Plastic Strain Patterns Research Articles

Computational Modelling and Comparative Analysis of Friction Stir Welding and Stationary Shoulder Friction Stir Welding on AA6061

This research focuses on the computational modelling and comparative analysis of friction stir welding (FSW) and stationary shoulder friction stir welding (SSFSW) applied to AA6061-T6 aluminium alloy. SSFSW, an FSW variant, employs a stationary shoulder and a rotating pin. This study introduces a numerical model for both processes, using the innovative Smoothed Particle Hydrodynamics (SPH) technique to capture their distinct thermo-mechanical characteristics. The aim is to unravel its mechanics and multi-physics in SSFSW and compare it with conventional FSW. The temperatures predicted by the model exhibited a close agreement between the advancing side (AS) and retreating side (RS). Plastic strain patterns show that regular FSW is different from SSFSW. In SSFSW, the strain is less, and the plastic area is comparatively slightly narrower. The distinct “ironing effect” resulting from the stationary shoulder in SSFSW reduces the heat-affected zone (HAZ). Yet, it maintains efficient plasticisation and material flow within the pin-affected zone (PAZ). This research emphasises the significant impact of temperature, strain, material flow, and thermo-mechanical characteristics on the quality of joints. Future suggestions include exploring process parameters more broadly, examining dissimilar welding techniques and hybrid approaches, and comprehensively investigating the diverse effects of SSFSW under various configurations and joint angles.

Mechanism of rippling deformation of pipe due to internal reflected detonation

The unique rippling deformation of pipe due to internal detonation and reflected shock was studied. Numerical model incorporating thermo-viscoplastic constitutive model and considering the fluid-structure coupling between detonation wave and pipe was developed. Two pipes made of 304 L steel and 6061-T6 aluminum with different diameter-to-thickness ratios were analyzed. The computed pressure histories, strain response and residual plastic strain patterns were in reasonably good agreements with experiments. Through detailed analysis of wave-pipe interaction and the propagation of incident and reflected flexural waves along the pipe, it is revealed that the rippling deformation is caused by two factors: 1) Plastic bugling deformation near the end wall due to reflected maximum peak pressure; 2) Interference between incident and reflected flexural waves. An analytical solution predicting the axial locations of the ripples was also derived. The ripple closest the reflecting end can be caused by only the reflected maximum pressure or together with the interference effect, which depends on the specific material parameter and diameter-to-thickness ratio of the pipe. The resulting plastic deformation was severer if the above two factors act together. The conclusions provide insights to this unique phenomenon.

Splitting of dissolving precipitates during plastic shear: A phase field study

Using a phase field model, we have investigated the role of plasticity on the morphological evolution of a precipitate during its diffusion-controlled dissolution, when submitted to shear loading. It is shown that the plastic strain pattern in the matrix strongly influences the local dissolution rate and consequently the final shape of the precipitate. Finally, it is demonstrated that for sufficiently fast and intense shear loadings, plasticity can induce splitting of the precipitate: this process could explain why small precipitates are observed in shear bands in Ti alloys forged parts.

FEA of reinforced concrete beam-column joint with steel fibers for cyclic loading

PurposeSteel fibers reinforced concrete (SFRC) is now widely accepted as a construction material for its added benefits. The proven increases in high shear capacity, toughness, bridging action of fibers and bond improvement from addition of steel fibers into mix design is a field yet to be explored, Therefore, Reinforced Cement Concrete (RCC) beam-column joint with steel fibers was modeled and analyzed for cyclic loading.Design/methodology/approachBeam-column joint is the most critical section of a structure under mixed loading such as that during a seismic episode. Therefore, in this research a reinforced SFRC beam column joint is modeled and analyzed for cyclic earthquake loading with the help of finite element analysis (FEA) software ABAQUS to compare the results with the experimental study.FindingsNonlinear static and nonlinear dynamic analysis are carried out on the SFRC joint for the comparison of simulated results with the experimental analysis.Originality/valueIn this paper, Initially, modeling of SFRC joint was done. Then, the finite element analysis of beam-column joint with steel fibers was carried out. After number of simulations, obtained FEA results were compared with the experimental work on the based on the load vs deflection curve, shear stresses, plastic strain region and plastic strain pattern. After the comparison, it was found that the performance of the numeric model for cyclic loading verified the experimental study, and the results obtained were quite promising.

Localization of plastic deformation in stretching sheets with a crystal plasticity approach: Competition between weakest link and instable mode controlled process

The development of plastic strain localization in a stretching tantalum sheet in the form of necking under dynamic loading conditions was investigated by crystal plasticity simulation in the aim of evaluating the role of phenomena taking place at the scale of the material microstructure. Both equi-biaxial and plane strain stretching have been computed and two grain sizes have been considered. As expected from previous studies at the macroscopic scale, pronounced necking is observed for mean deformations much higher than the one for which a maximum force condition is met.Interestingly, a transition between “Mott-type” fragmentation process and instability-driven necking is observed as a function of the grain size. For large grains (i.e. low number of grains in the sheet thickness) and moderate strain rate, the localization of the plastic strain pattern emerging at the grain scale in the early stages, partly correlated with local slip resistance, seems to play the role of the weakest links in what resembles an obscuration controlled defect interaction process. A pronounced texture may strengthen the role of the local behavior on strain concentration by combining the effects of slip system Schmid factors and self and latent hardening. In contrast, for smaller grains, the memory of the initial strain pattern is much less clear and, for high strain rate, the final neck formation is preceded by the development of strain modulations of larger wavelengths and higher amplitudes than the initial grain-wise heterogeneity. These modulations could be interpreted as unstable perturbation modes of the structure.

Валидация модели упругопластического контакта спироидных передач

The paper considers the problem of analyzing the elastoplastic contact of teeth in a heavy-loaded low-speed multi-pair spiroid gear. This problem is an integral part of the strength analysis that enables forecasting the load-carrying capacity of the product at the initial stage of its development. The relevance of the considered method and algorithm of calculating the load distribution and plastic strain of teeth is emphasized by its increased productive efficiency as compared to the widely used finite element method. The paper considers a common issue of validation of the developed algorithm, i.e. the correspondence of the obtained solution to the results of a real loading process. The main steps of the algorithm are given with account of the multi-pair contact and macro-roughnesses on the contact flanks that are represented as the set of areas (cells). The coordinates of the cell centers are calculated taking account of the factors influencing the load distribution in the spiroid gearing, such as manufacturing and/or assembly errors, surface micro- and macro-roughnesses, and deformations of the gearbox parts. To validate the algorithm, only one dominating factor — the gearwheel surface undulation — is chosen, since all the other factors are negligibly small. The object of the study is a gear in one of the mass-produced multi-turn spiroid gearboxes for pipeline valves. The criteria for the algorithm validation are formulated, namely, the plastic strain value, the area, shape and arrangement of the pattern of the plastic strain. By analyzing the results of numerical and experimental modeling it is possible to draw a conclusion on the validity of the results obtained by means of the studied numerical method of analysis. The divergence of the plastic strain value obtained experimentally and through calculation was under 10%, and the area of the plastic strain pattern was under 10%.

Micromechanical modeling of the effect of phase distribution topology on the plastic behavior of dual-phase steels

In this paper, a topology optimization based numerical method is proposed to investigate the micromechanical plastic behavior of dual-phase (DP) steels. Representative volume elements (RVEs) are constructed using the topology optimization based artificial microstructures. Micromechanical behavior under various loading conditions are predicted for the RVEs to investigate the plasticity, strain localization and strengthening mechanism affected by the microstructural characteristics of DP steels. Plastic strain patterns including shear band are found during the deformation. Due to the twisting movement of martensite grains, the direction of the strain localization bands in the shear loading case is 0° or 90° to the loading direction, while it is 45° in the tensile and compressive cases. Moreover, the effective flow behavior of the material under shear loading is lower than those found in tensile and compressive cases. The influence of various microstructural features, such as, martensite fraction, distribution of each phase, on the effective flow properties and the local strain partitioning has also been identified. Both of the effective flow properties and strain localization exhibit the tendency to be strengthened with the increase of martensite phase fraction. Furthermore, the RVE with more uniform martensite distribution leads to the decrease of effective flow properties and strain localization. Longer martensite-ferrite interface results from the clustering of martensite, which increases the strain localization effect during the plastic deformation.

Effects of grain-to-grain interactions on shear strain localization in Al–Cu–Li rolled sheets

Crystal plasticity finite element simulations of tensile tests on thin polycrystalline samples with grain orientations representative of the microstructure in Al–Cu–Li rolled sheets are carried out to study the influence of grain-to-grain interactions on plastic strain localization. Anisotropic work-hardening and rate-sensitivity of the material behavior are assumed. The grains are modeled as thin platelets in the through-thickness direction, elongated in the rolling and transverse directions. The only distinctive feature of the present simulations with respect to standard crystal plasticity calculations is the enforcement of tangential continuity conditions on the elastic and plastic distortion rates along grain boundaries, which introduces grain-to-grain interactions and renders the simulations nonlocal. Whereas standard crystal plasticity calculations do not predict any significant plastic strain pattern, slanted shear bands spontaneously emerge throughout the sample in the simulations involving tangential continuity, in agreement with experimental observations. Also in agreement with experimental data, shear banding is delayed when the tensile axis shifts from rolling to transverse direction, and the trend to shear banding is enhanced when grain thickness is decreased, particularly in loading along the rolling direction.

A novel artificial dual-phase microstructure generator based on topology optimization

The mechanical properties of dual-phase (DP) steel are mostly derived from its microstructure, e.g., volume fraction, size, distribution and morphology of each constituent phase. An artificial microstructure generator with an enhanced novel phase assignment algorithm based on material topology optimization is proposed to investigate the mechanical properties of DP steel. With this algorithm, phase assignment process is performed on a modified Voronoï tessellation to achieve the targeted representative volume element (RVE) with a good convergence. This method also includes a proper orthogonal decomposition (POD) reduction of flow curves (snapshots) to identify the optimal controlling parameters for DP steel. This numerical method significantly improves the representation of the generated RVE with low computational cost. The proposed method is verified using a DP590 steel which indicates a good agreement with experimental material behavior and RVE predictions based on real microstructures. Predictions of plastic strain patterns including shear bands using the artificial microstructure closely resemble the actual material behavior under similar loading conditions. Robustness of this approach provides a new dimension for RVE development based on artificial microstructure which can effectively be implemented in material characterization.

Formation Of Dislocation Pileup by Frank–Read Source

Dislocation pileups play an important role in the formation and propagation of strain in single crystals and polycrystals. They are the main source of cracking. Dislocation pileups are often referred to as the cause of serrated plastic strain pattern and degradation of the external quantum efficiency of UV LEDs. A dynamic physical model describing the formation of dislocation pileup by Frank–Read source has been presented that allows characterizing not only the structure but also time parameters of pileups. We provide data on the dislocation pile−ups e.g. dislocation configuration in a pileup, number of dislocations in a pile−up as a function of external stress, formation time of new dislocation loops and time to source blocking by the opposite strain generated by pileup dislocations. We compare our experimental results for pileups formed by Frank–Read source with results for pileups of straight edge dislocations. A large calculation effort is required to take into account the interaction of pileup dislocations. To accelerate our calculations we conducted them in parallel runs using a Т−Edge−10 38−nuclei cluster.

Plasticity of Crystals with Disordered Microstructure: Scale-dependent Fluctuations of Stress and Strain

ABSTRACTA generic model of bulk crystal plasticity with stochastic evolution of the local microstructure is formulated. The evolution of local fluctuations of internal stress and plastic strain, as well as the cross correlation between these variables, is investigated for different loading modes (stress control vs. displacement control) as a function of the coarse graining scale, and the spatial structure of the respective correlation functions is determined. The investigations demonstrate that, after an initial transient characterized by uncorrelated initiation of plasticity in different sample locations, nontrivial long range correlations emerge both within the strain pattern and between the internal stress and plastic strain patterns. The internal stresses, on the other hand, remain short range correlated throughout. Implications of our findings for larger-scale plasticity models are discussed.

Finite Element Model for the Behavior of Partially Restrained High Strength Web Angle Connections

This study investigates the behavior of Partially Restrained (PR) connections with high strength steel through the use of Finite Element (FE) modeling. The connection model is such that double web angles are represented by radiused corner section shell elements. The full interaction between the angle and the beam and/or column is simulated by the contact element.The analysis of the moment- rotation relationship and behavior characteristics of the connection with high strength steel are compared and discussed. It is established that the contact elements and strength enhancements of the corner regions employed in this model are important parameters for accurate predictions of Double Web Angle (DWA) connection behavior with cold-formed high strength steel. The proposed connection FE model is capable making highly accurate predictions about the ultimate load capacity and the plastic strain pattern. The model presented provides excellent results for significantly increasing the connection capacity as a result of employing a higher strength steel section. A power model expression was proposed to predict the ultimate moment and initial stiffness of the high strength DWA connection. A reasonable prediction was obtained for high strength PR connection.

응력 -간극수압 연계해석을 이용한 흙막이 굴착시 지하수저하에 따른 지반침하에 관한 연구

본 연구에서는 흙막이 굴착 공사시 지하수저하에 의한 주변 지반의 공학적 거동에 관한 수치해석 연구내용을 다루었다. 먼저 2차원 간극수압-응력 연계해석을 통하여 굴착공사가 지반침하 거동에 미지는 영향을 알아보았으며 그 결과를 토대로 벽체 수평변형, 벽체배변 변형, 소성변형률 분포, 유효응력분포 및 버팀보 축력분포 등을 분석을 수행하였다. 한편 다양한 지층조건과 초기 지하수위 조건에 대한 매개변수 연구를 통하여 주변지반 및 버팀보의 거동을 분석하였으며 해석 결과를 토대로 특정조건의 최대 지반변형범위를 제안하였다. This paper presents the results of a numerical investigation on the behavior of earth retaining wall system with emphasis on the groundwater lowering. Using the 2D stress-pore pressure coupled analysis, the effects of ground excavation and groundwater interaction were examined using wall horizontal deformation, ground surface movement, plastic strain pattern, effective stress distribution and axial stress of strut. In addition, based on the results from a parametric study on a wide range of soil profile and initial ground water table level, the ranges of wall displacement and ground deformation were suggested quantitatively.

Predicted Behaviour of Partially Restrained Connection with Cold Formed High Strength Steel by 3D Finite Element Modelling

Thispaper investigates the behavior prediction of partially restrained (PR) connection with high strength steel bythree-dimensional nonlinear finite-element (FE) analyses. The connectionmodel is such that angle cleats are represented by radiuses corner section shell elements. The full interaction between angle and beam and/or column is simulated by contact element. The analysis results of the moment- rotation relationship and behaviour characteristic of the connection with high strength steel are compared and discussed. It is found that contact element and strength enhancement of the corner regions employed to the model are very important parameters for accurate prediction of PR connection behaviour with cold-formed high strength steel. The moment capacity prediction of top and seat angle connections based on EC3 has been shown to be reasonable compared with FE modeling. Theproposed connection FE model is capable of predicting the ultimate load capacity and the plastic strain pattern with good accuracy. The model presented gives excellent results for increasing the connection capacity significantly due to employed higher strength steel section.

FEM Analysis of Joint Interface Formation in Magnetic Pressure Seam Welding

The magnetic pressure seam welding is one of the candidate methods to join thin sheet smart and multifunctional materials. In this research, to examine the mechanism of magnetic pressure welding from a dynamic viewpoint, numerical simulation of the impact was carried out by using a commercial Euler-Lagrange coupling software MSC.Dytran (MSC.Software) as a first step of the computational studies, where the joint between Fe and Al was employed according to the previous experimental researches. From the serial numerical results, it was found that the increase of temperature at the joint interface was not enough to melt Al or Fe in the range of collision velocity and angle studied in this report. Also, it was revealed that the very large mean stress occurred at the interface which could be considered as the pressure at joint interface and Al moved with high velocity along the interface. Moreover, it was found that there were two patterns of plastic strain distribution near the joint interface depending on the collision velocity and collision angle. Finally, it can be concluded that the plastic strain pattern might be related to the success of magnetic pressure seam welding.

Simulation of meso–macro dynamic behavior using steel as an example

Presented in this paper is a model, where strain hardening and strain rate sensitivity are taken into account. The cellular automata rules are included into a continuum mechanics formulation to describe shear band propagation at the mesoscale. We apply the model in simulating deformation of the 20MnMoNi55 steel as an example. The macro stress–strain behavior and plastic strain patterns at the mesolevel are analyzed in the course of a computational tension test.

Characterizing and Modeling Plastic Strain Inhomogeneity in Thin Metallic Sheets

AbstractUsing a newly developed plastic strain measurement technique based on digital image correlation, surface plastic deformation of polycrystalline aluminum alloys in a thin sheet form has been experimentally characterized at a length scale comparable to that of the thickness of the aluminum sheets but much larger than the average size of individual grains. Both static and dynamic local straining patterns in these aluminum alloys have been observed and these strain patterns can not be simulated using the conventional plasticity models. The texture clustering of grains may contribute to the static local plastic strain patterns detected in an Al-Mg alloy. Two distinctive dynamic straining behaviors resulted from the dynamic strain aging of dislocations due to the alloying elements have been experimentally established for 5XXX and 6XXX alloys, respectively. First observation of dynamic strain inhomogeneity is also made in a sheet metal specimen deforming predominately in a plane strain state.

Photodot investigation of plastic-strain pattern in flat sheet with a hole

The strain pattern was measured, using the photodot method, in a thin flat 24ST-3 aluminum sheet with a central hole, unidirectionally loaded into the plastic region of the material. Test results are presented and the accuracy of the photodot method is discussed.