Thermo-mechanical modelling of cellular ceramic composites by a multiphase approach of porous media

Refractory materials have a wide range of applications in the steel-making industry for example as lining of furnaces, oxygen converters or for ladles. Often, magnesia carbon bricks (MgO-C) are used. These are made of a periclase phase (MgO) with carbon inclusions and pores. In their applications, refractories are subjected to thermal and mechanical loads causing damage. The thermo-mechanical behaviour of MgO-C composites and hence their thermal stability could be improved significantly using cellular MgO-C composites based on carbon foams [1, 2]. The present contribution focuses on the development of a fully coupled phenomenological thermo-mechanical continuum model based on the theory of porous media (TPM) with a new kinematic coupling of the displacement field of all constituents. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermo-mechanical modelling of cellular hybrid refractories

Refractory materials are subjected to both quasi-static and dynamic thermal loading (thermal shock) causing damage up to mechanical failure. Typical refractories are magnesia carbon bricks consisting of periclase (MgO) and carbon inclusions. Recently, a significant improvement of the thermo-mechanical behaviour could be achieved by cellular hybrid composites made of periclase-filled carbon foams. The present contribution focuses on MgO-filled carbon foams and the investigation and optimisation of the structure-property relationship with respect to a reduction of thermally induced stresses and damage. It is a transient as well as static, fully coupled thermo-mechanical problem. According to the fact that, in general, refractories are brittle materials a linear elastic model, with a damage criterion was used. To optimise the structural morphology of the cellular refractories, the effect of micro structural changes has been determined. For the investigation of the thermal shock! behaviour, the results correlate very well with the experimentally motivated Hasselman relation. There is a significant size effect depending on the pore size. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

高体积百分比颗粒增强聚合物材料的有效粘弹性性质

聚合物材料通常表现为粘弹性性质．为了改进聚合物材料的力学性能,通常将某种无机材料以颗粒或纤维的形式填充到聚合物中,从而得到增强、增韧的聚合物基复合材料．提出了一个新的细观力学模型,用于预测颗粒增强聚合物复合材料的有效粘弹性性质,尤其针对高体积百分比的颗粒夹杂复合材料,该方法基于Laplace变换和双夹杂相互作用的弹性模型．计算了玻璃微珠/ED-6复合材料的有效松弛模量以及恒应变率下的应力应变关系．计算结果表明在高体积百分比下该文方法比基于Mori Tanaka方法预测的粘弹性效应明显减弱．     

Friction and wear of polymer-based composites

Polymeric materials containing different fillers and/or reinforcements are frequently used for applications in which friction and wear are critical issues. This overview describes how to design high temperature-resistant thermoplastics, e.g., filled with carbon fibers and internal lubricants, for operation under low friction and wear at elevated temperatures as sliding elements in, e.g., textile drying machines. Further information will be given on the systematic development of continuous fiber/polymer composites with high wear resistance, and on attempts for the prediction of their load-bearing capacity using a finite element approach. Finally, the application of such composites in thermoplastic filament-wound journal-bearings is discussed.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Institute of Composite Materials (IVW), University of Kaiserslautern, D-67663 Kaiserslautern, Germany. Published in Mekhanika Kompozitnykh Materialov, Vol. 34, No. 6, pp. 717–732, November–December, 1998.     

Thermal dependence of electric conductivity in thermoplastic composites

Thermal dependence of the electric conductivity of thermoplastic composites based on both amorphous (hiPS) and crystallized (PP) polymers is investigated in this study. Two types of carbon black fillers with different values of BET surface area were used as charge conductors. Composites based on crystallized polymer matrices indicate the sharp growth of electric resistivity just before the melting range. This maximum is followed by substantial decrease of resistance at T > T_melt. With the decrease of carbon black concentration both relative growth of resistance at the T T_melt and further dropping resistance at T > T_melt increase. Composites filled with particles of higher surface area are characterized by less pronounced matrix influence on thermal dependence of electric conductivity than composites filled with particles of lower surface area; this can be caused by more pronounced matrix/filler interaction in the first case. The range of temperatures at which the resistance increase occurs does not depend on the type of carbon filler and its concentration. Composites with amorphous matrices are characterized by distinct increase of resistance above glass transition. Thermal treatment of the sample significantly affects the initial values and intensity of the temperature dependence of the resistance.To be presented at the Ninth International Conference on the Mechanics of Composite Materials, Riga, October, 1995.Published in Mekhanika Kompozitnykh Materialov, Vol. 31, No. 4, pp. 526–532, July–August, 1995.     

Modeling of the Interphase of Polymer-Matrix Composites: Determination of Its Structure and Mechanical Properties

In this work, a model is developed which allows one to determine the thickness and properties of the interphase layer in unidirectional and filled composites, assuming that the materials of the interphase, matrix, and fillers may have a fractal structure, and to predict the properties of composites with interphases. Using a set of computer programs elaborated, the corresponding calculations are carried out for glass-epoxy composites, epoxy carboplastics, and graphite-filled epoxy polymers.     

Rheological and dynamic thermomechanical propert ies of epoxy composites reinforced with single- and multiwalled carbon nanotubes

An epoxy resin (Epon 828) was filled with single- and multiwalled carbon nanotubes (SWCNT and MWCNT) in two steps by using the high shear mixing and ultrasonication techniques. The melt flow of the composites was characterized in a plate/plate rheometer. The thermomechanical properties of the composites were determined in dynamic mechanical analysis tests performed at various frequencies and temperatures. It was found that the incorporation of SWCNT or MWCNT increased the viscosity and stiffness of epoxy above its glass-transition temperature. The time-temperature superposition principle was employed to estimate the storage modulus of the composites as a function of frequency (f = 10^–33–10³ Hz) in the form of master curves.     

Application of the reduced concentration principle to filled polymers

The filler-concentration dependence of the modulus of elasticity of composites based on polyester resin filled with various kinds of dispersed fillers has been investigated. The applicability of the reduced concentration principle to this class of materials is demonstrated. The question of the existence of a universal dependence of the modulus of elasticity of composites on the filler content, invariant with respect to the nature of the polymer and the filler, is examined.     

Wear resistance of filled epoxypolyamide composites in aggressive media

The authors investigate the influence of certain aggressive media (toxic chemicals) on the wear resistance of filled epoxypolyamide composites. The presence of toxic chemicals in the zone of friction causes a sharp fall in the wear of the polymers. The maximum wear resistance is displayed by epoxypolyamide composites filled with iron powder, cement, or graphite.     

Effect of a filler on the strength properties of thermosets

The effect of a filler on the strength properties of polymers in tension is investigated. The thermostructural stresses that develop in the composite during cure are taken into account. Relations are given for the strength of the filled polymer as a function of the percentage filler content. In the process of analyzing the thermostructural stresses an analytic expression is obtained for the linear expansion coefficient of the composite with allowance for the structural distribution of the components. Calculated values of the strength and thermostructural stresses are presented for composites with different filler contents. The theoretical determination of the strength of filled polymers is compared with the results of experimental investigations of composites based on epoxy resin filled with quartz dust.Leningrad Mechanical Institute. Translated from Mekhanika Polimerov, No. 1, pp. 97–101, January–February, 1973.     

Mechanical properties of hybrid composites made of a steel plate and a laminate connected by means of barbed studs

In this paper the research results of hybrid composite materials made of a steel plate and laminates are presented. The tested composites were made of a metal sheet plate and a laminate plate connected by means of barbed studs. The laminates were made of three different types of fabrics with: fibreglass, carbon fibres and aramid fibres. As a warp, epoxide resin and polyester resin were used. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

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

Conclusions 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.Translated from Mekhanika Kompozitnykh Materialov, No. 4, pp. 603–606, July–August, 1979.     

Investigation of the dynamic characteristics of composites

The dynamic characteristics E and G and the damping capacity δ* of polymeric resins and composites based on glass, carbon, and boron fibers have been investigated. It is shown that the mechanical losses are correlated with the modulus of elasticity and the shear modulus of the resin and composites with different types of reinforcement. The vibrational strength of various structural materials is estimated.     

Experimental Investigations on and Modelling of the Transient Phenomena of the Payne-Effect.

The wide majority of industrially–used rubber is filled with a considerable amount of active fillers like carbon black or silica. Due to this, the material is strengthend and mechanical key features like stiffness and strength are significantly increased. In contrast to unfilled rubber, filled elastomers show a pronounced amplitude dependence, which is widely known as Fletcher–Gent or Payne effect. Besides that, some recently published works show a significant history dependence of this effect with distinctive relaxation phenomena. In the present work, some experiments on typical tyre rubber compounds with focus on these amplitude dependent phenomena are presented. On this basis, an appropriate thermodynamic consistent phenomenological material model of finite viscoelasticity is introduced. In order to incorporate the history dependent phenomena of the amplitude dependence, this model is generalized with intrinsic time scales on the basis of inner structure variables, which are a measure of the materials microstructure. The performance of the model is critically demonstrated by a few simulation results. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure and Properties of Teflon Composites with Natural Diamond Powders

The results of experimental investigations of the structure and properties of composites based on polytetrafluorethylene (PTFE) containing natural diamond powders (NDP) of different dispersity are presented. To obtain diamond-containing compositions for antifrictional applications, we used a preliminary mechanical treatment of NDP (40 m) in a planetary mill. It was stated that the formation of the maximum ordered small-spherulite structure of PTFE after injection of NDP significantly increased the wear resistance and deformational and strength characteristics of the polymer composite materials. To produce abrasive materials, PTFE was filled with NDP having a larger graininess (from 40 to 125 m). It was found that the injection of NDP did not cause evident morphological changes in the binder — the bonds between diamond grains and the polymer are created by physicomechanical forces. To strengthen the adhesion interaction at the interface between the binder and diamond grains and to raise the wear resistance of the material, a complex modification of the polymer with inorganic and organic fillers was carried out. It is shown that the injection of the complex filler significantly improves the tribotechnical and operational properties of the diamond-containing composite material. The general laws of the influence of NDP on the formation of the supermolecular structure of PTFE are revealed. It is shown that, by varying the degree of dispersity and the content of NDP in PTFE, and by applying different methods of their injection into the polymer matrix, it is possible to control the operational properties of the composites and to produce materials of different functional application, from antifrictional to abrasive ones.     

Micro-macro modelling of fiber reinforced composites exhibiting elastoplastic deformation

Fiber reinforced plastics such as carbon fiber-reinforced composites are typically characterized by their high siffness to weight ratio making them particularly attractive in lightweight construction. In addition, the architecture of these materials means that the correct modelling of their orthotropy is very important. In this work, volume averaged stress-strain responses are generated from a micro representative volume element (RVE). A nonlinear macro constitutive material model accounting for anisotropic plasticity is proposed. The model is fitted and compared to the micro stress-strain response. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Physicomechanical Properties of One-Dimensional Periodic Structures by Transmission of Laser-Excited Wide-Band Acoustic Pulses

The strength-deformation characteristics of a low-density polyethylene filled with cellulose-containing products, such as microcrystalline cellulose Thermocell, pinewood grinding dust and sawdust, and technical Thermocell obtained by a thermocatalytic method from pinewood raw materials are studied. The effect of the type of the filler and its content in the composite on the tensile strength, relative elongation, and work of failure in tension is determined. The water sorption and change in the strength-deformation characteristics of the composites during water sorption and desorption are also studied. It is found that the thermocatalytic treatment of cellulose-containing fillers makes it possible to increase the tensile strength of composites and to decrease the strength drop caused by water sorption.     

高超声速飞行器热防护材料与结构的研究进展

高超声速飞行器是航空航天的一个重要发展方向,在未来国防安全中起着重要作用．高超声速飞行器热防护材料与结构是高超声速飞行器设计与制造的关键技术之一,它关系到飞行器的安全．高超声速飞行器热防护材料与结构主要有金属TPS热防护系统、超高温陶瓷、C/C复合材料等．从材料制备、抗氧化、力学与物理性能表征等方面综述了热防护材料与结构的研究与应用现状,评述了其发展趋势．     

Constitutive modeling of cyclic stress softening in filled elastomers

Quasi-static cyclic loading tests on filled rubber-like materials reveal a significant stress softening in the first cycle. The magnitude of this softening, widely known as the Mullins effect, reduces in the next cycles until it reaches a stabilized value referred to as hysteresis. In this contribution, we associate the hysteresis with the fracture of carbon bonds in the filler network. In order to calculate the cyclic energy dissipation, we modify the classic concept of network decomposition [1, 2] and add a new network considered to be responsible for the breakage and re-formation of carbon black aggregates during loading and unloading. The proposed model is in-line with a wide range of experimental observations. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Design of Dynamically Loaded Fiber-Reinforced Structures with Account of Their Vibro-Acoustic Behavior

Dynamically loaded structures for high-technology applications generally require high material damping combined with low construction weight and adequate stiffness. Advanced lightweight structures will have to meet not only these dynamic demands but also improved acoustic (low noise) standards. High-performance materials like magnesium, aluminum, or titanium, which are mainly used in today's lightweight applications, reach their limits with respect to these dynamic and especially vibro-acoustic requirements. They offer a high specific stiffness and strength, but a relatively low damping, which leads to intense acoustic radiation. Therefore, composites or compound materials with a dynamically and vibro-acoustically optimized property profile are needed. The structural dynamic and vibro-acoustic behavior of these types of lightweight structures cannot be described by the use of classical models. Here, the advanced methods developed at ILK are considered, which take into account the special mechanical properties of the fiber-matrix compound. Also, sophisticated numerical simulation techniques such as the finite and the boundary element method are successfully applied.