Advanced Materials Research Vols. 83-86

Abstract: The rolling process of corrugated waist rail is simulated by explicit dynamic FEM. The influence of rolling velocity, reduction and the initial thickness on the rolling force is analyzed. The rolling corrugated waist rail is experimented on the three-stands universal mill of Yanshan University. At the same rolling condition, the rolling force obtained from experiment is coincident with the simulation, this proves the theory analysis is correct. Therefore, the rolling parameters obtained from simulation can be instructive to the production site.

Abstract: Residual stresses are very important for the lifetime of pieces in their mechanisms. These kind of damages are mainly caused by mechanical, thermal, and metallurgical affectations of the machined material. To control these affectations, we need to link the cutting parameters to the residual stress state observed onto the workpiece surface and depth. These connections can be made with analytical works, experimental works or numerical works. In our case, it has been chosen to work with a numerical support in order to observe and understand precisely the phenomenon involved during cutting operation. While this way of study is really popular, we proposed to model the residual stress generation in a original way by keeping aside the chip formation. This new approach presented in a previous paper was simple and only use a 2D model. This first model moves thermo mechanical loadings onto the workpiece surface to recreate the relative motion between the tool and the workpiece. The new 3D model, presented in this paper, is now improved with an original friction law. It underlines the impact of each passage of the tool onto the others. The physical properties are thermo dependant and the flow stress model is based on a Johnson cook behaviour.

Abstract: Due to the intense concentration of heat in the welding process, residual stresses are produced in the specimen. One of the most effective ways to relief welding stress is Post Welding Heat Treatment (PWHT). In this paper, finite element method is employed to model and analyze PWHT for two pass butt-welded SUS304 stainless steel pipe. In this simulation, firstly, the welding process has been modeled. Then the stress distribution of the specimen has been transferred to a second analysis for stress relaxation modeling. Norton law is used to investigate creep in stress relief process. Experimental tests are also carried out to verify the effectiveness of the proposed numerical models. The hole drilling method is used to measure the stress distribution in the specimen. The residual stress distribution data before and after PWHT are compared to investigate the effect of heat treatment on residual stress. Based on the modeling and experimental results, the tensile and compressive stresses distributions have been reduced. They are in a reasonable agreement with each other and prove the capability of the proposed modeling technique to simulate PWHT.

Abstract: Reverse Engineering and Rapid Prototyping are integrated mostly using the tessellated STL (Solid-to-Layer) file. If copies of 3D scanned products are needed in a few time, the polygonization task is normally performed on the point cloud, often generating errors, requiring high computational effort, and heavy human intervention. In this paper it is proposed to overcome the limitations of polygonization by using direct slicing of point clouds, modelling the problem as a travelling salesman problem (TSP), solved basing on the heuristic technique called cheapest insertion. The point cloud is decomposed into elementary voxels, then, considering each Z level of the voxelized point cloud, the external non-void voxels are linked together, using the above mentioned heuristics, to generate the contour of the object with an automatic process. The contour of the object can be easily converted into commercial slice files suitable for Rapid Prototyping machines. The approach is applied to several complex shaped models to prove its robustness and efficiency.

Abstract: This paper presents the results derived from the research, whose first results were presented at AMPT 2005. At this conference, a new method for generation of rheological model to characterize non-conventional injection moulding by means of spiral mould was presented. The continuity of this research line has consisted of the development of several tests for validation of the rheological model obtained with the new method. Viscosity of a PEHD with different percentages of recycled has been tested, by means of several kinds of rheometers, like capillary rheometer and rotational rheometer, and the results has been compared to those obtained with the spiral mould. Conclusions of this research show the suitable parameters range, at which the results are comparable for the new method. On the other hand, another work line for the validation of the rheological models has begun, by applying the models to CAE injection moulding software, and checking the results by experimental trials with a industrial mould. This mould has been adapted to register pressure results during injection cycle. These trials take into account the influence of most of the injection process parameters, as well as different percentages of recycled.

Abstract: With the advance of the robotic arc welding process, procedure optimization which selects the welding procedure and predicts bead geometry that will be deposited is increased. A major concern involving procedure optimization should define a welding procedure which can be shown to be the best with respect to some standard and chosen combination of process parameters which give an acceptance balance between production rate and the scope of defects for a given situation. In this paper, bead-on-plate welding using an infrared thermography during robotic CO2 welding process has been conducted to obtain the thermal profile characteristics and develop the empirical models which influence process parameters on bead width with the help of a standard statistical package program SAS. The comparison with values of coefficient of multiple correlations for curvilinear and linear equations presents no differences, which indicate that the developed equations are reasonably suitable.

Abstract: In tissue engineering (TE), a porous scaffold structure of biodegradable material is required as a template to guide the proliferation, growth and development of cells appropriately in three dimensions. The scaffold must meet design requirements of appropriate porosity, pore size and interconnected structure to allow cell proliferation and adhesion. This paper presents a methodology for design and manufacture of TE scaffolds with varying porosity by employing open structure building units and Fused Deposition Modeling (FDM) rapid prototyping technique. A computer modeling approach for constructing and assembly of three-dimensional unit cell structure is presented to provide a solution of scaffolds design that can potentially meet the diverse requirements of TE applications. A parametric set of open polyhedral unit cells is used to assist the user in designing the required micro-architecture of the scaffold with required porosity and pore size and then the Boolean operation is used to create the scaffold of a given CAD model from the designed microstructure. The procedure is verified by fabrication of physical scaffolds using the commercial FDM system.

Abstract: In the recent years the rapid prototyping technology has become increasingly important as a manufacturing method for many medical devices. Although the advantage of such technology is evident, a precise presentation of the actual anatomical parts as well as shape accuracy and surface quality is a major indicator for choosing the best technique. In this paper, evaluation and validation of the shape accuracy of fabricated models using Fused Deposition Modelling technique is presented. The surface deviation between anatomical models (a mandible) derived from Computed Tomography and their virtual presentation was investigated. A high level of conformity with regard to the surface feature of the anatomical part was observed. Furthermore, surface deviations in the range of ±0.5 mm with an absolute mean deviation of 0.159 mm for the model were reported. The surface accuracies suggest that the reproduction of complex anatomical structures by FDM could potentially be used for surgical planning, custom-made implants and for surgical anatomy teaching.

Abstract: Quasi-static equations are presented for a magnetostrictive medium where mechanical and magnetic fields interact with each other. Finite element method is used in conjunction with the Hamilton's principle to deduce equations for the dynamic behavior of the magnetostrictive material. These equations form the basis for the magnetostrictive material to be utilized as a sensor or as an actuator. When used as an actuator, the material can provide enough power to actuate mechanical systems for vibration control. In this work, a cantilever beam with a magnetostrictive actuator is taken to demonstrate the modeling and use of the magnetostrictive actuator in attenuating structural vibrations. The position of the actuator is changed to observe its effect on the response of the system. This is important because it is a well-known fact that the actuator location has impact, sometimes big, on its performance.

Abstract: Nickel based super alloys are promising materials for high temperature structural applications because of their low density. The single grain super alloys are extremely creep resistant at high temperature, due to the fraction of Ni3Al based ' precipitates coherent with a Ni based  matrix [1, 3]. The cuboids group together and form semi-coherent interfaces after a long annealing at high temperature. The ' precipitate growths in nickel base super alloys often favor the parallelism of (111) planes between cubic dissimilar crystals [4]. In consequences, a hexagonal network of dislocations, that covers the hetero-interphase, is arranged by accommodation of the angular misfit between two semi coherent crystals ( ). In this work, the magnitude of the distortions is simulated as arising from a trigonal network of subsurface misfit dislocations partly dissociated in Shockley dislocations limiting intrinsic and /or extrinsic stacking faults. The results derived from a previous explicit formulation using double Fourier series [5]. Each harmonic term of the series depends on the anisotropic elastic constants and the thickness of each phase. The program built is in a double precision Fortran language and it shows the magnitude and the aspect of the distortions of the free surfaces when the dissociation change in the hetero-interphase. Also, the program has the advantage to fully apply to hetero-epitaxial systems, whatever is the thickness of the free surfaces.