Key Engineering Materials Vols. 385-387

Abstract: Friction stir welding (FSW) is a new solid-state welding process that can produce low-cost and high-quality joints of especially aluminum and mgnesium alloys. The welding zone consists of different regions with characteristic microstructuralal details such as a weld nugget, a thermo-mechanically-affected zone (TMAZ) and a heat-affected zone (HAZ). Tension-compression fatigue tests were performed using FSW aluminum alloy AA5454 sheet specimens at a stress ratio of –1. To investigate the propagation behavior of small fatigue cracks in those regions, an artificial defect was introduced into different defined locations in the FSW specimens as well as into the parent material specimens. The crack propagation rates depended on the defined locations and were a function of the hardness; that is, the lower the hardness was, the higher the propagation rate was. The crack paths were mostly perpendicular to the applied stress axis, but some crack paths exhibited deviations by the influence of the local anisotropy of the microstructure.

Abstract: The crystalline orientation significantly affects the fracture behavior of crystals. However, the orientation-dependent failure criterion is still lacking up to now. In this paper the failure criteria for different crystalline planes of aluminum have been developed. The critical normal stresses to separate two parallel crystallographic planes have been calculated based on Morse potential. The critical stresses on four different planes ({100}, {111}, {110} and {120}) were obtained. It has been found that plane {120} had the minimum critical normal stress. The developed failure criteria have been applied in the crystal plasticity finite element method (CPFEM) model to simulate the uniaxial tensile deformation of single crystal aluminum with a notch. The lattice orientation evolution during deformation has been predicted by the CPFEM model. Elements at notch tip reaching predefined orientation-dependent failure criterion were removed from the mesh so that the crack growing could be determined explicitly without any path assumption.

Abstract: The goal of this research project is the development of a simulation model for lifetime estimation of components manufactured from the AA6016-T4/FeP06 material compound. Components composed of this material are manufactured predominantly by rolling and deepdrawing. For this reason, the influence of the plastic deformations during the manufacturing process on the fatigue behaviour must be investigated. Particularly the cyclic hardening behaviour of FeP06 steel has a relevant effect on the fatigue life of this aluminium-steel compound. Simulation models for fatigue life estimation therefore have to consider the influence of this hardening effect, which occurs during the manufacturing process. In this work, test results and a simulation model to take into account the influence of the rolling reduction on the fatigue behaviour of components manufactured from the AA6016/FeP06 material compound are presented.

Abstract: Bottom hole assemblies (BHA) of oil drilling engineering were simplified as simply supported beam, and parametric resonances of BHA in mud drilling and air drilling were studied. Lateral vibration of BHA, which was induced by bit/formation interaction, was described and reduced into Mathieu equation by means of separation of variables and Galerkin method. Modified strained parameter method was adopted in stability analysis. The parametric resonance zones expressed by weight on bit (WOB) are presented here. It is found that drilling method, speed of rotation (SOR), material properties, and length of compression drillstring all can influence parametric resonance zones. So unstable responses can be avoided by adjusting these parameters.

Abstract: In this paper, the Turing reaction-diffusion model coupled with Finite Element Method (FEM) is implemented first by considering the biomechanical model iBone (Imitation Bone). Then the shape optimization of Metal Welded Bellows Seal (MWBS) is conducted based on the biomechanical bone forming process by considering the osteoclasts and osteoblasts process. The MWBS mass and shape is changed by changing the initial boundary condition, then some reasonable results are obtained by keeping the required forming value, and the new S type wave of metal welded bellow of mechanical seal are obtained. Finally, the strength evaluations are conducted for new optimized S type model and original V and S type models by using the FEM software.

Abstract: To improve the cracking resistance of lightweight aggregate concrete, rubber particles and polymer were added. Experimental results showed that the shrinkage rate increased when rubber particles were added into lightweight aggregate concrete, but when polymer was mixed, the shrinkage rate decreased dramatically. Microstructure analysis indicated that the interface transition zone (ITZ) influenced the shrinkage performance of rubberized lightweight aggregate concrete with polymer directly; the ITZ bondage between rubber particles and cement matrix was very poor and the restriction to shrinkage was weak, which were the main reasons for the increase of shrinkage rate of rubberized lightweight aggregate concrete; when polymer was mixed into the concrete, the hole and ITZ structure of concrete were improved, which made the strain energy absorbing function of rubber particles can be exerted entirely and the flexibility of ITZ was boosted, thereby the shrinkage performance and cracking resistance of lightweight aggregate concrete were improved.

Abstract: In this paper, interface element with de-cohesive constitutive law is used to predict the delamination progress of laminates in which delamination is the prominent failure mode. For this purpose, a finite element program is developed to perform nonlinear damage analysis. The analyses are carried out based on the interlaminar constitutive law of elastic-plastic-damage proposed before in the literature. Delamination initiation and propagation of several laminates with dominant interlaminar shear stresses at free edges are investigated to find the failure load. It is shown that the difference between the predicted failure loads using the present study and the experimental results are 3.1% to 19.4% for various laminates.

Abstract: In this paper, the temperature field and the thermal effects on a concrete box girder in the sunshine are investigated. For this purpose, the finite element method (FEM) package ANSYS is applied. By varying the values of different thermal parameters, the sensitivity of the thermal parameters is explored. Numerical results are presented and discussed to show the influences of the thermal parameters and the temperature field on the deflection and the tensile stress of a single-span concrete bridge with a box cross section.

Abstract: Diamond-like carbon (DLC) is an amorphous hard carbon, which has very high hardness, high resistivity, and dielectric optical properties. Economically and technologically attractive properties have drawn almost unparalleled interest towards the coatings. Eutectoid steel is a kind of material that has been widely used in shafts and various kinds of industrial components. Three kinds of fatigue specimens with different DLC conditions were used in this study. Fatigue test had been performed to investigate the effects of DLC on fatigue properties of eutectoid steel. The fractography was analyzed by a scanning electron microscope (SEM), and surface hardness was also evaluated. The fatigue limits of the DLC coated specimens did notincrease after DLC process, though the compressive residual stress which produced by DLC process can prevent fatigue fracture. According to the results of fatigue test, the optimal DLC method for improving the fatigue properties of eutectoid steel is determined and the relationship between fatigue limits and coating bias are obtained.

Abstract: A piping system including straight pipes, elbows and tee branches in a nuclear power plant is mostly subjected to severe loading conditions with high temperature and pressure. In particular, the wall-thinning of an elbow due to flow accelerated corrosion is one of safety issues in the nuclear industry. In this respect, it is necessary to investigate the limit loads of an elbow with a wall-thinned part for evaluating integrity. In this paper, three dimensional plastic limit analyses are performed to obtain limit loads of an elbow with different bend angles as well as defect geometries under internal pressure and in-plane/out-of-plane bending moment. The limit loads are also compared with the results from limit load solutions of an uninjured elbow based on the von Mises yield criteria. Finally, the effects of significant factors, bend angle and defect shape, are quantified to estimate the exact load carrying capacity of an elbow during operation.