Numerical Assessment of the Role of Slip and Twinning in Magnesium Alloy AZ31B During Loading Path Reversal PDF Download
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 12
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Book Description
Magnesium alloy AZ31B plastically deforms via twinning and slip. Corresponding to the unidirectional nature of twinning, the activity of twinning/detwinning is directly related to loading history and materials texture. Using the elastic viscoplastic self-consistent model implementing with the twinning and detwinning model (EVPSC-TDT), we revisited experimental data of AZ31B sheets under four different strain paths: (1) tension-compression-tension along rolling direction, (2) tension-compression-tension along transverse direction, (3) compression-tension-compression along rolling direction, and (4) compression-tension-compression along transverse direction, and identified the dominant deformation mechanisms with respect to the strain path. We captured plastic deformation behaviors observed in experiments and quantitatively interpreted experimental observations in terms of the activities of different deformation mechanisms and the evolution of texture. It is found that the in-plane pre-tension has slight effect on the subsequent deformation, and the pre-compression and the reverse tension after compression have significant effect on the subsequent deformation. The inelastic behavior under compressive unloading is found to be insignificant at a small strain level but pronounced at a large strain level. Lastly, such significant effect is mainly ascribed to the activity of twinning and detwinning.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 12
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Book Description
Magnesium alloy AZ31B plastically deforms via twinning and slip. Corresponding to the unidirectional nature of twinning, the activity of twinning/detwinning is directly related to loading history and materials texture. Using the elastic viscoplastic self-consistent model implementing with the twinning and detwinning model (EVPSC-TDT), we revisited experimental data of AZ31B sheets under four different strain paths: (1) tension-compression-tension along rolling direction, (2) tension-compression-tension along transverse direction, (3) compression-tension-compression along rolling direction, and (4) compression-tension-compression along transverse direction, and identified the dominant deformation mechanisms with respect to the strain path. We captured plastic deformation behaviors observed in experiments and quantitatively interpreted experimental observations in terms of the activities of different deformation mechanisms and the evolution of texture. It is found that the in-plane pre-tension has slight effect on the subsequent deformation, and the pre-compression and the reverse tension after compression have significant effect on the subsequent deformation. The inelastic behavior under compressive unloading is found to be insignificant at a small strain level but pronounced at a large strain level. Lastly, such significant effect is mainly ascribed to the activity of twinning and detwinning.
Author: Ashutosh Jain
Publisher: LAP Lambert Academic Publishing
ISBN: 9783843376013
Category :
Languages : en
Pages : 156
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Book Description
The role of twinning in the anisotropic behavior and ductility of magnesium alloys is analyzed at ambient as well as elevated temperatures. Magnesium alloy AZ31B sheet is investigated as a model system, because it is the most common wrought magnesium alloy. Uniaxial compression tests are conducted at room temperature and at elevated temperatures to measure the anisotropy of the strength and strain at various strain levels.A viscoplastic self-consistent polycrystal modeling approach was used to model the deformation behavior; including the anisotropy and texture evolution. Temperature dependence of parameters affecting activity of different deformation modes, such as Critical Resolved Shear Stress (CRSS) and strain hardening, and the volume fraction of twinned grains are investigated with the help of the polycrystal plasticity model.The model, thus developed, could find application for predicting material s response in complex loading conditions.
Author: Waqas Muhammad
Publisher:
ISBN:
Category :
Languages : en
Pages : 71
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Book Description
Finite element (FE) simulations are widely used in automotive design processes to model the forming behavior of sheet metals. Comprehensive material characterization and the availability of suitable constitutive models are prerequisites for accurate modeling of these forming operations. In the current research, monotonic tension, compression and large strain compression-tension-compression (CTC) and tension-compression-tension (TCT) experiments have been performed to characterize the mechanical behavior of AZ31B and ZEK100 magnesium sheets at room temperature. A digital image correlation system is used to measure the surface strains during monotonic tension and compression testing. The data is later processed to calculate the evolution of r-values with plastic deformation. Texture measurements of the annealed materials and fractography of deformed specimens under monotonic tension and compression are also performed. The results of mechanical testing are discussed in light of the crystallographic texture and deformation mechanisms such as slip, twinning and untwinning. It is observed that annealed AZ31B sheet has a strong basal texture where the majority of crystallographic c-axes are aligned in the sheet normal (ND) direction whereas the annealed ZEK100 sheet exhibits a comparatively weak basal texture, with significant basal pole spreading in sheet transverse direction (TD). The AZ31B sheet specimens exhibit higher in-plane flow stresses and lower ductility as compared to ZEK100 sheet specimens. The tension-compression yield asymmetry is found to be more pronounced in AZ31B sheet as compared to ZEK100 sheet. In addition to this, the ZEK100 sheet specimens exhibit a strong in-plane orientation dependency of flow stress when subjected to uniaxial tension. Furthermore, a significantly greater evolution of plastic anisotropy (r-values) is observed for AZ31B sheet specimens as compared to ZEK100 sheet specimens. Moreover, the unusual S-shaped hardening behavior is observed during reverse tension following previous compression portions of CTC and TCT flow curves of AZ31B and ZEK100 sheets. A constitutive model is proposed to capture the evolving asymmetric/anisotropic hardening response of magnesium alloys considering both monotonic and reverse loading paths. The hardening behaviour of magnesium alloys is classified into three deformation modes (i.e. Monotonic Loading [ML], Reverse Compression [RT], and Reverse Tension [RT]). A multi-yield surface modeling approach is used where a CPB06 type anisotropic yield surface is assigned to each deformation mode. For each deformation mode, the yielding criterion is modified to capture the evolution of subsequent yield loci with accumulated plastic deformation. A strain rate independent elasto-plastic formulation is used to implement the proposed constitutive model as a UMAT in LS-DYNA. The predictions of the model are compared against the experimental monotonic and cyclic (CTC and TCT) flow stresses of AZ31B and ZEK100 sheets along different test directions. An excellent agreement is found between the simulated and experimental results.
Author: Ali Asghar Roostaei
Publisher:
ISBN:
Category : Anisotropy
Languages : en
Pages : 188
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Book Description
Reducing fuel consumption and, thereby, greenhouse gas pollution has been the main thrust of lightweighting endeavours by transportation industries, particularly, automotive sector. Wrought magnesium alloys, being the lightest engineering alloys, are potential candidates for manufacturing automobile components. That said, more critical testing is still required to assess their mechanical and structural attributes toward new product development for a broad range of applications. Anisotropic fatigue and cyclic behaviour of AM30 Mg alloy extrusion is investigated by performing fully-reversed strain-controlled tension-compression cyclic tests at strain amplitudes between 0.3% and 2.3%, along extrusion (ED) and transverse (TD) directions. The shapes of half-life hysteresis loops suggest the predominance of slip and twinning/de-twinning mechanisms below and above the strain amplitude of 0.5%, respectively. The twinning/de-twinning occurrence is found to be more extensive during straining along ED, which results in higher asymmetry of hysteresis loops, and thereby, higher induced mean stress. This adversely affects the fatigue resistance and yields lower number of cycles before failure in ED. Optical microscopy and texture analysis are employed to validate the findings. In addition, fracture surfaces are studied by scanning electron microscopy to identify the sources of fatigue crack initiation. Persistent slip bands (PSBs) and twin lamellae interfaces are evidenced as crack initiation sites at low and high strain amplitudes, respectively. Cracks emanated from debonded inclusion interface are also observed. Lastly, estimated fatigue life by the Smith-Watson-Topper (SWT) and Jahed-Varvani (JV) fatigue models are compared with experimental life obtained through this study as well as the ones reported in the literature. The JV energy model is proven to yield better life predictions. Moreover, multiaxial fatigue characteristics of AM30 Mg alloy extrusion are studied through fully-reversed strain-controlled cyclic experiments including pure torsional and combined axial-torsional at 0, 45 and 90° phase angle shifts. Under pure torsional cyclic loading, AM30 extrusion is realized to exhibit better fatigue properties than AZ31B and AZ61A extrusions, especially in low-cycle fatigue regime. Under proportional axial-torsional cyclic loading, twinning/de-twinning in axial mode results in asymmetric shear hysteresis loop. The effect of non-proportionality of biaxial loading on various aspects of material response is also examined and observed to be depending on the magnitude of axial strain amplitude. Finally, the life prediction capabilities of two critical plane models, i.e., modified SWT and Fatemi-Socie (FS), as well as JV energy-based approach are assessed, employing fatigue life data of AM30 extrusion. Correlation data between experimental and estimated lives are found to lie within narrow scatter band. Basal-textured wrought magnesium alloys are inherently prone to mechanical twinning/de-twinning during cyclic deformation at room temperature. They, subsequently, exhibit distinctive flow curve attributes, which are impossible to describe using conventional plasticity models. A purely phenomenological plasticity model is herein proposed, in such way that accounts for various asymmetric/anisotropic aspects of cyclic flow response of wrought magnesium alloys. The proposed model entails an isotropic von Mises yield function which evolves in stress space according to a new generalized anisotropic kinematic hardening rule, based on Ziegler's rule. The phenomenological concept of plastic moduli matrix introduced in the kinematic rule is viewed as the key factor in representing material yield/hardening behaviour in different directions. The components of this matrix can independently be calibrated by conducting uniaxial experiments along each direction. An efficient and stable numerical algorithm is developed and then coded into both MATLAB®, and user material subroutine (UMAT) to use within Abaqus®/Standard finite element software. Thereafter, model validation has been successfully done using two different types of experiments: proportional and non-proportional biaxial axial-torsional cyclic tests on AZ31B, AZ61A, and AM30 Mg alloy extrusions, and notched plate tensile loading-unloading test on AM30 extrusion.
Author: J. Brian Jordon
Publisher: Springer Nature
ISBN: 3030366472
Category : Technology & Engineering
Languages : en
Pages : 400
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Book Description
The Magnesium Technology Symposium, the event on which this collection is based, is one of the largest yearly gatherings of magnesium specialists in the world. Papers represent all aspects of the field, ranging from primary production to applications to recycling. Moreover, papers explore everything from basic research findings to industrialization. Magnesium Technology 2020 covers a broad spectrum of current topics, including alloys and their properties; cast products and processing; wrought products and processing; forming, joining, and machining; corrosion and surface finishing; and structural applications. In addition, there is coverage of new and emerging applications.
Author: Marta Majkut
Publisher:
ISBN:
Category :
Languages : en
Pages : 344
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Book Description
Crystals with a hexagonal close-packed crystal structure are inherently anisotropic, and have a limited number of independent slip systems, which lead to strong deformation textures and reduced formability in polycrystalline products. In magnesium (Mg), all of the easy slip systems have a Burgers vector in the a direction making twinning necessary for arbitrary shape changes. The most common twinning system which allows extension along the c-axis is {10-12}10-11. A good predictor of slip is the global Schmid factor, which resolves the externally applied force onto the slip plane and direction of a crystal. The critically resolved shear stress (CRSS) at which a grain twins is not readily measured by experiment and the CRSS for twin initiation often appears larger than for twin propagation. In polycrystals, twin variants with both low and high Schmid factors have been observed indicating that this Schmid factor is inappropriate to predict twinning and more local effects play an important, though still uncertain role. In this work, experiments were devised to dynamically study extension twinning in a polycrystalline Mg alloy AZ31B with a strong basal rolling texture by tensile deformation parallel to the plate normal. Three-dimensional X-ray diffraction using a synchrotron source was used to map the centre-of-mass positions, orientations, and grain-resolved elastic strain tensors of over 1000 grains in-situ up to a true strain of 1.4%. The majority of twins formed in grains with a high local Schmid factor; however, low-ranked twin variants were common. The average grain-resolved stress did not always select the highest twin variant and resulted in some negative Schmid factors. The internal stress state of parent grains and twinned grains did not differ significantly within the large measurement uncertainties. The misorientations between grains ideally oriented for twinning and their nearest neighbours could not explain cases of no twin activity. Results suggest that the controlling factors for twin formation are much more local and not captured within the spatial resolution of the technique. Complimentary measurement of the strain rate sensitivity during twinning, by instantaneous strain rate change tests, suggest that basal slip is a part of this local process.
Author: Franz Roters
Publisher: John Wiley & Sons
ISBN: 3527642099
Category : Technology & Engineering
Languages : en
Pages : 188
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Book Description
Written by the leading experts in computational materials science, this handy reference concisely reviews the most important aspects of plasticity modeling: constitutive laws, phase transformations, texture methods, continuum approaches and damage mechanisms. As a result, it provides the knowledge needed to avoid failures in critical systems udner mechanical load. With its various application examples to micro- and macrostructure mechanics, this is an invaluable resource for mechanical engineers as well as for researchers wanting to improve on this method and extend its outreach.
Author: Amanda J. Levinson
Publisher:
ISBN:
Category : Materials science
Languages : en
Pages : 380
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Book Description
The quasi-static mechanical response of annealed, highly textured AZ31 rolled plate was measured in simple compression on two sample directions, each promoting a different twin family. A high plastic anisotropy with extreme strain hardening in both directions was observed. New insights on the influence of both twin types to this behavior were derived by correlating changes in the strain hardening rates with the microstructure evolution. Extension twins nucleated at low strains, grew to consume most of the structure, and saturated at strains below the peak hardening rates. Thin contraction twins were initially postulated to be responsible for the peak hardening rates by limiting the hard pyramidal c+a slip length (producing a Hall-Petch type strengthening). However, subsequent experimental investigations raised questions on whether these are not present at the spacing required to account for the peak hardening rate. Thus, neither twin family was deemed responsible for the peak strain hardening rates. The effect of grain size on deformation twinning during strain hardening was also investigated by producing a similarly textured AZ31 plate with a larger grain size. A lower twinning stress was confirmed in this material. An additional change in strain hardening rate was associated with the nucleation of secondary extension twins forming perpendicular to the primary twin, limiting the growth potential of the pre-existing twins. The microstructure evolution during isothermal static annealing was investigated to critically evaluate the contributions of extension and contraction twins to the recrystallized microstructure after room temperature deformation, and establish the potential of these twins to alter the recrystallized texture. Contraction twins were potent sites for recrystallized nuclei producing many favorably oriented orientations for reduction of the strong c-axis fiber texture; while extension twins were not very effective in recrystallization. Recovery before the onset of recrystallization was extensive when the c-axis in most grains was compressed. Incomplete recrystallization within the hardest grains was deemed responsible for the retention of the c-axis fiber texture. These new insights were employed to identify the benefits of laser-roller hemming versus conventional hemming. Hemming is an automotive processing operation used to join inner and outer body panels involving severe forming and design requirements.
Author: Ashutosh Jain
Publisher:
ISBN:
Category :
Languages : en
Pages : 278
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Book Description
Author: Guozheng Kang
Publisher: John Wiley & Sons
ISBN: 1119180805
Category : Technology & Engineering
Languages : en
Pages : 320
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Book Description
New contributions to the cyclic plasticity of engineering materials Written by leading experts in the field, this book provides an authoritative and comprehensive introduction to cyclic plasticity of metals, polymers, composites and shape memory alloys. Each chapter is devoted to fundamentals of cyclic plasticity or to one of the major classes of materials, thereby providing a wide coverage of the field. The book deals with experimental observations on metals, composites, polymers and shape memory alloys, and the corresponding cyclic plasticity models for metals, polymers, particle reinforced metal matrix composites and shape memory alloys. Also, the thermo-mechanical coupled cyclic plasticity models are discussed for metals and shape memory alloys. Key features: Provides a comprehensive introduction to cyclic plasticity Presents Macroscopic and microscopic observations on the ratchetting of different materials Establishes cyclic plasticity constitutive models for different materials. Analysis of cyclic plasticity in engineering structures. This book is an important reference for students, practicing engineers and researchers who study cyclic plasticity in the areas of mechanical, civil, nuclear, and aerospace engineering as well as materials science.
