| 1. |
- Croné, Philip, et al.
(författare)
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Analytical prediction of yield stress and strain hardening in a strain gradient plasticity material reinforced by small elastic particles
- 2022
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Ingår i: International journal of plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 151, s. 103200-103200
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Tidskriftsartikel (refereegranskat)abstract
- The influence on macroscopic work hardening of small, spherical, elastic particles dispersedwithin a matrix is studied using an isotropic strain gradient plasticity framework. An analyticalsolution for strain hardening, i.e. the flow stress as a function of plastic strain, based ona recently developed model for initial yield strength is proposed. The model accounts forrandom variations in particle size and elastic properties, and is numerically validated againstFE solutions in 2D/3D unit cell models. Excellent agreement is found as long as the typicalparticle radius is much smaller than the material length scale, given that the particle volumefraction is not too large (< 10%) and that the particle/matrix elastic mismatch is within arealistic range. Finally, the model is augmented to account for strengthening contribution from shearable particles using classic line tension models and successfully calibrated againstexperimental tensile data on an ?? − 2.8??%?? − 0.16??%?? alloy.
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| 2. |
- Cui, Luqing, et al.
(författare)
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Dependence of microstructures on fatigue performance of polycrystals : A comparative study of conventional and additively manufactured 316L stainless steel
- 2022
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Ingår i: International journal of plasticity. - : Elsevier. - 0749-6419 .- 1879-2154. ; 149
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Tidskriftsartikel (refereegranskat)abstract
- The fatigue properties and microstructural evolution of 316 L stainless steel (316LSS) manufactured by laser powder bed fusion (L-PBF) were systematically studied and compared with its wrought counterpart. The as-built L-PBF 316LSS shows a pronounced heterogeneity, not only structurally but also chemically, with a unique microstructure of highly serrated grain boundaries, bimodal grain structure, nano-precipitates, solidification cell structures, and chemical segregations. The microindentation test showed that the hardness of the as-built L-PBF 316LSS reached 2.589 GPa, which was about 1.6 times higher than that of the wrought solution annealed counterpart, and the sparser slip steps around indentations revealed its greater dislocation storage capability. The S-N curves indicated that the fatigue resistance of the as-built L-PBF 316LSS was significantly better than that of the wrought solution annealed samples, and this was ascribed to its unique microstructural characteristics, especially the pre-existing high-density dislocations and chemical microsegregation within cellular solidification features. Furthermore, the enhanced planar slip in L-PBF 316LSS by its unique microstructure, especially the formation of deformation twins, delays the strain localization and restrains slip band generation, thereby significantly inhibiting crack initiation, and contributing greatly to the fatigue performance. The unique cell structure appears to be more effective in improving the low-cycle fatigue performance of L-PBF 316LSS due to the enhanced ductility.
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| 3. |
- Cui, Luqing, et al.
(författare)
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New insights into the anisotropic ductility of additively manufactured Inconel 718
- 2023
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Ingår i: International journal of plasticity. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0749-6419 .- 1879-2154. ; 169
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Tidskriftsartikel (refereegranskat)abstract
- Anisotropic ductility in additively manufactured (AM) alloys, namely better ductility along the building direction (BD) has been extensively studied and traditionally attributed to the crystallographic texture. However, recent studies have shown significant ductility anisotropy in weakly or non-textured AM alloys, indicating that other factors may also play critical roles. To explore this, AM Inconel 718 with weak crystallographic texture was selected as the model material, and the in-situ high-energy X-ray diffraction tests together with multiscale microstructural characterization techniques were performed to explore the deformation micromechanisms. The results of this study, for the first time, revealed that the better ductility in the vertical specimen (loading parallel to BD) was partially due to the negative stress triaxiality factor (TF) of the {220} grains during plastic deformation, which results in the shrinkage or even healing of the microvoids. Furthermore, the & delta;-phase alignment in conjunction with grain boundary orientation were also proved to have a pronounced impact on the anisotropic ductility of AM alloys. On the other hand, though in the overall weak-textured microstructure, the proportion of 101 grains were marginally over other grains. Thus, the positive effect of {220} grains on ductility was stronger than the negative effect of {200} and {311} grains, contributing to the excellent failure elongation exceeding 12% for both samples. The findings of this study shed new light on the mechanisms underlying the anisotropic ductility of AM alloys and provide insight into strategies for enhancing their performance.
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| 4. |
- Deng, Dunyong, 1989-, et al.
(författare)
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High Temperature Mechanical Integrity of Selective Laser Melted Alloy 718 Evaluated by Slow Strain Rate Tests
- 2021
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Ingår i: International journal of plasticity. - : Elsevier. - 0749-6419 .- 1879-2154. ; 140
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Tidskriftsartikel (refereegranskat)abstract
- Strain rate dependent deformation behaviours of selective laser melted Alloy 718 (IN718) are systematically studied at 550 and 650 °C by slow strain rate testing, with a forged counterpart as a reference. Selective laser melted IN718 shows significant susceptibility to intergranular cavitation, resulting in ductility degradation with decreasing strain rate. Detailed fractography and cross section inspections are employed to identify the damage mechanisms. Creep rates are also estimated and compared with the conventional counterparts. The possible critical factors for the inferiority of time dependent damage resistance of selective laser melted IN718 are discussed.
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| 5. |
- Fischer, Tim, et al.
(författare)
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Relating stress/strain heterogeneity to lath martensite strength by experiments and dislocation density-based crystal plasticity
- 2024
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Ingår i: International journal of plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 174
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Tidskriftsartikel (refereegranskat)abstract
- To enhance the fundamental understanding for micromechanical lath martensite deformation, the microstructure as well as macro- and microscopic tensile properties of as -quenched 15-5 PH stainless steel are systematically analysed depending on the austenitisation temperature. Based on electron backscatter diffraction (EBSD) and backscattered electron (BSE) analysis, it is noted that the martensite morphology alters from a less defined to a more clearly defined parallel arrangement of the block and lath structure with increasing temperature. For an indepth quantification of the hierarchical boundary strengthening contributions in relation to local stress/strain heterogeneity, separate high-fidelity virtual microstructures are realised for the different scales (prior austenite grains, packets and blocks). This is consistent with the materials transformation process. The virtual microstructures are simulated employing the crystal plasticity finite element method (CPFEM) adapted for handling high dislocation density and encompassing all relevant strengthening mechanisms by boundaries, dislocations and solute atoms. While accurately capturing the measured size -dependent stress-strain behaviour, the simulations reveal in line with the experiments (Hall-Petch) that blocks are the most effective dislocation motion barrier, causing increased strain hardening and stress/strain heterogeneity. Furthermore, since strain localisation is predicted strongest in the distinct block structure, the experimentally observed early plastic material yielding is thought to be favoured here.
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| 6. |
- Lindström, Thomas, et al.
(författare)
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Constitutive model of an additively manufactured ductile nickel-based superalloy undergoing cyclic plasticity
- 2020
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Ingår i: International journal of plasticity. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0749-6419 .- 1879-2154. ; 132
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a transversely isotropic elasto-plastic model based on the multilinear Ohno-Wang model was developed to simulate the cyclic behaviour of an additively manufactured ductile nickel-based superalloy. The transverse isotropy was taken into account by the incorporation of a structural tensor in the modelling framework. To calibrate the model, a number of uniaxial isothermal low-cycle fatigue tests were carried out on smooth specimens manufactured in three different orientations with respect to the building platform. The test specimens were subjected to different strain ranges and load ratios, as well as four different temperatures, namely room temperature, 400 degrees C, 500 degrees C and 600 degrees C. By using a cycle jumping procedure, where the material properties are changed from virgin parameters to mid-life parameters, the mid-life behaviour, commonly used for fatigue life predictions, of the concerned material could be simulated with good agreements to the performed experiments. To validate the results, the maximum and minimum stress, as well as the plastic strain range and hysteresis area from the simulated mid-life hysteresis loops were compared to the values obtained from the experiments.
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| 7. |
- Subasic, Mustafa, et al.
(författare)
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Experimental investigation and numerical modelling of the cyclic plasticity and fatigue behavior of additively manufactured 316 L stainless steel
- 2024
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Ingår i: International Journal of Plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 176
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Tidskriftsartikel (refereegranskat)abstract
- This study addresses the critical need for a constitutive model to analyze the cyclic plasticity of additively manufactured 316L stainless steel. The anisotropic behavior at both room temperature and 300 °C is investigated experimentally based on cyclic hysteresis loops performed in different orientations with respect to the build direction. A comprehensive constitutive model is proposed, that integrates the Armstrong-Frederick nonlinear kinematic hardening, Voce nonlinear isotropic hardening and Hill's anisotropic yield criterion within a 3D return mapping algorithm. The model was calibrated to specimens in the 0° and 90° orientations and validated with specimens in the 45° orientation. A single set of hardening parameters successfully represented the elastoplastic response for all orientations at room temperature. The algorithm effectively captured the full cyclic hysteresis loops, including historical effects observed in experimental tests. A consistent trend of reduced hardening was observed at elevated temperature, while the 45° specimen orientation consistently exhibited the highest degree of strain hardening. The applicability of the model was demonstrated by computing energy dissipation for stabilized hysteresis loops, which was combined with fatigue tests to propose an energy-based fatigue life prediction model.
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| 8. |
- Wang, Bochao, et al.
(författare)
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A visco-elastic-plastic constitutive model of isotropic magneto-sensitive rubber with amplitude, frequency and magnetic dependency
- 2020
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Ingår i: International journal of plasticity. - : Elsevier. - 0749-6419 .- 1879-2154. ; 132
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Tidskriftsartikel (refereegranskat)abstract
- A three-dimensional visco-elastic-plastic constitutive model of isotropic magneto-sensitive (MS) rubber with amplitude, frequency and magnetic dependency under a continuum constitutive framework is developed. MS rubber is akind of smart material mainly composed of a rubber matrix and magnetizable particles. Under a magnetic field, there is an increase of its dynamic modulus due to the interaction between the magnetic field and MS rubber, which is often referred to as the magnetic dependency of MS rubber. Experimental results reveal that besides the magnetic dependency, there is a frequency and amplitude dependency of its dynamic modulus. In specific, the modulus of MS rubber increases with increasing frequency and dereases with increasing strain amplitude. To depict the above properties and to consider the balance of energy in continuum mechanics framework, a new constitutive model consisting of a viscoelastic fractional derivative element, a bounding surface model in series with a neo-Hookean elastic model with magnetic sensitivity and a magnetic stress tensor term for MS rubber is proposed. The contribution of this constitutive model is that by using a free energy based method, with only eight material parameters, the amplitude, frequency and magnetic dependency of MS rubber can be reflected. After parameter identification, the simulationresults show a good agreement with those of measurements. Therefore, by utilizing the model proposed, the ability of approaching the dynamic behavior of MS rubber-based vibration reduction devices in the design phase is possible which contributes to the application of MS rubber in noise and vibration reduction area.
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| 9. |
- Wang, Bochao, et al.
(författare)
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Modelling the influence of magnetic fields to the viscoelastic behaviour of soft magnetorheological elastomers under finite strains
- 2023
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Ingår i: International journal of plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 164
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Tidskriftsartikel (refereegranskat)abstract
- Isotropic soft magneto-rheological elastomers (s-MRE) are polymer-based composites where magnetically soft particles are randomly distributed in the elastomer matrix. Under a magnetic field, a strong modulus magnetic stiffening effect and a magnetostriction performance is exhibited for isotropic s-MRE, offering a wide application potential in vibration control, soft robotics and haptic displays. In the last decades, substantial theoretical work has focused on modelling the magnetostriction behaviour of isotropic s-MRE. Modelling the influence of magnetic fields to the viscoelastic behaviour of isotropic s-MRE has received less attention, despite the magnetic-dependent viscoelasticity is an essential component of the observed magneto-mechanical response and of great importance for the application of isotropic s-MRE. To predict the magneto-mechanical coupling behaviour accurately and provide guidance for the design of isotropic s-MRE-based applications, a multiplicatively-typed magneto-hyperelastic free energy and a new type of process-dependent viscosity evolution law is proposed in this work. Afterwards, the ability of the model to predict the modulus magnetic stiffening effect and magnetic-dependent nonlinear viscoelastic behaviour of isotropic s-MRE is examined. Finally, three sets of finite element case studies are presented to illustrate the feasibility of the model-based simulation and guide the design of isotropic s-MRE-related applications.
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| 10. |
- Wei, Daixiu, et al.
(författare)
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Si-addition contributes to overcoming the strength-ductility trade-off in high-entropy alloys
- 2022
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Ingår i: International journal of plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 159
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Tidskriftsartikel (refereegranskat)abstract
- Face-centered cubic single-phase high-entropy alloys (HEAs) containing multi-principal transition metals have attracted significant attention, exhibiting an unprecedented combination of strength and ductility owing to their low stacking fault energy (SFE) and large misfit parameter that creates severe local lattice distortion. Increasing both strength and ductility further is challenging. In the present study, we demonstrate via meticulous experiments that the CoCrFeNi HEA with the addition of the substitutional metalloid Si can retain a single-phase FCC structure while its yield strength (up to 65%), ultimate strength (up to 34%), and ductility (up to 15%) are simultaneously increased, owing to a synthetical effect of the enhanced solid solution strengthening and a reduced SFE. The dislocation behaviors and plastic deformation mechanisms were tuned by the addition of Si, which improves the strain hardening and tensile ductility. The present study provides new strategies for enhancing HEA performance by targeted metalloid additions.
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| 11. |
- Xu, W. W., et al.
(författare)
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Atomic origins of the plastic deformation micro-mechanisms of ?/?? : FeCoNiAlTi high-entropy alloys
- 2022
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Ingår i: International journal of plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 158, s. 103439-
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Tidskriftsartikel (refereegranskat)abstract
- The gamma/gamma' FeCoNiAlTi high-entropy alloys (HEAs) break the strength-ductility trade-off and possess an excellent combination of strength and ductility. However, lack of atomic-level understanding of plastic deformation behaviors restricts the exploration of full capacities of the FeCoNiAlTi HEAs. By computing the generalized stacking fault energies (GSFEs) of the gamma and gamma' phases, the relationships between planar stacking faults and work-hardening capacities, and the effect of chemical concentration and grain orientation on the deformation mechanisms were explored in depth for the FeCoNiAlTi HEAs. Our results demonstrate that the multicomponent nature lowers the GSFEs of the matrix but enhances those of the precipitate to achieve the strength-ductility balance of the HEA. An active factor (epsilon) defined as gamma isf/gamma apb (gamma isf: intrinsic stacking fault energy, gamma apb: anti-phase boundary energy) was introduced to bridge activation of microbands (MBs) and planar stacking faults in the gamma/gamma' alloys. Tuning a suitable low epsilon around 0.2 is an efficient strategy for acquiring the extended MBs-induced plasticity. Analyzing the individual/synergetic contribution of the principal elements to the GSFEs-related properties, we find that increasing the amount of Co and Ti promotes the strength-ductility balance and facilitates the MB activation by altering the GSFEs of both gamma and gamma'. Based on our comprehensive analysis, it is concluded that raising the Co/Fe ratio or lowing the Al/Ti ratio benefits the achievement of the desired mechanical properties of the FeCoNiAlTi HEA.
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