Ultimate Strength Of Composites Research Articles

Effect of the Reinforcing Particle Introduction Method on the Tribomechanical Properties of Sintered Al-Sn-Fe Alloys

The present paper reports the results of the comparative study of mechanical properties of sintered disperse-strengthened Al–40Sn alloy depending on the method of reinforcing particle introduction. The study is performed on two mixtures of aluminum and tin powders: one is admixed with 5.5–14.6 wt% of pure iron powder and the other contains the same amount of iron, but as a component of aluminide Al3Fe powders. The volume fraction of tin remains unchanged in all mixtures, being equal to 20%, and the concentration of hard particles increases due to a decrease in the volume fraction of the aluminum phase. Green compacts are sintered in the vacuum furnace at a temperature above the melting point of aluminum. The sintered material is a composite containing three phases: α-Al, β-Sn, and Al3Fe, in which the tin volume fraction is constant. Testing of the sintered composites for compression shows that the addition of finished Al3Fe particles has a more beneficial effect on their mechanical properties as compared to the addition of pure iron powders. In the latter case, aluminides are formed during sintering. The ultimate strength of composites reaches 180 MPa. Mechanisms of sintering of composites and the related structure and mechanical properties are discussed.

STUDY OF STRENGTH CHARACTERISTICS AND RADIATION-PROTECTIVE PROPERTIES OF POLYSTYRENE TUNGSTEN COMPOSITE MATERIALS

Samples of composite materials are made of polystyrene, which is reinforced with dispersed aluminum. The radiation protective additive was powdered tungsten or powdered steel. The tensile strength, for these samples of composites, was investigated. The tensile strength value was obtained at various temperatures. It has been found that the ultimate strength of composites increases with an increase in the metal component. Composites with different component compositions were studied. The relative attenuation of the absorbed dose of gamma radiation by these composite materials has been calculated. Composites were with different mass composition. The code of Geant4 v 4.9.6p03 applied for calculations. It is got, that experimental results coincide with calculation results.

Three notable design strategies for manipulating failure modes in open-hole tensile composite laminates

Different failure mechanisms can lead to very different mechanical responses of notched composite laminates. We are trying to address two scientific problems: how can the occurrence of failure mechanisms be manipulated, and which kinds of failure mechanisms in open-hole tensile (OHT) tests can be manipulated to help improve the ultimate strength of composites? In this paper, three design strategies were proposed to manipulate the failure mechanism of notched composites: decreasing ply thickness at the ply level, hybridizing thin- and thick-ply laminates, and designing helical structures with variable pitch angles and ply thicknesses. Numerical methods are adopted to investigate the influence of the three design strategies on the failure mechanism of notched composites. These three design strategies are not limited to use in an OHT test. The results suggest effective methods for manipulating failure mechanisms to help create laminates with better mechanical properties.

Effects of Nano TiC Particles on Recrystallization and Mechanical Properties of Al-Zn-Mg-Cu Alloy

The recrystallization and mechanical properties of 7085 alloy and TiC/7085 composites with different nano TiC content (0.1, 0.3, 0.5, and 1 wt%) were investigated in this work. Results showed that as the TiC content increased from 0.1 to 1 wt%, dynamic recrystallization was promoted in which the composites proceeded by hot deformation; after T6 treatment, static recrystallization was hindered. In addition, the ultimate strength of composites first increased and then decreased with the increase of nano TiC particle content from 0.1 wt% to 1 wt%. When the content of nano TiC particles reached 0.5 wt%, the tensile strength of the nanocomposites was improved to 608 MPa, 12% higher than that of 7085 alloy, via the reinforcing particle strengthening mechanism. Due to the grain coarsening and the TiC particle cluster, the ultimate tensile strength of 1 wt% TiC/7085 composite decreased to 585 MPa.

Launching particle to constant reinforcement ratio as a parameter for improving the nanoreinforcement distribution and tensile strength of aluminum nanometal matrix composites

Abstract Pelletization of ball milled powder, although a better technique for distributing nanoreinforcements into the metal melt, increases the production line. Here, we report our attempt to improve the distribution of nanoreinforcements without increasing the production line. We observed the effect of increase in a novel parameter, launching particle to constant reinforcement ratio (by weight; 1.5 wt.% Al2O3), on the nanoreinforcement distribution and ultimate strength of composites fabricated by stir casting. The medium used for launching the nanoreinforcements into the Al–Cu matrix is aluminum powder prepared by ball milling. An increase in the launching particle to constant reinforcement ratio leads to an improvement in the nanoreinforcement distribution and tensile strength of the composite. The X-ray maps indicate the absence of iron contamination and iron intermetallics.

Quasi-static and dynamic deformation behaviors of an in-situ Ti-based metallic glass matrix composite

Quasi-static and dynamic deformation behaviors of a dendrite reinforced metallic glass matrix composite: Ti58Zr16V10Cu4Be12 were investigated in this study. Upon quasi-static compression, the composite exhibits distinguished work-hardening capacity. The ultimate strength approaches 1970MPa, accompanied by the fracture strain of about 14.5%. The work-hardening of the ductile dendrites accounts for the macroscopic plasticity of the composite, and high strength of the glass matrix is responsible for the large ultimate strength of the composite. On the other hand, although the composites exhibit plasticity upon dynamic loading, the fracture strain decreases, due to the fact that there is not enough time for the initiation of multiple shear bands, leading to the decrease of the resistance to fracture. The ultimate strength and fracture strain of the present composites and some other in-situ and ex-situ composites upon dynamic loading reported by previous investigations are compared.

Effect of the loading rate on ultimate strength of composites. Application: Pressure vessel slow burst test

The strength of unidirectional elastic fibre composites is shown to depend on the loading rate as the viscoelastic nature of the matrix results in a fall in breaking load as the rate is reduced. The simulation of the accumulation of fibre breaks leading to failure, takes into account all physical phenomena involved fibre failure, including the stochastic nature of fibre strength, stress transfer through the matrix between reinforcements, interfacial debonding and the viscoelastic nature of the matrix. The kinetics of composite failure are seen to involve the initial formation of random fibre breaks which at higher loads coalesce into clusters of broken fibres. The rate at which this occurs depends on the viscoelastic properties of the matrix. These results have been shown to closely mirror the behaviour of carbon fibre composite pressure vessels.

Simulation and analysis of shape memory alloy fiber reinforced composite based on cohesive zone model

Shape memory alloy (SMA) composite has been wildly used in engineering fields as a smart structure. The interface between SMA fiber and matrix plays an important role in determining the effective response of the composites, since it is the medium through which stress transfer occurs. Therefore, it is necessary to investigate how the variation of interfacial properties affects the overall behavior of the composites. In this paper, the interfacial shear strength and ultimate strength of composites are evaluated based on pull-out tests and uniaxial tensile tests, respectively. An algorithm for the automatic generation of unidirectional random distribution short-fiber reinforced composites is developed by using Monte-Carlo method and boundary condition control equation via ANSYS Parameter Design Language (APDL). Cohesive zone model (CZM) approach is used to characterize the interfacial traction separation relationships. Uniaxial tensile test is simulated using finite element method to study the overall macroscopic behavior of the composite through varying fiber ratios and ambient temperatures. The effects of interfacial debonding process, fiber ratios and ambient temperatures on the response of composites are discussed under the same fiber volume fraction.

Numerical Modeling of Tensile Behavior of Fiber-reinforced Polymer Composites

Based upon micromechanical analysis of multiple damage events, a 2D theoretical model has been proposed to study tensile mechanical response of fiber-reinforced polymer composites, by considering the effect of statistic variations in fiber strength and shear failure of matrix. Stress profiles for any configuration of breaks in composites are derived by a superposition method under the framework of shear-lag arguments. A simulation scheme coupled with Monte-Carlo method has been executed to simulate progressive damage and to investigate failure behavior. Results show that the ultimate strength of composites is influenced by fiber strength statistics and stress distribution due to progressive microdamage.

Stress Corrosion Cracking of Basalt/Epoxy Composites under Bending Loading

The purpose of this research is to study the stress corrosion behavior of basalt/epoxy composites under bending loading and submerged in 5% sulfuric acid corrosive medium. There are limited numbers of research in durability of fiber reinforced polymer composites. Moreover, studies on basalt fibers and its composites are very limited. In this research, mechanical property degradation of basalt/epoxy composites under bending loading and submerged in acidic corrosive medium is investigated. Three states of stress, equal to 30%, 50% and 70% of the ultimate strength of composites, are applied on samples. High stress states are applied to the samples to accelerate the testing procedure. Mechanical properties degradation consists of bending strength, bending modulus of elasticity and fracture energy of samples are examined. Also, a normalized strength degradation model for stress corrosion condition is presented. Finally, microscopic images of broken cross sections of samples are examined.

The effects of composition and carbon dioxide injection time on the properties of wood-cement composites

The effects of wood fiber/cement ratio, water/cement ratio and carbon dioxide injection time on the carbonation reaction and strength of wood-cement composites were evaluated. Increasing fiber content usually led to stronger composites and lower carbonation degree while increasing water amount decreased strength of composites in most cases. Either insufficient water or excessive water reduced carbonation reaction rate. There was a significant interaction effect between fiber content and water content, which had to be considered in optimizing the variables. Prolonging carbon dioxide injection time gradually increased carbonation degree, but did not affect the ultimate strength of composites.

PERFORMANCE OF ACTIVATED SURFACE AREA OF COMBINED MACRO AND MICRO FIBERS IN CONCRETE

This research is oriented towards concrete reinforced with combinations of macro and micro polypropylene fibers with total volume fractions of about 1.0 percent, so it is most important to understand how the combinations of macro and micro polypropylene fibers behave in the cement composite matrix. Two groups of composite concrete were constructed using combinations of macro and micro polypropylene fibers. The experimental test results show a new interesting parameter to consider - the activated fiber surface area, which appears to be a good indicator of fiber performance. The combinations of macro and micro polypropylene fibers allowed a higher activated surface area of fibers that improve the composite concrete properties which are advantageous in achieving a high ultimate composite strength when compared to its individual fiber.

A design approach for the mechanical properties of polypropylene discontinuous fiber reinforced cementitious composites by extrusion molding

Polypropylene discontinuous fiber reinforced cementitious composites were prepared by extrusion molding and tested in uniaxial tension to determine the mechanical properties such as ultimate composite strength and strain, and the critical volume fraction for multiple cracking. It was shown that the experimentally determined critical fiber volume fraction reasonably agreed with the theoretical value predicted by a micromechanics model. The extruded fiber composites yielded the ultimate composite strength of 9.0 MPa and composite strain of 0.55% at the fiber volume fraction of 7.4%. Our experimental results suggest that there is an optimal fiber aspect ratio and fiber volume fraction for enhancing the fracture properties.

Neutron irradiation effects on the density, tensile properties and microstructural changes in Hi-Nicalon™ and Sylramic™ SiC fibers

Tensile results are presented for ceramic grade (cg) Nicalon™, Hi-Nicalon™ and Sylramic™ SiC fibers which have all been neutron irradiated in the high flux isotope reactor (HFIR) at damage levels of 0.1, 0.5, 2 and 5 dpa. Single fibers were tensile tested and the results were analyzed using Weibull statistics. Fiber axial displacements were measured with a laser micrometer which allowed for the determination of the tensile moduli. Density changes were measured with a gradient column. Transmission electron microscopy (TEM) was performed to assess microstructural damage and X-ray diffraction (XRD) was used to measure uniform strain, degree of crystallinity, average coherence length and root-mean-square microstrain. The physical and tensile results indicate that cg Nicalon™ and Hi-Nicalon™ are unstable in a neutron field. Both fiber types densify by 3–5% which would be detrimental to a composite's matrix cracking stress due to weakening or debonding of the interface. The Sylramic™ swells which is similar behavior to the monolithic SiC. The failure strength of the Sylramic™ drops by 50% after an irradiation temperature of 500°C which would have little effect on the matrix cracking condition of a composite. The Sylramic™ fiber strength decrease would significantly reduce the ultimate composite strength but the composite strength would remain above the matrix cracking strength such that the fibers may still potentially be viable for fusion applications.

Tensile Behavior of Fiber-Cement Hybrid Composites Containing Polyvinyl Alcohol Fiber Yarns

This paper presents the results of a study on fiber-cement hybrid composites containing high-performance continuous polyvinyl alcohol (PVA) fiber yarns or rovings. Two types of hybrid composites were constructed using fiber combinations of PVA and glass (either continuous glass or 38-mm chopped strand), and PVA and fibrillated polypropylene networks. The tensile stress-strain behavior of these hybrids was studied, showing that the fibers, when used in a hybrid form, could result in superior composite performance compared with their individual fiber reinforced cements. The PVA-glass hybrid composite allowed similar or more favorable composite properties to be achieved at a lower addition of the high elongation fibers when compared with polypropylene-glass hybrids. In comparison with the hybrids containing glass fibers such as polypropylene-glass and PVA-glass, the PVA-polypropylene hybrid was less efficient at small strains (up to approximately 1%) because of the high elongation of both fibers at small strains. However, the PVA-polypropylene combination was advantageous in achieving high ultimate composite strength, because the PVA and the polypropylene could simultaneously contribute to the composite strength and because of the synergistic interaction between the two reinforcing fibers.

A percolation-type fracture criterion for composites with randomly oriented fibres

A fracture model is built up for a solid composed of brittle fibres randomly oriented in the matrix volume. The fracture process includes a stable growth of microcracks caused by fibre breaking under the load and formation of an infinite cluster of the microcracks. Both upper and lower bounds for ultimate stress in a fibre system are found as functions of the fibre volume fraction. The calculation of the ultimate stresses are performed by using the percolation theory and the theory of branching processes. At the present stage of the theory under consideration, only two types of the microcracks are appraised, namely that of a delamination type which corresponds to a weak fibre/matrix interface, and that of a penny shape which corresponds to a strong fibre/matrix interface. A particular solid contains only one type of the microcracks. In both cases, non-linear dependencies of the ultimate composite strength on fibre volume fraction are obtained.

Influence of testing method on mechanical properties of ceramic matrix composites

Mechanical properties of a monolithic zircon and zircon-matrix composites reinforced with silicon carbide monofilaments and/or whiskers were measured in three-point flexure and uniaxial tension modes to study the influence of testing methods on mechanical behaviour. A number of composite characteristics, such as the first-matrix cracking stress and strain, the ultimate composite strength and strain, and the modulus were obtained from the load-deflection behaviour in flexure and tension tests. The results indicated that the modulus values and the qualitative dependence of mechanical properties on composite parameters were similar in flexure and tension tests. In contrast, all of the other mechanical properties of the monolithic and composites were different in tests performed in flexure and tension modes. Typically, the first-matrix cracking stress and strain were higher in flexure tests than in tension tests, and these stress and strain values were independent of the filament-matrix interfacial properties. Similarly, the ultimate strengths of the monolithic and composites were higher in flexure than in tension, and these strengths were independent of interfacial properties. Therefore, the mechanical properties of composites obtained in flexure should not be used for a quantitative comparison with the predictions of micromechanical models, which are derived under the assumption of a uniform tensile stress. However, the flexure data are perfectly valid in demonstrating the qualitative dependence of mechanical properties on composite parameters.

Flexural strength of steel fibre-reinforced cement composites

The paper considers two existing theories for the flexural strength of steel fibre-reinforced cement composites, which are based on the post-cracking strength concept and on the rule of mixtures, respectively. It is shown that the former theory has serious limitations because of the omission of the matrix strength contribution to the ultimate composite strength. The rule of mixtures is strictly valid for composites under a direct tensile state of stress and its extension to the flexural state of stress has not been theoretically verified. An expression for the flexural strength of steel fibre-reinforced cement composites has been derived, based on an assumed stress block and fundamental principles of flexural mechanics. The derived expression for flexural strength is shown to be valid to the experimental results of this investigation and to the flexural strength data available from previous research. In the experimental part of this investigation, theVf(l/d) ratio of fibres in a wide range of cement matrices was kept constant. Variations in composite strength were achieved by different mix proportions of the matrix and by long-term curing both under marine exposure and under laboratory curing. In the experimental results from previous research, however, changes in composite strength were caused by differentVf(l/d) ratios of fibres.