Short Steel Fibers Research Articles

Mechanical Properties of Epoxy Composites Filled with Short Steel Fibres for Hybrid Injection Moulds

Epoxide filled composites are being increasingly used for mouldings blocks of hybrid injection moulds. The filling is sought for improving both mechanical and thermal properties that are relevant for the mould performance. In spite of several works investigating the particulate filling of resins, there are only a few reports on fibre reinforcement. Composites based on an epoxy system with varying volume fractions of short steel fibres (SSF) were investigated. The mechanical properties were determined for each composite, and the topography of the fracture surfaces was analyzed by SEM. The mechanical properties of the epoxy filled composites were also compared to commercial particulate composites that are used for producing casting moulds. In spite of the SSF being more difficult to mix that the usual metal particulate fillers, it was found that the resulting composites show some improvement in the mechanical properties.

Friction Properties of Steel Fibre Reinforced Epoxy Composites Used in Moulding Blocks of Hybrid Moulds

Rapid tools for injection moulding are often produced by casting of epoxide filled composites. The moulding blocks obtained in this way are likely to undergo wear especially at the surfaces of the moulding cores during the ejection phase. In this study, tribological properties of epoxide composites containing different volume fractions of short steel fibres used in moulding blocks were assessed. Friction tests with the composites and moulded polypropylene were carried out with a prototype equipment that reproduces the actual ejection phase of injection moulding. The friction data were interpreted in terms of the roughness and compared with the microscopic features of the epoxy composite surface.

Effect of copper and nickel coating on short steel fiber reinforcement on microstructure and mechanical properties of aluminium matrix composites

Commercially pure Al base short steel fiber reinforced composites were prepared by stir casting method and poured into a cast iron mould. Steel fibers were coated with copper and nickel by electroless deposition method. The density, hardness and strength of composites increased as compared to matrix alloy. The mechanical properties of these composites were measured and the results were correlated with the microstructure observation. It was found that copper-coated short steel fiber reinforced composites show considerable improvement in strength with good ductility because copper form a good interface between Al matrix and short steel fiber. Nickel-coated steel fiber reinforced composites showed improvement in strength to a lower extent possibly because of formation of intermetallic compound at the interface. The improvement in strength with uncoated fibers and nickel-coated fibers is on the lower side because of formation of brittle intermetallic compounds like Fe 2Al 5 and FeAl 3. Fracture surface of tensile specimen was examined under SEM, which revealed a ductile fracture. Copper coating on steel fiber improved the strength properties while retaining a high level of ductility due to better interface bonding.

Wear properties of copper-coated short steel fiber reinforced stir cast Al–2Mg alloy composites

In the present investigation, wear properties on 2.5, 5 and 10 wt% copper-coated short steel fiber reinforced Al–2Mg alloy composites fabricated by stir casting process were carried out using pin-on-disc wear testing apparatus. The effects of sliding distance, applied load and wt% of fiber on the dry sliding behaviour were evaluated. Dry sliding wear tests at room temperature revealed that the wear rate of MMCs were significantly lower than alloy. The coefficient of friction and the wear rate also decreased with increasing fiber content. The worn surface and debris of specimens were examined under scanning electron microscopy (SEM) to find out the wear mechanism. SEM observations revealed that extensive microcracks occur on the surface of the alloy tested at lower loads. The growth of these microcracks eventually led to the delamination of debris from the alloy surface. The copper-coated steel fiber addition tended to reduce the plastic deformation in the surface layer there by reducing the occurrence of microcracking in the MMCs. The wear mechanisms of MMCs are dominated by oxidative wear at lower load but it changed to severe wear when applied load are increased. The composites containing 2.5 and 5 wt% of fibers exhibited a load dependent transition from mild to severe wear with increasing load. In case of 10-wt% fiber composites showed only mild wear even at higher applied load.

Mesomechanism of steel fiber reinforcement and toughening of reactive powder concrete

Reactive powder concrete (RPC) is a novel cement-based composite material with ultra-high strength. Embedding a certain amount of short steel fibers in the matrix can improve the RPC’s toughness and overcome the disadvantage of high brittleness. In this paper, a number of direct uniaxial tension tests have been carried out with ‘8-shape’ RPC200 specimens. The bond-slip process, mesoscopic structural variation and mechanical characteristics of a fiber pullout of the matrix have been investigated using the real-time SEM loading system and CCD observation techniques. The influence of the volume of embedded short steel fibers in matrix on the mesoscopic morphology of attachments on the surface of a pulled individual fiber, the initial cracking force, the ultimate pullout force, interfacial bond strength and the pullout rupture energy have been analyzed. A general formulation relating these quantities to the volume of fibers in matrix has been proposed. The components comprising the interfacial bond strength have been outlined. In addition, the contribution that fibers make to enhance and toughen the reactive powder concrete has been discussed. It is shown that there exists an optimal threshold of fiber volume ρ v, opt = 1.5% at which the bond performance of a fiber pullout of RPC behaves best.

Effect of wt% reinforcement on microstructure and mechanical properties of Al–2Mg base short steel fiber composites

Abstract Al–2Mg alloy composites with varying wt% of copper-coated short steel fiber reinforced were prepared through liquid process vortex method. Steel fibers were coated with copper by electroless deposition method. It is observed that density, hardness and porosity increased with increasing wt% of fibers. The mechanical properties of these composites were measured and the results are correlated with the microstructure observation. It was found that copper-coated short steel fiber reinforced composites showed considerable improvement in strength with good ductility. Tensile strength increased with increasing wt% of copper-coated steel fiber but % of elongation reasonably good for 2.5 and 5 wt% fiber composites. It is observed that 10 wt% fiber composites shows minimum strength among the composites due to high porosity. Fracture surface of tensile specimen was examined under SEM, which revealed a dimple formation and fiber pull out. Fiber pull out from the matrix increased with increasing wt% of fibers as a result composites lose ductility. Copper coating on steel fiber improved the strength properties while retaining a high level of ductility due to better interface bonding.

Influence of mechanical working on properties of aluminium base short steel fiber reinforced composites

In the present investigation aluminium base short plain steel fiber, copper and nickel coated steel fiber reinforced composites were prepared by vortex method. These were subsequently given deformation upto 40% by hot rolling. Microstructure of deformed sample showed random orientation of fibers. Breakdown of fibers due to the hot rolling was also predominant. Density of composites increased with increase in % of deformation due to reduced porosity. The hardness and strength improvement observed is attributed to decrease in porosity and increase in the number of fibers due to fiber breakage. In case of copper-coated fiber reinforced composite some additional mechanism is observed to operate. After 40% rolling, porosity level of 5-wt% copper coated fiber composites was decreased from 3.9% to 0.7%. Hardness of as cast Al-5FeCu composite was 38.2 BHN, which increased to 45.8 BHN on 40% reduction. UTS (Ultimate tensile strength) of 5-wt% copper coated steel fiber composites increased from 124 MPa to 145 MPa on 40% deformation along with an improvement of percentage of elongation from 9.2 to 11.6. The simultaneous increase in UTS and percentage of elongation indicate that reduction in porosity is the main factor-giving rise to improvement of the properties. Fracture surface investigation showed that cracks are initiated at the fiber matrix interface, propagated through the interface and linked up with other cracks or fiber/matrix interface leading to failure. In case of as cast composites micro-porosity played a vital role in failure which is noted from SEM fractographs.

Dry sliding wear behavior of stir cast aluminium base short steel fiber reinforced composites

Dry sliding wears behavior of die cast aluminium alloy composites reinforced with copper-coated short steel fibers were investigated using a pin-on-disk wear-testing machine. The composites were prepared by liquid metal route using vortex method. The weight percentage of copper-coated steel fibers was varied from 2.5 to 10. The density and hardness of the composite increased linearly with increasing wt% of steel fibers. The wear rate decreased by 40% with addition of 10% weight percentage of fibers. A linear dependence of wear rate on fiber content and hardness of MMC is observed. The unreinforced aluminium and composites containing upto 5-wt% of fibers exhibited a sliding distance dependent transition from severe to mild wear. However, composites containing 10-wt% fiber showed only mild wear for all sliding distance. It was also observed that with increase in the fiber content to 10-wt% the coefficient of friction decreased by 22%. The duration of occurrence of the severe wear regime and the wear rate decreased with increasing fiber content. For the composite the wear rate in the mild wear regime decreased with increase in fiber content reaching a minimum. From the analysis of wear data and detail examination of (a) wear surface and (b) wear debris two modes of wear have been identified to be operative, in these materials. These are (i) adhesive wear in the case of unreinforced matrix and in MMC with low wt% (upto 5-wt%) fibers (ii) abrasive wear in case of MMC with high wt% of fibers.

Influence of coating on short steel fiber reinforcements on corrosion behavior of aluminium base short steel fiber reinforced composites

Steel fiber reinforced aluminium composites are attractive materials of high specific strength but exhibit poor resistance against electrochemical corrosion. The study discusses the electrochemical corrosion behavior of uncoated, copper and nickel coated short steel fiber reinforced aluminium and Al–2Mg matrix composites in 1 (N) NaCl solution. Galvanic corrosion between the steel fiber and aluminium governs the corrosion behavior of these composites. It has been observed that open circuit potential (OCP) is shifted to more negative side with copper coating on the fibers and to the more positive side on coating the fibers with nickel. Compared to the uncoated fiber higher corrosion current density indicates corrosion rate was observed for the copper coated fiber reinforced composites where as a lower current density was noted for the nickel coated fiber reinforced composites was observed. Addition of 2 wt% magnesium to aluminium alloy matrix increased the corrosion current density. The corrosion mechanism in these composites is dominated by galvanic cell formation that is evident from the dissolution of Al matrix near the peripheral region of steel fibers.

Effect of coating on the wear properties of stir cast Al–2Mg base short steel fiber reinforced composites

The present investigation is on the wear behaviour of Al–2Mg base 5 wt% short steel fiber reinforced composites. The composites were prepared through stir casting. The short steel fibers were coated with copper and nickel by electroless deposition process for better fiber distribution and interface bonding to improved wear properties. Dry sliding wear behavior of cast Al–2Mg base composites has been investigated using a pin-on-disc wear-testing machine. The applied load was varied in the range of 10–40 N. The volumetric wear loss increased with increasing sliding distance and applied load. Composites with 5 wt% copper coated fibers considerably reduced the wear rate and coefficient of friction compared to matrix alloy. The wear rate increased with increasing applied load. Amongst the investigated composites, the copper-coated steel fiber reinforced composite showed maximum improvement in wear rate due to better interface bonding. The Al–2Mg base composites containing 5-wt% fibers exhibited a transition from mild to severe wear depending on sliding distance and applied load. Two modes of wear have been identified to be operative based on the detail examination of wear surface, wear debris and analysis of the wear data. The transition from mild wear to severe wear was influenced by the applied load, sliding distance, hardness and strength of the pin material adjacent to the contact surface as well as by the strain induced shear stress created by applied loads.

Processing and mechanical properties of Al, Al–2Mg and Al–4Cu alloy base short steel fibre reinforced composites prepared by vortex method

In the present work commercially pure Al, Al–2Mg and Al–4Cu alloy base short steel fibre reinforced composites were prepared by vortex method, and poured into cast iron mould. The steel fibres were coated with copper and nickel by electroless deposition techniques to avoid intermetallic formation and improve wettability. The microstructure observation revealed almost uniform fibre distribution with random orientation in matrixes. Density and hardness increased with addition of short steel fibres. Density measurement shows some interesting aspect on the influence of the coating. Coating with copper gives the best fibre distribution among composites with minimum porosity. Mg addition gives better fibre distribution because it reduced surface energy of steel fibre. Alloying element such as copper addition to the matrix improved hardness but increased porosity. The mechanical properties of these composites were measured and the results were correlated with the observed microstructure; the copper coated short steel fibre reinforced composites showed maximum improvement in strength with good ductility. Fracture surface of tensile specimen was examined under SEM, which revealed fracture mechanism dominated by dimple formation and fibre pull-out. Copper coating on steel fibre improved mechanical properties owing to better interface bonding. Mg and copper addition to the matrix helps to improve strength of different fibre reinforced composites with reduce ductility.

Microstructure and mechanical properties of Al–2Mg alloy base short steel fiber reinforced composites prepared by vortex method

Fabrication and characterization of cast Al–2Mg alloy matrix composites reinforced with short steel fibers are dealt with in the present study. Three types of steel fiber were used: uncoated, copper coated and nickel coated. All the composites were prepared by the liquid metal route using vortex methods. When tested in tension, all composites exhibited improvement in strength due to high relative strength of steel fibers. The ductility was lowered except for the composite with copper coated fibers. Copper coated fiber reinforced composites gave the highest strength. Higher strength accompanied with appreciable ductility demonstrated by composites with copper coated fibers is attributed to the solid solution and fiber strengthening as well as good bonding at the interface. Composites reinforced with uncoated and Ni coated steel fibers did not exhibit strengthening to the level exhibited with copper coated fibers because brittle intermetallic phases are formed at the interface. These phases promote initiation and facilitate propagation of cracks. The observed fracture mechanism of composites was dimple formation, fiber breakage and pullout of fibers. Fracture surface of uncoated and Ni coated composites showed extensive pull out of fibers as well as fiber breakage confirming the above inference. In case of the copper coated composites dimple formation and coalescence was more extensive. EDX analysis showed a build up Cu, Ni, and Fe at the interface.

Analysis of Tomography Images of Bonded Fibre Networks to Measure Distributions of Fibre Segment Length and Fibre Orientation

The architecture of bonded fibre networks produced by sintering of short stainless steel fibres has been characterised using computed X‐ray microtomography. Two important characteristics of such networks are the distributions of fibre segment length and fibre orientation. These have strong influences on the mechanical, thermal and electrical properties. To extract quantitative architectural data from the reconstructed fibre networks, a 3‐D skeletonisation algorithm was used to convert the reconstructed fibre surfaces into their corresponding medial axes.

Development of steel fiber reinforced high fluidity concrete segment and application to construction

The Metropolitan Expressway Central Circular Shinjuku Route tunnel is constructed by shield tunneling methods with 8 shield machines. Each section of tunnel has no secondary lining, so the segment is required as in high durability and with fireproof. To improve quality of the lining and to reduce construction cost, steel fiber reinforced highly flowable concrete segment has been developed. A trial field application of sixty rings was carried out in the SJ51-SJ53 outer tunnel section. This segment is manufactured with using highly flowable concrete, which has self-filling characteristic, mixed with short steel fibers. This paper describes the abstract of steel fiber reinforced highly flowable concrete segment, and reports the trial field application at the actual shield tunneling site (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. Reprinted with permission from Elsevier.

Effects of Strain Rate on Tensile Behavior of Reactive Powder Concrete

Reactive Powder Concrete (RPC) reinforced with short steel fibers is characterized by ultra-high strength and high fracture toughness. Because of its excellent properties, RPC may be suitable as an advanced material for reinforced concrete structures subjected to impact loading. Thus, the objective of this study was to find out the effects of strain rates on tensile behaviors of RPC specimens subjected to rapid loading. The influence of the loading rates on failure modes, tensile stress-elongation curves and tensile stress-crack opening curves was investigated. Furthermore, based on the test results, a rate-dependent bridging law expressing the relation between tensile stress and crack opening was proposed.

Numerical Study of strengthening concrete using short steel fibers

Numerical Study of strengthening concrete using short steel fibers

Influence of the mechanical behaviour specificities of damaged refractory castables on the Young's modulus determination

This paper deals with the problematic of the determination of the Young's modulus of refractory castables by the way of mechanical tests. Two materials are considered: a cordierite based refractory castable that is reinforced with short steel fibres and an andalusite based refractory castable. Discrepancies in Young's modulus values are noticed depending on whether they are determined on direct tensile test curves, four points bending test curves or compression test curves. Damage due to a first thermal cycle is underlined as enhancing these discrepancies. Original mechanical tests have been performed in order to understand the influence of such a damage on the four points bending and compression behaviours. Results show that depending on the method that is used to measure displacements and strains, the calculated Young's modulus values can be highly influenced by local strain effects that occur at the contact between the sample and the loading system. Related to the damage that develops in these materials during the first heat treatment, these effects are more important when samples have been previously fired.

Fibras metálicas e sua influência no comportamento mecânico de concretos refratários durante a secagem

A adição de fibras poliméricas pode auxiliar no aumento da resistência à explosão de concretos refratários por meio de dois mecanismos principais: aumento de permeabilidade ou reforço mecânico. Já as firas metálicas apresentam um potencial de reforço para a secagem, por manterem valores altos de resistência mecânica e de módulo de elasticidade na faixa de temperaturas crítica, entre 150 e 200 ºC. Neste trabalho, estudou-se o comportamento mecânico e de secagem de concretos contendo fibras metálicas curtas e longas, comparando-os com fibras poliaramídicas (PAr). As fibras metálicas aumentaram consideravelmente a energia de fratura, porém foram pouco eficientes na contenção do dano de secagem. O volume unitário dessas fibras, três ordens de grandeza superior ao da PAr, resulta em uma menor quantidade de fibras por unidade de volume. Por isso, solicitações mecânicas na matriz são menos beneficiadas pelo reforço gerado por essas fibras. Os resultados mostram a importância de considerar a escala das solicitações para definir a geometria dos elementos de reforço, a fim de otimizar seu desempenho.

Preliminary modeling of internal heterogeneities in fibre reinforced concrete

The Reactive Powder Concrete (RPC) is made of a very fine homogeneous and compact matrix, with short steel fibres. The material (matrix and fibres) is a composite and therefore heterogeneous. From this heterogeneity of the mechanical characteristics, elastic fields are influenced by the presence of fibres and are a function of the percentage of fibres as well as orientation of the fibrous reinforcement. During the preparation of the RPC the fibrous suspension is equivalent to a concentrated solution. The consequence is a local alignment of fibres, under effect of strong gradients of shearing, and a regrouping of fibres by cluster. The result is a particular configuration for the distribution from fibres within the structure. The purpose of this study is to model, with finite element method, the mechanical behaviour of RPC elements by taking into account internal heterogeneities. Ready-made structural elements (beams) have been tested under flexure. The comparison between numerical approach and experimental investigations confirms the role played by the internal heterogeneities on the mechanical behaviour before and after the initiation of cracking. Therefore, the results of this study can be used to understand how we can optimise the process of casting.

Wear and friction behavior of stir cast aluminium-base short steel fiber reinforced composites

The wear and friction behavior of aluminium matrix composites reinforced with short steel fibers has been investigated. The metal matrix composites were fabricated by liquid process using vortex method with commercially pure Al matrix reinforced with short plain steel fibers, copper-coated and nickel-coated steel fibers. A pin on disc type apparatus was employed for determining the sliding wear rate and the coefficient of friction. The applied load was varied in the range of 10–40 N. The study reports the effects of applied load and coating on the dry sliding wear rate and coefficient of friction of the composites. Addition of fibers reduced the wear rate considerably at all applied loads. The volumetric wear increased with increasing applied load. The wear mechanism was studied with scanning electron microscope. Oxidative wear was predominant at lower loads. With increasing load the dominant wear mechanism changed to delamination and subsurface cracking assisted adhesive wear. On the basis of microscopic observations and analysis of the wear surface, the wear debris and coefficient of friction a change in mode of wear from mild to severe was noted at varying loads depending on the percentage reinforcement present. The transition from mild wear to severe wear depends on the strength of the pin material adjacent to the contact surface and the strain induced shear stress created by applied loads.