Key Engineering Materials Vols. 525-526

Abstract: In this paper, the diffusion coefficient of vacancy-solute complex and diffusion coefficient of solute atoms, P, in non-equilibrium grain-boundary segregation under low tensile stress in steel 12Cr1MoV are calculated based on the model developed by Xu. Both the simulation and experimental kinetics curves are achieved. Results show that the calculated result with the kinetic equations perfectly fits with the experimental observations for phosphorus in steel 12Cr1MoV under low tensile stress. In the segregation process, the rate of phosphorus segregation is high due to a large diffusivity of the complex. In the de-segregation process, the level of phosphorus segregation decreases with increasing stress aging time. But the rate of phosphorus desegregation from grain boundaries to centre is slower compared with that in segregation for the diffusion coefficient of phosphorus atoms is far lower than the complexes.

Abstract: Pressureless sintering to obtain high density boron carbide-titanium diboride composites by in-situ reaction was studied. Pressureless sintering behavior of this material was investigated between 1800-2150 .The effects of composition, sintering temperature and tine were examined. Density up to 98.5% T.D. was reached at 2150. Maximum values of flexural strength (502 MPa), hardness (33 Gpa) and fracture toughnes (4.6 MPa·m^1/2) were observed in the specimens containing 15 vol.% TiB₂.

Abstract: The galvanic corrosion behavior of titanium/ Cu-Ni Alloy / high strength steel in multiphase material system has been studied under open circuit conditions using a zero-resistance ammeter (ZRA) in seawater. After the tests, the surface morphologies of the samples were detected by SEM. These results have been compared with results estimated from the polarization curves according to the mixed potential theory (imposed potential measurements). Results showed that Galvanic corrosion behavior of titanium (TA2)/Cu-Ni Alloy (B10) / high strength steel (921A) fulfill the mixed potential theory, 921A acts as the anode and bothTA2and B10 act as the cathodes. The overall galvanic reaction is mainly governed by the anodic oxidation of the 921A.

Abstract: Wear failure behavior of steel surface with palygorskite powders (Palys) as lubricant additives was investigated in this paper. Different content of Palys was added in different lubricating oils. The wear failure behavior of the steelsteel contact surfaces was studied by using an optimal SRV oscillating friction/wear tester. The elemental component and morphology on worn surface were analyzed by SEM and EDS. From the results of the friction/wear tests and analysis of the worn surfaces, we can see that specimens with Palys as lubricant additives exhibit excellent wear reducing properties and introduce a smooth and compact oxide layer on the worn surface. This may be attributed to the layer-chain fibrous crystal structure of palygorskite and the complex physicochemical nature in friction process.

Abstract: In recent years, Trimaran platform design has got the attention of naval architects owing to its superior seagoing performance. Trimaran structure experiences severe loads due to its unique configuration and high speed, causing stress concentration, especially in cross deck region and accelerate fatigue damage. This paper presents fatigue strength assessment of Trimaran structure by simplified procedure. A methodology is proposed to evaluate fatigue loads and loading conditions by load combinations of direct calculation procedure of Lloyds Register Rules for Classification of Trimaran (LR Rules). Global FE analysis, in ANSYS, is performed to investigate the stress response. The stress range is computed by hot-spot stress approach, and its long term distribution is specified by Weibull distribution. Fatigue damage of selected critical details is calculated using mathematical formulation of simplified fatigue assessment procedure of Common Structure Rules (CSR).

Abstract: Sandwich plate system (SPS) with polyurethane elastomer is more and more used on ship buildings as grillage. A Comparative Study on critical buckling loads between steel grillage and SPS stiffening plate are carried out in this paper. Plate elements and beam elements are used in numerical simulation and a rectangular model is taken as a calculating example. By using of FEA software ANSYS, ultimate buckling loads are calculated with different influential factors between steel grillage and SPS stiffening plate, including the number of stiffening ribs, inertia moment of stiffening ribs, and the thickness of plates. the analysis results of comparison shows that SPS stiffening plates have better performance than steel grillage under in plane compressive loadings.

Abstract: A modified Hill yield criterion considering tension-shear stress coupling was given and material parameters of nickel-based single crystal in this criterion was determined by the Least Square Method. Crack tip plastic zones of nickel-based single crystal plate were analyzed by using this modified yield criterion and the plastic zones corresponding to mixed mode I, II crack, were derived. The crack tip plastic zones of nickel-based single crystal were compared to that of isotropic material. The influences of tension-shear stress coupling, compound ratio of mixed mode I, II crack and temperature on crack tip plastic zones were discussed. The results obtained in this paper indicate that the increasing rate of crack tip plastic zones with compound ratio in the plane stress condition is greater than that in the plane strain condition for nickel-based single crystal and the temperature has greater influence on the size of crack tip plastic zones.

Abstract: The methods of Green's function, complex function and multi-polar coordinates are applied here to report interaction of an elliptical inclusion and a crack in half-space under incident SH-waves. Based on the symmetry of SH-waves scattering, the "conformal mapping" technology was developed to construct a suitable Green's function, a fundamental solution to the displacement field for the elastic half space containing elliptical inclusion while bearing out-plane line source load at arbitrary point, for creating a beeline crack with arbitrary length at any position combined with crack-division technology. The displacement field and stress field were then deduced while the inclusion coexists with the crack Lastly, numerical examples are presented to discuss the dependence of dynamic stress concentration factor (DSCF) around the elastic inclusion on different parameters.

Abstract: Residual stresses and residual plastic strains of the welded structures are the products of nonlinear behaviors during welding. The residual stresses will cause errors during the assembly of the structure and injure the beauty of appearance of the structure. Based on an elastic-plastic-model, finite element numerical simulation of a representative tube sheet penetration assembly with loop welding line joined by multi-pass welding is carried out and the influence of welding conditions on residual stresses of the tube sheet welds is studied in this paper. Nonlinear three dimensional transient temperature fields and real-time dynamic stresses field are analyzed by FEM. The heat source is modeled as a moving heat flux following a double ellipsoid distribution and the temperature-dependent properties of materials are considered. The method of birth and death of element in finite element analysis is applied to simulate the gradual growth of weld pass metal. It is shown that welding sequence, size of groove welding and weld toes dressing will obviously change the magnitude of the residual stresses of tube sheet welds.

Abstract: Under high temperature, many metals show viscoelastic properties, which are closely related to environmental factors and strain rate. Engineering practice also shows that time-dependent deformation of materials have great effects on the structural strength, rigidity and life duration. So visco-elasticity has drawn much attention in the mechanical and engineering fields.