Stress Principle Research Articles

Rock Damage Model Coupled Stress-Seepage and Its Application in Water Inrush from Faults in Coal Mines.

Mining-induced fractures often constitute water inrush channels, which lead to mine water inrush accidents. In this paper, a coupled model of stress–seepage–damage based on micromechanics is established, which simulates the initiation and propagation of cracks in rock materials and their interaction with fluid flow. The method combines the continuous damage model with the effective stress principle, in which the elastic modulus and permeability are related to the damage variables. The model is implemented via the COMSOL code based on the finite element method, and the reliability of the model is verified by the axial compression–seepage test of standard rock samples. According to the actual geological conditions of F13 fault in Wugou Coal Mine, Anhui Province, the damage of the floor rock mass and the risk of fault water inrush in the 1033 mining face with 50, 40, 30, and 20 m waterproof coal pillars are predicted. When the coal pillar width is 30 or 20 m, the fault, the surrounding rock of the fault, and the failure zone of the floor constitute the water inrush channel. This model provides an intuitive understanding of the rock damage and water inrush evolution, which is difficult to observe, and will contribute to prevent water inrush disasters in practical engineering.

An acoustic near surface soil profiler using surface wave method

An acoustic soil profiler, using a so-called the high-frequency multi-channel analysis of surface waves (HF-MASW) method, has been developed, which uses surface (Rayleigh) waves to measure soil profile in terms of the shear (S) wave velocity as a function of depth, up to a 2.5 m deep below the surface. Several practical techniques have been developed to enhance the HF-MASW method, including (1) a variable sensor spacing configuration, (2) the self-adaptive method, and (3) the phase-only signal processing. Fundamentally, the S-wave velocity is related to soil mechanical and hydrological properties through the principle of effective stress. Therefore, the measured two-dimensional S-wave velocity images reflect the temporal and spatial variations of soils due to weather effects, geological anomalies, and anthropologic activities. Several HF-MASW applications will be reported, including (1) near surface soil profiling, (2) a long-term-survey for studying weather and seasonal effects, (3) short-term monitoring rain fall events, (4) detecting fraigpan layers, and (5) a farmland compaction study. This acoustic soil profiler can be used for agricultural, environmental, civil engineering, and military applications.

Weld Fatigue Life Analysis of Truck Mixer Sub-frame Based on Equivalent Structural Stress Method

In order to accurately calculate the fatigue life of the sub-frame weld of the mixer truck during the design stage, fatigue analysis of the weld is carried out by equivalent structural stress method. Through the finite element analysis of the frame, the key weld position is researched. By using the inertial release method, the stress response of the frame under the single excitation of the unit load is obtained. Combined with the basic principle of equivalent structural stress, the stress at the weld position is calculated, and the main S-N curve with a survival rate of 50% is selected to predict the fatigue life of the weld. The results show that the fatigue life of the key weld is 105.803 cycles, which fails to reach the design target value. The equivalent structural stress method has the characteristics of grid insensitivity and can better predict the fatigue life of the sub-frame weld of the mixer truck.

A Model for Adapting Evidence-Based Interventions to Be LGBQ-Affirmative: Putting Minority Stress Principles and Case Conceptualization Into Clinical Research and Practice

The mental health field now possesses clinical trials attesting to the efficacy of affirmative practice with sexual minority individuals. With the goal of efficiently moving the results of these clinical trials into real-world clinical practice, this paper offers a model for adapting existing evidence-based practices originally developed for the general population to be lesbian, gay, bisexual, and queer (LGBQ)-affirmative. The adaptation model presented here guides clinicians to incorporate six LGBQ-affirmative transtheoretical principles of change into practice. These principles facilitate raising awareness of the impact of minority stress on sexual minority clients’ mental health and on client self-evaluation while drawing upon sexual minority resilience and intersectional experiences to build empowering coping skills and validating relationships. The adaptation model also provides a transtheoretical approach to case conceptualization that directs clinicians to consider the role of early and ongoing minority stress on sexual minority clients’ cognitive, affective, motivational, behavioral, and self-evaluative experiences that maintain current distress. This case conceptualization approach highlights common associations among these experiences, suggesting clear routes of interventions for many sexual minority client presentations. Case examples from recent clinical trials of LGBQ-affirmative cognitive-behavioral therapy illustrate how these principles and this case conceptualization can be effectively utilized in practice. While the principles and case conceptualization are meant to be transtheoretical and therefore applicable across therapeutic techniques, to date they have been tested only in clinical trials for cognitive-behavioral treatments. Therefore, this paper concludes with a call for future research to determine the effectiveness of implementing this adaptation model across diverse therapeutic modalities and client presentations.

Study on Overlying Strata Movement and Surface Subsidence of Coal Workfaces with Karst Aquifer Water

The overlying strata layers of coal workfaces with karst aquifer water normally causes serious safety problems due to the precipitation, drainage and water inrush, such as a wide range and long term of surface subsidence. In this study, by taking 10,301 working faces of the Daojiao coal mine in Guizhou Province as the engineering background, the numerical model of water-bearing strata with fluid-solid coupling was established by using UDEC to illustrate the laws of overlying strata movement and surface subsidence. A theory model was proposed to calculate the surface settlement caused by the drainage of aquifer based on the principle of effective stress modified by the Biot coefficient αb. The results showed that the corresponding maximum value (0.72 m) and the range of the surface subsidence with the occurrence of karst aquifer water were larger than that of the overlying strata without karst aquifer water (e.g., the maximum value of surface subsidence with 0.1 m). Moreover, the surface subsidence caused by the drainage of aquifer accounted for 17.8% of the total surface subsidence caused by coal mining. According to the field monitoring of surface subsidence in 10,301 working faces, the maximum value was 0.74 m, which was highly consistent with the results of numerical simulation and theoretical analysis. It verified the accuracy and reliability of the numerical model and the theory model in this study.

Influence of Multistage Target Temperature and Cyclic Loading/Unloading on the Permeability of Polypropylene Fiber Concrete

Due to the combined effect of temperature and cyclic loading and unloading, the gas permeability of polypropylene fiber reinforced concrete structures changes during service. However, the current gas permeability test of polypropylene fiber reinforced concrete is based on a single influencing factor or a single test condition (monotonic loading), and the test conditions are quite different from the actual working conditions of the structure. To explore the permeability of polypropylene fiber reinforced concrete under cyclic loading and unloading under the influence of temperature, based on the stress principle that the specimen does not have structural damage and according to the steady‐state equation of Darcy’s law, the Cembureau method is adopted. The gas permeability of polypropylene fiber reinforced concrete under single loading and unloading and multistage cyclic loading and unloading at eight target temperatures is tested by the triaxial permeability test system. The results showed that (1) when the target temperature was 120°C < T ≤ 200°C and 200°C < T ≤ 280°C, the fiber experienced two stages of “softening, melting‐cooling recovery” and “melting and absorption,” which caused damage to the matrix pore structure. The gas permeability at 200°C and 280°C was 246 times and 350 times that at 22°C, respectively. (2) The damage degree of the matrix strength structure increases during cyclic loading and unloading, and the permeability loss rate during cyclic loading and unloading is 1.24∼1.57 times that of single loading and unloading. (3) The high target temperature leads to pore structure damage of the matrix, which not only affects the permeability of the matrix but also affects the strength structure of the matrix. When the stress ratio R ≥ 0.37, the pore structure damage and the strength structure damage of the specimen are superimposed, resulting in the antipermeability effect of the specimen developing in the unfavorable direction. The test simulated the actual working conditions of polypropylene fiber reinforced concrete, providing a reference for building fire protection, seismic design or postdisaster evaluation.

The trans youth justice project: a political education and leadership development program

Research has demonstrated that systemic transphobia and cissexism harms transgender youth in terms of social, educational, and health outcomes. All too often, research and policy emphasizes vulnerability among trans youth in a way that denies their capabilities as agents of change or active participants in their liberation. This article analyzes the development of Trans Youth Justice Project, a political education and youth leadership development program for trans youth ages 15–22. Based in principles of gender minority stress and social justice youth development, the 6-week remote program aims to increase the capacity and resilience of trans youth, develop youth leaders, and contribute to addressing social, educational, and health inequalities. We conducted a formative program evaluation of 2 cycles of the program with a total of 25 youth. Pre- and post-test surveys indicated increased feelings of belongingness to a trans community. Follow-up interviews highlighted the impact the program had on skills for social justice, self-efficacy, and community connection. We offer suggestions for implementing the open-source program more broadly.

Research on the Coupled Water–Soil SPH Algorithm Improvement and Application Based on Two-phase Mixture Theory

An improved water–soil coupling algorithm was proposed based on the two-phase mixture theory within the framework of smoothed particle hydrodynamics (SPH). In this algorithm, the buoyant density was considered in saturated soil and the stress of two phases was completely exfoliated with the Terzaghi’s effective stress principle. Then the interaction between water and soil was only constituted by viscous drag force. The proposed algorithm was validated by several numerical tests to effectively solve a series of numerical problems caused by the truncation of the kernel approximation on the interface between submerged soil and water, and it can also be a feasible measure to simulate underwater soil excavation problems without drainage and underwater landside problems. Meanwhile, combined with frictional sliding contact algorithm, the interaction between water/soil and structure which was considered as rigid can be effectively modeled, and the calculated contact forces acting on the structure are more accurate. Furthermore, this improved algorithm can be applied to deal with large deformation problems involving complex water–soil–structure interaction in hydraulic and geotechnical engineering such as underwater excavation, shield dig, caisson sinking and other practical engineering problems. It is also significant to engineering design and the improvement of construction level.

Interference mechanism and damage accumulation in high-speed cross scratches on hard brittle materials

Precision and low damage grinding of aviation optical elements can effectively improve the overall processing efficiency. The mechanism of high-speed cross scuffing of multiple abrasive particles has become an important factor affecting the forming quality of workpiece. Interaction of abrasive trajectory determines machined surface and subsurface morphology and damage. According to the relative motion trajectory of wear particles on the workpiece surface, a theoretical model of the trochoidal trajectory intersection angle is proposed. High-speed scratches with different cross angles are experimentally obtained to explore the interference mechanism and damage accumulation of cross scratches. The results indicate that the Crack system I and Crack system II, produced by the two cross scratches, are mainly based on the stress principle and the strength principle, respectively. An increase in the damage radius is observed with a decrease in the crossing angle. Furthermore, as the duration of the normal cutting force decomposition curve at the entrance/exit of the intersection increases, the half-peak width also increases. The accumulation of cross-scratch damage promotes the propagation of deep subsurface lateral and median cracks. In other words, damage accumulation and interference mechanism formed by the cross scratches increase the longitudinal depth and lateral length of the damage.

Study on deformation of abutment and the influence on high arch dam during impoundment

High arch dams in China have been impounded and entered the operation stage in succession. The value and law of deformation during impoundment are different, which brings a great challenge to the performance and long-term safety of the arch dam. Based on the analysis of monitoring data of Jinping No.1 arch dam and Xiluodu arch dam, it is pointed out that the valley width deformation is irreversible plastic deformation, and there are two modes of valley width deformation of dam foundation: bank slope deformation mode and overall deformation mode. The bank slope deformation mode shows that the valley width of the upstream is significantly larger than that of the downstream, and the chord length of the dam is not large. Based on the principle of effective stress, the deformation mechanism of bank slope deformation mode is discussed. The overall deformation mode shows that the valley width of the upper and lower reaches is similar and the magnitude is large, and the chord length of the dam is large. The boundary displacement method is used to simulate the overall deformation mode. The model of Baihetan arch dam is established, and the structural model and geological conditions of the dam site are simulated in detail. Based on 3D nonlinear finite element calculation, the effects of two valley width deformation modes on the displacement, stress and local cracking of Baihetan arch dam are analyzed, and the calculated results are compared. The results show that the overall deformation mode can cause infinite valley width deformation, while the bank slope deformation mode can only cause limited valley width deformation. When the same valley shrinkage value is produced, the bank slope deformation mode can make the dam produce new stress concentration area, and the overall deformation mode has little effect on the dam stress, which indicates that the non-uniform deformation of the dam foundation is the key to affect the stress in the dam.

A New Method to Estimate Formation Pore Pressure in Fractured Areas of Shale Gas Reservoir

The matrix of shale gas reservoir has the characteristics of low porosity and ultra-low permeability, but also develop natural and hydraulic fractures. Many field operations observed that the formation pore pressure after hydraulic fracturing is higher than the original formation pore pressure. Drilling in the fractured areas of shale gas reservoir, including natural fractures and artificial fractures, always faces greater overflow risk. The pore pressure test after fracturing also shows that the test value is higher than the formation initial pore pressure. However the conventional formation pore pressure predicting methods are difficult to obtain the accurate pore pressure in the fractured areas of shale gas reservoir.In this paper, the causes of formation pore pressure changing and fracturing pressurization effect in the fractured zones of shale gas reservoir are analyzed. Based on the assumption of closed and constant volume material balance and the gas equation of state, the internal mechanism of the increase in pore pressure caused by fracturing operation in low-permeability shale gas formation is theoretically analyzed. A new method to predict pore pressure changing of shale gas reservoir during drilling and hydrofracturing operations is proposed. The pore connectivity of shale gas reservoir is poor, and the permeability is tens of nano-darcy. The permeability is usually between 0.01-0.20 millidarcy when natural fractures are developed. After fracturing, the permeability can be increased by 2-3 times. Based on the principle of effective stress, a pore pressure calculation model with the influence of permeability change is established by using logging data. Three influence terms are considered in the model: the first one is the overburden pressure term, the second one is the skeleton stress term, and the last one is the influence term of permeability change rate on local formation pore pressure. The proposed method shows simple principle, clear mechanism and easy to use in the field. Field applications show that this method could quickly and accurately predict dynamic formation pore pressure changing of shale gas reservoir. It offsets the shortcomings of traditional formation pore pressure calculation methods.

Ground settlement and fault deformation response to deep-buried tunnel excavation and groundwater drawdown

The groundwater drawdown caused by tunnel excavation may induce large-scale deformation, including uneven settlement deformation of rock mass and local deformation of faults, which poses a great risk to engineering safety, and requires the constraint of deformation stability. Based on the theory of deformation reinforcement and the effective stress principle, we study the nonuniform deformation and unbalanced force distribution of the rock mass and faults caused by the groundwater drawdown after the excavation and drainage of the deep tunnel. The results suggest that the groundwater level drawdown can increase the effective stress in a wide range, and significantly disturb the stress and deformation of the rock mass. It is noted that the fault crossing the tunnel is relatively dangerous under these disturbances, and deserves special attention. Moreover, the unbalanced force and the plastic zone can be transmitted to further distances along the fault, and reinforcement and support should be carried out in time. In addition, the greater the Biot coefficient can lead to the greater impact of groundwater drawdown on stress changes and deformation of the rock mass and faults.

Overcoming Environmental Stress Cracking of FDM 3D Printed Formwork for Counter-Pressure Casting of Concrete.

The rapid growth of interest toward concrete digital fabrication reflects the current aspiration for better, smarter, faster, and greener construction means. Among a broad variety of techniques developed by our community, digital casting presents clear advantages regarding dimensional precision, geometrical freedom, and surface finish of the produced elements. In contrast to robotic slip forming, the usage of digitally fabricated formworks requires simpler equipment. It, however, calls for easily shaped formworks, typically best three-dimensional (3D) printed, for example, by fused deposition modeling. While such molds can be easily fabricated with a wide range of commercially off-the-shelf available 3D printers, a shortcoming is the susceptibility of many polymers to environmental stress cracking, particularly when in contact with high pH solutions typical for cementitious materials. This article confirms the problem posed by this type of environmental stress cracking and presents two very effective means of circumventing it: A silicone coating and cyclic olefin copolymer. Apart from this, in the specific case of counterpressure casting (CPC), hydrostatic pressure must be resisted by a powder bed surrounding the formwork. The efficiency of such beds is examined and a particular mixture of sand and lead is shown to be particularly effective, provided its density is regulated to balance stress principles derived from soil mechanics. Presented applications include the successful CPC of thin prismatic formworks with a concrete height up to 3 m as representative of typical interfloor load-bearing elements. The combination of counterpressure and stress control is shown to be essential for such achievement, highlighting the potential of this approach as a viable member of the concrete digital casting family.

Experimental and numerical investigation of the failure mechanism and permeability evolution of sandstone based on hydro-mechanical coupling

The exploitation of natural gas and oil in the low-permeability reservoir is a severe challenge in the field of deep underground energy extraction. Therefore, a thorough understanding of the failure mechanism of reservoir sandstone under hydro-mechanical coupling is of great significance. The purpose of this study is to carry out triaxial compression tests of reservoir sandstone under different confining pressures and seepage pressures to investigate the failure mechanism and permeability evolution of reservoir sandstone. Laboratory experimental results show that the permeability of sandstone first decreases to a minimum and then increases with deviatoric stress, and finally reaches the maximum when a macroscopic fracture is formed. In addition, the permeability of sandstone gradually decreases with the increase of effective confining pressure, showing a good exponential function relationship. Axial strain stiffness is proposed to characterize the ability of the rock to resist deformation and failure, and an empirical equation of maximum axial strain stiffness, confining pressure and seepage pressure is established. Subsequently, the failure process of rock is reproduced in COMSOL based on elastic damage mechanics, porous elastic medium theory and the effective stress principle. The failure mechanism and the distribution of seepage pressure of rock feature points under different hydro-mechanical coupling are discussed. As a perfect tool, the distribution of streamline can intuitively reflect the impact of damage on porosity and permeability.

Finite elements for Mindlin and Kirchhoff plates based on a mixed variational principle

AbstractQuadrilateral finite elements with five displacements per corner node built up from four triangular elements are developed by a discretization of the Mindlin plate bending theory and based on a modified form of the mixed variational principle for stresses and displacements. The modified principle separates the contribution of shear deformation by taking the transverse shear strains as free functions. It also gives discrete element governing equations in a canonical form. Similar elements are developed based on the potential energy formulation. The elements can be readily specialized to the Kirchhoff plate theory. The discrete shear strains are transformed back to normal‐fiber rotations for enforcing general boundary conditions. The discretization procedure uses one‐dimensional polynomials instead of two‐dimensional shape functions. The discretization satisfies continuity for w, and continuity for the transverse shear strains. The Mindlin elements are tested with soft and hard boundary conditions. They are naturally free of shear‐locking. They are also capable of reproducing the boundary layer that occurs with some soft boundary conditions. Mindlin elements results tend to those of the Kirchhoff theory as the thickness decreases. Extensive numerical results are obtained for square plates some of which are compared with exact results or results obtained by other methods.

A meso-mechanical approach to time-dependent deformation and fracturing of partially saturated sandstone

In the present paper, we investigate how water acts to weaken rock in two complementary ways: mechanically through the generalized effective stress principle, and chemically through time-dependent rock-fluid reactions that allow subcritical crack growth. These processes, together with capillary suction and stress corrosion , were incorporated into a three-dimensional discrete element grain-based model to investigate both the time-independent and the time-dependent mechanical behavior of partially saturated sandstone at the mesoscale . The capillary parameters related to capillary suction and subcritical parameters related to stress corrosion in the model were calibrated to match the deformation behavior of partially saturated sandstone observed in laboratory. Following this calibration, numerical simulations of partially saturated sandstone with different levels of saturation were performed in uniaxial compression. The simulations show that both the peak strength and elastic modulus of the sandstone decrease as a function of increasing saturation and that the relationships between these properties can be expressed by negative exponential functions. The simulations are in good agreement with the experimental results. Second, the long-term brittle deformation of partially saturated sandstone with different levels of saturation under a constant stress level was modeled. The results show that time-to-failure during brittle creep decreases, and the initial strain and the minimum creep strain rate increases, as a function of increasing saturation, as also observed in laboratory. The simulations also highlight the formation of tensile cracks as the main deformation mechanism during brittle creep. Finally, brittle creep in partially saturated sandstone samples with different levels of saturation was studied under different stress levels. These simulations show that the minimum creep strain rate and the time-to-failure as a function of stress can be well described by exponential relations. We conclude that the proposed model permits a deeper understanding of time-independent and time-dependent deformation and failure of partially saturated sandstone at the mesoscale.

Voltage multiplier applied to boost DC–DC converter: Analysis, design, and performance evaluations

SummaryThis paper presents a new voltage multiplier with a small number of components, composed of a coupled inductor and a switched capacitor cell, which allow four different configurations. To evaluate these configurations, these cells were integrated into the boost converter, thus generating four new high voltage gain topologies. These topologies have different characteristics: thus, the principle of operation, voltage gain, voltage and current stress, and design guidelines of each converter were evaluated. Finally, four prototypes of 30 V/400 V and 200 W were built and evaluated experimentally.

LAMB’S PROBLEM AND CHARACTERISTIC OF ENERGY TRANSMISSION IN UNSATURATED HALF-SPACE

Because unsaturated soil is widely distributed on the earth’s surface, when the traditional saturated two-phase medium theory is used for dynamic analysis, the results are often inconsistent with the actual situation. Aiming at this problem, this paper takes unsaturated elastic half-space as the research object, firstly based on continuum mechanics and porous media theory, and then considers the basic equations of mass conservation equation, momentum conservation equation, constitutive equation and effective stress principle of each phase in unsaturated porous media, and finally, we established a dynamic control equation in which skeleton displacement, pore water pressure and pore gas pressure are basically unknown quantities. Aiming at the dynamic response and energy transmission of the unsaturated half-space surface under the action of vertical concentrated harmonic loads, an axisymmetric calculation model of the classical Lamb problem in the frequency domain is established. The Helmholtz decomposition method is used and the displacement component of the skeleton uses the potential function Φ and Ψ to represent, and combined with the constitutive equation, the analytical solutions of physical quantities such as the displacement field and energy field of the half-space surface under different boundary conditions are obtained. Finally, influencing factors such as load parameters (excitation frequency) and material parameters (saturation, permeability coefficient) are analyzed and discussed through numerical examples. The results show that: (1) An increase in saturation or a decrease in excitation frequency will increase the surface displacement amplitude of the unsaturated half-space; (2) When the permeability coefficient drops to a critical value, the surface displacement amplitude will tend to a limit value, and the influence of permeability coefficient under permeable (gas) boundary and impermeable (gas) boundary conditions shows obvious difference.

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.

Coupled thermo-hydro-mechanical mechanism in view of the soil particle rearrangement of granular thermodynamics

This paper established a coupled thermo-hydro-mechanical mechanism in view of the soil particle rearrangement for saturated/unsaturated soils under the framework of granular thermodynamics. This model avoids concepts such as the flow rule, yield function, dissipation potential function, and hardening criterion. The effects of the loading path and the soil structure are reflected by constructing a density function of elastic potential energy considering the structural strength of a solid skeleton with a degradation factor. That is, the changes in the stress states are closely related to soil particle rearrangement and the transitions between different matter phases. A generalized effective stress principle is derived and is suitable for the coupled thermo-hydro- mechanical process. The deduced generalized phase stresses differ from the classical effective principle based on linear elastic porous media and can automatically consider the impact of the stress path, temperature path and soil structure. The established model spans the complete process from unsaturated to saturated soils and is verified by the typical test results.