Prediction of the deformation properties of a polymeric composite with a granular-fibrous filler

Conclusion A variant of calculation of the characteristics of the deformation properties of a hybrid composite containing a complex disperse filler in the form of granular particles and short fibers was proposed. The effect of aggregation of the granular filler, the statistical distributions of the fibers by lengths and orientation in the material, and the anisotropy of the fibers are taken into consideration in the calculation. The statistical distribution of the orientation of the fibers is given by a function proportional to the distance from the center to the surface of a triaxial ellipsoid in the corresponding direction. The uniform random distribution of the fibers in bulk and in the plane is a special case of this distribution. The results of the analysis of the effect of the parameters of the statistical distributions of the length and orientation of short fibers on the elasticity characteristics of a composite are reported. The dependence of the creep of the composite on the ratio of the concentration of the components of the complex filler was determined, and the efficiency of partial replacement of a granular filler by a short-fiber filler to inhibit creep of the composite was demonstrated. The possibilities of predicting the long-term creep were experimentally confirmed on the example of LDPE filled with ground limestone and short glass fibers.Presented at the Sixth All-Union Conference on the Mechanics of Polymer and Composite Materials (Riga, November, 1986).Translated from Mekhanika Kompozitnykh Materialov, No. 5, pp. 898–909, September–October, 1987.     

Thermal expansion of a polymer composite with an aggregating disperse filler

Conclusion The thermal deformation of HDPE with an aggregating disperse filler was experimentally studied in a wide range of temperatures. The effect of the filler on the characteristics of relaxation transitions in HDPE, determined from dilatometric tests, was analyzed. A method of calculating the effective thermal expansion coefficient of a composite with an aggregating filler was proposed. Satisfactory agreement between the calculated and experimental data was obtained. It was shown that the effect of aggregation results in a significant decrease in the thermal expansion coefficient of the composite.Translated from Mekhanika Kompozitnykh Materialov, No. 1, pp. 70–77, January–February, 1989.     

Thermal deformation of a composite reinforced with hybrid cloth strips

Conclusion We tested (for mechanical and thermal effects) composites reinforced with hybrid cloth COS and VAI strips; five alternate schemes of material, which differred in terms of the content of VAI layers and layers reinforced with COS, were tested. The elasticity characteristics, tension diagrams, and CLTE of the composites were determined. It was established experimentally that variation in the relative content of the above-indicated layers makes it possible to regulate the thermal expansion of the composite in the longitudinal direction of the reinforcing strips Objectively over significant ranges; in this case, the elastic modulus varies negligibly, while the specific elastic modulus remains virtually unchanged,An alternate scheme for determining the elasticity characteristics and CLTE of laminar polymeric materials reinforced with hybrid cloth strips on the basis of component properties is developed. The model according to which the structural organization of the composite is subdivided into several levels is primarily a computational model. The stress-strain state of the repeating structural elements is evaluated by methods of the strength of materials. The proposed algorithm for computing the physicomechanical characteristics of laminar composites is implemented in the form of a computer program. The experimental elasticity characteristics and CLTE obtained for composites with a different content of COS and VAI layers are compared with those calculated in accordance with the method developed (the computed values correspond to the experimental with an accuracy acceptable for engineering applications).Translated from Mekhanika Kompozitnykh Materialov, No. 3, pp. 392–401, May–June, 1988.     

Dynamic mechanical spectroscopy of polyethylenes with aggregating disperse and hybrid granular-fibrous fillers

Conclusion Based on the results of dynamic experimental studies, it was shown that addition of mineral fillers to polyethylenes does not result in a significant change in the relaxation properties of the polymer matrix of CM. It was found that aggregation of the particles of the granular filler causes a significant increase in the real part of the modulus and a decrease in the mechanical loss tangent of the CM. The possibility of using a modified elastic solution for predicting the effective characteristics of the dynamic viscoelasticity of composites was demonstrated.Translated from Mekhanika Kompozitnykh Materialov, No. 4. pp. 579–586, July–August, 1989.     

Plane problems of stability of composite materials with a finite-size filler

The plane problem of three-dimensional stability is solved for a transversely compressed composite material reinforced with ribbons taking into account the inhomogeneous initial state. An approximate solution of the problems is based on the net method. The effect of the ribbon form factor, the ratio between the elastic moduli of the matrix and filler, and Poisson ratio of the filler on the critical deformation of the material is investigated. Translated from Mekhanika Kompozitnykh Materialov, Vol. 36, No. 1, pp. 77–86, January–February, 2000.     

Anisotropy of elasticity of a composite with irregularly oriented anisometric filler particles

The effects of orientation and shape of filler particles on the elastic properties of composites have been analyzed. The elastic constants of a composite with irregularly oriented filler particles were calculated by using the method of orientational averaging of the properties of a representative structural element. The elastic constants of the structural element were found according to a known generalized Eshelby solution for a finite concentration of ellipsoidal inclusions. The diagrams of elasticity anisotropy for a transversely isotropic structural element and an orthotropic composite with irregularly oriented inclusions are presented. A quantitative estimate for the degree of anisotropy of elastic properties of composites is suggested. Data on the influence of shape anisometry of inclusions on the anisotropy coefficient of filled composites are also reported.     

Thermal expansion of ferroelectrics

Using the interference method the thermal expansion of lithium hydrazinium sulphate [Li(N₂H₅)SO₄] has been investigated in the temperature range ?170° C. to +220° C. The principal expansion coefficients along the crystallographic axes have been determined and at room temperature (25° C.) the values ofa _a,a _b anda _c are respectively 17·7, 13·5, and 43·0, ×10^?6 (°C.)^?1. The expansion coefficients are found to vary nonlinearly, and, in particular, along thec-axis the thermal expansion shows an anomalous behaviour between ?160°C. and ?60°C. and also in the neighbourhood of +130°C. These anomalies are explained as due to homomorphous transitions in which there is a reorientation of the ?NH ₊ ³ group about the N-N axis or a re-alignment of the ?NH₂ group.     

Low-cycle fatigue of a composite substance containing a dispersed filler in cyclic compression

Conclusions 1. The lifetime of a composite material having a dispersed filler has been examined under conditions of low-cycle compression.2. It has been shown that, in distinction from materials of fibrous structure, the lifetime of this material is determined, not by a breakdown in the continuity of structure, but the deformability of the polymer matrix.3. The absence of a correlation between the static and fatigue strengths of composite mateials from cold and hot curing is caused by the different effect of the structure of the cured binder as a component of the material on the ultimate static characteristics and creep, whose relaxation character is more clearly expressed.4. Creep of the binder and the strength of the microspheres are the main factors which determine the lifetime of the material in question in cyclic compression.All-Union Scientific-Research Institute of Synthetic Resins, Vladimir. Translated from Mekhanika Polimerov, No. 4, pp. 653–657, July–August, 1978.     

Thermal expansion of oriented polyethylene

It is shown that the sign of the linear coefficient of thermal expansion is determined by the configuration and direction relative to the deformation axis of the molecular chains in the amorphous and crystalline phases of the polyethylene. An increase in orientation leads to a decrease in shrinkage temperature. The presence of a dispersed inorganic filler results in the formation of fibrillar structures in the polyethylene.