Homogeneous Stress Distribution Research Articles

Toughening Ceramic-Based Composites by Homogenizing the Lattice Strain at Phase Boundaries.

Ceramic-based composites generally have low fracture toughness, and toughening these materials without sacrificing their hardness has been a big challenge. This study presents an approach for toughening ceramic-based composites by modulating the strain partition and stress distribution in phase-boundary regions. A new concept of homogenizing the lattice strain to achieve high fracture toughness in ceramic-based composites is proposed based on the collective lattice shear of martensitic phase transformation. The strategy was demonstrated by ZrO2-containing WC-Co ceramic-metal composites as a prototype. The crystal planes along the WC/ZrO2 martensitic transforming phase boundaries exhibited significantly larger and uniform lattice strains compared with conventional dislocation pile-up phase boundaries with highly localized lattice strains. The homogeneous strain and stress distributions across interfaces enabled the composite to have simultaneously high fracture toughness and hardness. The "homogenizing the lattice strain" strategy proposed in this work is applicable to a broad range of ceramic-based composites to achieve superior comprehensive mechanical properties.

An investigation on the mechanical behavior of mixed adhesively bonded composite joints subjected to transverse pre-impact following by axial post-tensile

In this study, mixed adhesive joints were formed to create a more homogeneous stress distribution in order to increase the failure load that the joints could bear. Single-lap joints (SLJs) made of glass fiber-reinforced plastic (GFRP) composites were formed using a rigid adhesive (Araldite AV138) in the middle and a more flexible adhesive (3 M DP8005) at the ends of the joint. Rigid and flexible adhesives were applied to the surface with lf/lr = 1 and lf/lr = 0.5 bond-length ratio (lf is bond length for the flexible adhesive and lr is bond length for the rigid adhesive). Mono adhesive joints were also created using the same adhesives. Tensile tests at 1 mm/min were carried out without applying pre-impact to some joints and applying 2.5, 3.5, 7.5, and 10 J transverse impacts to other joints to reveal how joint strength changes with the potential impacts to which adhesive joints might be exposed. Mixed adhesive joints bore more load under impact and non-impact conditions compared to mono adhesive joints. The impacts applied in these tests increased the load-bearing capacity of mono DP8005 adhesive joints. The largest decrease of strength after impact was observed for the mixed adhesive joints with lf/lr = 0.5 bond-length ratio.

Mitigating inherent micro-cracking in laser additively manufactured RENÉ 108 thin-wall components

Thin-wall components made of a hard-to-weld Ni-based superalloy, RENÉ 108, are fabricated using laser powder bed fusion. Thirty-two parts, including ten different scan strategies and four different wall thicknesses between 0.25 mm and 1.00 mm, are studied and compared with the conventional continuous 67° scan rotation strategy. Microstructure characterization shows micro-cracks aligned with the build direction and melt-pool boundaries. All micro-cracks exhibit inter-dendritic morphologies in the vicinity of the cracked boundaries, suggesting a solidification cracking mechanism. Thicker parts and long vector length are more susceptible to micro-cracking due to earlier transition to positive stress triaxiality states demonstrated through finite element modeling.​ Parts are processed with alternating and continuous inter-layer scan rotation strategies. Scan rotations reduce micro-cracking propensities by 12%–62% compared to zero scan rotations due to more homogeneous stress distribution during build progression. Furthermore, alternating long vector lengths create 100%–230% more micro-cracks than alternating short vector lengths, which are more beneficial than the 67° continuous rotation strategy due to reduced in-process stresses. Shorter vector lengths with interlayer scan rotations are optimal for micro-crack mitigation.

Three-Dimensional Finite Element Study of Endodontically Treated Maxillary Central Incisors Restored Using Different Post and Crown Materials.

Restoring endodontically treated teeth is a common problem in dental practice. Post and core restorations are one of the major options in the rehabilitation of these teeth. However, there is no final decision regarding the best material or technique to be used with these restorations. So, this study aimed to evaluate the effect of different post and crown materials on the biomechanical behavior of restored maxillary central incisor using the finite element method. A total of 10 3D models of endodontically treated maxillary central incisors restored with two prefabricated posts and three custom-made posts were modeled and grouped according to post material (gold, nickel-chrome, zirconia, and glass fiber) and crown material (lithium disilicate, and zirconia). Finite element analysis was conducted, and stress distribution was evaluated using von Mises criteria. Both crown materials showed stress concentration at the force application site mainly on the intaglio palatal surface of the crown. However, more stress values were observed within zirconia crowns. All posts showed stress concentration at their buccal sides. However, more stress values were observed in zirconia and metal cast posts compared to glass fiber posts that transfer more stress to root dentin. Post and crown materials affect the stress distribution in the tooth-restoration complex. Using high elastic modulus posts slightly decreased stress in root dentin despite concentrating more stress within their structure. However, glass fiber posts resulted in more homogenous stress distribution in the tooth-restoration complex. Crown material did not influence the stress distribution in root dentin. Custom-made posts decreased stress within crowns, regardless of the crown material. However, more stress values were observed within zirconia crowns. Custom-made zirconia posts and cores showed a similar stress distribution as non-precious metal cast posts, so they may be used as a suitable option where esthetic is desirable.

The effect of the material used and the pulp chamber extension depth on stress distribution of endocrowns: A three-dimensional finite element analysis

Aim: The aim of this study was to examine the effects of materials used and the depth of extension into the pulp chamber on stress distribution in mandibular molar endodontically treated teeth with endocrown restoration using three-dimensional (3D) finite element analysis (FEA). Methodology: Three-dimensional finite element analysis models were obtained at two different pulp chamber extension depths by taking a tomography of a root canal-treated mandibular molar tooth extracted for periodontal reasons: 2.5 mm (Model A) and 3.5 mm (Model B). Models were divided into the following three groups according to material type used: Vita Enamic (VE), Lava Ultimate (LU), and IPS e.max CAD (EMX). The aforementioned model groups were further divided into the following two subgroups according to the types of cement used: NX3 and MaxCem Elite Chroma (MX). Maximum principal stress (MPa) values under 600 N vertical load were investigated to evaluate the effect of restoration design, material type, and cements used on stress distribution. Results: The maximum stress on the restoration was observed in the EMX material type (13.000 MPa) in the MX cement group in Model A, while the lowest was observed in the LU material (5.932 MPa) in the NX3 cement group in Model A. The areas of highest stress for both Models A and B were observed in the restoration areas corresponding to the enamel margins. Conclusion: Materials with a higher elastic modulus show a higher stress area on the restoration surface, while the stress values they transmit are lower. Materials with the elastic modulus close to dentin have more homogeneous stress distributions within the restoration. How to cite this article: Güntekin N, Mohammadi R, Tunçdemir MT. The effect of the material used and the pulp chamber extension depth on stress distribution of endocrowns: A three-dimensional finite element analysis. Int Dent Res 2022;12(Suppl.1):1-9. https://doi.org/10.5577/intdentres.436 Linguistic Revision: The English in this manuscript has been checked by at least two professional editors, both native speakers of English.

Addressing Thermal Distortion in Additive Manufacturing of Topology Optimized Structures Through Reverse Shape Morphing

Design of light weight structures is an important aspect in the aircraft industry, since minimizing the weightof components improves the overall aircraft performance. However, conventional manufacturing methods work on standard geometries and shapes, and often lead to overdesigning of parts. Additive Manufacturing (AM) overcomes these issues by allowing more design freedom. The present study focuses on two aspects of AM: (1) part consolidation through topology optimization, and (2) addressing thermal distortion through reverse shape morphing. An assembly of two load bearing brackets is first amalgamated into a single Topology Optimized (TO) part, which satisfies the displacement and stress requirements of the original design. After a series of optimization iterations, the final TO part (278 g) weighs 69 % lesser than the original assembled design (909 g), still meeting the design constraints. The TO part thus eliminates the need of fasteners to join both the brackets, thereby, making the design simpler yet effective. Moreover, a homogeneous stress distribution in the optimized part allows for efficient material utilization. In order to overcome thermal distortion that results during the AM process, the shape of the TO part is transformed in a sense opposite to the distortions produced. This is achieved through reverse shape morphing technique, that reduces thermal distortions in the printed part to sub-micron levels, and the morphed TO part conforms to the requirements meeting the design constraints. Therefore, the implementation of topology optimization along with reverse shape morphing makes the design simple and efficient having reduced distortion. This is achieved without any need of modifications in the manufacturing system or equipment, and such a strategy can be replicated and implemented at industrial scale as well.

Inside Back Cover: Volume 3 Issue 4

Inside back cover image: In this work, the bottlenecks of low cost polypyrrole in term of practical application, such as insufficient electrochemical performances and poor cycling stability, have been solved by an optimized pulse-potential polymerization strategy. This strategy effectively removed the concentration polarization effect during the electrodeposition process, leading to shorter molecular structure and homogeneous stress distribution of polypyrrole. In addition, the enhanced protonation level further boosted the charge transfer kinetics in polypyrrole. As a result, the optimized polypyrrole electrodes achieved outstanding specific capacitance and long cycle life simultaneously. The fabricated pouch supercapacitors of large size can exhibit a stable energy output and strong compressive endurance when suffering harsh scenarios of simulating real-world, which provides a promising commercial prospect for polypyrrole-based electrode materials. (DOI: https://doi.org/10.1002/smm2.1116)

Impact of Nodular Calcifications in the Aortic Annulus and Left Ventricular Outflow Tract on TAVI Outcome with New-Generation Devices.

The impact of nodular calcifications in left ventricular outlow tract (LVOT) and aortic annulus on the procedural outcome of transcatheter aortic valve implantation (TAVI) with new-generation devices is yet to be elucidated. Similarly, computational simulations may provide a novel insight into the biomechanical features of TAVI devices and their interaction with nodular calcifications. This retrospective single-center study included 232 patients submitted to TAVI with Evolut-R (53.4%), Portico (33.6%) and Lotus (13.0%) devices with available preoperative computed tomography (CT) angiography and evidence of nodular calcifications in aortic annulus and/or LVOT. Calcification severity was defined moderate in presence of at least two nodules or one nodule 5 mm. Three virtual simulation models of aortic root presenting a nodular calcification of increasing size were implemented. Stress distribution, stent-root contact area and paravalvular orifice area were computed. At least moderate calcifications were found in 123 (53.0%) patients, with no sex differences. Among the moderate calcification group, lower device success rate was evident (87.8% vs. 95.4%; p = 0.039). Higher rates of moderate paravalvular leak (PVL) (11.4% vs. 3.7%; p = 0.028) and vascular complications (9.8% vs. 2.8%; p = 0.030) were also observed. Among the Evolut-R group, higher rates of at moderate PVL (12.1%) were observed compared to Portico (3.8%; p = 0.045) and Lotus (0.0%; p = 0.044) groups. Calcification of both annulus and LVOT (odds ratio [OR] 0.105; p = 0.023) were independent predictors of device success. On computational simulations, Portico exhibited homogeneous stress distribution by increasing calfications and overall a larger paravalvular orifice areas compared to Evolut-R and Lotus. Evolut-R showed higher values of average stress than Portico, although with a more dishomogeneous distribution leading to greater paravalvular orifice areas by severe calcifications. Lotus showed overall small paravalvular orifice areas, with no significant increase across the three models. At least moderate nodular calcifications in the annulus/LVOT region significantly affected TAVI outcome, as they were independent predictors of device success. Lotus and Portico seemed to perform better than Evolut-R as for device success and moderate PVL. Computational simulations revealed unique biomechanical features of the investigated devices in terms of stent compliance and radial force.

Dynamic compressive strength of alumina ceramics

Dynamic (220–510 s−1) and quasi-static (0.001 s−1) compression experiments are conducted on alumina ceramics implemented with two types of tungsten carbide inserts, cylindrical and step-shaped. Split Hopkinson pressure bar (SHPB) tests with in-situ, high-speed optical imaging are adopted to capture the damage and failure of ceramic samples under dynamic compression. The compressive strength of alumina ceramic samples with step-shaped inserts is 15%–30% higher than that with cylindrical inserts commonly used in previous studies, under both dynamic and quasi-static loading. Damage occurs first at the two ends of ceramic samples with the cylindrical inserts, followed by edge fracture and splitting cracks penetrating the sample. However, damage is initiated in the sample region away from the sample ends for the step-shaped inserts, and oblique and secondary transverse cracks dominate the failure process. The different damage modes in the case of step-shaped inserts result in the delayed damage initiation and sample failure, and consequently high compressive strengths. Finite element modelling (FEM) of the SHPB tests provides strength and damage evolution features consistent with the experiment using the Johnson–Holmquist (JH-2) model. FEM reveals equivalent, tensile and shear stress concentrations at the two ends of samples with cylindrical inserts. The stress concentrations are responsible for the damage initiation and growth at the sample ends and the following splitting cracks, consistent with the high-speed images. In contrast, homogeneous stress distributions are achieved in the sample with the step-shaped inserts, ensuring simultaneous damage development across the sample. Overall, the step-shaped inserts in conjunction with cylindrical samples can yield reliable strength measurements for ceramics and ceramic-like materials.

IN BETWEEN: An Interlayer Material Study for Interlocking Cast Glass Blocks

Interlocking cast glass assemblies are a promising solution for architectural cast-glass applications aiming for high transparency and a reversible structure that allows the reuse of the glass components (Oikonomopoulou et al.,2018; Oikonomopoulou,2019b). In such a system, an interlayer material between the glass elements is essential, to assist the homogenous stress distribution and account for the surface microasperities of the glass elements. Towards circularity, this material should be dry (and not an adhesive), allowing for the eventual disassembly of the system. Previous experimental work by (Aurik at al.,2018; Oikonomopoulou at al.,2019b) has focused on the use of PU and PVC interlayers as suitable candidates; the focus in those studies has been solely placed on the mechanical performance of the interlayer material. This research provides a review of potential material candidates suitable for interlayers of an interlocking cast glass assembly based on a set of revised design and performance criteria that are divided into primary and secondary. Furthermore, the impact their unique material properties have on the potential application of the interlocking system is examined. The whole process, from fabrication to construction of the entire assembly, based on an assumed building scenario, is presented in a chain reaction manner, whose starting point is the interlayer itself. After defining the design criteria the interlayer should adhere to, the proposed candidates are: PETG sheets (Vivak®), Neoprene, Aluminum, Laminated Polyurethane (PU) and a Soft-core aluminum interlayer. The unique properties and fabrication challenges of all five proposed interlayers are considered, as well as their properties in relation to assembly, which leads to the development of two distinct assembly sequences. The main distinction concerns the interlayers that risk creeping and those that do not. The research concludes with a comparison between the interlocking assembly and the other glass block assemblies currently applied.

Topology based modelling of crochet structures

Crocheted textiles receive scarce scientific study and are at present not produced in automatized industrial scale. Computer-aided modelling and simulation offer capabilities for investigating possible technical fields of application. In this context a novel approach for modelling crocheted textiles consisting of chains, slip stitches and single crochets using a topology based and parameterized key point representation at the meso scale is proposed. According to the stitch size, yarn diameter and pattern spline interpolated models, which are free of interpenetrations up to approximately a 1/10 ratio of yarn diameter to stitch size, are generated by a developed Python program and software from the company TexMind. The models are suitable for finite element method (FEM) applications with LS-DYNA with which the mechanical properties of crocheted textiles can be studied. Exemplary simulations show anisotropic properties and homogeneous distribution of stresses in a crocheted textile. Due to the computationally simple and flexible modelling the presented approach may serve as a tool for designing planar crocheted textiles. This allows for estimation of the required yarn length and offers the prediction capabilities of simple and fast FEM simulations based on beam elements.

Evaluation methods for surface compression stress measurements with unknown principle stress directions

The birefringent properties of glass can be well utilized for non-destructive testing of thermally tempered glass. The surface compression stress as well as the compression zone depth of thermally tempered glass is commonly measured with a scattered light polariscope. The measurement with scattered light polariscope provides information about stresses acting perpendicular to the measurement direction. Therefore, the measurement depends on the direction. In order to make a statement about the rough level of the prestress, a measurement in one direction can be sufficient, assuming an isotropic stress state and a relatively homogeneous distribution of the surface compression stress. However, in order to be able to make a more detailed statement about a non-isotropic stress state, measurements in up to four directions are necessary. Information about the direction of principal stresses and differences of principal stresses can then be evaluated. In the present work, it is investigated which deviations can be expected by measurements performed in only one direction or by measurements using up to four directions. For this purpose, five methods are introduced, which deviate in the assumptions made for the current stress state. The methods are compared using measurements on thermally tempered glass in a four-point bending test and on thermally tempered glass specimens without any external load.

Determination of muscle strength and function in plesiosaur limbs: finite element structural analyses of Cryptoclidus eurymerus humerus and femur.

BackgroundThe Plesiosauria (Sauropterygia) are secondary marine diapsids. They are the only tetrapods to have evolved hydrofoil fore- and hindflippers. Once this specialization of locomotion had evolved, it remained essentially unchanged for 135 Ma. It is still controversial whether plesiosaurs flew underwater, rowed, or used a mixture of the two modes of locomotion. The long bones of Tetrapoda are functionally loaded by torsion, bending, compression, and tension during locomotion. Superposition of load cases shows that the bones are loaded mainly by compressive stresses. Therefore, it is possible to use finite element structure analysis (FESA) as a test environment for loading hypotheses. These include muscle reconstructions and muscle lines of action (LOA) when the goal is to obtain a homogeneous compressive stress distribution and to minimize bending in the model. Myological reconstruction revealed a muscle-powered flipper twisting mechanism. The flippers of plesiosaurs were twisted along the flipper length axis by extensors and flexors that originated from the humerus and femur as well as further distal locations.MethodsTo investigate locomotion in plesiosaurs, the humerus and femur of a mounted skeleton of Cryptoclidus eurymerus (Middle Jurassic Oxford Clay Formation from Britain) were analyzed using FE methods based on the concept of optimization of loading by compression. After limb muscle reconstructions including the flipper twisting muscles, LOA were derived for all humerus and femur muscles of Cryptoclidus by stretching cords along casts of the fore- and hindflippers of the mounted skeleton. LOA and muscle attachments were added to meshed volumetric models of the humerus and femur derived from micro-CT scans. Muscle forces were approximated by stochastic iteration and the compressive stress distribution for the two load cases, “downstroke” and “upstroke”, for each bone were calculated by aiming at a homogeneous compressive stress distribution.ResultsHumeral and femoral depressors and retractors, which drive underwater flight rather than rowing, were found to exert higher muscle forces than the elevators and protractors. Furthermore, extensors and flexors exert high muscle forces compared to Cheloniidae. This confirms a convergently evolved myological mechanism of flipper twisting in plesiosaurs and complements hydrodynamic studies that showed flipper twisting is critical for efficient plesiosaur underwater flight.

Topology Optimized Unit Cells for Laser Powder Bed Fusion

The rise of additive manufacturing has enabled new degrees of freedom in terms of design and functionality. In this context, this contribution addresses the design and characterization of structural unit cells that are intended as building blocks of highly porous lattice structures with tailored properties. While typical lattice structures are often composed of gyroid or diamond lattices, this study presents stackable unit cells of different sizes created by a generative design approach to meet boundary conditions such as printability and homogeneous stress distributions under a given mechanical load. Suitable laser powder bed fusion (LPBF) parameters were determined for AlSi10Mg to ensure high resolution and process reproducibility for all considered unit cells. Stacks of unit cells were integrated into tensile and pressure test specimens for which the mechanical performance of the cells was evaluated. Experimentally measured material properties, applied process parameters, and mechanical test results were employed for calibration and validation of finite element (FE) simulations of both the LPBF process as well as the subsequent mechanical characterization. The obtained data therefore provides the basis to combine the different unit cells into tailored lattice structures and to numerically investigate the local variation of properties in the resulting structures.

Comparative Evaluation of the Effect of Core Type and Antirotational Post on Stress Distribution in an Endodontically Treated Maxillary First Molar: FEA.

Background This study aims to analyze and compare the stress distribution in an endodontically treated maxillary first molar restored with various post and core systems and assess the benefit of the presence of an antirotational post and the effect of its length using finite element analysis. Materials and Methods Five 3D models of maxillary first molar restored with variable designs of post and core were constructed using CT scanning and information obtained from textbook and FEM software. Variables were types of core, presence or absence of an antirotational post, and length of the antirotational post. A load of 480 (N) vertically and a load of 240 (N) with 45° to the occlusal plane were applied. Results were analyzed using 3D von Mises criteria. Results The results showed that the most homogeneous stress distribution pattern along with dentin and the post-core system was observed in the model with one main post in the palatal canal and in the model with a two-piece core and one main post in the palatal canal and shorter antirotational post in the distal-buccal canal. However, models with one-piece core and antirotational post (either the same length or shorter than the main post) in the distal-buccal canal had the most stress concentration sites. Conclusion In this study, it was found that the presence of an antirotational post, its length, and type of core affected the distribution of stress along the dentin and post-core system. This study indicated that if the antirotational post is considered in the post-core design, it is better to use a two-piece core type due to more homogeneous stress distribution along the dentin and post-core system.

Reaching near-theoretical strength by achieving quasi-homogenous surface dislocation nucleation in MgO particles

The structural stability of the ceramic nanoparticle (NP) is essential for its versatile applications in broad fields. Due to inevitable imperfections on the surfaces, the NP usually yields at a stress that is far below its theoretical strength. Here we propose an effective way to approach the theoretical strength of the NPs by simply homogenizing the primary imperfections. Electron beam irradiation is utilized to modify the original uneven surface and achieve surface nano-crystallization in MgO NPs, which leads to more homogeneous stress distribution intrinsically as proved by numerical simulations. As a result, quasi-homogeneous surface nucleation of dislocations occurs and raises the compressive strength to be three times higher than the as-received particles with the original surface. The near-theoretical strength gained here indicates that the imperfection in materials can be homogenized to optimize the properties to approach that of perfect crystals.

Pulse‐potential electrochemistry to boost real‐life application of pseudocapacitive dual‐doped polypyrrole

AbstractPolypyrrole (PPy) is a very promising pseudocapacitive electrode material for supercapacitors. However, the poor electrochemical performances and cycling stability caused by volumetric change and counterion drain severely limited its practical application and commercialization. Herein, we present a pulse‐potential polymerization strategy for uniformly depositing a dual‐doped PPy with ordered and shorter molecular structure by balancing the concentration polarization. Such a strategy ensures more homogeneous stress distribution of PPy during ultralong cycling tests and improves the cycle stability. Moreover, the pulse‐potential polymerized PPy with dual anion doping behavior induces enhanced protonation level and improved electrical conductivity, which boosting the charge transfer kinetics. Therefore, the as‐synthesized PPy exhibits a remarkable capacitance performance (7250 mF/cm2 @ 3 mA/cm2), outstanding rate capability (3073 mF/cm2 @ 200 mA/cm2) and a long cycle life. The assembled symmetric and asymmetric supercapacitors (ASC) exhibit good energy densities (0.8 mWh/cm2 for ASC and 0.5 mWh/cm2 for symmetric supercapacitor), and excellent durability with zero capacitive loss after 35,000 cycles. In addition, we have fabricated small pouch devices, which can effectively operate a variety of electronic products (including the high‐voltage 5 V smartphone, and tablet) and well withstand the external extreme tests during operation, demonstrating the quantitative investigation of the real‐life application of aqueous supercapacitors.

Optimal Design and Processing Technology of 3D Printed Tibial Implants

It is necessary to study the design method and molding techniques of selective laser melting (SLM) tibial implants to improve the success rate of knee implant surgery and the quality of life of patients. In this study, the three-dimensional (3D) reconstruction of tibial implants was completed using the reverse combined with forward methods, optimization design was carried out on the constructed tibial implant model by adopting the parametric finite element method (FEM), and the SLM device was employed for the direct manufacture of tibial implants and to study its molding techniques. The results indicated that the tibial implant model completed using reverse and forward methods combined with FEM displayed favorable modeling effects, with more homogeneous stress distribution. After optimizing the molding techniques of SLM molding tibial implants, excellent molding effects could be achieved, with high tibial implant surface finish but no buckling deformation or obvious adhering slag. Studying the above modeling and molding methods can provide important foundation for the individualized design and direct manufacture of tibial implant.

Manipulation of the In Situ Nitrogen‐Vacancy Doping Efficiency in CVD‐Grown Diamond

Herein, the in situ generation of nitrogen‐vacancy (NV) centers in diamond during chemical vapor deposition (CVD) is investigated depending on the electric‐field strength at the sample position. The alteration of the electric‐field strength is induced by changing the resonance conditions within the resonator cavity while keeping the growth input variables constant. The electric‐field strength distribution is obtained by simulation results. During the growth experiments, optical‐emission spectroscopy data is collected, which shows the impact of the electric‐field strength on the radical concentrations within the plasma and the gas temperature. Through the reduction of the electric‐field strength, the synthesis of thick, high‐quality, nitrogen‐doped diamond without the formation of a polycrystalline rim around the sample edges and the twinning‐induced growth of polycrystalline grains was accomplished. Therefore, a reduced internal and more homogeneous stress distribution is achieved. Furthermore, significant influences on the in situ NV doping are discovered. In addition to a considerable gain of the in situ NV generation, also a major enhancement of the in situ incorporation efficiency of NV centers in comparison to centers up to almost 3% is observed. Depending on the application, this makes posttreatment processes for additional NV generation dispensable.

A Study of Compaction Densification Behavior of Composite Particles by Multiparticle Finite Element Method

In this paper, 3D particulate scale modelling on the die compaction of DEM generated initial packings of both soft and hard particles was conducted by employing the multiparticle finite element method (MPFEM). The effects of initial packing structures as well as the compaction pressure on the macroscopic and microscopic properties of the whole powder mass and local structures were investigated. In addition, corresponding physical experiments were carried out for model validation. The results show that the compact obtained from the initial dense packing under vibration undergoes yielding stage earlier than that with natural initial packing (without vibration), and the relative density is much higher. Pores that are significantly smaller and with more uniform size and homogenous stress distribution are observed in the former case. Highest stress regions occur in most cases at a grain boundary with large curvature after deformation. Moreover, the high stress in the central part of both soft and hard particles during compaction is significantly reduced after pressure unloading, reaching a new force balance. In this case, the stress is concentrated mainly at the corners of the deformed particles, which creates the risk of cracking during subsequent sintering at either the contact region between particles or the corners. The numerical results are found to be in good agreement with those from physical experiments, confirming the robustness and reliability of the numerical model used in the simulations.