Crystal Plasticity Finite Element Framework Research Articles

A dislocation density-based crystal plasticity constitutive model: comparison of VPSC effective medium predictions with ρ-CP finite element predictions

This work presents a dislocation density-based crystal plasticity constitutive model for glide kinetics, strengthening and dislocation density evolution, implemented in the effective medium-based visco-plastic self consistent (VPSC) framework and the spatially resolved, ρ-CP crystal plasticity finite element framework. Additionally, a distribution of intragranular stresses is introduced in the VPSC framework, instead of the conventionally used mean value of grain stress for effective medium calculations. The ρ-CP model is first calibrated to predict the mechanical response of a bcc ferritic steel with an initial rolled texture. The same set of constitutive model parameters are then used in VPSC to predict the aggregate stress–strain response and total dislocation densities. For these VPSC simulations, the interaction parameter governing the interaction between the grain and the effective medium in the Eshelby inclusion formalism, and a scalar parameter representative of the distribution of intragranular stresses within a grain, are used to calibrate the VPSC predictions in order to match the predictions of the ρ-CP model. A parametric study is performed to understand the effect of these two parameters on the VPSC predictions. Further, simulations are also performed for a random untextured polycrystal to identify the corresponding VPSC simulation parameters for predicting a similar response as the ρ-CP model. The novelty of the work is in the same set of constitutive models and associated parameters have been implemented in VPSC and ρ-CP to predict similar aggregate stress–strain response and total dislocation densities. This finite element-calibrated effective medium crystal plasticity approach reduces the computational time by at least two orders of magnitude and represents an advance towards the development of multiscale crystal plasticity modeling tools.

Comparison of Linear and Nonlinear Twist Extrusion Processes with Crystal Plasticity Finite Element Analysis.

The mechanical characteristics of polycrystalline metallic materials are influenced significantly by various microstructural parameters, one of which is the grain size. Specifically, the strength and the toughness of polycrystalline metals exhibit enhancement as the grain size is reduced. Applying severe plastic deformations (SPDs) has a noticeable result in obtaining metallic materials with ultrafine-grained (UFG) microstructure. SPD, executed through conventional shaping methods like extrusion, plays a pivotal role in the evolution of the texture, which is closely related to the plastic behavior and ductility. A number of SPD processes have been developed to generate ultrafine-grained materials, each having a different shear deformation mechanism. Among these methods, linear twist extrusion (LTE) presents a non-uniform and non-monotonic form of severe plastic deformation, leading to significant shifts in the microstructure. Prior research demonstrates the capability of the LTE process to yield consistent, weak textures in pre-textured copper. However, limitations in production efficiency and the uneven distribution of grain refinement have curbed the widespread use of LTE in industrial settings. This has facilitated the development of an improved novel method, that surpasses the traditional approach, known as the nonlinear twist extrusion procedure (NLTE). The NLTE method innovatively adjusts the channel design of the mold within the twist section to mitigate strain reversal and the rotational movement of the workpiece, both of which have been identified as shortcomings of twist extrusion. Accurate anticipation of texture changes in SPD processes is essential for mold design and process parameter optimization. The performance of the proposed extrusion technique should still be studied. In this context, here, a single crystal (SC) of copper in billet form, passing through both LTE and NLTE, is analyzed, employing a rate-dependent crystal plasticity finite element (CPFE) framework. CPFE simulations were performed for both LTE and NLTE of SC copper specimens having <100> or <111> directions parallel to the extrusion direction initially. The texture evolution as well as the cross-sectional distribution of the stress and strain is studied in detail, and the performance of both processes is compared.

An energy-CP-combined model for predicting the fatigue life of polycrystalline materials under high cycle and very high cycle fatigue

A fatigue life prediction model in the high to very high cycle fatigue (VHCF) regime of as-received 7075-T6 Al alloy material is proposed. The relative parameters in the life prediction model are obtained by crystal plasticity finite element (CPFE) framework. The modified Ohno-Wang constitutive model is embedded into the CPFE model considering the evolution of back stress during the cyclic loading. In the life prediction model, the range of energy efficiency factors is validated by verifying the plastic strain energy density (PSED) with fatigue experimental data. The fatigue experiments are performed using an ultrasonic fatigue system to validate the fatigue life prediction model. The predicted life is estimated using the maximum and minimum energy efficiency factors, it is found that the life prediction model can accurately predict the VHCF life. It is found that 72.8%–81.3% of the experimental fatigue life can be captured using the proposed model. Moreover, the localized deformation in the grain scale can be well-captured considering the heterogeneity of mechanical properties.

Deformation-Induced Surface Roughening of an Aluminum-Magnesium Alloy: Experimental Characterization and Crystal Plasticity Modeling.

The deformation-induced surface roughening of an Al-Mg alloy is analyzed using a combination of experiments and modeling. A mesoscale oligocrystal of AA5052-O, obtained by recrystallization annealing and subsequent thickness reduction by machining, that contains approx. 40 grains is subjected to uniaxial tension. The specimen contains one layer of grains through the thickness. A laser confocal microscope is used to measure the surface topography of the deformed specimen. A finite element model with realistic (non-columnar) shapes of the grains based on a pair of Electron Back-Scatter Diffraction (EBSD) scans of a given specimen is constructed using a custom-developed shape interpolation procedure. A Crystal Plasticity Finite Element (CPFE) framework is then applied to the voxel model of the tension test of the oligocrystal. The unknown material parameters are determined inversely using an efficient, custom-built optimizer. Predictions of the deformed shape of the specimen, surface topography, evolution of the average roughness with straining and texture evolution are compared to experiments. The model reproduces the averaged features of the problem, while missing some local details. As an additional verification of the CPFE model, the statistics of surface roughening are analyzed by simulating uniaxial tension of an AA5052-O polycrystal and comparing it to experiments. The averaged predictions are found to be in good agreement with the experimentally observed trends. Finally, using the same polycrystalline specimen, texture-morphology relations are discovered, using a symbolic Monte Carlo approach. Simple relations between the Schmid factor and roughness can be inferred purely from the experiments. Novelties of this work include: realistic 3D shapes of the grains; efficient and accurate identification of material parameters instead of manual tuning; a fully analytical Jacobian for the crystal plasticity model with quadratic convergence; novel texture-morphology relations for polycrystal.

A combined experimental and crystal plasticity study of grain size effects in magnesium alloys

This work presents a method to incorporate the micro Hall-Petch equation into the crystal plasticity finite element (CPFE) framework accounting for the microstructural features to understand the coupling between grain size, texture, and loading direction in magnesium alloys. The effect of grain size and texture is accounted for by modifying the slip resistances of individual basal and prismatic systems based on the micro Hall-Petch equation. The modification based on the micro Hall-Petch equation endows every slip system at each microstructural point with a slip system-level grain size and maximum compatibility factor, which are in turn used to modify the slip resistance. While the slip-system level grain size is a measure of the grain size, the maximum compatibility factor encodes the effect of the grain boundary on the slip system resistance modification and is computed based on the Luster-Morris factor. The model is calibrated using experimental stress-strain curves of Mg-4Al samples with three different grain sizes from which the Hall-Petch coefficients are extracted and compared with Hall-Petch coefficients predicted using original parameters from previous work. The predictability of the model is then evaluated for a Mg-4Al sample with different texture and three grain sizes subjected to loading in different directions. The calibrated parameters are then used for some parametric studies to investigate the variation of Hall-Petch slope for different degrees of simulated spread in basal texture, variation of Hall-Petch slope with loading direction relative to basal poles for a microstructure with strong basal texture, and variation of yield strength with change in grain morphology. The proposed approach to incorporate the micro Hall-Petch equation into the CPFE framework provides a foundation to quantitatively model more complicated scenarios of coupling between grain size, texture and loading direction in the plasticity of Mg alloys.

Incorporating dynamic recrystallization into a crystal plasticity model for high-temperature deformation of Ti-6Al-4V

During hot deformation of (α+β) titanium alloys, the simultaneous action of strain and temperature in the (α+β) regime facilitates dynamic recovery, dynamic recrystallization (DRX), and phase transformations via non-equilibrium paths. DRX is manifested in the form of fine recrystallized α or β grains. In the present study, a two-phase crystal plasticity finite element framework (CP-DRX) has been developed which incorporates DRX kinetics into the crystal plasticity (CP) model to predict the flow characteristics of Ti-6Al-4V alloys during thermo-mechanical processing. The CP slip system parameters, as well as elastic properties from both α and β phases of Ti, are calibrated for different strain rate conditions. An EBSD-informed two-phase microstructure representation has been utilized in the CP-DRX framework to explore the time-dependent evolution of DRX microstructure and crystal orientation for different strain rate conditions. The proposed CP-DRX can capture the evolution of crystal orientation and plastic flow stress–strain response of polycrystalline Ti-6Al-4V during the deformation process. Furthermore, the proposed model is able to capture the softening behavior, observed in average stress–strain response from experiments performed using a Gleeble thermomechanical simulator and predict the recrystallization texture.

Crystal plasticity evaluation of the effect of grain morphology on compressive deformation behavior of AA2099 Al–Li alloy

The strip-like grain shape is one of three important factors (the strip-like grain shape, strong crystallographic texture and plate-like T1 precipitate) influencing the mechanical properties of the third-generation Al–Li alloys. However, studies on its effect have seldom been investigated to date. In the present study, an extended crystal plasticity finite element (CPFE) framework considering the strain gradient effect via incorporating the geometrically necessary dislocation (GND) density is constructed to investigate the compressive deformation behavior of studied AA2099 Al–Li alloy with strip-like grain shape. Good consistency with respect to the true stress-strain curve and texture characteristics between experimental and predicted results confirms the validity of constructed CPFE framework, as well as these fitted material parameters. Simulation results show the occurrence of aggregation for GND density not only near grain boundaries but also at grain interiors, which benefits in blocking the motion of the statistically stored dislocation (SSD) and the occurrence of obvious stress concentration in the constructed polycrystalline model. This demonstrates that the strip-like grain shape could exsert a nonnegligible influence on the mechanical response of studied AA2099 Al–Li alloy. Moreover, the difference between the predicted orientation distribution functions (ODFs) and the difference about the evolution of accumulative shear strain in 12 slip modes collectedly confirm that the strip-like grain shape does exert some influence on slip activities of studied AA2099 Al–Li alloy.

Crystal plasticity analysis of fatigue-creep behavior at cooling holes in single crystal Nickel based gas turbine blade components

We build a crystal plasticity finite element framework to investigate slip localisation and fatigue-creep behaviour at the cooling holes of single crystal Nickel (Ni) based components under cyclic thermomechanical loading. The total slip rate is decomposed into a thermally activated dislocation glide rate which dominates at moderate/low temperatures (T) and/or high stresses, and a climb rate which dominates at high temperatures and increases as inelastic strain accumulates. This formulation captures the monotonic and long-term creep response of Ni alloys in the wide range 20 <T < 1100 °C and indicates that room temperature plasticity during unloading increases the high temperature creep rate during loading (creep dwell), eventually increasing the total slip accumulation per cycle; the effect depends on the way the inelastic strain accumulates upon successive slip reversals. Elastic material anisotropy is shown to modify drastically the stress concentration around holes such that slip tends to localise at locations where the max principal stress, tangent to the hole surface, aligns with stiff crystallographic directions. This highlights the importance of plastic and creep anisotropy and creates new avenues for optimising hole shape to minimise slip activity. Our study brings to light key material-component relationships that concern the wider material science, high temperature and fatigue communities.

Predicting residual stress in a 316L electron beam weld joint incorporating plastic properties derived from a crystal plasticity finite element model

Electron beam welding is an advanced joining technique which induces narrow weld region with minimal heat affected zone and weld-induced distortion. This reduces residual stresses in the joints which can be detrimental to structural performance of components in safety critical industries. Being an autogenous process, electron- beam welding generates a highly textured, columnar microstructure in the weld zone which have distinct properties when compared to the parent material region. Determining mechanical properties of the weld material assists in accurate assessment of the joint. However, extracting weld material specimens to determine plastic properties becomes increasingly cumbersome in thinner weld joints. An alternate approach has been demonstrated in this work wherein mechanical properties were derived using the weld microstructure in a crystal plasticity finite element (CPFE) framework. The initial calibration of the CPFE parameters was done using experimental data from thick weldment. These calibrated values were used to obtain the elastic and elastic-plastic properties of thinner weld materials by deforming corresponding synthetic microstructures whose attributes were determined by Electron Backscatter Diffraction analysis. The resultant properties were incorporated in a finite element (FE) based weld simulation to determine the residual strain. These results were compared with the residual strain data obtained using X-ray diffraction and good agreement was observed.

Crystal plasticity evaluation of laser peening effects on improving high-cycle fatigue life of Al-Li friction stir welded joints

The strengthening mechanisms behind surface modification processes must be evaluated to optimize surface treatment methods. This study developed a physics-based crystal plasticity finite element framework to evaluate multiple-laser-peening impacts on enhancing the high-cycle fatigue properties of AA2195-T6 friction stir welded joints. For this purpose, different contributions of laser peening effects were quantified on the variations of fatigue indicator parameters in the joint region. Extreme-value fatigue indicator parameters evaluated the laser peening effects in decreasing the driving force for fatigue crack initiation at near-surface grain boundaries. Moreover, grain-average fatigue indicator parameters investigated the fatigue property modification trends with depth. Experimental high-cycle fatigue tests were applied to validate the related modeling outputs. According to the crystal plasticity model, the improvement in joint near-surface fatigue properties majorly stemmed from cyclic mean stress alleviation under laser-peening-induced compressive residual stresses. This effect was followed by the increased resistance against cyclic plastic deformation under the growth in dislocation density and crystallographic texture intensity and the reduction in texture heterogeneity under the crystal morphology homogenization effects after laser peening. Fatigue tests revealed the enhancement in the joint fatigue life under the relocation of fatigue crack initiation regions to depth after LP and validated the numerical approaches.

A convolutional neural network based crystal plasticity finite element framework to predict localised deformation in metals

Convolutional neural networks (CNNs) find vast applications in the field of image processing. This study utilises the CNNs in conjunction with the crystal plasticity finite element method (CPFEM). This research presents a framework that enables CNNs to make rapid and high-fidelity predictions for materials under uniaxial tension loading. The inputs to the CNN model are material hardening parameters (initial hardness and initial hardening modulus), a global tensile strain value, and microstructure with a varying number of grains, grain size, grain morphology and texture. This input selection allows performing simulations for a wide range of materials, as defined by microstructure and flow curves. The outputs of the CNN are the local stress and strain values. The proposed framework involves the following stages: feature engineering, generation of synthetic microstructures, CPFEM simulations, data extraction and preprocessing, CNN design and selection, CNN training, and validation of the trained network. The trained CNN was successfully demonstrated to predict local stress and strain evolution for the completely new dataset (test set) containing synthesised microstructures. The test set predictions were evaluated, and the median, worst, and best predictions were presented and discussed. Overall, the CNN demonstrated excellent agreement with CPFEM simulations, thus validating its accuracy. Then, the CNN was applied to predict the stress and strain evolution for AA5754 and AA6061 microstructures obtained using electron backscatter diffraction. These two microstructures were entirely new for the CNN and displayed size and grain morphology different from the synthesised microstructures. For both microstructures, the obtained stress and strain evolution predictions demonstrated excellent agreement with CPFEM simulations, thus confirming the flexibility of the trained CNN model. Then, the framework was extended to predict strain localisation and was evaluated on an AA6061 microstructure. The results presented in this research demonstrate a clear computational advantage of CNN without loss of accuracy. Finally, the research offers prospects for future advances.

Revealing the effects of concomitant grain coarsening and refinement on the internal variable evolution and mechanical properties of gradient nanostructured nickel

The outstanding mechanical properties of gradient nanostructured (GNS) metals and alloys such as a superior combination of strength and ductility can be attributed to two important deformation mechanisms: hetero-deformation induced (HDI) strengthening and strain hardening, as well as grain growth. Recent experimental evidence indicates that GNS Ni specimens undergo concomitant grain coarsening and refinement during tensile deformation. Nevertheless, how such grain growth behaviors affect the evolution and distribution of their internal variables such as dislocation density and HDI hardening, and how such effects are manifested in their mechanical properties, are still unknown. Therefore, this work strives to answer these questions by incorporating a modified strain gradient plasticity formulation taking into account the saturation of geometrically necessary dislocations (GND) accumulation due to the dynamic equilibrium between dislocation source formation and deactivation into a crystal plasticity finite element framework, in conjunction with two other models accounting for the evolution of statistically stored dislocations (SSD) and HDI stress, respectively, to explore the effects of grain coarsening and refinement on the internal variable evolution and mechanical properties of GNS Ni specimens with different grain size gradients under deformation. It is revealed that SSD density increases throughout the samples as a result of reduced dynamic recovery in the fine grains induced by grain coarsening as well as enhanced dislocation storage in the coarse grains due to their refinement. In contrast, grain coarsening and refinement leads to a decrease in GND density and HDI stress in the fine grains and an increase in the coarse grains as a result of the corresponding changes in strain gradient intensity. Last but not least, the overall effect of grain growth on the mechanical behaviors of GNS Ni is the outcome of the synergy and competition between its individual effects on the Hall-Petch strengthening, forest dislocation hardening and HDI hardening, respectively, and the different grain size gradients of the GNS Ni specimens give rise to the opposite variations in their mechanical behaviors with respect to grain growth.

Multi-Scale Crystal Plasticity Model of Creep Responses in Nickel-Based Superalloys.

The current study focuses on the modeling of two-phase - nickel-based superalloys, utilizing multi-scale approaches to simulate and predict the creep behaviors through crystal plasticity finite element (CPFE) platforms. The multi-scale framework links two distinct levels of the spatial spectrum, namely, sub-grain and homogenized scales, capturing the complexity of the system responses as a function of a tractable set of geometric and physical parameters. The model considers two dominant features of morphology and composition. The morphology is simulated using three parameters describing the average size, volume fraction, and shape. The sub-grain level is expressed by a size-dependent, dislocation density-based constitutive model in the CPFE framework with the explicit depiction of - morphology as the building block of the homogenized scale. The homogenized scale is developed as an activation energy-based crystal plasticity model reflecting intrinsic composition and morphology effects. The model incorporates the functional configuration of the constitutive parameters characterized over the sub-grain - microstructural morphology. The developed homogenized model significantly expedites the computational processes due to the nature of the parameterized representation of the dominant factors while retains reliable accuracy. Anti-Phase Boundary (APB) shearing and, glide-climb dislocation mechanisms are incorporated in the constitutive model which will become active based on the energies associated with the dislocations. The homogenized constitutive model addresses the thermo-mechanical behavior of nickel-based superalloys for an extensive temperature domain and encompasses orientation dependence as well as the loading condition of tension-compression asymmetry aspects. The model is validated for diverse compositions, temperatures, and orientations based on previously reported data of single crystalline nickel-based superalloy.

Study of grain boundary orientation gradients through combined experiments and strain gradient crystal plasticity modeling

A combined experimental and strain gradient crystal plasticity framework is presented for studying the development of orientation and misorientation gradients at the grain boundaries during plastic deformation. The regions in the vicinity of prior-deformation grain boundaries experience localized plastic deformation and are referred to as Near Boundary Gradient Zones (NBGZs). Deformed microstructures of an aluminum–magnesium (Al–6wt.% Mg) alloy are studied using Electron Back Scattered Diffraction (EBSD) during progressive tensile deformation. Orientation and misorientation gradients at the prior-deformation grain boundaries are quantified on grain pairs with different combinations of crystallographic orientations. Realistic virtual microstructures are then simulated using a strain gradient crystal plasticity finite element framework to study the evolution of local misorientations, stresses and strains and their correlation with the underlying substructure. The simulated microstructures indicate that the average profiles of the Geometrically Necessary Dislocation (GND) density correlates with the local misorientation, while the average profiles of the Statistically Stored Dislocation (SSD) density correlates with the effective plastic strain in these NBGZs. The combined experimental and modeling analysis reveals that the width (mean with deviation) of the distribution of the length of NBGZs, normalized by the grain size, scales with the initial grain-average Schmid factor. Further, our results also suggest a possibly strong correlation between the length of the NBGZ and the grain size.

Modeling crystal plasticity with an enhanced twinning–detwinning model to simulate cyclic behavior of AZ31B magnesium alloy at various temperatures

In this study, a multiscale model within crystal plasticity finite element (CPFE) framework was developed to predict the cyclic loading behaviors of a wrought magnesium alloy, AZ31B, at various testing temperatures. The temperature dependency was systematically modeled by employing a modified strain-hardening model, implemented in the CPFE. The developed model was further extended to cyclic loading scenarios, under which abnormal mechanical responses were observed, using an enhanced twinning–detwinning model based on the well-known predominant twinning reorientation scheme. For the first time, the concept of variable residual twin fraction was introduced in the twinning–detwinning model as a criterion for the inactivation of detwinning. The newly developed model was employed to predict the mechanical responses under monotonic in-plane tension and compression at testing temperatures ranging from room temperature to 200°C. In addition, the mechanical behaviors of the alloy under cyclic loadings at these testing temperatures were also predicted using the CPFE model. These predictions were then compared with the experimentally measured data. The micromechanical responses, such as the evolution of twin volume fraction and activation of slip/twin/detwin systems, under various loading and temperature conditions were also predicted and compared with the reported data.

Dislocation-based crystal plasticity modelling of a nickel-based superalloy under dwell-fatigue: From life prediction to residual life assessment

In this work, a dislocation-based crystal plasticity finite element (CPFE) framework was implemented to investigate the effects of loading conditions on dwell-fatigue crack initiation life. Experimentally, a large number of strain-controlled dwell-fatigue tests were carried out at 650 °C in a nickel-based superalloy. The combinations of CPFE simulations and post-test examinations were used to reveal the dwell-fatigue crack initiation mechanisms. Then, a life prediction approach was presented on the basis of accumulated energy dissipation at half-life cycle. Good agreement between the experimental and simulated lives verifies the robustness as well as the accuracy of the present approach. Finally, a new three-dimensional (3-D) damage tolerance diagram was proposed by introducing a CP-based physical parameter to describe the degradation levels and evaluate the residual dwell-fatigue life.

Modeling and numerical investigation of mechanical twinning in β-HMX crystals subjected to shock loading

This manuscript establishes a crystal plasticity finite element (CPFE) model with large volumetric deformation for β-HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane) energetic crystals with emphasis on the deformation twinning behavior under shock loading conditions. The CPFE model captures the nonlinear response of the monoclinic crystal through the application of large volumetric change under shock condition, dislocation slip at low and high moving speeds and mechanical twinning idealized by the twin volume fraction evolution. The twinning behavior is distinguished from dislocation slip through the decomposition of the plastic velocity gradient in which dislocation slip, twinning and slip in the twinned region are separately considered. Third-order Birch Murnaghan EOS is incorporated in the CPFE framework to describe the volumetric deformation under extreme pressure induced by explosion or impact. The results of the numerical investigations show that the twinning behavior exhibits strong orientation dependency, which becomes more evident at higher loading regime. Particle shape significantly affects the twin concentration. Peak twin volume fraction in HMX polycrystalline with regularized particle shapes is lower compared with mesostructure with realistic particle morphologies.

Examining deformation localization of irradiated tungsten under uniaxial compression with crystal plasticity

In this work, the deformation behavior of irradiated tungsten at elevated service temperatures is examined using mechanism-based crystal plasticity finite element framework by considering multiple mechanisms, including thermal softening and irradiation hardening. The previously developed mechanism-based crystal plasticity model is first utilized to assess the yield stress of unirradiated and irradiated tungsten upon low-temperature irradiation. The engineering stress-strain response under uniaxial compression is then predicted by considering the effect of irradiation-induced defect clusters on the motion of deformation-induced dislocations, and the predicted results agree well with the experimental measurements. More importantly, the formation and evolution of plastic strain localization zones in the form of shear bands are qualitatively captured, and the maximal principal strain distribution is quantitatively linked to the dose of irradiation damage. Finally, the deformation-induced shear band as a result of plastic instability in the compressed tungsten specimen is discussed.

Crystal plasticity modeling of non-Schmid yield behavior: from Ni3Al single crystals to Ni-based superalloys

A crystal plasticity finite element (CPFE) framework is proposed for modeling the non-Schmid yield behavior of L12 type Ni3Al crystals and Ni-based superalloys. This framework relies on the estimation of the non-Schmid model parameters directly from the orientation- and temperature-dependent experimental yield stress data. The inelastic deformation model for Ni3Al crystals is extended to the precipitate (γ′) phase of Ni-based superalloys in a homogenized dislocation density based crystal plasticity framework. The framework is used to simulate the orientation- and temperature-dependent yield of Ni3Al crystals and single crystal Ni-based superalloy, CMSX-4, in the temperature range 260–1304 K. Model predictions of the yield stress are in general agreement with experiments. Model predictions are also made regarding the tension–compression asymmetry and the dominant slip mechanism at yield over the standard stereographic triangle at various temperatures for both these materials. These predictions provide valuable insights regarding the underlying (orientation- and temperature-dependent) slip mechanisms at yield. In this regard, the non-Schmid model may also serve as a standalone analytical model for predicting the yield stress, the tension–compression asymmetry and the underlying slip mechanism at yield as a function of orientation and temperature.

Influence of microstructural features on the yield strength of Ti–6Al–4V: a numerical study by using the crystal plasticity finite element method

In this paper, a numerical study was presented on the influence of microstructural features on the yield strength of bimodal α–β Ti–6Al–4V. Tensile tests and microscopic observations were conducted to provide experimental data of yield strength and microstructure characterization. Sets of representative volume elements were generated using characterization data collected from electron back-scattered diffraction. To investigate the sensitivity of macroscopic yield strength to the morphology of the microstructure, the geometrical parameters such as sizes of equiaxed α grains and lamellar colonies, lamellar widths, volume fractions of equiaxed α grains and Burgers orientation relationship, were studied systematically in a series of simulations. The simulations used crystal plasticity finite element framework to model the deformation behavior of the generated virtual samples under tensile loading condition. Yield strength trends as functions of investigated microstructural features were examined. Moreover, inspection of local deformation of individual equiaxed α grain and lamellar colonies provided an insight into the microstructure-properties relations.