Advanced Materials Research Vols. 538-541

Abstract: Natural or anthropogenic CO₂ pipelines have been in operation in USA, Europe and North Africa for almost three decades, which are aimed at implementing EOR(enhanced oil recovery) technology and (more importantly) developing CCS(carbon capture and storage) technology. At present, there is no specific pipe standard for CO₂ transportation pipelines. Instead, oil & gas pipeline system is directly introduced into the field of CO₂ transportation piping. Therefore, the technical details for oil & gas pipelines transporting supercritical CO₂ should be carefully taken into consideration due to the relevant effects of different impurities in the transported CO₂ and the different transportation environment for these two mediums, i.e. oil&gas mixture and CO₂. For the application of anthropogenic CO₂ pipe transportation technique, this paper will address a FE-based method which can evaluate fatigue life of a supercritical CO2 transmission pipeline containing an inner crack. Specifically, a portion of welded round steel pipeline is selected as the object of our analysis. And under the inner pressure fluctuation scenarios, an FRANC2D finite element procedure is generated to simulate mode-I crack extension from a given inner edge crack and to calculate the corresponding stress intension factors(SIFs) varied with different cracking depths. Afterwards, considering the effects of crack closure, the Paris equation is modified to build an integral analysis method for the fatigue life evaluation of CO₂ pipeline. Thus, the relation between the fatigue life and the inner pressure fluctuation range can be determined by performing the proposed fatigue crack growth analysis, which can also provide a LEFM-based pipeline selection method in terms of fatigue durability other than the conventional method coming from the structural strength theory.

Abstract: The flow stress behavior of 6016 aluminum alloy was investigated on the condition of temperature range from 420°C to 540°C and strain rate range from 0.001s^-1 to 1s^-1 based on hot compression experiment on Gleeble-1500 thermal simulation machine. The result shows that the flow stress of 6016 aluminum alloy decreases with the enhancement of temperature and increases with the increase of strain rate. Especially, the flow stress increases tendency becomes obvious when the strain rate greater than 0.1s^-1. Based on the results above, a constitutive equation for flow stress of 6016 aluminum alloy when the temperature is above 420°C is obtained by linear regression.

Abstract: Rotating bending fatigue tests had been performed using A5052 aluminum (Al) alloy with the hybrid coatings which consisted of tungsten carbide including 12% cobalt (WC-12Co) interlayer and diamond-like carbon (DLC) film, in order to investigate the effect of hybrid coating on the fatigue behavior. The WC-12Co layer was thermally sprayed by a high velocity oxygen fuel (HVOF) method on A5052 with the thickness of 70, 120 or 170μm. Subsequently, the DLC film was deposited with the thickness of 15μm. The fatigue strengths of the specimens with WC-12Co single layer were higher than those of the substrate and increased with increasing the thickness of WC-12Co layer. The fatigue strengths of the specimens with the hybrid coating of 70μm WC-12Co interlayer and 15μm DLC film were better than those of the specimen with 70μm WC-12Co single layer. Thus the hybrid coating structure was effective to improve fatigue strengths. However the beneficial effect of hybrid coating was not apparent in the specimens with thicker WC-12Co interlayer of 120 and 170μm.

Abstract: Zn-Al alloy microstructures were investigated, moreover, the strength and microstructures of pure aluminium brazed joint had been studied. Joint fracture mechanism was analyzed. The results indicate that the blocky microstructure in the cast 85Zn-15Al filler metal is granular and fine. Accordingly, the blocky eutectoid structure in the joint brazed by 85Zn-15Al is fine and even. Stress concentration emerges difficultly between fine blocky eutectoid structure and its surrounding structure. So the joint strength is highest. When Al content in the Zn-Al alloy exceeds 15wt.%, the blocky eutectoid structure become large in the cast filler metal and the brazed joint. The brazed joint strength decreases.

Abstract: The homogeneous solutions of the governing differential equations for shear lag are used as the displacement patterns of the finite segment are presented. A finite segment model with consideration of initial curvature, bending, torsion and shear lag is established. In addition, the tests of the two-span continuous curved box girder and numerical calculations of the model tests by finite segment method and finite element method are made. The results of the model tests and numerical calculation are consistent with each other. An actual example was given to investigate the shear lag effect of a continuous curved box girder under load. The research results show that the initial curvature has an obvious influence on the shear lag effect of a continuous curved box girder.

Abstract: Springback is the prominent problem in bending forming of sheet metal, which is difficult to control accurately, especially for the complex shaped bending parts. The change of blank-holder force will cause significant changes of bending springback amount. The theoretical analytical model of cap-shape parts bending, which takes into account of the harden ability, anisotropy and elastic deformation of material, is proposed in this paper based on the plane deformation assumption and the bending theory of sheet metal, the cap-shape parts bending of wide sheet is analyzed theoretically, the approximate calculation relational expression is derived between the blank-holder force and springback angle, and the influence of blank-holder force on springback is discussed. In the same conditions, the springback result deduced from theoretical formula is basically consistent with numerical simulation and experiment result.

Abstract: To reduce the coal mining risk, drainage of methane with drills and hydraulic fracture has been put in practice. In the paper, an advanced damage propagation model of brittle fracture is studied based on mode I crack. The localization band of damage is inducted, and the modal of localization of damage around crack-tip is established using fracture and damage mechanics. Besides, the stress distribution in localization of damage is assumed as obeying a quadratic function, thus the stress field around the crack is obtained, and the calculation formula of crack length is presented, which can provide reference for mine production.

Abstract: It is impossible to keep pipelines free from mechanical damage in the manufacturing, installation and servicing processes. In this paper, the geometric model for fatigue life of pipeline steel was introduced. The local plastic deformation was considered to imitate the mechanical damage on the pipe. The estimation models of the fatigue crack initiation life and the fatigue crack propagation life were proposed according to the plastic deformation. The result is expected to be beneficial to the understanding of the effect of damage on the safety of pipelines and fatigue life prediction.

Abstract: Plastic mold polished, in the mold cavity parting collapsed throwing angle appear, which seriously affect the dimensional accuracy and surface quality of the plastic parts, this article proposed two effective preventive measures: (1) cutting the model which having a same size as plastic model of the cavity at the parting surface, sticking the model and cavity parting with 502 glue together, within the required type of alignment, and then thrown together, polished finish will be a model to out; (2) in the plastic model cavity machining process, type in the mold cavity surface set aside allowance 0.5 ~ 1mm, polished until the cavity is completed, the surface of the cavity type 0.5 ~ 1mm rubbed off with a grinding allowance, it will ensure the cavity size and cavity to prevent the collapse of sub-surface angle at the phenomenon.

Abstract: The high-temperature deformation resistance of X120 pipeline steel was studied under different deformation temperature and different deformation rate through the hot compression test on the Gleeble-3500 thermal/mechanics simulation test machine. The influence of deformation degree, deformation temperature and deformation rate on deformation resistance was thoroughly investigated. The deformation resistance of X120 pipeline steel increased slowly when deformation degree was higher than 0.2. With the increase of deformation temperature, the work-hardening effect was weakened, so the deformation resistance decreased. And the deformation rate had dual influences on the deformation resistance, including the effect of temperature and time. Based on the experiment data, the parameters in the mathematical model were regressed by using SPSS (Statistic Package for Social Science), and the mathematical model of the deformation resistance of X120 pipeline steel was established finally. Through the regression analysis, the model had been proved to have great matching precision.