Cavity Formation Research Articles

Experimental and Simulation Studies on Stable Polarity Reversal in Aged HVDC Mass-Impregnated Cables

Mass-impregnated (MI) cables have been used for many years as cables in high-voltage direct current (HVDC) systems. In line commutated converter (LCC) HVDC systems, polarity reversal for power flow control can induce significant electrical stress on MI cables. Furthermore, the mass oil and kraft paper comprising the impregnated insulation have significantly different coefficients of thermal expansion. Load fluctuations in the cable lead to expansion and contraction of the mass, creating pressure within the insulation and causing redistribution of the impregnant. During this process, shrinkage cavities can form within the butt gaps. Since the dielectric strength of the cavities is lower than that of the surrounding impregnation, cavitation phenomena in impregnated paper insulation are considered a factor in degrading insulation performance. Consequently, this study analyzes the electrical conductivity of thermally aged materials and investigates the transient electric field characteristics within the cable. Additionally, it closely analyzes the formation and dissolution of cavities in MI cables during polarity reversal based on a numerical model of pressure behavior in porous media. The conductivity of the impregnated paper indicates that it has excellent resistance to thermal degradation. Simulation results for various load conditions highlight that the interval of load-off time and the magnitude of internal pressure significantly influence the cavitation phenomenon. Lastly, the study proposes stable system operation methods to prevent cavitation in MI cables.

In-situ TEM characterization and atomistic simulation of cavity generation and interaction in tungsten at 800 °C under dual W2+/He+ irradiation

In this work, we have investigated the role of pre-existing nano-scale cavities and irradiation sequence in helium clustering, and in the evolution of the cavity population in tungsten at 800 °C, by performing in-situ Transmission Electron Microscopy (TEM) characterizations under dual-beam W2+(600 keV)/He+(10 keV) irradiation to a total dose of 0.351 dpa, and supported by atomistic simulations. Pre-existing cavities, induced by single W2+ irradiation to 0.256 dpa, were seen to attract induced defects from subsequent irradiations, resulting in enhanced cavity size and a reduced number density in sequential irradiation when compared to concurrent irradiation. Such cavities developed faceted geometries and saturated in number density at an additional 0.051 dpa induced by He+ exposure in the sequential irradiation. In contrast, concurrent irradiations generate a denser cavity distribution that showed no sign of saturation or faceting up to the total irradiation damage of 0.351 dpa. In addition, Molecular Dynamics and Statics simulations were performed using LAMMPS software. These showed the pre-existing cavities to be trapping sites for helium atoms. Despite the large binding energy of ∼6 eV of those cavities, He-He interactions still occurred beyond the effective radius of such sinks, leading to additional He-He clustering not seeded by neighbouring cavities. These results point to the importance of selecting the irradiation conditions to simulate synergistic ion effects on cavity formation and evolution in plasma-facing tungsten-base materials.

Failure evolution and mechanism of ground collapse due to exfiltration of shallowly buried water pipeline

Exfiltration of defective water pipelines is one of the leading causes contributing to the frequent ground collapses in congested urban areas; hence, revealing the failure evolution and mechanism of this hazard is essential to its prevention and mitigation. In this study, comprehensive experimental model tests were conducted first to characterize the evolution of soil erosion and ground collapse due to exfiltration of shallowly buried defective water pipes and examine the effects of six critical parameters, i.e., opening size and location, pipe pressure and buried depth, groundwater level, and exfiltration condition. Three failure behaviors of strata around leaking waterpipe were identified, i.e., minor disturbance (slight), formation and collapse of an erosion cavity (moderate), and soil fluidization (severe). Moreover, the ground loosening zone induced by cavity collapse could be roughly estimated using the modified flow ellipsoid theory; soil fluidization would occur once the ratio of water pressure head inside the pipe to its buried depth was greater than 2. Subsequently, a validated computational-fluid-dynamics and discrete-element-method (CFD–DEM) coupling method was employed to explore the microscopic mechanism of cavity erosion under the exfiltration flow. It was disclosed that the formation and expansion of a temporary cavity resulted from internal soil erosion, including the emigration of massive fine particles and aggregation of coarse particles around the defective pipe. Finally, the numerical simulation results indicated that cavity erosion would be exacerbated by increasing flow velocity and particle size-ratio, reducing soil fines content, and changing the opening from the pipe crown to its invert.

Evolution of the cavity structure of HDPE/UHMWPE blends during cold stretching

AbstractThe cavitation process of high‐performance HDPE/UHMWPE blends with a uniform dispersion of UHMWPE during cold stretching was investigated. It was observed that incorporating a small amount of UHMWPE into the HDPE matrix resin can serve as a nucleating agent, increasing the number of contact sites and accelerating the crystallization rate. This leads to the formation of thicker lamellar crystals and tethered molecules, ultimately enhancing the mechanical properties of the HDPE matrix. Furthermore, the relationship between the natural tensile ratio and strain‐hardening modulus was confirmed. Microstructural changes within the blends were also explored. As the drawing tangles in the middle, the cavities subsequently evolve by collapsing and merging to align parallel to the tensile direction, culminating in tensile damage forming a large crack in the final macroscopic form. As a result, the presence of more tethered molecules in the later stages of stretching inhibits further cavity growth.Highlights The HDPE/UHMWPE blends were prepared by solution blending and ultrasound‐assisted twin‐screw extrusion. The mechanisms underlying the formation and evolution of cavities in HDPE/UHMWPE blends, which lead to stress whitening during tensile damage, were examined by using DSC and SAXS/WAXD. The relationship between microstructure and mechanical properties was analyzed by cold‐drawing the molded blended sheets at room temperature.

Nondestructive internal disorders detection of ‘Braeburn’ apple fruit by X-ray dark-field imaging and machine learning

'Braeburn' apples are susceptible to internal browning disorders when stored under controlled atmosphere (CA) conditions with unfavorable gas compositions. The progression of CA-related disorders in apple tissues is dynamic, noting a decrease in porosity during early storage due to cellular breakdown and pore flooding, and an increase in porosity in later stages due to structural collapse and cavity formation. Utilizing grating-based X-ray dark-field radiography, which leverages X-ray small-angle scattering to detect microstructural changes below the pixel scale, this study assesses the technique's efficacy in identifying internal disorders in 'Braeburn' apples at both early and later stages. A machine learning approach was applied to compare the diagnostic capabilities of dark-field imaging with those of X-ray absorption radiography at identical image resolutions. Results indicate that for early-stage disordered fruit detection, X-ray dark field radiography is 10 % more accurate than absorption radiography, regardless of the machine learning classifiers that were applied. In the later stage of browning, dark-field imaging performs similarly to absorption imaging. High-resolution micro-computed tomography scans suggested that the distinct detection performance of dark-field imaging may be attributed to the more pronounced microstructural differences between healthy and early-stage defective tissues than those between healthy and later-stage defective tissues. The insights from this work will guide the application of X-ray dark-field systems in fruit quality assurance, particularly in detecting internal disorders.

Short-Wave Infrared Colloidal QD Photodetector with Nanosecond Response Times Enabled by Ultrathin Absorber Layers.

Ultrafast short-wavelength infrared (SWIR) photodetection is of great interest for emerging automated vision and spatial mapping technologies. Colloidal quantum dots (QDs) stand out for SWIR photodetection compared to epitaxial (In,Ga)As or (Hg,Cd)Te semiconductors by their combining a size-tunable bandgap and a suitability for cost-effective, solution-based processing. However, achieving ultrafast, nanosecond-level response time has remained an outstanding challenge for QD-based SWIR photodiodes (QDPDs). Here, record 4ns response time in PbS-based QDPDs that operate at SWIR wavelengths is reported, a result reaching the requirement of SWIR light detection and ranging based on colloidal QDs. These ultrafast QDPDs combine a thin active layer to reduce the carrier transport time and a small area to inhibit slow capacitive discharging. By implementing a concentration gradient ligand exchange method, high-quality p-n junctions are fabricated in these ultrathin QDPDs. Moreover, these ultrathin QDPDs attain an external quantum efficiency of 42% at 1330nm, due to a 2.5-fold enhanced light absorption through the formation of a Fabry-Perot cavity within the QDPD and the highly efficient extraction (98%) of photogenerated charge carriers. Based on these results, it is estimated that a further increase of the charge-carrier mobility can lead to PbS QDPDs with sub-nanosecond response time.

From the experience of the technical examination of hydro-technical tunnels

A comprehensive methodology is proposed and the results of the technical examination of hydraulic tunnels are given. The technique takes into account the influence of water flow, the formation of cavities behind the shell, fixes defects, and reveals the prerequisites for their formation. It consists of visual inspection and non-destructive testing (ultrasonic, electromagnetic, vibro-acoustic). A unified presentation of the examination results is proposed. The optimal basis and operating frequency of the ultrasonic method are substantiated. The gradations of the processes of the formation of cracks in concrete are determined by the frequency of electromagnetic radiation. Examples of tunnel examination are given. Characteristic areas of the objects are identified. For main canals, this is a shell near the entrance and exit portals. Cavities behind the shell can be traced along the entire length of the tunnels. The main defect of the shells of pressure tunnels of power plants is cracks in the reinforced concrete lining. For structures of seasonal drainage, filtration in the bottom is characteristic. The examination results are used to develop projects for repair works. Some methodical regulations can be used for inspecting any underground structures.

Study on the evolutionary mechanism of the cavity inside aluminum nanoparticles while reacting with oxygen

Aluminum nanoparticles are often considered attractive choices for fuels in energetic materials. In this study, molecular dynamics simulation with the reactive force field (ReaxFF) was used to study the oxidation process of three different particle sizes (4 nm, 5 nm, 6 nm) of ANPs (aluminum nano-particles). The cavity formation mechanism was obtained during the ANPs oxidation process. The cavity size, the oxide layer thickness, and the active aluminum content of ANPs with time were obtained. The results indicated that the formation of cavities is highly dependent on particle size. Large particle size prevents the formation of cavities. In 0–100 ps, the average growth rate of the oxide layer is 0.33, 0.25, and 0.20 nm/ps, respectively. Within 100–250 ps, the average growth rate of the oxide layer is −0.017, 0.038, and 0.117 nm/ps, respectively. Our results emphasize the effect of particle size on cavity formation, which provides insights into the atomic-scale oxidation mechanism of metal nanoparticles.

Study on the influence of water supply and drainage pipeline damage on urban silt ground collapse

Underground drainage pipelines play crucial roles in urban construction and development. Over time, these pipelines may incur damage and leakage due to aging and changes in surrounding loads. Ruptures and leaks in pipelines can lead to water seepage through cracks, resulting in erosion of surrounding soil layers and the formation of underground cavities. The loss of support in the soil above these cavities can lead to structural instability and eventual ground collapse. Such collapses can disrupt urban transportation systems, leading to significant social and economic consequences. This study specifically investigates ground collapse phenomena resulting from damage to drainage pipelines in silty soil within the Yellow River flood area in Zhengzhou City. By considering the influence of seepage velocity at the damaged pipeline section, the study differentiates between seepage erosion and scour erosion, conducting theoretical analyses and calculations for each scenario. The results show that ① when the surrounding area of the pipeline is damaged and the slow seepage rate causes a change in the critical groundwater level ΔH ≥ (Lσt )/((1 – n)γw), the soil around the pipeline will be damaged by seep erosion; ② when the water flow velocity at the damaged area of the pipeline is reached V 0 = 2λ(γs – γw )a 2 B 2/(9μ(B 2 – b 2)), the water flow impacts the soil and causes erosion damage. The critical pressure within the pipeline can be derived from the stress state where the pipeline is damaged P1=ρ2[2λ(γs−γw)a2B2/(9μ(B2−b2))] ; ③ the underground cavity formed by water flow erosion is assumed to be an “soil arch.” The stress analysis on it obtains the critical span of the “soil arch” when the “soil arch” is damaged 2b = [2c(H + h) + Kaγ(H + h)2 tan φ – P]/(H + h/3). This study provides a theoretical basis and technical support for the management of silty ground collapse in the Yellow River flood area.

The pull-out capacity of torpedo anchor in clay considering the full opening cavity

Torpedo anchors are increasingly being considered for mooring floating facilities in deep waters owing to their efficient and economical installation. The anchor was released from a specified height above the seabed to allow it to gain velocity as it fell freely into the water before penetrating the seabed. A cavity was formed above the anchor shaft after the anchor installation. The formation of this post-installation cavity is largely dependent on the soil strength conditions and affects the anchor capacity after installation. However, there is a lack of understanding regarding the formation mechanisms of the cavity and its effect on the bearing capacity of a torpedo anchor. Thus, this study focuses on the effects of the post-installation cavity on the bearing capacity of the torpedo anchor. The impact of a fully open post-penetration cavity on both the vertical and inclined bearing capacity of a torpedo anchor without fins was investigated using the Coupled Eulerian–Lagrangian (CEL) method in ABAQUS with three-dimensional large deformation finite element (LDFE) analysis. A method for evaluating the vertical bearing capacity of a torpedo anchor, considering the effect of a post-installation cavity, was proposed. This study provides insight into the installation effect on the bearing capacity of torpedo anchors.

Low-temperature superplastic deformation mechanism of ultra-fine grain Ti–6Al–4V alloy by friction stir processing

The ultra-fine grain Ti–6Al–4V alloy sheet was successfully achieved by friction stir processing (FSP). The low-temperature superplastic deformation mechanism of Ti–6Al–4V alloy under the strain rate of 3 × 10−4 s−1 at 600 °C was studied by scanning electron microscope, electron backscatter diffraction and superplastic tensile test. It is found that the grain size of Ti–6Al–4V alloy by FSP is refined from 7.48 μm to 0.82 μm, and there is no preferential crystallographic orientation of the uniform grain. After FSP, the β phase of the base material (BM) in the grain boundary is refined and homogenized. During the superplastic tensile processing, with the increase of strain, the grain is refined continuously, and the α→β phase transition is induced by the dislocations pile-up at the β grain boundary, and the content of β phase increases. The grain near the fracture was refined to 0.35 μm, and the stress concentration led to the formation of cavities near the β phase, which eventually caused the fracture. The dynamic recrystallization in superplastic tensile processing is mainly geometric dynamic recrystallization and discontinuous dynamic recrystallization. The elongation of superplastic tensile (1033%) is 19.7 times higher than that of BM (50%). The order of superplastic deformation mechanism in the low-temperature superplastic deformation of the ultra-fine grain Ti–6Al–4V alloy sheet is as follows: intragranular dislocation slip and diffusion, grain boundary sliding, and phase boundary sliding. Phase boundary sliding is the main deformation mechanism for low-temperature superplastic deformation.

Percutaneous Drainage of Pediatric Pulmonary Abscesses: An Effective Therapy

IntroductionPulmonary abscess is a complication of lung infection with localized necrosis and purulent cavity formation. Pulmonary abscesses are typically managed using antibiotic therapy with anatomic surgical resection reserved as a rescue. Percutaneous drainage is considered relatively contraindicated in some centers due to perceived risk of bronchopleural fistula. However, drain placement has been frequently employed at our institution. The purpose of this study was to review and describe our longitudinal experience. MethodsMedical records of children diagnosed with lung abscess and treated with percutaneous drainage from 2005 through 2023 were reviewed. Patient clinical parameters, follow-up imaging, and clinical outcomes were evaluated. ResultsPercutaneous drainage (n = 24) or aspiration alone (n = 4) under imaging guidance was performed by interventional radiologists for 28 children with lung abscesses. A single catheter (8–12 Fr) was deployed in the pulmonary abscess cavity and remained for a median of 6 days (IQR: 6–8 days). The median hospital stay was 10 days (IQR: 8.8–14.8 days). The technical success rate for percutaneous drainage or aspiration of primary pulmonary abscesses was 100% (26/26). Two children were later diagnosed with secondarily infected congenital pulmonary airway malformations that were both successfully drained and ultimately surgically resected. The abscess cavities resolved in all patients and catheters were removed upon clinical, radiographic, and laboratory improvement. Complications included the presence of two bronchopleural fistula, both of which were treated with immediate pleural drain placement. ConclusionPercutaneous drainage of pulmonary abscesses is an effective therapeutic option in children and can be considered alongside antibiotics as part of the initial treatment for pulmonary abscesses. Bronchopleural fistula can occur, but at a lower frequency than previously reported. Level of EvidenceLevel V.

Understanding the high-temperature deformation behavior of additively manufactured γ'-forming Ni-based alloys by microstructure heterogeneities-integrated creep modelling

Additively manufactured (AM) alloys present unique and heterogeneous microstructures due to the complex, highly dynamic laser-material interactions. These AM-inherent heterogeneities impede the widespread adoption of AM components, necessitating a profound comprehension of their impact on mechanical properties. Despite extensive research on AM of Ni-based alloys, limited attention has been paid to their creep behavior due to the time-intensive nature of creep tests and the long research cycles. Moreover, experiments and conventional alloy-centric approaches to creep modelling are deemed insufficient in quantifying the effects of AM-specific heterogeneities on creep cavity acceleration and in incorporating the microstructural evolution during creep. To address this critical knowledge gap, a novel computational framework was developed within the structure-property paradigm to unravel the intricate mechanisms governing creep properties. A mechanistic creep model was formulated based on fundamental dislocation creep mechanisms, encompassing dislocation climb-glide motion controlled by γ' precipitates, grain-boundary-sliding (GBS) resistance resulting from M23C6 carbides, and the kinetics of cavity formation. The framework integrates the in situ nucleation, precipitation, and coarsening of γ' precipitates during creep by a precipitation model. The results revealed an excellent agreement in terms of γ' precipitate evolution, creep strain, and strain-rate evolution, the predicted creep life, and times to 1 % strain. By elucidating the intricate interplay between microstructural heterogeneities and creep behavior on the cavity nucleation and GBS mechanisms, the developed computational framework provided valuable insights for enhancing the performance of Ni-based alloys manufactured through AM.

Characteristics of entrapped jet and cavity instability following the water entry of a superhydrophobic sphere

Following the impact of a superhydrophobic sphere on water, the formation of a stable-streamlined gas cavity undergoes several stages characterized by impact load slamming, cavity flow forming, cavity collapse, and unstable cavity. The former three stages have been extensively investigated. However, limited attention has been given to the post-collapse instability of the gas cavity. In the present study, a systematic experiment is conducted to investigate the evolution of the cavity subsequent to the water entry of a superhydrophobic sphere. The pattern of cavity collapse significantly influences the dynamic characteristics of the downward liquid jets entering the cavity. The liquid jets entrapped in the cavity behave as liquid films composed of tiny individual cavities generated with cavity collapse. Deep sealing with a relatively low Weber number consistently promotes the onset of jet penetration, whereas surface sealing results in droplet penetration. The repulsion of entrapped liquid films from the inner rim of the sphere plays a pivotal role in stimulating the periodic instability experienced by the descending gas cavity. The obtained conclusions shed light on the dynamics of the liquid films entrapped in a gas cavity and the cavity stability.

Tanshinone IIA Regulate Inflammatory Response and Promote Functional Recovery in Rats with Spinal Cord Injury

<i>Purpose</i>: The treatment of spinal cord injury (SCI) is a clinical challenge. The study attempted to investigate the effects of Tanshinone IIA on SCI in rats. <i>Methods</i>: The SCI model of rat was established based on Allen's animal model. The rats were randomly divided into four groups as follows: Control, Sham, SCI model, SCI + Tanshinone IIA. Rats were administrated with Tanshinone IIA (30mg/kg) respectively daily within one week after establishment of SCI model. Scores of Basso, Beattie, Bresnahan (BBB) was evaluated on the 1<sup>st</sup>, 3<sup>rd</sup>, 5<sup>th</sup> and 7<sup>th</sup> day after operation. Rats were sacrificed seven days after SCI, and the pathological injury of spinal cord tissue was assessed by HE staining. The levels of inflammatory cytokines (IL-1β and TNF-α) were detected by ELISA. <i>Results</i>: On the 7th day after operation, the BBB score of SCI + Tanshinone IIA group was significantly better than that of SCI group (P<0.01). Compared with SCI group, the pathological changes, neuronal pyknosis, hemorrhage, inflammatory infiltration, and white matter cavity formation in SCI + Tanshinone IIA group were reduced. Compared with SCI group, the level of IL-1 β and TNF-α in SCI+ Tanshinone IIA group were significantly lower (P<0.01). <i>Conclusion</i>: Tanshinone IIA can significantly improve motor function inhibit inflammation and repair spinal cord function after SCI.

Mathematical Modeling of SOIC Package Dynamics in Dielectric Fluids during High-Voltage Insulation Testing

The efficient testing and validation of the high-voltage (HV) insulation of small-outline integrated circuit (SOIC) packages presents numerous challenges when trying to achieve faster and more accurate processes. The complex behavior these packages when submerged in diverse physical media with varying densities requires a detailed analysis to understand the factors influencing their behavior. We propose a systematic and scalable mathematical model based on trapezoidal motion patterns and a deterministic analysis of hydrodynamic forces to predict SOIC package misalignment during automated high-voltage testing in a dielectric fluid. Our model incorporates factors known to cause misalignment during the maneuvering of packages, such as surface tension forces, sloshing, cavity formation, surface waves, and bubbles during the insertion, extraction, and displacement of devices while optimizing test speed for minimum testing time. Our model was validated via a full-factorial statistical experiment for different SOIC package sizes on a pick-and-place (PNP) machine with preprogrammed software and a zero-insertion force socket immersed in different dielectric fluids under controlled thermal conditions. Results indicate the model achieves 99.64% reliability with a margin of error of less than 4.78%. Our research deepens the knowledge and understanding of the physical and hydrodynamic factors that impact the automated testing processes of high-voltage insulator SOIC packages of different sizes for different dielectric fluids. It enables improved testing times and higher reliability than traditional trial-and-error methods for high-voltage SOIC packages, leading to more efficient and accurate processes in the electronics industry.

Conditioned medium-enriched umbilical cord mesenchymal stem cells: a potential therapeutic strategy for spinal cord injury, unveiling transcriptomic and secretomic insights.

Spinal cord injury (SCI) leads to significant destruction of nerve tissue, causing the degeneration of axons and the formation of cystic cavities. This study aimed to examine the characteristics of human umbilical cord-derived mesenchymal stem cells (HUCMSCs) cultured in a serum-free conditioned medium (CM) and assess their effectiveness in a well-established hemitransection SCI model. In this study, HUCMSCs cultured medium was collected and characterized by measuring IL-10 and identifying proteomics using mass spectroscopy. This collected serum-free CM was further used in the experiments to culture and characterize the HUMSCs. Later, neuronal cells derived from CM-enriched HUCMSC were tested sequentially using an injectable caffeic acid-bioconjugated gelatin (CBG), which was further transplanted in a hemitransection SCI model. In vitro, characterization of CM-enriched HUCMSCs and differentiated neuronal cells was performed using flow cytometry, immunofluorescence, electron microscopy, and post-transplant analysis using immunohistology analysis, qPCR, in vivo bioluminescence imaging, and behavioral analysis using an infrared actimeter. The cells that were cultured in the conditioned media produced a pro-inflammatory cytokine called IL-10. Upon examining the secretome of the conditioned media, the Kruppel-like family of KRAB and zinc-finger proteins (C2H2 and C4) were found to be activated. Transcriptome analysis also revealed an increased expression of ELK-1, HOXD8, OTX2, YY1, STAT1, ETV7, and PATZ1 in the conditioned media. Furthermore, the expression of Human Stem-101 confirmed proliferation during the first 3 weeks after transplantation, along with the migration of CBG-UCNSC cells within the transplanted area. The gene analysis showed increased expression of Nestin, NeuN, Calb-2, Msi1, and Msi2. The group that received CBG-UCNSC therapy showed a smooth recovery by the end of week 2, with most rats regaining their walking abilities similar to those before the spinal cord injury by week 5. In conclusion, the CBG-UCNSC method effectively preserved the integrity of the transplanted neuronal-like cells and improved locomotor function. Thus, CM-enriched cells can potentially reduce biosafety risks associated with animal content, making them a promising option for clinical applications in treating spinal cord injuries.

Using sectional blasting to improve the efficiency of making cut cavities in underground mine workings

Introduction: The research concerns how making cut cavities improves drilling and blasting operations as well as the optimum parameters to arrange both snubber and auxiliary blastholes.Methods: The research methods include experimental and industrial activities to identify the optimum depth of the first-section snubber blastholes relative to the second-section blastholes. It also identifies optimum parameters of the snubber blastholes while driving mine workings and ore breaking in stopes with different mine working sections and different rock mass strengths broken using the technique of cut-cavity formation.Results and Discussion: Experimental explosions executed in a production environment have proved the efficiency of the proposed technique of sectional formation of a cut cavity, which helped increase the blasthole use coefficient (BUC) from 0.88 to 0.97. The depth of the first-section boreholes should be determined relative to the length of the second-section boreholes and the broken rock mass strength. The higher the strength of the broken formation, the larger the ratio between the first and the second-section blasthole lengths should be. The results of the experimental explosions indicate that the depth of first-section snubber blastholes varies from 0.5 and more of the second-section boreholes, depending upon the depth of the latter and the broken rock mass strength. If the strength of the broken rock mass is 12 on the Protodyakonov scale, and the second-section blasthole depth increases from 1.6 m to 2.6 m, then the depth of the second-section boreholes should be increased from 0.9 m to 1.54 m so as to be 0.55–0.56 of the second section blasthole length. If the strength of the broken rock mass is 18, and the length of the second section increases from 1.8 m to 2.82 m, then the first-section length varies from 0.9 m to 1.75 m, being 0.5–0.62 of the second section blasthole length. Applying the novel proposed procedure for a cut-cavity formation will increase the blasthole use coefficient and reduce the cost of drilling and blasting operations. Moreover, the procedure may also be practical for driving underground mine workings and for ore breaking within stopes.

МИНЕРАЛИЗОВАННЫЕ БУРОВЫЕ РАСТВОРЫ

A method is described for preventing the formation of cavities when drilling wells in the intervals of occurrence of water-soluble minerals through the use of mineralized drilling fluids. The composition of the natural brine of the Znamenskoye deposit and the salt concentrate obtained from it by spray dry-ing, suitable for mineralization of drilling fluids, is given

Material testing for injection molded and 3D printed pristine/glass reinforced nylon at various strain rates

With the advent of new polymer material and non-conventional methods of manufacturing, the effect of loading conditions on mechanical properties has now been in huge demand to facilitate their industrial applications. Present paper has been focused on investigating the strain rate effects on mechanical properties of pristine nylon-6 and 20% glass reinforced nylon-6 material fabricated using injection molding and SLS (Selective Laser Sintering) printing manufacturing methods, respectively, at three strain rates of 0.0003, 0.003, and 0.01 per second. Tensile strength of injection molded nylon-6 has shown a positive relationship with strain rate whereas compressive strength has shown a reciprocal effect. At highest strain rate of 0.01 s−1, tensile strength exhibits 10.27% more as compared to lowest strain rate of 0.0003 s−1. Tensile strength at highest strain rate is found 60 MPa whereas at lowest strain rate it exhibits 54.41 MPa. At higher values of strain rate, rising of maximum strain is found very much sensitive than the rise in tensile strength. It also shows high percentage of deformation at higher value of strain rate. On the other hand, SLS printed 20% glass reinforced nylon-6 shows variable tensile strength with respect to strain rate due to uneven distribution of glass particles into nylon matrix created due to manufacturing process of SLS printing. FESEM images shows the cavity formation as observed before loading conditions whereas the glass fracturing phenomenon observed at the after loading conditions. However, compressive strength is found minimal with strain rate with an average value of 175.61 MPa. The findings of this study have contributed in avoiding the improper selection of material and its strain rate application during numerical modeling for industrial application purpose.