Initial Preform Research Articles

Mixed Particle Size Effect on Improvement of Mechanical Properties of Reaction Bonded B4C

The research was aimed for improving the mechanical properties of reaction bonded boron carbide (RBBC) through use of two boron carbide (B4C) powders in the initial preform. Experimental results show that the Young’s modulus, Knoop hardness, and flexural strength of RBBC, produced with the combination of two powders, are greater by ∼15.2%, ∼33.8% and ∼15.5%, respectively, compared to that produced with single, i.e. fine B4C powder. The increase in ceramic phase (B4C and B4C +SiC) and reduction in residual Si content in the RBBC produced with mixed powders lead to an enhancement in its mechanical properties. Both RBBC exhibit indentation size effect and such characteristics are corroborated by their respective brittleness index.

Fabrication of SiC matrix composite material by pressureless aluminum melt infiltration in air atmosphere

The microstructure of SiC matrix composite materials produced by pressureless aluminum melt infiltration at 950° was investigated. The oxygen containing phases fraction in silicon carbide preform does not considerably change after soaking in molten aluminum due to the formation of a dense flux film at the surface. It is established that during the direct infiltration of aluminum from the melt into sintered SiC preform, several areas are observed: aluminum saturated zone, transition zone, and a porous silicon carbide zone. The depth of the first area is 1.0–1.2 mm. The open porosity of the infiltrated composite material significantly improved from 8.5% for a SiC preform to 2.4% as well as density increased from 2.17 to 2.85 g/cm3. Even aluminum content in the zone of porous silicon carbide has grown 5.5 times. The corundum phase has formed at the composite material surface within cooling in the air atmosphere. The hardness distribution over the specimen depth has a parabola-like appearance with a clear maximum on the surface (5.9± 0.6 GPa) and an obvious minimum coinciding in value with the hardness of the initial preform in the geometric center of the sample (2.5± 0.3 GPa). The developed silicon based composite material could be considered as a prospective wear resistant lining.

Microstructural and infiltration properties of woven preforms during chemical vapor infiltration

AbstractInterface‐resolved direct numerical simulations (DNSs) of chemical vapor infiltration (CVI) have been performed over a range of furnace‐operating conditions (Thiele moduli) and for practical woven preform geometries. A level‐set method is used to resolve the geometry of the initial preform at tow scale. The interface between the vapor and solid phase is then evolved in time through the entire CVI densification cycle, fully resolving the time‐varying topology between the two phases. In contrast to previous level‐set methods for CVI simulation, the physical reaction and diffusion processes govern the level‐set movement in the current approach. The surface deposition kinetics is described by the usual one‐step model. In this paper, the DNS data are used to study the evolving porosity, surface‐to‐volume ratio, and flow infiltration properties (permeability and effective diffusivities). Comparisons are made to popularly‐assumed structure functions and the standard, Kozeny–Carmen porous media model commonly employed in modeled CFD simulations of CVI. The virtual DNS experiments reveal a Thiele modulus and preform geometry (fabric layup) dependence which the existing microstructural and infiltration models are not able to describe throughout the entire densification process. The DNS‐based, woven geometry‐specific correlations can be applied directly to mean‐field, furnace‐scale CFD simulations.

Combined FIB/SEM tomography and TEM analysis to characterize high aspect ratio Mg-silicate particles inside silica-based optical fibres

The evolution of particles, during the fabrication step of particle-containing glass fibres, was investigated. The aim of this study was to characterize quantitatively the composition, size and shape distribution of Mg-silicate particles within the initial silica-based preform and the final fibre, these information being crucial to better understand the mechanisms involved during the drawing step. A combined experimental approach using Scanning electron microscopy, Transmission electron microscopy and FIB/SEM tomography was implemented. The particle composition was found to stay unchanged during the drawing step. On the other hand, strong modifications of their shape within the fibre is observed and discussed. • The microstructure of high aspect ratio particles within optical fibres is analysed by electron microscopy techniques • The measured composition of particles is the one of the enstatic phase • 3D imaging of the particles by FIB/SEM tomography reveals their morphology changes induced by the drawing step

Influence of the inicial porous preform shape on the deformed state evolution and force parameters of the forging process in a semi-closed die

Abstract. The results of simulation of hot forging process for porous powder preforms of two initial configurations (cylindrical shape and in the form of a cut cone) in a die with detachable matrix are presented. Numerical assessment of the effect of the boundary conditions of the deformation scheme on the evolution of the stress-strain state of the forged piece was performed using the model of rigidly plastic porous body. The evolution of the relative density distribution, the deformed state along the cross section of the workpiece at different stages of deformation and the overall effort of deforming the process were studied. The fundamentally different nature of the evolution of density distribution and components of deformation tensor in the forged pieces volume is shown in deformation of the preforms of different initial configuration, which is manifested in a substantially higher level of deformations intensity in the volume for the initial preforms, which are made in the form of a cut cone in a cut cylindrical shape. The maximum value of the forging force for the initial preforms of both configurations is practically the same, but the intensity of the deformation force increase is much higher for the cylindrical blanks.

Simulation on Effect of Preform Diameter in Injection Stretch Blow Molding

Polyethylene terephthalate (PET) is the most common material of resin for manufacturing plastic bottle by injection stretch blow molding due to its excellent properties. As various issues of health and environmental hazards due to the PET use have risen, PET bottle manufacture may be improved by minimizing the wall thickness to reduce the PET use. One of the critical qualifications of the manufacturing process which lead to the wall thickness distribution is the initial preform diameter. In this project, we used the ANSYS Polyflow with aim to evaluate the wall thickness distribution of PET bottle for different diameter of initial preform. As a result, only 4 mm preform diameter presented wall thickness below than 1 mm. On the other hand, at least 6 mm preform diameter can permit the wall thickness 1.3 mm i.e. at the shoulder area.

Bacillus cereus AR156 Extracellular Polysaccharides Served as a Novel Micro-associated Molecular Pattern to Induced Systemic Immunity to Pst DC3000 in Arabidopsis.

Non-host resistance (NHR) is a broad-spectrum plant defense. Upon colonizing on the surface on the root or leaves of non-host species, pathogens initial encounter preform and induce defense response in plant, such as induced hypersensitive response, PAMPs triggered immunity (PTI), and effector triggered immunity (ETI). The ability of plants to develop an induced systemic response (ISR) in reaction to the colonization by non-pathogenic rhizobacterium depends on interactions between host plants and the colonizing rhizobacterium, and the ISR also can be defined as a NHR. However, how the colonization signal is and how systemic resistance to pathogens is developed is still unclear. In this study, we demonstrated that the extracellular polysaccharides (EPSs) of Bacillus cereus AR156 could act as novel microbe-associated molecular patterns (MAMPs) and function in the early perception status of the ISR of B. cereus AR156. The results revealed that B. cereus AR156 EPS could induce systemic resistance to Pst DC3000 in Arabidopsis. Cellular defense response markers such as hydrogen peroxide accumulation, callose deposition, and defense-associated enzyme were induced upon challenge inoculation in the leaves primed by EPS. Moreover, the defense-related genes PR1, PR2, and PR5 and mitogen-activated kinases (MAPK) cascade marker gene MPK6 were concurrently expressed in the leaves of EPS-treated plants and induced higher resistance to Pst DC3000 in Col-0 than that in the jar1 or etr1 mutants. The protection was absent in the NahG transgenic plants and npr1 mutant, suggesting an activation of the salicylic acid (SA)- and the MAPK-dependent signaling pathways with NPR1-dependent by B. cereus AR156 EPS. In conclusion, B. cereus AR156 EPS play an important role in MAMP perception during the process of rhizobacteria-triggered NHR. This study is the first to illustrate how AR156 induces systemic resistance to Pst DC3000 in Arabidopsis. It also provides the first explanation of how plants perceive colonization of non-pathogenic bacteria and how rhizobacteria trigger ISR to plant pathogens.

Edge behaviour in the glass sheet redraw process

Thin glass sheets may be manufactured using a two-part process in which a sheet is first cast and then subsequently reheated and drawn to a required thickness. The latter redrawing process typically results in a sheet with non-uniform thickness and with smaller width than the cast glass block. Experiments suggest that the loss of width can be minimized and the non-uniformities can be essentially confined to thickening at the sheet edges if the heater zone through which the glass is drawn is made very short. We present a three-dimensional mathematical model for the redraw process and consider the limits in which (i) the heater zone is short compared with the sheet width, and (ii) the sheet thickness is small compared with both of these length scales. We show that, in the majority of the sheet, the properties vary only in the direction of drawing and the sheet motion is one-dimensional, with two-dimensional behaviour and the corresponding thick edges confined to boundary layers at the sheet extremities. We present numerical solutions to this boundary-layer problem and demonstrate good agreement with experiment, as well as with numerical solutions to the full three-dimensional problem. We show that the final thickness at the sheet edge scales with the inverse square root of the draw ratio, and explore the effect of tapering of the ends to identify a shape for the initial preform that results in a uniform rectangular final product.

Experimental and Numerical Analysis of Liquid-Forming

The packaging of liquid products is conventionally realized by using two production stages, which are the stretch blow molding and the filling. In the stretch blow molding process, hot polyethylene terephthalate (PET) preforms are inflated by pressurized air into a cavity to form plastic bottles. In a follow-up process, these packages are filled by a separate machine with the desired liquid product. In contrast to that, liquid-forming combines the blowing and filling stages by directly using the liquid product to form a plastic bottle. Through this substitution, two main challenges arise. Firstly, there are significant inertia effects through the liquid mass, leading to additional reaction forces and a spatially inhomogeneous pressure distribution inside the preform. Secondly, the heat transfer between preform and fluid is drastically increased. Because of this cooling effect, a specific combination of forming speed as well as initial preform and liquid temperatures is necessary to avoid thermally induced preform rupture. This is based on the fact that the formability of PET rapidly declines below its glass transition temperature (Tg). Consequently, a process control requires the knowledge of how the process parameters influence the preform cooling. In this paper, a numerical simulation of the liquid-forming process (LF) is introduced including the preform cooling during forming. In addition, the strain-dependent self-heating effect of PET is implemented. Process experiments under different parameter combinations are conducted using simplified bottle geometry. Through a comparison of the results from experiments and from simulation, the influence of process parameters on the temperature drop and thus on thermally induced failure is determined. In this way, process understanding and control are increased.

Distinctiveness of Initial Preform Properties in Renovation

Distinctiveness of Initial Preform Properties in Renovation

Synthesis of Ti3SiC2-based materials by reactive melt infiltration

In this paper, Ti3SiC2-based materials were fabricated by reactive melt infiltration (RMI), and the effect of carbon and Al on the formation of Ti3SiC2 was discussed. In the infiltration process of Si melt, the existence of carbon in the initial preform is beneficial to the formation of Ti3SiC2. Carbon can react with TiSi2 to form new TiC with more carbon vacancies than the initial TiC, promoting the formation of TiC twins and Ti3SiC2. In the infiltration process of Al–Si alloy, the existence of Al can effectively decrease the twin boundary energy of TiC grains, leading to the formation of TiC twins and nucleation of Ti3SiC2. There is a diffusion–competition process existing between Si and Al melts, leading to a higher Si/Al ratio in the final samples than in the Al–Si alloy. A possible formation mechanism was proposed to explain the final products.

The analysis of photonic crystal fibers optical-geometrical properties and their impact on transfer parameters

In microstructured optical fibers some defects are inherent to the fabrication process. One can mention, for example, the inhomogeneity of the initial preform: diameter, position of the inclusions (when the hexagonal stack is assembled before drawing) and refractive index that evolves along its axis. These defects will lead to transverse disorders in the final fiber. Therefore, the analysis of photonic crystal fibers optical-geometric properties and their impact on transfer parameters is very important. We note that in our investigation we use finite-element method. The obtained results show that at any of considered defect types the mode field will have two pronounced maximums. The results presented in this work show that total mode field power increases with decreasing the mean diameter of air holes. Another important result is that random variations of diameter of inclusions (air holes) can lead to an increase of total mode field power. We also have shown that random variations of inclusions diameter can increase the total mode field power. In the part 2 the signal losses caused by the difference of mode fields effective areas of connected fibers are determined. Further research in this sphere is directed to the study of influence of other optical-geometric PCF parameters, as well as their connection to the signal transmission. All presented results will be helpful for tolerance of fabrication processes and for better understanding the role of random variation of geometrical behaviors (arising at fabrication processes) on operation parameters of microstructured optical fibers

Reaction bonded boron carbide: recent developments

Reaction bonded boron carbide composites are among the hardest ceramics with low specific gravity values, a combination that makes them eminently suitable for light armour applications. The present review covers the main issues involved in the reaction bonding process based on the infiltration of boron carbide preforms with molten silicon. The importance of achieving high green density values before infiltration is emphasised. Separate sections deal with the morphology of the composite material, the thermodynamics of its microstructure formation, the static mechanical properties and the dynamic mechanical properties at strain rates up to 105 s−1. All along the review, emphasis is placed on describing the effect of free carbon presence in the initial preform on the morphology and properties of the final composite.

Effect of process features of pressure treatment on the microstructure and quality of parts of pipeline fittings from high-strength cast iron

Methods of form changing of parts from high-strength cast iron with globular graphite by plastic deformation aimed at widening the possibilities of forming the required structure and properties in the metal and the range of its application are considered. Processes for obtaining semiproducts from high-strength cast iron with the help of form-changing and separating operations are described. Results of analysis of the microstructure and hardness of the initial preforms and of the semiproducts obtained are presented.

Workability studies on sintered Cu–10SiC preforms during cold axial upsetting

An investigation has been carried out for the determination of the workability behavior of Cu–10SiC composite under triaxial stress state condition. Cylindrical preforms with three different initial preform densities (namely 85%, 90% and 95% of the theoretical density), possessing aspect ratios of 0.60, 0.50 and 0.40 were prepared using a die and punch assembly with a 1.0MN capacity Universal Testing Machine (UTM). Then the preforms were sintered in a muffle furnace at a temperature of 850±10°C for a period of 1h. Based on the experimental results the phenomena like axial strain (εz), various stress ratio parameters, namely (σθ/σeff) and (σm/σeff), the formability stress index (βσ) under triaxial stress state conditions were systematically analysed. It was found that lower initial aspect ratio with higher initial relative density preforms exhibited enhanced formability stress index compared to higher aspect ratio with lower initial relative density preforms.

Development of a Numerical Optimization Method for Blowing Glass Parison Shapes

Industrial glass blowing is an essential stage of manufacturing glass containers, i.e., bottles or jars. An initial glass preform is brought into a mold and subsequently blown into the mold shape. Over the past few decades, a wide range of numerical models for forward glass blow process simulation has been developed. A considerable challenge is the inverse problem: to determine an optimal preform from the desired container shape. A simulation model for blowing glass containers based on finite element methods has previously been developed (Giannopapa, 2008, “Development of a Computer Simulation Model for Blowing Glass Containers,” ASME J. Manuf. Sci. Eng., 130, p. 041003; Giannopapa and Groot, 2007, “A Computer Simulation Model for the Blow-Blow Forming Process of Glass Containers,” 2007 ASME Pressure Vessels and Piping Conference and 8th International Conference on CREEP and Fatigue at Elevated Temperature). This model uses level set methods to track the glass-air interfaces. The model described in a previous paper of the authors showed how to perform the forward computation of a final bottle from the given initial preform without using optimization. This paper introduces a method to optimize the shape of the preform combined with the existing simulation model. In particular, the new optimization method presented aims at minimizing the error in the level set representing the glass-air interfaces of the desired container. The number of parameters used for the optimization is restricted to a number of control points for describing the interfaces of the preform by parametric curves, from which the preform level set function can be reconstructed. Numerical applications used for the preform optimization method presented are the blowing of an axisymmetrical ellipsoidal container and an axisymmetrical jar.

Numerical Analysis of Electrochemical Erosion for Functionally Graded Tungsten/Copper Materials

One innovative approach for producing functionally graded tungsten/copper composites involves infiltrating a porous tungsten structure with molten copper. The porous structure is created by sintering tungsten powder to create an initial porous preform and then connecting the preform to the anode of an electrochemical cell. The porosity increases with time as the tungsten oxidizes in the alkaline electrolyte. The rate of porosity increase depends on the local value of electric-potential difference between the electrode and electrolyte, while the local electrical properties are a function of the porosity. Therefore, the porosity distribution, which determines the material-property gradient of the resulting material, can be modeled by a system of coupled equations describing porosity and electric potential. The present work develops a numerical tool capable of predicting the evolution of porosity in the rectangular-slab geometry (the extension to cylindrical-shell and elliptical-shell geometries is straightforward). Analysis of the results suggests that the shape of the gradient can be varied by adjusting parameters such as initial porosity and current density.

Preform optimization for reduction of forging force using a combination of neural network and genetic algorithm

In this article, preform optimization in closed-die forging has been studied. The main objective of the optimization process is to reduce forging force by changing the preform shape as a variable parameter. In this respect, a combination of neural network and genetic algorithms has been employed. The finite volume method (FVM) is used as a simulation tool for the forging process. Simulation results have been used in a neural network analysis and a genetic algorithm to optimize the forging force. The neural network was used in several stages for modelling the system. The optimization process contains three stages. In stage 1 the preform shape is obtained by open die forging. Stage 2 is used for closed-die forging process to obtain the forging force. Stage 3 is for the filling of the die cavity. The geometrical parametric design process was used to accelerate the operation. An aeronautical forging component has been selected as a case study. The final results showed a negligible discrepancy of 0.3 per cent for forging force between neural network and direct simulation results. The optimization results prove that a reduction of forging force equal to 50 per cent can be achieved in comparison with an initial preform with 10 per cent extra volume.

Processing and impact behavior of Al/SiCp composites fabricated by the pressureless melt infiltration method

In the current investigation, pressureless melt infiltration was applied to fabricate the Al/SiC composites based on the SiC porous preforms. The process was conducted by introducing the aluminum melt into the SiC preforms at 950 °C under the nitrogen atmosphere, without the aid of pressure. To explore development of melt infiltration, initial preforms were produced with variable SiC fractions (40, 50, and 60 vol.%) using three different SiC powders with the mean particle size of 20, 50, and 90 μm. While the infiltration of aluminum melt into the preforms with 40 vol.% initial SiC volume fraction (SiC particle size of 90 μm) resulted to the composites with final density of 0.94 theoretical density (TD), this value drops down to ∼0.9 TD for the composites produced by preforms with the SiC (90 μm) volume fraction of 60 vol.%. On the other hand, composites fabricated by 50 μm SiC powder (SiC volume fraction of 40 vol.%) demonstrated the final density of ∼0.91 TD. The impact resistance tests performed on the composites demonstrated an enhancement in the value of impact energy with an increase of SiC powder particle size. Results, additionally, revealed a significant superiority of impact energy for the composites fabricated by a combined melt infiltration and sintering (MIS) procedure compared to those produced by infiltration at 950 and 1350 °C.

Effect of geometric work-hardening and matrix work-hardening on workability and densification of aluminium–3.5% alumina composite during cold upsetting

The densification is a measure of deformation in upset forming of Powder Metallurgy (P/M) processes. A complete experimental investigation on the deformation behaviour of aluminium–3.5% alumina powder composite has been discussed for the case of triaxial stress state condition. Cold upsetting of aluminium–3.5% alumina composite with and with no annealing having different initial preform relative density and with different aspect ratio was carried out and the densification behaviour of the preform under triaxial stress state condition was determined. A new true strain considering the effect of bulging was taken into account for the case of determination of the hoop strain. Plots made for different preforms were analyzed for the densification behaviour of preforms considering the effect of both geometrical work-hardening (GWH) and the matrix work-hardening (MWH).