Minimum Equivalent Stress Research Articles

Numerical and experimental investigation of the effect of heat input on weld bead geometry and stresses in laser welding

Abstract Nowadays, laser welding is a powerful joining method. Thanks to the advantages it has, its usage area is increasing day by day. However, getting the desired result from the laser welding process is possible with the proper welding parameter selections. Otherwise, many problems may be encountered, including significantly incomplete penetration. For this reason, parameter selection has been discussed in many studies in the literature. At this point, validated numerical simulation models are precious. Since these models reduce experiment costs and save time. Especially numerical simulation of the structural steel, which is the one of most used materials, is crucial. In this study, the effects of laser power (LP) and welding speed (WS), which are among the vital parameters of laser welding, on weld width and stress were investigated numerically and statistically. Structural steel was selected as the material, and the Taguchi method was carried out for the simulation case study design. Simufact Welding software was used for simulation studies, and simulations were carried out thermomechanical. Thus, more realistic results were obtained via the thermomechanical method. One of the simulation results was verified through an experimental study. The results were evaluated with signal-to-noise (S/N) ratio and a statistical analysis of variance (ANOVA), and as a result of the study, it was seen that the welding speed was a more effective parameter, the optimal parameter combination was found to be 3500 W for laser power and 40 mm/s for welding speed to get maximum weld width and minimum equivalent stress. In addition, it was observed that correctly created simulation studies may provide very close results to experimental studies.

Effects of geodesic dome trajectories on the specific strength of composite overwrapped pressure vessels: FE modelling

In this study, it was aimed to find out geodesic dome trajectories of composite overwrapped pressure vessels, and investigate the effect of dome profiles on the structural performances. In this context, geodesic paths for 0.2, 0.3, 0.4, 0.5 and 0.6 dimensionless polar opening radii were determined by solving elliptical integrals and filament winding angles were calculated throughout the dome and cylindrical portions. Afterward, finite element analysis was performed to obtain mechanical properties by using the Ansys ACP module. As a result of the current study, it has been concluded that dome profile and filament winding angle are highly dependent on the polar opening radii. When the performance factor was considered, it has been determined that the optimum pressure vessel has 0.6 dimensionless polar opening radii. Moreover, it was observed that minimum equivalent stress, strain, deformation and inverse reverse factors have occurred in the pressure vessel with 0.6 dimensionless polar opening radii. Furthermore, it was showed that effective parameters in the mechanical performance of pressure vessels can be optimized to obtain strengthened and lighter structures.

Estimation of three-point bending behavior using finite element method for 3D-printed polymeric sandwich structures with honeycomb and reentrant core

Sandwich structures are known as ultra-light porous materials. Because the structure has advantages in terms of acoustics, fatigue, and impact resistance that conventional stiffened plates cannot match, it has become a popular material in aerospace, automotive, marine, windmill, and architectural applications. One promising method for decreasing production waste and enhancing flexural stress is to employ Additive Manufacture (AM) technologies for sandwich structure manufacturing. In this study, polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), and polyethylene terephthalate glycol (PETG) sandwich structures with reentrant and honeycomb cores were designed and then a finite element analysis (FEA) was carried out to compare the stress distributions in these sandwich composites. According to the findings, higher flexure stresses and specific energy absorption were obtained in the reentrant sandwich structures compared to honeycomb sandwich structures. A minimum equivalent stress value was found in the ABS material, while a maximum equivalent stress value was found in the PLA material.

Optimization of ventilated brake disc rotor geometry for enhanced structural characteristics

This paper focuses on analyzing the effect of geometrical parameters on structural performance of the ventilated brake disc. Multi-objective optimization through response surface methodology was deployed for improving the structural performance of ventilated brake discs. Simulation runs were designed based on central composite design technique. The second order regression models correlating the geometry parameters with maximum deformation and equivalent stress were developed. ANOVA was performed to test the significance of disc geometry parameters. The deformation and equivalent stress were influenced by flange outer peripheral radius. While the spigot radius had a significant effect on the deformation but not on equivalent stress. Also, the mounting surface radius influenced the equivalent stress developed on the ventilated brake disc rotor. The multi-objective optimization of geometrical characteristics for minimum deformation (4.2332 µm) and minimum equivalent stress (4.00989 MPa) yielded significant reduction in total deformation and equivalent stress i.e., 10.28 % and 9.12 % respectively at optimal levels of geometrical parameters.

Thermo-mechanical analysis and estimation of turbine blade tip clearance of a small gas turbine engine under transient operating conditions

Turbine blade tip clearance is one of the significant factors that influence turbine efficiency, Specific Fuel Consumption (SFC), Exhaust Gas Temperature (EGT), and emissions. Controlling these parameters in a small gas turbine engine (SGT) is a challenging task due to small blade height and viscous working environment. SGT are subjected to high-temperature gradients at the combustor outlet, which affects the turbine blade tip clearance. This paper presents the thermo-mechanical analysis of a typical SGT engine to study the blade tip clearance influenced by the deformation of turbine stage components (turbine rotor, nozzle guide vane (NGV) with integral blade shroud) during transient phases. ANSYS Workbench is used to perform transient thermal and structural analyses. The structural analysis is performed taking the material properties to be temperature-dependent. The SGT engine under consideration operates at a design speed of 45,000 rpm. Initially, steady-state thermal analysis and static structural analysis were carried out to understand the structural behaviour of the system under a thermal and centrifugal loading environment. Since different components of the engine assembly operate at different temperatures, the effects of convection and conduction at the interfaces influence the radial clearances between the static and rotating parts of the engine. A one-way coupled transient thermal-structural analysis was performed on a three-dimensional model to capture the actual behaviour of the tip clearance during transient operating conditions. Significant growth of blade and rotor was observed relative to the casing resulting in minimal clearances during these transient operations. Hence, it is important to estimate desired cold clearance, considering transient phenomena, to avoid mechanical blade rub with the shroud. It is observed that high-temperature gradients contribute primarily to the stresses and radial displacement of the rotor compared to centrifugal effects. The turbine rotor takes more time (t = 600 s) to reach steady-state temperatures compared to NGV (t = 120 s) due to the solid mass of the disc. The location and magnitude of maximum and minimum equivalent stress changes with time in NGV and rotor, and they experience maximum stress at the initial time steps compared to steady-state.

Improvement Design of Adhesive Layer on Honeycomb Structure for Railway Vehicle System by Uniform Design Method

The purpose of this paper focuses on adhesive layer strength while having a thermal cycling of honeycomb composite sandwich structure by using the uniform design of experiments method improving the von Mises stress of honeycomb structure. Three system parameters of the honeycomb structure are selected as the control factors to be improved. Uniform design of experiment is applied to create a set of simulation experiments. Applying ANSYS/Workbench software, the finite element modelling is investigated and the von Mises stress of the honeycomb structure is calculated under metal-honeycomb core flatwise tensile test. From the numerical results, the best honeycomb structure dimension of all the experiments which causes the smaller von Mises stress is selected as the improved version of design. Finally, the best model of the experiments which causes the minimum equivalent stress is regarded as the improved version of design. Compared with the original design, the result of ASTM C297 improved version is 17.386 MPa, which mean improved 36.28%, ASTM C364 improved version is 19.015 MPa, which mean improved 25.26%, ASTM C365 improved version is 16.86 MPa, which mean improved 12.35%.

Relationship between sliding-induced wear and severity of sliding contact for polyamide 66 filled with hard filler

We studied the factors that affect the sliding-induced wear of polyamide 66 (PA66) composites. The dimensionless severity parameter Ssc was defined from the minimum equivalent stress in the sliding contact area and calculated by using approximations. Subsequently, we conducted the friction tests for the PA66 composites filled with hard fillers under dry conditions. The hard fillers included rice bran ceramics particles, glass beads, carbon fibers, and glass fibers. According to the relationship between the wear rate and the severity parameter, the specific wear rate increased exponentially with increasing Ssc for all the materials. Obtaining low-wear PA66 required improving the yield strength and reducing the Young’s modulus and the friction coefficient.

Strength variation of gas cooling turbine blade pin‐fin with different array

As an important measure of cooling, the pin fin array has been widely used in the cooling blade of turbine. However, most of the cracks in turbine blade are found near the pin fin due to stress concentration. In order to study the strength variations of pin fin in various shapes and with various longitudinal and transverse pitches, this paper establishes 10 rectangular, 3 elliptical and 1 diamond‐shaped slab models of pin fin array. The results indicate the existence of high stress area and low stress area around the pin fin. In the rectangular pin fin model, the maximum equivalent stress is detected on the side perpendicular to the load applied, the low stress area is on the side parallel to the load applied, and the high and low stress areas are semi‐elliptically distributed along their own track. For a rectangular pin fin array, the equivalent stress along each side of the bottom first increases and then decreases, with the maximum equivalent stress at the corners and the minimum at mid‐point of each side; along the height direction, the minimum equivalent stress of a rectangular pin fin array is near the ends while that of a square pin fin array is at the mid‐points. Under the same conditions, the stress of the rectangular pin fin array decreases with the decrease of the aspect ratio (h1/b). The position of the maximum stress around the elliptical pin fin array varies from the two axis ratio (a/b). When a/b is 2, the maximum equivalent stress around the bottom is at the positions with a horizontal angle of 75°/120°/255°/300°; when a/b is 1, the maximum equivalent stress is at the positions with a horizontal angle of 60°/135°/240°/315°; and when a/b is 0.5, the maximum equivalent stress is at the positions with a horizontal angle of 45°/150°/220°/330°. Under the same conditions, the stress of a round pin fin array is smaller than that of a square one. In all the analytical models, the diamond‐shaped pin fin array presents the largest equivalent stress and the highest stress concentration.

Turbine Blade Straddle Root and Rim Structural Optimization Using Finite Element Contact Analysis

The development of turbine blade root style is one of the key problems in the blade design technology as the root carries most of the loads of the whole blade. The optimal design problem and the corresponding numerical method were established for a straddle root structure with the minimum equivalent stress of the root and rim as the optimal objective. A multi-variable parametric model of the blade and rim, which took eight critical geometrical variables of the root and rim as design variables, was built by APDL (ANSYS parametric design language) and the optimal problem was numerically solved by combining pattern search algorithm with finite element method. The results indicate that the optimized structure has better strength performance, whose maximum equivalent stress of the root sharply decreased by 25.18% comparing with the original design. It eventually confirms the feasibility and validity of the proposed optimal design method.

COUPLING THE BIONIC SURFACE FRICTION CONTACT PERFORMANCE AND WEAR RESISTANCE ANALYSIS

This article is mainly to study the frictional contact performance of biomimetic flexible pits surface of different structure under the preload using the coupled bionic technology. And using finite element analysis software to conduct the contact analysis of bionic pit surface of different sizes, establish bionic flexible pit surface and rigid surface friction contact, discussion force and deformation of the surface of a flexible pit when bionic flexible pit surface and the rigid surface contact, and analyze the wear resistance. The results showed that the model of 1mm radius of pit has minimum equivalent stress, longest life and best wear resistance. Index Terms: finite element analysis, bionic, rigid -flexible contact, frictional contact, wear-resistant

Effect of Optimum Autofrettage on Pressure Limits of Thick-Walled Cylinder

In optimal design of thick-walled cylinders, there are two main objectives to be achieved: increasing its strength-weight ratio and extending its fatigue life. This can be achieved by autofrettage where a residual stress field is generated in the cylinder wall prior to use. An analytical autofrettage procedure of a thick-walled cylinder is proposed, with the aim of predicting the required autofrettage pressure for various levels of allowable pressure and hence achieving maximum fatigue life. A Finite Element Method (FEM) validation is provided. The results reveal three scenarios in the design of thick-walled cylinders. For maximum load carrying capacity, non-autofrettage is suitable when, in service, the whole wall thickness will be yielded. Full autofrettage is suitable when, during subsequent operation, yielding is limited at the inner surface. Optimum autofrettage of the cylinder is suitable if a minimum equivalent stress and maximum fatigue life are to be achieved. The analytical solutions compared satisfactorily to the numerical results where a very good correlation in form and magnitude was obtained.