The effect of rate of deformation on the mechanical characteristics of plastics

An experimental investigation of the effect of the rate of deformation on the strength and modulus of elasticity of vinyl plastic and glass-reinforced laminate is described. It is established that when the rate of relative tensile deformation of vinyl plastic at 25°C is reduced from 2000×10^–6 sec^–1 to 5×10^–6 sec^–1, and that for glass-reinforced laminate from 1000×10^–6 sec^–1 to 1.3×10^–6 sec^–1, the decrease in the modulus of elasticity is about 40% and the decrease in ultimate strength 30 and 48%, as the case may be.Mekhanika polimerov, Vol. 1, No. 1, pp. 76–81, 1965     

The dynamic properties of polyethylene and an acrylonitrile — Butadiene — Styrene material in a broad range of temperature and strain-rate variation

Conclusions The mechanical properties of an acrylonitrile-butadiene-styrene material and polyethylenes of densities =0.92 and 0.96 g/cm³ are studied within the temperature range of from 100 to –196°C and at strain rates of from 10^–3 to 1.3 · 10³ sec^–1. It is observed that under low-temperature and high-strain-rate conditions, the laws governing the mechanical properties of the acrylonitrile-butadiene-styrene material and polyethylenes are similar. Regions of strain rates and temperatures are found for which the behavior of the test materials is in good agreement with the Ree-Eyring equation, and, consequently, conforms to a temperature-time analogy. No embrittlement of the polyethylene is observed during tests at strain rates to 1.3 · 10³ sec^–1 and temperatures down to –196°C. In approximating these values of and T, the mechanical properties of polyethylenes will cease to be dependent on initial density.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 6, 1027–1033, November–December, 1978.     

Dynamic properties of some polymer materials in loading and unloading

A series of quasi-static tests have been carried out on kapron fiber, vinyl plastic, and fluoroplastic specimens with small cross sections. Stress-strain diagrams have been obtained at strain rates from 1 · 10^–3 to 1 · 10² sec^–1. In the experiments the strain rate changed sign, which corresponded to loading and unloading. In each regime the strain rate remained constant. The experimental data are analyzed using the model of a standard linear viscoelastic solid.Mekhanika Polimerov, Vol. 3, No. 1, pp. 118–122, 1967     

Aircraft control for flight in an uncertain environment: Takeoff in windshear

The design of the control of an aircraft encountering windshear after takeoff is treated as a problem of stabilizing the climb rate about a desired value of the climb rate. The resulting controller is a feedback one utilizing only climb rate information. Its robustness vis-a-vis windshear structure and intensity is illustrated via simulations employing four different windshear models.Notations ARL aircraft reference line - D drag force, lb - g gravitational force per unit mass=const, ft sec^–2 - h vertical coordinate of aircraft center of mass (altitude), ft - L lift force, lb - m aircraft mass=const, lb ft^–1 sec² - O mass center of aircraft - S reference surface, ft² - t time, sec - T thrust force, lb - V aircraft speed relative to wind-based reference frame, ft sec^–1 - V _e aircraft speed relative to ground, ft sec^–1 - W _x horizontal component of wind velocity, ft sec^–1 - W _h vertical component of wind velocity, ft sec^–1 - x horizontal coordinate of aircraft center of mass, ft - relative angle of attack, rad - relative path inclination, rad - _e path inclination, rad - thrust inclination, rad - air density=const, lb ft² sec² Dot denotes time derivative.     

Statistical characteristics of the mechanical properties of glass-reinforced plastics

A statistical analysis has been made of experimental data on the mechanical properties of a glass-reinforced plastic based on T₁ glass fabric (Soviet standard GOST 8481-61) and IF-ÉD-6 epoxy resin (Elektroizolit Plant, tech. spec. TU 26-59) obtained by testing specimens cut from the waste of wound cylindrical shells. The data obtained can be used for estimating the mechanical reliability of products composed of glass-reinforced plastics of this type.Moscow. Translated from Mekhanika Polimerov, No. 1, pp. 131–134, January–February, 1971.     

Apparatus for groving large monocrystals of ice with radial refining

Résumé On discute un procédé radial de purification et on décrit son application; un appareil pour la production de monocristaux de glace. Les cristaux purs (50 mm, de diamètre et 300 mm de longueur) possèdent un cur de 25 mm de diamètre ayant une conductivité moyenne de 1,5·10^–7 ohm^–1 à–10°C. On peut également produire des monocristaux transparents dotés d'acide fluorhydrique qui ne présentent qu'une faible inhomogénéité (20%) si la concentration dans la glace est inférieure à 3·10^–5HF/H₂O.     

Pulsanregung von Hg. Ionenlaserlinien

In gepulsten Hg Niederdruckentladungen ohne Fremdgaszusatz konnten vier sichtbare und erstmals auch 14 ultraviolette Ionenübergänge zur Lasertätigkeit angeregt werden. Zur Untersuchung des Lasermechanismus wurden bei Entladungsdurchmessern von 7 mm, 10 mm und 30 mm die Pulsdauern im Bereich 10 sec<<5 msec und der Hg Fülldruckp im Bereich 10^–3 torr<p<10^–2 torr variiert. Die gemessenen Strahlungsleistungen der ultravioletten Hg II Linien lagen im mW-Bereich, während jeder der drei sichtbaren Hg III Uebergänge Leistungen im Bereich 10–100 Watt lieferte.     

Effect of the rate of deformation on the mechanical properties of compact bone tissue

Conclusions The results of this study show that the ultimate stress increases with increasing deformation rate from 10^–5 to 1 sec^–1 but the initial elasticity modulus remains virtually constant. A characteristic feature of bone tissue is the significant increase or even maximum in specific deformation energy for destruction in the range of deformation rates corresponding to normal physiological conditions for bone function. The deformation diagrams of human bone tissue for the same values of moisture content and deformation rate in tensile testing do not differ from the analogous curves for the bone tissue of cattle. Quantitatively, the ultimate stress ₁₁ and the initial elasticity modulus E₁ are 5–10% and 15–25% greater, respectively, than for cattle bone tissue, while the ultimate deformation eu is virtually the same. An increase in the moisture content of bone tissue leads to a more pronounced dependence of the mechanical parameters on the deformation rate.Translated from Mekhanika Kompozitnykh Materialov, No. 3, pp. 512–517, May–June, 1982.     

Method of estimating the strength of glass-reinforced plastic shells

A combined method of estimating the strength of glass-reinforced plastic shells in the plane stress is described. The method consists in a combination of destructive and nondestructive methods of determining the necessary starting characteristics for use with a criterion of the strength of orthotropic materials in the form of a fourth-degree polynomial.Ritm Scientific-Production Association. Central Scientific-Research Institute of Shipbuilding Technology, Leningrad. Translated from Mekhanika Polimerov, No. 3, pp. 571–573, May–June, 1972.     

Control of stochastic distributed-parameter systems

A scheme is proposed for the feedback control of distributed-parameter systems with unknown boundary and volume disturbances and observation errors. The scheme consists of employing a nonlinear filter in the control loop such that the controller uses the optimal estimates of the state of the system. A theoretical comparison of feedback proportional control of a styrene polymerization reactor with and without filtering is presented. It is indicated how an approximate filter can be constructed, greatly reducing the amount of computing required.Notation a(t) l-vector noisy dynamic input to system - A(t, a) l-vector function - A frequency factor for first-order rate law (5.68×10⁶ sec^–1) - b distance to the centerline between two coil banks in the reactor (4.7 cm) - B k-vector function defining the control action - c(, ) concentration of styrene monomer, molel ^–1 - C _p heat capacity (0.43 cal · g^–1 · K^–1) - C _ij constants in approximate filter, Eqs. (49)–(52) - E activation energy (20330 cal · mole^–1) - expectation operator - f(t,...) n-vector function - g ₀,g ₁(t,...) n-vector functions - h(t, u) m-vector function relating observations to states - H(t) function defined in Eq. (36) - k dimensionality of control vectorv(x, t) - k _i constants in approximate filter, Eqs. (49)–(52) - K dimensionless proportional gain - l dimensionality of dynamic inputa(t) - m dimensionality of observation vectory(t) - n dimensionality of state vectoru(x, t) - P ^(vv)(x, s, t) n×n matrix governed by Eq. (9) - P ^(va)(x, t) n×l matrix governed by Eq. (10) - P ^(aa)(t) l×l matrix governed by Eq. (11) - q _i (t) diagonal elements ofm×m matrixQ(x, s, t) - Q(x, s, t) m×m weighting matrix - R universal gas constant (1.987 cal · mole^–1 · K^–1) - R(x, s, t) n×n weighting matrix - R _i (t) n×n weighting matrix - s dimensionless spatial variable - S(x, s, t) matrix defined in Eq. (11) - t dimensionless time variable - T(, ) temperature, K - u(x, t) n-dimensional state vector - u _c (t) wall temperature - u _d desired value ofu ₁(1,t) - u _c * reference control value ofu _c - u _c ^max maximum value ofu _c - u _c ^min minimum value of _c - v(x, t) k-dimensional control vector - W(t) l×l weighting matrix - x dimensionless spatial variable - y(t) m-dimensional observation vector - _i constants in approximate filter, Eqs. (49)–(52) - dimensionless parameter defined in Eq. (29) - H heat of reaction (17500 cal · mole^–1) - dimensionless activation energy, defined in Eq. (29) - (x) Dirac delta function - (x, t) m-dimensional observation noise - thermal conductivity (0.43×10^–3 cal · cm^–1 · sec^–1 · K^–1) - density (1 g · cm^–3) - time, sec - dimensionless parameter defined in Eq. (29) - spatial variable, cm - * reference value - ^ estimated value     

Properties of multicomponent polymers systems

In order to design materials having different mechanical properties combined with a permittivity of 2.2–2.6 and tg =2·10^–4-4.10^–4 at 20±1° C and 10⁶ Hz, it is possible to use compositions consisting of polystyrene, polyisobutylene and polyethylene. Projections of the three-dimensional triangular composition-property diagrams are presented for selecting the composition corresponding to spcified properties (hardness at 20 and 50° C and breaking stress and elongation).Central Scientific-Research Institute of Communications, Moscow. Moscow Krupskaya Regional Pedagogical Institute. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 133–1135, November–December, 1968.     

Changes in the mechanical properties of polyimides induced by electron bombardment

The change in the tensile strength and relative elongation of PM polyimide with absorbed dose has been investigated. It is shown that after irradiation with very large doses (5 · 10¹⁰ rad) the mechanical properties are still satisfactory.Scientific Research Institute of Electrophysical Apparatus, Leningrad. Translated from Mekhanika Polimerov, No. 6, pp. 1111–1112, November–December, 1969.     

Rheological characteristics of melts of low-molecular-weight branched polyethylene in the region of critical molecular weights

The viscosity and the first difference of the normal stresses have been measured at stationary shear rates from 5.68 to 4500 sec^–1 for melts of low-density polyethylenes obtained by thermal degradation of commercial polyethylene in a nitrogen atmosphere. In addition, the complex modulus has been measured on the angular frequency range from 0.396 to 198.5 sec^–1. Three regions of molecular weights differing with respect to the value of the exponent in the relation ₀ = kM have been established. At > normal stresses are observed in the region of shear rates corresponding to a linear dependence of the shear rate on the shear stresses.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga; Plastpolymer Research and Production Association, Leningrad. Translated from Mekhanika Polimerov, No. 6, pp. 963–967, November–December, 1973.     

Blocking Sets and Derivable Partial Spreads

We prove that a GF(q)-linear Rédei blocking set of size q ^t + q ^t–1 + ··· + q + 1 of PG(2,q ^t) defines a derivable partial spread of PG(2t – 1, q). Using such a relationship, we are able to prove that there are at least two inequivalent Rédei minimal blocking sets of size q ^t + q ^t–1 + ··· + q + 1 in PG(2,q ^t), if t 4.     

Impact strength of high-density polyethylene with various molecular weight distributions

The Charpy impact strength of high-density polyethylene specimens prepared under low pressure with average molecular weight from 60·10³ to 1.5·10⁶ and differing substantially in molecular weight distributions has been studied at room temperature and at –190°C. It is shown that, both at room temperature and at temperature considerably below the glass-formation temperature, the impact strength of polyethylene in the range of molecular weights mentioned is determined mainly by the content of fractions with molecular weights about 10⁵ and more and does not depend on the width of the molecular weight distribution."Plastpolimer" Scientific-Research Association, Leningrad. Translated from Mekhanika Polimerov, No. 5, pp. 919–921, September–October, 1973.     

Moisture and low temperature impact on the properties of a polyether glass-reinforced plastic

The cyclic action of water and the combined action of water and low temperatures on the physical-mechanical properties of a polyether glass-reinforced plastic are studied. For experimental investigations, methods of sorption, thermogravimetry, and mechanical testing in static bending were used. It was found that the most aggressive external factor for the glass-reinforced plastic was the cyclic action of water, but not the change in its phase state at cooling. The process of sorption-desorption of the glass-reinforced plastic is irreversible.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Institute of Non-Metallic Materials, Siberian Branch of the Russian Academy of Sciences, Yakutsk, Russia. Translated from Mekhanika Kompozitnykh Materialov, Vol. 34, No. 4, pp. 519–524, July–August, 1998.     

Deformation of viscoelastic thick-walled shells in the post-critical stage

The progressive buckling of a viscoelastic cyclindrical shell with initial imperfections in axial compression is investigated in the geometrically nonlinear formulation. As distinct from previous research, shell deformation curves in the post-critical stage (after snap-through) are obtained for various load levels. The results obtained are in agreement with the experimental data. The experiments show that in the case of thick glass-reinforced plastic shells in the post-critical stage of deformation the material fails by debonding.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 1, pp. 96–99, January–February, 1976.     

Return probabilities for random walk on a half-line

A random walk with reflecting zone on the nonnegative integers is a Markov chain whose transition probabilitiesq(x, y) are those of a random walk (i.e.,q(x, y)=p(y–x)) outside a finite set {0, 1, 2,...,K}, and such that the distributionq(x,·) stochastically dominatesp(·–x) for everyx{0, 1, 2,..., K}. Under mild hypotheses, it is proved that when xp _x>0, the transition probabilities satisfyq ⁿ(x, y)C_xyR^–nn^–3/2 asn, and when xp _x=0,q ⁿ(x, y)C_xyn^–1/2.Supported by National Science Foundation Grant DMS-9307855.     

Seismoacoustic prediction of the fracture processes in glass-reinforced plastics

A technique and equipment for investigating the seismoacoustic emission associated with the fracture of a loaded glass-reinforced plastic are described. It is shown that the emission is present from the beginning of loading and increases regularly up to failure. Glass strands consisting of 100 plain elementary fibers of varying diameter and resin-impregnated strands have been investigated in tension and specimens of glass-reinforced plastic and unreinforced epoxy resin in tension and bending. Experimental data on short-time, static and repeat loading are presented for the glass-reinforced plastic. It is shown how the integral pulse distribution and the pulse amplitude frequency function depend on the applied load level.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 421–429, May–June, 1971.     

Kinematic approach to the description of autowave processes in active media

The kinematic approach formulated in the paper is very general. The main results obtained above also remain valid for active media of a more complicated nature than the simple ones described by Eqs. (1). To construct the kinematic theory, it is necessary to know only a few phenomenological parameters such as the propagation velocity of a plane front and the critical curvature. In principle, these parameters can be calculated using the particular equations of the active medium, for example, (1).The value of the phenomenological parameters for an active medium can also be obtained experimentally. For example, for a medium with the Belousov-Zhabotinskii chemical reaction [1] the propagation velocity of a plane front is V₀=2–3 mm/min, D is the diffusion coefficient for the solution and equal to D=1.8·10^–5 cm²/sec, and the rotation frequency is =5 min^–1. Then, as follows from (16), the critical curvature at the free end must be 70 cm^–1, in good agreement with the experimental data.