Deviation Stress Research Articles

Characteristics of Permeability Changes in Bituminous Coal Under Conditions of Stress Variation Due to Repeated Mining Activities

The factors affecting permeability change under repeated mining of coal seams are important study aspects that need to be explored. This study combined various stress variation characteristics of protective seam mining and simplified the stress path of repeated mining in protective seam mines. Based on the results from the bespoke gas flow and displacement testing apparatus, seepage tests for simulated repetitive mining were carried out. The results simulated the actual behavior very well. With any drastic increase in the mining influence, the axial deviation stress in the stress path increased, and the greater the difference in coal permeability during the unloading and stress recovery stage, the more substantial the increase in permeability. The change in coal permeability was significantly influenced by the severity of simulated repeated mining cycles. When the mining stress exceeded a critical value, the permeability of the coal sample increased with the increase in the number of loading and unloading cycles, but the reverse was true when the mining stress was lower than the critical value. The effective sensitivity of seepage to the applied stress decreased with an increase in the number of stress cycles. With a decrease in the deviation stress, that is, with lower severity of mining influence, the effective sensitivity of coal seepage to stress gradually decreased.

Evaluation of the Relationship Between Nasal Septum Deviation and Oxidative Stress Markers.

Nasal septum deviation (NSD) may lead to chronic hypoxia and increased oxidative stress.The main goal of this study was to investigate the effect of NSD on malondialdehyde (MDA), catalase (CAT), superoxide dismutase (SOD), and glutathione (GSH) levels. There were 30 patients with NSD and 30 healthy subjects in this study. Malondialdehyde, CAT, SOD, and GSH levels were determined in the control and study groups. The measurements were done preoperatively and postoperatively. Study group patients completed the Nasal Obstruction Symptom Evaluation questionnaire preoperatively and postoperatively to determine the success of the septoplasty. Higher CAT, SOD, and GSH levels and lower MDA levels were found in the control group compared with the study group (P < 0.05). After septoplasty, Nasal Obstruction Symptom Evaluation scores improved significantly and CAT, SOD, and GSH levels increased significantly (all, P < 0.05). Malondialdehyde levels did not decrease significantly after surgery (P > 0.05). Nasal obstruction due to nasal septal deviation led to lower antioxidant enzyme levels, and correction of the septum led to an increase in antioxidant levels.

Dimensional precision of implant-supported frameworks fabricated by 3D printing

Statement of problemSelective laser melting (SLM) is a promising additive technology for clinical practice, but data on dimensional precision assessed by marginal fit combined with stress and strain investigations of implant-supported fixed partial dentures (FPDs) are lacking. PurposeThe purpose of this in vitro study was to verify whether the SLM additive manufacturing technology provides better dimensional precision for 3-unit FPD frameworks than subtractive manufacturing with soft metal block (SMB) milling and the standard casting technique. Material and methodsThirty 3-unit implant-supported FPDs with Co-Cr frameworks were made by the casting, SMB milling, and SLM methods (n=10). The marginal fit between the framework and the implant abutment was evaluated with photoelastic (PH) and strain gauge (SG) models. Stress and strain in the implant-supported system were measured by quantitative PH and SG analyses after prosthetic screw tightening. Data were subjected to the Kruskal-Wallis test, Mann-Whitney U test, and Spearman correlation test (α=.05). ResultsThe framework manufacturing method affected the marginal fit (P<.001), stress, and strain values (P<.05). The SLM group showed the best mean ±standard deviation marginal fit (μm) (PH model: 8.4 ±3.2; SG model: 6.9 ±2.1) in comparison with SMB milling (PH model: 42.3 ±15.7; SG model: 41.3 ±15.3) and casting (PH model: 43.5 ±27.8; SG model: 41.3 ±24.6) (P<.05). SLM showed lower mean ±standard deviation stress and strain values (60.3 ±11.6 MPa; 91.4 ±11.1 μstrain) than casting (225.5 ±142.8 MPa; 226.95 ±55.4 μstrain) and SMB milling (218.6 ±101.7 MPa; 289.7 ±89.3 μstrain) (P<.05). A positive correlation was observed between fit and stress or strain for all groups (P<.05). ConclusionsThree-unit FPD frameworks made using the SLM technology showed better dimensional precision than those obtained with the casting or SMB milling methods.

The mechanisms of a loess landslide triggered by diversion-based irrigation: a case study of the South Jingyang Platform, China

Continuous use of diversion-based irrigation has been associated with an increase in the frequency of loess landslides on the South Jingyang Platform, Shaanxi, China. A loess landslide event with a maximum sliding distance of 278 m occurred near the village of Miaodian on May 26, 2015. This landslide event was characterized by four individual landslides. Field investigations, geological exploration, numerical simulation, isotropically consolidated undrained (ICU) triaxial tests, and ring shear tests were conducted to identify its initiation and movement mechanisms. The ICU tests revealed that saturated loess samples were highly liquefiable. High pore water pressure was quickly produced and deviation stress increased the highest value even at low values of axial strain. Geological investigations revealed that cracks penetrated into the saturated zone from the ground surface, and simulation results revealed that these cracks played a dominant role in the infiltration of surface water and led to a rise in the groundwater table. When the infiltration recharge exceeds the holding capacity of the paleosol, the latter behaves as aquifuge under relatively undrained conditions. This process results in the accumulation of water at the bottom of the loess layer, thereby contributing to soil liquefaction and landslide initiation. The ring shear tests revealed that the saturated sand layer of the landslide substrates was subjected to easily inducible high pore water pressure under undrained conditions which led to the thrusting of the sand layer onto the deposit surface and explains the high speed and long runout distance of this landslide.

Study on dynamic undrained mechanical behavior of saturated soft clay considering temperature effect

In order to study the influence of temperature on soil dynamic characteristics, a temperature-controlled triaxial test apparatus was developed, in which a curved heating plate was designed as heating cell. The heating system can achieve the accurate control of the sample temperature within the scope of 10–100 °C. The dynamic undrained characteristics of saturated soft silty clay in Ningbo were studied under different temperatures, dynamic stress amplitude, confining pressure and initial static deviation stress by using the newly developed temperature-controlled triaxial test system. The test results showed that the temperature has great influence on the accumulative plastic strain, pore water pressure, damping ratio and dynamic elastic modulus of soft clay. As temperature increases, the cumulative plastic strain, the dynamic damping ratio and the dynamic pore pressure decrease, while the dynamic elastic modulus increases. Furthermore, the saturated soft clay exhibited a tendency of thermal hardening. Finally, a unified empirical strain model, which can consider the effect of temperature, dynamic stress amplitude, confining pressure and initial static deviator stress on accumulative plastic strain, was proposed. By using the test results, it is confirmed that the proposed empirical model is capable of predicting the undrain cumulative plastic strain of soft clay under different conditions.

Liquefaction of loess landslides as a consequence of irrigation

Most landslides on the Loess Tableland (Shaanxi, China) are of the sliding-flow type, with long run-out distances. These landslides, which tend to be triggered by irrigation, result in loss of life and damage to infrastructure. In order to reveal the characteristics and mechanisms of sliding-flow landslides, field investigations, surveys and indoor tests, including consolidated undrained triaxial tests and ring-shear tests, were conducted. The apparent friction of sliding-flow loess landslides triggered by irrigation in the study area ranged from 0.01 to 0.25, with a mean of 0.159. These values are lower than those associated with the landslides triggered by the Wenchuan Earthquake. The deviation stress decreased to about 99% of its peak value, while the path of the effective stress revealed that the effective normal stress approached zero. Consequently, saturated loess samples were highly liquefiable under consolidated undrained triaxial tests. The pore pressures increased sharply and up to their peak value (mean of 130 kPa), corresponding to 92% of the applied normal stress. The path of effective stress did not reach the failure line. The loose structure and macro-pore content of loess provide the framework for static liquefaction to occur as a consequence of the generation of fine particles.

Full-Stokes modeling of a polar continental glacier: the dynamic characteristics response of the XD Glacier to ice thickness

The steady-state diagnostic and prognostic simulation for the Xiao Dongkemadi glacier (XD) of the Tibetan Plateau was performed with the thermo-mechanically-coupled-with-Full-Stokes code Elmer ( http://www.csc.fi/elmer/ ). In this paper, some changes of glacial thermodynamic parameters caused by ice thickness and atmospheric temperature variation were simulated in view of different thickness. The purpose of this study was to fill the gap in analyzing the ice dynamic characteristic of a polar continental glacier. The diagnostic simulation revealed the following conclusions: (1) when the thickness change was small, surface velocity, ice temperature, and deviation stress variation in the bedrock showed a tendency to change with thickness, and when the terrain was gentle, the thickness variation dominated the ice velocity. (2) The ice temperature of the bedrock was high in the whole profile and reached the pressure melting point in the terminus, and it was easy to slide at the bottom, which was consistent with the measured ground penetrating radar data near the terminus. (3) The static friction forces decrease with thickness, and they showed a complex nonlinear relationship, which revealed that the deviation stress in the bottom was influenced by thickness and ice temperature at the bedrock. The prognostic simulating from 2007 to 2047 presented: (1) The simulation forecasted a shrinkage of nearly 600 m in the terminus and the longitudinal section, and wound up diminished by nearly 25% by the end of 2047; (2) the change of thickness was small at the region between 5650 and 5700 m.a.s.l, which might be related to lower atmospheric temperature; (3) thickness dominated the deviation stress ( $$\sigma _{xx}$$ and $$\sigma _{xz}$$ ) in the bottom, and the impact of the terrain was little higher compared to deviation stress ( $$\sigma _{xx}$$ ). In other words, the glacial thickness dominated the glacial force and movement to a great extent and the low temperature at high altitude reduced the XD’s sensitivity facing future climate warming.

Quality dependence study on dimensions for plano‐concave molded glass lenses

AbstractA comprehensive study was conducted to analyze the quality dependence of a plano‐concave molded glass lens on its own dimensions, i.e. the effective diameter, sag ratio, and center thickness ratio. To achieve this goal, a thermal‐displacement coupled finite element analysis was carried out on the whole molding process, in order to get the results of curve deviation, temperature gradient, and residual stress with sets of variations in these dimensions. Then Taguchi method, one approach for design of experiments, was incorporated to conduct sensitivity analysis on the simulation results to figure out the dominating sequence of these dimensions. The results show that the effective diameter is the most influential factor among these three dimensions. In addition, curve deviation is sensitively proportional to diameter and sag ratio, but decreases insignificantly with greater center thickness ratio. However, residual stress is distinctly proportional to diameter and center thickness ratio, but increases very slightly with greater sag ratio. Results also confirmed the consequential relationship between temperature gradient and residual stress. These discoveries are fundamentally meaningful in getting an overall understanding of the dimensions’ influence on the molded lens quality, thus will help make decision in choosing proper dimensions for optical design.

Process influences and correction possibilities for high precision injection molded freeform optics

Abstract Modern injection molding processes offer a cost-efficient method for manufacturing high precision plastic optics for high volume applications. Besides form deviation of molded freeform optics, internal material stress is a relevant influencing factor for the functionality of a freeform optics in an optical system. This paper illustrates dominant influence parameters of an injection molding process relating to form deviation and internal material stress based on a freeform demonstrator geometry. Furthermore, a deterministic and efficient way for 3D mold correcting of systematic, asymmetrical shrinkage errors is shown to reach micrometer range shape accuracy at diameters up to 40 mm. In a second case, a stress-optimized parameter combination using unusual molding conditions was 3D corrected to reach high precision and low stress freeform polymer optics.

A Dual Three-Level T-NPC Inverter for High-Power Traction Applications

This paper proposes a dual three-level, T-type, neutral-point clamped (T-NPC) inverter fed dual permanent magnet synchronous motor topology for low-voltage, high-power traction applications. The switching pulses of the T-NPC inverters are interleaved and controlled, such that they produce equal and opposite three-phase currents at their output. This maintains balanced dc-link voltages in steady-state and transient conditions, even with slight mismatches between two sets of three-phase loads. Thus, the proposed configuration decouples the modulation strategy from the capacitor balancing control. Simulation and experimental results demonstrate that in comparison to the conventional single T-NPC inverter, the proposed topology reduces dc-link capacitors’ voltage deviation and current stress by more than 90% while avoiding additional switching instances to balance capacitor voltages.

不同偏离率下铝合金半球体壳体旋压模拟及应力、变形分析

利用SuperForm/Marc软件模拟半球体壳体的旋压过程，研究了旋压过程中壳体壁厚位移的变化，并重点分析了影响旋压工件形状的一个重要因素即壁厚偏离率对工件应力分布及变形程度的影响规律。模拟结果显示：针对三种偏离率(0 (无偏离)、+5%、−8%)，旋压过程中壳体变形随着壁厚减薄率增加而增加，外层变形呈台阶状增加；同一变形时刻，变形大小顺序为：负偏离 > 零偏离 > 正偏离；不同的偏离率对壳体贴模情况影响很大，对应大尺寸半球壳体的旋压成形贴模性好坏顺序为：正偏离 > 零偏离 > 负偏离。 The process of aluminum alloy hemispherical shell spinning was simulated by use of the software of SuperForm/Marc. The change of the shell’s thickness was studied and the effect of the thickness deviation rate (an important factor for the influence law of deformation) and stress distribution in the spinning process was analyzed. For the three deviation rates (0 (no deviation), +5% and −8%), the simulation analysis showed that the deformation of shell increases as the thickness reduction ratio increases in the process of spinning, and the outer deformation of the shell increases with a shape of stair; in the meantime, the order of the shell’s deformation was: −8% > 0 > +5%. And the wall thickness showed a great difference under different deviation rates, and the order of the wall thickness precision of the shell in the spinning process was: +5% > 0 > −8%.

Evaluation of the swelling characteristics of bentonite–sand mixtures

The swelling characteristic of bentonite–sand mixtures is an important index in evaluating the long term performance of the deep geological repository of nuclear waste. In this study the swelling characteristics of different types of bentonite–sand mixtures with various sand contents are compared. It is concluded that for pure bentonite and bentonite–sand mixtures with less sand than the critical sand content, the relationship between montmorillonite void ratio and vertical stress can be expressed as a unique line in a double logarithmic plot, and volumetric strain under a given vertical stress and swelling pressure at a constant volume after full saturation can be predicted based on this line; however, for mixtures with more sand than the critical sand content, the above relationship deviates from the line when the stress is larger than the starting deviation stress, which can be determined using the sand skeleton void ratio. Before the sand skeleton forms, the vertical stress is borne mainly by montmorillonite particles and the amount of swelling at full saturation is determined by the content of montmorillonite per unit volume, however, after the sand skeleton forms the vertical stress is borne by both the montmorillonite and the sand skeleton. The stress distribution coefficient is proposed to present a proportion of the vertical stress that is borne by both parts. A predictive method, verified by the swelling tests on bentonite–sand mixtures with various sand contents, is suggested to predict the amount of swelling due to saturation in the full range of sand content.

PROBABILISTIC SPECIMEN PROPERTY-FATIGUE LIFE MAPPING AND P-S-N CURVE FITTING

Fitting P-S-N curve with small-size sample of fatigue test data is significant in engineering applications. Although several small sample-based P-S-N curve fitting methods have been developed, complexity in mathematics and/or the unrealistic assumption of the methods hinder their application seriously. Based on the principle of probabilistically mapping from the probability distribution of specimen property to that of fatigue life of the specimen, this paper presents a new, easy to apply P-S-N curve fitting method. By collecting the life distribution information dispersed in several small-size samples of fatigue lives tested under different cyclic stress levels, a large-size sample of equivalent fatigue life data can be built based on the mapping mechanism as well as the uniqueness of the relationship between fatigue life standard deviation and cyclic stress level. The basic viewpoint is that the fatigue lives tested at any cyclic stress levels can be equivalently converted to an arbitrary baseline stress level according to the life distribution–stress relationship, and this principle can be applied to determine the P-S-N curves with a limited number of test data. Test results illustrate that the P-S-N curves obtained by such methods with 30, 24 or 20 samples, respectively, are close to those obtained by the conventional test method with 60 or 40 samples.

Design Considerations for Dual-Output Quasi-Resonant Flyback LED Driver With Current-Sharing Transformer

In this paper, a quasi-resonant (QR) flyback dual-output LED driver with current-sharing transformer (CST) is analyzed thoroughly. Although the CST is utilized to balance the currents in two LED strings, from the theoretical analysis, it shows that the parasitic capacitance of CST and its magnetizing inductance have a significant effect on the output current deviation and diode's voltage stress. In order to achieve the optimal current sharing ability between two outputs with minimum auxiliary components, a design guideline for the CST in QR flyback is proposed according to the theoretical analysis. A 100-W dual-output dc-dc prototype is built up to verify the theoretical analysis.

Die separation and rupture strength for deep reactive ion etched silicon wafers

The work herein analyzes the bending stress required to separate and rupture die from notched silicon wafers. Trenches are formed on the wafers using either a dicing or Bosch deep reactive ion etching (DRIE) process. Weibull distribution parameters are reported for all variations of the fracture experiments. Additionally, the relative defect rate associated with DRIE-based die separation are compared with traditional saw methods for a variety of notch depths. Results indicate that the DRIE-based separation technique offers improved rupture strength over the traditional methods, but can also greatly reduce die strength if performed improperly. Dies completely separated by the DRIE process showed a mean failure stress of 1.16 GPa with a Weibull standard deviation of 682 MPa compared to 452 and 65 MPa mean and standard deviation stress for die completely separated by a traditional dicing saw.

Finite Element Analysis of Axis Deviation between Rivet and Plate Hole

The riveting joint is the main connection method in aircraft assembly. There are some kind of rivets, such as slug rivet and protruding rivet, that riveting quality will be impacted while rivets axis are not coincident with the plate holes axis. By using the finite element method with ABAQUS software, this paper built the 3D riveting joint structure of finite element, and analyzed the axis deviation effect on the deformation, stress and strain of riveting. Through statistical data, the relationship among axis deviation value, deformation, stress and strain of rivet are built.

Analysis of main shock of thrust fault earthquake by catastrophe theory

The relationship between work and energy increment of a thrust fault system with quasi-static deformation can be decomposed into two parts: volume strain energy and deviation stress energy. The relationship between work and energy increment of the deviation stress of a simplified thrust fault system is analyzed based on the catastrophe theory. The research indicates that the characteristics displayed by the fold catastrophe model can appropriately describe the condition of earthquake generation, the evolvement process of main shock of thrust fault earthquake, and some important aftershock properties. The bigger the surrounding press of surrounding rock is, the bigger the maximum principal stress is, the smaller the incidences of the potential thrust fault surface are, and the smaller the ratio between the tangential stiffness of surrounding rock and the slope is, which is at the inflexion point on the softened zone of the fault shearing strength curve. Thus, when earthquake occurrs, the larger the elastic energy releasing amount of surrounding rock is, the bigger the earthquake magnitude is, the larger the half distance of fault dislocation is, and the larger the displacement amplitude of end face of surrounding rock is. Fracturing and expanding the fault rock body and releasing the volume strain energy of surrounding rock during the earthquake can enhance the foregoing effects together.

A Repeated Loading Triaxial Test Study on Resilient Modulus of Graded Crushed Stone

To investigate the effect of confining stress, deviation stress, moisture content and gradation type on resilient modulus of graded crushed stones, three types of graded crushed stone with three moisture content levels(optimum moisture content and ±2% of the optimum moisture content, respectively ) were used, and repeated loading triaxial (RLT) tests with twenty five stress levels were carried out. The RLT test results demonstrate that resilient modulus of graded crushed stone remarkably increases with decreasing moisture content and/or increasing confining stress; resilient modulus of graded crushed stone slowly increases, or minor decreases at the beginning and then slowly increases with increasing deviation stress at low stress state. Results also indicate that gradation type has a certain impact on resilient modulus of graded crushed stone.

Ultimate Bearing Capacity Analysis of Concrete Filled Steel Tubular Arch Considering the Initial Defects’ Influence

In the CFST arch bridge construction process, for the reasons of arch axis deviation as prefabricated or constructed, the bearing capacity of arch-rib decreased. This paper considers material and geometric non-linear double factors, calculates the arch-rib ultimate bearing capacity of a CFST arch/continuous beam bridge with defects of arch axis deviation and steel yield stress decrease because of heat treatment, obtain the influence of defects to arch bearing capacity.

Specific features of fields of stresses associated with aftershock processes in the Altai-Sayan mountainous region

The cataclastic method developed by Yu.L. Rebetsky is applied to reconstruct the recent field of stresses related to aftershock sequences of earthquakes that occurred in the Altai-Sayan mountainous region, specifically the Altai earthquake of 27 September 2003 (М=7.3; φ=50.061o; λ=87.966o) and the Busingol earthquake of 27 December 1991 (М=5.0; φ=51.1o; λ=98.13o). Upon reconstruction of the field of stresses from data on aftershocks of different magnitudes, it is revealed that orientations of maximum stresses are misaligned, and this may suggest a lack of similarity of fields of stresses in different scale ranks. The fields of stresses reconstructed from data on sequences of weak aftershocks of the Altai and Busingol earthquakes show changes in orientations of major stress axes at opposite sides of the shear faults under study. The orientation of the maximum deviation stress axes due to strong aftershocks is consistent with the regional field of stresses and does not change in the vicinity of the fault plane associated with the strong earthquakes the Altai and Sayan regions.