Dynamically Compacted Research Articles

Influence of particle breakage on bulk density of dynamically compacted coarse aggregates

The article presents the first discrete element method (DEM) simulations of dynamic compaction in the Proctor test. The aim of the simulations was to analyze the influence of particle breakage on the density of intensely compacted granular assembly. Results from simulations and laboratory tests were compared. Simulations with non-breakable aggregates enabled separation of the influence of change in particle size distribution and particle rearrangement. Both factors play an essential role in increasing the bulk density of the sample in the case of the tested (gap-graded) aggregate. Simulations with breakable particles reproduce the laboratory tests results better, both qualitatively and quantitatively. The conclusions provide a better understanding of the aggregate compaction process, which is crucial for developing novel compaction strategies and minimizing the environmental impact of the construction process.

Effect of Static and Dynamic Methods of Compaction on Mechanical Properties of Silt

Engineered fills, such as roads, earthen dams, embankments, and earthen sites, are enhanced by compaction to increase strength and decrease compressibility. Static and dynamic compaction are the most popular and important methods in geotechnical engineering practice with different compaction mechanisms. However, the significant differences in the physical and mechanical properties between both compaction methods that have been reported in the literature were limited to clay or sand. Limited attempts have been made to quantify the variations in silt’s mechanical attributes that were caused by the sample preparation method. A series of consolidated drained triaxial shear tests and some mercury intrusion porosimetry (MIP) tests were constructed to interpret this. The results showed that static and dynamic compaction had a significant influence on the mechanical properties of the silt coupled with the molding water content. The shear strength of the dynamically compacted samples was higher than those of the statically compacted samples, as was cohesion (c), and the sample preparation method had little effect on the internal friction angle (φ). Furthermore, samples that were compacted at optimum water content (wot) had greater strength than those compacted on the dry or wet side of the optimum. Compared with the static compaction sample, the pore size distribution curve of the dynamic compaction sample shifted to the left with the peak pore size, distribution density, and the interaggregate pores proportion decreased. The strength discrepancy could be traced to differences in the silt structure features, for example, pore size distribution and particle orientation between statically or dynamically compacted specimens.

Effects of Loading Rate Range on Mechanical and Microstructural Properties of Dynamically Compacted Iron Powder

In this paper, an attempt was made to investigate the effects of dynamic loading rate on the properties of iron powder with a focus on the microstructural characteristics of the compacted material. Dynamic compaction tests were performed using an instrumented die equipped with a load cell under the low loading rate ranging from 20 to 44 kN/ms in a drop hammer and the high loading rate ranging from 308 to 665 kN/ms in a one-stage light gas gun. Optical and scanning electron microscopes, diametric compression test, and Vickers hardness measurement were used to investigate microstructural and mechanical properties of the green compacts. The obtained results show that the range of loading rate completely changes the behavior of the powder by changing the number and velocity of the propagating stress waves. Comparison of the properties of specimens with equivalent density compacted under two ranges of loading rates indicates that the high range significantly increases the strength and hardness, distributes stress and porosity more uniformly, and reduces initiation and growth of inter-particle cracks as well as the compaction force required to achieve a specific density.

A novel approach for dynamic compaction of Mg–SiC nanocomposite powder using a modified Split Hopkinson Pressure Bar

ABSTRACTIn this paper, fabrication and characterisation of Mg–SiC nanocomposite are investigated. Micrometre-sized Mg powder with the different volume fraction of SiC nano particles were dynamically compacted using a modified Split Hopkinson Pressure Bar. Moreover, the compaction process was simulated using AUTODYN commercial software to demonstrate that the stress in the powder sample was sufficient for consolidation. To achieve the best quality samples, the effects of lubrication and compaction velocity on dynamic compaction process were initially studied by experiment. It was observed that the temperature of 450°C and the compaction velocity of 15.5 m/s led to the best samples with relative density more than 99%. The effects of reinforcing phase content on the relative density, micro-hardness, and compressive behaviour of the compacted samples along with their microstructures were investigated. The results showed that the micro-hardness and the compressive strength of the samples fabricated at 450°C increased about 70% and 50%, respectively.

Interpretation of the loading–wetting behaviour of compacted soils within the “MPK” framework. Part II: Dynamic compaction

Dynamic compaction is commonly used to construct structural fills for various geo-infrastructures. Current practice is to specify a minimum dry density and moisture content criterion to be used in the field on the basis of Proctor compaction carried out in the laboratory. However, there are still no practical methods for predicting compacted clay behaviour under expected mechanical and environmental loadings. Current theories are difficult to apply in practice due to difficulties in determining the necessary parameters. In this paper, the recently developed “void ratio – moisture ratio (volume of water / volume of solids) – net stress space” (MPK) framework is extended to cover dynamically compacted soils, with significant supporting experimental evidence. Two types of soils are used: lightly reactive kaolin and reactive Merri Creek clay. As the compaction stress was unknown for dynamic compaction, recompression of soil specimens from compacted soil was used to establish the “loading wetting state boundary surface” (LWSBS). Independent tests show that the framework can predict well the behaviour of compacted soils under loading–unloading and yielding, collapse during wetting, change of loading yield stress after wetting, and swelling pressure development during constrained wetting. The value of the approach is that the testing methods are straightforward, do not require specialized equipment, and testing times are much shorter. In addition, the uncertainty that laboratory dynamic compaction may not relate directly to field roller compaction can be addressed with the developed framework. Soil specimens obtained from field soil pads compacted by actual rollers can be used to establish the LWSBS. This information will allow prediction of the likely behaviour of field-compacted fills under expected environmental and mechanical loadings subject to one-dimensional conditions. Extension to triaxial conditions would require further experimental work and theoretical modelling.

Comparison of Static and Dynamic Powder Compaction: Experiment and Simulation

In this work, the static and dynamic compaction response of a six-material mixture, containing both brittle and ductile constituents, is compared. Quasi-static and dynamic compaction experiments were conducted on samples and the results compared to simulations. Optical analyses of compacted samples indicate that dynamically compacting samples to near 300 m/s is not sufficient for complete compaction or localized grain melt. Simulations indicate that a wide distribution of temperature and stress states are achieved in the dynamically compacted samples; compaction speeds should be increased to near 800 m/s at which point copper grains achieve melt temperatures on their surfaces. The experimental data is used to fit a bulk P-α equation of state (EOS) that can be used for simulating large-scale dynamic compaction for industrial applications.

A comparative study on hot dynamic compaction and quasi-static hot pressing of Al7075/SiCnp nanocomposite

Quasi-static and hot dynamic compactions of Al7075/SiC nanocomposite powder are studied in this work. Mechanically milled micron-sized Al7075 with different amounts of SiC nano particles (SiCnp), 0vol%, 5vol%, and 10vol%, are used to fabricate the samples. Dynamic and quasi-static hot compaction is conducted at strain rates of 103s−1 and 8×10−3s−1, respectively. The hot compaction conducted at the process temperature of 698K produces nanocomposite samples with relative densities up to 98%. The micro-structural and mechanical behaviors of samples such as micro hardness and stress–strain curves under quasi-static and dynamic loadings are also investigated. The results show improvement in micro hardness of the material. The quasi-static and dynamic tests are carried out using Instron testing machine and split Hopkinson pressure bar (SHPB), respectively. The improvement is believed to be due to strengthening mechanisms such as Orowan and enhanced dislocation density induced by thermal mismatch phenomenon and not by grain refinement described by the Hall–Petch effect. The results from quasi-static compressive tests reveal higher strength for quasi-static hot pressed samples than those produced under dynamic compaction. However, the dynamic compressive tests using SHPB indicate similar compressive strength for both quasi-statically and dynamically compacted samples.

Mechanical and microstructural characterization of Al7075/SiC nanocomposites fabricated by dynamic compaction

This paper describes the synthesis of Al7075 metal matrix composites reinforced with SiC, and the characterization of their microstructure and mechanical behavior. The mechanically milled Al7075 micron-sized powder and SiC nanoparticles are dynamically compacted using a drop hammer device. This compaction is performed at different temperatures and for various volume fractions of SiC nanoparticles. The relative density is directly related to the compaction temperature rise and indirectly related to the content of SiC nanoparticle reinforcement, respectively. Furthermore, increasing the amount of SiC nanoparticles improves the strength, stiffness, and hardness of the compacted specimens. The increase in hardness and strength may be attributed to the inherent hardness of the nanoparticles, and other phenomena such as thermal mismatch and crack shielding. Nevertheless, clustering of the nanoparticles at aluminum particle boundaries make these regions become a source of concentrated stress, which reduces the load carrying capacity of the compacted nanocomposite.

Investigation of dynamically compacted ground by HVSR-based approach

This paper proposes a HVSR (horizontal to vertical spectral ratio)-based approach to assess a deep and dynamically compacted fill area in Western Sydney. In addition to recognizing that the predominant resonance peak of the HVSR curve is a reflection of the impedance contrast between the surface layers and bedrock, the present paper recognizes that the secondary resonance peaks of the curve at higher frequencies may reflect strong impedance contrast within surface layers. This concept has been applied to develop a methodology of HVSR-based approach relying on the measurement of the HVSR of microtremors at measuring stations, and calibration and verification by independent mechanical and MSOR (multichannel simulation with one receiver) tests. The use of MSOR tests is introduced in this paper to facilitate the calibration of the HVSR forward model, particularly in terms of providing information for the initial guess of the shear wave velocity, Vs, profile in the HVSR forward modelling. The present paper demonstrates the effective use of the HVSR-based approach to assess dynamic compaction in the gaps away from and not covered by the mechanical tests. The mapping between the depth of bedrock and the predominant resonance frequency is also extended to include the mapping of the depths of layers with strong impedance contrasts to the secondary resonance peaks, after the data have been verified by independent mechanical tests.

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...

Static Fatigue, Time Effects, and Delayed Increase in Penetration Resistance after Dynamic Compaction of Sands

Dynamically compacted sands often exhibit a drop in cone penetration resistance immediately after compaction, but a gradual increase in the resistance occurs in a matter of weeks and months. An explanation of the former is sought in analysis of the stress state immediately after a dynamic disturbance, and a justification for the latter is found in the micromechanics process of static fatigue (or stress corrosion cracking) of the micromorphologic features at the contacts between sand grains. The delayed fracturing of contact asperities leads to grain convergence, followed by an increase in contact stiffness and an increase in elastic modulus of sand at the macroscopic scale. Time-dependent increase in small-strain stiffness of sand under a sustained load is a phenomenon confirmed by earlier experiments. It is argued that the initial drop in the cone penetration resistance after dynamic compaction is caused by a drop in the horizontal stress after the disturbance. The subsequent gradual increase in the penetration resistance is not a result of increasing strength, but it is owed to the time-delayed increase in stiffness of sand, causing increase in horizontal stress under one-dimensional strain conditions. This process is a consequence of static fatigue at contacts between grains. The strength of sand after dynamic compaction increases as soon as the fabric of the compacted sand is formed and is little affected by the process of grain convergence in the time after compaction. Contact stiffness, with its dependence on static fatigue, holds information about the previous loading process, and it is a memory parameter of a kind; this information is lost after a disturbance, such as dynamic compaction, in which new contacts are formed. The scanning electron microscope (SEM) observations, discrete element simulations, and energy considerations are carried out to make the argument for the proposed hypothesis stronger.

Dynamic compaction domain (shock compaction energy vs. ρ0/ρ) for a Fe-15 atomic % Cu nanometric alloy obtained by mechanical alloying

A Fe-15 atomic percentage Cu mixture was processed by Mechanical Alloying, in a Spex 8000D, and Dynamically Compacted, in a light gas gun. The MA as-powder product was a supersaturated solid solution with a BCC structure (a=0.28736 nm). Nanometric grain sizes between 6 to 30 nm were obtained. Different impact velocities on precompacted cylindrical specimens were used to obtain bulk specimens. The energy used for compaction was between 6 to 10% of the impact energy. XRD and TEM showed no structural changes after DC. We are proposing a Dynamic Compaction Domain in the shock compaction energy vs. ρ 0 /ρ plane, were consolidation of nanometric powders can take place.

Response of dynamically compacted tungsten to high fluence neutron irradiation at 423–600°C in FFTF

When pure tungsten produced by dynamic compaction at 95.3% theoretical density was irradiated in FFTF at temperatures of 423–600°C and neutron doses as high as 14.4 × 10 22 n cm −2 ( E > 0.1 MeV), it densified 2–3% and became very brittle. The brittle behavior resulted in failure at grain surfaces and appears not to be related to neutron-induced transmutation or segregation of transmutants. Based on density change measurements, it can be concluded that significant cavity formation did not occur at these high neutron exposures.

Lithium Ion Conductivity of a Statically and Dynamically Compacted Nano-structured Ceramic Electrolyte for Li-Ion Batteries

The densification of a ceramic electrolyte for rechargeable lithium ion batteries by using different compaction methods is described. The ceramic electrolyte for lithium ions, BPO4- Li2O, is compacted using either static or dynamic compaction methods. A difference in peak width in the X-ray diffraction spectra and a difference in lithium ion conductivity is observed. The dynamically compacted BPO4-Li2O shows an increase of up to three orders of magnitude in total ionic conductivity as compared with statically compacted samples. The total lithium ion conductivity is up to 2.10-4 S/cm at room temperature, which can compete with polymer electrolytes.

Dynamically compacted rechargeable ceramic lithium batteries

A rechargeable ceramic battery is made of a Li x Mn 2O 4 ( x = 1.1) cathode, a graphite anode and a BPO 4: yLi 2O ( y ∼- 0.035) solid electrolyte by dynamic compaction. This battery system has a theoretical open-circuit potential of 4.2 V and a high energy density, which makes it interesting for application in electric vehicles.

特集 粉末の成形・加工 Ｎｄ‐Ｆｅ‐Ｂアモルファス粉末の衝撃成形固化

Nd-Fe-B amorphous powders were produced by two different techniques; mechanical grinding and melt-spinning. These powders were dynamically compacted using gun method at shock pressures between 10GPa and 30GPa. When a shock pressure of 10GPa was applied, the powders were compacted into bulk form without loosing the amorphous state. The resultant bulk amorphous materials showed very low coercivities as same as the amorphous powders. On the other hand, crystallization occurred during dynamic compaction when the powders were shocked at relatively higher shock pressures. When a shock pressure of 20GPa was applied, the bulk material produced by using mechanical grinded powders had Nd2Fe14B ferromagnetic phase, but those produced by using melt-spun powders had a-Fe phase together with Nd2Fe14B phase.

Formation of amorphous TiSi powdered alloys and their shock consolidation

TiSi powder mixtures were milled in a low energy rotational ball mill under an Ar atmosphere, and the milled powders were dynamically compacted using a propellant gun. During milling of Ti 100− x Si x powder mixtures containing 20–50 at.% Si, α-Ti and Si phases were refined progressively to average grain sizes 20–30 nm in diameter and subsequently the structure was amorphized. On dynamic compaction of the amorphous Ti 50Si 50 powder at a shock pressure of 32.6 GPa, a partially crystallized amorphous alloy with high hardness (HV ≈ 1300) was obtained. Crystallization occurred on annealing the materials at 1023 K for 1 h, accompanied by grain growth to about 15–20 nm, and the hardness increased to a maximum value (HV ≈ 1700).

Dynamic compaction of AlLiX powder obtained by a rotating electrode process

The microstructures of dynamically compacted AlLiX powders obtained by the rotating electrode process were studied. Dynamic compaction was carried out using a LEXAN projectile whose velocity was 1520 m s −1 and the dynamic pressure obtained in the area of the (pseudo) planar shock wave was 7.1 GPa. Strong bonding between AlLiX particles with a thin melted contact zone was observed after dynamic compaction. Coarse particles had fewer interparticle contacts, but the contacts were stronger than for small particles. In the first layer of the sample in the area of (pseudo) planar shock wave the presence of 0.44 pores mm −2 and a total porosity of 4.6% were detected by quantitative metallography. Interparticle bonding was not detected in the first particle layer in the area affected by the release wave.

Microstructural characterization of self-propagating high-temperature synthesis/ dynamically compacted and hot-pressed titanium carbides

Titanium-Carbide produced by combustion synthesis followed by rapid densification in a high-speed forging machine was characterized by optical microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). The density of the combustion synthesized/dynamically compacted TiC reached values greater than 96 pct of theoretical density, based on TiC0.9, while commercially produced hot-pressed TiC typically exceeded 99 pct of theoretical density. The higher density of the hot-pressed TiC was found to be attributable to a large volume fraction of heavy element containing inclusions. The microstructure of both TiCs consists of equiaxed TiC grains with some porosity located both at grain boundaries and within the grain interiors. In both cases, self-propagating high-temperature synthesis (SHS)/dynamically compacted (DC) and hot-pressed, the TiC is ordered cubic (NaCl-structure,B1; Space Group Fm3m) with a lattice parameter of ≈0.4310 nm, indicative of a slightly carbon deficient structure; stoichiometric TiC has a lattice parameter of 0.4320 nm. For the most part, the grains were free of dislocations, although some dislocation dipoles were found associated with the voids within the grain interiors. In one SHS/DC specimen, a new, complex Ti-Al-O(C) phase was observed. The structure could not be matched with any previously published phases but is believed to be hexagonal, with a c-axis/a-axis ratio of ≈6.6, similar to the AlCTi2 phase which has a point group 6 mmm. In all other SHS/DC TiC samples, the grains and grain boundaries were devoid of any second-phase particles. The hot-pressed TiC exhibited a greater degree of porosity than the SHS/densified specimens and a large concentration of second-phase particles at grain boundaries and within grains. The structure and composition of these second-phase particles were determined by con-vergent beam electron diffraction (CBED) and X-ray microanalysis.

Sintering enhancement in dynamically compacted commercial iron powders

Powder metallurgy compacts of near theoretical density have been made from commercial sponge iron and atomized iron powders, the latter with and without admixed lubricant. Equivalent compacts were made by conventional quasi-static die pressing and by the dynamic powder compaction method to allow for comparative testing of mechanical properties. The compacts were sintered over a range of temperatures from 700 to 1120°C. Test specimens were cut from the compacts and tested to produce data on tensile strength, ductility (area reduction) and cantilever beam (Izod) impact strength. Compacts made dynamically from both the sponge iron and atomized iron powders exhibited higher tensile strengths and ductilities than those made quasi-statically and sintered to the same temperature. However, there were marked differences in the impact strength. With the sponge iron powder, dynamic compacts had lower impact strength than equivalent quasi-static compacts, but the reverse result was obtained with the atomized powder. The atomized powder was of much higher purity than the sponge iron and the microstructural evidence indicated that the inferior impact strength of the dynamically compacted sponge iron was due to interaction between the shock waves used for compaction and the numerous brittle inclusions present in this material. The results with the lubricated powder showed no sintering enhancement attributable to dynamic powder compaction. This suggests that the mechanism for the sintering enhancement that can be achieved with this consolidation technique is related to the friction processes at the particle boundaries, possibly coupled with the elevated temperatures present at these boundaries during dynamic compaction.