Conventional Compaction Research Articles

Quantitative Investigation into the Relation between Force Chains and Stress Transmission During High-Velocity Compaction of Powder

High-velocity compaction (HVC), an innovative approach to obtain green compacts with high and uniform density, is widely used in the powder metallurgy industry. In this study, meso force chains, macro stress transmission, and their relation were investigated using the discrete element method. The simulation details of HVC and the quantitative characterization of force chains and stress transmission were shown. Then, the relation between force chains and stress was investigated. The evolution of force chains showed the same change tendency as the stress distribution. They evolved from top to bottom and then reflected backwards in HVC while they did not show this trend in conventional compaction. The strength of the force chains maintained good consistency with the stress magnitude. Meanwhile, the length of the force chains presented a negative correlation with the stress magnitude, and high stress may cause new force chains to shorten. The average collimation coefficient was affected by the transmission of stress, and the short force chains had better straightness. Furthermore, force chains parallel to the direction of gravity were observed in the region with no stress concentration. The directional coefficient of force chains also had the same fluctuation trend as the variation in the principal stress angle.

Effects of the Molding Method and Blank Size of Green Body on the Sintering Densification of Magnesia.

The bulk density of sintered magnesia is significantly influenced by molding methodology and blank size of the green body during dry pressing. The entrapped air in the green body plays a critical role in determining the bulk density of magnesia samples. Herein, high-density magnesia samples, with different sizes, are prepared by using vacuum compaction molding and conventional compaction molding. The physical properties, such as bulk density and pore size distribution, and morphology or as-sintered magnesia samples were characterized by using Archimedes method, mercury porosimetry, and scanning electron microscopy (SEM). The results indicate that the bulk density of conventional compaction magnesia samples decreased below 3.40 g·cm−3 with the increase of thickness due to the presence of entrapped-air induced large pores and intergranular cracks. In addition, the large pores and intergranular cracks in conventionally-compacted samples are observed by SEM images. However, vacuum compaction of magnesia samples resulted in a bulk density of higher than 3.40 g·cm−3 for all thicknesses. Moreover, the defects in vacuum-compacted magnesia samples are mainly in the form of small circular pores.

Mechanical behaviors of bimsoils during triaxial deformation revealed using real-time ultrasonic detection and post-test CT image analysis

Real-time ultrasonic experiments were conducted to investigate the mechanical responses of block-in-matrix soil (bimsoil) samples under triaxial deformation. Although the mechanical behaviors of bimrocks and bimsoils have been widely studied, the rock-soil (block-matrix) interface cracking, rock-soil interaction, block occlusion, and interlocking effects during triaxial deformation are still incompletely understood. This paper aims to investigate the effect of confining pressure and block proportion on ultrasonic and mechanical properties of bimsoils using ultrasonic pulse velocity (UPV). Conventional compaction soil testing was adapted to produce cylindrical bimsoil samples of different rock block percentages (RBP) with various hammer counts, to ensure roughly the same compactness of soil matrix. The experimental results show that UPV reflects the complex mechanical behavior of bimosils during deformation. UPV measurements became more variable as samples deformed at the pre-peak and post-peak stages. It is suggested that the UPV is affected not only by stress level but also the meso-structures that develop during failure in bimsoils. Observation of macroscopic fracture morphology combined with image analysis of mesoscopic computed tomography (CT) scans reveals that multiple localized tortuous bands form during deformation due to the presence of rock blocks in bimsoils. The changes of UPV are mainly attributed to the interactions of soil matrix and rock block. The post-test CT images further confirm this result.

Effective Compaction for Kernel Memory Allocator Using Workload Distribution

Low latency is one of the most important requirements for smart devices. Even though they have a small amount of memory, end users often want to run multiple applications concurrently without delays. Memory fragmentation is a critical obstacle to this aspect. To recover from it, the operating system uses compaction to create contiguous space from scattered free pages. Memory compaction tends to secure as many contiguous memory pages as it can, which may affect the user experience adversely at application launches. In this paper, a new page compaction method is proposed to improve the user experience. This method employs an efficient mechanism to find candidate pages to move. It also uses a bitmap to represent the status of the physical pages and find compactable pages effectively. The experiment performed on the proposed method demonstrates that the interruptions for compaction occur more frequently, but with a significantly lower workload than conventional compaction. According to the experiment, the success rate after compaction increased by about 22%, and the elapsed time to scan free pages decreased dramatically compared to conventional compaction. Moreover, the proposed method reduced the worst-case time for a new process creation by about 67%.

Improvisation of mechanical and electrical properties of Cu by reinforcing MWCNT using modified electro-co-deposition process

Multi-walled Carbon nanotubes–copper (MWCNT/Cu) composite powders with variable MWCNT content were synthesized by modified electro-co-deposition method. The electro-co-deposited MWCNT/Cu powders were consolidated by conventional compaction and sintering process. The consolidated products were then hot rolled and cold drawn to fine wires. The MWCNT/Cu composite wire samples were characterized for electrical and mechanical properties. We have been able to achieve an increase of around 8% in electrical conductivity of the form wires repeatedly. It has been observed that there was gradual improvement in the properties with reinforcement of MWCNT in the copper matrix. The betterment of electrical property has been achieved with simultaneous improvement in mechanical properties of the wire. The yield strength of MWCNT/Cu composite wire was found to be four times and the tensile strength two times greater than that of pure copper. The improved properties are attributed to the proper distribution of MWCNTs in the copper matrix and excellent interfacial bonding between MWCNT and composite copper fabricated by the modified method.

Fabrication of high-density magnesia using vacuum compaction molding

High-density magnesia was fabricated using vacuum compaction molding, and effects of forming pressure and sintering temperature on bulk density, apparent porosity, diameter shrinkage ratio, volume shrinkage ratio, pore size distribution, cold compressive strength, and thermal shock resistance of the magnesia samples were investigated. There were two ranges of pore distribution in samples that were formed via conventional compaction molding, and these ranges were about 350–2058nm and 6037–60527nm. It was considered that the range of larger pores mainly influenced the densification of magnesia. Using vacuum compaction molding, large size pores were removed, and high-density magnesia (with a density greater than 3.40gcm−3) was easily prepared when forming pressure was higher than 200MPa and sintering temperature was higher than 1600°C. Magnesia samples prepared via vacuum compaction molding showed better performance compared to that of samples prepared via conventional compaction molding.

Improvement of product strength of bonded magnets by extrusion with counter pressure

A forming process composed of pre-compaction and extrusion with counter pressure was proposed to improve the strength of bond magnets. The pores of the compact reduced by the flow and breaking of the powder particle during the extrusion, hence the density and strength of the products were improved. Nd-Fe-B magnetic powder was formed into a ring magnet by conventional compaction and the proposed process. The density of the magnet was improved to be 3% compared with that of compacted ones. The hardness of the magnet expressing the bonding strength of powder particles was improved. The radial crushing strength was higher than 60% from the result of the compacted magnet.

Fabrication of bulk nanostructured permanent magnets with high energy density: challenges and approaches.

Nanostructured permanent magnetic materials, including exchange-coupled nanocomposite permanent magnets, are considered as the next generation of high-strength magnets for future applications in energy-saving and renewable energy technologies. However, fabrication of bulk nanostructured magnets remains very challenging because conventional compaction and sintering techniques cannot be used for nanostructured bulk material processing. In this paper we review recent efforts at producing bulk nanostructured single-phase and composite magnetic materials with emphasis on grain size control, anisotropy generation and interface modification.

Cone-beam computed tomography as advanced diagnostic aid in endodontic treatment of molars with multiple canals: Two case reports.

The purpose of these case reports is to emphasize the importance of knowledge regarding the root canal morphology and current diagnostic aids one should have as both of these important factors going to affect the prognosis of the endodontic treatment. These two case reports describe the maxillary and mandibular first molars with multiple canals. After clinical and radiographic diagnosis, additional help of cone-beam computed tomography (CBCT) of mandibular molar has been taken to evaluate the morphology and canal pattern; while maxillary molar was evaluated using CBCT scan to evaluate the canal configuration and obturation. In CBCT evaluation, the mandibular molar was diagnosed with six separated canals with three mesial and three distal canals and with radix paramolaris and radix entomolaris. The maxillary molar had five canals with three mesiobuccal (MB) canals. Both molars were instrumented with conventional hand and rotary file systems and obturated by conventional lateral compaction method. The axial images from CBCT show Vertucci Type VIII canal pattern in both roots of first mandibular molars and in MB root of maxillary first molar Sert and Bayirli Type XVIII canal configuration and no accessory canal in distobuccal and palatal root. With the recent innovations in diagnostic and operating aids, we can come across many variations in the root canal morphology of both mandibular and maxillary teeth, especially multi-rooted one (i.e., molars), and the knowledge of which leads to successful endodontic treatment with an excellent prognosis.

Evaluation Of Three Different Obturation Techniques Using Three-Dimensional Cone Beam Computed Tomography: In Vitro Study

Aim: The purpose of this study was to evaluate the adequacy of three different obturation techniques namely, the conventional lateral compaction, warm vertical compaction (SybronEndo, System B) and a core carrier obturation technique (DENTSPLY, GuttaCore) using three-dimensional Cone beam computed tomography (Care Stream CS 9000 3D CBCT) to measure the pulp space volume. Materials and Methods: The study sample comprised of 30 freshly extracted human mandibular and maxillary single-root premolars which were randomly divided into three groups of 10 teeth each. Biomechanical preparation was done in all teeth using WaveOne primary reciprocating files. All three sets of teeth were imaged in Cone Beam Computed Tomography (CBCT) scanner before and after obturation. Volume of the pulp space before and after obturation were calculated using OnDemand3D software and adequacy of the obturation techniques were measured by calculating the percentage differences of the obturated volume between the groups. Results: The data statistically analyzed using One-way ANOVA and Multiple-Range Tukey Test. There was a statistically significant difference in the obturated volume of the root canal space between the Gutta Core group and the lateral condensation group. Conclusions: Non obturated space (voids) was seen in all three obturation techniques. GuttaCore obturators showed the greater percentage of volume (POV) of obturation followed by the system B then the lateral condensation techniques.

Development of the Asphalt Multi-Integrated Roller Field and Experimental Studies

Asphalt pavements have been compacted using steel drum rollers for a century. However, the problems that are observed today on these pavements are universal with no solution in sight. Intensive research work has been invested to identify the mechanisms that cause these problems. A recent development was the introduction of SuperPave mix design, GP asphalt cements, and the use of reinforcing elements ranging from polymer to steel bars. Yet it seems that none of these solutions have succeeded in eliminating any of the old problems. The pavements suffer from serious distresses regardless of the geographic location of the pavements and its design, materials, traffic loads, and climate condition. This paper presents a new approach to deal with the problems facing the asphalt pavements. While the research efforts to date concentrated on materials-related solutions, this paper identifies conventional compaction equipment as the cause of many problems observed on the pavements. The paper provides the development of the new Asphalt Multi-Integrated Roller, AMIR, and discusses new developments leading to a number of commercial field trials on several Ontario highways. The paper concludes that current compactors must be replaced with soft flat plates in order to achieve the required specifications for long term performance.

The Comparison of the Characteristics of Displacement Isolines in the Cylindrical Green Compact under Ultrasonic Vibration

This research is a comparison of the characteristics of the displacement isolines due to powder-die-wall friction that arise during the compaction of ceramic powders in conventional die. It has been done using the CosmosWorks software package of the SolidWorks simulation software. The results of comparative simulation with FEM showed that the comparison of the displacement isolines and distribution of deformation of the ceramic powders. In the case of conventional uniaxial dry compaction for long length cylindrical green compact, considerable bending of the layers in the form of a cone can be observed. It is symmetry along centerline of cylindrical green compact. The distributions of the deformation of the green compacts (diameter 14 mm, height 20 mm) as a result of conventional compaction under ultrasonic vibration with power 1 and 2 kW are reduced to 4% and 6.5% when compared with conventional compaction without ultrasonic vibration respectively. Thus, density distribution can be minimized by increasing the power of ultrasonic vibration.

Test method for determination of optimum moisture content of soil and maximum dry density

A method for accurately determining the optimum water content of soil and the corresponding maximum dry density has been developed using a small number of soil samples, based on the physical parameters of the confined compression modulus of soil. The peak value of the compression modulus on the force-compression modulus curve is used to determine the optimum moisture content and maximum dry density. The proposed method is validated using four different types of soils: Qinghai-Tibet clay, SiO2-clay, Lanzhou loess, and Qinghai-Tibet sand soil. The results show that as opposed to conventional compaction methods, the new method allows for accurate determination of the optimum water content and the maximum dry density for various types of soil. Additionally, for certain moisture contents, when the compaction of soil is the greatest, clay and SiO2-clay attain the theoretical saturation status, whereas sand soil and loess do not.

Experimental studies and modelling of high-velocity loaded iron-powder compacts

A production technique with the capacity to significantly improve the mechanical properties of powder metallurgy (PM) parts is high-velocity compaction (HVC). To extend the usage of the HVC method, detailed knowledge of the HVC process is important. To facilitate the development of production processes, numerical simulations can be utilised. In the development of high-precision simulation models, constitutive data of HVC specimens at high strain rates are required. In this study, the dynamic compressive properties of cylindrical specimens made by HVC were measured using a split Hopkinson pressure bar (Kolsky bar) assembly. For this technique, a specimen is placed between two elastic bars. The impact loading is achieved by a projectile accelerating inside an air gun, which impacts the end of the input bar and generates elastic-wave propagation.The powder material used for the experiments is a press-ready iron-based premix. Among specimens made by HVC and conventional compaction (CC), the effects of the specimen density and the strain rate on the compressive properties, such as failure stress, Young's modulus and failure behaviour, are investigated. During dynamic compression, the failure behaviour of the specimens was also recorded using a high-speed video camera. The difference in the mechanical behaviour between HVC-pressed specimens and conventionally pressed specimens are also investigated. The stress–strain curves of HVC-pressed specimens are identical to those of conventionally pressed specimens, but the failure behaviour differs are concluded.A well-established numerical method for forming simulations also conducted for powder compaction is the finite element method (FEM). The impact loading of the powder is modelled and simulated using nonlinear three-dimensional FEM. To model the impact process, a constitutive relation for the powder behaviour is proposed, taking into account the strain rate and density variations. To capture the global response caused by cracking during impact, a damage model is implemented. The numerical results in terms of the stress and strain history in the specimen during impact are compared with the experimental measurements. In conclusion, the proposed material model captures the increase in the yield stress due to the higher strain rates and the decrease in stress due to cracking.

Theoretical Analysis on Underwater Vibrating Compaction Technology of Scattering-Filling Rubble Stone Layer

This paper studied on the underwater vibrating compaction technology of scattering-filling rubble stone layer. At HongKong-Zhuhai-Macao bridge project, in order to satisfy the project time limit, underwater vibrating compaction technology with hydraulic hammer instead of conventional dynamic compaction technology was used to tamp scattering-filling rubble stone layer with no dead angle in a short time. Owing to the shortage of engineering example, the theoretical analysis was needed before field application. In this paper, the rubble stone layer and the vibration system were simplified to a mechanical model. Vibration system’s work on rubble stone was obtained by mathematical derivation, and effects of parameters were analyzed. The result shows that work on scattering-filling rubble stone layer increases with the increase of system quality, equivalent damping, exciting force and angular velocity and decreases with the increase of equivalent stiffness, water stiffness and buoyancy.

Strength characteristics of fiber-reinforced compacted pond ash

This paper reports the strength properties of compacted pond ash reinforced with randomly oriented polyester fibers. The pond ash sample, collected from ash pond of Rourkela Steel Plant (RSP), was subjected to compactive energies varying from 357 to 3488 kJ m−3, and the optimum moisture content (OMC) and maximum dry density (MDD) corresponding to these compactive energies were determined by conventional compaction tests. The shear strength parameters and unconfined compression strength (UCS) of pond ash specimens compacted to standard and modified Proctor densities with 6 and 12 mm length fibers and fiber contents varying as 0, 0·1, 0·2, 0·3, 0·4, 0·5, 0·75, and 1·0% were evaluated and reported. The test results show that the inclusion of fibers in pond ash increases the peak compressive strength and peak friction angle, and imparts ductility to the specimens. For a given compacted density and fiber content, the 12-mm-size fiber gives higher strength than 6-mm-size fibers. The strength values obtained in the present study are comparable and even better than the good quality, similar graded conventional earth materials.

Compaction Management: Results of a Demonstration Project

Compaction management, also referred to as intelligent compaction (IC), is a real time automatic operation adjustment and continuous compaction control technology of soils or asphalt layers. It is essentially a technology for optimization and evaluation of the compaction process, being capable of adjusting the compaction energy applied to the material, increasing or decreasing compaction efficiency in the necessary areas according to an acceptance target value, thus attaining maximum stiffness, while preventing overcompaction and minimizing the total number of passes. This study seeks to assess in a case study the IC performance, in comparison with conventional compaction methods in terms of efficiency in compaction of a sandy soil. For this purpose, a specific experimental section was carried out in which the performance of an IC compactor was compared with a conventional heavier class compactor. Data was obtained and analysed by the IC continuous information, as well as by the application of several different conventional compaction control tests and methods. Results show that the IC technology presents a superior performance, as well as various advantages when compared to conventional compactors.

Strength characteristics of compacted pond ash

Strength properties of compacted ash layers depend to a great extent on the moulding conditions. This paper focuses on the effects of compaction energy and degree of saturation on strength characteristics of compacted pond ash. The pond ash sample, collected from the ash pond of Rourkela Steel Plant (RSP), was subjected to compactive energies varying from 357 kJ/m3 to 3488 kJ/m3. The optimum moisture content and maximum dry densities corresponding to different compactive energies were determined by conventional compaction tests. The shear strength parameters, unconfined compressive strengths (UCS) and California bearing ratio (CBR) values of specimens compacted to different dry densities and moisture content were assessed and reported. The effects of compaction energy and degree of saturation on shear strength parameters i.e. unit cohesion (cu) and angle of internal friction (Ф) values and also the UCS values are evaluated and presented herein. The results indicate that the dry density and strength of the compacted pond ash can be suitably modified by controlling the compactive energy and moulding moisture content. The strength achieved in the present study is comparable to the good quality, similar graded conventional earth materials. Hence, it may be safely concluded that pond ash can replace the natural earth materials in geotechnical constructions.

삼축압축시험을 통한 섬유로 구속된 흙의 응력-변형률-강도 거동 평가

Recently, there are an increasing number of studies on the method of wrapping the outer wall of granular piles with geosynthetic fibers such as geotextile or geogrid that has a certain level of tensile strength as an alternative method for the ground improvement techniques. In this study, triaxial compression tests are performed on the sand and clay specimen encased with various textiles to evaluate the reinforcing effect with regard to the tensile strength of the textile. Furthermore, triaxial compression tests are performed on the clay specimen inserted by sand only and sand encased with geosynthetics to compare behavioral differences between the conventional sand compaction pile and geosynthetic encased sand pile with regard to the replacement ratio, and the tensile strength of the geosynthetics. Based on the experimental results, the strength enhancement due to the textile is affected by the longitudinal tensile strength rather than the transverse one of the applied textile. The effect of the confinement by the textile encasement results in the large increase of the cohesions. The overall behaviors, such as shear strength, pore pressure parameter at failure and stress ratio, of the geosynthetic encased sand pile is quite different from those of the conventional sand compaction pile.

Investigation of Composite Compacted Ground Using Microtremors

AbstractThis paper presents an interesting and unique case study of a composite compacted site where the upper section of dynamically compacted material achieved in the first stage of compaction was subsequently removed, reinstated, and recompacted in lifts in the second stage using conventional roller compaction. Dynamic compaction was employed initially in this area because of the need to densify deep fill materials. Although a number of mechanical methods are already available for assessing deep compaction, it has been particularly rare to find a cost-effective method that can be applied to a deep and extensive compacted site. Noninvasive techniques based on measurement of the horizontal-to-vertical spectral ratio (HVSR) of ambient vibrations (microtremors) are proposed in this paper to assist in a pilot appraisal of this area, which occupies a part of a deep and laterally extensive compacted site. First, the key features of the measured HVSR curves were interpreted to give a preliminary insight into t...