bluuebunny/crossref_metadata_2025 huggingface dataset:
Advanced modeling of shrinkage porosity in castings
Authors: Esser P , Schankies C , Khalajzadeh V , Beckermann C
Published: June 2020

Porosity due to solidification shrinkage is a troublesome defect in all types of metal castings. It limits the performance of cast components by adversely affecting the material’s strength, fatigue and creep properties. By reliably predicting porosity in casting process simulation, it can be minimized or eliminated. Here, a newly developed model for predicting porosity is presented. The model is based on the recent discovery that all shrinkage porosity nucleates and grows in regions of a casting where the solid fraction is the lowest. It calculates the feeding flows and pressure distribution in the liquid while accounting for the liquid density variation during cooling and solidification. It predicts the location, extent and amount of all types of shrinkage porosity in a casting, including riser pipes and large internal holes, surface sinks, and distributed micro-shrinkage. The model is numerically implemented in a standard casting simulation code. Comparisons to measurements in specially made steel castings demonstrate the capability of the model to accurately predict various types of shrinkage porosity.
A meshless solution of a of lid-driven cavity containing a heterogeneous porous medium
Authors: Hatić V , Rek Z , Mramor K , Mavrič B , Šarler B
Published: June 2020

The main objective of the present paper is to define and evaluate a benchmark test for solving the Navier-Stokes equations in heterogeneous porous medium. The benchmark is of high relevance for proper numerical simulation of flow pattern in the liquid-solid phase-change related phenomena. The test case represents a lid-driven square cavity which consists of a solid, a liquid, and a mushy part. Three different variations of the problem are solved, in which the ratio between the liquid and the mushy part is modified. The Reynolds and the Darcy number of this case are equal to 400 and 2.5×10−10, respectively. The Navier-Stokes equation, with an additional source term to take into account the Darcy effect, is solved with the local meshless diffuse approximate method. The method is structured by using the second-order polynomial basis vector and the Gaussian function to evaluate the weighted least squares approximation. The explicit Euler scheme is used to perform the time discretisation. The non-incremental pressure correction scheme is used to couple the pressure and velocity fields. Results are presented in terms of stream function, velocity magnitude, and mid-plane velocity profiles in the steady state. The accuracy of the numerical method is evaluated by a comparison with the finite volume solution obtained with a commercial solver and an investigation of the node arrangement effect.
Prediction of solidification structures in a 9.8 tonne steel ingot
Authors: Gerin B , Combeau H , Založnik M , Poitrault I , Cherif M
Published: June 2020

The control of the carbon macrosegregation level in steel ingots is important for the structural integrity of the final component. Previous studies using the SOLID® multiscale modelling software have shown that in order to obtain predictive results for the macrosegregation and the grain structure (CET, grain morphology) in steel ingots, a model needs to account for fragmentation of columnar dendrites as a source of equiaxed grains. The goal of this study is to show that a numerical model that takes into account fragmentation can describe the formation of the structures and the macrosegregation during solidification of a large steel ingot. The present article describes how fragmentation is taken into account in the multiphase numerical model used in the simulations. The simulation results are compared to experimental data from a 9.8 tonne ingot cast in A5/6 steel by ArcelorMittal Industeel. The model correctly reproduces the major features of the experimentally observed structure and macrosegregation. We show that the structures are formed very early on during solidification, whereas macrosegregation develops much more gradually. Our results also underline the importance of liquid flow and grain movement in order to correctly predict the final structure and macrosegregation.
Multiscale solidification simulation of Sr-modified Al-Si-Mg alloy in die casting
Authors: Zhou B , Laschet G , Eiken J , Behnken H , Apel M
Published: June 2020

Thermomechanical casting simulations incorporating solidification models are widely applied to improve the dimensional accuracy of casting components. The solidification path is commonly described based on Scheil-Gulliver assumptions which however fail to describe the effect of Strontium in Sr-modified Al-Si-Mg casting alloys. Strontium, even in small amounts, strongly affects the solidification morphology of the Al-Si eutectic together with its growth undercooling and hence the fraction solid–temperature relation during later stages of solidification. In order to address this problem, a dedicated micro-macro simulation approach is proposed here. The macroscopic thermomechanical casting simulation is linked with a spatially resolved multi-phase field simulation of the microstructure. Due to the fine fibrous morphology of the Si eutectic, a two-level homogenization scheme was applied to derive the effective mechanical properties of the Al alloy during its solidification. The proposed multiscale simulation and homogenization approach was applied to a permanent mould casting using an axisymmetric bowl cast from A356 for experimental validation.
A verification of thermophysical properties of a porous ceramic investment casting mould using commercial computational fluid dynamics software
Authors: Jones C A , Jolly M R , Jarfors A E W , Irwin M , Svenningsson R , Steggo J , Eriksson J
Published: June 2020

Defects in cast metals remain a common problem in many areas of the foundry industry, particularly in the investment casting of large area, thin-walled components for aerospace applications. During previous research, the thermophysical properties, density and porosity of a fibre reinforced ceramic investment casting mould were determined using several experimental techniques. Without verification, these experimental results remain nothing more than educated guesswork. The purpose of this study is to verify previous results and to more fully characterise the ceramic mould material with complementary measurements. A commercially available computational fluid dynamic (CFD) simulation package, Flow-3D®, was used in conjunction with a full-scale Ni-superalloy (IN718) casting to assess the accuracy of these results. By placing thermocouples strategically across the mould thickness, temperature profiles were determined and compared directly to predicted profiles extracted from the simulation by a custom-written Python script.
X-ray tomography, digital volume correlation and FE modelling: A synergistic combination to study the processing-structure-property relations in ductile iron
Authors: Andriollo T , Zhang Y , Fæster S , Thorborg J , Tiedje N S , Kouznetsova V , Hattel J
Published: June 2020

The mechanistic understanding of the processing-structure-property relations in ductile iron is still far from complete. One reason is that the impact on the mechanical properties of some of the microstructural features arising from the casting process can be hard or even impossible to investigate using experimental methods alone. The present work shows that a solution can be the synergistic combination of X-ray tomography, digital volume correlation (DVC) and finite element modelling, which are applied here to study the effect played by the Si micro-segregation and local residual stresses upon mechanical loading. First, miniaturized tensile and compact tension specimen are loaded incrementally while imaging with X-ray tomography. Then, the micro-scale displacement is reconstructed with DVC and used to prescribe the boundary conditions in high-fidelity 3D finite element models of the microstructure. Simulations are run considering or not the formation of the local residual stresses and build-up of micro-segregation during manufacturing. The numerical predictions are compared to the corresponding experimental data both at the macro-scale – applied load – and at the micro-scale – strain field reconstructed with DVC. This allows for a first assessment of the impact of the local residual stresses and Si micro-segregation on the mechanism of tensile deformation as well as of crack propagation of ductile iron.
Impact of local Si segregation on strain localization in ductile cast iron
Authors: Xu C L , Andriollo T , Lin F , Zhang Y B , Hattel J , Tiedje N
Published: June 2020

The distribution of Si content in tensile deformed ductile cast iron has been characterized using electron microscopy and correlated to the strain distribution determined based on 3D tomography data collected before and after tensile deformation and digital volume correlation analysis. The results show that the high plastic strain regions localize in bands consisting of large graphite nodules and deformed matrix with high Si content connecting the graphite nodules in the first-to-solidify regions. The bands are aligned about 45° with respect to the loading direction, which is close to the maximum shear direction.
Impact of crystal sedimentation and viscoplastic semi-solid dynamics on macrosegregation
Authors: Rodrigues C M G , Ludwig A , Wu M , Kharicha A , Vakhrushev A
Published: June 2020

A numerical investigation of melt convection with solid-phase transport during equiaxed solidification is performed to examine the structural and compositional evolution of an Al-Si alloy. Nucleation and growth kinetic laws are coupled with the general conservation equations employed in fluid dynamics to predict the development of the solidification structure. Besides crystal sedimentation due to buoyancy-induced forces in the low solid fraction range, the model covers also the viscoplastic semi-solid dynamics at high solid fractions. A test case is devised such that two viscoplastic structures grow from the vertical walls towards the centre of the domain and eventually merge at an arbitrary distance from the bottom of a simple cavity setup. This introduces difficulties for the solidification-driven feeding flow which has been associated with pressure drops across the domain. Dilatation of the mush is also predicted in the lower part of the solidifying viscoplastic mush, which means that additional melt is drawn to this area. Interestingly, besides liquid feeding, also a significant amount of solid feeding has been detected to compensate for solidification shrinkage. Such synergetic behaviour between the phases is analysed in terms of macrosegregation.
Sensitivity of macroscopic transport calculations to uncertain microscale relationships during metal alloy solidification
Authors: Coleman J , Krane M J M
Published: June 2020

The formation of grains during metallic solidification results in a multiphase system consisting of many moving interfaces. Models have been formulated in terms of variables describing the microscopic details of interface motion during solidification, but the computational cost prohibits their extension to the length scale of industrial castings. For this reason, macroscopic transport equations are mathematically formulated using averaging methods to replace the instantaneous description of interfaces. The most common approach is the volume-averaged, Eulerian approach relying on both the proper derivation of macroscopic field equations as well as uncertain interfacial conditions used to account for the average behavior of the interphase transfer occurring on the sub-grid length scale. In this work, common models used to describe the microsegregation occurring during solidification are evaluated in terms of the uncertainty of parametric inputs invoked in each model and their effect on macroscale predictions. We show that the qualitative macroscale predictions are not significantly changed by using more sophisticated microsegregation models, however significant uncertainty in input parameters used to describe the unresolved sub-grid interface is accumulated. Therefore, the use of simplified models is preferred until the uncertainty in model inputs can be reduced.
Microsegregation model including Soret effect: an application for Sn-Bi alloy
Authors: Santos Filho J E , Heringer R
Published: June 2020

We present an application of a microsegregation model that takes into account the Soret effect. This model, summarized here, lies in the context of the evaluation of thermodiffusion influence in alloys solidification. Initially, we deal with the thermodiffusion effect on the microsegregation scale. Subsequently, the Soret effect on macrosegregation shall be analyzed. The present model was conceived with similar considerations compared to the Gulliver-Scheil approach. A dimensionless parameter emerged from the model, which is potentially useful for assessing the Soret effect on the solidification of binary alloys. In the present work, this parameter was applied to an Sn-Bi alloy. The microsegregation model including the Soret effect can be widely used in the study of solute redistribution.
Cellular automaton modelling of M7C3 carbide growth during solidification of Fe-C-Cr alloy
Authors: Zhang H W , Zhang S , Wang Y C , Hao Y Z , Miao M , Nakajima K , Lei H , Wang Q , He J C
Published: June 2020

A microscopic cellular automaton combined with macroscopic heat and solute transport was developed to simulate the mutual growth and evolution of austenite and M7C3 carbide grains during Fe-C-Cr ternary alloy solidification process. The diffusion of solute C and Cr are contributed together to the constitutional undercooling, together with curvature undercooling, for obtaining the grain growth rate of austenite and M7C3 carbide. Results show that, the absorption of solute C and Cr by M7C3 grain and rejection by austenite grain promote the two grains’ cooperative growth. Once they approach to each other, the austenite grain quickly overgrows towards the M7C3 grain till finally envelops it. The simulated solidification morphology of the Fe-4wt%C-17wt%Cr alloy, predicted averaged grain size of M7C3 carbides and C and Cr concentration in austenite grains agree with the experimental measurements and solidification path prediction. The predicted average liquid concentration curve fits with the LR, GS and PE prediction at the initial M7C3 precipitation regime and after austenite grains fully enveloping towards the M7C3 grains, returns to overlap the LR, GS and PE prediction curves.
Three-dimensional needle network model for dendritic growth with fluid flow
Authors: Isensee T , Tourret D
Published: June 2020

We present a first implementation of the Dendritic Needle Network (DNN) model for dendritic crystal growth in three dimensions including convective transport in the melt. The numerical solving of the Navier-Stokes equations is performed with finite differences and is validated by comparison with a classical benchmark in fluid mechanics for unsteady flow. We compute the growth behavior of a single equiaxed crystal under a forced convective flow. As expected, the resulting dendrite morphology differs strongly from the case of the purely diffusive regime and from similar two-dimensional simulations. The resulting computationally efficient simulations open the way to studying mechanisms of microstructure selection in presence of fluid flow, using realistic alloy and process parameters.
3D cellular automaton modelling of silicon crystallization including grains in twin relationship
Authors: Pineau A , Guillemot G , Reinhart G , Regula G , Mangelinck-Noël N , Gandin Ch-A
Published: June 2020

Production of silicon for solar cells in photovoltaic systems is mainly based on directional casting processes. Twin nucleation is favoured during silicon growth due to the low-level twin energy of formation. As a consequence, in all solidification process, a large amount of grain boundaries (GB) are in twin relationship. A 3D cellular automaton (CA) model has been recently developed for the growth of multi-crystalline silicon including facet formation and nucleation of new grains in twin relationship. Activation of facets is based on an undercooling parameter assigned to each grain and for each of the <111> crystal directions. The model also considers nucleation and growth of grains on <111> facets corresponding to Σ3 twin relationships between twin grains. This model is first applied to comparison with experimental observations. It is found that impingement of growing grains that nucleated in Σ3 twin relationships meet during growth and form Σ3, Σ9 and Σ27 GB, in good agreement with experimental observations. Finally, the model is applied at a larger scale to generate grain structures representative of industrial practice. While quantitative experimental data is missing for comparison at such scale, the model is promising and its implementation in heat and mass transfer models should be considered for assistance to production of silicon for solar cells dedicated to photovoltaic systems.
Molecular dynamics simulation of heterogeneous nucleation from concave cavity at surface of grain refiner
Authors: Fujinaga T , Shibuta Y
Published: June 2020

Grain refiners are often used in practical production processes of metallic materials to promote and control nucleation. Although morphology of the grain refiner strongly affects nucleation behaviour, it is not well understood how unevenness of surface of the grain refiner affects nucleation from atomistic viewpoint. In this study, effect of concave cavity at surface of the grain refiner on heterogeneous nucleation is investigated by molecular dynamics (MD) simulation. HCP-Ti cube with a concave cavity is employed in the MD simulation as a grain refiner of the solidification of undercooled Al melt as a model study. HCP-Al solid is firstly formed at the tip or on the side wall of cavity and FCC-Al growth is followed on the exposed (0001) surface of HCP-Al for most of the cavities, whereas FCC-Al solid is directly formed on HCP(0001) terraces at the side wall of the cavity with large-obtuse apex angle.
The integration of structural mechanics into microstructure solidification modelling
Authors: Soar P , Kao A , Djambazov G , Shevchenko N , Eckert S , Pericleous K
Published: June 2020

In situ structural mechanics are an often neglected area when modelling alloy microstructure during solidification, despite the existence of practical examples and studies which seem to indicate that the interaction between thermal or mechanical stresses and microstructure can have a significant impact on its evolution and hence the final properties at a macroscopic level. A bespoke structural mechanics solver using the finite volume method has been developed to solve the linear elasticity equations, with design choices being made to facilitate the coupling of this solver to run in situ with an existing solidification model. The accuracy of the structural mechanics solver is verified against an analytic solution and initial results from a fully coupled system are presented which demonstrate in a fundamental example that the interaction between structural mechanics and a solidifying dendrite can lead to a significant change in growth behaviour.
Calphad-based phase-field study of the interplay between spheroidal graphite growth and chemical segregation in ductile cast iron
Authors: Eiken J
Published: June 2020

Spheroidal graphite in ductile cast irons forms in a divorced eutectic solidification, controlled by interstitial diffusion of carbon through the enveloping austenitic shell. As technical cast irons are multicomponent alloys, carbon diffusion can strongly be affected by content and chemical gradient of other solute elements. During growth of a eutectic cell, all solute elements are partitioned at the austenite/liquid interface. Substitutional diffusion within the austenite is almost negligible, but expansion-induced spatial displacement of the iron-rich matrix and solute atoms during graphite growth significantly complicates multidimensional numerical simulation. A recently developed volumetric multi-phase-field approach, implemented in the Micress software, now accounts for the volume expansion and related matter and solute transport. In the present case study, this approach is applied to investigate the evolving chemical gradients and their potential effect on carbon diffusion during growth of a three-dimensional eutectic cast iron cell. Phase and concentration dependent thermodynamic data, partial molar volumes and diffusion coefficients are evaluated from linked Calphad-databases. The interface properties of the polycrystalline spheroidal graphite nodule are modelled based on a dedicated effective multi-facetted anisotropy function. A special target is to investigate whether increase in Si content may result in a significant reduction of the carbon flux, eventually favoring graphite degeneration and chunky growth.
Effects of Bi addition on Si features, tensile properties and wear resistance of hypereutectic Al-15Si alloy
Authors: Pereira C L , Gomes L F , Spinelli J E
Published: June 2020

Al-Si alloys are very important in the automotive industry. This is thanks to their high strength to weight ratio, suitable fluidity, good corrosion resistance and high productivity. The shape of the eutectic Silicon (Si) has been widely studied since it is considered an index of quality regarding many application properties. Understanding the effects of alloy additions on the morphology of Si has drawn researcher’s attention. One of these elements of interest is Bismuth (Bi), which may be part of the composition of Al-Si alloys either as an addictive or a contamination. Hence, the microstructure aspects related to the presence of Bi are important requiring further consideration. In the present study, Al-15wt% Si hypereutectic alloy is modified with 1.0 wt% Bi. The goal is to compare the effect of this addition on the morphology of the phases forming the microstructure and on tensile/wear properties. In order to pursue that comparison, previously available data for the binary Al-15wt% Si alloy will be used. Various samples characterized by distinct cooling rates were generated by transient directional solidification of the ternary Al-Si-Bi alloy. The experimental variations of the eutectic spacing will be compared to each other based on their trends. It was found that the addition of minor Bi content (∼1%) permitted tensile strength and ductility of 195 MPa and 14%. Furthermore, wear resistance was improved thanks to Bi. The reasons for that will be outlined.
Applications of pattern recognition for dendritic microstructures
Authors: Strickland J , Nenchev B , Dong H B
Published: June 2020

The Primary Dendrite Arm Spacing (PDAS) is the most important length scale in directionally solidified single crystal alloys. It determines the propensity for defect formation, solution heat treatment times and mechanical properties of the material. In this work a CMSX4 single crystal sample was imaged under a Scanning Electron Microscope (SEM). An automatic dendritic mapping (DenMap) algorithm using Normalised Cross-Correlation (NCC) is combined with Shape-Limited Primary Spacing (SLPS) to determine the local nearest neighbour dendrites and the corresponding dendritic packing. The algorithm located the dendritic centres, calculated the local PDAS, packing pattern, and relationship between PDAS and packing pattern for 256 dendrites in 1 minute 10 seconds. This is the first fully automatic method to produce a clear Gaussian distribution of local PDAS and packing pattern; thus, enabling rapid data gathering potential for single-crystal microstructures.
Cellular automaton modelling to predict multi-phase solidification microstructures for Fe-C peritectic alloys
Authors: Ogawa J , Natsume Y
Published: June 2020

In this study, we developed a cellular automaton (CA) model to simulate the multiphase microstructural evolution of the solidification of Fe-C binary peritectic alloys. Three phases were considered in the model: δ, γ, and liquid (L). To simulate microstructures formed by the peritectic transformation, moving interfaces at δ-γ, δ-L, and γ-L transformations were introduced for diffusion-controlled growth. The coarsening growth of γ grains after solidification of peritectic alloys was modelled using the CA method. Numerical simulations of multi-phase microstructure evolution for hyper-peritectic and hypo-peritectic alloys were performed in two and three dimensions. In these simulations, the nuclei of γ phases were formed at the δ/L interface below the peritectic temperature. After nucleation of the γ phase in hyper-peritectic alloys, the δ phase in the calculation domain disappeared before γ solidification was completed. Conversely, in hypo-peritectic alloys, the L phase disappeared before the δ-γ transformation was complete. Moreover, the coarsening of γ grains occurred for both alloys after the end of the peritectic transformation. These outcomes agree with the fact that the phase transformation of alloys involves the solidification of peritectic alloys. Thus, we confirmed that the proposed model was a valid approach to simulating multi-phase microstructures formed by the solidification of peritectic alloys.
A cellular automaton approach for the prediction of grain size in grain refined alloys
Authors: Jacot A
Published: June 2020

Grain refinement by inoculation is widely practised in metal casting, in particular for aluminium alloys. During the last decades several modelling techniques have emerged to quantitatively predict solidification microstructures. The prediction of grain size remains however a challenge due to the complex competition between nucleation and growth, and physical phenomena taking place at very different length scales. Models often address the thermal recalescence and sometimes the suppression of nucleation by the solute boundary layers. The possible clustering tendency of the nucleant particles is however usually not considered, although it can play an important influence on the final grain size. This effect is particularly difficult to quantify because it requires a small-scale approach to describe the clusters, while a large computational domain is needed for grain size statistics. A cellular automaton (CA) model tracking the grain envelopes was developed to address this challenge. The spatial distribution of the nucleant particles and the solute diffusion field in the intergranular liquid were represented directly on the CA grid. Predicted grain sizes were first compared successfully with published experimental and modelling data. An investigation of the role of clustering of nucleant particles was then carried out, which demonstrated the potential of the model to address this topic.
Castings distortion of gas turbine engine parts during solidification and cooling
Authors: Inozemtsev A , Dubrovskaia A , Dongauzer K , Alapanova A , Maleev A
Published: June 2020

The paper studies the matters of numeric simulation of the processes of casting, crystallizing and cooling down to room temperature, and addresses the related problem of the stress-strain state of the casting process in manufacturing the cast parts of a gas turbine engine. The influence of the technological parameters of casting onto the development of the deformation defects was evaluated. The works were performed on incorporating predeformation into the burn-out model for compensating temperature deformations during casting, and on production and control of the above casting with predeformation.
Molecular dynamics study of composition dependence of solid-liquid interfacial energy of Fe-Ni binary alloy
Authors: Ueno K , Shibuta Y
Published: June 2020

Interfacial properties strongly affect solidification microstructure of practical alloy materials. Therefore, it is essential to understand interfacial properties including composition dependence for target alloys. In this study, composition dependence of solid-liquid interfacial energy of Fe-Ni alloy is investigated by molecular dynamics simulations in conjunction with a capillary fluctuation method. The solid-liquid interfacial energy of Ni-rich composition taking FCC-solid phase is larger than that of Fe-rich composition taking BCC-solid phase. Moreover, solid-liquid interfacial energy has a high anisotropy at the composition with FCC-solid phase compared to the one with BCC-solid phase.
Concurrent and coupled resolution of fluid flow and solid deformation in solidification processes
Authors: Zhang S , Guillemot G , Gandin C-A , Bellet M
Published: June 2020

Control of macrosegregation phenomena and deformation related defects is the main issue in solidification processes. Numerical modelling of casting provides an answer to industrial needs to master these defects. As a first step, it is essential to achieve a concurrent computation of the fluid flow in the bulk liquid and stress-strain evolution in the already solidified regions. For this specific purpose, a partitioned solution algorithm is developed to model both ingot casting and continuous casting processes: liquid flow induced by natural convection or filling step, solidification shrinkage as well as thermal deformation of solid phase are all taken into consideration. This article is mainly composed of two parts. In the first part, details of the model itself are described. In the second part, applications dedicated to steel solidification are proposed.
The ultrasound effects on the formation of the solidification structure of A356 ingots processed via a 2-zone induction melting furnace
Authors: Dong A , Nastac L
Published: June 2020

To study the formation of the solidification structure including the columnar-to-equiaxed transition (CET) under the influence of ultrasound, a 2-zone furnace system and an ultrasound equipment were utilized. The 2-zone furnace system consists of an induction furnace with a top coil and a bottom coil, a graphite crucible, and. a water-cooled chill block located at the bottom of the crucible. By controlling both the top and bottom coil output power independently, the furnace can create various temperature gradients and cooling rates in different regions of the graphite crucible. The ultrasound probe was inserted at the top of the crucible. The top of the crucible was also thermally insulated. Temperature measurements were performed at different locations in the crucible. Optical microscopy was used to characterize the microstructure of the A356 cylindrical ingots. The effects of ultrasound on the microstructure formation during solidification of A356 alloy was studied. A numerical model was developed to compute the temperature gradients and mushy zone evolution in the crucible and to assist in developing of solidification maps.
In situ X-ray observations of transient states in arc weld pools
Authors: Wu F , Falch K V , Drakopoulos M , Mirihanage W U
Published: June 2020

Metallic alloys coalesce via extremely rapid melting and subsequent solidification to form fusion welded joints. The melt pool evolution in melting and solidification sequences during the welding process determines the formation of the final weld joint shape, microstructure and defects. The scientific insight on weld pool evolution and related phenomena can be a key contribution to enhance structural integrity and resilience of the welded structures or components. However, inherent complexity with multi-physics phenomena, associated high temperatures and the rapidness of the processes make direct experimental investigation of welding is extremely demanding. Thus, internal flow behaviour during welding or other melt-pool-based metal processing such as additive manufacturing remains unclear and hinders progression to process optimisation. In this contribution we report the observation of melt pool dynamics that take place during electric arc welding, obtained through in situ synchrotron imaging at millisecond scale. The analysis flow patterns along with the quantified weld pool surface dynamics revealed us to how different contributing forces dictate the flow conditions over the distinct durations of the relatively short existence of the liquid phase. Our preliminary results suggest the existence of arc, surface tension and gravity dominant regimes during the evaluation of the weld pool. Further, we present our observations on how different welding parameters influence these regimes and develop into different transient conditions.
Phase-field study on microstructure formation in Mar-M247 during electron beam welding and correlation to hot cracking susceptibility
Authors: Böttger B , Apel M , Jokisch T , Senger A
Published: June 2020

Ni-base superalloys are frequently used for cast components in the aero-engine and power generation industries. For joining and repair of these components, beam welding is often the method of choice in industrial praxis. However, precipitation-strengthened nickel alloys generally present poor weldability as a consequence of their high weld cracking susceptibility, with high segregating alloys like Mar-M247 even being considered unweldable. Therefore, strong efforts are taken on optimizing techniques and parameters to reduce crack formation during welding of these alloys. Optimization of welding parameters can be assisted by virtual modelling methods through different scales. To be able to focus onto the factors which eventually are responsible for crack formation during welding, comprehensive modelling of the whole process chain is required, starting from a realistic model of the base material and a simulation of the heat source on the macro-scale, and including melting and microstructure formation during welding on the micro-scale. Then, based on the thermal history and the exact microstructure, cracking susceptibilities during solidification can be deduced by hot cracking models adapted to the specific conditions. In this paper, results of microstructure simulations are presented for the technical superalloy MAR-M247 using the phase-field software MICRESS with coupling to Calphad databases. Based on prior phase-field simulations of equiaxed and columnar microstructures of the base material as well as results of a macroscopic simulation of the heat source, melting and subsequent solidification of MAR-M247 has been simulated for two different welding parameter sets. As-weld microstructures are compared to experimental welds, and the virtual hot cracking susceptibility, obtained from the simulation results using a modified Rappaz–Drezet–Gremaud (RDG) hot cracking criterion, is discussed against experimental crack observations.
Simulation study on the effect of fuel injection and air intake boundary setup on the brake torque response by using comprehensive vehicle model for natural gas vehicle (NGV)
Authors: Rahim M F A , Jaafar A A , Taha Z , Mamat R
Published: June 2020

An analytical, dynamic and comprehensive vehicle model, replicated a high-pressure direct injection compressed natural gas (HPDI-CNG) engine in a vehicle is proposed with the objective to study the effect of fuel injection and air intake boundary condition on the brake torque response. The model simulated the output torque in transient simulations of the natural gas vehicle (NGV) in speed-sweep mode test. The vehicle model has coupled an analytical engine model developed in Simulink with a Simscape driveline model which consists of a clutch model, a simple transmission gear and a simplified vehicle model. In all problem, independent input to the model is the throttle opening ramp. The adjusted parameter in the first study is the methods to calculate the mass of fuel inlet which is based on i) fully experimental data, ii) measured air to fuel ratio (AFR) and (iii) constant injector mass flow rate. In the second problem, the pressure limit of the manifold absolute pressure (MAP) is adjusted as (i) fully experimental data (ii) 1.2 bar (iii) 1.5 bar and (iv) unlimited pressure limit. The dependent parameter in all problem is engine output torque. The results have been compared with the actual data of torque from chassis dynamometer measurement. For the effect of fuel inlet boundary set up, in the fully predictive mode, the model predicted an almost constant maximum torque at a value about 70 Nm, whereas the measured data only produced the same peak value at a very limited instant. If the model used measured AFR as the fuel input boundary, the model overpredicted the maximum peak torque of 70 Nm. In the study on the effect of MAP limit, the maximum torque for 1.2 bar, 1.5 bar and unlimited pressure set up has produced a maximum torque of 45, 62 and 70 Nm, respectively. Results of the first study showed that the use of constant injector mass flow rate has a tendency to simulate an ideal engine acceleration process. The prediction is closed to the measured data if the fuel mass is calculated based on the measured AFR. However, the use of measured AFR in our opinion have reduced the model predictability. In the second study, the increased MAP limit significantly increased the maximum brake torque response. However, the model cannot predict the abnormalities found in the experimental data. The use of MAP limit demonstrated the sensitivity of the output torque on the maximum value of the engine MAP. The results indicated that the injection fuel inlet boundary and the MAP limit have a strong significance on the model prediction and need to be improved for future use of the model.
A review of ultra-high temperature materials for thermal protection system
Authors: Al-Jothery H K M , Albarody T M B , Yusoff P S M , Abdullah M A , Hussein A R
Published: June 2020

Ultra-High Temperature Materials (UHTMs) are at the base of entire aerospace industry; these high stable materials at temperatures exceeding 1600 °C are used to manage the heat shielding to protect vehicles and probes during the hypersonic flight through reentry trajectory against aerodynamic heating and reducing plasma surface interaction. Those materials are also recognized as Thermal Protection System Materials (TPSMs). The structural materials used during the high-temperature oxidizing environment are mainly limited to SiC, oxide ceramics, and composites. In addition to that, silicon-based ceramic has a maximum-use at 1700 °C approximately; as it is an active oxidation process over low temperature and water vapor environment condition. However, a great emphasis is required for developing structural materials in oxidation and rapid heating environment where the temperature is greater than 1700 °C. This review covers briefly all main types of Thermal Protection Systems (TPSs) and all the materials are used to fabricate them with the maximum operational temperatures. Also, it covers the promised UHTMs (SiC, ZrB2, HfB2, SiB6 and B4C) which are currently using for several aerospace applications, especially for TPS. Besides, it discusses the oxidation of SiC, B4C, SiB6, ZrB2 and HfB2. Therefore, the carbides and borides of the transition metals, Zr and Hf have a high-melting temperature and good stability in forming high-melting temperature oxides.
The effects of temperature, residence time and particle size on a charcoal produced from coconut shell
Authors: Ahmad R K , Sulaiman S A , Inayat M , Umar H A
Published: June 2020

Coconut shell charcoal is an important product obtained from coconut shells, which are widely used as domestic and industrial fuel. Wastes of coconut residues (shells, husks and coir) from processing of coconut milk and oil industries are widely generated everywhere all over the world. They have the potential of use as a fuel in renewable energy for different applications. In this study, the production of charcoal from coconut shell through the process of pyrolysis was conducted to determine the influence of particle size, temperature and residence time on the charcoal weight loss. Pyrolysis is a thermochemical conversion method which converts biomass into more valuable products in form of solid (charcoal, bio-char and activated carbon), liquid (oil) and gas in the absence of oxygen. The process was carried out under various process conditions of temperature (300 °C, 400 °C, and 500 °C), residence time (15 minutes, 30 minutes, and 60 minutes), and particle size (5.0 mm and 25.0 mm). It was found that for both the temperature and the residence time, the weight loss from the coconut shell increase linearly with increase in temperature and residence time. The particle size has influence in percentage weight loss. The resulting charcoal obtained can be utilized as an alternative energy resource for different applications.
Effect of reaction time and microwave power on coil temperature during microwave-metal interaction pyrolysis of plastics
Authors: Arshad H , Sulaiman S A , Hussain Z , Moni M N Z
Published: June 2020

Rapid rise in production of plastic waste has posed a threat to environment due to its nonbiodegradable nature. In recent years, microwave assisted pyrolysis of plastic waste has emerged as a promising solution toward reduction of waste and recovery of value-added products and fuels. Previous works on microwave-metal interaction pyrolysis estimated only the peak value of coil temperature at a constant microwave power without monitoring complete reaction. The current study was directed toward investigating the effect of reaction time and variable microwave power on the coil temperature during microwave-metal interaction pyrolysis of plastics. The experiment was performed on individual plastics PS (polystyrene), PP (polypropylene) and LDPE (low density polyethylene) for comparative analysis. Pyrolysis was carried out for a reaction time of 30 minutes at different values of microwave power in the range of 500-2500 W. Type K thermocouple was used to monitor temperature of metal coil. Fluctuation in temperature of coil was found to be a consequence of interaction of coil and thermocouple with the microwaves. Maximum heating rate was observed in the first 5 minutes of microwave exposure. The slopes of average temperature versus microwave power were found to be nearly equal estimated as: PS = 0.24 °C/W, PP = 0.20 °C/W, LDPE = 0.18 °C/W, which indicated consistency in heating process for each plastic, achieved by the current set-up. Further, it was inferred that nature of plastic pyrolyzed had insignificant influence on coil temperature due to absence of direct contact between plastic and the coil.
Characterisation of oil palm trunk and frond as fuel for biomass thermochemical
Authors: Umar H A , Sulaiman S A , Ahmad R K , Tamili S N
Published: June 2020

The rate of oil palm production in Malaysia increases annually and as a result, the oil palm wastes, especially oil palm trunk (OPT) and oil palm fronds (OPF) remain abundant. A suitable way of converting this abundant waste to renewable energy is through thermochemical conversion. Thus, this study investigates the characteristics of OPT and OPF biomass, for use as feedstock in thermochemical processes like gasification, pyrolysis, and combustion. The analysis carried out includes; ultimate (CHNSO) and proximate (thermogravimetric) analysis, calorific value, field emission scanning electron microscopy (FESEM) and x-ray fluorescence (XRF). Both feedstocks exhibited potential for use as fuel in biomass thermochemical conversion. The CHNSO analysis showed the presence of sufficient carbon, hydrogen and oxygen elements in both feedstocks, with carbon being the highest 45.42% in OPT and 43.35% in OPF. The percentages of nitrogen and sulphur which are required to be less for a good fuel were also obtained in low quantities for both fuel; 0.47% and 0.13% in OPT and 0.76% and 0.45% in OPF, respectively. The thermogravimetric analysis revealed both feedstocks to be having high volatile matter 62.28% in OPT and 66.10% in OPF. Meanwhile, sufficient fixed carbon content of 26.18% in OPT and 25.68% in OPF with low ash content of 9.82% in OPT and 6.32% in OPF were obtained in the analysis. FESEM and XRF were used to investigate the surface morphology, elemental and mineralogical nature of the samples. The findings were compared with those of other biomass and non-biomass materials. The EDX graph showed the presence of carbon and oxygen in a higher amount while in the XRF analysis CaO and K2O were the major oxides present in both OPT and OPF, with a low amount of SiO making the feedstocks less prone to agglomeration during thermochemical conversion.
Study of effect of moisture and temperature on thermal and physical properties of limestone using a transient plane source technique
Authors: Anjum F , Rasool F , Mohyudin F , Ameen A , Naz M Y , Ghaffar A , Shukrullah S
Published: June 2020

This study investigated the thermophysical properties of limestone in its dry and moist states. A thermal constant analyser, based on Transient Plane Source (TPS) technique, was used to study the thermophysical properties. Temperature dependence of thermophysical properties of limestone was investigated by elevating the temperature up to 433 K. The chemical and mineral composition of samples were studied using SEM-EDS and XRD analysis. The thermal conductivity of dry and moist limestone showed that in situ measurements are necessary for the precise determination of thermal properties. The variations in thermal properties of limestones as a function of temperature were described by mineral composition and heat transfer mechanism. The thermal conductivity of limestone was measured in the range of 2.586 to 3.054 Wm−1K−1. The thermal diffusivity of samples was ranged from 1.390 to 1.601 mm2s−1while specific heat capacity of limestone was in the range of 1.847 to 2.066 MJm−3K−1. A noticeable change in thermal properties of moist limestone was observed as compared to the dry limestone.
Viscosity impact investigation on erosion of carbon steel in sand-mixed-polivinyl alcohol
Authors: Naz M Y , Khan N A , Naeem M , Sharif F , Heral F A , Ghaffar A , Shukrullah S
Published: June 2020

Erosion in oil and gas production sector is predominantly caused by fine particles’ migration into the processing facilities. Fine particles are mostly transported to the facilities via carrier fluid. Other than sand, the viscosity of the carrier fluid also contributes to the sand erosion phenomenon. However, the impact of viscosity on sand erosion is not fully discovered by previous researchers. Therefore, this paper investigated the impact of fluid viscosity on erosion of carbon steel surface. In the presented work, an experimental rig was fabricated and tested for the study of impact of fluid viscosity on erosion of the carbon steel by considering the water mixed-polyvinyl alcohol as a carrier fluid. The metal coupons were impacted with sand slurries of different viscosities. Scanning electron microscopy along with energy dispersive spectroscopy and Universal scanning probe microscopy were used to analyse the centred and adjunct areas of the coupons. These analyses revealed that the viscous slurry is least effective in removal of metal surface in comparison with the pitting erosion. The obtained results reflected a decrease in erosion rate as the fluid viscosity upsurges and the type of metal surface erosion changes from uniform erosion to pitting erosion by fluid viscosity increment.
Experimental investigation of impact of dust accumulation on the performance of photovoltaic solar module
Authors: Naz S , Nadeem M , Zain-ul-Abideen M , Buttar S K , Shukrullah S , Naz M Y , Jamil Y
Published: June 2020

The effect of dust and sand on the surface of photovoltaic module has been investigated experimentally in this paper. The size distribution analysis of each sample was carried out using digital microscope. The chemical composition was investigated through EDX analysis. Experiments on photovoltaic solar module were conducted under controlled conditions by using artificial light source at different tilt angles and a dust blower. It has been concluded that there was only a small difference of degradation in maximum voltage and current when dust and sand was deposited on photovoltaic panel. The voltage decrement was 9.1%, 3.1%, 1.2% and 6.1% at tilt angles of 35°, 45°, 55° and 65°, respectively. These results reveal that the solar panel should be installed at angles between 45° and 55° in order to minimize the dust impact.