Strength Characteristics Of Composites Research Articles

THE EVALUATION OF CURRENT RESEARCH ON THE STRENGTH OF DENTAL RESTORATIVE COMPOSITE MATERIALS

The aim of the study: to analyze the sources of scientific and metric information on the state of research on the strength of dental composites for tooth restoration.
 It has been determined that the range of composite materials available on the dental market is very wide. They differ significantly in chemical, mechanical, physical, and biological characteristics, operating properties, techniques of their usage. All this requires special training to use the composites effectively and to get high quality restoration results. The optimal choice of material and suitable technique taking into account a particular clinical situation can increase the durability of restorations and prevent the development of complications that largely depends on the strength characteristics of composites.
 At present, the problem of selecting and creating the perfect filling material has not been completely solved that is confirmed by the large number of new developments in materials science. At the same time, composite polymers are gaining ground in dental practice. The new concept of adhesive preparation of dental tissues before inserting filling material and improving the properties of the composite materials themselves contribute to the maximum preservation of healthy dental tissues, increase the aesthetics, durability and functionality of dental restorations.
 It has been determined that the mechanical strength characteristics of composite materials play a significant role in the longevity/durability of restorations depending on different chewing force and occlusal loading. It is important to investigate factors, which may cause the destruction of dental composites during the functional loading.
 The physical and mechanical properties of dental composites are impacted by a number of factors, including the type of polymer matrix, the amount of material takes, size and distribution of the filler, the state of the bond between the filler and the matrix, the degree of polymerization. The choice of a material also depends on a number of characteristics in terms of the combination of main components. Since the material parameters set by the material manufacturers can not be changes, the deep understanding of its properties will help to choose the best material in each clinical situation.
 The main physical properties of dental composites include compressive and tensile strength, modulus of elasticity, coefficient of thermal expansion, wear resistance, polymerization shrinkage, X-ray contrast, density and thixotropy, optical effects (transparency, fluorescence, etc.).
 The AE method based on the registration of elastic waves arising from the formation, change and destruction of the structure of various materials, is currently the most effective for studying the processes and stages of development of material defects. It enables in detecting initial changes in the material structure, the initial location of defects, the direction of their spreading and determining the maximum strength of the material. The advantages of this method include the ability to obtain information about the destruction in the early stages, its high accuracy and sensitivitys.
 The AE method is commonly used to study the resistance to destruction of various composite materials, the study of the tooth / composite interface, the analysis of polymerization stresses and the degree of shrinkage.

Whole-Field Stress Sensing and Multiscale Mechanics for Developing Cement-Based Composites Containing Recycled Municipal Granular Wastes

Worldwide, there is a growing level of interest to develop sustainable cement-based products and processes in which the usage of natural resources such as sand and limestone are reduced from the current levels. One of the ways to achieve this is by replacing them with suitable inclusions of recycled granular materials from municipal wastes where possible. However, to understand the effects of such inclusions in concrete structures, research advancements are needed to sense and characterise the distribution of stresses (/strains) at the local scale and to establish their links with the fracture and bulk strength characteristics under external loading environments, which is the focus here. In this research, polyethylene (PE)-based granular materials derived from municipal wastes and fly ash obtained from the incineration of municipal solid wastes are used together as secondary raw materials in preparing the concrete mixtures. Photo stress analysis (PSA) is performed here, making non-contact and whole-field digital measurements of maximum shear stress distribution and the directions of the principal stresses at any point of interest on the surface of the samples under external loading. Their links with the fracture toughness and flexural strength of the samples cured at different times are presented. The novel PSA-based stresssensing helps to establish new understandings of the strength characteristics of composites across scales in the applications involving recycling and reusing conventional wastes and possibly in otherengineering applications in the future.

Modeling the process of biodeterioration of cement compositions

The paper studies the problem of developing the theoretical foundations of the processes of diffusion biodegradation of mineral building materials (cement composites) under the action of aggressive microorganism vital products. The impact of the aggressive environment of microorganisms on the material is taken into account on the basis of Fick’s 2nd law. The resulting equation is solved by the finite difference method. Some experimental and theoretical studies of influence of the aggressive environment of microorganisms on the strength characteristics of the samples of cement composites have been carried out. The mathematical regularities of influence of the exposure time to the aggressive environment of microorganisms and the diffusion coefficient on the strength characteristics of composites have been established.

Justification of the Water-Cement Ratio Decision for Cement Mixtures Using CBPB Wastes

An unconventional approach to the design of cement mixtures with the addition of cement bonded particle board (CBPB) production waste is presented, which is characterized by high water consumption. For various compositions of fine-grained concrete prepared in accordance with the simplex-lattice design of the experiment, compressive strength and bending, as well as density of the samples, depending on the mixture factors, were researched. The fractions of CBPB wastes, water and sand at constant cement consumption were chosen as the influencing factors. For practical purposes, related to the design of cement composite compositions with the addition of CBPB wastes and with the determination of optimal values of the selected factors, mathematical models have been constructed on the basis of laboratory experiment data and with their help, the optimal ratios of components in the mixture have been determined. It was found that the content of water for the mixture mixing in the mixture has a significant effect on the strength characteristics of composites: increase of the strength of materials with a decrease in the water-cement ratio is a characteristic for compositions with the minimum amount of CBPB waste; increasing the content of the CBPB waste in the mixture the increase of the water-cement ratio leads to gain in strength. Optimal ratios of the mixture components providing maximum utilization of CBPB waste without loss of strength of composites are given.

The study of the behaviour of the ceramic composites ZrO2(MgO)-Al2O3 in a wide temperature range

The paper presents the results of experimental studies of the temperature dependence of the strength characteristics of porous ceramic composites. It is known that the most significant factors affecting the mechanical characteristics of brittle ceramic composites are the pore structure parameters. Increase of porosity leads to decrease of strength characteristics of ceramic composites, however researches about mutual influence of porosity and temperature of tests on strength characteristics were not carried out. The results of studies to determine the strength characteristics of composites under compression showed that the increase in test temperature led to a decrease in compressive strength for specified types of composite porosity by an average of 10%. Experiments carried out at negative temperatures have shown that samples with a porosity of 21% have the greatest strength sensitivity to temperature test conditions.

Modified composites of Al2O3–(Ce-TZP) system as materials for medical use

This article presents an investigation of the influence of modification of Al2O3–(Ce-TZP) with alkaline earth elements Ca+2 and Mg+2 on the phase composition, microstructure, and strength characteristics of composites. It is established that modification of Mg+2 compositions leads to a decrease in the strength parameters of composites, while introduction of Ca+2 contributes to an increase in the strength parameters of the respective composites owing to aggregation of effects of transformational and dispersive hardening. The obtained high-strength composites can be applied as constructional materials in engineering and medicine.

NONWOVEN COMPOSITE CHARACTERISTICS FORECASTING DEPENDING ON THE OPERATING CONDITIONS

In order to determine and to predict the composite properties taking the operating conditions into account, the mathematical processing of data of the experimental studies on nonwoven composite materials has been carried out. As a result, the dependences of strength characteristics of composites on the base density have been obtained, as well as the recommended nonwoven fabric parameter values.

Features of structure and properties of biopolymer composites with inorganic nanoparticles

The morphology, atomic structure, and strength characteristics of composites of barium titanate and silicon dioxide nanoparticles with biopolymers (collagen, lignin, starch) were investigated. Both changes in the inner structures and oriented ordering of morphology were found in the composites of barium titanate with collagen. Formations of quasi-parallel rows from silicon dioxide nanoparticles were found in the collagen composites with silicon dioxide. Thermal resistance of the collagen increased significantly in the process. Formation of a three-dimensional periodic structure from spherical nanoparticles was found in the composites of silicon dioxide with lignin. Interaction mechanisms of nanoparticles and biopolymers causing formation of the observed structures are discussed.

Criteria for the evaluation of strength characteristics of composites working in large-sized honeycomb structures

The results of determining the criterion of the working capacity of a five-ply structure of a glass-reinforced plastic fairing of a DRLOA-50 aircraft are reported. As a result of the performed accelerated climatic tests, it is revealed that, for the glass-reinforced plastic honeycomb structure of the fairing wall, the most sensitive characteristic to aging processes and the action of service and climatic factors is the tensile strength of the adhesive joint prepared with VK-36RD film adhesive. The range of admissible values of this and other strength characteristics of the composite constituting the wall of a large-scale fairing are additionally revealed.

Thermal Prehistory, Structure, and Deformation and Strength Characteristics of Composites Based on Polar Polymers

Thermal Prehistory, Structure, and Deformation and Strength Characteristics of Composites Based on Polar Polymers

Evaluation of Deformation and Strength Characteristics of Composites Based on Low-Density Polyethylene and Linen Yarn Production Waste by the Methods of Mathematical Statistics

The possibilities of using various methods of mathematical statistics for processing and analyzing the results of deformation and strength tests on composites made from a low-density polyethylene and linen yarn production waste are evaluated. The hypothesis that the experimental strength data agree with the Gaussian distribution is examined by the Shapiro–Wilk test (W-test.) It is shown that the Gaussian distribution, both for systems unmodified and modified with diphenylmethane diisocyanate (DIC), is valid only for two parameters: the maximum tensile strength σmax and the elastic modulus Et. For the other parameters (the relative elongation emax corresponding to σmax, the specific total work of failure Ab), and the specific work of failure to the tensile strength Amax), a non-Gaussian distribution is observed. An analysis of measurements for different specimens by the Bartlett test shows that the Et data have equal variances for both systems (with and without DIC), but for the system containing DIC, the σmax data have different variances. A two-factor ANOVA analysis reveals that DIC considerably affects the tensile strength and modulus of composites, but the influence of test conditions is a statistically significant factor only for the modulus. The coefficient of variation is considerably lower for σmax than for Et and can be used as a quantitative measure for the degree of heterogeneity of the composites investigated.

Carbon Fabric Reinforced Composites Based on Modified Epoxy Resins and Prediction of Their Strength Characteristics

The strength characteristics of composites based on four types of modified epoxy resins and reinforced with carbon fabric were studied as influenced by the filler content. The experimental and theoretical strength parameters of the composites were compared. The correlation between the adhesion strength at the polymeric binder-filler boundary and the impact resilience of the composites was evaluated; a procedure was proposed for predicting the impact resilience of the reinforced composites.

Estimating the fatigue strength characteristics of multilaminated composite materials

Since calculations of the fatigue strength characteristics of composites and components from them require long-term and expensive experiments, it is important to develop a fatigue endurance criterion which would make it possible to predict the corresponding characteristics on laminated composites from the results of testing individual layers. Since it is complicated to describe the nucleation and development of structural damage in the case of composites it is more efficient to use phenomenological approaches of which the models based on the hypothesis of damage cumulation are used most extensively. Damage cumulation in composites under cyclic loading is described by means of hereditary relations [1-3] which make it possible to take into account in an integral manner the effect of loading history on degradation on the mechanical properties of materials. The existence of several defect cumulation mechanisms has made it possible to describe damage cumulation as a multidimensional process and introduce tensor [1] and vector measures of damage [3]. In this work we use the force criterion of the hereditary type described in [4] and linked with the nonlinear determining equation derived by Rabotnov [4], and on the basis of the linear variant and the theory of laminated plates, we propose a method of predicting the fatigue strength characteristics of multilaminated composites with a polymer matrix using the results of fatigue tests on unidirectional specimens loaded under different angles in relation to the reinforcement direction. The failure condition of unidirectional composite materials [4] was formulated assuming that two types of failure were possible in a plane stress state: the first type of failure -failure from rupture of reinforcement fibres, the second type of failure -failure at the interface between the fibre and the matrix. Damage cumulation is described by the stresses acting in the main axes of orthotropy of the material and fracture of fibres takes place under the effect of stresses in the reinforcement direction, whereas fracture at the interface takes place as a result of the combined effect of stresses in the direction normal to that of reinforcement and shear stresses. According to [4] failure as a result of rupture of the fibres takes place when characteristic stresses a h [[, acting along the fibres and linked with the level of cumulated damage, reach the critical value a* LL' which are regarded as the strength of a defect-free material in the reinforcement direction. Similar failure at the fibre--matrix interface takes place when the combination of the characteristic stresses %x in the direction perpendicular to the reinforcement, and of the shear stresses %, related to the corresponding values of the strength of the defect-free material in tensile loading across the reinforcement direction a*x and shear strength r* reaches the critical value equal to unity: ahll = ai~ ; CTh .1. T h ---7+ ~ = 1. (1) Gl

Rheological and deformational-strength characteristics of polyethylene containing powdered and fibrous fillers

1. The viscosity, elasticity, and stress relaxation of a melt of composites of HDPE containing chalk, FG, and a mixture of the two were studied. The deformational-strength and relaxation characteristics of composites with a different previous history were investigated. 2. There are significant differences in the rheological behavior of melts of composites containing a coarsely disperse filler in shear and uniaxial extension. 3. There is a correlation between the relaxation and strength characteristics of composites based on HDPE on one hand and the relaxation and rheological properties of their melts on the other hand. An increase in the viscosity and elasticity of a melt of the composites with a change in the concentration or nature of the filler results in an increase in the strength of the oriented composite. 4. Addition of a disperse filler to a fibrous filler decreases the viscosity of the composites in shear and extension while not significantly affecting their strength. 5. Doping of HDPE decreases the viscosity of its composites and improves the strength characteristics of shaped and oriented material.

Properties of polymer composite materials formed under the action of a nonuniform constant magnetic field

1. A nonuniform constant magnetic field exerts a substantial influence on the strength characteristics of composite materials based on epoxide binders, particularly on the characteristics of organoplastics and glass-plastics. 2. The changes in the properties of composite materials under the action of a nonuniform constant magnetic field are due to changes in the structure and in the properties of the epoxide binder, particularly due to its structure becoming more regular. 3. The trend of changes in the strength and diffusion characteristics of composites and epoxide binders is determined by tne presence of hardening zones, which form where the gradient of the nonuniform constant magnetic field is largest.

Effect of surface treatment of carbon fibers on the strength properties of carbon fiber plastics

The strength characteristics of composites based on carbon fibers having a coating of silicon carbide are in direct dependence on the coating thickness and on the porosity, which makes it possible to assume the possibility of increasing the degree of realization of the strength characteristics of fibers having a coating in a composite by increasing the degree of impregnation of the carbon cord with the binder. The latter finds confirmation also in the fact that at a small coating thickness on the carbon fiber (of the order of 5 nm) the porosity of the composite obtained is equal to the porosity of the material based on the carbon fiber without coating. Moreover, as is evident from Fig. 3c, the casing of silicon carbide does not form a continuous coatting over the whole perimeter of the cord. The presence of these prerequisites, and also the high resistance of carbon fibers having a silicon carbide coating to oxidation [9], open up wide prospects for creating new composite materials based on them.

Dependence of elastic and strength characteristics of high-modulus composites on schemes of reinforcement

The elastic and strength characteristics of high-modulus composites with 12 different reinforcement schemes have been studied thoroughly. The effect of reinforcement schemes on change in elastic and strength characteristics of composites has been evaluated. A calculation of the elastic characteristics of high-modulus composites has been performed from the properties of the reinforcement and binder, and a comparison of the results with experimental data is given. Diagrams of deformation upon extension of the composites studied are given.