Deviation Stress Research Articles

Influence of double-side symmetric oblique laser shock peening on shape deviation, surface integrity, and fatigue properties of the blades in small-sized blisk

Double-sided symmetric oblique laser shock peening (DSOLSP) was adopted to experiment on a small-sized blisk with restricted space. The influences of different laser energies on the shape deviation, surface roughness, microhardness, and residual stress of the blades were studied. The optimum process parameters were selected based on the shape deviation results of the blades and the microstructural evolution of the surface layers was investigated. The strengthening effect of DSOLSP treatment on notched blades was evaluated by vibration fatigue tests. It was found that DSOLSP can effectively cover the fatigue vulnerable regions without interference. Two-way bending deformation was formed after DSOLSP, and the shape deviation of the blades could be controlled within ±0.02 mm. With the increase of laser energy, the surface roughness and the depth of work-hardened layer increased. The full-thickness compressive residual stress (CRS) field was induced. A gradient microstructure was generated on the surface of the blade, and the size of average nanograins on the topmost surface is approximately 36.5 nm. The fatigue strength of the DSOLSP treated blades with notches was increased by 25.9 %. The enhancement can be attributed to the synergistic strengthening of CRS and gradient microstructure.

Comparison of Thermal Behaviors of Carbon and Stainless Steel Billets during the Heating Process.

The effect of thermal properties on the thermal behavior of a steel billet was investigated during the heating process to understand each effect and to provide process engineers with sufficient data to choose the optimal design conditions in reheating the furnace for hot rolling. Carbon steel and austenitic stainless steel (STS) were compared based on numerical simulations owing to the completely different thermal properties of these two steels: carbon steel having a phase transformation with a relatively high thermal conductivity and STS having no phase transformation with a relatively low thermal conductivity. The thermal conductivity affected the thermal behavior of the billet in the initial stage of heating owing to the high temperature difference between the surface of the billet and the gas in the furnace, i.e., the high Biot number. Accordingly, a non-firing zone and/or a preheating zone with a low gas temperature are necessary for high-alloyed steels including STS because the thermal conductivity of these steels is relatively low. The phase transformation of the carbon steels needs to occur in the primary heating zone, and this zone needs to have a relatively low gas temperature to reduce the temperature deviation or thermal stress in the billet. The heating pattern of the carbon steels and STSs in the reheating furnace should be designed differently considering the thermal conductivity and latent heat by the phase transformation of steels to obtain a high heating quality for the billet.

Evaluating the Potential of Multi-Walled Carbon Nanotube-Modified Clay as a Landfill Liner Material.

In this paper, the feasibility of multi-walled carbon nanotube (MWCNT)-modified clay as a landfill liner material is investigated. Experiments were conducted on the modified clay with 0.5%, 1%, and 2% MWCNTs. The effects of the MWCNTs on the compaction characteristics, permeability coefficient, stress-strain curve, peak deviation stress, shear strength parameters (internal friction angle and cohesion), microstructures, and adsorption performance of the clay were analyzed. The results showed that the optimum moisture content (OMC) increased from 16.15% to 18.89%, and the maximum dry density (MDD) decreased from 1.79 g/cm3 to 1.72 g/cm3 with the increase in MWCNTs. The permeability coefficients firstly fell and then gradually rose as the MWCNTs increased; the minimum permeability coefficient was 8.62 × 10-9 cm/s. The MWCNTs can also effectively increase the peak deviation stress of the clay, and at the maximum level, the peak deviation stress was increased by 286%. SEM images were processed using the Pore and Crack Analysis System (PCAS), and the results showed that the appropriate amount of MWCNTs could fill the pores and strengthen the clay structure. The effect of the MWCNT-modified clay on the adsorption performance of common heavy metal ions Cd2+, Mn2+ and Cu2+ in landfill leachate was analyzed by batch adsorption tests. The maximum adsorption capacities (Qmax) of Cu2+, Cd2+ and Mn2+ in the 2% MWCNT-modified clay were, respectively, 41.67 mg/g, 18.69 mg/g, and 4.97 mg/g. Compared with the clay samples without MWCNTs, the adsorption properties of Cu2+, Cd2+, and Mn2+ were increased by 228%, 124%, and 202%, respectively. Overall, the results suggest that MWCNT-modified clays have the potential to be suitable barrier materials for the construction of landfills.

Effect of Latent Heat by Phase Transformation on the Thermal Behavior of Steel Billet during Heating.

The effect of latent heat via phase transformation on the thermal behavior of a billet was investigated during the heating process. The latent heat of the billet strongly affected the temperature distribution of the billet during heating, although the heating rate of the billet was not high during the process. The temperature profile of the center region of the steel billet with latent heat had a strong flat shape compared with the other regions, as the heat supply to the center region was limited during the heating process owing to the finite thermal conductivity and mass effect of the billet. The latent heat by phase transformation typically occurred in the middle stage of heating, and the latent heat increased the temperature deviation of the billet during heating owing to the delay in the temperature rise at the center region of the billet. During the phase transformation of carbon steels during heating, the gas temperature needs to be low to reduce the temperature deviation or thermal stress of the billet. Industrial hot rolling mills are required to consider the latent heat by phase transformation of the billet to properly design the heating pattern for the billet. The heating pattern in the reheating furnace should be varied with the materials to obtain a high heating quality for the billet.

Experimental Study on the Effect of Coarse Grain Content on the Dilatancy and Particle Breakage Characteristics of Coarse-Grained Soils

The dilatancy deformation and particle breakage effects of coarse-grained soil have a significant influence on the safety and stability of high earth and rock-fill dams. To study the shear deformation and particle breakage characteristics of coarse-grained soil, four groups of soil sample with different coarse grain contents were to conduct consolidated drained triaxial compression tests by DJSZ-150 large-scale triaxial compression test machine. The results showed that the volume of coarse-grained soil changes significantly under deviation stress. The soil samples underwent positive dilatancy under the confining pressures of 200 kPa and 400 kPa but negative dilatancy under the confining pressures of 600 kPa and 800 kPa. When increasing the coarse grain contents in the soil sample under the same confining pressure, the positive dilatancy was more significant. A three-parameter dilatancy equation of coarse-grained soil considering confining pressure was established, in which the parameter L = 4 could serve as a criterion for whether the coarse-grained soil underwent positive dilatancy. Under the load, the coarse-grained soil showed three particle breakage modes: abrasion, attrition, and fracture. The coarse-grained soil particle size distribution before and after breakage conformed to the fractal characteristics, and the particle breakage rate increased significantly with larger soil particle size fractal dimension differences before and after the test. The coarse grain content and the confining pressure are two important factors affecting the mechanical properties of coarse-grained soil, and they control the shear deformation of soil.

Research on dynamic characteristics of marine engine transmission system

As the main component of marine engine, the transmission system often produces serious vibration and noise, which will significantly affect the performance and service life of the driving mechanism. In order to provide reasonable structural design basis for marine engine transmission system, the dynamic characteristics under different working conditions were studied in this paper. A simplified rectangular structure was applied to express the instantaneous motion state model of the chain link, and the equation was expressed according to Euler kinematics theory. The MNF (modal neutral file) model was derived by making the links and pins flexible parts, and the rigid flexible coupling model of the transmission system was established based on ADAMS. Since invalid constraints were adjusted and replaced, the transmission system model could be simulated and calculated precisely under the conditions of different tension, spindle rotation speed and driving sprocket teeth number. By changing the model parameters through the single variable method, the variation rules of transmission ratio, spindle radial force, transmission ratio deviation and maximum transient stress of chain link were obtained respectively. According to the design and construction of vibration test platform, the simulation result was verified, and the spectrum response results of the chain drive system were obtained. The results show that the rigid flexible coupling model can achieve high simulation accuracy in the chain drive system. Reasonable tension and sprocket teeth number can not only reduce the amplitude, but also reduce the fluctuation of output torque and transmission ratio.

Influence of Coarse Grain Content on the Mechanical Properties of Red Sandstone Soil

Coarse-grained red sandstone soil is often used as embankment filling material but is prone to being broken by extrusion, which lowers the stability of the roadbed. This paper aimed to clarify the influence of the variation in coarse-grain content on the mechanical properties of coarse-grained red sandstone soil. Soil with a grain size greater than 5 mm is regarded as coarse-grained soil, and coarse-grained red sandstone soils with different contents of coarse grains were prepared as cylindrical specimens with a diameter of 300 mm and a height of 600 mm. Under three different confining pressures, a large-scale triaxial apparatus was used to carry out triaxial shear tests. The results showed that as the content of coarse grains of red sandstone (denoted as p) increased, the deviation stress of static failure increased, showing a hyperbolic relationship. The internal friction angle also increased hyperbolically, while the cohesion reached a peak value and then decreased, and the maximum value of 133.8 kPa was reached at p = 30%. As the content of coarse grains increased, the maximum dilatancy increased. The maximum amount of shrinkage reached a peak value and then decreased, and the maximum value was reached when p = 30%. A coarse grain content p equal to 30% was the optimum value when coarse-grained red sandstone soil was used as a filling material.

Analysis and prediction of temperature of an assembly frame for aircraft based on BP neural network

Temperature is one important factor which decides the assembly accuracy and reliability of the aircraft. Especially with the development of large-sized aircraft, the small temperature change in the aircraft assembly will result in a large displacement deviation and non-negligible internal stress. Therefore, it’s crucial to characterize and predict the temperature during the assembly process of aircraft. Selecting one type of assembly frame for aircraft wing as the study object, temperature in this structure was measured and recorded for one year. Based on the measured data, a model of an optimized BP neural network is proposed to analyze and predict the temperature distribution. The trained temperature model shows a good result with a relative error of 1% and an absolute error of [Formula: see text]C. Finally, the displacement of assembly frame is obtained from the temperature distribution.

Research on casing deformation mechanism and prevention technology in salt rock creep formation

Aiming at casing damage in the salt rock, the creep characteristics of the salt rock in the southeastern China are investigated by triaxial creep test. Based on the experimental results, an unsteady creep model which can describe the creep and steady stage of the salt rock is set up combined with the Kelvin model and the Heard model by the deviation stress. The unsteady creep model was used to calculate the radial displacement of the wellbore based on ABAQUS platform. The results show that the higher casing pressure can effectively reduce the creep displacement of the rock, and the higher horizontal principal stress and the overburden pressure can increase the formation deviation stress, thus increasing the creep displacement of the salt rock. The maximum displacement of the casing caused by the formation is 25 mm by a string simulation device. The elastic modulus of the cement is effectively reduced by adding hollow ceramic particles to the cement, so that the strain energy added to the wellbore system by the formation radial creep can be fully absorbed by this cement sheath. Combined with the numerical simulations and the cement tests with the addition of hollow ceramic particles, a casing deformation prevention method is finally established in this paper.

Effect of Sand Particle Size on Hydraulic-Mechanical Behavior of Bentonite-Sand Mixtures

Bentonite-sand mixtures can be used as the base material of engineered barriers in deep high-level radioactive waste geological repositories. Swelling, compression, and permeability tests were conducted out on bentonite-sand mixtures with 30%, 50%, 70% and 85% sand content. Influence of sand content and particle size on the deformation and permeability characteristics of bentonite-sand mixtures were analyzed. The sand particle size affects the deformation characteristics by influencing the vertical stress required to form a sand skeleton, and the skeleton's stability. When the sand content is less than the critical sand content, bentonite-sand mixtures cannot form a sand skeleton, and particle size has no effect on their characteristics. When the sand content is greater than the critical sand content and the vertical stress exceeds the initial deviation stress, a sand skeleton forms. In this case, smaller the sand particle size, lesser will be the vertical stress required to form a sand skeleton, and more the swelling of bentonite-sand mixtures. Further, more uniform particle size, more stable will be its structure and lesser the compressibility of bentonite-sand mixtures. The hydraulic conductivity is related to the flow area and the seepage path length, and particle size has no obvious effect on either with the same sand content. Therefore, the sand particle size has no obvious effect on mixtures' permeability.

Mechanical properties of sandstone under hydro-mechanical coupling

Abstract Study of mechanical properties of rock under hydro-mechanical coupling. The MTS815 rock mechanics system is used to perform triaxial compression tests of water-saturated sandstones under different confining pressures and pore water pressures. The results show that the peak deviation stress and its corresponding axial strain, residual deviation stress, initial deviation stress of dilation and deformation modulus of water-saturated sandstone are related to pore water pressure and confining pressure. They decrease with the increase of pore water pressure and increase with the increase of confining pressure. Poisson’s ratio and angle of rupture of water-saturated sandstone increase with pore water pressure. Based on the effective stress principle and Mohr–Coulomb criterion, the effective cohesion and effective residual cohesion of sandstone are 11.49 and 3.13 MPa, respectively, and the effective angle of internal friction and effective residual angle of internal friction are 38.32° and 25.32°, respectively. In addition, according to the variation relationship of sandstone strength, the relative strength criterion of sandstone under hydro-mechanical coupling is established.

Improving the Soil Properties by Adding Rice Husk Ash (RHA) and Ordinary Portland Cement (OPC): An Experimental Analysis

The stabilization capability of rice husk ash (RHA) and Ordinary Portland cement (OPC) was scrutinized using laboratory scrutiny. Three soils (Soil A, B, and C) were improved with various percentages (via weight of dry soil) at 0, 2, 4, 6, 8, and 10% for all stabilizing agents and compacted via BSL (British Standard light) energy. Their impacts were assessed on the strength physiognomies such as UCS (unconfined compressive strength), OMC (optimum moisture content), California bearing ratio (CBR), and MDD (maximum dry density tests based on ASTM (American Standard Testing Materials) codes. The result reveals the optimum values for three lateritic samples, A, B, and C, illustrated a reduction in plasticity for rice husk ash (RSA) stabilizer from 17.32%, 12.67%, and 19.07% (at 6% cement) to 16.32%, 9.90% and 17.00% (at 6% cement and 6% RHA) respectively. Likewise, the optimum Triaxial test result for RHA at 6% with a specified cement content of 6% are A (Deviation stress 595.45KN/m2, Cohesion 10KN/m2, Angle of internal friction 280, and Shear stress 175.5KN/m2), B (Deviation stress 514.75KN/m2, Cohesion 9KN/m2, Angle of internal friction 280 and Shear stress 168.5KN/m2), and C (Deviation stress 530.58KN/m2, Cohesion 10KN/m2, Angle of internal friction 290 and Shear stress 162.0KN/m2.

Experimental characterization and crystal plasticity modeling of dual-phase steels subjected to strain path reversals

This paper is concerned with monotonic and load reversal deformation of four dual-phase (DP) 590, 780, 980, 1180 and one martensitic (MS) 1700 steel sheets. While the monotonic data are presented for all steels, the load reversal data are provided for DP 590, DP 780, and DP 1180. Particularities pertaining to the reversal deformation including the decreasing hardening rate during forward tension, a linear and then a non-linear unloading, followed by the Bauschinger effect, and a shift in the hardening rate during continuous straining were quantified and discussed as a function of loading history. Moreover, parameters such as the reloading stress differential, reloading softening stress, ratcheting strain, and unloading deviation stress were determined and discussed as a function of martensite fraction. The data were interpreted and predicted using an elasto-plastic self-consistent (EPSC) crystal plasticity model incorporating anisotropic elasticity, a dislocation density based hardening law, and a slip system backstress law. The model parameters associated with the slip strengths of ferrite and martensite and backstress were established. This work demonstrated the ability of crystal plasticity modeling to account for the co-dependent nature of crystallographic slip in ferrite and martensite and the sources of hardening caused by history-dependent dislocation density evolution and backstress to predict not only monotonic but also hysteresis in plastic response during the forward-reversal cycles. The combination of comprehensive experimental data and modeling results allowed us to infer that the tradeoff between the magnitude of backstress per phase and the volume fraction of ferrite versus martensite per steel governs the unloading and subsequent yielding per steel, while the dissolution of dislocations facilitates capturing the hardening rates during load reversal deformation.

An Experimental Study Into the Effects of Cumulative Energy Damage on the Mechanical Properties of Coal

The accumulated damage of the surrounding rocks induced by the existing coal mining activities (such as excavation and extraction) is the initial mechanical background of the rock and coal for the further mining operations. An energy-based Cumulative Initial Damage (CID) variable was proposed to account for such existing damage. With the MTS815 electro-hydraulic servo-controlled system, coal samples with different CID value were prepared by cyclic pre-loading and unloading process, and a novel experimental framework was presented to investigate the effect of CID on the further mechanical properties of the CID coal samples. The deformation characteristics, peak strength, peak strain, dilatancy characteristics, brittle-ductile transformation behavior, and microscopic structure of the CID coal samples were investigated in detail. The triaxial compression tests showed that with the increased of CID value, the compaction part of the coal samples was shorter and the strain softening stage became longer. When the CID value was increased from 0 to 0.521, the deviation stress and peak strain of the coal decreased by 31.4 and 37.7%, respectively and the main characteristic of the fracture morphology changed from cleavage steps to dimpling.

Application of Grey Relational Approach and Artificial Neural Network to Optimise Design Parameters of Bridge-Type Compliant Mechanism Flexure Hinge

The investigation proposed a hybrid Grey-artificial neural network to optimise the design parameters of a two degree of freedom (2-DOF) bridge-type compliant mechanism flexure hinge (BTCMFH). The design variables play a vital role in determining the deformation and stress of the mechanism. The investigation is different from the previous studies where the hybrid method is a combination of grey relational analysis and artificial neural network based on finite element method (FEM) in ANSYS to maximise output displacement (DI) and minimise the stress (ST) of the mechanism. The simulation and ANOVA results identified the design variables have significantly affected the output displacement and stress by their contribution. The grey relational analysis and artificial neural network predicted values are in agreement with the simulation results at optimal combination parameters with a deviation error displacement and stress being 0.57% and 2.1%, respectively. The optimal combination parameters with a deviation error of displacement and stress of 0.52% and 2.1%, respectively. The optimal values of DI and ST were obtained as 0.957 mm and 104.74 MPa, respectively. The optimal value of displacement amplification ratio gained is 95.7.

Evaluation of Warpage and Residual Stress of Precision Glass Micro-Optics Heated by Carbide-Bonded Graphene Coating in Hot Embossing Process.

A newly developed hot embossing technique which uses the localized rapid heating of a thin carbide-bonded graphene (CBG) coating, greatly reduces the energy consumption and promotes the fabrication efficiency. However, because of the non-isothermal heat transfer process, significant geometric deviation and residual stress could be introduced. In this paper, we successfully facilitate the CBG-heating-based hot embossing into the fabrication of microlens array on inorganic glass N-BK7 substrate, where the forming temperature is as high as 800 °C. The embossed microlens array has high replication fidelity, but an obvious geometric warpage along the glass substrate also arises. Thermo-mechanical coupled finite element modelling of the embossing process is conducted and verified by the experimental results. Based on trial and error simulations, an appropriate compensation curvature is determined and adopted to modify the geometrical design of the silicon wafer mold. The warpage of the re-embossed microlens array is significantly decreased using the compensated mold, which demonstrates the feasibility of the simulation-oriented compensation scheme. Our work would contribute to improving the quality of optics embossed by this innovative CBG-heating-based hot embossing technique.

Alternative constitutive relation for momentum transport of extended Navier–Stokes equations* *Project supported by the National Natural Science Foundation of China–Outstanding Youth Foundation (Grant No. 51522903), the National Natural Science Foundation of China (Grant Nos. 11602276 and 51479094), and the Fund from the Key Laboratory for Mechanics in Fluid Solid Coupling Systems of the Chinese Academy of Sciences.

The classical Navier–Stokes equation (NSE) is the fundamental partial differential equation that describes the flow of fluids, but in certain cases, like high local density and temperature gradient, it is inconsistent with the experimental results. Some extended Navier–Stokes equations with diffusion terms taken into consideration have been proposed. However, a consensus conclusion on the specific expression of the additional diffusion term has not been reached in the academic circle. The models adopt the form of the generalized Newtonian constitutive relation by substituting the convection velocity with a new term, or by using some analogy. In this study, a new constitutive relation for momentum transport and a momentum balance equation are obtained based on the molecular kinetic theory. The new constitutive relation preserves the symmetry of the deviation stress, and the momentum balance equation satisfies Galilean invariance. The results show that for Poiseuille flow in a circular micro-tube, self-diffusion in micro-flow needs considering even if the local density gradient is very low.

Mechanical Mechanism of Fault Dislocation Based on in situ Stress State

Fault dislocation occurs under certain stress conditions. Based on the mechanical relationship between the direction of crustal stress and the occurrence of fault plane, three criterions of fault strike dislocation trend, dip dislocation trend and fault dislocation or not are put forward, According to these three criteria, the fault slip and the type of slip can be inferred. The parameters that have great influence on the characteristics of fault slip are: fault dip angle, angle between horizontal principal stress and fault strike, depth, lateral pressure coefficient, internal friction angle and cohesion of fault plane. Fault slip is more likely to occur in the environment of high deviation stress, low friction angle and dip angle of about 40°. Fault rupture is a point-to-surface and deep-to-shallow process. When the criterion f2 of the local position of the fault is greater than 0, it will lead to the slip of the nearby fault. When the slip range of the fault extends to the surface, it will cause large earthquakes with large-scale surface rupture. The theoretical calculation is basically consistent with the numerical simulation results. According to the theory in this paper, the slip instability state of Longmen Mountain Fault Zone under different stress conditions is calculated, the results show that when the lateral pressure coefficient is greater than 2.5, dislocation occurs in the deep part of the fault.

Dimensional Deviation Management for Selective Laser Melted Ti6Al4V Alloy Blade

Selective laser melting (SLM) is prone to generate large thermal stresses, which could induce a heavy geometric change in the parts. In this study, Ti6Al4V blade was prepared by Selective laser melting (SLM). Microstructure, dimensional deviation and residual stress were investigated. Microstructure is acicular α' martensite in prior columnar β grain. The smaller the grain size, the larger the dimensional deviation. The directions of dimensional deviation at the leading and trailing edges of blade are opposite to those in the middle. The distribution of dimensional deviation exhibits a parabolic law at the trailing edge of blade. The thermal stress is big at the edges of the blade body. The large tensile stress along the edges of the blade body caused the edges to deform toward the suction side of the blade. The residual stress distribution of the pressure surface by the XRD measured has a good agreement with thermal stress distribution by calculated.

Psychologic stress and burnout among dental staff: A cross-sectional survey

Backgraound: Professional burnout, a prolonged response to stress, may affect standards of patient care. Burnout is defined as emotional exhaustion (EE), depersonalization, and diminished personal accomplishment (PA). Aim: The aim of the current study is to identify and compare the psychologic stress and burnout levels among different job titles and specialties in the dental services department. We also examined the effects of marital status, age, and sex on stress and burnout levels. Settings and Design: A cross-sectional study conducted in the department of dental services at a tertiary medical complex. Materials and Methods: A convenient sampling approach was used to distribute the questionnaire in the dental services department (n = 177, response rate = 88.5%). Two-validated questionnaires, the Psychological Stress Measure-9, and Maslach Burnout Inventory–Human Services Survey, were used. Statistical Analysis: SAS 9.4 (SAS Institute Inc., Cary, NC, USA) was used for data analysis. P Results: The mean (± standard deviation) stress level was 32.6 (±11.43), with the highest stress levels seen in consultants and residents (39.17% and 38.33%, respectively). Hygienists and technicians exhibited the highest lack of PA (24.53%), consultants exhibited the highest EE (24.64%), and residents exhibited the highest impersonal response toward patients (26.67%). Conclusion: Participants with the job title “Consultant” or “Resident” are the most stressed and burnt-out dental personnel. Specialty, sex, age, and marital status were not identified as risk factors for stress and burnout in our study. Stress and burnout should be reduced to maintain standards of patient care.