Pulse load on a stationary barrier during an explosion in water

С использованием экспериментальных данных о взрывах в воде найдена аналитическая зависимость распределения удельного импульса взрывной нагрузки по длине балки. Учтены эффекты отражения возмущенного потока воды от поверхности преграды, глубина ее расположения в водоёме, взаимное расположение сферического заряда ВВ и преграды в воде, физические характеристики заряда. Using experimental data on explosions in water, an analytical dependence of the distribution of the specific impulse of the explosive load along the length of the beam is found. The effects of reflection of the disturbed water flow from the barrier surface, the depth of its location in the reservoir, the mutual location of the spherical explosive charge and the barrier in the water, the physical characteristics of the charge are taken into account.

Thermochemical-Pulse Fracturing of Tight Gas: Investigation of Pulse Loading on Fracturing Behavior

Unconventional and tight gas reservoirs are located in deep and competent formations, which requires massive fracturing activities to extract hydrocarbons. Some of the persisting challenges faced by operators are either canceled or non-productive fractures. Both challenges force oil companies to drill new substitutional wells, which will increase the development cost of such reservoirs. A novel fracturing method was developed based on thermochemical pressure pulse. Reactive material of exothermic components are used to generate in-situ pressure pulse, which is sufficient to create fractures. The reaction can vary from low pressure pulse, to a very high loading up to 20,000 psi, with short pressurization time. In this study, Finite Element Modeling (FEM) was used to investigate the impact of the generated pressure-pulse load, by chemical reaction, on the number of induced fractures and fracture length. Actual tests of pulsed fracturing conducted in lab scale using several block samples compared with modeling work. There was a great relationship between the pressure load and fracturing behavior. The greater the pulse load and pressurization rate, the greater the number of created fractures, and the longer the induced fractures. The developed novel fracturing method will increase stimulated reservoir volume of unconventional gas without introducing a lot of water to formation. Moreover, the new method can reduce formation breakdown pressure by around 70%, which will minimize number of canceled fracturing.

Effect of intracanal diode laser irradiation on fracture resistance of roots restored with CAD/CAM posts

Aim: To evaluate the fracture resistance of roots restored with CAD/CAM-fabricated posts, receiving or not intracanal laser treatment, compared with glass fiber posts under mechanical cycling. Methods: Twenty-seven endodontically treated, single-rooted teeth were divided into 3 groups: group 1 (control), prefabricated glass fiber posts relined with resin composite; group 2, CAD/CAM-fabricated intraradicular posts using Resin Nano Ceramic (RNC) blocks; and group 3, CAD/CAM-fabricated intraradicular posts using RNC blocks in canals irradiated with a 940-nm diode laser (100 mJ, 300-um optic fiber, coronal-apical and apical-coronal helical movements, speed of 2 mm/second, 4 times each canal). After cementation of the coping, cyclic loading was applied at an angle of 135° to the long axis of the root, with a pulse load of 130 N, frequency of 2.2 Hz, and 150,000 pulses on the crown at a point located 2 mm below the incisal edge on the lingual aspect of the specimen. Every 50,000 cycles, the specimens were evaluated for root fracture occurring below or above the simulated bone crest. Results were analyzed by one-way ANOVA followed by Tukey’s test (p<0.05). Results: Group 1 was the least resistant, while groups 2 and 3 were the most resistant. Group 1 differed significantly from groups 2 and 3 (p<0.01), but there was no difference between groups 2 and 3 (p<0.01). Conclusion: Treatment of the intracanal surface with diode laser had no influence on fracture resistance of roots restored with CAD/CAM-fabricated posts, but a longer cycling time is required to evaluate the real benefits of diode laser irradiation.

THE INVESTIGATION OF DYNAMIC EFFECTS UNDER MICROSCALE PULSE LOAD

Axisymmetric problem of heat pulse irradiation of a cylindrical solid is considered. Nonlinear behavior of the material is described by the generalized Bodner-Partom model of flow. The nature of generalization lies in applying the rule of mixtures for the determination of parameters of the model responsible for yield point and ultimate strength. The considered model enables one to estimate the residual stress-strain state more exactly. During subsequent in-service loading of cylindrical solids, this state strongly affects the fatigue resistance of elements. The problem is solved by the time step integration method, iterative method, and finite element method. In each time step, we realize a double iteration process. The first is connected with the integration of the system of nonlinear equations of flow, the second with the solution of equations of motion and heat conduction. The calculations are performed on a grid FEM, especially in the region of irradiation, for the correct modeling of thermomechanical behavior of the material. The grid parameters are chosen with the help of the criterion of practical convergence of the solutions. The investigation of the stress-strain state of an inelastic material with regard for the dependence of parameters of the flow model on the phase composition of a material is carried out by using of numerical simulation. The main result is the following: qualitative and quantitative effects of phase composition influence on inelastic characteristics are established, namely change of tensile residual stresses on compression. The results obtained in the work can be used in calculations of parameters of surface hardening technologies.

The Influence of Background Ultrasonic Field on the Strength of Adhesive Zones under Dynamic Impact Loads

The influence of background ultrasonic field on the ultimate dynamic strength of adhesive joints is studied using fracture mechanics analysis. Winkler foundation-type models are applied to describe the cohesion zone, and the incubation time fracture criterion is used. The challenging task is to study whether relatively weak ultrasound is able to decrease the threshold values of the external impact load depending on a joint model, such as an “elastic membrane” or “beam” approximation, and various boundary conditions at the ends. The specific task was to investigate the case of short pulse loading through application of time-dependent fracture criterion instead of the conventional principle of critical stress. Three different load cases, namely, step constant force, dynamic pulse, and their combination with ultrasonic vibrations, were also studied. The analytical solution to the problem demonstrates that background vibrations at certain frequencies can significantly decrease threshold values of fracture impact load. Specific calculations indicate that even a weak background sonic field is enough to cause a significant reduction in the threshold amplitude of a dynamic short pulse load. Additionally, non-monotonic dependency of threshold amplitude on pulse duration for weak background field was observed, which demonstrates the existence of optimal regimes of impact energy input. Moreover, this phenomenon does not depend on the way in which the beam edges mount, whether they are clamped or hinged, and it could be applied for micro-electro-mechanical switch design processes as an additional tool to control operational regimes.

Thermochemical-Pulse Fracturing of Tight Gas: Investigation of Pulse Loading on Fracturing Behavior

Unconventional and tight gas reservoirs are located in deep and competent formations, which requires massive fracturing activities to extract hydrocarbons. Some of the persisting challenges faced by operators are either canceled or non-productive fractures. Both challenges force oil companies to drill new substitutional wells, which will increase the development cost of such reservoirs. A novel fracturing method was developed based on thermochemical pressure pulse. Reactive material of exothermic components are used to generate in-situ pressure pulse, which is sufficient to create fractures. The reaction can vary from low pressure pulse, to a very high loading up to 20,000 psi, with short pressurization time. In this study, Finite Element Modeling (FEM) was used to investigate the impact of the generated pressure-pulse load, by chemical reaction, on the number of induced fractures and fracture length. Actual tests of pulsed fracturing conducted in lab scale using several block samples compared with modeling work. There was a great relationship between the pressure load and fracturing behavior. The greater the pulse load and pressurization rate, the greater the number of created fractures, and the longer the induced fractures. The developed novel fracturing method will increase stimulated reservoir volume of unconventional gas without introducing a lot of water to formation. Moreover, the new method can reduce formation breakdown pressure by around 70%, which will minimize number of canceled fracturing.

Current Sensorless Microcontroller-Based Battery Management System with SOC and Active Cell Balancing

Battery management system (BMS) has become an important research topic following the trend and development of the electric vehicle. Although research on Active Cell Balancing, SOC, and current estimation has been carried out, the previous work mostly focused on comparing and developing methods. In this research, we demonstrate the process of designing BMS hardware using a low-cost microcontroller and without using a current sensor. The SOC simulation results produce an RMSE of 0.0832% for the 100% -10% SOC-OCV curve, and the current estimation simulation produces an RMSE of 0.2576 A, while for testing using a 6-ohm pulse load, the RMSE error value is 0.3960 A. The Active Cell Balancing method was successfully performed in simulation with Simulink. Furthermore, our simulation and test results suggest that complex battery models and multiple SOC-OCV curves can be used for better current and OCV estimation results. Our experimental results are also useful to develop a guideline to design a microcontroller-based BMS.

Equipment and materials for shock-intermittent cutting

The article considers the shock-intermittent processing method, which is used for cutting blind threads M12x1.5 in nuts made of steel grade X18N9T. Compared to the conventional method, it allows increasing the processing productivity; the durability of the thread taps has increased to 300 holes (with manual thread cutting, the durability of the taps is 100 holes). The method allows mechanizing labor-intensive threading operations. The optimal conditions of processing by this method are determined based on ensuring sufficient strength of the cutting wedge of the tool under repeated loading and, at the same time, creating the most intense impact on the material of the cut layer of the workpiece. The destruction of the processed material on impact most easily occurs at critical deformation rates, which, for instance, equal 60 m/s for corrosion-resistant steel. This leads to an overestimation of the impact pulse values, and consequently, chipping of the cutting edges of the tool. Therefore, for these processing conditions, there is an optimal value of the pulse load transmitted by the spindle to the tool. For threads M10 and M12 with pitches of 1.25 and 1.5 in parts made of steel grades X18N10T, the best results are achieved at loads corresponding to the increment of the dynamic moment of the driven bushing with the tool. At high pulse loads, the durability of the working tool is sharply reduced, and at lower loads, the cutting performance is reduced. One of the positive features of shock-intermittent cutting is the presence of breaks that facilitate the operation of the cutting wedge due to the better penetration of the coolant. Therefore, shockintermittent cutting is carried out at more intensive modes than conventional continuous cutting. However, the tool life does not decrease as a result, but even increases. The relative length of the cutting area, determined by the angle, should be chosen based on the fact that the temperature in the cutting area does not have time to reach its steady value, equal to the cutting temperature during the normal long-duration cutting, carried out continuously.