Multi-Parameter Optimization to Improve the Erosion Resistance of Coating by Fe Simulation

Finite element method (FEM) was used to study the stress peak of stress S11 (Radial stress component in X-axis) on the steam turbine blade surface of four typical erosion-resistant coatings (Fe2B, CrN, Cr3C2-NiCr and Al2O3-13%TiO2). The effect of four parameters, such as impact velocity, coating thickness, Young's modulus and Poisson's ratio on the stress peak of stress S11 were analyzed. Results show that: the position of tensile stress peak and compressive stress peak of stress S11 are far away from the impact center point with the increase of impact velocity. When coating thickness is equal to or greater than 10μm, the magnitude of tensile stress peak of stress S11 on the four coating surfaces does not change with the coating thickness at different impact velocities. When coating thickness is equal to or greater than 2μm, the magnitude of tensile stress peak of stress S11 of four coatings show a trend of increasing first and then decreasing with the increase of Young's modulus. Meanwhile, the larger the Poisson's ratio, the smaller the tensile stress peak of stress S11. After optimization, When coating thickness is 2μm, Poisson's ratio is 0.35 and Young's modulus is 800 GPa, the Fe2B coating has the strongest erosion resistance under the same impact conditions, followed by Cr3C2-NiCr, CrN, and the Al2O3- 13%TiO2 coating, Al2O3-13%TiO2 coating has the worst erosion resistance.

Titanium alloy cannulated screws and biodegradable magnesium alloy bionic cannulated screws for treatment of femoral neck fractures: a finite element analysis

Background Cannulated screws (CS) are one of the most widely used treatments for femoral neck fracture, however, associated with high rate of complications. In this study, we designed a new type of cannulated screws called degradable magnesium alloy bionic cannulated screws (DMBCS) and our aim was to compare the biomechanical properties of DMBCS, the traditionally used titanium alloy bionic cannulated screws (TBCS) and titanium alloy cannulated screws (TTCS). Methods A proximal femur model was established based on CT data of a lower extremity from a voluntary healthy man. Garden type III femoral neck fracture was constructed and fixed with DMBCS, TBCS, and TTCS, respectively. Biomechanical effect which three type of CS models have on femoral neck fracture was evaluated and compared using von Mises stress distribution and displacement. Results In the normal model, the maximum stress value of cortical bone and cancellous bone was 76.18 and 6.82 MPa, and the maximum displacement was 5.52 mm. Under 3 different fracture healing status, the stress peak value of the cortical bone and cancellous bone in the DMBCS fixation model was lower than that in the TTCS and TBCS fixation, while the maximum displacement of DMBCS fixation model was slightly higher than that of TTCS and TBCS fixation models. As the fracture heals, stress peak value of the screws and cortical bone of intact models are decreasing, while stress peak value of cancellous bone is increasing initially and then decreasing. Conclusions The DMBCS exhibits the superior biomechanical performance than TTCS and TBCS, whose fixation model is closest to the normal model in stress distribution. DMBCS is expected to reduce the rates of post-operative complications with traditional internal fixation and provide practical guidance for the structural design of CS for clinical applications.

The Role of the Reverse Fault on the Permeability Evolution in Mining Coal

To prevent and control the coal seam gas disaster affected by the reverse fault, we performed gas seepage tests, which consider stress-loading and unloading schemes, to investigate the stress change and coal permeability of the mining coal with reverse fault. The experimental results show that the mechanical behavior and permeability change of the mining coal are related to the distance between the coal and the reverse fault. The stress concentration coefficient of the coal body gradually increases. The closer is the distance between the coal and the reverse fault, the larger are the deviatoric stress peak and strain. In comparison with the coal sample M1 that is 5 m away from the reverse fault, the deviatoric stress peak and axial strain of the coal sample M3, 35 m away from the reverse fault, increase by 40.74% and 26.73%, respectively. In this stage, the permeability of M1, M2, and M3 coal samples increases by 22.1%, 28.0%, and 36.7%, respectively. In another stage, the stress concentration coefficient of coal increases to the peak and then decreases, causing the deviatoric stress peak and strain of coal to rise first and then fall. In comparison with the coal sample M4 that is 65 m away from the reverse fault, the deviatoric stress peak and axial strain of coal sample M6, 5 m away from the reverse fault, decrease by 29.48% and 5.55%, respectively. The permeability of coal samples M4, M5, and M6 increases by 23.6%, 37.2%, and 20.8%, respectively. Based on the gas seepage test results, we established the permeability model of mining-induced coal under the influence of a reverse fault, with consideration of the volume changes of coal fractures induced by adsorption and desorption. In the model, the variations of permeability in both stages of the prepeak and postpeak were deduced, which was verified with the experimental data. The verification results demonstrate that the proposed model has the capacity to predict the permeability evolution of mining coal under the influence of a reverse fault.

Multi-Parameter Optimization to Improve the Erosion Resistance of Coating by FE Simulation

Finite element method (FEM) was used to study the stress peak of stress S11 (Radial stress component in X-axis) on the steam turbine blade surface of four typical erosion-resistant coatings (Fe2B, CrN, Cr3C2-NiCr and Al2O3-13%TiO2). The effect of four parameters, such as impact velocity, coating thickness, Young’s modulus and Poisson’s ratio on the stress peak of stress S11 were analyzed. Results show that: the position of tensile stress peak and compressive stress peak of stress S11 are far away from the impact center point with the increase of impact velocity. When coating thickness is equal to or greater than 10μm, the magnitude of tensile stress peak of stress S11 on the four coating surfaces does not change with the coating thickness at different impact velocities. When coating thickness is equal to or greater than 2μm, the magnitude of tensile stress peak of stress S11 of four coatings show a trend of increasing first and then decreasing with the increase of Young’s modulus. Meanwhile, the larger the Poisson’s ratio, the smaller the tensile stress peak of stress S11. After optimization, When coating thickness is 2μm, Poisson’s ratio is 0.35 and Young’s modulus is 800 GPa, the Fe2B coating has the strongest erosion resistance under the same impact conditions, followed by Cr3C2-NiCr, CrN, and the Al2O3-13%TiO2 coating, Al2O3-13%TiO2 coating has the worst erosion resistance.

On the Phonology and Semantics of Deaccentuation

The deaccentuation of given and/or repeated elements is familiar from many dialects of English. We propose that deaccentuation is essentially an optional postlexical phonological process of stress retraction triggered by two constraints: *Stress-Copy, which assigns a violation to a stress peak on a word with a segmentally identical copy in the left context, and Rightmost, which assigns a violation to every word between a stress peak and the right phrase edge. We quantify deaccentuation by defining it as being perceived with less stress than expected, where expected stress is calculated by an implementation of Liberman and Prince's (1977) phrasal stress algorithm. We provide empirical evidence for our analysis based on the first inaugurals of six former U.S. presidents.

Biomechanical Comparison of Vertebral Augmentation and Cement Discoplasty for the Treatment of Symptomatic Schmorl’s Node Combined With Modic Change: Finite Element Analyses

Study design: Finite element simulation study.Objective: To compare the biomechanical effects of percutaneous vertebral augmentation (PVA) and percutaneous cement discoplasty (PCD) in patients with symptomatic Schmorl’s node combined with Modic change.Methods: CT data from a single patient was assembled into finite element models, from which we constructed four distinct surgical models, including PVA-ideal, PVA-nonideal, PCD-ideal, and PCD-nonideal, to compare the stress and strain differences of parapodular tissues.Results: The validity of our model was confirmed. PVA-ideal model showed a moderate reduction in the stress peak of the Schmorl’s node (0.48 vs. 0.81–0.89 Mpa) in the erect position. In the PCD-ideal model, the stress peak of the Schmorl’s node increased significantly when the spine was moved toward the lesion (3.99Mpa). Both PVA-ideal and PCD-ideal models showed global strain inhibition at the Schmorl’s node and BMEZ, which was attenuated in the non-ideal models. The PCD-ideal model significantly reduced segmental ROM (-76.8% to -59.3%) and significantly increases endplate stress (up to 220.8%), with no such effects seen in the PVA-ideal model.Conclusions: Both PVA-ideal and PCD-ideal models facilitated a more stable parapodular biomechanical microenvironment. The PVA-ideal model yielded minimal stress disturbance on the augmented or adjacent vertebral endplate but offered no improvement to segment stability. The PCD-ideal model provides adequate segment stability, but also carries a greater risk for adjacent vertebral fracture. As nonideal implementations of both surgeries can result in poor biomechanical outcomes, the surgical indications of PVA or PCD need to be carefully selected.

Temporal evolution of a shear-type rock fracture process zone (FPZ) along continuous, sequential, and spontaneously well-separated laboratory instabilities—from intact rock to thick gouged fault

Summary The development of shear-type fault analogues from intact rock at the laboratory scale provides a unique opportunity for investigating tectonic-scale phenomena through the lens of geophysics. The transition from rock fracture creation to laboratory fault slip must exist. We observe three spontaneously temporally well-separated mechanical instabilities attributed to the continuous evolution of a shear-type rock fracture between two artificial flaws. Their separation is validated with rapid mechanical stress drops and stabilizations, periodical AE behaviors (AE event number and AE moment release rate), and b-value drops. One instability occurs near the stress peak and corresponds to fracture incipience where fault development is mostly identified via optical observations; the other two instabilities are in the post-stress-peak domain and correspond to the fault nucleation and slip stages, respectively, with distinguishable AE releases from the fault region. The macroscale fracture has been created at the moment of rapid-stress drop for the second instability; off-fault damage, increasing gouge powder generation, and slip acceleration can be identified within the fault slip stage. AE behavior throughout fault nucleation shows a reversal of the Omori-Utsu (O-U) law. AEs attributed to the fault slip display regular O-U law decay and the distinction between the AE behavior for fault nucleation and fault slip is pronounced. These observations and analyses can provide further understanding on the analogue relationship between a laboratory loading-induced fault and a natural fault.

The Phenomenon of the “First Stress Peak” at the Yielding in the Dynamic Compression Tests of FCC and BCC Microalloyed Structures

In the presented work two grades of steel i.e. microalloyed ferrite (M_F) and microalloyed austenite (M_A) where subjected to the grain refinement processes using MaxStrain system and thermomechanical rolling. The wide range of grain size, starting from 200 µm down to submicrometer level was produced in this way. The specimens of both steels were subjected to the dynamic compression tests using the Split Hopkinson Pressure Bar (SHPB) apparatus and applying the strain rates in the range between ε˙ = 3750s-1 and ε˙ = 6000s-1. In addition, different temperatures were used in the tests, i.e.200 °C and 400 °C. The first peak of stress which is observed during elastic-plastic transition during the dynamic compression tests can be treated as a characteristic feature of the tested material. The results obtained in the present investigations showed a significant dependence of the “first stress peak” in the dynamic compression curve on the degree of the microstructure refinement for the samples of M_F and almost complete absence of this dependence for M_A.

Correlation Analysis of Macroscopic and Microscopic Parameters of Coal Measure Soil Based on Discrete Element Method

Numerical simulation of the triaxial test of coal measure expansive soil distributed along the highways in Pingxiang District, Jiangxi, was carried out by means of discrete particle flow, during which the macromechanical properties and the formation and developmental patterns of shear displacement field of the coal measure expansive soil were studied from a mesoscopic perspective. The result showed that the macroscopic stress and strain of test specimens can be significantly influenced by the interparticle friction coefficient of the coal measure expansive soil. Peak value of the deviatoric stress of test specimens increased with increasing friction coefficient, and before reaching the deviatoric stress peak value, the stress-strain relationship of the soil body basically presented a linear variation trend; the soil interparticle contact stiffness varied hyperbolically with the deviatoric stress peak value of test specimens, and the increasing contact stiffness ratio led to a gradual decrease of the deviatoric stress peak value but had only a small impact on the residual strength of test specimens; confining pressure was found to have remarkable influence on both the deviatoric stress peak value and the residual strength of test specimens; when the experimental confining pressure increased from 0.2 MPa to 1.2 MPa, the deviatoric stress peak value and the residual strength of test specimens increased by 2.14 times and 5.11 times, respectively. This paper reveals the macroinstability and failure mechanism of coal measure expansive soil from a microperspective.