Thin-walled Plates Research Articles

An accelerated convergence approach for real-time deformation compensation in large thin-walled parts machining

Abstract Excessive static deformations often occur during the end-milling of large thin-walled parts, which play an important role in the aerospace industry. The real-time adjustment of axial cutting depth (ACD) is often adopted to compensate deformation errors. Owing to the coupling effect between the ACD and the force induced deformation, the iterative adjustment of ACD is needed. However, it may not converge with the limited adjustment times especially in high-speed machining with large ACD. We hereby propose an approach to speed up the convergence of the ACD iterative adjustment. Firstly, the real-time full compensation process, which is commonly used in the existing real-time compensation methods, is mathematically analyzed and proved to be only first-order convergent. Then, an approach based on the secant method, which provides a higher order of convergence, is developed and introduced into the real-time compensation process for large thin-walled plate machining. Finally, the superiority and effectiveness of the proposed approach are demonstrated through an ACD iterative adjustment simulation and an experiment of cutting square pockets.

High-Quality Machining of Edges of Thin-Walled Plates by Tilt Side Milling Based on an Analytical Force-Based Model

The milling of thin-walled workpieces is a common process in many industries. However, the machining defects are easy to occur due to the vibration and/or deformation induced by the poor stiffness of the thin structures, particularly when side milling the edges of plates. To this problem, an attempt by inclining the tool to a proper tilt angle in milling the edges of plates was proposed in this paper, in order to decrease the cutting force component along the direction of the lowest stiffness of the plates, and therefore to mitigate the machining vibration and improve the machined surface quality effectively. First, the milling force model in consideration of the undeformed chip thickness and the tool-workpiece engagement (TWE) was introduced in detail. Then, a new analytical assessment model based on the precisely established cutting force model was developed so as to obtain the optimum tool tilt angle for the minimum force-induced defects after the operation. Finally, the reliability and correctness of the theoretical force model and the proposed assessment model were validated by experiments. The methodology in this paper could provide practical guidance for achieving high-quality machined surface in the milling operation of thin-walled workpieces.

Investigation on the vibration and machined surface quality in tilt side milling of thin-walled plates

Tilting milling tools to proper angles could help significantly suppress machining vibrations and enhance machined surface quality. The aim of this study is to investigate how the two fundamental variables, tool helix angle (β) and tilt angle (θ), could influence milling vibrations and machined surface topography when milling sidewall surfaces of thin-walled plates with solid end mills. A series of side milling tests were carried out at different tilt angles utilizing tools with different helix angles, during which the accelerations, instantaneous vibration displacements, cutting forces, machined surface roughness, and topographies of the workpiece were carefully measured. The results showed that the minimum machined surface roughness across the measured surface, Ra, was 0.37 μm when β = 40° and θ = 30°. In addition, optimal tilt angles for the lowest Ra on the machined surface with tools of different helix angles are in accordance with the optimal angles for the minimum absolute value of Z-axis force Fz, rather than ones for the weakest vibrations. This result indicates that, when milling sidewall surfaces of thin-walled plates, Ra is more highly dependent on the cutting force component along the lowest stiffness direction of plates than the vibration amplitudes. The results presented in this paper are useful insights for milling process parameter optimization to improve machined surface quality in milling sidewall surfaces of thin-walled components.

Equivalent model of close-packed film cooling holes in nickel-based single crystal cooled blade based on crystallographic theory

The mechanical properties of nickel-based single crystal thin-walled plate with close-packed film cooling holes were studied based on the equivalent solid material concept. The effective plastic parameters inversion method based on crystallographic theory were proposed. A simplification method for close-packed film cooling hole plates with square and triangular penetration patterns was presented. A large number of finite element analysis results covering different ligament efficiencies and penetration patterns were provided to verify the feasibility of the plastic equivalent principle and simplification method. The results show that the stress–strain curve and resolved shear stresses of simplification models are in consistence with the plate models with close-packed film cooling holes. The equivalent errors of yield strength are all within the error band and the values of equivalent errors are all less than 10%. In addition, the equivalent errors of the positions where maximum resolved shear stress occurs are all less than 15°, indicating the accuracy of plastic equivalent model and simplification method.

Enhanced impact strength of injection-compression molded parts by controlling residual stress distribution

The objective of this study is to elucidate the relation between the results of ball drop tests and the residual stress distribution of an injection-compression molded part. To improve the ball drop property, a high impact material and a robust manufacturing process were employed. For the application to the transparent plastic window, it is of great importance to increase the impact strength of plastic products. Thin-walled plates were molded with use of rubber nanoparticles embedded poly(methyl methacrylate) (PMMA). Different compression gaps were considered during injection-compression molding (ICM) to adjust the residual stress distribution developed in the specimens. The ball drop tests were carried out to evaluate the impact strength of the prepared samples. In addition, the ICM was numerically simulated to predict the residual stress distribution in the parts.

Study of buckling stability of cracked plates under uniaxial compression using singular FEM

Buckling is one of the major causes of failure in thin-walled plate members and the presence of cracks with different lengths and locations in such structures may adversely affect this phenomenon. This study focuses on the buckling stability assessment of centrally and non-centrally cracked plates with small-, intermediate-, and large-size cracks, and different aspect ratios as well as support conditions, subjected to uniaxial compression. To this end, numerical models of the cracked plates were created through singular finite element method using a computational code developed in MATLAB. Eigen-buckling analyses were also performed to study the stability behavior of the plates. The numerical results and findings of this research demonstrate the effectiveness of the crack length and location on the buckling capacity of thin plates; however, the degree of efficacy of these parameters in plates with various aspect ratios and support conditions is found to be significantly different. Overall, careful consideration of the aspect ratio, support conditions, and crack parameters in buckling analysis of plates is crucial for efficient stability design and successful application of such thin-walled members.

Research on Rigid-flexible Coupling Dynamics of Flexible Cone-probe Docking Mechanism

In this paper,a new kind of flexible cone composed of the thin-walled plates based on space probe-cone docking mechanism for small-sized spacecraft is presented.The theoretical model of docking impact dynamics,which takes into account the additional stiffness terms,is derived based on Lagrange Analytical Mechanics theory and Hertz contact theory.Finite element method is employed for the discretization of the thin-walled plate.The results show that the traditional dynamic model without considering the additional stiffness terms will be difficult to reach steady state.The method proposed in this paper can correctly predict the dynamic behavior of the system.

Stiffening material impact on the work of thin-walled element

The subject of research is a numerical analysis of a thin-walled plate with a cut-out and stiffening, made of laminate and subjected to axial compression. The plate was made of a carbon-epoxy composite - a laminate consisting of eight symmetrically oriented plies. The scope of the research included a linear and nonlinear numerical analysis using Finite Element Method (FEM). The main objective of the study was to investigate behaviour of the considered plate made of various stiffening materials, under quasi-static compression to achieve Tsai-Wu criterion. The numerical analysis was conducted with the Abaqus, commercial FEM software package.

Vibrodiagnostic of Welded Thin-Walled Plates with the Usage of Laser Sensors in Network Infrastructure

Vibrodiagnostic of Welded Thin-Walled Plates with the Usage of Laser Sensors in Network Infrastructure

Transient wave propagation in Cosserat-type shells

The aim of this paper is to find the magnitudes of velocities of transient waves which could be originated and propagate in thin shells made of Cosserate-type material in the form of surfaces of strong and weak discontinuity. Thus, starting from the 3D Cosserat continuum, the velocities of four transient waves propagating in a thin shell with micro-structure have been determined according to a wave theory for thin-walled plates and shells proposed recently by the authors. Using the expansion ray theory and conditions of compatibility for thin-walled structures, it has been found that (1) the velocities depend only on material constants, and (2) only one micropolar modulus α, which governs the asymmetry of the stress tensor, influences the velocity of the quasi-shear wave, while the Láme moduli λ and μ do not affect the velocities of Cosserat waves, which are generated due to micropolar rotations. This results to the fact that the mathematical theory due to Cosserat is not coupled one. The knowledge of the velocities of transient waves in thin shells made of Cosserat-type materials will allow one to solve boundary-value transient dynamic problems resulting in the propagation of surfaces of strong and weak discontinuity.

The response of laminated composite plates and profiles under low-velocity impact load

The effect of impact load with low velocity in thin-walled plates and profiles has been investigated. The paper deals with the relation between damage propagation, size and shape as a function of boundary conditions, layer arrangements and impact energy. The structures under consideration were made of eight-layer Glass Fiber Reinforced Polymer (GFRP) laminate with a quasi-isotropic, quasi-orthotropic and angle ply arrangement of layers. The standardised plates predefined to CAI tests and channel section profiles have been subjected to impact load. Based on the performed tests, the impact characteristics have been obtained and compared with the theoretical model (one degree of freedom mass-spring system). Further, despite it not being mentioned in the ASTM 7136 standard, characteristic curves were identified. It was noted that the impacts introducing matrix damages and the partial fracture of the fibres significantly change the course of the Force-Time histories, particularly after the maximum impact force is reached.

Equivalent and simplification of nickel-based single crystal plates with film cooling holes

The mechanical properties of orthotropic material thin-walled plate with close-packed film cooling holes were studied based on the equivalent solid material concept. The equivalent principals of plane stress conditions, plane strain conditions, generalized plane strain conditions and general stress conditions were considered. A simplification method for square and triangular penetration patterns was presented. Extensive numerical simulation results covering different ligament efficiencies, penetration patterns and stress conditions were provided for the directionally solidified superalloy and nickel-based single crystal superalloy to verify the feasibility of equivalent principals and simplification method. Three crystal orientations [001], [011] and [111] of nickel-based single crystal superalloy were analyzed. The stress concentration factors were obtained for the mechanical behavior analysis of cooled blade. The values of equivalent error are all less than 10% when the ligament efficiency is larger than 0.4. The tensile deformation, Mises equivalent stress and stress distribution under the same stress level show the crystal orientation correlation. The tensile deformation of three crystal orientations is: [001] > [011] > [111]. The maximum Mises equivalent stress of [001] orientation and [011] orientation around the film cooling hole are basically the same, and they are all less than [111] orientation. The maximum and minimum values of stress concentration factors are 3.49 and 1.82 respectively.

Equivalent and Simplification of Nickel-Based Superalloy Plates with Close-Packed Film Cooling Holes

ABSTRACTThe mechanical properties of thin-walled plate with close-packed film cooling holes are studied based on the equivalent solid material concept. The equivalent principals of the method of equivalent strain energy, homogenization theory and uniform static deformation are considered. A simplification method of square penetration pattern for pitch and diagonal direction loading is presented. The goodness of fit is calculated to determine the optimal method. The tensile deformation, bending deflection, rotation displacement and maximum Mises equivalent stress of simplification plate models are in good agreement with plate models with close-packed film cooling holes. For square penetration pattern for pitch direction loading, the equivalent errors of Mises equivalent stress are all less than 10% when the ligament efficiency is more than 0.6.

THE MORPHOLOGY FEATURES OF NANOSTRUCTURE OF ZIRCONIUM, MOLYBDENUM AND WOLFRAM OXIDES SYNTHESISED BY LASER ABLATION OF METALS IN WATER

The paper gives the investigation results of composition and morphology of oxide nanostructures of transition metals – zirconium, molybdenum and wolfram synthesized by laser ablation pure metals in water. High temperatures and pressures in zone of interaction of the pulse laser beam with the surface of metal in water contribute to the intensive synthesis of oxides in the form of clusters of particles with size about 1−2 nanometres. This is characteristic for metals with high ionization potential. As it follows from the data of X-ray diffraction analysis and scanning electron microscopy, specifically, the clusters are amorphous building material for nanostructures of the oxides of the metals enumerated above. The paper demonstrates the general pattern of their structure, namely, the stratification of the material from which the foam formations, thin-walled hollow round particles, plates, filaments, and other forms of nanostructures are composed. The research of morphological features of the nanostructures of zirconium, molybdenum and wolfram oxides obtained by the authors indicates that their use as substrates will achieve high gain values of Raman scattering ~ 10 4 −10 8 . In this range, there are the gain data previously obtained by the authors in the experiments on the synthesis of zirconium nano-oxides when using them as a substrate. This indicates that the nanostructures of molybdenum and wolfram nano-oxides also can serve as the effective substrates and can be used as a sensor in the high sensitive composition of substances analyzers based on surface enhanced Raman scattering.

Replicability of Ultrasonic Molding for Processing Thin-Wall Polystyrene Plates with a Microchannel.

Ultrasonic molding is a new technology for processing small and micro polymeric components with reasonable cost and energy savings when small and medium batch sizes are required. However, when microcomponents are manufactured, the replicability of different micro features has to be guaranteed. The aim is to investigate the capability of ultrasonic molding technology for processing thin-wall plates of polystyrene with a microchannel, analyzing the filling behavior, the optical transparency, and the dimensional accuracy of the thin plate. The replicability of the manufactured microchannel is studied according to dimension and shape. The results reveal that plunger velocity influences transparency and filling cavity, whereas the vibration amplitude has less effect in both cases. The thickness deviation achieved on the final part is below 7% and the replication of the microchannel is better in depth than width, obtaining an average deviation of 4% and 11%, respectively. This replication also depends on the orientation of the microchannels and the distance from the injection gate. The replicability and repeatability for processing thin-wall plates with microchannel in polystyrene polymer are proved in this paper.

Energy absorption performance of thin-walled metal plate due to upheaval deformation based on experiments and numerical simulation

To explore an energy-absorbing device satisfying the crashworthy requirements of railway vehicles, a new type energy-absorbing structure (EAS) was developed according to the energy-absorbing mechanism of a thin-walled metal plate subjected to plastic upheaval deformation. Quasi-static tests were performed on rectangular and U-shaped thin-walled plates to validate the feasibility of the proposed EAS. Additionally, the numerical simulation test was conducted to investigate the influences of the spacing between pressure plates, punching parameters and the thickness of thin-walled plates on the energy-absorbing properties of the proposed structure. The results showed that the structure had favourable repeatability in compression and the deformation of thin-walled plates was shown to be regular and controllable. In the whole compression stage, the force effects exceeded 70% with no peak being found. In the first stage, the force rapidly increased with the growth of height of the upheavals on the thin-walled plates; in the second stage, the force slowly rose when the increase in the height of the upheavals was ceased in which the mean forces in two groups of tests were both about 12 kN. The energy-dissipation forms of the structure appeared as two types: energy dissipation induced by plastic deformation of thin-walled plates and that caused by friction between the thin-walled plates and the punch.Increasing the height of the punch and the thickness of the plates cannot significantly improve the energy absorption of the structures. Additionally, decreasing the spacing between pressure plates and enlarging the width of the punch also can increase the amount of energy absorbed. After decreasing the inclination angle of the punch, there was a lag in the change of force.

Study of random fatigue behavior of C/SiC composite thin-wall plates

As an alternative method of acoustic experiment, vibration tests of C/SiC thin-wall plates were conducted to study the random fatigue behavior. The vibration specimen was clamped with cantilever boundary and subjected to limited-bandwidth vibration excitation. The strain history and fundamental frequency of the specimens were monitored during the vibration test. It was found that the measured strain value and strain amplitude value accorded with Gauss and Rayleigh distribution, respectively. The fundamental frequency decreased greatly when the vibration specimen failed, which could be recognized as failure criterion for the specimen under random loading. The microscopic fracture morphologies showed that the majority failure mode of fibers in the longitudinal and transverse directions were fiber pull-out and fiber splitting, respectively. The tensile force induced by reversed bending load is the main driving force for damage in specimen.

Prediction method for creep life of thin-wall specimen with film cooling holes in Ni-based single-crystal superalloy

Considering the effects of numbers and drill processes of film cooling holes, the effect of a multiaxial stress state on the creep behavior of Ni-based single-crystal superalloy was investigated. The thin-wall plate specimens with film cooling holes, including multiholes and a single central hole, have been designed. The drilling processes are electro stream machining (ESM), electrical discharge machining (EDM) and laser drilling (LD). The results show that creep lives were longer in the thin-wall specimens with a single central hole and shorter in specimens with multi-holes due to the multihole interference effect. Under the same stress and temperature, the specimens with multiholes using the LD process have the longest creep lives compared with the other two processes. To predict the creep life of a specimen with film cooling holes, a creep damage constitutive model under the crystal plasticity framework was proposed by adding geometric structure variables β and m. Coupling with the modified skeletal point stress method (SPSM), the creep rupture lives of the specimens with film cooling holes were well predicted. The error of creep life between the finite element (FE) calculation and experimental results is within 28.03%.

Non-linear stability and load-carrying capacity of thin-walled laminated columns in aspects of coupled buckling and coupled stiffness submatrix

To assess a load-carrying capacity of compressed thin-walled plate structures in the paper the coupling buckling phenomenon of compressed columns was analyzed. The columns were of open cross-sections and made of coupled laminate. Selected configuration of laminate layers enables different types of coupling between membrane and bending states which describes the coupling stiffness submatrix B. Element values of stiffness matrix ABD were determined with application of classical laminate plate theory CLPT.The main aim of the work is to estimate an influence of chosen submatrix B elements on buckling, postbuckling and load-carrying capacity of analyzed thin-walled structures. The problem was solved with the Koiter’s theory application. The detailed computations were performed for uniformly compressed lip channel and top hat channel. The dimensions of both columns were chosen in a way which allowed to observe the strong coupling effect among different buckling modes. It were two laminate configurations considered which differed in value of stiffness reduction coefficients.

Effects of tool helix angles on machined surface morphology in tilt side milling of cantilever thin-walled plates

For milling the side wall surfaces of cantilever thin-walled plates, to tilt the tool to a proper angle could decrease the cutting force component in the direction of the lowest stiffness of the plates, and then mitigate the chatter, resulting in the improvement of the machined surface finish. The tool helix angle and tilt angle are the two major variables determining the cutting force component, accordingly having significant effects on the machined surface morphology. In this paper, these effects are investigated through experiments with solid end mills of different helix angles.With the surface roughness Ra as the quantification assessment parameter for machined surface morphologies, variations of surface morphologies not only with the tool tilt angles but also with the tool helix angles are investigated. The mathematical model expressing the relation between the tool helix angle and the corresponding optimal tilt angle is built when the quality of the machined surfaces is the best. For better understanding the effects of these two variables on the dynamic vibrations of the workpiecethat directly contributes to the formation of surface morphologies, especially chatter marks, the instantaneous vibration displacements of plates during the milling process are also measured by a laser range sensor, and the effects on the surface roughness are analyzed. This study could provide guidance for process parameters optimization in milling the sidewall surfaces of thin-walled components.