This paper aims to propose a generalizable parameter calibration framework for discrete element method (DEM) and to develop the refined dynamic compaction DEM (RDCD) model for red-bed soft rocks ...(RBSR), which is used to investigate the contribution of tamping weight (W) and drop distance (H) to dynamic compaction quality control. Firstly, the linear model (LM) and the linear parallel bond model (LPBM) were selected to accurately represent the dynamic behavior of RBSR based on dynamic compaction characteristics. A generalizable calibration framework for LM and LPBM contact models was further proposed. Secondly, based on the calibration framework, a series of DEM simulations, parameters significance analysis, and physical tests were conducted to accurately calibrate the contact parameters of RBSR. Finally, the RDCD model for RBSR was developed, which was used to investigate the contribution of W and H to dynamic compaction quality control from a micro perspective. All results indicated that the proposed generalizable calibration framework could provide an accurate determination of RBSR contact parameters for dynamic compaction simulation. Specially, the lightweight inversion model for LPBM parameters was developed, enabling the rapid acquisition of contact parameters for RBSR. The LM parameters of RBSR were determined directly and indirectly, which could be directly applied to various RBSR. Moreover, the shockwaves generated by a heavier tamper with a lower drop distance had longer durations and larger propagation, enhancing the compactness of the overall specimen and generating larger and more uniformly distributed strong force chains. The dynamic compaction simulation results indicated that increasing the W could enhance dynamic compaction quality control. This paper contributes to the theoretical refinement of the contribution of W and H on-site dynamic compaction quality control.
•A generalizable parameter calibration framework for discrete element method.•The refined dynamic compaction DEM model for red-bed soft rocks is developed.•The contribution of W and drop distance H to dynamic compaction is investigated.•The shockwaves generated by a heavier W have longer durations and propagation.
A three-dimensional multiparticle finite element method(3D MPFEM) model of laser shock compaction powder was established, and the forming process and densification mechanism of dynamic compaction ...were studied. The effects of the laser peak pressure(1–5 GPa) on the powder density was studied. The compaction density increased with the laser peak pressure and reached the highest at 5 GPa. A comparison of the different energies of the system revealed that the increase in powder temperature was mainly due to the plastic deformation. In the process of powder springback, large pressure can induce rebound, and the powder may produce an interparticle separation phenomenon due to the difference in particle velocities in different layers. Analysis of the densification process of the inner particles, revealed that the upper layer particles undergo first plastic deformation, and then the second plastic deformation occurs due to the inertia effect, which contributes to the improvement of the powder density.
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•3D MPFEM was used to simulate the laser shock powder dynamic compaction process.•Adiabatic temperature rise effect is related to powder plastic deformation.•Laser shock powder has springback phenomenon and large strain rate.
In this paper, a method of dynamic compaction of nanopowders by laser shock is proposed, which is suitable for the compaction of micro-parts with the advantage of high strain rate and ...controllability. The effect of pre-pressure and laser energy on the mechanical properties and microstructural characteristics of nickel compacts were analysed experimentally. The results indicate a progressive improvement in the mechanical properties of nickel billets with increasing prepressure and laser energy. Notably, under the prepressure of 3 GPa and laser energy of 1.8 J, dense nickel compacts were achieved with the relative density of 94.45% and the microhardness of 170–240 Hv. Molecular dynamics simulation reveals that at a certain pressure threshold, plastic deformation, lattice modification, and dislocation slip occur among nanoparticles, causing strain hardening and a gradual increase in relative density. Furthermore, nanoparticle size inversely correlates with the compaction pressure. The main bonding mechanism of particles is cold welding.
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•A novel technology of dynamic compaction by laser shock was Applied in nano powder compaction.•Obtained high density and uniform nickle nanopowder compacts.•MDS was used to analyse the densification process.•Precompression can promote the further compaction of nano-powder.
Laser impact can generate high-strain impact loads. On this basis, a laser impact dynamic compaction (DC) of the tungsten carbide particles (WCp)/Al composite powder with large differences in ...stiffness and plasticity was performed in this study. Then, the influences of laser energy and WCp content on relative density (actual density/theoretical density), mechanical properties, and microstructure of the pressed billet surface, damage surface, and cross section of the Al matrix composites (WCp/Al) were analyzed. Along with the analysis of the high-strain compaction process, the spread of shock wave process in the compacted billets and the densification behavior of the powder compacts were evaluated via 2D multiparticle finite element method (MPFEM). Results showed that relative density of the compacted billets tended to increase and then decrease with the rise in of WCp content (5%, 10%, 15%, and 20%). In the DC of the composite powder by the laser impact, the pore filling was mainly filled by plastic deformation of the relatively soft Al particles, and the hard WCp did not undergo plastic deformation due to its high strength. A composite powder compact with high relative density was successfully prepared with a WCp content of 10% at 1800 mJ of laser energy. The eventual relative density reached 97.72%, and the overall microhardness increased by approximately 23.25%. The 2D MPFEM simulations could sufficiently predict the dynamic mechanical response in the DC by the laser impact and depict the strain and stress variation patterns at the particle-scale level. Finally, the densification mechanism of the composite powder billets was investigated. The simulation results pertaining to the relationship between the final laser energy and relative density were in significant agreement with the experimental results.
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•A novel technology of dynamic compaction by laser shock was proposed.•Obtained high density and uniform composite powder (WCp/Al) compacts.•2D MPFEM was used to analyse the densification process.•Dense powder contributes to better compact performance.
•Compression of nanoporous Al with different pore shapes and porosities is considered.•The process is investigated by the MD, and a reference data set is collected.•Neural network and micromechanical ...model with Bayesian parameterization are tested.•Both machine-learning approaches adequately approximate MD data.•These approaches are used to model shock waves in nanoporous Al.
We compare two machine-learning-based approaches, artificial neural network (ANN) and micromechanical model with automatic Bayesian identification of the model parameters, in application to mimicking the deformation behavior of nanoporous aluminum extracted from molecular dynamics (MD) simulations. Reference data are generated by means of MD simulation of both hydrostatic and uniaxial deformation with compression of representative volume elements of aluminum single crystal with nanopores of spherical, cubic and cylindrical shapes at the temperatures of 300, 500, 700 and 900 K. Several typical sizes of the nanopores are considered: The smallest one corresponds to the initial porosity less than 1%, while the largest one gives the initial porosity in the range of 30–50%. Plastic collapse of nanopores in all cases occurred by the mechanism of emission of partial Shockley dislocation half-loops from the pore surface. The emission of initial loop occurred earlier in the case of cylindrical pore; however, this did not lead to an explosive increase in the number of dislocations in the system at this stage. In general, flat free surfaces of pores are less subjected to the dislocation nucleation than the rounded ones. A new physically-based micromechanical model of the plastic compaction of nanoporous metal is formulated with accounting of different pore shapes and anisotropy of the compaction process. Both tested machine-learning approaches show an adequate approximation of MD data. The developed ANN and parameterized micromechanical model are applied to simulate the propagation of a shock wave in nanoporous aluminum in comparison with direct MD simulations of this process; this comparison shows an adequate description of the shock wave structure by means of both approaches incorporated into continuum mechanics modeling. Thus, the developed machine-learning-based approaches can be applied as constitutive equations of nanoporous aluminum in macroscopic simulations of the dynamic compaction and shock-wave processes in this material.
Dynamic compaction establishes shock waves that produces a violent dynamic mechanical response in powder. This process can realize the high-density compaction of powder to fabricate the compact of ...powder metallurgy parts with excellent performance. A new method for dynamic compaction of powder using laser shock on a small scale is proposed. It exhibits the unique advantages of a pulsed laser, such as high strain rate and dynamic shock force, and suitable for micro-part manufacturing. The experiment on the dynamic compaction of spherical aluminum powder was completed under five different laser energies. The effects of laser energy and powder packing state on the mechanical properties of the final compact and Microstructure of the compact, including the upper, failure, and cross section surfaces, were analyzed. Results showed that the mechanical properties of the aluminum compacts gradually improved with the increase of laser energy. The nearly fully dense aluminum compacts were successfully compressed at 1800 mJ laser energy with a final relative density of 99.72%. Moreover, the Microhardness of the compacts improved by approximately 60%. The simulation results using multi-particle finite element method (MPFEM) show that with the propagation of the generated shock wave in the compact, particles had large plastic deformation that filled the pores during the laser shock dynamic compaction of aluminum powder. The simulation and experimental results show that the main connection mechanism of particles is cold welding. The dense packing of powder before compaction could considerably improve the propagation of shock waves, and the initiation and growth of inter-particle cracks were reduced.
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•A novel powder dynamic compaction technology by laser shock was proposed.•The aluminum powder compacts with high relative density and uniform microstructure distribution were obtained.•The densification process of aluminum powder compaction was analyzed by 2D MPFEM.•Densely packed powder improves shock wave propagation and obtain better final compaction performance.
Rolling dynamic compaction (RDC) utilises a heavy (6 to 12-tonne) non–circular module (impact roller) that pivots about its corners as it is towed, causing the module to fall to the ground and ...compact the underlying soil dynamically. This paper presents the development of a transient, non–linear finite element (FE) model of the Broons BH–1300 4–sided 8 tonne impact roller, undertaking multiple passes, using LS–DYNA, validated against a field trial and observations presented in the literature for the same coarse–grained material. The results of the numerical analyses demonstrate that the FE model provides reliable predictions of the 4-sided roller as observed in the field. Thus, the use of this FE model may provide high resolution insights into the capability of the impact roller, namely in predicting the settlement and densification of an underlying coarse-grained material. The FE model demonstrates significant soil improvement directly beneath the width of the roller to approximately 1.2 m depth. Residual improvement is shown to extend to approximately 2.5 m depth and 1.25 m laterally.
This study elucidates the laser shock dynamic compaction (LSDC) mechanism of Nano-aluminum powder and its influence on changes in crystal defects at the atomic scale. The molecular dynamics method ...was utilized to simulate the LSDC and develop a model for the compaction of Nano-aluminum powder. An independently designed LSDC device was employed to examine the effects of Quasi-Steady Compaction (QSC) and QSC + LSDC on the relative densities of Nano-aluminum compacted billets under varying loads. The experimental results revealed that the QSC + LSDC composite process yielded compacted billets with a relative density of 97.8 %, which was 15 % higher than that of the compacted billets prepared under the QSC process. Post-LSDC composite compaction, the compacted billets exhibited a maximum hardness of 103.56 HV, an increase of 26.59 HV compared to that achieved under the QSC process. The average grain size in the compacted billet was reduced from 67.2 nm to 54.7 nm, indicating grain refinement. Molecular dynamics simulations showed that during the LSDC, the Nano-aluminum compacted billets transitioned from a face-centered cubic to a hexagonal close-packed structure. The LSDC process was predominantly characterized by 1/6〈112〉Shockley dislocations, constituting approximately 76.47 %, whereas 1/3〈111〉Frank dislocations were minimally present, accounting for approximately 0.31 %. Activating slip surfaces by moving incomplete Shockley dislocations with Burgers vectors of 1/62–11 and 1/6−11–2 led to the formation of laminar dislocations.
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•A non-contact measurement method P3P-RPE algorithm for measuring ramming settlement is proposed.•A circular active identification recognition considering the location of characteristic points for ...P3P-RPE algorithm is designed.•The applicability of P3P-RPE algorithm in laboratory environments and engineering sites is validated.•Error propagation model for the P3P-RPE algorithm is constructed.•Error sensitivity analysis is performed to analyze the factors and their weights on the influence of measuring ramming settlement.
Ramming settlement is a key index to reflect the quality of dynamic compaction. It mainly relies on manual monitoring, which seriously affects construction efficiency, and safety cannot be guaranteed. In this paper, an algorithm Perspective 3-Point Rammer Pose Estimation (P3P-RPE) based on monocular vision measurement is proposed, which can be carried out simultaneously with the construction, effectively avoiding the problem that the dynamic compaction operation needs to be terminated during manual monitoring. Then the error propagation model of P3P-RPE is proposed, and the influencing factors are analyzed comprehensively. The results show that the accuracy can reach 30 mm, which is less than the upper limit of 50 mm specified in the specification. And pitch angle of camera θ and feature point recognition have a great influence on the results. This method has good practicability in ramming settlement monitoring, and can provide reference for the monitoring of other similar projects.
