scholarly journals A microstructure model for viscoelastic–thixotropic fluids

2020 ◽  
Vol 32 (12) ◽  
pp. 123106
Author(s):  
K. Le-Cao ◽  
N. Phan-Thien ◽  
N. Mai-Duy ◽  
S. K. Ooi ◽  
A. C. Lee ◽  
...  
Keyword(s):  
Microstructure Model

scholarly journals A novel physics-based and data-supported microstructure model for part-scale simulation of laser powder bed fusion of Ti-6Al-4V

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Jonas Nitzler ◽  
Christoph Meier ◽  
Kei W. Müller ◽  
Wolfgang A. Wall ◽  
N. E. Hodge
Keyword(s):  
Selective Laser Melting ◽  
Microstructure Evolution ◽  
Powder Bed Fusion ◽  
Laser Powder Bed Fusion ◽  
Laser Melting ◽  
Cooling Rates ◽  
Powder Bed ◽  
Proposed Model ◽  
Microstructure Model ◽  
Transformation Diagrams

AbstractThe elasto-plastic material behavior, material strength and failure modes of metals fabricated by additive manufacturing technologies are significantly determined by the underlying process-specific microstructure evolution. In this work a novel physics-based and data-supported phenomenological microstructure model for Ti-6Al-4V is proposed that is suitable for the part-scale simulation of laser powder bed fusion processes. The model predicts spatially homogenized phase fractions of the most relevant microstructural species, namely the stable $$\beta $$ β -phase, the stable $$\alpha _{\text {s}}$$ α s -phase as well as the metastable Martensite $$\alpha _{\text {m}}$$ α m -phase, in a physically consistent manner. In particular, the modeled microstructure evolution, in form of diffusion-based and non-diffusional transformations, is a pure consequence of energy and mobility competitions among the different species, without the need for heuristic transformation criteria as often applied in existing models. The mathematically consistent formulation of the evolution equations in rate form renders the model suitable for the practically relevant scenario of temperature- or time-dependent diffusion coefficients, arbitrary temperature profiles, and multiple coexisting phases. Due to its physically motivated foundation, the proposed model requires only a minimal number of free parameters, which are determined in an inverse identification process considering a broad experimental data basis in form of time-temperature transformation diagrams. Subsequently, the predictive ability of the model is demonstrated by means of continuous cooling transformation diagrams, showing that experimentally observed characteristics such as critical cooling rates emerge naturally from the proposed microstructure model, instead of being enforced as heuristic transformation criteria. Eventually, the proposed model is exploited to predict the microstructure evolution for a realistic selective laser melting application scenario and for the cooling/quenching process of a Ti-6Al-4V cube of practically relevant size. Numerical results confirm experimental observations that Martensite is the dominating microstructure species in regimes of high cooling rates, e.g., due to highly localized heat sources or in near-surface domains, while a proper manipulation of the temperature field, e.g., by preheating the base-plate in selective laser melting, can suppress the formation of this metastable phase.

A stochastic microstructure model for particle reinforced aluminium matrix composites

2018 ◽  
Vol 273 (2) ◽  
pp. 115-126 ◽  
Author(s):  
K. LOSCH ◽  
S. SCHUFF ◽  
F. BALLE ◽  
T. BECK ◽  
C. REDENBACH
Keyword(s):  
Aluminium Matrix ◽  
Matrix Composites ◽  
Aluminium Matrix Composites ◽  
Microstructure Model

Ballistic penetration of conically cylindrical steel projectile into 3D orthogonal woven composite: a finite element study at microstructure level

2010 ◽  
Vol 45 (9) ◽  
pp. 965-987 ◽  
Author(s):  
Xiwen Jia ◽  
Baozhong Sun ◽  
Bohong Gu
Keyword(s):  
Finite Element ◽  
Impact Damage ◽  
Woven Composite ◽  
Strain Wave ◽  
Microstructure Model ◽  
Wave Distribution ◽  
Cylindrical Steel ◽  
3D Orthogonal Woven ◽  
The Impact ◽  
Ballistic Penetration

Ballistic penetration of conically cylindrical steel projectile into 3D orthogonal woven composite (3DOWC) was investigated from finite element analyses and ballistic impact tests. Based on the observation of the microstructure of the 3DOWC, a microstructure model was established for finite element calculation. In this model, the cross-section of warp, weft and Z-direction fiber tows was regarded as rectangular. The noninterwoven warp and weft yarns were bonded together with Z-yarns. The impact damage and energy absorption of the 3DOWC penetrated by a conically cylindrical steel projectile were calculated from the microstructure model and compared with the testing results. Good agreements with experiments have been observed, especially for deformation, damage evolution, and strain wave distribution in the 3DOWC under ballistic penetration.

Evaluation Methods of Line Profiles

2014 ◽  
pp. 171-211
Keyword(s):  
Fourier Transforms ◽  
Qualitative Assessment ◽  
Peak Width ◽  
Line Profiles ◽  
Line Broadening ◽  
Evaluation Procedures ◽  
Fitting Procedures ◽  
Microstructure Model ◽  
Diffraction Peaks

The evaluation procedures of X-ray line profiles are overviewed in this chapter. These methods can be classified into four groups, namely (1) the most simple methods that evaluate only the breadths of diffraction peaks, (2) procedures using the Fourier-transforms of line profiles for the determination of the parameters of microstructures, (3) variance methods evaluating the restricted moments of peaks, and (4) procedures fitting the whole diffraction pattern. The crystallite size distribution and the densities of lattice defects cannot be determined from the peak width alone as the rule of summation of breadths of size, strain, and instrumental profiles depends on their shape. However, the breadth methods can be used for a qualitative assessment of the main origins of line broadening (size, dislocations, planar faults) (e.g. for checking the model of microstructure used in whole powder pattern fitting procedures). The application of Fourier and variance methods is limited if the diffraction peaks are overlapping. In the case of pattern fitting procedures, usually a microstructure model is needed for the calculation of the theoretical fitting functions. The reliability of these methods increases with increasing the number of fitted peaks.

A Microstructure Model from Conventional Diffusion MRI of Meningiomas: Impact of Noise and Error Minimization

2021 ◽  
pp. 25-35
Author(s):  
Letizia Morelli ◽  
Giulia Buizza ◽  
Chiara Paganelli ◽  
Giulia Riva ◽  
Giulia Fontana ◽  
...  
Keyword(s):  
Diffusion Mri ◽  
Error Minimization ◽  
Microstructure Model

THE STUDY OF HIGH DIELECTRIC CONSTANT MECHANISM OF La-DOPED Ba0.67Sr0.33TiO3 CERAMICS

2018 ◽  
Vol 25 (02) ◽  
pp. 1850056
Author(s):  
JING XU ◽  
BO HE ◽  
HAN XING LIU
Keyword(s):  
Dielectric Constant ◽  
Rare Earth ◽  
High Dielectric Constant ◽  
Temperature Stability ◽  
Current Voltage ◽  
Microstructure Model ◽  
Bst Ceramics ◽  
High Dielectric ◽  
Rare Earth La ◽  
La Doped

It is a common and effective method to enhance the dielectric properties of BST ceramics by adding rare-earth elements. In this paper, it is important to analyze the cause of the high dielectric constant behavior of La-doped BST ceramics. The results show that proper rare earth La dopant ([Formula: see text]) may greatly increase the dielectric constant of BST ceramics, and also improve the temperature stability, evidently. According to the current–voltage ([Formula: see text]–[Formula: see text]) characteristics, the proper La-doped BST ceramics may reach the better semiconductivity, with the decrease and increase in La doping, the ceramics are insulators. By using the Schottky barrier model and electric microstructure model to find the surface or grain boundary potential barrier height, the width of the depletion layer and grain size do play an important role in impacting the dielectric constant.

An integrated hot rolling and microstructure model for dual-phase steels

2014 ◽  
Vol 22 (4) ◽  
pp. 045005 ◽  
Author(s):  
D Bombac ◽  
M J Peet ◽  
S Zenitani ◽  
S Kimura ◽  
T Kurimura ◽  
...  
Keyword(s):  
Hot Rolling ◽  
Dual Phase ◽  
Dual Phase Steels ◽  
Microstructure Model

A Study on Microstructural Parameters for the Characterization of Granular Porous Ceramics Using a Combination of Stochastic and Mechanical Modeling

2017 ◽  
Vol 09 (05) ◽  
pp. 1750069 ◽  
Author(s):  
Matthias Kulosa ◽  
Matthias Neumann ◽  
Martin Boeff ◽  
Gerd Gaiselmann ◽  
Volker Schmidt ◽  
...  
Keyword(s):  
Coordination Number ◽  
Elastic Properties ◽  
Three Dimensional ◽  
Porous Ceramics ◽  
Average Coordination Number ◽  
Mechanical Modeling ◽  
Element Analysis ◽  
Coordination Numbers ◽  
Microstructural Parameters ◽  
Microstructure Model

To correlate the mechanical properties of granular porous materials with their microstructure, typically porosity is being considered as the dominant parameter. In this work, we suggest the average coordination number, i.e., the average number of connections that each grain of the porous material has to its neighboring grains, as additional — and possibly even more fundamental — microstructural parameter. In this work, a combination of stochastic and mechanical modeling is applied to study microstructural influences on the elastic properties of porous ceramics. This is accomplished by generating quasi-two-dimensional (2D) and fully three-dimensional (3D) representative volume elements (RVEs) with tailored microstructural features by a parametric stochastic microstructure model. In the next step, the elastic properties of the RVEs are characterized by finite element analysis. The results reveal that the average coordination number exhibits a very strong correlation with the Young’s modulus of the material in both 2D and 3D RVEs. Moreover, it is seen that quasi-2D RVEs with the same average coordination number, but largely different porosities, only differ very slightly in their elastic properties such that the correlation is almost unique. This finding is substantiated and discussed in terms of the load distribution in microstructures with different porosities and average coordination numbers.

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