Fig 6 - uploaded by C. Teodosiu
Content may be subject to copyright.
Left: front view of the hexahedral 3D-mesh of Level 1-domain and schematic illustration of the boundary conditions. All dimensions in mm, the domain thickness is 0.04 mm. Right: zoom over the central necked region of Level 1-domain.
Source publication
In this study, finite element simulations synchronized with in-situ tensile tests have identified microstructural damage models in a 600 MPa grade dual-phase steel with 10% martensite volume fraction. Firstly, in-situ tensile tests have been carried out on a double-notched, flat-plate, tensile specimen. These experiments have shown that the damage...
Context in source publication
Context 1
... mesh of the 3D geometric model used at Level 1 consisted of 5 layers of 8-nodes finite elements, with linear inter- polation and selective reduced integration (59,410 hexahedra, 72,276 nodes, 216,828 degrees of freedom). As shown in Fig. 6, the mesh was rather rough close to the ends of Level 1-domain, while its density in the xy-plane has been sharply increased towards the necked part of the specimen that was subsequently used for merging with the Level 2-domain, thus increasing the precision of the transfer of nodal displacement histories between the two ...
Similar publications
Cold forming processes are very efficient for bulk production. However, the achievable geometries are restricted not only by the process kinematics and tools but also by work hardening. Especially with metastable austenitic steels higher deformation degrees cannot be achieved due to the deformation induced martensitic transformation of austenite wh...
Citations
... The initial yield stress of the coarse-grained specimens decreased and the tensile strength increased relative to that of the original material before coarsening. Table 1 Table 2 A microtensile specimen 30) , as shown in Fig. 2, were used as the tensile test specimen. This test specimen was designed with a centrally located notch (width: 0.2 mm) to ensure that the entire deformation region of the specimen was within the field of view during SEM observations. ...
Martensite-matrix dual-phase (DP) steel is increasingly used for high-strength automobile parts owing to its excellent compatibility, ductility, and tensile strength. However, its higher fracture strain, reflected by the hole expansion ratio, hinders further adoption of this material. Therefore, in this study, we conducted a microscale investigation of the ductile fracture behavior of 1,180-MPa class martensite-matrix DP steel to obtain a guideline for microstructural design and improve fracture strain. In situ tensile test was conducted simultaneously with scanning electron microscopy (SEM) and crystal plasticity finite element analysis (CP-FEA). The in situ tensile test results indicated that microcracks initiated at certain martensite packets, not propagating into other packets. The CP-FEA results revealed that the martensite crystal orientation caused this behavior to induce remarkable stress and strain localization at interfaces within the vicinity of ferrite islands, relaxing the stress and strain localization at distant martensite packets. Although the cracks observed around the ferrite–martensite interfaces were similar to those observed in conventional ferrite-matrix DP steels, such matrix-phase cracks have rarely been reported, except for those immediately before final fracture. Thus, the optimization of the ferrite island distribution to suppress the formation of stress and strain localization sites was identified as the key aspect of martensite-matrix DP steel microstructural design. This design can be achieved using a combination of data science and CP-FEA.
... Commonly, M/F interface damage is expected to originate from the large M/F phase contrast since martensite is regarded as a hard constituent compared to ferrite (e.g. [5][6][7][8]). This understanding, however, is contradicted by recent experimental observations (e.g. ...
... This is in sharp contrast to most literature where the M/F interface damage occurrence has been presumed to be due to a high M/F strain partitioning considering the hard nature of martensite (e.g. [5][6][7][8]). Furthermore, it has been recently demonstrated that martensite can behave in a soft and ductile manner (see e.g. ...
Martensite/ferrite (M/F) interface damage is relevant to failure of many dual-phase (DP) steels, but the underlying microscale mechanisms remain unclear. Through an integrated experimental-numerical study, this work examines the recent hypothesis that (lath) martensite substructure boundary sliding triggers and dominates M/F interface damage initiation accompanied by apparent martensite plasticity. The mesoscale morphology and prior austenite grain reconstruction are used as modelling inputs. A multi-scale framework is adopted to predict the interface damage initiation. The M/F interface damage initiation sites predicted by the model based on a sliding-triggered interface damage mechanism adequately agree with those identified from in-situ experiments, confirming the key role of substructure boundary sliding. Moreover, the M/F interface damage initiation strongly correlates with a low M/F strain partitioning rather than the commonly accepted strong M/F strain partitioning. This fundamental understanding is instrumental for the future optimization of DP steel microstructures.
... For the modelling of void nucleation and growth among ferrite grains, Modified Mohr-Coulomb (MMC) [10] and Gurson-Tvergaard-Needleman (GTN) [13,14] models are used in the literature. Martensite cracking on the other hand, has been modeled with various approaches such as the extended finite element method (XFEM) [14], maximum principal stress criterion [10] and Bao-Wierzbicki failure criterion [15]. Ferrite/ferrite [13] and ferrite/martensite [9,11,16] grain boundary decohesion have been observed by the incorporation of cohesive zone model (CZM). ...
... The parameter identification of the model is performed by the simulation of a tensile specimen to match the experimental data of the martensite phase given in [6] (see e.g. [15]). Obtained model parameters are α=1.54, ...
Having brittle martensitic islands diffused in a ductile ferrite matrix, dual-phase (DP) steels are known for their high formability and favorable material properties. Although they have already proven their advantages in the industry, there are still discussions regarding their microstructure-macroscopic response link. In order to effectively exploit their advantages and analyze their ductility in metal forming operations, the failure mechanisms of DP steels must be well examined following a micromechanics-based approach. There are a number of failure mechanisms to be addressed at the micro scale such as ferrite-martensite and ferrite-ferrite interface decohesion as well as martensite cracking depending on the different microstructural parameters and stress state. A crystal plasticity based finite element framework for RVE calculations is followed here based on the previous work which focuses solely on the plastic deformation (see [1]). Isotropic J2 plasticity model is employed for the hard martensite phase while the rate-dependent crystal plasticity framework is used for the ductile ferrite phase. Cohesive zone elements are inserted at the ferrite-martensite and ferrite-ferrite interfaces for intergranular cracking analysis, besides, intragranular cracking in martensite phase is addressed through an uncoupled damage model. First, a preliminary study was performed in order to identify and calibrate aforementioned failure models, then, various 3D polycrystalline RVEs having different microstructural parameters loaded with different stress triaxialities are analyzed and discussed adding up to the preliminary discussions presented in [2].
... is the equivalent plastic strain to fracture in uniaxial tension and α is the fitting parameter used for large triaxiality values. Matsuno et al. (2015) proposed and verified by experiments that for martensite grains these parameters can be taken as C 1 = 0.02, C 2 = 0.02 and α = 3.0 which will also be used throughout this study. Further, damage accumulation is calculated by considering the following integral: ...
Ferrite-martensite dual-phase (DP) steels have become popular in weight-reduced automotive components due to their straightforward thermomechanical processing and excellent mechanical properties. Even though it has been a popular and productive area of research, there are still many open questions related to their interesting microstructure. Being composed of brittle martensitic clusters dispersed in a ductile ferrite matrix, DP steels benefit from the properties of both phases, which induce interesting failure mechanisms at the same time. The microstructural parameters such as martensite volume fraction, grain size, carbon content, martensite/ferrite morphology, ferrite grain size, and texture, as well as micro and mesoscale segregation, make them difficult to analyze. However these aspects have to be studied in order to link the underlying microstructural influence to macroscopic behaviour. Therefore, the modelling techniques at the microstructure scale should be utilized for physical understanding. In this work, a multi scale modeling strategy is followed for the analysis of plastic deformation and failure in DP steels. A rate-dependent crystal plasticity framework and the isotropic J 2 plasticity model are employed for the simulation of the plastic deformation in ductile ferrite phase and in the hard martensite phase respectively at the RVE scale. Moreover, the intergranular cracking is studied by the incorporation of a cohesive zone model at the ferrite-martensite grain boundaries and the failure in martensite phase is addressed through a ductile failure model. The effect of microstructural parameters on both plastic and fracture behaviour is analyzed under axial loading conditions.
... Despite these experimental evidences demonstrating the complex anisotropic, morphological and crystallographically dependent deformation behavior of lath martensite, these aspects are often neglected in FE modeling of DP steels or martensitic steels. Indeed, martensite phase is generally assumed as an homogeneous phase with either an isotropic elasto-plastic behavior [18][19][20][21][22][23][24][25], or a crystal plasticity behavior similar to bcc ferrite [26][27][28][29] considering the twelve {101}⟨111⟩ and {112}⟨111⟩ slip systems so that it behaves as a hard ferrite. More recent numerical approaches attempt to include the hierarchical nature of lath martensite through the explicit modeling of the block morphology and its crystallography [30][31][32], up to the lath scale [33], but no distinction between in-and out-of-lath slip systems was made. ...
In this study, the effect of different modeling hypotheses for the plastic deformation of lath martensite was investigated through an integrated experimental-numerical approach. The local plastic strain distribution of a dual-phase steel with a coarse microstructure was quantified by high-resolution digital image correlation analysis. The same area was reproduced in a crystal plasticity finite element model using the electron backscatter diffraction measurement of the specimen surface prior deformation. Different modeling hypotheses in terms of in-lath and out-of-lath slip strength as well as boundary and bulk elements were explored. It was found that early plastic deformation in lath martensite grains predominantly took place at various interfaces in the form of slip bands parallel to the in-lath slip planes in blocks exhibiting high in-lath Schmid factor. A comparison between experiment and simulations suggested that assuming a lower strength and hardening rate for in-lath slip systems of boundary elements better reproduced the plastic strain fields in martensite grains. However, the different models showed limited effect on the strain distribution within ferrite grains and on the local stress–strain path at void nucleation sites. This suggested that the main factor affecting early strain concentration and subsequent damage initiation in ferrite grains was the phase morphology and strength contrast.
... 1-6 7, 8 9 10 11 Avramovic-Cingara 9 Kikuzuki 11 Tasan DIC Digital Image Correlation 12 Matsuno 13 FLD: ...
In this study, we investigated the strain-history dependence of ductile fracture behavior in ferrite–pearlite (FP) two-phase steels. The mechanism of this dependence was analyzed using finite element (FE) simulation. The orthogonal strain path changes were subjected to single-phase ferrite steel, two types of FP steels with different pearlite fraction, and single-phase pearlite steel. After the tensile pre-deformation, secondary tensile deformation was applied in the same direction or orthogonal to the first direction. The results showed that the elongation was higher when the secondary deformation was applied in the direction orthogonal to the pre-deformation, compared with that in the no-path change case. The elongation improvement due to the path change was greater with higher pre-deformation and pearlite fraction. The mechanism was investigated by analyzing the localization behavior of plastic deformation in the microstructure via FE simulation using a three-dimensional heterogeneous microstructure model. The simulations showed that the deformation path change in FP steel suppressed local accumulation of damage by changing the strain localization region owing to strength heterogeneity between the two phases.
Fullsize Image
... On the other hand, the Voce law was employed for predicting the flow behaviour of martensite [23], as shown in Eq. (2): where p,m and p,m are the true plastic stress and plastic strain of martensite, o,m is the yield strength of martensite, sat is the saturation threshold stress for deformation at 0 K, C Y is a constant. ...
... There are considerable studies devoted to the elastoplastic models and damage criteria of DP steel sheet consisting ofthe mixed F/M [33,34], but few have addressed the void nucleation and growth of mixed B/M heterogeneous boron steel sheets with varying volume fractions. This work aimed to predict the constitutive equation and ductile damage evolution of quenchable boron steel 22MnB5 with varying volume fractions of martensite and bainite phases, and to consider its microstructure characteristics from the micro-to the macro-scale. ...
Hot stamping components with tailored mechanical properties have excellent safety-related performance in the field of lightweight manufacturing. In this paper, the constitutive relation and damage evolution of bainite, martensite, and mixed bainite/martensite (B/M) phase were studied. Two-dimensional representative volume element (RVE) models were constructed according to microstructure characteristics. The constitutive relations of individual phases were defined based on the dislocation strengthening theory. Results showed that the damage initiation and evolution of martensite and bainite phases can well described by the Lou-Huh damage criterion (DF2015) determined by the hybrid experimental–numerical method. The calibrated damage parameters of each phase were applied to the numerical simulation, followed by the 2D RVE simulations of B/M phase under different stress states. To study the influence of martensite volume fraction (Vm) and distribution of damage evolution, the void nucleation and growth were evaluated by RVEs and verified by scanning electron microscope (SEM). Three types of void nucleation modes under different stress states were experimentally and numerically studied. The results showed that with the increase of Vm and varying martensite distribution, the nucleation location of voids move from bainite to martensite.
... However, the complexity of the microstructure makes it difficult to capture such strain partitioning and damage response. Many numerical and experimental studies have been performed on dual phase steels and some of these studies have combined both numerical and experimental methods in order to study the damage mechanism [37][38][39][40][41][42][43][44][45][46][47][48][49][50]. But there exist only few studies on the damage and strain partitioning phenomena in the complex bainitic microstructures [35,51] such as Continuously Cooled Carbide Free Bainitic Steels (CC-CFBS) (industrially known as B360). ...
... For the former, Abaqus software and for the latter the framework of DAMASK [44] are used. DAMASK provides various constitutive models, of which phenomenological power law (a dislocation-based model) [46,47] is applied in this research. The flow curves of individual phases are calculated by using a dislocation-density-based strain hardening model (section 2.2.2.) and later used to calibrate these material models. ...
Microscopic stress and strain partitioning control the mechanical and damage behavior of multiphase steels. Using a combined numerical and experimental approach, local strain distributions and deformation localization are characterized in a carbide free bainitic steel produced by continuous cooling. The microstructure of the steel consists of bainite (aggregate of bainitic ferrite and thin film retained austenite), martensite and blocky retained austenite.
Numerical simulations were done using a von Mises J2 plasticity flow rule and also a phenomenological crystal plasticity material model. The representative volume element (RVE) was created using a realistic 2D geometry captured through Electron Backscatter Diffraction (EBSD). These simulations describe the strain distribution and deformation localization in this steel. To validate the simulation results, local strain maps were obtained experimentally via in-situ tensile testing using micro digital image correlation (µDIC) in scanning electron microscopy (SEM). The information gained from numerical and experimental data gave valuable insight regarding the microstructural features responsible for strain partitioning and damage initiation in this carbide free bainitic steel. The results of the modelling show that martensite, martensite/bainitic ferrite interfaces, interface orientation with respect to tensile direction, bainitic ferrite size and phase composition influence the strain partitioning in this carbide free bainitic steel.
... Material properties like elastic modulus (E), Poisson's ratio (ν), and flow behavior of the constituent phases are the essential inputs required to execute the nanoindentation simulation. In FE modeling, the same values of E and ν are often considering for different phases for simplicity of modeling and on the basis of common assumption that the deformation of DP steels are homogeneous on macroscopic scale [29][30][31][32][33][34]. For example, E = 200 GPa and ν = 0.3 are taken for ferrite, pearlite and martensite phases in micromechanical modeling by Al-Abbasi et al. [29,30]. ...
This study aims to achieve insight related to the role of various microstructural parameters on nanohardness of different phases in ferrite-martensite (FM), ferrite-bainite (FB) and ferrite-pearlite (FP) steels. Low-carbon microalloyed steel has been subjected to suitable heat treatment schedules to develop FM, FB and FP dual-phase (DP) microstructures with nearly the same amount of ferrite. Macro, micro, and nanohardness values and tensile properties of the developed DP steels have been measured while their microstructures have been characterized. It has been found that the characteristics of hard phase strongly affect the nanohardness of the ferrite phase. Load-depth profiles of diverse phases obtained from the nanoindentation tests have been simulated by the finite element (FE) technique. The dislocation-based model has been modified to estimate the flow behavior of constituent phases which have been provided as input to the FE simulations. The predicted nanoindentation load-depth profiles are found to be in good agreement with the experiment ones. Subsequently, FE simulations have been performed by incorporating the microstructural parameters to predict the nanohardness of individual phases in the developed DP microstructures. Finally, statistical analyses following the Taguchi method and ANOVA have been conducted to demonstrate the influence of different microstructural parameters on nanohardness in various DP steels. It has been revealed that the nanohardness values of constituting phases are significantly influenced by the percentage of carbon and the hardness ratio of two phases in FM, FB and FP DP steels except the pearlite for which the interlamellar spacing is the most contributing factor.
Data availability
The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.
