Leveraging active-source seismic data in mining tailings: Refraction and MASW analysis, elastic parameters, and hydrogeological conditions

We applied active-source seismic method for the interpretation of elastic parameters in tailings facilities which is essential for evaluating stability and seismic response. The methodology uses different analysis methods on the same dataset, i.e., conventional seismic refraction (SR) to determine compressional-wave velocity (Vp) and multichannel analysis of surface wave (MASW) to estimate shear-wave velocity (Vs). Seismic velocities in conjunction with tailings physics approach revealed interpretable data in terms of elastic parameters and hydrogeological conditions. The results determined the empirical linear relationships between Vp and Vs that are particular to an unconsolidated media such as tailings and showed that variability of hydrogeological conditions influences the elastic seismic response (Vp and Vs) and the elastic parameters. The analysis of the elastic parameters identified the state condition of the tailings at the time of the survey. The Bulk modulus K that relates the change in hydrostatic stress to the volumetric strain was predominant between 1.0−2.0 GPa. The Young’s modulus E in the tailings media was in the low range of 0.15−0.23 GPa. Poisson’s ratio values in all sections were in the upper limit in the range of 0.37−0.49, meaning that the tailings media is highly susceptible to transverse deformation under axial compression.

A Novel Force Variation Fine Blanking Process for the High-strength and Low-plasticity Material

Fine blanking is a kind of metal forming process with the advantages of high precision, good surface quality and low cost. Influenced by the concept of lightweight, a large number of metal materials with high strength are widely used in various fields. High strength materials are prone to be cracked during plastic deformation due to their poor plasticity, which limits the application range of them. This paper proposed a force variation fine blanking process for high-strength and low-plasticity materials. At the same time, a method to find the curve of forming force for this novel process was presented. A 2D finite element fine blanking model was established for the TC4 material. Combining genetic algorithm and neural network methods, a model was built up to find the optimal forming force loading curve. The parts fabricated by force variation loading and constant loading fine blanking process were compared through experiments. The mechanism of force variation fine blanking is also revealed. The forming force mainly affects the length of clean cutting surface by affecting hydrostatic stress. According to the ultimate optimal loading curve, the forming force should be kept at a low level in the early stage of blanking stroke, and increased gradually in the ending stage. In the application of force variation fine blanking, the part with long length of clean cutting surface can be obtained with lower die load.

Hydraulic Fracture Propagation Near the Cavity in a Poroelastic Media

In this paper, we investigate the problem of the propagation of hydraulic fractures in a poroelastic medium that has a circular cavity. The research was conducted using the extended finite element method (XFEM) implemented in the ABAQUS software package. The problem was considered in a plane formulation. The initial crack was oriented parallel to the surface of the cavity. It was shown that the path of the hydraulic fracture depends strongly on the hydrostatic stress in the medium and the distance between the crack and the cavity. We studied the influences of the poroelastic parameters, such as permeability and the Biot coefficient, on the propagation of cracks. It was shown that the cracks were less curved when the coupled problem of poroelasticity was considered. The features of fluid pressure changes inside the fracture and at the opening of the mouth were studied. It was shown that the fluid pressure in the fracture during injection was minimally sensitive to the state of the stress in the medium, to the position of the initial crack, and to the poroelastic parameters. The solution to the problem in this setting can be used to simulate hydraulic fracturing close to mine workings during a controlled roof’s collapse to prevent it from hanging, and the formation of impervious screens to reduce airflow from the mine to degassing boreholes through the rock, for example.

Hydrostatic Stress and Fatigue Crack Growth of Notched Ti6Al4V in Aggressive Media

The behavior of structures, machine or components made of composite materials or light high-performance alloys is still a great concern for applications in which high strength-to-mas-ratio is a fundamental requirement. Procedures to detect flaws of small initial cracks and evaluate fatigue crack growth are nowadays essentials for high performance flying or ground machines (airplanes, automobiles,...). Structural reliability and structural health monitoring are considered in this paper and the surface replica method is deepened. Numerical FEM models were developed to assist the surface replica method analysis of the results. Ti6Al4V alloy was considered. This paper is a short technical communication.

Strain-Softening Analyses of a Circular Bore under the Influence of Axial Stress

Strain-softening analyses were performed around a circular bore in a Mohr–Coulomb rock mass subjected to a hydrostatic stress field in cross section and out-of-plane stress along the axis of the bore. Numerical procedures that simplify the strain-softening process in a step manner were employed, and on the basis of the theoretical solutions of the elastic–brittle–plastic(EBP) medium, the strain-softening results of the displacements, stresses and the plastic zones around the circular bore were obtained. The numerical solution was validated based on the fact that the strain-softening process became EBP when the softening slope was very steep and elastic-perfectly plastic(EP) when the softening slope was near zero. The results illustrated that the stresses and displacements in the rock mass surrounding the bore was affected by axial stress and that a proper consideration of out-of-plane stress is necessary. Moreover, the presented results can be used for the verification of numerical codes.

Size-Dependent Solute Segregation at Symmetric Tilt Grain Boundaries in α-Fe: A Quasiparticle Approach Study

In the present work, atomistic modeling based on the quasiparticle approach (QA) was performed to establish general trends in the segregation of solutes with different atomic size at symmetric ⟨100⟩ tilt grain boundaries (GBs) in α-Fe. Three types of solute atoms X1, X2 and X3 were considered, with atomic radii smaller (X1), similar (X2) and larger (X3) than iron atoms, respectively, corresponding to phosphorus (P), antimony (Sb) and tin (Sn). With this, we were able to evidence that segregation is dominated by atomic size and local hydrostatic stress. For low angle GBs, where the elastic field is produced by dislocation walls, X1 atoms segregate preferentially at the limit between compressed and dilated areas. Contrariwise, the positions of X2 atoms at GBs reflect the presence of tensile and compressive areal regions, corresponding to extremum values of the σXX and σYY components of the strain tensor. Regarding high angle GBs Σ5 (310) (θ = 36.95°) and Σ29 (730), it was found that all three types of solute atoms form Fe9X clusters within B structural units (SUs), albeit being deformed in the case of larger atoms (X2 and X3). In the specific case of Σ29 (730) where the GB structure can be described by a sequence of |BC.BC| SUs, it was also envisioned that the C SU can absorb up to four X1 atoms vs. one X2 or X3 atom only. Moreover, a depleted zone was observed in the vicinity of high angle GBs for X2 or X3 atoms. The significance of this research is the development of a QA methodology capable of ascertaining the atomic position of solute atoms for a wide range of GBs, as a mean to highlight the impact of the solute atoms’ size on their locations at and near GBs.

A new analytical model to predict the formation of necking instabilities in porous plates subjected to dynamic biaxial loading

In this paper, we have developed a linear stability analysis to predict the formation of necking instabilities in porous ductile plates subjected to dynamic biaxial stretching. The mechanical behavior of the material is described with the Gurson-Tvergaard-Needleman constitutive relation for progressively cavitating solids (Gurson, 1977; Tvergaard, 1981, 1982; Tvergaard and Needleman, 1984) which considers the voids to be spherical and the matrix material isotropic with yielding defined by the von Mises (1928) criterion. The analytical model is formulated in a two-dimensional framework in which the multiaxial stress state that develops inside the necked region is approximated with the Bridgman (1952) correction factor, superimposing a hydrostatic stress state to the uniform stress field that develops in the plate before localization. As opposed to the linear stability models published so far to model dynamic necking in ductile plates, which consider the material to be fully dense and incompressible, the approach developed in this paper provides new insights into the interplay between porosity and inertia on plastic localization. In addition, the predictions of the theoretical model for the critical strain leading to necking formation have been compared with unit-cell finite element calculations performed in ABAQUS/Explicit (2019). Satisfactory quantitative and qualitative agreement has been found between the theoretical and computational approach for loading paths ranging from plane strain tension to nearly equibiaxial tension, loading rates varying from 100 s−1 to 10000 s−1, and different values of the initial void volume fraction ranging from 0.01 to 0.1. Both analytical and finite element results suggest that the influence of porosity on necking localization increases, due to early voids coalescence, as the loading rate increases and the loading path approaches equibiaxial tension. The original formulation developed in this paper serves as a basis for analytically modeling the dynamic formability of porous ductile plates, and it can be readily extended to consider more complex porous plasticity theories, e.g. constitutive models which consider the anisotropy of the material (Benzerga and Besson, 2001) and/or voids with different shapes (Gologanu et al., 1993; Monchiet et al., 2008).