Papers by Keyword: Inverse Method

Abstract: The friction stir welding (FSW) process was developed by the Welding Institute (TWI) in 1991. The idea started from the need to use materials with high strength and low density in the aerospace and automotive industries to increase their performance. The FSW process enables the welding of dissimilar metals such as Al/Mg, Al/Cu, Cu/Mg, etc., without melting the base metal and avoiding the defects seen during fusion welding. FSW joining leads to a core and heat-affected zones with a behaviour different from that of the base metal. The behaviour of these zones influences the global behaviour of the welded structure and for this reason it is important to define the local behaviour. The present study focuses on identifying the local behaviour of a weld using numerical simulation. For this, the global model of the welded joint is created, by defining the specific areas of friction welding with rotating active element (the base material-MB; the thermally affected zone from the retreating side of tool- HAZ RS; the thermo-mechanically affected zone from the retreating side of the tool - TMAZ RS; the core of the weld - N, the thermo-mechanically affected zone from the advancing side of the tool - TMAZ AS; the thermally affected zone from the advancing side of the tool - HAZ AS) and the simulation of the tensile test is carried out. The local behaviour obtained after the simulation is compared with the behaviour obtained experimentally in the specialized literature. Next, the correlation of Abaqus and Matlab programs is presented to analyze and compare experimental data from the literature with those obtained from the simulation by applying the reverse method. This consists of introducing experimentally identified parameters into the numerical simulation, determining an eloquent comparison criterion, defining the error function and minimizing it. The inverse method presented in this paper opens new opportunities for its use in much more in-depth analyses.

Abstract: Cam mechanisms are used as the control system in several industrial fields such as filling and canning, textiles, automotive. This paper introduces the development of a software for designing planar cam mechanism adapting the dynamic and kinematic requirements. The designed cam profile is then changed into numerical data used to generate the machine codes served for CNC-based fabrication. Traditional cam design is very complicated and has accumulated errors. The envelope theory and inverse method are utilized to perform constraint in pressure angle and motion. The smallest cam radius is then determined in a non-linear optimization adapting the constraints. The paper also presents the design of a CNC machine for cam profile fabrication. The design includes the control system and the circuit board. The CNC control program is built to receive numerical data from cam design section, to simulate the cam profile fabrication and then to fabricate. The optimal design and fabrication are applied to the cam mechanisms with knife-edge/roller reciprocating/oscilating followers. The verification shows that the designed and fabricated cam adapts the requirement of accuracy.

Abstract: The radial spokes of non-pneumatic tire have been developed to absorb impacts. In order to obtain its property for the further developments, it had to cut into the curve beam specimens. The 3-point bending was selected to test referring to ASTM D790. Subsequently, the finite element method was employed to simulate the 3-point bending test of specimens. The inverse method was used to determine the modulus of elasticity for specimen material. The gradient based on optimization scheme was used to optimize the modulus of elasticity by the input and output condition which was the vertical deflection and force, respectively. The optimized process was terminated at the desirable force tolerance of 0.00071 N. The elastic modulus of spoke was implemented in the finite element model of the 3-point bending test. There was found that the simulation result of vertical displacement obtained an average error of 4.87% by comparing with physical experiment.

Abstract: This research proposed an inverse method to calculate the mechanical property of a chicken eggshell. The optimization method had been performed to determine the simulated results of the finite element analysis in order to predict Young’s Modulus of the eggshell. To obtain an accurate mechanical property of the eggshell, the finite element analysis was verified by comparison with the experimental results. There was found that the error of the coupling calculation method between the inverse method and finite element method was less than 0.1%. Consequently, the inverse method and finite element analysis can be used to determine the mechanical property of the other eggshell types in the further work.

Abstract: The Selective Laser Melting (SLM) process of metallic powder is an additive technology. It allows the production of complex-shaped parts which are difficult to obtain by conventional methods. The principle is similar to Selective Laser Sintering (SLS) process: it consists, from an initial CAD model, to create the desired part layer by layer. The laser scans a powder bed of 40 μm thick. The irradiated powder is instantly melted and becomes a solid material when the laser moves away. A new layer of powder is left and the laser starts a new cycle of scanning. The sudden and intense phase changing involves high thermal gradients which induce contraction and expansion cycles in the part. These cycles results in irreversible plastic strains. The presence of residual stresses in the manufactured part can damage the mechanical properties, such as the fatigue life. This study focuses on the thermal and mechanical modelling of the SLM process. One of the key points of the mechanical modelling is the determination of the heat source generated by the laser in order to predict residual stresses. This work is divided in three parts. In a first part, an experimental protocol is established in order to measure the temperature variation during the process. In the second part, a thermal model of the process is proposed. Finally, an inverse method to determine the power and the shape of the heat source is developed. Experimental and computational results are fitted. The influence of several geometries of the heat source is investigated.

Abstract: The competitive adsorption isotherm of etodolac enantiomers on a cellulose carbamates-based chiral stationary phase (Chiralcel OD) at 25°C was determined in this study by the inverse method (IM). An equilibrium dispersive (ED) model combined with bi-Langmuir adsorption model was used in predicting the elution profiles. The adsorption isotherm model with 5 parameters was determined by fitting the two overloaded band profiles. The non-dominated sorting genetic algorithm (NSGA-II) and Levenberg-Marquardt algorithm (LMA) were crucial tools and utilities in this process. Suitable model parameters have been obtained and the experimental results were in good agreement with the model predictions.

Abstract: The present work reports an experimental procedure designed to validate a particular solution for the distribution of artificial light sources in the sealing of an enclosure obtained by the inverse method IMIbyOPTIM. An illumination design assuming the free placement of purely diffuse light sources aims to generate a uniform illumination field on a work plane. A reduced scale enclosure is built to validate the method effectiveness, by comparing the experimental results to an illuminance target. An equally non-optimized light source distribution is placed on the enclosure and measurements confirm the hypothesis of distortion of the illumination field, already predicted by simulations. After the optimization of the light sources distribution, the measured illumination field becomes closer to the dimensionless unitary target, with a standard deviation of less than 0.021. This particular experiment verifies IMIbyOPTIM predictions and allows continuing the validation process of the method for a broad variety of design combinations.

Abstract: The paper presents the results of fatigue crack growth rate test of iron sinters. The samples were produced by means of the impact sintering. Applied production method allowed to obtain dense sinters with fine grain size resulted from large shear strains. Due to the limited size of the final products the mechanical tests were carried out in mini-samples. Optical, non-contact method of displacement measurement, namely Digital Image Correlation (DIC), was applied for determination of the displacement fields near the crack tip at the maximal force of selected loading cycles. The results of DIC measurement were utilized in the calculations of stress intensity factors and crack tip coordinates by means of the iterative procedure based on inverse method. These parameters were used for measuring crack development rate. There were investigated two types of materials produced by the consolidation of two different kinds of Fe powders and sintered in different temperatures. The results of crack growth rate tests were correlated with the microstructure changes, as well as yield and ultimate strength of the materials.

Abstract: With the elution curves of glycine and taurine, the ion exchange isotherm parameters of glycine and taurine on D290 anion exchange resin are determined by the inverse method. In this work, with the multi-component competitive ion exchange isotherm and the equilibrium dispersion chromatographic model, the elution curves of glycine and taurine on D290 anionic fixed bed are fitted. The parameters of competitive isotherm are determined, K_tau is 2.55, K_gly is 1.65. The result s showed good agreement between the elute curves fitted by the model and the separation data which confirmed the validity of the model selected.Keywords-taurine; glycine;competitive isotherm;inverse method;

Abstract: Established process in the automotive industry, the hot stamping process consists in heating a blank until complete austenitization in a furnace before transferring it to a press where it is formed at high temperature before being quenched by contact with the cold tools. During the forming step the hot blank slides on the die radius. Locally, the contact pressure can reach very high values. Due to this contact, heat transfer between the hot blank and the die can be significant. Using an omega die instrumented with eight thermocouples localized in the die radius, a 2D inverse method is used to estimate the heat flux that crosses the Blank/Die interface and the temperature field in the die radius and on the die surface. Four thermocouples are located in the blank thickness and a FE analysis is performed to estimate their positions as function of the time. The temperature in the thickness of the blank is considered as uniform according to Biot number value. This assumption is checked afterward. Thus, it is possible to estimate the sliding thermal contact resistance between the blank and the die as a function of time in front of each thermocouple of the blank. The estimation of the temperature field in the die can be useful for investigating the fatigue that occurs in the die. On the other hand, the knowledge of the interface condition in the die radius can present a high interest for improving the numerical simulations of this process.