Papers by Keyword: Numerical Modeling

Abstract: The dependency of morphology development and dendrite growth on welding conditions (laser power, welding speed and welding configuration) is numerically analyzed to decrease nucleation and growth of stray grain formation during laser processing aerospace component surface of ternary Ni-Cr-Al single-crystal superalloy. Proper (001)/[100] welding configuration crystallographically initiates three axisymmetrical distributions of microstructure development, i.e. stray grain formation, morphology development and dendrite trunk spacing, alongside the advancing solid/liquid interface of molten pool, whereby metallurgical properties are increased. Unpromising (001)/[110] welding configuration tends to crystallographically possesses unaxisymmetrical microstructure development to favor substantial crack-vulnerable dendrite size and morphology. Epitaxial [001] columnar dendrite growth region is favored for single-crystal dendrite growth, while vulnerable [100] equiaxed dendrite growth region is more susceptible to solidification cracking. The lower heat input is used, the smaller stray grain formation, negligible columnar/equiaxed transition (CET) and finer dendrite trunk spacing are consistently promoted by narrower constitutional undercooling ahead of solid/liquid interface to improve crack-resistant microstructure development and weld integrity. When comparing between [100] dendrite growth region on the right side and [010] dendrite growth region on the left side, (001)/[110] welding configuration spontaneously engenders severer stray grain formation, insidious columnar/equiaxed transition and coarser dendrite trunk spacing on the right side to deteriorate microstructure development with restriction of the same heat input on both sides of weld pool. The mechanism of asymmetrical solidification cracking as result of crystallography-induced microstructure degradation is therefore proposed. The theoretical predictions of asymmetrical solidification cracking susceptibility are comparable with experiments.

Abstract: The article describes the strength characteristics of the material used for highly loaded structural elements by modeling their stress-strain state (SSS) and testing special laboratory samples for strength. The typical biaxial SSS is characterized by a different ratio of the main stresses in the focus of possible destruction, which affects the strength characteristics and requires the use of special equipment for determining strength values in laboratory conditions. To create a biaxial SSS under these conditions is a difficult task, since it requires non-standard laboratory samples and test systems with several power drives or complex lever devices for loading these samples, which limits the use of this testing method in determining the mechanical properties of materials. The article describes a simpler method for testing materials under complex stress-strain using special laboratory disc samples on standard test equipment with one power drive. The disk sample design and methods of deforming and creating test conditions are described.

Abstract: This work is based on a numerical study of the fluid-structure thermal coupling in a concrete slab intended for habitable heating. A rectangular cross-section pipe in which a hot fluid flow is installed in this concrete slab. The Navier-Stokes equations that govern this flow have been solved numerically. To this end, these equations have been discretized by an implicit finite difference method. The systems of algebraic equations thus obtained have been solved by the Gauss and Thomas algorithms. The conduction equation in the concrete slab was solved using the same methodology as that of flow. In fact, we have based on an algorithm that makes an unsteady solid medium interact with a fluid medium consisting of permanent states series while ensuring the equality of fluxes and temperatures on the common interface between both media at every moment. The numerical simulation of heat transfer and the thermal behavior of the heating slab were analyzed for different parameters influencing thermal diffusion. The results obtained by the numerical model adopted for the control of the fluid-structure coupling are in good agreement with those of the literature results.

Abstract: There have been no breakthroughs in ferrous metallurgy for the last 80 years. Automation and digitalization arrived, while the actual steel making processes saw almost no changes. Today, almost all industries experience rapid changes. In 2018 we will see a launch of trains that can travel as fast as1,200 km/h. In 2022 we will see aircrafts capable of flying from London to New York in 1 hour. They already know how to grow human arms and legs. And driverless taxis have become extremely popular. Should we be expecting to see a major breakthrough in metallurgy any time soon? In this paper you will learn about this and other problems, as well as possible ways to solve them. Also, the paper focuses on the results of the development of theory, mathematical models and novel processes, which were helpful in the forming of the ultra-high strength materials by combining the conventional methods of forming such as stamping, plate rolling, plastic bending and asymmetrical rolling. The ultimate aim was to manufacture parts having complex geometries of ultra-high strength sheets. Metalworking techniques like asymmetrical rolling gave rise to very high shear strains and it was used for increasing the strength of the materials. The addition of the incremental sheet forming to the varied combinations of conventional forming processes was used for increasing in the flexibility of the manufacturing process for ultra-high strength. The results of the research project were also encompassing numerical simulation and experimental investigations of the combined process accompanied by the development of the theoretical models for the same.

Abstract: The finite-difference model for calculating temperature fields in linear friction welding is described. A feature of the model is the heat transfer across the friction surface accounting, which makes it possible to study the case of welding parts with different physical and mechanical properties. Modelling results, obtained for combination of VT6 and VT8-1 titanium alloys welding, are described. An assessment of the temperature field and heat transfer during the parts from VT6 and VT8-1 welding is given.

Abstract: The article is devoted to the modeling of structural-phase transformations during automatic MIG welding of high-strength steel X80 in a welded seam and the heat affected zone in the ANSYS / Mechanical package. Based on the results of numerical modeling the relationship between the initial morphology of the steel microstructure and the parameters of the weld seam geometry was revealed.

Abstract: Subject of this paper is numerical modelling of steel assembling bolt connections of CHS (circular hollow sections) or L-profiles respectively in the FEM software ANSYS 12.0 and their subsequent comparison with performed laboratory experiments. Non-linear calculations with both plastic behavior of materials and influence of large deformations were taken into account. Comparison of results, in the form of load-deformation curves, showed that numerical models describe the basic behavior of those joints. The direct numerical model outputs were modified. This modification was made with respect to real laboratory conditions taking into account the effect of the trial press machine slip stiffness and the initial slip.

Abstract: Piezoelectric composite materials with a polymer matrix are important for underwater acoustic and biomedical imaging applications. The dependence of electromechanical properties of piezoelectric composite on constituent material characteristics and shape of piezoelectric inclusions is a central problem that provides the opportunity to tailor the performance of piezoelectric composites according to design needs. A numerical model has been developed to investigate the electromechanical properties of 1-3 piezoelectric composites with a passive and active polymer matrix. Maxwell Homogenization method is employed to homogenize the solution domain. It is demonstrated that the use of PVDF as an active polymer matrix has a significant influence on piezoelectric charge coefficient d₃₁, hydrostatic coefficient d_h, voltage coefficient g_h, and hydrophone figure of merit g_hd_h when compared to the passive Araldite-D polymer matrix. Overall, a 5 to 30% volume fraction of PZT-7A fiber inclusions in an active polymer matrix is the optimum ratio that has a significant effect on piezoelectric properties. The accuracy and effectiveness of homogenized material constants were verified by comparing the derived composite properties with experimental work published elsewhere. These results provide much needed intuitiveness in the development of piezoelectric polymer composite with better performance for transducer applications.

Abstract: Use of nanocomposites is increasing rapidly due to their enhanced thermal and structural properties. In the present work, the numerical modelling of nanocomposites is conducted with the help of the (GA) genetic algorithm and (FD) finite difference techniques to find out a set of nanocomposites with best thermal and structural properties. The genetic algorithm is utilized to find out the best set of nanocomposites on the basis of thermal and structural properties while the finite difference technique is utilized to solve the heat conduction equation. Different nanocomposites considered in the present work are Al-B₄C, Al-SiC and Al-Al₂O₃. The weight percentage of these nanocomposites is varied to see its effect on the nanocomposites properties. In the end, the solidification curve for all the nanocomposites is plotted and analysed. Result reveals that GA helps in identifying the best set of nanocomposites while FD technique helps in predicting the solidification curve accurately. Increment in the wt. % of nanocomposites makes the solidification curve steeper.

Abstract: The article is devoted to the investigation of the influence of columns’ concrete body destruction size on the bearing capacity of building structures. The joint spatial work of steel strengthening structures with reinforced concrete constructions is investigated. The results of numerical modeling the stress-strain state of damaged reinforced concrete columns in the middle row of the industrial building are presented. The numerical modeling was executed in the system NASTRAN. It was carried out the numerical calculation of reinforced concrete column in the middle row without damages. Then it was modeled the column damage in form of a "downed" concrete angle to a depth of 50, 100 and 200 mm and denudation of bearing longitudinal armature at length of 1000 mm from supporting part of the column. In this case two separate models were investigated - with the location of damage from the compressed or extended side of the column. The conclusions about feasibility of columns strengthening by steel clip are made.