Advanced Materials Research Vols. 291-294

Abstract: Put forward and develop a pipeline cleaning robot. Relying on finite element analysis software ANSYS，establishing finite element model of pipeline robot swinging rod with the solid92 as the basic unit，it was found that the swing rod of the pipeline robot was the weak link by a large number of on-site experiments. After analysis the fatigue properties of pipeline robot's swing rod，compared with the results of its static analysis and evaluation of failure mode of pipe robot's swing rod，reasonable proposals are put forward for the follow-up study of the pipeline robot.

Abstract: This paper investigates nonlinear responses of honeycomb sandwich composite under externally applied loads theoretically and experimentally. In the experimental work, honeycomb sandwich composites made of an aluminum honeycomb core and glass fiber reinforced polymer (FRP) laminate surfaces were loaded under in-plane tension and out-of plane bending up to failure. Stress-strain curves or load deflection plot together with elastic moduli and ultimate strengths were obtained. An energy approach was used to establish a nonlinear constitutive relationship for the honeycomb sandwich composites. Making use of the superimposition ability of the strain energies of all of the walls of the RVE, a nonlinear constitutive relationship for the honeycomb core was obtained. The thus obtained relationship was incorporated with a laminate theory and the bridging model to analyze nonlinear responses of the honeycomb core and FRP surface sandwich composites up to failure. The composite failure was detected micromechanically, i.e., based on the failure status of its constituent aluminum core, reinforcing fiber, polymer matrix, and adhesion layer. Stiffness discount was applied respectively to the failed composing element. The predicted nonlinear stress-strain curves under tension and load-deflection relationship under three-point bending were compared with the experimental measurements. Favorable correlations have been obtained.

Abstract: In the present work, the resistance to crack extension of 2524-T3 aluminum alloy under Mode I loading was studied by using the middle-cracked tension M (T) specimens. The curve, plane-stress fracture toughness and apparent plane-stress fracture toughness were calculated by test data. The average value of measured fracture toughness at room temperature was 161 MPam^1/2. The results and conclusions can be referred in airplane skin design.

Abstract: The finite element model of a straight attachment lug subjected to an oblique loading less than 45 degrees is built by using the finite element software ANSYS, a cosine pin-bearing pressure distribution is applied on the hole of lug as a boundary condition. The stress intensity factor (SIF) expression for the straight attachment lug with a single through-the-thickness crack, which is subjected an oblique pin-load less than 45 degrees, is determined by studying on the influence law of dimensionless crack length (a/R₁)，ratio of outer radius to inside radius (R₂/R₁), inside radius (R₁) and pin-load angle (β) on the SIFs values. The expression is validated by contrasting with the ANSYS results and the data of residual strength test. The stress intensity factor’s amplitude (ΔK) are calculated by the SIF equation to get the values of the Paris constants. The fatigue crack growth model of attachment lug subjected to oblique pin-load is established, offering an analytical as well as experimental method for assessing and designing damage tolerant attachment lugs.

Abstract: Based on the isothermal compression experiment under constant strain rate, the deformation behavior and flow stress of as-extruded 7075 aluminum alloy at high temperature was studied. Then the fracture behavior and mechanism of 7075 aluminum alloy were investigated, the results showed that longitudinal cracking was easy to occur at a high temperature due to additional tensile stress and low melting point alloy in grain boundaries melting. Through analysis and comparing of C&L and Oyane fracture criteria, it was proved that C&L fracture criterion was more reasonable to predict fracture in 7075 aluminum alloy hot deforming, and the critical damage factor in a forming temperature range(300~450°C) for 7075 aluminum alloy was obtained.

Abstract: To investigate the plasticity distribution of microstructurally small crack tip in FCC crystals, the crack tip opening displacment(CTOD), crack tip plastic zone and maximum plastic work for stationary microstructurally small cracks were calculated with the three dimensional crystal plasticity finite element theory, which was implemented in the finite element code ABAQUS with the rate dependent crystal plasticity theory code as user material subroutine. Results show that crystallographic orientation has significant influence on CTOD and maximum plastic work. The CTOD and maximum plastic work in hard orientation are larger than that in soft orientaion under the displacement controlled boundary condition, which means that crack in hard orientation is more likely to extend than that in soft orientaion. The high-angle grain boundary shows a tendency to reduce crack extension, and the dislocation ahead of the crack tip becomes blocked by high-angle grain boundary.

Abstract: There were different degree scale shelling defects on running surface of 60kg/m U71Mn rail after used on the curve for a period of time, the characteristics and the generating reasons of the defects were analyzed, and the improvement measures were presented. There test results indicated that the scale shelling defects found on rail running surface were a sort of typical rolling contact fatigue damage, which caused mainly by the excessive contact stress, as a result of the wheel long-term contact with rail on the gauge corner of the rail on curve. It is effective to prevent and reduce rolling contact fatigue damage by following measures, such as improving the wheel/rail shape matching, and guaranteeing the wheel/rail interface locating on the rail tread center position, and strengthening the railway maintenance, and reasonable preventive grinding and corrective grinding for rails, and strict executing the system that rail grading use, the heat-treated rails should be used on small curve radius and heavy-load railway.

Abstract: Thickness thinning is the principal quality problem in the vacuum forming process of the refrigerator inner liner. In this paper, the structural parameters of refrigerator inner liner were analyzed based on orthogonal experiments and numerical simulation. Optimized structural parameters combination scheme and the significance level of structural parameters to thickness were obtained by analyzing the results of orthogonal experiments. Validation experiment results shown that the quality of refrigerator inner liner based on the optimized structural parameters combination scheme improved effectively.

Abstract: Depending on the size of sets, a wrapped phase map is unwrapped by either region or pixel. In region phase unwrapping, the jump point threshold value is adjusted to search the region boundary after filtering a wrapped map with higher noise and then phase unwrapping ±2nπ in each region without filtering. The latter compares if the phase difference of adjacent pixels is greater than π as a reference for determining pixel point ±2π to perform phase unwrapping point by point. Although the former unwraps phase by means of boundary search and the latter with the phase difference of adjacent pixels, phase unwrapping errors occur in both cases in detecting surface cracks on materials as data on both sides of a crack are discontinuous. This paper proposes a solution for phase unwrapping on discontinuous surfaces by means of crack search and marking with region assembly phase unwrapping technology to locate boundaries in both region splits and crack splits and further extends the scope of application of region assembly phase unwrapping.

Abstract: In the present research, the influences of different extrusion ratios (15, 30, 45, 60, and 75) and extrusion temperature (300°C, 330°C, 360°C, 390°C, 420°C) on the mechanical properties and microstructure changes of AZ80 magnesium alloy have been investigated through tensile test and via ZEISS digital metallographic microscope observation. Research indicates that the alloy’s plasticity gradually decreases as the temperature increases, and that the alloy’s tensile strength varies with the extrusion ratio. At 330°C, the alloy’s particle grain is small and a small amount of black hard and brittle second-phase β (Mg17Al12) are precipitated uniformly along the grain boundary causing the gradual increase of the alloy’s tensile strength. When the extrusion temperature is up to 390°C, the grain size increases significantly, but the second phase precipitation along grain boundaries transforms into continuous and uniform-distribution precipitation within the grain. In this case, when the extrusion ratio is 60, the alloy’s tensile strength reaches its peak 390 Mpa. As the extrusion temperature increases, inhomogeneous precipitation of the second-phase along grain boundaries increases, causing the decrease of the alloy’s strength. At the same temperature, both the tensile strength and plasticity increases firstly and then decreases as extrusion ratio increases. With the gradual increase of the refinement grain, the dispersed precipitates increase and the alloy’s tensile strength and plasticity reach their peaks when the extrusion temperature is 390°C. As the grain grows, the second phase becomes inhomogeneous distribution, and the alloy’s strength and plasticity gradually decrease.