Key Engineering Materials Vols. 385-387

Abstract: In this study, the effect of combined environmental factors such as ultraviolet ray, high temperature and high moisture on mechanical and thermal analysis properties of glass fabric and phenolic composites are evaluated through a 2.5KW accelerated environmental aging tester. The environmental factors such as temperature, moisture and ultraviolet ray applied of specimens. A xenon-arc lamp is utilized for ultraviolet light and exposure time of up to 3000 hours are applied. Several types of specimens - tensile, bending, and shear specimens that are warp direction and fill direction are used to investigate the effects of environmental factors on mechanical properties of the composites. Mechanical degradations for tensile, bending and shear properties are evaluated through a Universal Testing Machine (UTM). Also, storage shear modulus, loss shear modulus and tan δ are measured as a function of exposure time through a Dynamic Mechanical Analyzer (DMA). From the experimental results, changes in material properties of glass fabric and phenolic composites are shown to be slightly degraded due to combined environmental effects.

Abstract: Recently, permanent magnet motors are widely used in many industrial fields because they are suitable for compact mechanical system. The motor core is usually manufactured from magnetic steel sheet with press machine. However, usually most parts of the plate are scraped, and only small percent of the sheet is used for the core. The spiral accumulating core system is suitable for manufacturing the core more ecologically because in this system more than 50% of the magnet steel sheet can be used. In this study, therefore, the effective Young’s modulus of the spiral accumulating core is considered in order to find out a good method to fix the core. In this analysis, the finite element method is applied to 3D models, whose layers and slits are periodically arranged. Stress and thickness distributions are also analyzed in the bending process. When the spiral core is manufactured through spiral accumulating system with plate-bending process, the thickness change should be minimized because that may deteriorate dimensional accuracy of the spiral core. Also residual bending stress is investigated because that may cause an electric loss. The results indicate that plastic zone is limited at localized regions and therefore an electric loss is not very large. The effective Young’s modulus of the 3D dimensions model of the real spiral accumulating core is estimated about 127.5 GPa.

Abstract: Reinforced concrete beams strengthened with externally bonded CFRP sheet and prestressed CFRP are analyzed in this paper. Crack developments and displacements with curvatures for different beams are analyzed. Test results show that prestressed CFRP are able to control the development of macro cracks in concrete and prestressed CFRP is an effective method to improve the toughness of concrete, reduce strengthening cost and meanwhile enhance bearing capacity of concrete beams.

Abstract: The damage of thin steel plate subjected to contact explosions was a very complex nonlinear process. The initial crevasse of plate subjected to contact explosions had influence upon the whole damage process, so the critical damage study was significant on the anti-explosion of ship structure. In virtue of the wave solution of the plate plastic dynamic response and the dynamic fracture theory, the critical blasting charge was derived theoretically when onset of initial circumferential crack namely critical damage happened. And the expression of critical deformation was also obtained. Lastly the results calculated using proposed method was compared with numerical simulation and the experiment in the published literature, which were almost coincided. It could be seen that the present method could perfectly solve the critical damage of thin plate under contact explosions theoretically, and provide references for defensive engineering.

Abstract: Asymmetric arrangements of stored crack-wake dislocations and low values of the size ratio SR, the plastic zone size / the characteristic microstructural distance, were found to be of basic importance for the shear misfit of crack flanks causing the roughness-induced crack closure in case of plain strain conditions. The crack wake dislocations produce also the plasticity induced crack closure as a result of a near-tip mismatch perpendicular to crack flanks. According to a recently published theoretical concept, an estimation of these extrinsic shielding effects in the threshold region of fatigue crack propagation was made for austenitic steel of Japan provenience. Related fatigue experiments were based on a standard load shedding technique associated with monitoring of the crack closure level. The surface roughness was analysed by means of the optical chromatography that enables a 3D reconstruction of fracture morphology. Calculated and measured effective threshold values of about 2.2 MPa.m1/2 are practically identical. Total levels of the extrinsic toughening induced by the austenitic microstructure are rather low when compared to those identified in ferritic- and ferritic-austenitic steels.

Abstract: Based on the strain energy function proposed by GAO Y C and the theory of finite deformation dynamics, the question about the cavity dynamic formation and bifurcation of the incompressible homogeneous solid sphere under a suddenly applied uniform tensile dead-load was studied. The condition under which a dynamic bifurcated solution exists was examined. The relationship between the dead-load and the cavity radius, the critical load, the stress distributions after the cavity formation, the vibration phase diagram of the cavity radius and the approximate vibration period were also determined.

Abstract: In this paper the contact fatigue behaviour of gears coated with PVD (Physical Vapor Deposition) thin hard film was studied. Contact fatigue tests (R = 0) were carried out on both coated and uncoated automotive transmission spur gears. The bulk material and the coating analysed throughout the tests were, respectively, case hardened 18NiCrMo5 and CrN. The influence of the coating was both experimentally and numerically evaluated. Several FEM models were developed to assess the stress and strain distributions from tooth flank surface to in-depth layers. The influence of the surface treatments on the bulk material was taken into account with the models and the Coffin-Manson equation was used to predict the number of load cycles necessary for initial fatigue damage to occur. All the tested tooth flanks were observed using optical microscope and SEM.

Abstract: Based on the theories of fracture mechanics and composite materials mechanics, fibrous composite model that interacted on stratum, cement loop and casing was firstly established. Boundary conditions that the repaired force acted in fibrous composite model were also given. The influences of interface damage evolution and fracture process of fiber and matrix on the cement loop mechanical properties were studied as well. Meanwhile the distributions of stress and displacement fields were obtained. Finally, the debonded length and variation of the optimum repaired force were also determined, which can restrict the cement damage length to the lowest scale. The results given here can provide a reliable design references for improving the technology of repairing casing damage well.

Abstract: The solute segregation to grain boundaries may be classified into equilibrium and non-equilibrium segregation. The models and kinetics calculation equations were proved in previous work. However, the computational task for grain-boundary segregation kinetics process is complex and cumbersome as it can involve a vast amount of numerical data. It is therefore necessary to develop an easily usable computational program which can provide the researchers with a powerful tool in grain-boundary segregation kinetics process analysis in addition to having a sound theory. A computational program of non-equilibrium grain-boundary segregation (NGS) kinetics of solute is therefore developed in this paper. It includes programs for critical time calculation, effective time calculation and diffusion coefficients calculation, the program of Auger Electron Spectroscopy test data disposal, the program of curve fitting and the program of NGS kinetics simulation. A simulation example by using the computation program of NGS kinetic equations is in good accordance with the experimental observation of phosphorus in steel 12Cr1MoV. The computational program of NGS is therefore proved to be appropriate and helpful.

Abstract: This paper describes a method to measure the 3D-microstructure of a material which can be used to perform fracture simulations. A model concrete is made and the 3D structure is obtained with a CTscanner. Uni-axial tensile tests are performed on cylindrical specimens of the model concrete a regular concrete and of a mortar. The model concrete shows more micro-cracking, a more tortuous crack path, a lower tensile load and a less brittle behaviour compared to the mortar and the regular concrete. Furthermore it is found that the opening of the crack is more uniform when the material is more heterogeneous, which results in a more stable fracture.