Yu. F. Lugovskoi

Fatigue failure of rolled high-porosity materials made of copper fiber at resonance bending oscillations

ConclusionsFatigue failure of rolled high-porosity materials based on copper, tested in the conditions of resonance oscillations,is accompanied by a considerably slower drift of the resonance frequency (lower rate of fatigue damage) then failure of dense copper.The relative variation of the resonance frequency can be used to evaluate the residual endurance of the porous materials and also as a fatigue strength criterion.In bending, the dense and low-porosity materials fail under the effect of normal stresses, whereas high-porosity materials fail under the effect of shear stresses.

Mechanical and Fatigue Properties of Powder Titanium Strips, Obtained by Asymmetric Rolling

The mechanical properties of titanium powder strips obtained by asymmetric rolling technique are investigated. It is found out that the use of asymmetric rolling during the consolidating and repeated compacting rolling allows obtaining a strip with better mechanical properties than that obtained by conventional technique. The fracture surface of a titanium strip obtained by symmetric rolling has a significant ratio of the interparticle fracture. After asymmetric rolling, the fracture surface is totally dimpled. It is shown that the asymmetric rolling improves the quality of interparticle contact and, consequently, the ductility and fatigue resistance increase significantly.

Mechanical Properties and Fracture Mechanisms of Commercially Pure Multilayer Iron Produced by Strip Joint Rolling

Multilayer materials (1.2–0.25 mm thick) are produced by sintering in a container at 850°C and cold rolling of ten-layer briquettes of commercially pure iron. It is shown that the tensile strength of the materials studied is proportional to the total true strain value by rolling and reaches 1400 MPa at percentage extension 1%. Endurance limit increases up to 670 MPa. With increasing strain degree by rolling, the structural elements inside layers reduce in size, when high interlayer strength between macro layers. The best correlation of endurance limit of materials with micro yield strength is observed, when 0.01% of residual strain.

Effect of porosity on the structure parameters of cellular porous and fibrous copper-based materials

The effect of porosity on the structure parameters of highly porous cellular and fibrous materials is studied. It is shown that the structure of porous cellular materials is close to the spherical-phase model proposed by Skorokhod and Kondrachuk with coauthors. The structure of sintered fibrous materials shows no noticeable fiber penetration in contact areas, and their structure parameters are better described by models without spherical phase.

Influence of the structure on the elastic modulus of highly porous copper-based materials

The effect of the structure on the elastic modulus of two groups of highly porous sintered copper-based materials (foam and fiber metal) with 40 to 90% porosity is investigated. The elastic modulus of the materials is described within the sphere-rod model developed for foam plastic with an open porosity; the model uses an equation containing a structure parameter.

Effect of structure on the fatigue strength of dispersion-hardened Ni - 20% Cr - Al2O3 condensed materials

The effect of the mean free path between particles A and the average grain size D, and also the duration of cyclic loading N in the range (0.2–5)·107 cycles, on the fatigue limit of dispersion-hardened Ni - 20% Cr -Al2O3 condensed materials is studied on the basis of fatigue curves. With a correlation coefficient of more than 0.9 these dependences on A−1/2 and D−1/2 correspond to an equation of the Mott—Stroh type. It is shown that particle boundaries affect the cyclic strength of the materials to a greater extent than grain boundaries up to a concentration of 1.1%. A change in the fracture mechanism occurs with a correlation coefficient of less than 0.9.

Effect of structure on the fatigue strength of dispersion-hardened condensates based on copper III. Analysis of the second coefficient of a mott—Stroh type relation and data on strength under static loading

The second coefficient of the Mott—Stroh type equation is considered as the stress intensity factor in a microcrack edge under external cyclic stresses and internal ones. The individual length of a critical microcrack is defined more exactly for some dispersion-hardened materials relatively to their average value. The experimental equations for dependences of a limit of strength and yield point in three groups of the materials in question are analyzed using structure parameters in two levels.

Effect of structure on the fatigue strength of dispersion-hardened condensated based on copper II. Analysis of the first coefficient of the Mott—Stroh relation

A relationship of Mott-Stroh type has been considered for studying the strength of structure element models of dispersion-hardened material (particle, matrix, and interlayer) under the effect of external cyclic and internal residual stress. The residual stress and the interlayer strength and thickness have been estimated. The experimental and calculated values of the first coefficient in the Mott-Stroh relationship nearly coincide.

ELASTICITY AND FATIGUE STRENGTH OF CONDENSED MICROLAYERED MATERIALS Cu-Y-Mo

The article [1] generalized the results of the investigation of the structure and the physicomechanical characteristics of microlayered materials (MLM) of the system Cu-(0.01-0.3)% Y-Mo subjected to uniaxial tension. It is of interest to investigate the regularities of the change of the mechanical properties of these materials, especially of the modulus of elasticity and of the fatigue limit, in dependence on the thickness of the layers of molybdenum and of the alloy Cu- Y under cyclic loading. The modulus of elasticity E was determined by the method of longitudinal resonance vibrations on an installation UP1. Specimens 100 × 100 × (0.8-1.2) mm were cut into rods with constant cross section size (30-50) × 5 × (0.8-1.2) mm, and with the aid of an installation V15DS- 1500 on a base of 5.107 test cycles the endurance limit of the materials in bending tr I was determined by methods described in [2, 3]. The experimental values of the modulus of elasticity in dependence on the volume content of molybdenum (Fig. 1) were compared with the calculated values obtained by the rule of mixtures. For that we used the equation