Changes in the strength characteristics of human intervertebral disks under compression

Conclusions 1. The strength of intervertebral disks undergoes significant changes during the human lifetime. The data obtained allow the distinction of three periods: 1) a period of strength gain (newly born babies-18 years); 2) a stable period (20–40 years); and 3) a period of strength loss (from 50 to the death). The safety factor of strength of the intervertebral disks is the highest during the first two decades and decreases during the following age periods.2. The sex has a significant influence on the strength characteristics of the intervertebral disks.3. Changes in the limiting load of the intervertebral disks of the spine are characterized by a caudocranial gradient and the changes in the strength and the safety factor of strength, by a cranio-caudal gradient. The existing relationships do not depend on age or sex and reflect the significance of the functions of support and motion in different sections of the spinal column.4. The strength of the intervertebral disks depends on the degree of the degenerative-distrophic process, the mineral content of the tissues, the water content, and the ability of the disk tissues to retain water.S. V. Kurashov Kazan' State Medical Institute. Translated from Mekhanika Polimerov, No. 5, pp. 897–902, September–October, 1976.     

Effect of the shape and size of the cell on the compressive strength of honeycomb cores

The effect of cell shape and size and panel thickness on the strength of honeycomb materials is studied. Three types (shapes) of core cells are investigated: 1) regular (symmetric) hexahedral; 2) hexahedral offset by one-half pitch; 3) reinforced hexahedral. It is found that the strength of the investigated types of core increases in the following order; 1) cores with hexahedral cells offset by one-half pitch; 2) cores with regular hexahedral cells, and 3) cores with reinforced hexahedral cells. It is shown that cores with reinforced cells obey all the laws characteristic of other cores. It is confirmed that the facing strengthens the core material.Mekhanika Polimerov, Vol. 1, No. 3, pp. 29–32, 1965     

Strength properties of the human aorta and their variation with age

Conclusions 1. The strength of the aorta wall in a direction transverse to the vessel axis exceeds the strength in the longitudinal direction by on average a factor of 1.9 in the thoracic and 1.8 in the abdominal sections.2. The strength of the wall of the thoracic aorta is greater than that of the abdominal aorta. The differences between the strength characteristics of the aortal wall in the transverse direction are statistically reliable (up to 8th decade of life).3. As the organism ages, the strength of the walls of the thoracic and abdominal aortas decreases in the longitudinal and transverse directions. This is indicated by the close inverse correlation between ₁, ₂ and age.4. The strength of the aorta wall changes according to the period or stage of life. In each stage it is approximated by an exponential function.5. The rate of decrease of the strength of the wall is less in the transverse than in the longitudinal direction during the initial or evolutive stage of life.6. The decrease in strength (according to the criteria , , ) indicates more rapid aging of the tissues of the abdominal (relative to the thoracic) aorta. This difference appears after the age of 40 in the transverse and 50 in the longitudinal direction of the aorta wall.Chita State Medical Institute. Translated from Mekhanika Polimerov, No. 1, pp. 104–108, January–February, 1977.     

Study of the two-dimensional deformation of polymers

The authors have investigated the effect of the degree of extension on the strength and shrinkage of polyisoprene chloride rubber film. It is shown that the breaking strength and shrinkage at elevated temperatures are determined only by the degree of extension in the corresponding direction and are almost independent of the extension in the other direction.Mekhanika Polimerov, Vol. 2, No. 3, pp. 350–354, 1966     

Statistical aspects of the failure of organic-fiber-reinforced plastics

Conclusions Dispersion of the strength of filaments and of the Weibull coefficient leads to a drop in strength of a strand compared with the strength of the components when the adhesion by gluing together does not amount to 2–5%. The drop in strength is determined by the dispersion of strength which depends on the length of the tested specimens.Gluing together of the fibers in filaments changes the nature of the load diagrams - of a filament when its length exceeds ₀. A consequence is that the mechanism of rupture of the strand changes, and this leads to an additional drop of its strength. When specimens are 500 mm long, the drop in strength of the strand compared with the mean strength of the filaments amounts to 10%.Because of the dispersion of the Weibull coefficient, the strength of filaments does not correspond exactly to the strength of the microplastic obtained from these filaments. When there is dispersion of the strength of the filaments, failure of the plastic proceeds by failure of the microplastics as a whole.Gluing together of fibers has a double effect on the strength of the material: increased degree of gluing together of the fibers reduces the noneffective length from ₀ to 0.4–0.5 mm, and this leads to an increase of approximately 50% of the strength of the microplastic; increased gluing together leads to a change in the mechanism of failure of the strand and of the organic-fiber-plastic made from it if there is dispersion of the strength of the component filaments, and this reduces the strength of the material in accordance with (3) (by 12–14% in our case). The longitudinal instability of the properties of the filament leads to an additional drop in strength of the material by 4.5%.Translated from Mekhanika Kompozitnykh Materialov, No. 6, pp. 1011–1017, November, 1984.     

Some characteristics of the strength properties of crystallizing rubbers at elevated temperatures

A study has been made of the reasons for the considerable scatter of the strength properties and the failure of specimens based on crystallizing rubbers outside the gauge length when tested in accordance with Soviet standard GOST 270-53 at elevated temperatures. The relation between the strength distribution and degree of vulcanization is clarified. It is shown that the strength properties of the product are affected by the thermal prehistory of the rubbers.Mekhanika Polimerov, Vol. 2, No. 1, pp. 82–86, 1966     

Effect of elevated temperatures on the strength of cured resins and resin-based materials

An investigation of the thermal stability of polycondensation cured resins has confirmed the previously established linear relationship between loss of strength and loss of weight. In the process of thermal degradation three qualitatively different stages are observed. The first is characterized by a fall in strength at low weight loss, pointing to a highly stressed structural network. The second stage, characterized by smooth variation of strength and weight, corresponds to thermo-oxidative degradation, which in the case of organophosphorous and melamine-formaldehyde resins ends in the formation of stable structures (third stage) with a residual strength of 8–10%. It is proposed to estimate the thermal stability of resins from three-dimensional diagrams in strength-temperature-time coordinates. Plane diagrams can be used for the rapid comparative evaluation of different resins.Mekhanika Polimerov, Vol. 2, No. 5, pp. 746–754, 1966     

Effect of thermal aging on the adhesive strength of joints of double-chain polymers with fibers and on the properties of unidirectional CFRPs based on them

The paper presents a study on the effect of thermal aging on the adhesive strength of joints of some double-chain polymers and fibers. It is shown that the initial shear strength of joints of a steel wire with double-chain polymers based on bisaminonitrile (R = −CH₂−) is significantly higher than that in the case of polymers based on the “A-B” monomer. The type of thermal stabilizer affects the strength of the fiber/matrix interface only slightly. Prolonged heating (up to 100 hours) of the joints at 350 °C does not reduce the strength of joints based on the “A-B” monomer, while that of joints based on bisaminonitrile decreases by 20-30%. The thermal stability of carbon-fiber-reinforced plastics appeared to be higher, which was likely due to the effect of scale factor. The strength of a test specimen batch decreased only upon exposure to 400 °C for more than 100 hours.     

General criteria of the strength of isotropic media

The limit surfaces of isotropic materials are considered in the invariant spaces of the stress tensor. The general requirements that must be met by limit surfaces are formulated. A three-invariant strength criterion for isotropic media sensitive and insensitive to hydrostatic pressure is given in general form. The convenience of analyzing strength criteria in the two-dimensional space of the base invariants of the stress tensor is demonstrated.Moscow. Translated from Mekhanika Polimerov, No. 2, pp. 251–261, March–April, 1971.     

Analysis of the zonal winding pattern of thin spherical shells

Conclusions 1. A method has been proposed for calculating the zonal pattern of winding thin spherical shells.2. The tested strength of shells wound by the calculated pattern correlates with the theoretical.3. The proposed calculation apparatus makes it possible to calculate winding patterns with any variants of angles and number of zones.4. A zonal pattern in a spherical shell having a connecting pipe of small diameter can give a mean constructional strength which does not exceed 0.39 times the strength of the unidirectional plastic (as against 0.5 in the ideal case for a sphere of bidirectional material), i.e., not more than 78% of the strength of the plastic is realized.5. The bearing ability of a sphere wound by the zonal method is 22% less than that of a long cylinder (with no bottom) made by the same winding method.All-Union Scientific-Research Institute of Aviation Materials, Moscow. Translated from Mekhanika Polimerov, No. 4, pp. 625–631, July–August, 1978.     

Effect of UV radiation and vacuum on the strength and failure of polymer films

The effect of UV radiation and vacuum on the strength and failure of polytetrafluorethylene (PTFE) films has been studied. After irradiation samples were extended in air. It was found that the strength and plasticity of the films is diminished by irradiation in vacuum or in air.Mekhanika Polimerov, Vol. 2, No. 3, pp. 359–364, 1966     

Problems of the anisotropy of strength

The concept of a strength tensor, analogous to the tensor of elastic constants, has been introduced with a view to using its components for approximate determination of laws governing the variation of strength of anisotropic materials in uniaxial tension or pure shear as a function of the orientation of the stress state. It has been shown that the plasticity condition postulated by Mises can be used as a criterion of strength of many "weakly" anisotropic materials, if one rejects the hypothesis according to which the condition is invariant in respect to hydrostatic pressure. In the case of "strongly" anisotropic materials, wood in particular, the Mises condition is at variance with the results obtained for variously oriented specimens tested in uniaxial tension. A strength condition in the form of a fourth-degree polynomial, based on the assumed existence of a strength tensor analogous to the tensor of elastic constants, has been postulated for these materials. The validity of this criterion has been demonstrated by constructing surfaces of equicritical plane stress states from experimental data obtained for pine wood, plywood, and glass-reinforced plastic laminates.Mekhanika Polimerov, Vol 1, No. 2, pp. 79–92, 1965     

Influence of SiO2 in SiCp on the microstructure and impact strength of Al/SiCp composites fabricated by pressureless infiltration

The effect of SiO₂ in SiC_p and the following processing parameters on the microstructure and impact strength of Al/SiC_p composites fabricated by pressureless infiltration was investigated: Mg content in the aluminum alloy, SiC particle size, and holding time. Preforms of SiC_p in the form of rectangular bars (10 × 1 × 1 cm) were infiltrated at 1150°C in an argon→nitrogen atmosphere for 45 and 60 min by utilizing two aluminum alloys (Al-6 Mg-11 Si and Al-9 Mg-11 Si, wt.%). The results obtained show that the presence of SiO₂ in SiC affects the microstructure and impact strength of the composites significantly. When Al₄C₃ is formed, the impact strength decreases. However, a high proportion of SiC to SiO₂ limits the formation of the unwanted Al₄C₃ phase in the composites. Also, a higher content of Mg in the Al alloy lowers the residual porosity and, consequently, increases the composite strength. The impact strength grows with decrease in SiC particle size and increases considerably when the residual porosity is less than 1%. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 3, pp. 401–418, May–June, 2006.     

Improving the strength of plastics by vacuum molding

An account is given of a completely new method of processing thermosets by molding them under vacuum. The authors' vacuum-molding equipment is briefly described. Data on the compressive, tensile, static bending and impact strength of vacuum-molded specimens are given. These indicate that in every respect the strength of vacuum-molded materials is considerably superior to that of plastics molded in the usual way (in the atmosphere).Mekhanika Polimerov, Vol. 2, No. 5, pp. 722–727, 1966     

Effect of small additives of oligomer on the viscoelastic properties of carbon fiber plastics

The viscoelastic properties of carbon fiber composites whose phenol-formaldehyde matrix is modified by thermodynamically incompatible isocyanate derivatives have been investigated. Data are given on fiber wetting (Table 11), internal stress (Table 2), viscoelastic properties (Fig. 1), and tensile strength (Fig. 2). The modified composites are strengthened by the addition of 0.5–4% oligomer additive. This process involves the formation of a two-phase structure, in which the additive phase microparticles act as a polymer filler. Due to selective interactions, the intermediate layer formed at the fiber-binder interface leads to changes in the viscoelastic properties and tensile strength of the matrix and improved maintenance characteristics for the material as a whole.Translated from Mekhanika Kompozitnykh Materialov, Vol. 29, No. 4, pp. 440–445, July–August, 1993.     

Effect of certain additives and the ambient medium on the static and fatigue strengths of polyamides

The change in the static strength of polycaprolactam during heat treatment has been investigated in relation to the type of additive and the ambient medium, and the change in dynamic strength in relation to the method of introducing the stabilizer. It has been observed that there is a slowdown in the thermal oxidation and loss of strength of polyamides exposed to heat in a medium containing stabilizer vapors and of polycaprolactam heat-treated after being coated with lacquer containing a thermostabilizer.On the basis of the experimental material it is suggested that the loss of strength of polyamides associated with thermal oxidation is due principally not to a reduction in molecular weight or crosslinking but to stress concentrations and microdefects associated with rupture of the molecular chain. An effective method of increasing the dynamic strength of polyamides has been found.Mekhanika Polimerov, Vol. 2, No. 1; pp. 60–66, 1966     

Problem of evaluation of activation energy from the temperature-rate dependences of strength

Conclusions 1. A method has been developed for treating the experimental data on strength, obtained under conditions of uniaxial extension at v_e = const.2. It has been proposed that the deformation-strength properties of polymers of different structures be characterized by the value of coefficient L, i.e., by the relative lowering of the potential barrier of degradation under the action of mechanical stress.3. A high structure sensitivity of the proposed strength characteristics has been shown using vulcanized rubbers with different structure of the vulcanized lattice point as examples.Moscow Technological Institute of the Meat and Milk Industry. Translated from Mekhanika Polimerov, No. 4, pp. 591–596, July–August, 1976.     

Current state and prospects for development of the physical theory of brittle strength of polymers

Various mechanisms of brittle fracture and theories of the time dependence of the strength of rigid polymers are examined. The effect of various types of mechanical losses (deformation, dynamical, surface) on polymer strength and life is analyzed. The principal shortcomings of Griffith's theory of strength are pointed out. From an examination of the two basic mechanisms of brittle fracture of polymers-nonthermal and thermal (thermal fluctuation)-it is concluded that the latter is the more important. A comparison is made of the fluctuation theory of polymer strength with new experimental data on polymethyl methacrylate, and the causes of the transition from brittle to nonbrittle fracture are discussed. The effect of molecular orientation on the strength of polymers is examined on the basis of the fluctuation theory of strength.Mekhanika Polimerov, Vol. 2, No. 5, pp. 700–721, 1966     

Prediction of changes in the strength of filled thermoplastics upon aging in an oxidizing atmosphere

Problems related to analyzing specimens with damaged surface layers have been examined using polyamide, trioxane—dioxolane copolymer, and polycarbonate as source materials. A model was developed for the brittle fracture of block specimens with damaged surface layers, which provides an estimate of the restraints to plastic deformation in these layers. Three segments are seen in the strength—time curves featuring 1) increasing strength, 2) decreased strength with brittle fracture, and 3) constant low strength. The strength of filled specimens of a specific period permits us to evaluate the effect of the filler on the fracture resistance of the matrix. A method was proposed for predicting the strength of filled samples using the matrix aging data.Translated from Mekhanika Kompozitnykh Materialov, Vol. 29, No. 3, pp. 375–380, May–June, 1993.