bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Blended Lime-GGBS Slag on the strength of Laterite
Authors: Md Nayan Khairulnisa’ bt. , N. L. Ling Felix , Abu Talib Zaihasra bt. , Irwan P. Harahap M. , Ho S. C.
Published: May 2019

Residual soils are referred to soils that formed through process of physical and chemical weathering of in-situ rocks. Reactions of various physical and chemical weathering agents had resulted in physical and chemical variability of residual soil and site dependent. The structure and minerals of in-situ rock were degraded physically and chemically and thus making its less resistance to load compared to un-weathered parent rock. Hence, it is important to stabilize the residual soil. Different ratios of blended hydrated lime and Ground Granulated Blast Furnace Slag (GGBS) namely 10:0, 9:1, 8:2 and 5:5 were utilized in this study. The percentage of admixtures was set at 10% with respect to its dry mass of soil. Unconfined compressive strength of treated soil specimens were determined after 7 days, 14 days and 28 days of humid curing. The water contents of the specimens were found to decrease slightly with an increment of curing periods while the strengths of the stabilized specimens were increased with curing periods. The highest unconfined shear strength at 28 days was recorded as 321.74 kPa with 8.18% axial strain. Thus, it showed that the use of blended lime and slag can improve the strength of residual soil. However, the treated samples failed to achieve the minimum strength increment of 345 kPa to be considered as an effective stabilization as stated in ASTM D4609. Some other factors namely curing temperature and Initial Consumption of Lime (ICL) should be considered to optimize the strength of the stabilized materials.
Monitoring strain development of soil slope using distributed optical fibre sensor
Authors: Awang Ismail Dayangku Salma bt , Kassim Azman , bin Mohamad Hisham , A Rashid Ahmad Safuan , Bunawan Aliff Ridzuan
Published: May 2019

Rainfall infiltration is well-known as one of the important factors that lead to slope failure in tropical areas such Malaysia because it’s significant fluctuation of pore water pressure due to monsoon seasons. In this paper, a distributed sensing optical fibre system named Brillouin Optical Time Domain Analysis (BOTDA) is used to monitor the strain development of a laboratory soil slope model. The aim of study is to determine the plane failure of a residual soil slope under rainfall infiltration and subsequent loading impact using BOTDA technology. A soil slope model was constructed from Malaysian residual soil slope and tested under various rainfall infiltration patterns and sequential loadings. A continuous ribbon optical fibre has been directly embedded in the soil slope to measure the soil strain. The paper only presented on soil strain response due to rainfall infiltration and relations to the pore pressure development within the finite slope. From the experiments, it has been observed that the optical fibre has been able to capture soil strain during infiltration which proven the sensitivity of optical fibre to measure soil strain. The maximum strain observed was about 850 microstrain (µε) which occurred at the third layer of slope height (L1) at 8-hour of infiltration. After 24-hours of infiltration, the strain was observed to be constant for all layers; Layer 1 (L1) = 302 µε, Layer 2 = 210 µε and Layer 3 (L3) = 190 µε in which the whole sample was clearly seen in a fully saturated condition and the negative pore pressure has remained constant throughout the depth.
Strain and temperature calibration of Brillouin Optical Time Domain Analysis (BOTDA) sensing system
Authors: Ismail Awang , binti Siat @ Sirat Qurratu Aini , Kassim Azman bin , Mohamad Hisham bin
Published: May 2019

Instrumentation plays an important role in monitoring the performance of the geotechnical structures especially slope as it can be an effective approach for many unstable or potentially unstable. In the recent study, BOTDA interrogator is used to monitor the strain development on a laboratory soil slope model in order to assess the failure mechanism of residual soil slope under rainfall infiltration and surcharge loading. By understanding the concept of BOTDA technology which based on the Brillouin frequency shift (Δv

b
), it possible to monitor changes in soil movement. Thus, the aim of the paper is to evaluate the parameter configuration of the BOTDA interrogator by determining both strain and temperature coefficients associated with the signal differences. The methodology presented as for acquiring the coefficients by calibrating the signal difference in terms of strain and thermal characteristics only for 12 ribbon Fujikura optical fibre sensor. As a result, the coefficient over a Brillouin signal for Fujikura optical fibre is 20 µε and 1°C for strain and temperature respectively. Therefore, the raw data obtained by the interrogator which in Megahertz unit can be evaluated in term of strain and temperature with respect to the coefficients.
Deformable unsaturated laterite soil under vibration impact with dissimilar moisture content
Authors: Abd Rashid MF. , Alias N. , Ahmad K. , Sa’ari R. , Ramli MZ. , Ibrahim Z.
Published: May 2019

Vibrations from vehicle traffic, machinery and operations from construction activities such as blasting are examples of some natural and man-made vibration phenomenon’s that can cause dynamic stress when imposed onto soils. In order to ensure sustainability of the geo-environment, the impacts caused by these vibrations as well as the changes in moisture content needs to be addressed. To achieve this, the behaviour of vibrated deformable double-porosity under dissimilar moisture content in non-repeated vibration was assessed and characterized through laboratory experiments. Investigation of deformable unsaturated laterite soil by aggregating laterite soil using 29%, 30%, 32% and 34% moisture content was carried out and presented in this paper. An acrylic soil column, accelerometer and vibrating table were used to conduct the experiments. The acrylic columns were filled with each aggregated soil and the soil was then compressed to a height of 10 cm, which had been pre-determined beforehand. Accelerometers were installed to a vibrating table where each soil column was tested to measure the time histories of high-frequency acceleration on the surfaces of both the laterite soil and vibrating table. Acceleration was observed at two points, namely; (1) the surface of the soil sample and (2) the surface of the vibrating table. The amplitude of the vibrating table was increased in order to test for repeated vibration. Maximum amplitudes were recorded by collecting the acceleration time histories and the amplitude of displacement was increased in order to carry out the tests. The outcome of the tests demonstrated that there was an increase of the acceleration response in non-repeated vibration when moisture contents were also increased. For the vibrated samples that were used, it was found that there was a rearrangement of the soils structure and as expected, the porosity characteristics that were identified had influenced the liquid penetrations’ speed.
Infiltration type slope stability method using non-linear shear strength behaviour
Authors: Md Noor M J , Muda M A , Ramle M M
Published: May 2019

Shallow slope failure in hilly area triggered by rainfall infiltration is very common in the tropics and this is very difficult to quantify using the conventional slope stability methods. Those methods assess the failure by elevating the groundwater table (GWT) and apply the Terzaghi’s linear shear strength envelope with cohesion intercept. This is despite knowing that the location of the GWT is far below to have any influence on the failure at the slope face and the true soil shear strength behaviour is perhaps non-linear at the low stress levels with zero cohesion intercept. As a result such failure cannot be pre-detected and this pose risk to the public safety if the slope is close to human activity. In order to replicate the true mechanics of failure an Infiltration Type Slope Stability Method using the non-linear failure envelope with zero cohesion intercept has been applied to assess a slope failure in Bandar Baru Selayang, Selangor, Malaysia. Consolidated Undrained Triaxial tests have been conducted on undisturbed soil specimens to substantiate that the failure envelope is perhaps non-linear at low stress range and has zero cohesion intercept. The slope stability analyses back calculate the failure by considering various depths of infiltration. This approach managed to prove that the factor of safety (FOS) is less than unity when the wetting front reached the depth of the actual slip failure surface.
3-D numerical model of jack force interaction to segmental tunnel lining in soft soil
Authors: Mohamed El-Sayed Osama , Norafida Jusoh Siti , Asnida Adbullah Rini , Abang Hasbollah Dayang Zulaikha
Published: May 2019

The construction process of a bored tunnel is a complicated process. During tunnelling, loads were acting on tunnel and tunnel lining were installed to support excavation. Simultaneously, soil redistribution induced by tunnel excavation leads to lining to deform. One of the parameters that affect global soil-tunnel behaviour is the jack forces. Jack force is exerted during the tunnel advancement to install the lining and the same time to enhance tunnel face stability. The complexity of jack force application to ensure the overall tunnel stability is not fully studied yet. Hence, the impact of jacking force on segmental tunnel lining and surrounding soil during the tunnel advance is still unclear. This paper presents a numerical simulation by using ABAQUS/Standard 3D FE software to determine and investigate the lining deformations/jacking force relationship. The behaviour of different tunnel lining thickness applied with a variation of jack forces in the tunnel-boring machine (TBM) were examined. The result based on the numerical model explained that the jacking force required to advance is related to the cross section area of segments. Finally, a relation has been established between the segment’s thickness and the jacking force t hat required advancing through a certain soil block with specific loads cases. The findings showed that the complex geological features and loads case applied to cause great stress on the tunnel face which have to be encountered by a certain thrust magnitude to advance the tunnel. The model analyses the contact reaction and radial reaction to the segment as a result of the axial force that is exerted by jack thrust and bending moment due to strata load, respectively. However, a proposed model that suggests a certain step to investigate and analyse the magnitude of jack forces is required.
Dam break test for scaled down slab beam and flat slab Dom-ino house structural system
Authors: Hanafi Roslan Muhammad , Kadir Marsono Abdul
Published: May 2019

Tsunami is a succession of waves travelling throughout water body which is resulted by the sudden displacement of a substantial volume of water on the ocean. This disastrous event typically generated due to seismic activity occurs on the seabed or any kind of disturbance that happen either naturally or man-made, below or above the ocean. The hydrostatic pressure produced during this catastrophic event might cause significant damage to many common structures should that they are not being built to resist such imposed load by the tsunami. Tsunami field survey observations also indicate that the structural failure would be escalated more in the presence of water borne debris such as wooden logs, vehicles, containers or other heavy objects. Through this paper, the outcomes of the experimental study are obtainable for the quantification of the hydrodynamic pressure force on the structures. The structure used for the experiment is a scaled down 1:10 model by utilizing the flat slab structural system, a typical structural system that being used in most building worldwide other than the slab beam structural system, thus resembling the exact behaviour of failure to the real structure when it imposed with the tsunami pressure.
Geomechanical strength of carbonate rock in Kinta Valley, Perak, Malaysia
Authors: Goh T L , Ailie S S , Amanina M Nur , Ainul M M R , Abdul Ghani R , Norbert S , Lee K E
Published: May 2019

The geomechanical strength of rock materials plays a significant role in influencing the stability of both cut rock slopes and underground openings. The strength characteristics are influenced by both material characteristics and the condition of weathering. This paper presents a systematic approach to quantify the rock material strength characteristics for material failure and material & discontinuities failure by using uniaxial compressive strength, point load strength index and Brazilian tensile strength for carbonate rocks. The mean value of compressive strength, point load strength index and Brazilian tensile strength for with material failure and material & discontinuities failure were 76.8±4.5 and 41.2±4.1 MPa respectively. The Point load strength index for material failure and material & discontinuities failure were 3.1 ± 0.2 MPa and 1.8 ± 0.3 MPa respectively. The Brazilian tensile strength with material failure and material & discontinuities failure were7.1 ± 0.3 MPa and 4.1 ± 0.3 MPa respectively. The results of this research revealed that the geomechanical strengths of rock material of carbonate rocks for material & discontinuities failure deteriorates approximately ½ from material failure.
Monitoring subsurface ground movement using fibre optic inclinometer sensor
Authors: Ghazali M.F , Mohamad H
Published: May 2019

The monitoring of subsurface ground movement is important for the prevention and control of geological disaster including land subsidence, ground fissure, surface collapse, and landslides. Inclinometer and extensometer are examples of the conventional geotechnical instruments for monitoring the subsurface ground movement. However, most conventional geotechnical instruments for subsurface monitoring are limited to discrete sensing, high cost, and susceptible to various reading errors. This paper presents the advancement of technology mechanism to monitor horizontal ground movements as well as the data processing technique involved. Distributed optical fibre inclinometer is developed through laboratory pipe bending tests whereas the data is corroborated with conventional instruments. This system was installed on site, measuring the performance of the sensors as well as to monitor the associated ground movements. A simple cost comparative study between fibre optic inclinometer and conventional geotechnical instrumentation indicates the new technology is cost-effective for applications in ground monitoring particularly when monitoring a large number of borehole points and measurement arrays.
Prompt analysis of condition priority for road improvement planning
Authors: Buchari E , Oktaviansyah D , Putranto D D A P , Nawawi N
Published: May 2019

The need for quick analysis for road pavement survey is inevitable, especially in a developing country. A new data collection method by using small format photo, which is recorded by drone is developed. The function of drone is not only for photographic purposes, but also developed to measure and record road damage. Digital aerial photogrammetric methods are developed faster than before. A small format areal imagery based on pixel size is developed for this study, so that the degree of road damage can be obtained quickly. In order to obtain a maximum pixel size to detect a maximum damage level of 1 cm, the shooting is done at a height of 24 m drone from the road surface. The result of road damage measured by measuring distance through image is then tested based on the measured sample, directly in the field with a trust level of 97.83%. These results show that the accuracy of road damage measurements made above high resolution photo images is very effective for data collection of road damage. Analysis of Condition Priority can be obtained in one day in complement with contour map and road level, while in previous time it is done within a week without contour map and level.
Development of operation and maintenance sustainability index for penarafan hijau jabatan kerja raya (pHJKR) green road rating system
Authors: Adzar J. A. , Zakaria R. , Aminudin E. , Rashid M. H. S. A. , Munikanan V. , Shamsudin S. M. , Rahman M. F. A. , Wah C. K.
Published: May 2019

The significant impact of infrastructure projects on the environment has created needs to assess its sustainability and responsiveness which indirectly respond to carbon emission reduction. A rating system is widely utilized as a tool to analyze the sustainability of buildings or infrastructures. Malaysia is one of the advanced nations which applies in road green rating system, whereby two rating systems for roads are established; MyGHI for highways and pHJKR (Roads) for non-tolled roads. Preliminary study on pHJKR (Roads) identified that this rating tool assesses road sustainability performance only at planning, design & construction stages. Since the establishment of pHJKR (Roads), no re-assessment has been carried out after the roads begin to operate. Whilst in sustainability resiliency, it is important to sustain its engineering and enhance its performance and services including carbon assessment, under operation and maintenance (O&M) of roads. This paper highlights the methodology of development for assessment criteria and elements during the operation and maintenance phase. The methodology leads to proposed score development which later will be used in association to index indicator for O&M pHJKR (Roads). The data for this study is gathered and analyzed from a comprehensive review of current pHJKR (Roads) with a comparison made to national and cross-nation green road rating index. An expert panel discussion will also be utilized as a method of verification in order to identify suitable sustainability factors during O&M. The outcome of the study will be proposed for the enhancement of pHJKR (Roads) with assessment criteria for operation and maintenance phase and eventually leads to the establishment of multiple life cycle phases for pHJKR (Roads).
Recycled concrete aggregate as a road base material
Authors: Giwangkara G. G. , Mohamed A. , Khalid N. H. A. , Nor H. M. , Hainin M. R. , Jaya R. P. , Sani W. N. H. M. , Ismail C. R. , Aziz M. M. A.
Published: May 2019

Natural crushed aggregate (NCA) is the most common material for aggregate throughout the world. The consumption of the NCA itself is rising up through the years. Concrete structures and road construction are some of the most consuming aggregate material, especially NCA. Therefore, aggregate such as recycled concrete aggregate (RCA) has become an alternative material for some particular civil construction. The implementation of RCA as road construction material has been raised for a long time ago especially in road base layer. Road base layer as foundation for road pavement must provide an adequate strength to hold the working load on the pavement surface. RCA is more heterogeneous material compared to NCA as the RCA contain many substances, such as aggregate, cement, sand, and some additive substances. Hence, it effects the strength of the RCA as construction material. In this paper, the properties of the RCA are investigated to get the characteristic of the aggregate. Density, water absorption, aggregate crushing value (ACV), compaction, and penetration test (CBR) were conducted in this research. An improvement by using plastic strips as addition also proposed to strengthen the RCA as road base material.
Properties of bitumen modified with latex
Authors: Daniel N. H. , Hassan N. A. , Idham M. K. , Jaya R. P. , Hainin M. R. , Ismail C. R. , Puan O. C. , Azahar N. M.
Published: May 2019

A lot of effort has been made to improve the base bitumen properties by adding different types of modifier. The current issue of pavement failure has raised a concern that high specification of bitumen is essential to counter the asphalt pavement challenges. This is to ensure that the bitumen could perform better as a road material. Natural rubber, particularly latex, has potential to be used as a modifier in bitumen compared to other types of rubber as it is cheaper, accessible and easily dispersed in the liquid bitumen when heated. This study evaluates the physical and rheological properties of the bitumen when added with latex rubber. Difference percentages of latex i.e. 2.5%, 5.0%, 7.5% and 10% were added to the 60/70 PEN bitumen and tested for penetration, softening point, viscosity, ductility, loss on heating and dynamic shear rheometer tests. As a result of the modification, it was found that latex hardened the control bitumen, increases the viscosity and provides better resistance against rutting.
Field performance of asphalt pavement maintenance using Cup Lump Rubber Modified Asphalt (CMA)
Authors: Razali R. , Hainin M. R. , Hassan N. A. , Idham M. K. , Malek M. S. C. , Warid M. N. M. , Yaacob H. , Mohamed A. , Ismail C. R.
Published: May 2019

It was typical in Malaysia that pavement failures at high stressed area were due to the bituminous layer aging subjected to extreme long loading times by the slow moving of heavy commercial vehicles. This scenario causes major structural deteriorations and permanent deformation of the bituminous road surfacing. In order to fix this problem, the used of Polymer Modified Asphalt (PMA) in asphalt mixture to form PMA mixtures was selected as an alternative method to increase the durability and lifespan of the pavement. PMA had been observed for a long time in improving the performance of asphalt pavement and increase the pavement lifespan. Although, it significantly improves the quality of the asphaltic layer and prolongs the life of the pavement, the construction cost was very high. Cup lump rubber was referred to the natural rubber in frozen form and it had been used as an additive in the conventional asphalt to produce cup lump modified binder (CMB). The mixture of cup lump modified binder with aggregates will produce the cup lump modified asphalt (CMA). Recently, Public Work Department of Malaysia and Malaysian Rubber Board recently had been conducted a field study at several locations to identify the benefits and CMA levels of performance as well as the constructability of the CMA pavement in actual field site. The monitoring and testing elements in this research were including mix design, construction methods and performances monitoring. The results have been showed that the performance of CMA was not shown significant improvement as compared to conventional asphalt section after six-month construction. From the result, it was noted that the longer observation period was needed to identify the actual field performance of cup lump asphalt pavement compared to the conventional asphalt pavement.
Transportation mode choice binary logit model: a case study for Johor Bahru city
Authors: Puan O. C. , Hassan Y. A. H. , Mashros N. , Idham M. K. , Hassan N. A. , Warid M. N. M. , Hainin M. R.
Published: May 2019

The mode choice stage in transportation planning is the analysis process to estimate the number or percentage of trips performed by each mode of transport. In practice, the number of trips is used to estimate the demand for each mode of transport. Such information is important for planning and designing transportation facilities in an urban area. A mathematical model of individuals’ mode choice is usually required in such an analysis. This paper discusses the result of a study carried out to evaluate the attributes that influence the mode choice of transport in Johor Bahru city by interviewing the individuals living for more than one year in the study area. The investigation conducted through one of attitudinal survey techniques known as stated preference survey. Stated preference survey conducted on a random sample of 384 respondents. Investigated attributes have been identified in analysis stage by applying binary logistic regression analysis procedure before deriving binary logit model for individuals’ mode choice of transport in Johor Bahru city. Based on stated preference survey and logistic regression analysis of data, the model of mode choice of transport in Johor Bahru has been derived and attributes of age, income, vehicle ownership, comfort of car, reliability of bus service, affective motives and instrumental motives were found statistically correlated to the mode choice of transport in Johor Bahru.
Parameters affecting fluctuation in traffic stream on urban roads
Authors: Al-Bahr T. M. , Puan O. C. , Hassan S. A. , Idham M. K. , Ismail C. R.
Published: May 2019

Moving Observer Method (MOM) is one of traffic data collection techniques that being used to collect the traffic flow at the urban roads. However, this technique is sensitive to the normal fluctuation of the traffic flow. Road length, intersection density, and driveway density are three main parameters contributed to the fluctuation of traffic flow in urban roads. This paper attempts to determine how much range of these parameters are affecting the fluctuation of the traffic flow. By using MOM technique, twenty urban roads in Johor Bahru city are selected randomly to analyse how these parameters contribute to this fluctuation of the traffic flow. Regression analysis is performed to identify the range of the effect of these parameters on the accessibility and fluctuation rate of traffic flow in urban roads. It is found that driveway density is significantly affecting the fluctuation of traffic flow followed by road length.
Analysis of hexagonal paving block as a better paving shape
Authors: Rachmat M. , Salsabilla T. N.
Published: May 2019

Because of the raise of road infrastructure, the use of paving block pavement increases as well. One of the problems of using paving block is the shape of it which influences of its interlock. The soil deformation over pavement makes it defect easily causing the paving block surface becomes uneven and the soil settled. The aim of this research is to prove that hexagonal paving block is a better paving shape than the other shape of paving. Therefore, analysis comes to the advantage and disadvantage of the installation process and interlocking from any different shape of paving. In order to be able to analyse hexagonal paving shape as the most optimum shape, this research utilizes literature review as the methodology research, to analyse the calculation we used SAP2000, Plaxis, Interlocking and installation pattern. The conclusion from the analysed result of SAP2000 output, Plaxis output, Interlocking and pattern installation can be concluded that hexagonal paving block is the most optimum shape caused its best for lock the pavement and easy to install. Analysis results for moment of force of paving block 10 cm are obtained 201612.46 kg/cm for cube, 6764.09 kg/cm for hexagon, 67460.04 kg/cm for octagonal and 171363.84 kg/cm for rectangular Therefore the deformation results are obtained -0.632 cm for cube, -0.097 cm for hexagon, -0.109m for octagon, -0.355 cm for rectangular. Deformation of soil deflection caused by paving block pavement is obtained 5.21 cm for cube, 3.38 cm for hexagon, 3.43 cm for octagon, 4.45 cm for rectangular. From the analyse of moment and deformation, soil deflection, interlocking and paving block installation can be concluded that hexagonal paving block is a better paving shape of paving block.
Measurement of percent time spent following on two-lane highways: an exploration of spot and space-based methodologies
Authors: Ibrahim M. N. , Puan O. C. , Mustaffar M.
Published: May 2019

Percent Time Spent Following (PTSF) is used as a key performance measure for two-lane highways as recommended by the HCM2010. PTSF is the average percent of total travel time that vehicles must travel in platoons behind slower vehicles due to inability to pass. Despite its acceptance as performance indicator, PTSF is difficult to measure directly in the field. It is therefore estimated using a surrogate measure based on the spot percent of vehicles travelling with headways less than three seconds (3 s) at a fixed point. However, the application of the 3 s headways as the sole criterion in the surrogate measure is still contentious. On the basis of definition, PTSF is both spatial and temporal variable whereas its estimation is based on fixed point. It is therefore desirable to develop a spatial measurement approach for PTSF that takes into consideration of travel time. A new method was therefore developed for spatial measurement of PTSF using a test vehicle equipped with a GPS-based speed acquisition and video recording system. This study explores the spot and spatial measurement techniques of PTSF. The indicator was then measured using the two approaches concurrently. Data for the study were sampled from 18 directional segments of two-lane two-way highways in Johor and Pahang States, Malaysia. Subsequently, the estimates from these approaches were compared. On comparing the PTSF values from the spot and space-based approaches, it was discovered the latter approach produced lower values than the former in most instances. A statistical test of difference of means at 95% confidence level indicated that the estimates from the two techniques do not differ significantly. This implies that PTSF from spot measurement do not differ much from those based spatial approach developed in this study. Finding from this effort would at least substantiate the application of the spot-based PTSF measuring technique; an issue that has been debatable. It also serves as a response to the contentious issue, which has not received the desired attention from experts previously.
Estimation of critical gap at small roundabout
Authors: Azhari S. F. , Puan O. C. , Hassan S. A. , Mashros N. , Warid M. N. , Lopa R. S.
Published: May 2019

The gap acceptance theory is basically implied to describe the driver’s behavior in the minor stream at the entry of roundabout searching for a suitable gap at the major stream to merge. The critical gap is an important parameter in the gap acceptance theory. However, the critical gap cannot be measured directly on the field. One way to measure the critical gap is by measuring only the rejected and accepted gaps. This study attempts to determine the critical gap at small roundabout using three different methods namely Raff’s Method, Wu’s Method, and Simple Logit Method. The data is collected at a two-lane roundabout in Skudai – Johor Bahru at the morning and afternoon peak hour using video camera technology. Accepted and rejected gaps are then extracted from the recorded videotape. The accepted and rejected gaps obtained are analysed to determine the critical gap. The findings from the study reveal that the critical gap values from the three methods are almost similar, having a critical gap of 3.45s, 3.60s and 3.45s for Raff’s Method, Wu’s Method, and Simple Logit Method respectively.
Particle scale modelling of porosity formation during selective laser melting process using a coupled DEM – CFD approach
Authors: Aggarwal Akash , Kumar Arvind
Published: May 2019

Selective Laser Melting (SLM), the most popular metal additive manufacturing (AM) process, is well suited for making complicated parts which are difficult to manufacture by conventional manufacturing techniques. Currently, the main bottlenecks inhibiting the usage of the Selective Laser Melting (SLM) parts include the problems, such as porosity, low resolution, low surface finish quality and low build rate. In order to overcome the aforesaid problems, latest SLM machines are now being equipped with laser having small spot radius for enhanced resolution and surface finish, and high power to increase the build rate. The combination of high power and small spot radius leads to high energy density, exceeding the threshold value, resulting in transition of melting mode in the SLM process from conduction mode to keyhole mode and a formation of porosity due to collapsing of keyhole. In this study, high fidelity particle scale model is developed using open-source codes LIGGGHTS and OpenFOAM to understand the formation of porosity and to describe the physical phenomena (convection, melting, evaporation and solidification), melt flow dynamics and melting mode transition occurring in the SLM process.
The formation of Al6 (Fe, Mn) phase in die-cast Al-Mg alloys
Authors: Zhu Xiangzhen , Ji Shouxun
Published: May 2019

In aluminium alloys, iron is a common impurity as it is unavoidably picked up in practice. The excessive Fe is strongly prone to form various intermetallic phases. These Fe-rich intermetallics are generally brittle and act as stress raisers to weaken the coherence with Al matrix, therefore decreasing elongation. However, Fe addition in Al-Mg alloys may be beneficial because of the improvement in the yield strength with the scarification of ductility of die-cast aluminium alloys. The morphology of intermetallic phases has a vital effect on the properties of aluminium alloys. In the present work, the 3D morphology of Al6 (Fe, Mn) in die-cast Al-Mg-Mn alloys with different levels of Fe contents were revealed. The formation of Al6 (Fe, Mn) was also studied through crystal features and solidification behaviours.
Recent advances in the understanding of the role of vanadium carbonitride precipitation to improve surface edge cracking on continuous casting of blooms
Authors: Erdem Hornauer E , Grafe U , Plociennik U , Klos W , Reifferscheid M , Luettenberg M
Published: May 2019

This study aims in combining the material properties and numerical modelling techniques through practical application to provide understanding of surface edge cracking caused by V(C, N) precipitation to enhance the yield of the continuous bloom caster at ArcelorMittal Duisburg. The investigation for this work is carried out on three different micro-alloyed steel grades; one of them being the most crack sensitive 20MnV6. A process model is used which calculates the solidification process of the strand to design an optimum cooling strategy. Therefore, two cooling patterns are employed for the steel grade 20MnV6. Reduction of area values of the steel grades 20MnV6, 27MnSiVS6 and 38MnSiVS5 evaluated from hot tensile tests using a Gleeble simulator have been used as an indication in assessing steel’s cracking behaviour. Further precipitates have been analysed by SEM at ArcelorMittal. These laboratory results suggest that precipitation kinetics of V(C, N) influences the crack sensitivity of the micro-alloyed steel. The software MatCalc® is used to simulate precipitation for process parameters of continuously cast blooms at Arcelor Mittal Duisburg as well as the parameters of the Gleeble experiments. From these simulations the Zener pinning force (ZPF), resulting from V(C, N) particles on grain boundaries, is evaluated which can be used as a measure for the crack sensitivity. Using the values of the ZPF it is possible to identify the set of casting parameters of the steel grade 20MnV6 which lead to the minimum crack intensity on the surface of the blooms. Moreover it is possible to make a ranking list with respect to the ductility drop occurring in the Gleeble experiments for the analysed steel grades. The proposed statement is an issue for a continuing investigation of precipitation modelling.
Control of Solidification Pattern of Cast Irons by Simultaneous Thermal and Contraction / Expansion Analysis
Authors: Riposan I , Stan S , Chisamera M , Neacsu L , Cojocaru A M , Stefan E , Stan I
Published: May 2019

An experimental device conducts thermal analysis and volume change measurements in a single ceramic cup with cast iron quality as the variable. The recorded data are processed using specialized software. Experiments compare solidification patterns for white [WI], grey [GI] and ductile [DI] irons, to correlate the most important events between the cooling curves and contraction curves, to evaluate the sensitivity to shrinkage formation. All of the irons have similar values for initial expansion up to the start of eutectic freezing [0.437 – 0.443%]. Graphite formation promotes expansion [WI-0.002%, GI-0.109%, DI-0.596%], resulting a difference in the reached maximum expansion [WI-0.465%, GI-0.552%, DI-1.032%], placed between the end of eutectic recalescence and the end of solidification. Higher graphite expansion, greater the shrinkage sensitivity: open shrinkage increased while the density of a casting when considering total shrinkage and micro-shrinkage formation decreased. Prolonged graphitization at the beginning of eutectic reaction increased the expansion and, consequently, shrinkage sensitiveness. More graphite formation at the end of this stage also increased expansion, but this phenomena contributed to reduce of shrinkage level, due to the better access of liquid iron to compensate contraction holes. Special metallurgical treatments can favour a strong graphitization process at the end of solidification, with beneficial effects on the castings soundness.
Cellular-to-Dendritic and Dendritic-to-Cellular Morphological Transitions in a Ternary Al-Mg-Si Alloy
Authors: Brito C. , Nguyen-Thi H. , Mangelinck-Noël N. , Cheung N. , Spinelli J.E. , Garcia A
Published: May 2019

The study is focused on the influence of solidification thermal parameters upon the evolution of the microstructure (either cells or dendrites) of an Al-3wt%Mg-1wt%Si ternary alloy. It is well known that the application properties of metallic alloys will greatly depend on the final morphology of the microstructure. As a consequence, various studies have been carried out in order to determine the ranges of cooling rates associated with dendritic-cellular transitions in multicomponent alloys. In the present research work, directional solidification experiments were conducted using either a Bridgman (steady-state) device or another device that allows the solidification under transient conditions (unsteady-state). Thus, a broad range of cooling rates (Ṫ), varying from 0.003K/s to 40K/s could be achieved. This led to the identification of a complete series of cellular/dendritic/cellular transitions. For low cooling rate experiments, low cooling rate cells to dendrites transition happens. Moreover, at a high cooling rate, a novel transition from dendrites to high cooling rate cells could be observed for the Al-3wt%Mg-1wt%Si alloy. Additionally, cell spacing λC and primary dendritic spacing λ1 are related to the cooling rate by power function growth laws characterized by the same exponent (-0.55) for both steady-state and unsteady-state solidification conditions.
Direct observation of dendrite fragmentation in the solidification of undercooled melts
Authors: Mullis Andrew M , Haque Nafisul
Published: May 2019

The fragmentation of dendrites immediately following the recalescence phase of growth during the solidification of undercooled melts has been invoked to explain various rapid solidification microstructures. Despite this, little direct evidence of such a fragmentation process usually survives in the as-solidified material. We report on the rapid solidification of the single phase, congruently melting intermetallic β-Ni3Ge. During equilibrium solidification this material solidifies to the chemically ordered L12 crystal structure. Conversely, during rapid solidification, disorder trapping results in solidification to a random fcc solid solution, thereby providing a means to distinguish the rapidly solidified structures. We present results which show a range of microstructures in which the dendrite fragmentation process has been captured in progress. Results from EBSD Euler mapping reveal that dendrite fragmentation is a potential, but not particularly efficient, route to grain refinement.
Primary Dendrite Trunk Diameter in Al-7wt% Si Alloy Directionally Solidified Aboard the International Space Station
Authors: Upadhyay SR , Tewari SN , Ghodes M , Grugel RN , Poirier DR , Lauer M
Published: May 2019

Under a NASA (National Aeronautics and Space Agency)-ESA (European Space Agency) collaborative research project, MICAST (Microstructure formation in casting of technical alloys under a diffusive and magnetically controlled convection conditions), three Al-7wt% Si samples (MICAST-6, MICAST-7 and MICAST2-12) were directionally solidified at growth speeds varying from 10 to 50 µm s-1 aboard the International Space Station to determine the effect of mitigating convection on the primary dendrite array. The observed primary dendrite trunk diameters during steady-state growth of MICAST samples show a good agreement with predictions from a coarsening based model developed by the authors. The trunk diameters in the terrestrial-grown equivalent samples were larger than those predicted from the model. This suggest that thermosolutal convection increases the trunk diameter of primary dendrites, perhaps by increasing their tip radius due to compositional changes.
Characterization of dendritic growth in Fe–C system using time-resolved X-ray tomography and physics-based filtering
Authors: Yasuda H , Kawarasaki T , Tomiyori Y , Kato Y , Morishita K
Published: May 2019

Time-resolved in situ tomography of dendritic growth in Fe–0.45 mass% C carbon steel was performed using synchrotron radiation X-rays at SPring-8 synchrotron radiation facility (Japan) with improvement of the image quality using a physics-based filter. The voxel size of the reconstructed image was approximately 6.5 μm × 6.5 μm × 6.5 μm, and the time resolution (duration of 360° rotation) was 4 s (0.25 rps). Three-dimensional images of the dendrites were reconstructed even without image processing; however, the low contrast resolution in Fe–C alloys led to poor image quality. Consequently, it was impossible to precisely track the solid/liquid interface or evaluate the average curvature. To improve the image quality, a physics-based filter (a PF filter) was developed using a phase-field model. In the PF filter, images were retrieved in terms of interface curvature. The PF filter significantly improved the computed tomography image quality. As a result, dendritic growth was clearly observed even in Fe–C alloys. Moreover, the average curvature of the solid/liquid interface was evaluated as a function of solidification time (solid fraction). The ability to systematically characterize growing dendrites will be beneficial for modeling and simulation of solidification phenomena.
Efficient model for the prediction of dendritic grain growth using the lattice Boltzmann method coupled with a cellular automaton algorithm
Authors: Jäger Stephan , Ludwig Andreas
Published: May 2019

An efficient model for the prediction of dendritic grain growth is developed coupling the lattice Boltzmann method for solving the transport of solute and a cellular automaton algorithm for determining the evolution of grains’ envelope and the release of solute during phase change. In contrast to solving equations from the field of continuum mechanics the new model is more related to particular occasions what is more similar to the behaviour of cellular automaton algorithms. The resulting dendritic grain growth shows qualitative correctness, although the consideration of solute conservation is still missing. It is shown that neglecting proposed conditions regarding the choice of time step size can destabilize the solid-liquid interface resulting in secondary and ternary dendrite arms.
Finite diffusion microsegregation model applied to multicomponent alloys
Authors: Maguin V. , Guillemot G. , Jaquet V. , Niane N. T. , Rougier L. , Daloz D. , Zollinger J. , Gandin Ch.-A.
Published: May 2019

During casting, diffusion phenomena are often simplified by Lever-Rule or GulliverScheil hypotheses, thus simplifying chemical diffusion to extreme configurations. The present work proposes an extension of the Tong-Beckermann microsegregation model to multi-component alloys while considering finite diffusion in liquid and solid phases plus the effect of tip undercooling of the columnar front. The behaviour of this model is studied according the solidification conditions (growth velocity and thermal gradient) and comparison with microprobe measurements is proposed for a seven components nickel-base superalloy.
Three-phase numerical modeling for equiaxed solidification of Sn–10 wt.%Pb alloy under forced convection driven by electromagnetic force
Authors: Wang T , Wang E , Delannoy Y , Fautrelle Y , Budenkova O
Published: May 2019

A three-phase equiaxed solidification model where macroscale heat transfer and fluid flow are coupled with microscale nucleation and dendrite growth, is applied to the simulation of the macrosegregation in binary alloy solidification subjected to the electromagnetic stirring. The investigated experimental solidification case is conducted in a cavity which has a good control of the thermal boundary conditions. The proposed model uses a double time step scheme to accelerate the solution. Electromagnetic force is introduced as a source term into momentum equation in analytical form. To account for the friction from the side walls, a 2D½ flow model is applied to a three-dimensional experimental configuration. A comparison between the results of simulation and experimental ones is made.
Numerical simulation of wave-like nucleation events
Authors: Yuan Lang , Prasad Arvind , Lee Peter D , StJohn David
Published: May 2019

The Interdependence model [1] predicted that nucleation would occur in waves of events with regions of no nucleation in between each wave. The waves continue to form until nucleation covers the sample. The cause of this phenomenon was attributed to the formation of a nucleation-free zone which incorporates solute suppressed nucleation and inhibited nucleation zones. Recent real-time synchrotron x-ray studies by Prasad et al [2], Liotti et al [3] and Xu et al [4] have confirmed this hypothesis showing nucleation occurs in a step-wise fashion with a number of events occurring followed by little or no nucleation for a short period before another set of events occurs. A microscale solidification model that predicts diffusion-controlled dendritic growth has successfully shown the effect of the developing constitutional supercooling on the selection of nucleation events. In this study, we use this model to predict the solidification behaviour under the conditions experienced during these real-time synchrotron studies.
Increasing the Liquidus Temperature by Employing the Controlled Diffusion Solidification (CDS) Process: A Potential Route to Improved Castings
Authors: Pourgharibshahi Mohammad , Divandari Mehdi , Saghafian Hassan , Fabrizi Alberto , Timelli Giulio
Published: May 2019

Recent theories suggest the existence of an incubation time, over which a liquid alloy prepares for nucleation by decomposing into compositional fluctuations. Accordingly, in a recent work by the present authors, the solidification path of a Controlled Diffusion Solidification (CDS) mixture was calculated. The calculated CDS path begins at a higher liquidus temperature comparing to conventional solidification and the fraction solid values are achieved at a relatively higher temperature. To provide information on the CDS mechanism and physical structure of the CDS mixture in the mushy zone, Al-7.8Zn-2.6Mg-2Cu alloy was solidified, in this study, via conventional and CDS process in the presence and absence of recalescence. Typical grain structures obtained via the two solidification conditions is characterized using Electron Back Scattered Diffraction. Results showed that the nucleation continues to occur in the presence of recalescence, while it is suppressed in its absence. According to the two step nucleation theory, the increase in the nucleation temperature causes sufficient recalescence in the mixture, allowing the unnucleated liquid phase to decompose into chemical fluctuations and prepares for further nucleation. As a result, in the presence of recalescence, nucleation in a CDS mixture is not as readily halted as during the conventional solidification, which is in contradiction with the recent theories developed based on the classical theory of nucleation.