (HyFRC) beams, with the combination ofScrim bled Steel (ST) Fibre and synthetic fibre like Recycled Polyethylene Therephthalate (RPET) and Polypropylene (PP) in thevolume fraction of 0.5%. The grade of concrete is M40 was designed by using codal provision of IS 10262-2009. The mechanicalproperties and shear performance were studied for concrete prepared using different hybrid fibre combinations like ST-PP and STRPET. The dosage of fibres are 0-100, 25-75, 50-50, 75-25, 100-25. Addition of steel fibres generally contributed towards bridgingaction where as synthetic fibres resulted in delaying formation of the micro cracks. Compared to the ST-RPET combination, the shearperformance of the hybrid fibre reinforced concrete is superior in ST-PP combination. Then the experimental results were exploredwith the nonlinear Finite Element Analysis (FEA) using ANSYS 12 that has been carried out to simulate the behaviour of failuremodes of HyFRC beams. The result shows that the combination of ST-PP is relatively similar with the experimental investigation. The maximum result obtain in combination of ST75PP25 combination, Allowable strength of the Polyethylene Theraphthalte fibre iscomparatively lower than the Steel and Polypropylene fibre.

Experiments on Tensile and Shear Characteristics of Amorphous Micro Steel (AMS) Fibre-Reinforced Cementitious Composites

Jeong-Su Kim,Chang-Geun Cho,Hyeong-Joo Moon,Hoyeon Kim,Seung-Jung Lee,Wha-Jung Kim 한국콘크리트학회 2017 International Journal of Concrete Structures and M Vol.11 No.4

Amorphous micro-steel (AMS) fibre made by cooling of liquid pig iron is flexible, light and durable to corrosion, then to be compatible with high flowable and disperable states of mixing as well as high ductile post-cracked performances to apply in fibre-reinforced cementitious composites. In the current research, AMS fibre-reinforced cementitious composites based on cement and alkali-activated ground granulated blast furnace slag mortars were newly manufactured and evaluated for the strength and ductile characteristics mainly by direct tensile and shear transfer tests in the variation in the volume of AMS fibres with two different lengths of 15.0 and 30.0 mm. As a result, it was found that 1.0–1.25% fibre volume fractions were recommendable for AMS fibre-reinforced cementitious composites to maximize direct tensile strength, ductile tensile strain, and shear strength of the composites. However, a further fraction of AMS fibre lowered these mechanical characteristics. Simultaneously, it could be said that AMS fibre-reinforced cementitious composites exhibited up to about 3.7 times higher in direct tensile strength and up to 2.3 times higher in shear strength, compared to AMS fibre-free specimens.

Impact Properties of the Chemically Treated Hemp Fibre Reinforced Polyester Composites

Mohammad Mazedul Kabir,Mohammad Yousef Al-Haik,Saud Hamad Aldajah,Kin Tak Lau,Hao Wang 한국섬유공학회 2020 Fibers and polymers Vol.21 No.9

Plant based hemp fibre properties were found to be highly influenced by changes in the amounts of cellulose,hemicellulose and lignin constituents within the fibre. These fibre constituents play a major role for effective interfacialadhesion between the fibre and the matrix. Chemical treatments such as alkali (NaOH), acetyl (acetic acid & aceticanhydride) and silane (siloxane) treatments have the potential to react with constituent contents by varying their amounts. Inthis study, hemp fibre was treated with alkali (0-10 % NaOH), acetyl and silane chemicals. Treated fibres were mixed withpolyester matrix to produce composites. The effects of chemical treatments on hemp fibres and the resulted polyester matrixcomposite were analysed through impact testing of the composite samples. Alkali treatments on hemp fibres enhanced theimpact resistance properties (around 43 % lower absorbed energy and 40 % higher rebounded energy) of its compositescompared to the untreated cases. Lower absorption energy and higher rebounded energy indicates strong interfacial bondingbetween the fibre and matrix. Improvements are governed by the removal of hemicellulose and lignin from the fibre, whichprovides a platform for better chemical reactions between fibres and matrix. On the other hand, acetyl treatments on thehigher concentrations of NaOH pre-treated fibres reduced the fibres’ ability to support impact loadings (22 % higherrebounded energy compared to the untreated cases). In the two treatment conditions, fibre lessen their strength due toexcessive removal of hemicellulose and lignin constituents, and composites exhibited lower impact properties compared tothe NaOH treated samples. Similar impact properties were also recorded for alkali pre-treated silanised composites. As alkalipre-treatment removed the hydroxyl groups from the fibre, further silane treatment could not develop silanols to create stronginterface bonding. As a result, composites failed under lower impact resistance compared to the NaOH treated samples.

Experimental and microstructural evaluation on mechanical properties of sisal fibre reinforced bio-composites

B. Ravi Kumar,S.S. Hariharan 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.33 No.2

The natural fibre composites are termed as bio-composites. They have shown a promising replacement to the current carbon/glass fibre reinforced composites as environmental friendly materials in specific applications. Natural fibre reinforced composites are potential materials for various engineering applications in automobile, railways, building and Aerospace industry. The natural fibre selected to fabricate the composite material is plant-based fibre e.g., sisal fibre. Sisal fibre is a suitable reinforcement for use in composites on account of its low density, high specific strength, and high hardness. Epoxy is a thermosetting polymer which is used as a resin in natural fibre reinforced composites. Hand lay-up technique was used to fabricate the composites by reinforcing sisal fibres into the epoxy matrix. Composites were prepared with the unidirectional alignment of sisal fibres. Test specimens with different fibre orientations were prepared. The fabricated composites were tested for mechanical properties. Impact test, tensile test, flexural test, hardness test, compression test, and thermal test of composites had been conducted to assess its suitability in industrial applications. Scanning electron microscopy (SEM) test revealed the microstructural information of the fractured surface of composites.

Correlations between Fibre Diameter, Physical Parameters, and the Mechanical Properties of Randomly Oriented Biobased Polylactide Nanofibres

Mantsopa Koena Selatile,Suprakas Sinha Ray,Vincent Ojijo,Rotimi Sadiku 한국섬유공학회 2019 Fibers and polymers Vol.20 No.1

In this study, the tensile properties of systematically optimised, biodegradable polylactide (PLA) electrospum fibres are investigated in order to illuminate the influences of the factors that affect their mechanical properties such as fibre diameter, alignment, inter-fibre bonding, mat porosity, and packing density. The effect of fibre diameter was studied by varying the PLA concentration. The effect of fibre-fibre interaction enhancement was also investigated. The extent of anisotropy on the mechanical properties of the mats was evaluated as a function of the collector drum speed in the rotational (0 o), transverse (90 o), and diagonal (45 o) directions. The results demonstrate a strong correlation between the fibre diameter and the mechanical properties. Thinner fibres exhibit better mechanical properties, which are then further enhanced by fibre fusion and alignment. Other mat characteristics have minimal effects on the mechanical properties. The fibres produced atdrum speeds of <250 rpm, exhibit isotropic character. Fibre alignment is observed beyond this speed, with strong enhancement of properties in the direction of drum rotation. In summary, randomly oriented fibres with isotropic responses to mechanical properties may be used in applications such as air filtration.

Optimal dimension of arch-type steel fibre-reinforced cementitious composite for shotcrete

Lee, S.J.,Eom, A.H.,Ryu, S.J.,Won, J.P. ELSEVIER (APPLIED SCIENCE) 2016 COMPOSITE STRUCTURES -BARKING THEN OXFORD- Vol.152 No.-

In this study, the optimal dimension of arch-type steel fibre for cementitious shotcrete was derived based on the bond properties with a cement matrix, as a function of the length of the steel wire, the radius of curvature of the arch, and bend length at the fibre end. Our results indicated that a smaller radius of curvature of the arch-type steel fibre was able to withstand a higher maximum load, without fibre fracture or pullout. Pullout was evident for a larger radius of curvature of the fibre; however, fibre fracture was not observed. Additionally, the arch-type steel fibre end with a longer bend length showed excellent bond properties and pullout behaviour as the radius of curvature increased, due to stable anchoring within the cementitious composite. Statistical analysis of the experimental results indicated that the steel wire length had no effect on the bond properties of the fibre; also, a bend length >2.0mm was identified as optimal for a radius of curvature of 20mm. Our optimised fibre configuration was compared with a 35-mm hooked-end-type steel fibre, which is commonly used as reinforcing material in shotcrete.

Comparison of macrosynthetic and steel FRC shear-critical beams with similar residual flexure tensile strengths

Francisco Ortiz-Navas,Juan Navarro-Gregori,Gabriel Leiva,Pedro Serna 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.76 No.4

This study extends previous experimental research on the shear behaviour of macrosynthetic fibre-reinforced concrete beams and compares them to steel fibre-reinforced concrete beams with similar mechanical and geometrical properties. This work employed two fibre types: 60/0.9 (long/diameter) double hooked-end steel fibre and 60/85 monofilament polypropylene fibre. Beams were tested by shear loading covering parameters, such as two different cross-section widths, two shear-span-to-effective-depth ratios, two fibre types and using repetitions with and without transverse reinforcement. For quantitative comparison purposes, crack pattern evolution was studied along increasing loads levels. Effects were studied by photogrammetry, including influence of fibres on crack propagation in uncracked and dowel zones, influence of fibres on stirrup behaviour, and shear deformation or kinematics of critical shear cracks. The results evidenced similar effectiveness for both fibre types in controlling shear crack propagation and horizontal dowel cracking. Both fibres provided similar shear ductility and shear deflections. Consequently, the authors confirm that residual flexural tensile strengths are a convenient parameter for characterising the shear behaviour of fibre-reinforced concrete beams.