Influence of material anisotropy on void coalescence by necking for face-centered cubic single crystals

This paper presents the coalescence of microvoids embedded in an anisotropic copper single crystal using a micromechanics approach. Crystal plasticity framework was used to account for the anisotropy arising from the orientation and slip. A full 3D representative volume element (RVE) with void was considered to circumvent spurious loading. The constant load path parameters were enforced on the RVE using multi-point constraints. Various loading conditions that lead to necking were studied. The key finding from the present study is the interplay of the load path parameters (triaxiality and Lode parameter), material anisotropy, and initial void volume fraction on the void coalescence. It is noticed that at high triaxiality, the ductile failure mechanism is dominated by the necking mechanism, and at medium to low triaxiality, the ductile failure mode is a combination of shearing and necking mechanisms. It was observed that non-homogenous crystallographic slip manifests the material anisotropic effects in void cell RVE across various crystallographic orientations. The crystal orientation [110] exhibited higher shearing than the orientation [100] and [111]. Further, material anisotropy significantly affected void morphology but not the void coalescence strains at high triaxial values

Effect of Wall Flexibility on the Deformation during Flow in a Stenosed Coronary Artery

The effect of varying wall flexibility on the deformation of an artery during steady and pulsatile flow of blood is investigated. The artery geometry is recreated from patient-derived data for a stenosed left coronary artery. Blood flow in the artery is modeled using power-law fluid. The fluid-structure interaction of blood flow on artery wall is simulated using ANSYS 16.2, and the resulting wall deformation is documented. A comparison of wall deformation using flexibility models like Rigid, Linear Elastic, Neo-hookean, Mooney-Rivlin and Holzapfel are obtained for steady flow in the artery. The maximum wall deformation in coronary flow conditions predicted by the Holzapfel model is only around 50% that predicted by the Neo-Hookean model. The flow-induced deformations reported here for patient-derived stenosed coronary artery with physiologically accurate model are the first of its kind. These results help immensely in the planning of angioplasty

Investigation of Single Fiber Composite residual strength pre and post fragmentation: Using Progressive Damage Analysis and HFGMC framework

Single fiber composites (SFC) provides an insight of damage behavior in the fiber reinforced polymer (FRP). Study of stress redistribution after the fiber breakage in the SFC reveals the development of different damage modes that occur in FRPs. Two separate analysis are presented in the current work. The first one being the effective property calculation of multi fiber composite and the second is the analysis of the fiber breakage in the SFC under tensile loading in the direction of the fiber. Analysis of multi fiber composite is carried out using the representative volume element of SFC (SFCRVE) with periodic boundary conditions. High Fidelity Generalized Method of Cells (HFGMC) has been used for the stress analysis to capture the influence of the length scales in both SFC-RVE and SFC fiber fragmentation test. Progressive damage in the SFC-RVE is detected using the MultiContinuum Theory (MCT). The choice of MCT to detect damage is purely based on the convenience to obtain the single damage metric in the SFC-RVE analysis. In order to detect the damage of fiber in SFC with fiber fragmentation test, a maximum stress criterion is employed. Further, the use of sudden material property degradation rule is common to both SFC-RVE and SFC fiber fragmentation test. It assists in degrading the property of damaged subcells. Above three steps constitutes the progressive damage analysis (PDA) and it is performed numerically in the FORTRAN language. The analysis of the SFC-RVE determines the average properties of the multi-fiber composite. In the result of SFC fiber fragmentation test, the evolution of matrix crack, fiber-matrix interface failure, stress redistribution around the fiber failure is discussed. Realizing stress interactions along the fiber-matrix interface provides and insight of load transfer from the matrix to the fiber. The effect of fiber fragment length on the strength of fiber is also presented

Additive friction stir processing and hybrid metal additive manufacturing of high melting point materials: A review

Ever since the beginning of 4th industrial revolution, metal additive manufacturing has revolutionized the paradigm of printing high melting point materials. In this context, this paper reviews experimental and computational aspects of friction stir processing and hybrid techniques applied for metal additive manufacturing of high melting point materials like steel, and titanium alloys. Initially, friction stir processing working principle has been discussed. Secondly, friction stir processing is compared with other severe plastic deformation techniques and summarized their advantages, disadvantages and applications in a tabular form. Then based on the state-of-the-art of literature, additive friction stir processing and hybrid metal additive manufacturing processes are discussed for high melting point materials and results have been presented with respect to their microstructural developments, mechanical behavior, etc. Finally, gaps are highlighted for high melting point materials that shows importance of selecting process parameters, tooling capacity, computational analysis, mathematical modelling, etc., and presented these as future scope of work

Theoretical and Experimental Characterization of Surface Cracks in FGM and Anisotropic Thin Films

Fracture toughness of Barium Titanate thin film investigated. The deposition of BTO thin film is done with pulsed laser deposition technique. The fracture toughness of BTO thin film determined with an indirect method of micro-indentation [1]. The experimental results are validated with the analytical solution of the surface crack on the anisotropic thin films [2]. The stress intensity factor variation and dependency on the non-homogeneity parameter of the material is shown in the present study

Effect of substitutional and vacancy defects on the electrical and mechanical properties of 2D-hexagonal boron nitride

Defects in the nanoscale are common in the 2D materials irrespective of the fabricated method. Material performance gets significantly affected due to the presence of defects in 2D materials. In the present study, electronic and mechanical properties of 2D-hexagonal boron nitride (hBN) are investigated. At the electronic scale, the formation energies, band structures were obtained for pristine and defected hBN. The substitutional defects of carbon (C-at-NS, C-at-BS) and oxygen (O-at-NS, O-at-BS) at boron and nitrogen sites, single vacancy defects (BV, NV) and triangular vacancies (3B + N)v and (3N + B)v of boron and nitrogen, and Stone-Thrower-Wales (STW) type-1 and type-2 defects were considered. We found that with the inclusion of defects in 2D-hBN, the bandgap decreases, and carbon substitution at the boron site produces n-type characteristics, whereas substitution of carbon at the nitrogen site produces p-type characteristics. Boron vacancies increased the p-type character. At the atomistic scale, stiffness, ultimate tensile strength, and fracture strain were simulated for the pristine and defected hBN with molecular dynamics (MD) simulations using Tersoff potential. We found that the vacancy defects dominated by Boron atoms are energetically favorable and shift the electric conductivity from insulating to conducting. The stiffness and ultimate tensile strain of the 2D-hBN in the zigzag direction are higher than that of armchair direction. A strength reduction of around ~ 50% is observed with a defect concentration of 2.1%. It is observed that pristine and defective 2D-hBN is stronger in ZZ than AC configuration. [Figure not available: see fulltext.]

Interface delamination in stepped lap repaired CFRP panel under tensile loading

The thin adhesive layer between the parent structure and the patch in adhesive bonding is the weakest link where interface delamination occurs. This interface delamination exhibits a mixed mode in nature due to the orthotropic behavior of composite and stepped con�guration of joint. For analysis of mixed-mode interface delamination in the single stepped scarf joint, Benzeggagh-Kenane model[1] has used. Under static loading, the result shows that the corners of the steps are in the high-stress concentration zone. And the delamination starts from the tip of the step in a symmetric manner (from the �rst and the last step) and then propagates to the middle of the joint. The tensile strength, peel stress, and shear stress distribution were investigated numerically concerning parameters such as some steps, scarf angle change on varying step length and step height and the adhesive bond line thickness. The results show that on increasing the number of steps and scarf angle by changing step length, the tensile strength of joint increases. And note the signi�cant e�ect on the tensile strength with varying step height and bond line thickness. So better design of the stepped lap joint in the composite structure increases the performance of the joint

Computational Modeling of Growth with and without discontinuities in the biological structure

Growth problems come under open system thermodynamics. The open system thermodynamics developed by Ellen Kulh et al. is used. Bone growth and healing with and without discontinuity are studied. A crack block element is introduced to discrete mesh geometry to capture the stress singularity at the crack,. Influence of stress singularity near the crack tip is currently being investigated

Friction Stir Processing on Two Overlapping (side by side) Metal Beads of Wire Arc Additive Manufacturing

The Wire Arc Additive Manufacturing(WAAM) is the best method for manufacturing large metal additive parts due to its high deposition rates, less buy to fly ratio, low production costs and the ability to produce parts of large build volume. However, like any other process, the WAAM process too has got its own drawbacks/limitations. The localized heat input in a particular direction in this WAAM process for that matter in any welding process leads to thermal gradients which inturn leads to residual stresses and finally distortions. So predicting thermal cycles, working on mitigating residual stresses and improving the mechanical properties of deposited material on each layer is very much essential to build the components of large build volume. Thus to use WAAM for large production we need a mechanism that should be incorporated in the WAAM machine so that the stresses developed after each layer are reduced and the mechanical properties of each layer are improved. In this project, the work is concentrated on using Friction Stir Processing(FSP) to achieve the above things. Friction stir processing(FSP) is a method that is generally used to alter microstructure according to the requirement of mechanical properties like Ductility, Strength, Fatigue life, e.t.c on welded joints. It is also the only method to manufacture surface composites, which represents the capability of the process for altering the microstructure. In this undertaking, I Considered working with two overlapping(side by side) metal beads so that this layup can be used as a way for building large parts with superior properties. So in this process, I have started with the analysis of two overlapping metal beads predicting the thermal cycles, stresses and the distortions produced in base plate due to weld deposition using finite element package in Abaqus. Also, the stresses and distortions produced in the deposited weld beads can be analyzed. After obtaining the analysis results of deposited layers, the analysis of Friction Stir Processing on this two overlapping metal beads is performed, again using Finite Element package in Abaqus. This is done in order to get an idea about the temperature histories of the material points so that the phase transformations if any can be predicted. Experimental Study of Thermal cycles, Residual Stresses and the Distortions produced in the workpiece due weld deposition is performed. The Simulated results matched well with performed experimental results. This study also suggests the optimal Tool rotation speed of the tool in Friction Stir Processing so as to get the required microstructural properties on the overlapping metal beads. In this study, the parameteric study of only Rotational speed of the tool is considered keeping all the other parameters constant. In this study we have observed that,using Friction Stir Processing one can alter the microstructure thus mechanical properties on two overlapping metal beads using only the tool rotation speed as the varying parameter, and this was proved here by doing simulations and performing experiments

Strain gradient effects on FCC single crystal

In the last two decades, experimental studies and numerical simulations expressed the size e�ect on the plastic distortion of ductile materials at small scales(Micron and Sub-Micron). Several studies have been performed on size effects on the rate of void growth using plasticity models with strain gradient effects on models with plane strain assumption. In the present work, a finite element model using crystal plasticity was proposed to understand the size effects on void evolution in a single crystal by incorporating the Borg [1] crystal plasticity theory with strain gradient effects in the Huang [2] user material subroutine developed for crystal plasticity formulations