Values Of Normal Stress Research Articles

Prediction of the Damage Effect on Fiberglass-Reinforced Polymer Matrix Composites for Wind Turbine Blades.

The structure of wind turbine blades (WTBs) is characterized by complex geometry and materials that must resist various loading over a long period. Because of the components’ exposure to highly aggressive environmental conditions, the blade material suffers cracks, delamination, or even ruptures. The prediction of the damage effects on the mechanical behavior of WTBs, using finite element analysis, is very useful for design optimization, manufacturing processes, and for monitoring the health integrity of WTBs. This paper focuses on the sensitivity analysis of the effects of the delamination degree of fiberglass-reinforced polymer composites in the structure of wind turbine blades. Using finite element analysis, the composite was modeled as a laminated structure with five plies (0/45/90/45/0) and investigated regarding the stress states around the damaged areas. Thus, the normal and shear stresses corresponding to each element of delaminated areas were extracted from each ply of the composites. It was observed that the maximum values of normal and shear stresses occurred in relation to the orientation of the composite layer. Tensile stresses were developed along the WTB with maximum values in the upper and lower plies (Ply 1 and Ply 5), while the maximum tensile stresses were reached in the perpendicular direction (on the thickness of the composite), in the median area of the thickness, compared to the outer layers where compression stresses were obtained. Taking into account the delamination cases, there was a sinuous-type fluctuation of the shear stress distribution in relation to the thickness of the composite and the orientation of the layer.

STRESS-STRAIN STATE OF REINFORCED CONCRETE PIPES UNDER THE INFLUENCE OF CLIMATIC TEMPERATURE CHANGES IN THE ENVIRONMENT

The research analysis on determining temperature fields, stresses and deformations of transport structures under the influence of variable climatic temperature changes in the environment is carried out. It is established that climatic temperature changes in the environment cause the occurrence of temperature stresses and deformations of transport structures. The main damages and defects of reinforced concrete pipes in operation are given. It is established that one of the causes of defects and damages to reinforced concrete pipes is the level of temperature stresses and deformations that occur in the contact of a metal structure with a reinforced concrete pipe due to the action of variable temperatures caused by climatic temperature changes in the environment. A finite element model is developed for estimating the temperature fields and stresses of reinforced concrete pipes reinforced with metal corrugated structures, taking into account the action of variable climatic temperatures of the environment. The distribution of temperature fields in the transverse and longitudinal directions of reinforced concrete pipe under the action of positive ambient temperatures is calculated. It is established that the temperature field will be unevenly distributed over the pipe surface. In the transverse direction of the pipe, a temperature difference of +10° C was recorded between the reinforced concrete and metal shells. The calculation of temperature stresses and deformations of the pipe under the action of positive ambient temperatures is performed. It is established that the maximum value of normal stresses occurs at the contact of a metal pipe with a reinforced concrete one. At the same time, the value of temperature stresses in the transverse direction of the pipe is 321.61 kPa, in the longitudinal direction it is 321.61 kPa and in the vertical direction, it is 253.84 kPa. It is established that improving the theory and practice of determining the impact of climatic temperature changes on reinforced concrete pipes in the future will allow using appropriate materials and methods to strengthen these structures that meet the real conditions of pipe in operation, which will cause an increase in the service life of these structures in operation.

Hip joint mechanics in patients with osteonecrosis of the femoral head following treatment by advanced core decompression

BackgroundOsteonecrosis of the femoral head is a serious disease which, if left untreated, leads to destruction of the affected hip joint. For treatment of early stages of this disease, core decompression is the most common procedure. This study investigated the influence of the necrotic lesion and core decompression on the stress pattern in the hip joint using finite element analysis. MethodsSubject-specific models were generated from CT scan data of 5 intact hips. For each intact hip, twelve affected hip models were created by imposing a necrotic lesion in the femoral head, and four treated models were then created from four affected ones with central lesion, respectively. Treated models were created by supposing that the defect zone and the drill canal were filled with a bone substitute. Totally 105 hip models from three groups (intact, affected and treated) were simulated during normal walking activity. FindingsNecrotic lesion modified the stress distribution within the femoral head. Peak stress increased significantly up to 186% in mean in hips with a large lesion indicating an increased risk of femoral head collapse. Additionally, the presence of a medium to large necrosis altered significantly stress values (P < 0.05) and pattern in the articular cartilage. Our study revealed that advanced core decompression can recover normal cartilage stress values and pattern in treated joint. InterpretationThe presence of a large lesion increased the risk of femoral head collapse. Advanced core decompression with bone grafts can restore normal cartilage mechanics in hip postoperatively.

Distribution Law of In Situ Stress and Its Engineering Application in Gateroad Maintenance: A Case Study

In this study, the stress relief method of hollow inclusion and mathematical-statistical analysis are used to study the in situ stress distribution law of the Guotun coal mine, and the optimization strategy of roadway support is put forward. The test site is located in the city of Heze, Shandong Province, China. The main conclusions included the following: (1) among the three large-scale tectonic movements experienced by the Guotun coal mine, the middle Yanshan period has the strongest impact on it. According to the geological evolution process, it is preliminarily inferred that the maximum principal stress direction of the Guotun coal mine is northwest by west to southeast by east (NWW∼SEE). (2) Compared with the surrounding mines, the average value of the maximum principal stress in the Guotun coal mine is slightly higher, and there is a significant difference in the direction of in situ stress. The arc structure within the mine is the main reason for the deflection of the stress direction. (3) The lateral pressure coefficients KH, Kh, and Kav show a nonlinear distribution with increased depth, and the three coefficients have a decreasing trend. The value of the stress gradient in the Guotun coal mine is greater when it is compared with the surrounding mines. (4) Field tests show that the new strategy proposed in this study is effective, which provides a good reference for engineering practice under similar geological conditions.

RELATIVE DENSITY EFFECTS ON DRAINED SAND BEHAVIOR AT HIGH PRESSURES

A high-pressure triaxial compression and extension apparatus was employed to investigate the effects of initial relative density on the drained behavior of sand. Experiments were performed on cylindrical specimens of Cambria sand with initial relative densities of 30% and 60%, and compared with previously published results for 90%. Confining pressures in the range of 0.25 to 60 MPa were employed to obtain the characteristic behavior of the sand over a large range of pressures. As the confining pressure increased particle crushing increasingly influenced the stress-strain and volume change relations, producing increasing strains to failure and increasingly contractive volume changes. Beyond certain high values of mean normal stress at failure, increasing with initial relative density, the volumetric contraction and strains to failure began to decrease. The Mohr-Coulomb failure envelopes show the greatest curvature for the highest density, but the failure envelopes merge at high pressures where, due to particle crushing, the relations between void ratio and isotropic pressure are described by a single curve. The experiments show clearly that the rates of dilation at failure and the friction angles are directly related to each other, as has been proposed by many investigators. The friction angles are higher in extension than in compression for lower confining pressures, but a crossover occurs and the friction angles are higher in compression than in extension for higher confining pressures.

Geosynthetic Interface Friction at Low Normal Stress: Two Approaches with Increasing Shear Loading

The evaluation of geosynthetic interface friction is a key parameter for the stability of coupled geosynthetics, as in landfill capping liner. At the present time, few types of tests are suitable for measuring the interface friction at low normal stress: one of these is the inclined plane, usually carried out under a vertical stress of 5 kPa. This type of test is not without critical aspects, mainly due to the nonuniform normal stress state induced by the inclination of the plane, but, on the other hand, the most widespread direct shear test generally cannot be performed at such low values of normal stress. After a short discussion on the pros and cons of these two types of test, the paper presents a comparison of the interface friction angles obtained, for three interfaces, by means of an inclined plane and an unconventional direct shear apparatus, under the same low normal stress. The peculiarity of this latter device is of ensuring a gradual increase of the mobilized strength, in a way similar to what occurs during the inclined plane test. The good correspondence of the results of the two types of tests confirmed the validity of both the test approaches.

Effect of Bottom Blowing Mode on Fluid Flow and Mixing Behavior in Converter

Bottom blowing agitation plays a crucial role in improving the reaction kinetics condition of molten bath during the steelmaking process. Herein, the influence of bottom blowing mode on the flow and mixing characteristics of molten bath and the abrasion characteristics of refractory lining in a 6:1 scaled-down model of a 100 t converter were investigated using physical and numerical simulations together. Eight bottom blowing modes were designed (uniform, three-point linear co-direction, three-point linear unco-direction, two-point linear, circumferential linear, A-type, V-type, and triangle alternating). The results indicated that bottom blowing mode has a significant effect on the local flow field at the inner ring of bottom tuyeres, the velocity interval distribution, and the turbulent kinetic energy, which in turn determines the tracer diffusion path and rate as well the mixing time of molten bath. Reasonable non-uniform bottom blowing modes promote the interaction between the various stirring sub-zones of the molten bath. Among them, the three-point linear co-direction mode and A-type mode have the highest mixing efficiency under the conditions of bottom blowing and combined blowing, respectively, which is superior to the uniform mode. In addition, the bottom blowing mode changed the location and degree of abrasion of the refractory lining, and the total abrasion of the non-uniform mode was reduced. The average value and fluctuation degree of integral wall shear stress for the A-type mode were minimal.

CAM ATIKLARININ HARÇ ÜRETİMİNDE KULLANILABİLİRLİĞİNİN İNCELENMESİ

The Objective: In order to protect the cement preservatives, the energy consumption and its ecological reflections on the world are important for our present and future. For this reason, sustainable building materials production and recycling of wastes in this area can provide advantages. For this purpose, waste glass substituted mortar samples were produced in this study. The Method: The cement and waste glass replacement ratios in the produced test samples were 5%, 10%, and 15% respectively. In order to determine the workability of the fresh mortars, the manual spreading table test was applied. In order to determine the physical properties, water absorption and unit weight tests were applied, and in order to determine the mechanical properties, pressure and bending strength tests were conducted. The Findings: In the compressive strength test, the control sample was found to be 36.23 Mpa, in the sample with 15% waste glass, the average stress value was found to be 22,52 MPa. The flexural strength of the control sample was 8.70 MPa, in the sample with 15% waste glass, the average stress value was found to be 6,37 MPa. Similar results were found for the control sample and waste glass-added samples in the unit volume weight and water absorption tests. The Outcome: Depending on the increase in the waste glass additive ratio in the mortar samples, a decrease in the compressive and flexural strength values was detected. No significant differences were observed in the values measured in the spreading table and the water absorption values compared to the control sample. In the study, it was found that the mortar's physical properties didn't change much when the amount of waste glass was increased.

Исследование влияния температурно-скоростных условий на механические свойства биорезорбируемого цинкового сплава Zn–4Ag–Cu в процессе равноканального углового прессования

Recently, innovative medical techniques for restoring lost functions of patients have been actively developed, in which the use of bio-soluble (bioresorbable) materials is of particular importance. Such materials include alloys based on Mg, Fe, and Zn, and can significantly reduce the cost of surgical operations and shorten the duration of treatment. However, these metals have such disadvantages as insufficient strength and increased fragility to be used in medical implants. Therefore, increasing the mechanical characteristics of bioresorbable alloys is an urgent problem. In this work, the authors solve this problem using an advanced method of plastic treatment – severe plastic deformation (SPD), which, due to active initial structure refinement to nano- and ultrafine state, allows effective improvement of the mechanical strength of metal materials. The authors used the most effective and well-spread SPD method –equal-channel angular pressing (ECAP). The paper presents the results of computer ECAP research of Zn–4Ag–Cu zinc alloy at different deformation rates (0.4 and 7.8 mm/sec) and temperature conditions (150, 200 °C) chosen based on equipment performance potential and conditions to ensure thermal stability of the structure. The patterns of distribution of accumulated deformation degree, deformation rate, average stress values, and temperature-force conditions are obtained. According to the results of computer modeling, the authors recommended carrying out ECAP processing at the temperature of 150, 200 °C and a speed of 0.4 mm/s, which ensures a uniform thermal field at the deformation zone. During the experimental work according to the selected modes, the authors obtained samples after four ECAP cycles, which had advanced mechanical properties improving performance characteristics. The increased strength will allow minimizing the implants’ sizes ensuring less trauma during their installation and faster dissolution in the physiological environment of the body when retaining functionality.

Influence of edge effects on the bearing capacity of connections made of polymer composite elements

The volume of polymer composite materials application in transport construction sector increases annually. The positive experience of the construction maintenance with the composite bearing elements pushes to the development of this direction and improvement of the bearing constructions solutions. The connections of the elements require special attention due to the peculiarities of their structure and properties. The durability and reliability of connections with the use of composites is one of the most important tasks when designing new structures. The regulated techniques for calculating connections, which are included in the normative documents on designing structures of transport structures, are based on the assumption that the forces are evenly distributed over the area of the joint; possible deviations from the average are taken into account by the reliability and operating conditions coefficients. This paper shows how edge effects in adhesive and bolted connections affect their load-carrying capacity. The results of calculations of adhesive in terms of average tangential stresses and values of edge stresses in the adhesive layer are given, and the nature of the distribution of tangential stresses along the length of the adhesive is shown. For bolt connections analytical dependences for calculating bolt diameter depending on various conditions of connection strength and expressions for calculating stress concentration coefficients are presented. Calculations of bolt connections have been performed, the results of which reflect the strength ratio of the joint under different conditions, taking into account the boundary effects in the polymer composite material. The effect of edge effects in the adhesive and bolted joints of polymer composite material elements has been analyzed and the rationality of each of them for transport structures has been evaluated.

ПРИЧИНЫ ПОВРЕЖДЕНИЙ КАМЕННОЙ КЛАДКИ ПОСЛЕ РЕСТАВРАЦИИ

The article provides the analysis of the causes of damage in the masonry of historical buildings after their restoration. It has been established that the use of mortars of an increased grade and, accordingly, stiffness during repairs of historical masonry leads to an increase in tensile stresses in bricks under temperature and humidity effects. The reasoning behind the use of such mortars is to increase the strength and durability of the restored areas of historical masonry. The results of numerical simulation show that the masonry mortar must be sufficiently strong in compression and, at the same time, sufficiently plastic. It is shown that the use of hard mortars based on a cement binder, compared with plastic mortars based on a lime binder, on average doubles the value of normal tensile stresses at a temperature difference ∆Т=+100С.. This effect is much higher when stones swell due to their moisture. According to the results, for restoration work with brickwork, one should use mortars in accordance with the technology corresponding to this historical period, i.e., lime with additives that were identified during laboratory tests of samples taken from historical masonry. Low-grade mineral solutions with a low modulus of elasticity are preferable. It increases the crack resistance of the masonry under temperature and humidity effects. The article also shows that improper jointing of masonry joints facilitates the destruction of masonry. It happens when areas of accumulation of rainwater are formed, leading to increased wetting of stones in areas of direct impact of rainfall.

Новый алгоритм обработки данных метода фотоупругости

The photoelasticity method is a reliable tool for studying the stress state of flat elements in building structures using the models made of optically sensitive materials. In this paper, the classical photoelasticity is considered. The experimental data obtained with the use of the method are presented as interferograms. A decoding procedure implies the obtaining of some normal and tangential stress values in the plane of the model. The polarization-projection installations that are used in optical methods are rather simple. However, the digital processing of the images obtained during the loaded model transmission requires high-intelligent software. Nowadays, national and international laboratories, working with polarization-optical methods, strive to develop digital photoelasticity. For some reasons, the authors of the presented work needed to develop their own algorithms for decoding experimental data of the photoelasticity method. This work is mainly devoted to a formulation of the problems to be solved. Some of them have already been solved, and the results obtained are presented here. The authors place special emphasis on the description of the algorithm for tracing of interference fringes based on the analysis of the image gradient.

Research on interfacial zone failure of asphalt mixture mixed with recycled aggregates

Construction and demolition wastes (CDW) is a complex mixture containing cement mortar and mineral aggregate, recycled aggregates (RA) are further prepared by CDW after the crushing process. Investigating the effect of RA on interfacial zone failure of asphalt mixture is beneficial to promote the utilization of CDW in pavement engineering. Firstly, RA without strengthening treatment was used to prepare recycled aggregate asphalt mixture (RAAM), then the physical and mechanical properties of RA and RAAM were studied using microstructure analysis and performance tests. To comprehensively understand the influence of RA percentage on interface damage, the interfacial zone in RAAM was classified into cement mortar interface and natural aggregate interface. Results show that the attached cement mortar of RA is a porous material and leads to a weak interface adhesion with asphalt mortar. The cement mortar interface presents greater porosity and lesser modulus compared with the natural aggregate interface. Increasing RA percentage causes more interface failure during deformation, and the damage of cement mortar and its interface with asphalt mortar are the primary resources of failure. According to numerical simulation for fracture processing, the influence of replacing natural aggregate with RA on energy consumption is obvious, and it increases the average stress value of the interface. This study shows that RA can be used as an effective alternative for natural aggregate after enhancing its attached cement mortar.

© ПНИПУ Numerical and experimental research of the evaluation of the mechanical behavior of carbon fiber reinforced polymerspecimens with an embedded Smart-layer

Currently, scientists have paid special attention to the possibility of creating so-called Smart-structures that are capable of real-time self-diagnostics and/or functional changes. Within the framework of this work, the possibility of creating structures capable of diagnosing the deformation state in real-time is considered. When creating such Smart-structures, fiber-optic, piezo-, and strain-gauge sensors are usually used as control sensors. The use of such sensors is due to a number of their advantages, such as small size, the ability to integrate into a single measuring network, ease of use, a wide range of measured values, the ability to transmit data over long distances. However, when such sensors are embedded into the structure, several difficulties arise in installation/dismantling or implementation due to the fragility of the fiber, the difficulty of locating the sensitive element, ensuring the integrity of the fiber-optic sensors at the exit from the polymer structure. The team of the Scientific and Educational Center of Aviation Composite Technologies, PNRPU, has developed a prototype of a Smart-layer based on 3D-printing technology, capable of solving the problems described above. However, the influence of such an embedding on the structure of structures made of carbon fiber reinforced polymer (CFRP) remains open. Thus, this work aims to carry out computational and experimental studies to assess the mechanical behavior of CFRP samples with an embedded Smart-layer. Within the framework of this work, the technology and scheme for manufacturing a Smart-layer with embedded fiber-optic sensors, as well as a scheme for laying a Smart-layer into CFRP samples, are described. Since the properties of molded plastic specimens differ from those of printed specimens, mechanical tensile tests of printed specimens were carried out. The obtained values of the strength limit and the modulus of elasticity were used to identify the mathematical model. Within the framework of the experimental part, mechanical tests for tension, compression, and interlayer shear of CFRP samples with an embedded Smart-layer were carried out. When analyzing the obtained experimental results, it was found that the maximum percentage deviation of the physical and mechanical characteristics (PMC) is no more than 15 %, which lies within the spread of the PMC of carbon fiber in a prepreg roll. As a result, we can conclude that the embedded of such Smart-layers does not significantly affect the PMC of the final CFRP structure. According to the results of mathematical modeling of the tensile strength of a CFRP sample with an embedded Smart-layer, it was found that the maximum value of normal stresses in the sample reaches 540,28 MPa, which is 1,46 % higher than the maximum value for the statistical ultimate strength of the sample. The maximum values of the Mises stress for the Smart-layer do not exceed the ultimate strength, while for the epoxy binder there is a significant excess of the ultimate strength, on the basis of which one can make an assumption about its destruction during deformation.

Quantifying the non-Newtonian effects of pulsatile hemodynamics in tubes

• A new hemorheological constitutive TEVP model able to reproduce experimental data. • Pulsating hemodynamic conditions are studied. • At high pressure-gradient, RBC aggregation primarily affects hysteresis phenomena. • The streamwise normal stress is the dominant stress component. • Inelastic models underestimate the kinematic phase-lag compared to the TEVP model. We investigate in silico the pulsatile blood flow in straight, rigid tubes using an elasto-viscoplastic, constitutive model coupled with thixotropy (TEVP) (Varchanis et al., 2019; Giannokostas et al., 2020). In addition to blood viscoelasticity, our model accounts for RBC aggregation through a kinetic equation that describes the level of blood structure at any instance and the viscoplasticity at stasis conditions. We evaluate the model parameters using steady, simple shear, and transient multi-shear rheometric experiments for human physiological subjects with normal blood aggregation. Then, we accurately reproduce previous experimental results (Thurston, 1975; Bugliarello and Sevilla, 1970; Thurston, 1976; Womersley, 1955) and provide reliable predictions for the pressure, stress, and velocity fields. We also investigate blood flow under sinusoidal and experimentally determined waveforms of the pressure-gradient with different frequencies, amplitudes, and patterns, providing a thorough parametric study. We find that the streamwise normal stress is of considerable magnitude. This stress component stretches the RBCs and their aggregates in the flow direction. Commonly used inelastic hemorheological models (e.g., Casson and Newtonian) cannot predict this. Typical values of the time-averaged wall normal-stress are found in the range of 2 Pa − 30 Pa , which are an order of magnitude larger than the corresponding wall shear-stress for the same hemodynamic conditions. The inelastic models systematically underestimate the shear-stress and overestimate the mean velocity. Finally, the TEVP model accurately predicts the phase-lags between the pressure-gradient and the flow-rate, and between the pressure-gradient and the structure-parameter for the whole range of the frequencies expressed in terms of the Womersley number, indicating its physical completeness and robustness.

A Practical Design Method for Reducing Postconstruction Settlement of Highway Subgrade Induced by Soil Creep

The postconstruction settlement of the bridge approach is usually uneven, which could create a bump in the roadway. Indeed, this is a typical situation at the end of the bridge approach and requires a solution. One of the main causes of postconstruction settlement is the creep of soil. This paper is aimed at generalizing a new design method for controlling highway postconstruction settlement by replacing subgrade with expanded polystyrene (EPS). In the new method, the creep coefficient can be calculated based on the Yin-Graham EVP model. Thus, the relationship between the overloading ratio (OLR) and overconsolidation ratio (OCR) is obtained. The new method involves five steps: (a) determine the creep coefficient based on the relationship between the creep coefficient and over consolidation ratio, (b) divide the ground into a suitable number of sublayers, (c) select groups of different overloading ratios and then calculate the average values of the additional stress and overconsolidation ratio for each sublayer under different OLRs, (d) calculate the postconstruction settlement under different OLRs, and (e) determine the replacement capacity for different sections. This method can be used for quantitative design according to different requirements of postconstruction settlement of foundation. Taking Huzhou Avenue as an example, the case study illustrates the calculation process of the new method in detail.

Surface characteristic and wear resistance of QT-700-2 nodular cast iron after laser quenching combing with shot peening treatment

Laser quenching is an effective method to improve the surface performance of steel and iron. However, temper softening in overlapping zone often exists in multi-track laser quenching process and results in non-uniform hardness and residual stress distribution in the surface of component. Here, QT-700-2 nodular cast iron (QT-700-2) was performed by laser quenching with the maximum power of 3000 W and subsequent dual shot peening . With optimized laser quenching power of 1200 W and dual shot peening intensity of 0.5 mmA +0.25 mmA, the surface characteristics and wear resistance of treated QT-700-2 were investigated. The results showed that the average residual stress and hardness values of QT-700-2 after laser quenching plus dual shot peening were increased to −564 MPa and HRC 56.8, which were 179% and 9% higher than that of samples treated only by laser quenching. Meanwhile, the uniformity of the residual stress and hardness distribution were greatly improved. Comparing the wear testing results, it found that the friction coefficient and wear scratch width of QT-700-2 after laser quenching-shot peening treatment were larger than that original matrix in the load range of 10–30 N. However, the wear loss of QT-700-2 with combined treatment of laser quenching and dual shot peening was only one-third of that for matrix. The mechanism was discussed and it can be ascribed to the formation of refined microstructure constituting martensite and graphite, high compressive residual stress and enhanced hardness in the surface layer. • Laser quenching plus shot peening was used as a composite surface treatment. • Subsequent shot peening further improved the uniformity of surface mechanical properties. • The wear performance of the samples after surface treatment was improved.

Experimental research of the conditions for the transfer of rock pressure by saliniferous rocks to the casing

The analysis of field data from casing failure on the fields of the Borislav and Dolinsky oilfield regions has been carried out. It has been found that the most significant negative factors that have a bearing on the preservation of the integrity of the casing strings are the presence of saliniferous rock intervals in the borehole log and not taking into account the possible impact of rock pressure when designing casing strings in these rocks. In saliniferous rocks, under certain conditions, rock pressure can be transferred to the column. To study the thermobaric conditions of the external pressure transfer to the casing from the saliniferous rock, experimental tests have been carried out on the core materials of the rocks of the Vorotyshchensk floor, sampled at different depths of the Oriv-Ulychniansk field. For this purpose, a special laboratory installation was made, which allows to study the stress conditions and rock flowage on exposure to formation temperature and rock pressure. Because it was difficult to directly measure the radial pressure transmitted to the pipe and the temperature inside the chamber during the experiments, the installation was calibrated by pressure and temperature. This made it possible to determine the temperature inside the chamber by the value of the voltage supplied to the heating element, and the value of the radial pressure supplied to the pipe - by the value of the pressure inside the pipe. Based on the results of experimental research, the depen-dences of the lateral earth pressure coefficient of saliniferous rocks on temperature were obtained at various values of normal stresses. It was found that when the temperature rises to 70 ° C and higher, the value of the lateral external pressure on the pipe approaches the vertical component of the pressure. According to the results of the experimental research, the temperature and pressure conditions for accounting for rock pressure were recommended when calculating casing strings for external overpressure in the intervals of occurrence of saliniferous rocks of the Carpathian fields.

Dynamic Shearing Resistance of an Energetic Material Simulant: Sucrose

Sucrose is a commonly used energetic material simulant for β-HMX. However, its behavior under extreme loading conditions remains poorly understood. Pressure-Shear Plate Impact (PSPI) experiments have been conducted to provide an experimental foundation for developing a suitable constitutive model for sucrose. Experiments have been performed at two different nominal normal stress values, 3 and 9.5 GPa, with nominal shear strain-rates of the order of 106s−1. Sucrose exhibits a shear strength of ∼400-500 MPa in this pressure range, with a relatively small pressure sensitivity. However, pronounced strain softening is observed in sucrose at sufficiently large shear strains - even a dramatic drop in shearing resistance in some cases. A thermodynamically-consistent constitutive theory is presented to model the thermoelastic, thermo-viscoplastic response of sucrose. The use of the logarithmic strain and an appropriate set of invariants allows for separation of the Cauchy stress into pressure and deviatoric terms. A complete Mie-Gruneisen equation of state is presented to model the volumetric behavior while the deviatoric response is captured through the Johnson-Cook Model. The material model is able to capture experimental observations and predicts localization in the form of adiabatic shear bands, which explains the catastrophic drop in shearing resistance of sucrose observed in the experiments. Such localization events carry important implications for energetic materials in the context of hot-spot formation and underline the importance of dynamic shearing strength measurements.

Study on the drop impact characteristics and impact damage mechanism of sweet potato tubers during harvest.

Collision of falling in the mechanical harvesting process of sweet potato is one of the main causes of epidermal destruction and damage to sweet potato tubers. Therefore, a sweet potato mechanical characteristic test and a full-factor sweet potato drop test were designed. Based on the analysis of the fitting mathematical model, the impact of the drop height, collision material and sweet potato chunk size on the damage of the sweet potato were studied. The mathematical models were established by fitting analysis of the IBM SPSS Statistics 22 software between the drop height and the sweet potato chunk size with each test index (impact force, impact stress, broken skin area and damaged area). The critical epidermal destruction height and the critical damage height of a certain size of sweet potato when it collides with a collision material can be calculated by the mathematical model, and the critical epidermal destruction mass and critical damage mass of sweet potato when it falls from a certain height and collides with a collision material can also be calculated. Then a series of critical values (including critical epidermal destruction force value, critical epidermal destruction impact stress, critical damage force value, critical damage impact stress) of mechanical properties of sweet potato were obtained. The results show that the impact deformation of sweet potato includes both elastic and plastic ones, and has similar stress relaxation characteristics. The critical damage impact stress of sweet potato is that the average value of the impact stress on the contact surface is less than it’s Firmness. The results provided a theoretical basis for understanding the collision damage mechanism of sweet potato and how to reduce the damage during harvest.