Some problems in experimental fracture mechanics

A standard procedure for the determination of fracture toughness K_IC is discussed. The insufficiency of the existing K_ic determination confidence criteria is stressed and the following criteria are proposed instead: φ_max ? 1.5%; $\text{σ}{}_{\mathrm{fr}}{}^{\mathrm{net}}\text{σ}{}_{\mathrm{0.2\; ?\; 0.8}}$, in conjunction with the old criterion $\text{P}{}_{\max }\text{P}{}_{\mathrm{Q}}\text{? 1.1}$. Determination of K_IC from P_max should be used instead of from P_Q.A method for the determination of a point on the “force-displacement” diagram corresponding to crack growth initiation is set forth. The method is based on specimen compliance tests under repeated load-relief cycles. The crack growth initiation point is used to determine both the critical crack opening and plane strain fracture toughness. The indefinite effect of the growing crack (in the ease of crack opening or Cherepanov-Rice integral calculations) is thereby eliminated. Necessity is emphasized to determine the share of the J-integral which contributes to fracture process. A method for plotting the elastic displacement diagram is proposed which allows on the basis of preliminary estimates to determine fracture toughness of small-sized specimens without using special setups. The area ratio between the plastic and elastic strain diagrams is proposed to be adopted as fracture type criterion. Certain experiments to determine crack resistance of material specimens are described and discussed.     

Estimation of the Filtration Parameters of a Bed by the Data of Nonstationary Inflow of Liquid to Vertical Wells

Numerical algorithms based on the theory of illposed problems are suggested for estimation of the filtration parameters of a bed using the results of hydrodynamic studies of vertical wells. These algorithms allow determination of the coefficients of compressibility, efficiency, and hydraulic conductivity of the critical and distant zones and interpretation of the results of the hydrodynamic studies with account for the dependence of the filtration parameters on pressure.     

Effect of strain-heat treatment on the tendency for corrosion cracking of pipe steel under stress

Strain-heat treatment conditions were found to affect the overall properties and structural state of 06G1NDB steel, which in turn affect resistance of the steel to stress corrosion cracking. The technique used in this paper enables strain-heat treatment conditions to be ranked by their effect on stress corrosion cracking of type 06G1NDB steel. Type 06G1NDB steel was found to have relatively high resistance to stress corrosion cracking for all strain-heat treatment conditions studied. This arises out of the fact that the chemical composition of the steel and all strain-heat treatment conditions used led to the formation of steel structure with highly disperse grains, high homogeneity, and a lack of banding or well-defined structurally inhomogeneous zones (axial liquation).     

The effect of external stresses on the behavior of photoacoustic signals inside vickers indenter marks on a steel surface

It is experimentally established that the characteristics of photoacoustic signals inside Vickers indenter marks in metals significantly change under the action of external stresses. Relative changes in the signal amplitude are estimated in the framework of a quasi-static approximation based on the temperature dependence of the elastic modulus of the metal.     

A streamlined, cost-effective database approach to manage requirements traceability

Requirements traceability offers many benefits to software projects, and it has been identified as critical for successful development. However, numerous challenges exist in the implementation of traceability in the software engineering industry. Some of these challenges can be overcome through organizational policy and procedure changes, but the lack of cost-effective traceability models and tools remains an open problem. A novel, cost-effective solution for the traceability tool problem is proposed, prototyped, and tested in a case study using an actual software project. Metrics from the case study are presented to demonstrate the viability of the proposed solution for the traceability tool problem. The results show that the proposed method offers significant advantages over implementing traceability manually or using existing commercial traceability approaches.     

Relative equilibrium stability of a space station consisting of two solid bodies connected by an elastic rod

The problem is considered for stability of a relative equilibrium of a mechanical system in orbit that consists of two solid bodies connected by a thin inextensible elastic rod. The problem for stability of a relative equilibrium position reduces to the problem of a minimum of a changed potential system energy comprising the potential energy of elastic, gravitational and centrifugal forces.     

Comparative analysis of the effect of mechanical activation in an attritor on the structure and behavior of β-RuAl and β-NiAl alloy powder mixtures during reactive sintering

The structure of Ni + Al (two ductile fcc metals) and Al + Ru (ductile aluminum and hard-to-deform hcp ruthenium) powder mixtures subjected to short-term (≤16 h) mechanical activation (MA) is studied. During MA of a 50Ni + 50Al mixture, the powder particles undergo multiple compressive and shear deformation, and large layered granules form due to contact welding and flattening of the layers of both metals. The related increase in the internal stresses, the increase in the dislocation density in particles of both metals, and the decrease in the coherent domain size (CDS) lead to the fracture and fragmentation of the powder particles. In a 49Ru + 48Al + 3Re mixture, aluminum particles are deformed and “spread” over “rigid” ruthenium particles. The formed granules consist of disperse undeformable ruthenium particles connected by an Al binder. The work hardening of ruthenium occurs due to a decrease in CDS. An increase in the contact area between metal particles and a decrease in the diffusion path lengths (aluminum in nickel and ruthenium) cause a decrease in the temperature of the onset of interaction with the participation of liquid aluminum, the activation of solid-phase interaction, and the formation of aluminum-rich nickel (ruthenium) aluminide NiAl (RuAl). Nevertheless, unreacted nickel (ruthenium) particles are retained. A microhomogeneous distribution of the basic and alloying elements and phases in a compacted material is achieved Annealing at temperatures ≥0.8T _m is required to complete reactive alloy formation.