Evolution of Mechanical Properties in Tissues Undergoing Deformation-Related Fiber Remodeling Processes

We consider a biological fibrous soft tissue in which fibers are distributed in all directions. The mechanical properties of the fibers evolve due to a continuous remodeling process. The model to describe these fiber properties is based on the strain energy density of the protofibers and a survival kernel which describes the deformation-related property changes. In particular, this study investigates the development of the fiber orientation density for different choices of the fiber creation rate and fiber dissolution rate models. It has been shown that the fiber orientation density depends on both the history of the deformation and the deformation state of the fibers at the time of their creation. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electret composite materials based on polymers: Main properties and new fields of application

Data are given on the effect of an electret charge on wetting, spreading, sorption, and diffusion of liquids in polymers and composites. The modification of polymers in electric fields or by electret and electrochemically active fillers improves the physical-mechanical and tribological characteristics of materials. It is shown that the electret composites used in machines for protecting the metal-polymer joints against corrosion increase their rigidity and tightness and improve their tribological characteristics. Electret composites are new-generation materials (smart or intelligent materials) since they respond to recent developments in technology and are capable of raising the efficiency of machines with simultaneous reduction in energy and consumption of materials.Submitted to the 10th International Conference on Mechanics of Composite Materials, April 20–23, 1998, Riga, Latvia.Belyi Metal-Polymer Research Institute, National Academy of Sciences, Gomel 246652, Belarus. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 2, pp. 153–162, March–April, 1998.     

Interaction at the Interface of Phosphorus-Containing Carbon Fibers and Diglycidil Ether of Bisphenol-A

Two-component blends of phosphorus-containing carbon fibers (PCF) and diglycidyl ether of bisphenol-A (DGEBA) are investigated. It is found that PCF are better wetted by the epoxy oligomer considered than unmodified carbon fibers. It is stated that the equilibrium work of adhesion of the epoxy oligomer to PCF increases considerably. Heating the two-component blends is accompanied by conversion of epoxy groups and formation of a gel-fraction nonextractable from the fiber surface. The investigation results indicate that chemical bonds are formed at the fiber-oligomer interface, which causes grafting of the DGEBA immediately to the surface of PCF without the use of intermediate compositions usually employed in such cases. It is shown that a transition layer is formed whose morphology differs from that of the fibers and polymer in the blend volume.     

Anisotropy of torsional rigidity of sheet polymer composite materials

Wide application of polymer composite materials (PCM) in modern technology calls for detailed evaluation of their stress-strain properties in a broad temperature range. To obtain such information, we use the dynamic mechanical analysis and with the help of a reverse torsion pendulum measure the dynamic torsional rigidity of PCM bars of rectangular cross section in the temperature range up to 600 K. It is found that the temperature dependences of the dynamic rigidity of the calculated values of dynamic shear moduli are governed by the percentage and properties of the binder and fibers, the layout of fibers, the phase interaction along interfaces, etc. The principles of dynamic mechanical spectrometry are used to substantiate and analyze the parameters of anisotropy by which the behavior of a composite can be described in the temperature range including the transition of the binder from the glassy into a highly elastic state. For this purpose, the values of dynamic rigidity are measured under low-amplitude vibrations of the PCM specimens with a fiber orientation angle from 0 to 90°. It is shown that for unidirectional composites the dependence between the dynamic rigidity and the fiber orientation angle is of extreme character. The value and position of the peak depend on the type of the binder and fibers and change with temperature. It is found that the anisotropy degree of PCM is dictated by the molecular mobility and significantly changes in the temperature range of transition of the binder and reinforcement from the glassy into a highly elastic state (in the case of SVM fibers). The possibility of evaluating the anisotropy of composites with other reinforcement schemes, in particular, of orthogonally reinforced PCMs, is shown.Translated from Mekhanika Kompozitnykh Materialov, Vol. 35, No. 3, pp. 291–308, May–June, 1999.     

Non-uniformly scaled buckling modes of reinforcing elements in fiber reinforced plastic

We consider a problem about non-uniformly scaled buckling modes of isolated fiber (without accounting of interaction with the surrounding epoxy) or bundle of fibers, which are structural elements of fiber reinforced plastics under the transverse tension (compression) and shear stresses in prebuckling state. Such initial state is formed in fibers and bundles of fibers at tension-compression tests of flat specimens from cross ply composites with unidirectional fibers. For problem statement we use equations recently constructed by reduction of consistent version of geometrically nonlinear equations of theory of elasticity to one dimensional equations of rectilinear beams. Equations are based on refined shear S. P. Timoshenko model with accounting of tension-compression stresses in transverse directions. We give theoretical explanation of developed phenomenon as reducing shear modulus of elasticity of fiber reinforced plastic during the increasing of shear strains. We show that under the loading process of specimens under review uninterruptedly structure reconstruction of composite trough implementation and uninterruptedly changing of internal buckling modes at changing wave parameter is feasible.     

Evolution of the Fiber Density in Biological Tissues

An important challenge in the field of biomechanics is to understand and to model the properties of fibrous tissues. We consider a matrix-fiber composite for which the matrix microstructure and its mechanical properties are taken to be constant. The initial fiber distribution is assumed to be unstructured and the mechanical properties of the fibers evolve during deformation. Further we assume that the fiber creation rate is constant while the fiber degeneration is stretch-dependent. In particular, this study investigates the change of the fiber orientation density when a sudden simple shear is applied to the material. The fiber orientation density depends on the current deformation, the history of the deformation, and the deformation state of the fibers at the time of their creation. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural Changes in the Surface Friction Layer of a Polymeric Endoprosthesis Cup

A concept of creation of a polymeric insert for hip joint endoprostheses with the physiological and biomechanical properties typical of natural cartilage is proposed. The spherical friction surface of the insert is coated with a microporous layer imitating cartilage. This layer carries an electret charge, which improves the lubrication of the endoprosthesis with synovia and serves as a carrier of drugs, thus ensuring their prolonged discharge into the operation wound. Tribotechnical characteristics of an endoprosthesis with such an insert are investigated. It is shown that a drop in the friction coefficient of such a pair is accompanied by a change in the microrelief of the friction surface and in the degree of crystallinity of the material of the porous layer.     

Investigation of Friction in a Natural Cartilage-Microporous Ultrahigh-Molecular-Weight Polyethylene Pair

Investigation results for a friction pair incorporating a UHMWPE specimen with a microporous surface layer carrying an electret charge and a counterbody of an animal cartilage are presented. Based on the results obtained, theoretical and experimental bases for manufacturing metal-polymer unipolar heads of hip joint endoprostheses have been developed. The experimental results have proved that the modified polymer head of the unipolar hip joint excels the initial one when operated in a human organism.     

圆管纤维悬浮湍流场中粒子运动的研究

利用从细长体理论出发得到的三维分段积分法和湍流简化方法模拟了大量纤维粒子在圆管湍流内的运动．统计了不同Re数下计算区域内的纤维的取向分布,计算结果与实验结果基本吻合,结果表明湍流的脉动速度导致纤维取向趋于无序,且随着Re数的增加,纤维取向的分布越来越趋于均匀．其后又考虑了纤维速度和角速度的脉动,二者都充分体现了流体速度脉动的影响,且纤维速度的脉动在流向上的强度大于横向,而其角速度的脉动在流向上的强度小于横向．最后统计了纤维在管道截面上的位置分布,说明Re数的增加加速了纤维在管道截面上的位置扩散．     

Relationship of the ultrastructure and mechanical properties in tendinous collagen,a highly ordered macromolecular composite

A relationship has been found between the stress and deformation in tendon and, from an analysis of the data obtained, it was established that there is a major stress-bearing fiber, the diameter of which increases with increasing age of the animal. The relationship of the results obtained with the structure and properties of tendon as well as with the aging process is stressed. Models of the ultrastructure of collagen fibers in rat tail tendon or in other soft connective tissue were prepared by sealing rigid fibers in a considerably softer elastic matrix. Loss of fiber resistance was achieved by contraction of this matrix. These synthetic composite systems exactly reflect a number of the features of the collagen ultra-structure. Models were also used for studying stresses in the matrix about the fibers as this necessary information could not be obtained by a direct study of the biological tissues. Examination of the reaction between tropocollagen and the connective tissue polysaccharides in the process of collagen fiber formation shows that a mechanism exists through which the fibers may lose their resistance also in vivo.     

Analysis of Cracks with Bridged Zone of Large Scale

ABSTRACT. The direct boundary element method is used to analyze of the stress–strain state and fracture parameters of fiber–reinforced and layered composites with bridged interface cracks under transient thermal and mechanical loadings. It is supposed that unbroken fibers make up a bridged zone along of whole or part of a delamination region between layers of composite materials. For modelling purposes a bridged zone is considered as a part of a crack between joined materials and supposed that distributed spring–like bonds with given nonlinear deformation law link and constrain crack surfaces. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

张量封闭模型与三维取向分布对纤维悬浮槽流稳定性的影响

应用3种不同的纤维方向张量封闭模型,数值模拟了纤维悬浮槽流的流动稳定性问题,从而研究封闭模型和纤维的三维取向分布对稳定性分析的影响．结果发现,采用3种不同封闭模型所得到的流动稳定特性与纤维参数之间的关系是相同的,但采用三维混合封闭模型时,由于纤维的取向与流向的偏差程度较大,所以纤维对流动的不稳定性具有最强的抑制作用．而采用二维混合封闭模型时,由于纤维在平面取向条件下,其轴线整体上趋于呈流向排列,使得对流体的作用削弱,导致纤维对流动不稳定性抑制的作用最弱．     

Change in the Surface Properties of Carbon Fibers as a Result of Plasmochemical Modification

The influence of plasmochemical modification of carbon fibers on their surface properties and compatibility with the PTFE matrix is investigated. It is shown that the thin PTFE coating formed on the carbon fiber surface improves the wetting of the fibers by PTFE. As a result, the mechanical characteristics of PTFE-based composites are improved.     

Effect of thermal treatment temperature on the structure and properties of carbon fibers

Conclusions 1. It has been shown that the presence of a maximum in the dependence of strength on Young's modulus for carbon fibers made from PAN fiber may be explained by an effect of the process of temperature stress accumulation which takes place under the conditions of isometric heating. The start of this process, which causes a rearrangement of the internal structure of the high-modulus fiber, coincides with the start of the anomalous rise in fiber density.2. The interconnection between surface and internal defects and the elastic-strength properties of carbon fibers made in the temperature treatment range 600–3000°C has been studied.3. Original data on the elastic-strength properties of borided carbon fibers have been obtained; the structure of these is marked by a high degree of perfection. It has been shown that in boriding, which facilitates graphitization of the carbon, the process of regular reduction in fiber strength which is reached in the precrystallization stage is somewhat retarded.All-Union Scientific-Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, No. 6, pp. 1036–1042, November–December, 1976.     

Stress Distribution in an Elastic Body with a Periodically Curved Row of Fibers

Within the framework of a piecewise homogeneous body model, with the use of exact three-dimensional equations of elasticity theory for anisotropic bodies, a method is developed for investigating the stress distribution in an infinite elastic matrix containing a periodically curved row of cophasal fibers. It is assumed that fiber materials are the same and fiber midlines lie in the same plane. The self-balanced stresses arising in the interphase in uniaxial loading the composite along the fibers are investigated. The influences of problem parameters on these stresses are analyzed. The corresponding numerical results are presented.     

Investigation of the stability of the physicomechanical properties of carbon fibers 1. Dependence of Young's modulus on the cross-sectional area of the fiber

The modulus of elasticity in tension and the density of various carbon fibers (re-inforcement for high-modulus carbon-reinforced plastics) have been studied. There is an experimentally confirmed dependence of the modulus of elasticity on the orientation and density of the monofilament which explains the variation of this characteristic in a fiber bundle. It is shown that the principal factor determining the modulus of elasticity and its stability in a bundle of carbon fibers is the orientation and its variation for the individual fibers.     

An interphase layer in organic fibrous composites

Conclusions In this work, it was attempted to demonstrate the special features of polymer fibers manifested primarily in a special mechanism of formation of the interphase layer during formation of the composite material. The role of the interphase layer in this case is not reduced just to dissipation of the energy generated during rupture of a fiber. It can also play the role of an element of the structure of the composite acting as a possible source of initial cracks. From this viewpoint it would be useful to re-examine the micromechanics of failure of the composite and attempt to take into account the role of the interphase layer in a real system of many fibers, not just in the fiber-interphase layer-matrix triad.Translated from Mekhanika Kompozitnykh Materialov, Vol. 29, No. 1, pp. 10–18, January–February, 1993.     

Compaction and Consolidation of Aramid and Composite Fibers. 1. Compaction of Aramid Fibers

The transverse compaction and consolidation of various aramid fibers used as a reinforcement of plastics are studied with the aim to assess the behavior of the fibers during their processing. The transverse deformation of fiber bundles is considered in the context of viscoplastic flow of the fiber-forming polymer squeezed out into the interfiber space upon the contact interaction of the fibers. This process is analyzed as a flow of a polymer melt having a certain viscosity. A gradual increase in the viscosity with development of transverse deformations is revealed, which corresponds to the morphology of fibers of the skin-core type. It is found that, under these conditions, the transverse deformation and sintering of Terlon fibers are insignificant compared with that of SVM fibers, therefore, they are preferably used for reinforcing heat-resistant thermoplastics.