Главная Прочие Актуальные направления научных исследований XXI века, 2014, № 3, часть 2 (8-2)
СЕКЦИЯ: ДЕРЕВООБРАБОТКА И ДЕРЕВОПЕРЕРАБОТКА В РОССИИ: КЛЮЧЕВЫЕ ФАКТОРЫ УСПЕХА
COMPOSITE - IMPROVING ITS MONOLITHIC STRUCTURE
ДРЕВЕСНЫЙ КОМПОЗИТ УЛУЧШЕНИЕ EEO МОНОЛИТНОЙ СТРУКТУРЫ
Doctor of Engineering Science, Assoc, Professor FGBOU VPO "Voronezh State Forestry Academy", Voronezh, Russia
Summary: The results of theoretical and experimental studies to identify the influence of physical factors on the fracture toughness improved monolithic structure of the composite material.
Аннотация: приведены результаты теоретических и
экспериментальных исследований по выявлению влияния физических факторов на вязкость разрушения, улучшение монолитности структуры композиционного материала.
Keywords: wood, waste, composites, strength.
Ключевые слова: древесина, отходы, композиты, прочность.
Rail transport, including forestry one, with extremely slow construction of roads in Russia in the coming decades will be the primary means of transportation.
One of the main, but also the most vulnerable, from a position of operational life, elements of the superstructure of railroad tracks is a sleeper. Statistics show that in the world of railway construction the most common material for sleepers is wood. Sleepers on this basis are up to 80% of the total number and have normative service life in the impregnation with antiseptics of 14 ... 25 years, which is reduced due to the intensification of traffic and increasing loads and speeds up to 8 ... 10 years. At the same time, we know that to replace each year sleepers and on the development of the rail network it is necessary to cut down up to 12 million m3 of forest which are the lungs of the planet, and these are the trees at the age of 80 ... 100 years.
In view of the above, it is important to study the effect of various physical factors on polymer matrix of glass fiber composite material (GFCM), wood filler and, in general, on WGFCM taking into account the anisotropy of its properties.
The aim of study, whose results are given in this paper, is to develop of material science, technology and other methods on their basis to ensure crack resistance of WGFCM for a specified service life of sleepers, including logging railroads. The dependence of ultimate strength and modulus of elasticity in tension and compression of wood and GFCM on the temperature in the range 0 ... 100 °C were studied. As a result of approximating the experimental data, these relations are linear. Temperature of 100 °C is critical, because when it starts pentosans decay takes place in wood, which can characterize its mechanical properties, and in GFCM - thermal degradation of the polymer FA. The values of the temperature coefficients of the strength and stiffness are got, which are used in subsequent calculations.
The formula to calculate the thermal stress on the surface of products from WGFCM is suggested that refines formula derived by V.V. Paturoev . It uses the new results obtained in the study of the effect of temperature on the modulus of elasticity of GFCM and coefficients of thermal expansion. It is shown that the diagrams of normal stresses in the section of the cube from WGFCM perpendicular to normals «а», «t», «г» are limited to parabola. This allows you to calculate for certain, for example, voltage on surface of the product, the maximum stress at the center, and vice versa.
Attention was paid to the fact that in certain studies of the shrinkage process of polymeric materials the authors took into account only the facts of strength growth, modulus of elasticity and the most shrinkage during curing. It was absolutely not taken into account that this process is accompanied by temperature increaser, and it is associated with a decrease of the strength and elastic properties, which we took into account, along with the anisotropy of the properties of wood in studies of WGFCM shrinkage.
To identify the stress and deformed condition arising in WGFCM under physical factors associated with the curing process of FA oligomer and moisturizing during operation of sleepers, cube of the material was adopted as the object of study which is a cube of pine wood, the faces of which coincide with planes of its elastic symmetry and which is enclosed in a polymer shell of GFCM, and cross-sectional area ratio of the matrix and wood filler in a cube of WGFCM and real sleeper are the same.
It was found that the curing of FA polymer solution proceeds exponentially, i.e. unevenly in time T. Initially it is quite intense due to its self-heating in an exothermic polymerization reaction. Then, the solution thickens and from that moment free shrinkage strains begin to interfere with its elements of wood filler, in the case - faces of wooden block. Thus at its edges stress concentration is possible.
Their consideration leads to the conclusion that the presence of residual thermal stresses on the surface of the product do at some point the state of stress in the cube of WGFCM and, of course, any product of this material more dangerous than when it was cooled completely. Similar condition can occur, for example, in railroad sleeper, in summertime and, in particular, through the rails on switches and in curves, when they are heated to a temperature of 100 0 C when driving on them.
As a result of input of necessary data into the computer and use of a special program two variants of stress and strain state in cube of wood were analyzed. Values of the principal stresses were found, the principal provisions of sites are determined through the direction cosines and then the principal values of relative deformations were defined.
The greatest danger is value of main relative deformation (calculation of the second limit state) towards the axles «г» and «t», which is equal to 0.01 or 1 %. It is higher than the maximum relative strain at the beginning of the crack-formation, equal to 0.0066 or 0.66 %. Since similar deformation without water activity was 0.48%, this means that, as expected, its effect increased deformability of GFCM in two times. However, this does not mean that the cracks in the polymer shell after increasing its thickness should appear as reduction of the modulus of elasticity in tension of GFCM exposed to water and reduce the actual tension in it (such a statement needed experimental validation).
The next stage of our work was to investigate the influence of water on WFGCM without and taking into account the simultaneous action of constant bending load. In particular, part of the total relative strain was revealed, characterizing the effect of pressure of constrained swelling of wood cube on polymer shell. It made possible to determine its absolute strain, and then - relative to the edges of the cube of WFGCM that, when the shell thickness is 12.5 mm was higher than limit tensile of WFGCM.
It is concluded that a simple increase in its thickness does not solve completely the problem of protecting wood from swelling, so you need simultaneously produce surface treatment of sleepers, for example, with water- repellent solutions.
We hold the original experiment to determine the absolute deformation of edges of the cube of WFGCM immersed in water. It was found that in the shell of the cube of GFCM with thickness of 12.5 mm, non-treated with water-repellent solution after two months of exposure in the water, cracks at an angle, almost coinciding with the angle of main area with the highest principal tensile stress occur, which fully confirmed the correctness of theoretical calculations.
Surface treatment of the cube polyethylene wax and divinyl styrene thermoplastic elastomeric solutions plus colophony in kerosene oil reduces relative deformations in two or three times. While increasing the thickness of the shell up to 27.5 mm WFGCM crack resistance can be guaranteed within 6 months, i.e. in the most dangerous fall-winter-spring period and then.
An experiment to detect resistance of sample-beam of WFGCM of basic composition, immersed in water, which are then tested in pure bending, was held. Approximating functions were obtained with high accuracy of the experimental data and for determining the coefficient of resistance, equal to that at the end of a given period of operation of sleepers - 40 years, 0.47 ... 0.48, and for 260 days - 0.50 ... 0.51. For WFGCM with reinforcing frame these are 0.76 and 0.76, respectively .
Experimental studies of the process of creep in pure bending of beams samples of WFGCM of basic composition, immersed in water were done. Obtained from experimental data precision approximating functions, allowing calculating the coefficients of duration at the end of a given period of operation 0.41 and for 260 days - 0.45 and long deformation coefficients equal to 0.37 and 0.46, respectively were got. The absolute value of a long resistance limit can be taken equal to 9 MPa, and extended secant modulus of deformation - 0.36 * 104 MPa and 0.45 * 104 MPa for the same term of exposure to water. Difference
between C"'v and C^r for 260 days (0,50...0,51 against 0,41) and tensile strength at the same time point (11 MPa to 9 MPa) can be explained by different rates of loading: in machine testing to determine the coefficient of resistance in the water - 10 mm / min and in creep strain - developing with a rate of 0.5 mm / min.
We must also consider that the values of the coefficients are relative values as if they are equal absolute values of ultimate strength and limits of prolonged resistance may be higher, for example by applying reinforcing frame, using hydrophobic solutions, restoring strength and elastic properties of the material at high summer temperatures, etc.
In connection with the foregoing, the selection of components of waterproof WFGCM matrix composition was done and the technology of casting of railway sleepers of it was developed, for example, in the existing workshops of sleepers sowing.
The results of theoretical and experimental studies described in this article, make a significant contribution to solving the problems of replace of traditional materials, wood and reinforced concrete, for WGFCM in railway sleepers for various purposes. Its implementation should help to preserve the forest, use the huge amount of waste of forestry and woodworking industries, improve the environment and create employment.
УДК 674.8: 574