Value Of Equivalent Stress Research Articles

Designing and modeling U-notch fatigue sensor to predict the fatigue life of structural components

Fatigue sensors are used as Structural Health Monitoring (SHM) mechanisms to detect damage on structural components before any failures occur. In this study, a U-notched fatigue sensor was designed and analyzed to predict the fatigue life before catastrophic failure occurs. The ANSYS workbench software and 7075-T6 aluminum alloy were used to model and analyze our U-notch type fatigue sensor. The sensor model consisted of four beams of 305 × 76.2 × 1.6 mm (length × width × thickness) dimensions with different fatigue U-notch radii. It was observed that fatigue life increased with an increase in the U-notch radius. However, the value of the maximum equivalent stress decreased with an increase in the notch radius. In addition, fatigue damage occurred around the U-notch radius when the U-notch radius was equal to or less than 6.4 mm.

Numerical Analysis on Stress Evolution During GTA-Additive Manufacturing of Thin-Walled Aluminum Alloys

GTA-Additive Manufacturing (GTA-AM) is one of the Wire Arc Additive Manufacturing (WAAM) technologies based on Gas Tungsten Arc Welding (GTAW). During the GTA-AM process, non-uniform heating, as well as rapid heating and cooling of deposited materials lead to inevitable temperature stress, while repeated remelting in subsequent deposition introduces complexity to the evolution of it. Finite element modeling was conducted in this work to investigate the stress evolution during the GTA-AM of thin-walled 5183-Al. Several thin-walled 5183-Al components with different bead widths are included to understand the influences brought about by geometry dimensions. Hole-drilling method is used to measure the residual stress of 5183-Al components manufactured by GTA-AM, which proves the reliability of this numerical model. Results of modeling show that the temperature stress is generated and released alternately and repeatedly as the deposition proceeds. The cycles of equivalent stress are in synchronization with the thermal cycles, in which equivalent stress reaches peak when temperature gets to its valley value. However, as the deposition layers pile up, the peak value of equivalent stress decreases gradually, and finally achieves stability after a certain layer. As for the influences of geometry dimensions, larger bead width results in higher level of stress due to much larger heat input as well as grater constraints.

The influence of structure parameters on stress of plate-fin structures in LNG heat exchanger

In order to ensure the structural safety of plate-fin structures in actual operation process and guide the structural design of LNG plate-fin heat exchanger, the influence of structure parameters was investigated on stress of plate-fin structures based on Finite Element Method and thermal elastic theory. The results show that the stress is complex at the brazed joints in actual operation process of LNG PFHE and the equivalent stress will reach the peak value at brazed joint near fin side due to the influence of the direct stress in y direction. Meanwhile, the peak value of equivalent stress in plate-fin structures is slightly impacted by the fin height and plate thickness and is obviously impacted by the brazing seam thickness, fin thickness and fin distance. The influence of the brazing seam thickness, fin thickness and fin distance for that is mainly induced by the direct stress in y direction. These results will provide some constructive instructions in the structural design for plate-fin heat exchanger in a large-scale LNG cold-box.

Investigation on stress characteristics of plate-fin structures in the heat-up process of LNG heat exchanger

In order to ensure the structural safety of plate-fin structures, the stress characteristics of plate-fin structures in the heat-up process of LNG plate-fin heat exchanger (PFHE) was investigated by a model which has been validated in the literature. The results show that the stresses of plate-fin structures are complex and reach the peak value in the brazed joint. A crack and fatigue failure would firstly occur in the area of the brazed joint near both the plate side and the fin side. The peak value of equivalent stress in plate-fin structures steadily increases with the increase of temperature difference between natural gas (NG) and mixture refrigerant (MR), decreases with the increase of NG pressure and it is slightly impacted by the temperature rise rate as the temperature rise rate of NG is the same as that of MR in the heat-up process. These results will provide some constructive instructions in safe operation and improvement of the heat-up process for PFHE in a large-scale LNG cold-box.

Optimization of geometry parameters for ceramic cutting tools in intermittent turning of hardened steel

For the purpose of improving the ceramic cutting tool lives in intermittent hard turning, investigations on optimization of tool geometry parameters were conducted in the present study. The initial damage of the ceramic cutting tool was determined based on damage mechanics. The initial damage was more sensitive to the changes of porosity when it was relatively low. The stress distribution of the tool body was obtained using finite element simulation. The initial damage of the cutting tool and the tool stress were integrated on the basis of the concept of damage equivalent stress. The evolutions of the maximum value of damage equivalent stress on the tool body were acquired for different cutting length ratios and different combinations of tool geometry parameters. The highest value of damage equivalent stress in one cutting cycle was proposed as a new indicator for optimization of tool geometry parameters. The contribution order of tool geometry parameters for the indicator was corner radius, cutting edge angle and rake angle. This order stayed the same at different cutting length ratios. The optimization method for ceramic tool geometry parameters was proposed and it was validated through intermittent turning tests.

The influence of operation parameters on stress of plate-fin structures in LNG heat exchanger

In order to ensure the structural safety of plate-fin structures, a model was proposed to simulate the stress of plate-fin structures in actual operation process of LNG heat exchanger based on Finite Element Method and thermal elastic theory. The influence of operation parameters were investigated on stress of plate-fin structures. The results show that the stress reaches the peak value in brazed joint near the fin side, and a crack would initiate in this region. This is consistent with the experiment result based on pressure burst of partial model of PFHE. The peak value of equivalent stress increases steadily with the increase of the temperature difference between natural gas (NG) and mixture refrigerant (MR) and is slightly impacted by the temperature gradient along the flow direction of NG. Additionally, the peak value of equivalent stress increases with the increase of NG or MR pressure and the influence of NG pressure is more remarkable. These results will provide some constructive instructions in the design and safe operation for plate-fin heat exchanger in a large-scale LNG cold-box.

Analysis of PCBN tool failure mechanisms in face milling of hardened steel using damage equivalent stress

An attempt was made in the present study to apply damage mechanics to investigate the polycrystalline cubic boron nitride (PCBN) tool failure mechanisms in face milling of hardened steel. Experimental phenomenon relating to damage accumulation was found by means of analyzing the tool wear evolution and macroscale failure of the cutting tool. Damage equivalent stress was used as an indicator to reveal the tool failure mechanisms under different cutting conditions. Because of the larger value of damage equivalent stress, there was greater likelihood of tool fracture in down milling than that in up milling. Deflection of the shear angle changed the tool stress component and distribution substantially in up milling, leading to the emergence of the peak value of damage equivalent stress in spite of lower values of cutting force and tool temperature. Calculated damage equivalent stress and tool lives obtained in milling tests were compared and analyzed. It was found that damage equivalent stress can be used as an effective tool to analyze the tool failure mechanisms and assess the optimum cutting condition.

Stress characteristics of plate-fin structures in the cool-down process of LNG heat exchanger

In order to ensure the structural safety of plate-fin structures, a model is proposed to simulate the stress characteristics of plate-fin structures in the cool-down process of LNG heat exchanger based on Finite Element Method and thermal elastic theory. The simulation results show that the equivalent stress rapidly changes and consistently reaches the peak value in the brazed joint, and a crack initiates in this region in the cool-down process. The peak value of equivalent stress in plate-fin structures steadily increases with the increase of temperature difference between natural gas (NG) and mixture refrigerant (MR) and it is slightly impacted by the temperature drop rate as the temperature drop rate of NG is the same as that of MR in the cool-down process. The simulation results are consistent with the experiment results. These results will provide some constructive instructions in safe operation and improvement of the cool-down process for plate-fin heat exchanger in a large-scale LNG cold-box.

A critical analysis of plane shear tests under quasi-static and impact loading

This paper presents an extensive investigation of the real testing conditions of plane shear tests under quasi-static as well as impact loading. In particular, it aims at analyzing the role played by the empirical corrective coefficients commonly used in this kind of tests. For this purpose, a complete numerical model including not only specimen but also clamping device is built. Compared with usual simulations of only a shear specimen used to establish these corrective coefficients, the proposed complete numerical model permits to evaluate the influence of clamping device on the distribution of stress and strain fields. It shows that there are only limited effects under static loading, except for the early stage of loading (elastic part) where the stiffness of clamping device has to be taken into account. Under dynamic loading, a similar conclusion as the static case has been made. However, the transient effect due to the wave propagation within clamping pieces is rather important before an equilibrium state is reached. Numerical results indicate also that the shear loading on the specimen is mainly guided by the compressive wave in the massive clamping pieces, and the shear wave propagation inside the shear area is negligible. Besides, the way to calculate the equivalent strain from experimentally measured displacement is discussed. Eulerian cumulated strain, which is the default large strain definition in most commercial codes, should be used instead of the idealized small strain shear assumption. Finally, this work indicates that when the average value of equivalent stress in the whole shear area and cumulated Eulerian strain are used, commonly used corrective coefficients are no longer needed.

Study on plastic deformation behavior of hot splitting spinning of TA15 titanium alloy

The plastic deformation behavior of hot splitting spinning of TA15 titanium alloy is a complex metal forming problem with multi-factor coupling interactive effects. In this paper, on condition of considering various thermal effects, a three-dimensional (3D) elastic–plastic coupled thermo-mechanical finite element (FE) model of hot splitting spinning of TA15 titanium alloy is established using the dynamic, temp-disp, explicit module of FE software ABAQUS. Based on the analysis of flow behaviors of TA15 titanium alloy, the mechanism and influence of materials plastic deformation behavior during the forming process are studied. The results show that, the flow stress of TA15 titanium alloy generally decreases with the increase of deformation temperature; at the same strain rate, the higher temperature is, the lower flow stress is. The temperature distributions along the circumferential direction of disk blank are even and the temperature of plastic deformation area is about 984°C. The heat from plastic deformation and friction at local plastic deformation area is less than the dissipated heat, so the temperature just falls into approximately 945°C. Radial spinning force as the driving force of plastic deformation increases gradually and reaches about 35kN at the end. The maximum value of equivalent stress is presented in fillet part between disk blank and two mandrels. The distributions of equivalent plastic strain appear the large strain gradients and the obvious characteristics of inhomogeneous deformation. When friction factor on interfaces between disk blank and dies ranges from 0.4 to 0.6, the forming quality and precision are highest.

Stress Analysis of Perforated Plate Based on ANSYS

Based on nonlinear FEA software ANSYS, 3D simulation models of eighteen-type perforated plate that have different open-pore number was established. Analysis results indicate: Maximum equivalent stress of perforated plate mainly takes place on symmetry center of outer open-pore for open-pore area. With increasing open-pore number, maximum equivalent stress and each-direction maximum stress of perforated plate presents to enlarge trend. When open-pore number less than or equal to twelve, value of maximum equivalent stress mainly is decided by Z-direction maximum stress. When open-pore number greater than twelve, value of maximum equivalent stress mainly is decided by Y-direction maximum stress. When ratio m less than 2, with increasing ratio m, maximum equivalent stress and each-direction maximum stress of perforated plate presents to reduce trend. When X-direction and Y-direction open-pore numbe of perforated plate is basically equilibrium distribution, X -direction maximum stress is about equle to half of maximum equivalent stress.

A Three-Dimensional Atomic-Scale Finite Element Model for a Copper Nano Thin Film Subject to a Uniaxial Tension

A three-dimensional atomic-scale finite element model was developed in this paper for simulation of a nano-scale uniaxial tension. First, the Morse’s potential function was used to simulate the forces acting among particles. Furthermore, a non-linear spring and dashpot element with a lumped mass was used to establish an atomic model. The elongation of the spring at fracture was used to simulate the radius of fracture of the atomic link. This method was applied to investigate the proportional tension test of an idealized FCC single crystal copper film along the x direction. The study includes the stress-strain curve, the effect of five categories of atomic distances on the stress-strain curve; and the effect of strain-rate on the stress-strain curve. The results showed that (1)the simulated maximum stress for copper is very close to 30.0GPa, which is also the value of maximum equivalent stress obtained by Lin and Hwang [6], verifying the validity of the calculation of this paper. In the tension test of copper, necking develops gradually and eventually leads to fracture. The simulated deformed material element during each stage of deformation was similar to that simulated by Komanduri et al.[2](2)the influence of =6.2608 on the five categories of atomic distance considered was limited and it may be neglected to save computation time,(3)when the strain-rate was large, the resistance to deformation was also large, leading to an increase in the yield stress and fracture stress.

Stress Analysis of Tubular Turbine Based on Fluid-Structure Coupling

A brief introduction of fluid-structure coupling and its classification were given, then according to the solving characteristics and application conditions of different coupling methods; sequential coupling method is chosen to calculate the stress distribution of a tide power plant tubular turbine. Stress calculations of the tubular turbine were conducted under the maximum water head, the designed water head, the average water head and the minimum water head working conditions in ANSYS Workbench. The research shows that in all of the four calculated working conditions, the maximum equivalent stress of the runner is located at the connection between the blades and the hub where stress concentration is obvious; the maximum deformation of the runner lies in the outer edge of the blades and the deformation increases from the root to the outer edge; the maximum equivalent stress of the guide vane is located at the root and the maximum deformation lies in the outer edge. The maximum value of maximum equivalent stress of the runner and the guide vane occurs on the maximum water head working condition, whereas it is far less than the material yield limit, which means that static stress will not lead to the cracks of the blade or the guide vane. But it is still necessary to avoid stress concentration appearing periodically in case it causes fatigue failure.

Research on continuous multi-point forming method for rotary surface

In order to realize high efficient and flexible manufacturing for 3-D surface, continuous multi-point forming (CMPF) is researched. Firstly, principle of CMPF is described, and its characteristics are analyzed by comparing with the conventional spinning methods. Secondly, FEA model of CMPF for disc-shape surface is established, forming load is analyzed theoretically, equivalent stress and plastic strain distributions of disc-shape surface are analyzed. Thirdly, wrinkling is analyzed through simulation results. Fourthly, forming process of tube-shape surface is studied. Finally, CMPF equipment is developed, and experiments are carried out. Results indicate: For disc-shape surface, equivalent stress in regions of center fixture and flexible roller exceeds yield stress; the maximum plastic strain is generated in center region; plastic strain in region of flexible roller takes the second place; shell elements in wrinkling region generate tangent direction compress deformation. For tube-shape surface, maximum value of equivalent stress appears in region of flexible roller; plastic strain field presents annular distribution, its maximum value appears in marginal region. Measure results of curvature radius of disc-shape surface and tube-shape surface almost accord with simulation results. Simulation results of stress field, strain field and wrinkling almost accord with practical situation.

A FEM Study on Thermal Stress in Laminated Composite

The 3-D elasto-plastic finite element method (FEM) was used to analyze the thermal stress in the laminated composite (SiC/6061Al) under the condition of a temperature cycling of 200 0C-30 0C- 200 0C-30 0C. The results from the FEM analysis showed that the hysteretic peak value of the von Mises equivalent stress in the substrate 6061Al was increased significantly as the temperature loading cycles processed on but it was nearly the same after the first cycle in the interface layer SiC of the laminated composite. The elastic strain in the substrate 6061Al varied within the range of -0.15% to 0.15% and the maximum plastic deformation was equal to about 0.26 %. The results also showed that the maximum normal stress Sx was increased from 32.8 MPa to 87.9 MPa after ten cycles and the work-hardening of the substrate 6061Al occurred during the stress and strain hysteresis loop.

Failure analysis of prestressing steel wires

This paper treats the failure analysis of prestressing steel wires with different kinds ofrnlocalised damage in the form of a surface defect (crack or notch) or as a mechanical action (transversernloads). From the microscopical point of view, the micromechanisms of fracture are shear dimplesrn(associated with localised plasticity) in the case of the transverse loads and cleavage-like (related to arnweakest-link fracture micromechanism) in the case of cracked wires. In the notched geometries thernmicroscopic modes of fracture range from the ductile micro-void coalescence to the brittle cleavage,rndepending on the stress triaxiality in the vicinity of the notch tip. From the macroscopical point of view,rnfracture criteria are proposed as design criteria in damage tolerance analyses. The transverse load situationrnis solved by using an upper bound theorem of limit analysis in plasticity. The case of the cracked wire mayrnbe treated using fracture criteria in the framework of linear elastic fracture mechanics on the basis of arnprevious finite element computation of the stress intensity factor in the cracked cylinder. Notchedrngeometries require the use of elastic-plastic fracture mechanics and numerical analysis of the stress-strainrnstate at the failure situation. A fracture criterion is formulated on the basis of the critical value of therneffective or equivalent stress in the Von Mises sense.

Effect of Prestrain at Elevated Temperature on Ductile Fracture of High Strength Steel

The processes of ductile fracture of KD32 steel specimens subjected to prestrain at elevated temperature are observed. Although several large voids are observed at a relatively small strain level, they have no important role in fracture processes. As soon as micro-voids nucleate at some strain level, which is the stage just before final fracture, they rapidly grow and coalesce. It is proposed that ductile fracture of KD32 steel specimens occurs when the value of equivalent stress reaches a critical value. It seems that the most important reason for the decrease in fracture strain with prestraining at elevated temperature is the strain hardening according to amount of prestrain and prestraining temperature.

高温予ひずみ材を用いた高張力鋼の延性破壊に関する研究

The processes of ductile fracture in KD32 steel specimens subjected to prestrain at elevated temperature are observed in detail by using fractographic and sectioning techniques. A criterion of ductile fracture and a mechanism of decrease in ductility with prestraining at elevated temperature are also investigated. The results are summarized as follows.(1) The processes of ductile fracture in KD32 steel specimens are as follows: Although several large voids are observed at a relatively small strain level, they have no important role in fracture processes. As soon as microvoids nucleate at some strain level, which is the stage just before fracture, they rapidly grow and coalesce.(2) Ductile fracture of KD 32 steel specimens occurs when the value of equivalent stress reaches to a critical one.(3) It seems that the most important factor of decrease in ductility with prestraining at elevated temperature is the work hardening according to amount of prestrain and prestraining temperature.