Action Of Mechanical Loads Research Articles

Effect of microdefects on the adhesion-separation work for joint materials

Practical applications require physical models for estimating the adhesion characteristics of interfaces between joint materials and the effect of crystal-structure defects in these materials on those characteristics [1]. In [2‐4], a thermodynamic model using the Gibbs equation was proposed for estimating the variation in the surface tension of interfaces with the content of vacancies, dislocations, and impurities. In this study, we developed a general model describing the effect of lattice defects on an important characteristic of the interlayer-connection strength, namely, the work w I of separation of two adjacent (crystalline) materials. The case where such defects are vacancies is analyzed in detail. It turns out that, as the concentration of vacancies increases, w I passes through a maximum (minimum) or decreases monotonically depending on the physical conditions and properties of materials. Generating a sufficient concentration of vacancies in one of the materials, it is possible to make w I vanish or even negative, which must result in the spontaneous separation of materials. These theoretical results for the strength properties of interfaces are important for designing new (in particular, layered) materials with an increased fracture strength and for estimating the durability of the joints under the action of mechanical loads and physicochemical fields. We consider a plane interface between two crystalline materials 1 and 2 with structural defects of types 1 and 2, respectively. Similar to [2‐4] (see also [5]), we consider the interface as a surface that can adsorb (desorb) defects from the bulk. Let these materials be subjected to a mechanical stress σ that is perpendicular to the interface and gradually increases the gap between them up to their complete separation. This stress σ = σ(δ) is a certain function of the displacement δ of the interface walls with respect to their position in the initial (unloaded) state. In this case, the work w I (per unit interface area) spent on the separation of materials is equal to

Physical Relations for Wood at Variable Humidity

Abstract. The paper discusses the physical relations between wood at a plane state of stress and variable humidity. A simple theory for wetted wood under stress is constructed based on the balance equations and the thermodynamics of irreversible processes. The theoretical curves are compared with experimental curves for pine sapwood wetted at uniaxial and biaxial states of stress. The so-called mechano-sorptive effect, which arises during the simultaneous action of mechanical loading and wetting process, is taken into account. A high consistency of the theoretical and experimental curves is stated.

MIS sensor for investigation of mechanical properties of metals

Abstract A method has been developed to investigate the effect of gas release from metal specimens under the action of mechanical loading. The method is based on the use of a chemical MIS (metal-insulator-semiconductor) sensor of Pd-SiO 2 -Si type. The developed method allows investigations to be carried out in different gaseous media in a wide range of pressures both above and below atmospheric pressure. A set-up has been designed and used for the measurement of H 2 mass released on rupturing test specimens of steel, aluminium, copper and zirconium. The H 2 mass released from different metals is different and varies in the range 10 −9 -10 −10 g. The measurements are carried out in an inert medium (He) at atmospheric pressure. The effect of gas release from stainless steel specimens before the threshold of failure has been observed. The character of the gas release from strained specimens enables one to judge their mechanical strength.

Action of mechanical load on mineral formation in ash ceramics

Action of mechanical load on mineral formation in ash ceramics

Change in the crack resistance of steam pipes of steel 12Kh1MF as a result of long service

Steam pipes in electric power plants are subjected in service to the long-term action of mechanical loads and high temperatures. Since emergencies can arise due to slow crack growth and subsequent sudden fracture of a structural element, the optimum design and reliable use of power plants require data on the crack resistance of the structural materials used. The goal of the present study is to evaluate the change in the resistance of the metal of steam lines in heat and electric power plants to brittle fracture in relation to structural changes in service. Microstructural analysis showed the initial ferrite-pearlite structure is transformed during service into a ferritecarbide structure. It is found that the structural and phase transformations which occur in the metal of steam pipes during service cause a significant reduction in resistance to brittle fracture. There is a simultaneous deterioration in the strength properties of the steel. The study results show a need to allow for the embrittlement of steam-pipe metal during service when performing periodic cold hydraulic pressing. This pressure-testing may, according to the authors, cause the nucleation and growth of brittle cracks capable of leading to pipe fracture.

Possible mechanisms of degradation of macromolecules in mechanical and electrical fields

The initial stages of rupturing of polymers under the action of mechanical loading and electrical fields are discussed. Mechanisms of rupture of macromolecules in mechanical and electrical fields are considered, and models are proposed. These include ionization of macromolecules as a result of tunnel transitions of electrons and subsequent decay of positive macroions.

Determination of the damage to a hybrid composite resulting from the action of mechanical loads

Determination of the damage to a hybrid composite resulting from the action of mechanical loads

Effective conductivity of a body with a large number of cracks taking into account their capacitance and the action of mechanical loads

The problem of cracks acting as electrical capacitors and subjected to mechanical loads is considered.

Evaluation of the strength of granular ion exchange resins and the relationship between the strength of gel-like anion exchange resins and osmotic stability

The breaking load was evaluate in compression of granular gel-like AN-22, AV-17 anion exchange resins and AN-251 porous anion exchange resins. It was established that the average arithmetical value of the breaking load P av shows a linear dependence on diameter d = 0·4–0·9 mm for AN-251. For AN-22 linearity is disrupted with an increase of d of granules to 0·7 mm and higher. The non-linear dependence of P av ∥ d∥ is due to a variation of indices. It was shown that the type of distribution curves differs from the normal. To explain the effect of recycling on the strength of granules, the latter value was determined after 150, 300 and 600 test cycles and also using initial granules. After 150 cycles the distribution curves showed a contraction of the variation interval, compared with the initial curve. With an increase in the number of cycles to 600 the type of distribution curves remained unchanged. A comparison of osmotic stability with breaking load showed that AN-22 granules swollen in water and characterized in the initial state by a value of P av > 1·2 kg do not break down by the action of osmotic forces. Apparently, there is a relation between breakdown by the action of mechanical load and osmotic forces. Osmotic forces and stress causing failure in compression were calculated. Using gel type anion exchange resins it was shown that when stress causing failure in swollen granules is at least 1·5 times higher than osmotic forces, granules do not break down by the action of osmotic forces.

Effect of material properties on the stability of transversely isotropic shells with an elastic filler subjected to the action of mechanical loads and temperature

The effect of the low shear strength of the material (glass-reinforced plastic) on the stability of cylindrical shells with an elastic filler is investigated in relation to axial compression, external pressure, and heating. The equations of the thermoelastic problem of the theory of monotropic shells, constructed with allowance for the effect of tangential shearing stresses, are used in the calculations.