Stress Rupture Life Prediction Method for Notched Specimens Based on Minimum Average Von Mises Equivalent Stress

Creep tests were carried out on notched plate specimens of nickel-based superalloy GH4169 with different stress concentration coefficients. It was found that the duration of the first stage of the creep curve increases with the increase of stress concentration coefficient, while the fracture ductility decreases with the increase of stress concentration coefficient. To predict the life of notched plate specimens, four constitutive models were used to analyze the stress and strain of the notches. It was found that the average Von Mises equivalent stress (AVES) on the minimum notch section first decreases and then increases with the creep time, resulting in a minimum value. The minimum average Von Mises equivalent stress (MAVES) is considered as the characteristic stress of notched specimens in this paper. The creep life equation is fitted according to the results of creep tests of smooth specimens, and then the predicted life of notched specimens is obtained by substituting the minimum average Von Mises equivalent stress of notched specimens into the creep equation. The prediction results of the four constitutive models are within 2 times the dispersion band, and the three-stage model is within the 1.5 times dispersion band.

Structural Optimization and Application Research of Alkali-Activated Slag Ceramsite Compound Insulation Block Based on Finite Element Method

The research and application of new wall materials have been attracting increasing attention owing to the continuous promotion of sustainable development in the building industry. An alkali-activated slag ceramsite compound insulation block (AASCCIB) is used as the research object. Based on the finite element method, the effects of different numbers of hole rows and hole ratios on the thermal and mechanical performances of AASCCIBs are analyzed using ANSYS CFX. On this basis, the AASCCIB with the optimal comprehensive performance is determined by a multi-objective optimization analysis. Finally, the improvement effect of the AASCCIB wall on the indoor thermal environment relative to an ordinary block (OB) wall is quantitatively analyzed using ANSYS CFX. The results show that the von Mises equivalent stress and heat transfer coefficient of the AASCCIB decrease with the increase in the hole ratio when the hole shape and number of hole rows are constant. AASCCIB B1 has the optimal comprehensive performance among six AASCCIBs, with the heat transfer coefficient and average von Mises equivalent stress of 0.446 W/(m2∙K) and 9.52 MPa, respectively. Compared with the indoor lowest and average temperatures of the building with the OB wall, those of the building with the AASCCIB wall increased by at least 1.39 and 0.82 °C on the winter solstice, respectively. The indoor temperature difference decreased by at least 0.83 °C. In addition, the indoor highest temperature, average temperature, and temperature difference decreased by at least 1.75, 0.79, and 1.89 °C on the summer solstice, respectively.

Comparative Evaluation of Distribution of Stresses in Osseointegrated Crestal and Basal Implant in Zygomatic Region of Maxilla

Aim The aim of this study was to evaluate the distribution of stresses in osseointegrated crestal and basal implant in zygomatic region of maxilla and to identify the preferable implant option for better stress distribution. Material and Method The present in vitro study was performed to evaluate stress patterns in bone around basal and crestal dental implant under axial and oblique loading in maxillary zygomatic region with the help of a finite element analysis (FEA). To conduct this study, the following materials were used: computer software ANSYS, basal implants with dimensions 3.7 × 10 mm, and crestal implants with dimensions 3.7 x 10 mm. The amount of load transferred on the bone adjacent to the implant in an axial and transverse load of 100 N at 0 and 45 degrees, respectively, was placed on both types of implants. A three-dimensional (3D) scanner was use to generate 3D simulated model of basal and crestal implants. FEA modelling was generated that replicated the zygomatico maxillary region with special emphasis on bone architecture, bone density, angulation, width, and length of implant prototype. Further, material properties were defined for cortical bone, dense trabecular bone, low density trabecular bone, and titanium on the basis of Young’s modulus of elasticity. Results These values were used by FEA software (ANSYS) to generate a 3D mesh model of bone and implant. Finally, Von Mises (equivalent stress) (MPa) values on the implant were computed using FEA software. The values of maximum Von Mises equivalent stress on the implant collars, body, apex, and bony interface were obtained. Conclusion Maximum stresses were seen at the cortical bone with basal implant placed inside the bone. Stresses that are transferred more to the bone through implant promote bone remineralization. Maximum Von Mises stresses were observed on basal implant body. Thus, these greater stresses have the capacity to simulate mineralization in the cortical bone; this makes basal implant a suitable option for placement inside the cortical bone.

Impact of Grooves in Hydraulically Expanded Tube-to-Tubesheet Joints

The stress corrosion cracking of tube-to-tubesheet joints is one of the major faults causing heat exchanger failure. After the expansion process, the stresses are developed in a plastically deformed tube around the tube-to-tubesheet joint. These residual stressed joints, exposed to tube and shell side fluids, are the main crack initiation sites. Adequate contact pressure at the tube-to-tubesheet interface is required to produce a quality joint. Insufficient tube-to-tubesheet contact pressure leads to insufficient joint strength. Therefore, a study on the residual stress and contact pressure that have a great significance on the quality of the tube-to-tubesheet joint is highly demanded. In this research, a 2D axisymmetric numerical analysis is performed to study the effect of the presence of grooves in the tubesheet and the expansion pressure length on the distribution of contact pressure and stress during loading and unloading of 400 MPa expansion pressure. The results show that the maximum contact pressure is independent of the expansion pressure length. However, the presence of grooves significantly increased the maximum contact pressure. It is proven that the presence of grooves in the tubesheet is distinguishable from the maximum contact pressure and residual von mises equivalent stress. The tube pull-out strength increases with the expansion pressure and the number of grooves. In conclusion, the presence of the grooves affects the tube-to-tubesheet joints.

Influence of Emergency Stop Operation for Strength of Brazed Structure With Rectangular Fins and Plates in Liquefied Natural Gas Heat Exchanger

In order to ensure the structural safety of a liquefied natural gas (LNG) heat exchanger in emergency stop operation process, the strength of a brazed structure with rectangular fins and plates is investigated by means of the finite element method. The microstructure of brazed joints and brazing filler is tested by metallographic examination with a scanning electron microscope (SEM). The results show that the maximum shear stress is the main reason for the structural failure at the brazing seam while the brazed joint is mainly subjected to the maximum normal stress. The peak value of the Von Mises equivalent stress in brazed structure with rectangular fins and plates linearly increases with the HMR pressure when the temperature difference is less than 10 K between HMR and LMR. At the same time, the peak value of Von Mises equivalent stress also increases with the equilibrium temperature and temperature difference between LMR and HMR. The aggregation of the elemental Si in the brazed joints and brazing seam will exacerbate the structural safety of the brazed structure in the emergency stop operation process. The above results provide some constructive guidance for the emergency stop operational process for an LNG heat exchanger.

Topping-off surgery vs posterior lumbar interbody fusion for degenerative lumbar disease: a finite element analysis

Background Adjacent segment disease (ASD) is a common complication after posterior lumbar interbody fusion (PLIF). Recently, a topping-off surgery (non-fusion with Coflex) has been developed to reduce the risk of ASD, yet whether and how the topping-off surgery can relieve ASD remains unclear. The purpose of this study was to explore the biomechanical effect of PLIF and Coflex on the adjacent segments via finite element (FE) analysis and discuss the efficacy of Coflex in preventing ASD. Methods A FE model of L3–L5 segments was generated based on the CT of a healthy volunteer via three commercially available software. Coflex and PLIF devices were modeled and implanted together with the segment model in the FE software. In the FE model, a pre-compressive load of 500 N, equal to two-thirds of the human body mass, was applied on the top surface of the L3. In addition, four types of moments (anteflexion, rear protraction, bending, and axial rotation) set as 10 Nm were successively applied to the FE model combined with this pre-compressive load. Then, the range of motion (ROM), the torsional rigidity, and the maximum von Mises equivalent stress on the L3–L4 intervertebral disc and the implant were analyzed. Results Both Coflex and PLIF reduced ROM. However, no significant difference was found in the maximum von Mises equivalent stress of adjacent segment disc between the two devices. Interestingly enough, both systems increased the torsional rigidity at the adjacent lumbar segment, and PLIF had a more significant increase. The Coflex implant had a larger maximum von Mises equivalent stress. Conclusions Both Coflex and PLIF reduced ROM at L3–L4, and thus improved the lumbar stability. Under the same load, both devices had almost the same maximum von Mises equivalent stress as the normal model on the adjacent intervertebral disc. But it is worthy to notice the torsional rigidity of PLIF was higher than that of Coflex, indicating that the lumbar treated with PLIF undertook a larger load to reach ROM of Coflex. Therefore, we presumed that ADS was related to a higher torsional rigidity.

Topping-off surgery vs posterior lumbar interbody fusion for degenerative lumbar disease: a finite element analysis

Background Adjacent segment disease (ASD) is a common complication after posterior lumbar interbody fusion (PLIF). Recently, a topping-off surgery (non-fusion with Coflex) has been developed to reduce the risk of ASD, yet whether and how the topping-off surgery can relieve ASD remains unclear. The purpose of this study was to explore the biomechanical effect of PLIF and Coflex on the adjacent segments via finite element (FE) analysis and discuss the efficacy of Coflex in preventing ASD.Methods A FE model of L3-5 segments was generated from the CT of a healthy volunteer via three commercially available software. Coflex and PLIF devices were modeled and implanted with the segment model in the FE software. In the FE model, a pre-compressive load of 500 N, which was equal to two thirds of the human body mass, was applied to the top surface of the L3. In addition, four types of moments (anteflexion, rear protraction, bending and axial rotation) set as 10 Nm were successively applied to the FE model combined with this pre-compressive load. Then the range of motion (ROM), the torsional rigidity and the maximum von Mises equivalent stress on L3-L4 disc and the implant were analyzed.Results Both Coflex and PLIF reduced ROM. However, no significant difference was found in the maximum von Mises equivalent stress of adjacent segment disc between the two devices. Interestingly enough, both systems increased the torsional rigidity at the adjacent lumbar segment, and PLIF had a more significant increase. The Coflex implant had a larger maximum von Mises equivalent stress.Conclusions Both Coflex and PLIF reduced ROM at L3-L4, and thus improved the lumbar stability. Under the same load, both devices had almost the same maximum von Mises equivalent stress as the normal model on the adjacent intervertebral disc. But it is worthy to notice the torsional rigidity of PLIF was higher than that of Coflex. It indicated that the lumbar treated with PLIF would undertake a larger load to reach ROM of Coflex. Therefore, we presumed that ADS was related to higher torsional rigidity.

Evaluating the Effect of Wheel Polygons on Dynamic Track Performance in High-Speed Railway Systems Using Co-Simulation Analysis

With increases in train speed and traffic density, problems due to wheel polygons and those caused by wheel–rail impacts will increase accordingly, which will affect train operational safety and passenger ride comfort. This paper investigates the effects of polygonal wheels on the dynamic performance of the track in a high-speed railway system. The wheel–rail interaction forces caused by wheel polygons are determined using a dynamic vehicle–track model, and the results are entered into a slab track finite element model. The influence of the harmonic order and out-of-roundness (OOR) amplitude of wheel polygons on the transient dynamic characteristics of the track(von Mises equivalent stress, displacement, and acceleration) is examined under high-speed conditions. The results indicate that the vibration acceleration and von Mises equivalent stress of the rail increase in proportion to the harmonic order and the OOR amplitude and velocity of a polygonized wheel. The vibration displacement of the rail first increases and then decreases with a change in the harmonic order, and reaches a maximum at the ninth order. The dynamic responses of the concrete slab layer, cement-asphalt layer, and support layer increase linearly with the harmonic order and amplitude of wheel polygons and decrease from top to bottom. Through a combination of numerical simulations and real-time monitoring of rail vibrations, this study provides guidance on potential sensor locations to identify polygonized wheels before they fail.

Dynamic Behavior of FGM Doubly Curved Panel due to Mechanical Loading

This study presents the dynamic response analyze of a simply supported and isotropic functionally graded (FG) double curved panel under mechanical loading. The aim of the research was to investigate mechanical behavior in a FGM curved panel due to different excitation mode of dynamic loading. The novelty of this research is an investigation of von Mises equivalent stress distribution in double curved panel due to different excitation mode. Computed results are found to agree well with the results reported in the literature. Moreover, influence of volume fraction of the material is studied.