Blend Radius Research Articles

IMPACT OF DIFFERENT TPMS TESSELATION APPROACHES ON MECHANICAL PROPERTIES OF PARTS

In the paper influence of several factors on shape accuracy and compressive strength of parts is analysed. First simulation software is used for prediction. Parts are cylindrical with 20 mm diameter, manufactured via SLA additive manufacturing technology. 1mm thick Gyroid TPMS structure is generated in cylinders with different volume % (30,40,50 %). Thanks to drainage holes it was possible to create parts that are hollowed, but have solid shell around and TPMS inside. Different tesselation approaches are tried (cylindrical and rectangural). Different radius of roundness is also tried on the surfaces joining tpms and shell of cylinder (0, 0.5, 1mm) Compression tests are then conducted and results are analysed in the form of graphs and colour map of deviations. Results are also compared with solid and fully hollow cylinders. Study finds that the maximum strength of the bodies is influenced by tessellation method, infill percentage, and blend radius. Higher infill percentages generally result in increased strength due to greater material volume transmitting loading force. While tessellation affects samples without shells, its impact is negligible on samples with shells.

Beam dynamics and cavity design of an 8 MeV CW IH-DTL for SYSU-PAFA

As a part of the Particle Accelerator Facility at Sun Yat-sen University (SYSU-PAFA), a 200 MHz drift tube linac (DTL), operating under continuous wave (CW) mode, has been designed. PAFA-DTL is expected to accelerate a 10 mA proton beam from 2.5 MeV to 8 MeV. Using the alternative phase focusing (APF) beam dynamics scheme, a compact cell array has been designed and optimized in order to limit the cavity length to 2.4 m with high acceleration efficiency. As a result, PAFA-DTL contains 31 acceleration cells with beam transmission efficiency reaches 100%, and better output beam quality is obtained by optimizing the input beam parameters. Interdigital H-mode (IH) structure is utilized in the PAFA-DTL cavity, which has achieved a high unloaded quality factor of 13987. Additionally, to ensure the stability of PAFA-DTL under CW operation, a low Kilpatrick factor (Kp) of 1.42 is obtained by adjusting the blending radius of the drift tubes (DTs) to reduce the risk of RF breakdown. The gap voltage distribution through RF design is compared with that from the beam dynamics, and the maximum absolute value of deviation is only 0.73%. In this paper, the detailed design and results of PAFA-DTL, including beam dynamics and RF design, are presented.

Edge Blending to Enhance the Flow Over Double delta wing configuration during re-entry

During re-entry of space vehicle, the vehicle undergoes flow variation from hypersonic flow to subsonic flow, which causes huge heat transfer over the wing configuration. The double delta wing of configuration 76 degree - 40 degree is considered and effect of blending the wing at edges showed variation and enhancement of flow over the double delta wing configuration. Heat flux calculations were carried out at regions of shock-shock interactions and the effect of blend radius at edges were analyzed using simulations done in ANSYS Fluent. It was observed that aerodynamic efficiency increases with the edge blending which ultimately enhanced the flow field over the double delta wing.

Numerical and experimental analysis of rounded fins for high speed air-cooled heat exchangers

The implementation of Surface Air-Cooled Oil Coolers (SACOCs) in new generation of turbofans is becoming more and more common. The main reason behind this is the need of improving the engine thermal management system as lubricants and components are working under increasingly severe demands. The idea of using the cold air from the bypass duct as a cold sink not only can be beneficial to cool down the oil, but because the enthalpy can be released into this flow to enhance the propulsion. However, it is extremely important to maintain the aerodynamic impact of the heat exchanger to its minimum so the propulsive efficiency is not worsened.In this investigation, the effect of rounding the sharp edges of a finned heat exchanger working under realistic conditions of very high Reynolds numbers is addressed. Firstly, a parametric study to determine the blend radius was numerically conducted and then, both geometries were experimentally tested for different Reynolds. The rounded version presented not only better results in terms of heat exchange, but also a considerable reduction in the aerodynamic impact of the fins. A detailed numerical analysis of both cases under nominal conditions showed that rounding the sharp edges enables the airflow to remain better attached to the fins, decreasing thus the aerodynamic impact in terms of velocities and vorticity and improving the thermal performances.

Numerical Simulation of Low-Pressure Drop Static Mixers for Mixing Enhancement

Static mixers (SM), also generally known as inline mixers, form a newly developing industry trend. They have no moving parts, hence have lower energy consumption, lower installation cost, and very low maintenance cost, and are thus an attractive alternative to the conventional agitators. Modifications were made in the design to reduce pressure drop and increase the mixing intensity across the mixer and increase the application of inline mixers in the industries. Three hybrid geometries (different combinations of Kenics and LPD) of static mixers were constructed and simulated using computational fluid dynamics (CFD) tools. Kenics is an excellent radial mixing device, and low-pressure drop (LPD) an excellent axial mixing device. The key design parameter to modify LPD was the slope angle of elliptical plates which affects the mixer performance. Different slope angles from 90o to 120o were simulated. Kenics was modified for different aspect ratios, and the edge of Kenics was curved. Pressure drop, thermal, and Discrete Phase Model (DPM) analysis were performed on these three different classifications of hybrid geometries. The most promising geometry to emerge based on the low-pressure drop and good mixing efficiency both was the curved edge Kenics. Keen-sighted these results, further analysis was performed on curved edge Kenics after the modification of blend radius. It was concluded that for a lower Reynold number, the curved edge with a higher blend radius dominates all other mixers. Result validation was done by comparing the trends and sensitivity of process variables with the established results and standards.

Shape modification of Ahmed body to reduce drag coefficient and determination of turbulence model

In this study, the aerodynamic analysis of Ahmed body which is generic automobile model is performed to determine convenient turbulence model and reduce drag coefficient by modifying shape of model. For this purpose, Computational Fluid Dynamics (CFD) analysis is carried out using different turbulence models that are Spalart-Allmaras, (Shear Stress Transport) SST k-ω, Standard k-ε, Realizable k-ε, (Re-Normalisation Group) RNG k-ε turbulence models. The results are compared with experimental data that is available in literature. The results show that RNG k-ε turbulence model gives superior performance when compared with other models. In order to reduce drag coefficient, the upper region of sides of model is rounded by applying fixed blend radius with 25 mm. The smooth surface can provide high performance in point of aerodynamics. CFD solution is then repeated for the modified model and the result show that drag coefficient value reduces about 6%. In addition, the second modification is performed by applying fixed blend radius with rounded both upper sides and rear underside of body and chamfer with 50 mm is also applied to rear sides of body. However, drag coefficient reduction level is approximately same with first modified model. The pressure coefficient contours and velocity streamlines are presented to show results for baseline and modified bodies.

Simulation of thin-walled workpieces ends expanding for pipelines making

Experience of pipelines operation shows that their failures are often connected with thinning of walls in bending areas and with abrupt transition from one wall diameter to another. It is possible to make this transition smoother by using of connecting pipes with variable diameter. Such parts can be obtained by forming process of expanding. In this paper, the process of cold expanding of the end of thin-walled tubular workpiece, which is made from aluminium alloy AMg6M, against hard die, is investigated by finite-element method in ANSYS. It is used the saddle-shaped die, which makes it enable to produce connecting branches similar to the form of two joined pipes with specified blending radius. It has been investigated maximal and residual stresses in deformed part, as well as wall thinning. This stresses do not exceed tensile strength of the material. Therefore, it has been proved the possibility to obtain connecting pipes per one processing step, which do not require subsequent mechanical treatment. Wall thinning corresponds to technological norms.

Automatic blade blend modeling and hexahedral mesh regeneration for aircraft engine optimization

Multidisciplinary Design Optimization (MDO) method has been widely investigated and applied in the aircraft engine design. In the conceptual and preliminary design phase of the aircraft engine turbine MDO, automatic modeling and mesh generation of the blend between the blade and the shroud are two key technologies. A robust algorithm should be able to perform well without the target recognition of the geometric feature of the blend. A strategy of hexahedral mesh regeneration based on the Topological Homeomorphism is presented in this paper, where improved parametric modeling can be obtained for the turbine blade and disk. The optimal solutions of low pressure turbine of an aircraft engine could be obtained to examine the feasibility and availability of automatic modeling and mesh regeneration. The simulation results demonstrate that the proposed method is capable of satisfying the requirement on material strength by optimizing the blade blend radius, where the total weight of blade and disk can be reduced by 5.882%.

Optimization of a high pressure turbine blade tip cavity with conjugate heat transfer analysis

The current study aims to understand the aero-thermal performance of a cooled cavity tip in a single stage transonic turbine. The squealer tip of the uncooled turbine blade was reduced to an aerodynamic loss with suppressing leakage flow. However, the aerodynamic loss study of the cooled turbine blade tip is rare. It is necessary to study the tip cavity of the cooled turbine blade. Depth, front blend radius and aft blend radius of the cavity were set as design variables, and 30 cases were chosen using design of experiments. These cases were calculated with conjugate heat transfer method. Approximation model was made using the Kriging method, and tip cavity shape was optimized with multidisciplinary design optimization. Average total pressure loss behind the trailing edge and cooling effectiveness of blade tip surface were set to the objective function. The aerodynamic optimization model decreased 1.6 % of total pressure loss, the heat transfer optimization model increased 1.3 % point of cooling effectiveness and aero-thermal optimization model were found. Volume of tip cavity becomes larger when three design variables are grown. Amount of tip leakage flow and its distribution over the tip region increases and total pressure loss and cooling effectiveness increase. In terms of heat transfer, blade tip without cavity is advantageous. Total pressure loss coefficient, however, also increases over 5 %. To improve both aero-thermal characteristics of cooled blade tip, the design using the multidisciplinary design optimization is recommended.

FE Simulation and Full-field Strain Measurements to Evaluate the Necking Phenomena

During airbag production, many parts are obtained by plastic deformation such as the lid of the gas generator. Since the airbag gas generator is a significant vehicle safety part, several pressure tests have been developed in order to prove the reliability of this product. A ductile fracture problem initialized by a localization of the deformation is observed along the blending radius. In order to understand the mechanical processes involved in the forming operation, a numerical and experimental study was developed. A tensile test specimen extracted from the sheet of study, undergoes elastic deformation that is followed by a transition to plastic deformation. Although during this stage of the test the deformation is stable, the strains begin to localize within a relatively broad zone known as diffuse necking. The stable deformation, with continuously rising load, is followed by the instability whereby a local neck or shear band is produced due to strong localization of deformation. The localization is explainable by the inhomogeneity in macroscopic material properties in the specimen. The necking behavior is a vital precursor to the final failure. A Digital Image Correlation (DIC) method is used in 2D and 3D to evaluate the necking and localization of deformation, which shows clearly the two stage of necking phenomena. Moreover, a numerical modeling was developed of tensile test under ABAQUS commercial software. In this model we use Gurson Tvergaard Needleman (GTN) ductile model of damage to predict the necking phenomenon. Furthermore the results from FE simulations are compared with experimental results from uniaxial tensile tests. Finally we develop the numerical model of the lid of the gas generator obtained by forming process.

Numerical Simulation of Two-Dimensional Bluff Body Aerodynamic Noise Using Lattice Boltzmann Method

Aerodynamic noise generated by air-moving devices is a common problem. In this paper, the aerodynamic noise around two-dimensional bluff body flow was simulated by Lattice Boltzmann Method. Utilizing blend radius can reduce the aerodynamic noise around the bluff body notably, and the greater the blend radius, the better the noise reduction effect will be. When the basic shape model is simulated and post-processed, the speed nephogram and the streamline chart of the flow field were obtained. Then Sound Pressure Level (SPL) of some key points was tested. Changing the shape of the bluff body’s vertices to blend radius, the results were compared with those of the basic shape, and the aerodynamic noise was reduced.

ENHANCING TERAHERTZ RADIATION FROM DIPOLE PHOTOCONDUCTIVE ANTENNA BY BLENDING TIPS

We study the rectangular tips of the dipole photoconduc- tive antenna, which has been widely used for terahertz radiation and detection, with difierent blend radii efiect on the emission performance of terahertz (THz) radiation. For the amplitude of THz radiation pulse is proportional to the local electric fleld in the gap, the increased max- imum bias electric fleld by blending tips is able to achieve higher THz radiation power. Both considering the in∞uence to the maximum bias electric fleld and the emission e-ciency, the blend radius of the rect- angular tips is suggest to be larger than 5m and the radiation power is largely enhanced. Comparing to the previous work, our method has better THz radiation performance.

Mesh blending

A new method for smoothly connecting different patches on triangle meshes with arbitrary connectivity, called mesh blending, is presented. A major feature of mesh blending is to move vertices of the blending region to a virtual blending surface by choosing an appropriate parameterization of those vertices. Once blending is completed, the parameterization optimization is performed to perfect the final meshes. Combining mesh blending with multiresolution techniques, an effective blending technique for meshes is obtained. Our method has several advantages: (1) the user can intuitively control the blending result using different blending radii, (2) the shape of cross-section curves can be adjusted to flexibly design complex models, and (3) the resulting mesh has the same connectivity as the original mesh. In this paper, some examples about smoothing, sharpening, and mesh editing show the efficiency of the method.

Stress concentration at crossholes in thick cylindrical vessels

Elastic stress concentration factors (SCFs) for internally pressurized thick cylindrical vessels with radial and offset circular and elliptical crossholes are presented. Three forms of intersection between the crosshole and main bore are considered: plain, chamfered and blend radiused. The minimum SCF was found to occur for the plain intersection configuration, with the peak stress at the crotch corner between the main bore and crosshole on the longitudinal plane of symmetry. Incorporating a chamfer or blend radius at the intersection reduces the stress concentration at the main bore but introduces higher peak stress elsewhere in the chamfer or blend region.

Characterization of fretting fatigue crack initiation processes in CR Ti–6Al–4V

A study was conducted to quantify fretting fatigue damage and to evaluate the residual fatigue strength of specimens subjected to a range of fretting fatigue test conditions. Flat Ti–6Al–4V specimens were tested against flat Ti–6Al–4V fretting pads with blending radii at the edges of contact. Fretting fatigue damage for two combinations of static average clamping stress and applied axial stress was investigated for two percentages of total life. Accumulated damage was characterized using full field surface roughness evaluation and scanning electron microscopy (SEM). The effect of fretting fatigue on uniaxial fatigue strength was quantified by interrupting fretting fatigue tests, and conducting uniaxial residual fatigue strength tests at R=0.5 at 300 Hz. Results from the residual fatigue strength tests were correlated with characterization results. While surface roughness measurements, evaluated in terms of asperity height and asperity spacing, reflected changes in the specimen surfaces as a result of fretting fatigue cycling, those changes did not correspond to decreases in residual fatigue strength. Neither means of evaluating surface roughness was able to identify cracks observed during SEM characterization. Residual fatigue strength decreased only in the presence of fretting fatigue cracks with surface lengths of 150 μm or greater, regardless of contact condition or number of applied fretting fatigue cycles. No cracks were observed on specimens tested at the lower stress condition. Threshold stress intensity factors were calculated for cracks identified during SEM characterization. The resulting values were consistent with the threshold identified for naturally initiated cracks that were stress relieved to remove load history effects.

Fracture case studies of industrial structures under corrosion-fatigue loading

At the design stage of engineering structures, the fatigue behaviour is generally not included in the analysis. Shoulder reinforcements may be machined with too small blending radii. Even if fatigue is taken into account, the influence of the environment is almost always ignored. This paper shows that corrosion-fatigue is not an uncommon cause of failure in industry and that it may result in significant damages. The survey of such failures and the observation of the fracture surfaces allow to identify the typical features of this phenomenon.

Effect of sample thickness on local contact behavior in a flat-on-flat fretting fatigue apparatus

Thin plate samples of Ti–6Al–4V contacted on both sides with pads of the same material were used to simulate contact conditions in real structures subjected to fretting fatigue. Laboratory tests on specimens of varying thicknesses were used to determine the stresses that correspond to a fatigue life of 10 7 cycles using a step-loading procedure. For the specific apparatus used in this study, changes in thickness produced changes in the ratio of shear load to clamping load for a specific fretting pad geometry. Specimen thicknesses of 1, 2, and 4 mm, and stress ratios of R=0.1 and 0.5 were investigated for two different contact pad lengths. Fatigue limit stresses in the specimen were found to be relatively insensitive to the average clamping or shear stress. Finite element analyses of the test geometry were used to provide details of the stress distribution in the contact region for the flat-on-flat geometry with blending radius. Results show that stress and displacement fields for a variety of test conditions corresponding to a fatigue life of 10 7 cycles vary widely and do not provide any clear indication of the existence of a simple parameter equivalent to a uniaxial fatigue limit stress. The stress and displacement fields are also shown to be very sensitive to the coefficient of friction used in the analysis.

Aspects of Testpiece Design Responsible for Errors in Cyclic Plasticity Experiments

A uniaxial cyclic plasticity copper testpiece has been simulated, using the Continuum Damage Mechanics based finite element programme Damage XX, under conditions of cyclic plasticity at temperatures of 20°C and 500°C. The results obtained have been compared with the results of experiments carried out under the same conditions. It has been shown that inhomogeneous fields of strain and stress are generated in the gauge length region of the testpiece, which result from standard cyclic plasticity testpiece features, namely, the blend radius linking testpiece shank and gauge length, and the extensometer ridges. The influence of these features on the inhomogeneity is exacerbated by the short gauge length which is necessary in cyclic plasticity testpieces to prevent buckling. At the temperatures of 20°C and 500°C, cracks were predicted to occur, and found experimentally, at the extensometer ridges. Testpiece failure at 20°C occurred outside the gauge length; and at 500°C failure took place from cracks growing within the gauge length region. The formation and growth of the latter gauge length crack was accurately predicted. The results obtained clearly demonstrate the dependence of cyclic plasticity data on testpiece design and suggest that the range of scatter observed experimentally in cyclic plasticity testing for nominally identical testing conditions may result from variations in testpiece design. This is of some concern, and the establishment of a methodology which overcomes these problems will be the subject of a future paper.

Frit salvage innovation of cathode ray tube by initiating to crack along the seal edge

This article describes a thermal stress boundary element analysis which was carried out to select a mechanical device that would innovate the frit salvage of cathode ray tubes (CRT). The panel and funnel of a CRT are fritted at the seal edge. To reuse a CRT, the panel and funnel are separated by etching and then applied a thermal shock. This procedure is known as frit salvage. Current yield of the frit salvage success rate is about 61 %, which means that 39% of the components are lost and cannot be reused. The financial burden can be reduced if the salvage rate is improved through a better understanding of the thermal shock mechanism. During thermal shock, a crack was observed to initiate at the end of the axes and traverses towards the corner along the seal end. A CRT is lost when the crack travels along the diagonal corner. A thermal stress analysis was carried out using the boundary element method. The analysis determined that maximum stresses are located near the blend radius on the panel skirt at approximately 1–2 inches on either side of the diagonal. Also it was found that the stresses along the frit seal edge are uniform from the end of the major and minor axes towards the diagonal. The stresses at the diagonal location were reduced by approximately 29%. The direction and location of the crack obtained by the boundary element anlysis were consistent with those observed in the frit salvage procedure. The crack's promoter along the seal edge is used to protect thermal shock on the outer face panel near the heel radius in order to prevent thermal failure on the diagonal corner. The resultant stresses' directions through the crack's promoter have two holds. The directions of the dominant high stresses at the seal edge through the crack's promoter were changed perpendicular to the seal edge. Therefore, it induces the crack to follow along the seal edge. Secondly, the stresses' directions on a diagonal corner have also been changed to be perpendicular to the seal edge. Consequently, this will prevent the crack along the seal edge from propagating to the diagonal corner, as the crack will advance normally to the maximum principal stress. The crack continues to traverse along the dominant high stress lines at the seal edge as required for a successful frit salvage process. This application is an excellent example of the advantages of using the boundary element method in an industrial setting.

Fatigue Strength of Thick-Walled Cylinders Containing Cross Bores with Blending Features

This paper reports on an investigation into the fatigue strength of thick-walled cylinders that contain a small transverse hole or cross bore in the cylinder wall having either a chamfer or a blending radius at its intersection with the main cylinder bore. Fatigue tests surprisingly show that plain cross-bore cylinders having thickness ratios K = 1.4 and 2.0 have a fatigue life that is marginally greater than comparable cylinders with blending features. A finite element investigation shows that local high stresses are produced on the surface of blending features and these stresses are considerably greater in magnitude than those found in plain cross-bore cylinders. These stress findings are used to explain the experimental fatigue life results obtained.