Cutout Region Research Articles

Analytical Assessment of Composite L Angle Strength Under Internal Fuel Pressure in Composite Wing

The Interspar (IS) box stores the turbine fuel in the composite wing of an Aircraft. The filled fuel is under pressure that induces out-of-plane stresses on all the wing’s structural members around the fuel tank’s boundary. The wing is designed using carbon fiber reinforced plastic (CFRP) with the co-curing of the bottom skin and its stringers along with front and rear spars. A suitable number of cut-outs are made on the top and bottom sides of the IS ribs for the stringer to pass through them. The global finite element analysis showed that the stringer cut-out regions in the IS ribs are highly stressed, as they are subjected to out-of-plane load due to internal fuel pressure, which induces transverse tensile stress in the cut-out region. Resin is the weakest material in the composite laminate, but it has to resist the high-stress component due to out-of-plane loads. The top and bottom flanges of the ‘C’ section IS ribs geometrically form an L angle section with a stringer cut-out made in it. At the L angle location, the IS ribs are critical from both the strength and stiffness point of view. Strength and stiffness at the interface of the fastener joint are essential factors in maintaining the composite wing’s overall structural integrity under internal fuel pressure. The authors adopted the same standalone finite element (FE) modelling approach developed for the Bond Energy Method and carried out appropriate analytical studies to ascertain the safety and structural integrity of the composite wing under internal fuel pressure. This article presents the analytical study carried out on the standalone FE model of an L angle with the stringer cut-out introduced at its appropriate position. The static stress analysis is carried out by enforcing the global displacement on this standalone FE model and extracting three force components in CBAR beam elements representing the resin property in the transverse direction of the composite laminate. The stresses are calculated outside the analysis deck using Excel® spreadsheets. The maximum Normal Stress (σn) in the L angle flange is found to be 13.25 MPa, which is well within the resin or transverse tensile strength of the composite laminate 53 MPa, and the shear stress is found to be 11.10 MPa, which is less than the resin shear strength property of 23 MPa. Hence the study showed that the L angle is safe for carrying internal fuel pressure of 12.5 PSI. The study also showed that the strain and displacement values distribution in the standalone FE model are comparable with that of the global wing box model within the range of (8-10) % and (4-5) % difference, respectively.

CT-VOS: Cutout prediction and tagging for self-supervised video object segmentation

We propose a novel self-supervised Video Object Segmentation (VOS) approach that strives to achieve better visual correspondence across frames and object-background discriminability for accurate object segmentation. Distinct from previous self-supervised VOS methods, our approach is based on a learning loss formulation that takes into account both object and background information to ensure object-background discriminability, rather than using only object appearance. The objective function comprises cutout-based reconstruction (cutout region represents part of a frame, whose pixels are replaced with some constant values) and tag prediction loss terms. The cutout-based reconstruction term utilizes a simple cutout scheme to learn the pixel-wise correspondence between the current and previous frames in order to reconstruct the original current frame with added cutout region in it. The introduced cutout patch guides the model to focus on the reappearance of scene parts , thereby implicitly equipping the model to address occlusion-based scenarios Next, the tag prediction term encourages object-background separability by grouping tags of all pixels in the cutout region that are similar, while separating them from the tags of the rest of the reconstructed pixels. Additionally, we introduce a zoom-in scheme that addresses the problem of small object segmentation by capturing fine structural information at multiple scales. Our proposed approach, termed CT-VOS, achieves state-of-the-art results on two challenging benchmarks: DAVIS-2017 and Youtube-VOS. A detailed ablation showcases the importance of the proposed loss formulation to effectively establish correspondences, object-background discriminability, and the impact of our zoom-in scheme to accurately segment small-sized objects.

Modified Geometry of 106Ru Asymmetric Eye Plaques to Improve Dosimetric Calculations in Ophthalmic Brachytherapy.

Ru/Rh asymmetric plaques for ophthalmic brachytherapy have special geometric designs with a cutout intended to prevent irradiation of critical ocular structures proximal to the tumor. In this work, we present new geometric models for PENELOPE+PenEasy Monte Carlo simulations of these applicators, differing from the vendor-reported geometry, that better match their real geometry to assess their dosimetric impact. Simulation results were benchmarked to experimental dosimetric data from radiochromic film measurements, data provided by the manufacturer in the calibration certificates, and other experimental results published in the literature, obtaining, in all cases, better agreement with the modified geometries. The clinical impact of the new geometric models was evaluated by simulating real clinical cases using patient-specific eye models. The cases calculated using the modified geometries presented higher doses to the critical structures proximal to the cutout region. The modified geometric models presented in this work provide a more accurate representation of the asymmetric plaques, greatly improving the agreement between Monte Carlo calculations and experimental measurements. Lack of consideration of accurate geometric models has been shown to be translated into notable increases in dose to organs at risk in clinical cases.

Matrix-Pencil Approach-Based Interference Mitigation for FMCW Radar Systems

A novel matrix pencil-based interference mitigation approach for FMCW radars is proposed in this paper. The interference-contaminated segment of the beat signal is firstly cut out and then the signal samples in the cut-out region are reconstructed by modeling the beat signal as a sum of complex exponentials and using the matrix pencil method to estimate their parameters. The efficiency of the proposed approach for the interference with different parameters (i.e. interference duration, signal-to-noise ratio (SNR), and different target scenarios) is investigated by means of numerical simulations. The proposed interference mitigation approach is intensively verified on experimental data. Comparisons of the proposed approach with the zeroing and other beat-frequency interpolation techniques are presented. The results indicate the broad applicability and superiority of the proposed approach, especially in low SNR and long interference duration situations.

A Deep-Learning Method for Radar Micro-Doppler Spectrogram Restoration.

Radio frequency interference, which makes it difficult to produce high-quality radar spectrograms, is a major issue for micro-Doppler-based human activity recognition (HAR). In this paper, we propose a deep-learning-based method to detect and cut out the interference in spectrograms. Then, we restore the spectrograms in the cut-out region. First, a fully convolutional neural network (FCN) is employed to detect and remove the interference. Then, a coarse-to-fine generative adversarial network (GAN) is proposed to restore the part of the spectrogram that is affected by the interferences. The simulated motion capture (MOCAP) spectrograms and the measured radar spectrograms with interference are used to verify the proposed method. Experimental results from both qualitative and quantitative perspectives show that the proposed method can mitigate the interference and restore high-quality radar spectrograms. Furthermore, the comparison experiments also demonstrate the efficiency of the proposed approach.

Fatigue behavior of typical details of orthotropic steel bridges in multiaxial stress states using traction structural stress

In this study, the fatigue property of arc-shaped cutout region in orthotropic steel bridge crossbeam in multiaxial stress states is investigated. The analytical equation of traction structural stress method considering normal structural stress and shear structural stress is applied for analyzing multiaxial fatigue of crack initiation. It is found that the arc-shaped cutout in OSB crossbeam is in multiaxial stress states and 9th spot in arc-shaped cutout region under specified loading conditions is evaluated as crack initiation position.

Influence of shape, size and location of cutouts on crashworthiness performance of aluminium conical frusta under quasi-static axial compression

Abstract The influences of different shape, size and number of lateral cutouts at various locations on the load-bearing capacity, buckling behaviour and energy absorption (Eabs) characteristics of aluminium conical frusta under quasi-static axial loading condition were studied from both experimental and numerical procedures. In this regard, 18° semi-apical angled aluminium conical (AC18) frusta were fabricated through the metal spinning process; and circular, square, and trapezoidal shapes of cutouts with required dimensions were introduced at various lateral locations of the frustum. These conical frusta were subjected to quasi-static axial loading at a rate of 2 mm/min using a universal testing machine (UTM), and the corresponding load-deformation characteristics were recorded for axial compression of 50 mm from its original height. In addition to that, similar to experimental studies, Finite Element Analysis (FEA) was performed with conical frusta having various cutouts using ABAQUS® finite element software to study the influence of cutouts on the changes on crashworthiness performance of conical frusta. From both studies, it is observed that the energy absorption capacity of 18° semi-apical angled aluminium conical frusta was found to be decreasing in the range of 3.67%–47.60% according to the shape, size, number and location of cutouts. Further, the load resistance parameters such as first peak load (Pfst), maximum peak load (Pmax) and average load (Pavg) also are found to be decreasing with an increase of cutout size. The change of cutout location from mid-height to three-fourth from the base of the frustum also resulted in a reduction of Eabs capacity, regardless of shape, size and number of cutouts. From these studies, it observed that the energy absorption characteristic of conical frusta having circular cutouts are found to be better than the conical frusta having square and trapezoidal cutouts at same locations. It is also observed that the Eabs capacity of conical frusta having cutouts was found to be non-linearly decreasing with the linear increase in the number, location, shape and size of cutouts. The specimens with a large-size of cutouts had exhibited large deformation over the cutout region that led to an unstable non-linear global buckling during axial compression. Consequently, their Eabs capacity was found to be decreased significantly as compared with the conical frusta with a small size of cutouts. The specimens with the small size of the cutouts exhibited progressive local buckling during axial compression, and they exhibited better energy absorption characteristics as compared with the conical frusta with large size of cutouts.

Stress and damage tolerance analysis of stiffened panel with passenger door cutout in airframe structure using FEA

It is very essential to design the airframe structure with minimum possible weight without compromising on the structural safety. Fuselage has many stress concentration areas. Passenger door cutout region is one among such critical regions. Current work includes stress and damage tolerance analysis of a critical region in the fuselage structure. The structure considered for the analysis includes a stiffened panel with a passenger door cutout and surrounding area with the presence of stiffening members. The present work also includes the damage tolerance analysis of the panel in presence of a crack emanating from the high stress location. The pressurization load case is one of the critical load cases considered for the design of the aircraft structure. The tensile loads at the edge of the panel corresponding to pressurization will be considered for the linear static analysis of the panel. A location of maximum tensile stress and its magnitude will be identified from the stress analysis. Stress intensity factor calculation is carried out for different incremental crack lengths for a crack emanating from the high stress location. Modified virtual crack closure integral method is used for stress intensity factor calculation.

TRAINING TECHNIQUE FOR TOPOLOGICAL STRUCTURES DESIGNING BASED ON A VARIABLE DENSITY BODY MODELS

The article describes the training principles for topological structures designing. The ontology of subject area "The structural load-carrying layout designing" is given. The training technique of automated designing structural layouts using deformed solid body model with variable density is proposed. The educational process is based on creative pedagogy methods and is carried out in the environment of an educational and scientific virtual enterprise. The classification of training assignments for structural layouts designing is presented. Assignments are characterized by a multiplicity of engineering solutions and uncertainty in decision-making by rational structural layout. An example of a training assignment with the spatial design area, showing the aircraft fuselage structural layout designing in cutout region, based on deformed solid body model with variable density is given. The problems of assessment of training results the topological structural designing are considered. The results of the pedagogical experiment, demonstrating efficiency of the proposed training technique, are presented.

FATIGUE LIFE ESTIMATION OF REAR FUSELAGE STRUCTURE OF AN AIRCRAFT

Integrity of the airframe structure is achieved through rigorous design calculations, stress analysis and structural testing. Finite element method (FEM) is widely used for stress analysis of structural components. Each component in the airframe becomes critical based on the load distribution, which in-turn depends on the attitude of the aircraft during flight. Fuselage and wing are the two major components in the airframe structure. The current study includes a portion of the fuselage structure. Empennage is the rear portion of the aircraft, which consists of rear fuselage, Horizontal tail and vertical tail. The air loads acting on the HT also get transferred to rear portion of the fuselage. First step in ensuring the safety of the structure is the identification of critical locations for crack initiation. This can be achieved through detailed stress analysis of the airframe In this project one of the major stress concentration areas in the fuselage is considered for the analysis. Rear fuselage portion with a cargo door cutout region will be analysed. The structure considered for the stress analysis consists of skin, bulkheads and longerons, which are connected to each other through rivets. Aerodynamic load acting on the aircraft components is a distributed load. Depending on the mass distribution of the fuselage structure the inertia forces will vary along the length of the fuselage. The inertia force distribution makes the fuselage to bend about wing axis. During upward bending, bottom portion of the fuselage will experience tensile stress. A cutout region in the tensile stress field will experience high stress due to concentration effect. These high stress regions will be probable fatigue crack initiation locations in the current work, fatigue damage calculation will be carried out to estimate the fatigue life of the structure under the fluctuating loads experienced during flight. Miner’s rule will be adopted for fatigue damage calculation.

Modeling and Experimental Validation of Composite Stiffened Panels under Uniaxial Tension

A finite element model implemented with a progressive damage propagation mechanism was generated to study the mechanical behavior of stiffened composite panels under uniaxial tension. Typical damage modes including fiber breakage, matrix crushing and delamination were considered in the model. Failure criteria with corresponding stiffness degradation technologies was used to predict the initiation and evolution of intra-laminar damage modes by a user-defined subroutine. Cohesive elements with thickness of 0.01mm were defined along the interface areas between the filler and the adjacent laminate layers for predicting the initiation and propagation of delamination. Corresponding tests on composite stiffened panel with a web cut-out were conducted. A good correlation between the numerical results and test data was obtained, which validated the finite element models. Both the numerical and experimental results conclude that the delamination in the flange around the cut-out region is the most critical failure mode for the composite stiffened panel under the uniaxial tensile load.

Finite Element Analysis of Composite Cylinder with Centre Cutout under Axial Load and Internal Pressure

Results from Finite Element (FE) study on the response of composite cylinder shells with cutouts and subjected to internal pressure and axial compression are presented. The objective of the study is to improving the buckling load by applying the internal pressure whilst the compression load is applied. The effect of localized stress concentration distributed around the cutout region also being examined. The numerical results are obtained using ABAQUS finite element code software package. The composite cylinder shells were tested in two conditions which are a combination of axial compression load with internal pressure and a single axial compression load. The effects of varying internal pressure and cutout size on the pre-buckling, buckling, and post-buckling responses of the shell are demonstrated. Reasonable results comparison was obtained by reviewing previous literature. Results indicated that the load distribution and displacement of the cutout significantly influence the structural response of the shell. The results also indicate that the stress distributions can be affected by the size of the cutout under axial compression load.

Modified COMS Plaques for 125I and 103Pd Iris Melanoma Brachytherapy

Novel plaques are used to treat iris melanoma at the Mayo Clinic Rochester. The plaques are a modification of the Collaborative Ocular Melanoma Study (COMS) 22 mm plaque design with a gold alloy backing, outer lip, and silicone polymer insert. An inner lip surrounds a 10 mm diameter cutout region at the plaque center. Plaques span 360°, 270°, and 180° arcs. This article describes dosimetry for these plaques and others used in the treatment of anterior eye melanomas. The EGSnrc user-code BrachyDose is used to perform Monte Carlo simulations. Plaques and seeds are fully modeled. Three-dimensional dose distributions for different plaque models, TG-43 calculations, and (125)I (model 6711) and (103)Pd (model 200) seeds are compared via depth-dose curves, tabulation of doses at points of interest, and isodose contours. Doses at points of interest differ by up to 70% from TG-43 calculations. The inner lip reduces corneal doses. Matching plaque arc length to tumor extent reduces doses to eye regions outside the treatment area. Maintaining the same prescription dose, (103)Pd offers lower doses to critical structures than (125)I, with the exception of the sclera adjacent to the plaque. The Mayo Clinic plaques offer several advantages for anterior eye tumor treatments. Doses to regions outside the treatment area are significantly reduced. Doses differ considerably from TG-43 predictions, illustrating the importance of complete Monte Carlo simulations. Calculations take a few minutes on a single CPU, making BrachyDose sufficiently fast for routine clinical treatment planning.

Globally inconsistent figure/ground relations induced by negative parts

In conventional accounts of figure/ground organization, and in traditional Gestalt theory, figure/ground assignment is assumed to be globally consistent along the entire contour of a figure. If figure and ground reverse at one point on an object boundary, the entire boundary reverses, as in classical bistable figures such as the Rubin face/vase. Here we investigate a situation where local configural cues to figure/ground conflict with global cues: “negative parts.” We constructed displays in which a circular shape included a “bay” or cut-out region. We tested figure/ground interpretation locally by using a moving probe (a region of the contour set in “trembling” motion). We asked subjects which color (the interior or exterior color) seemed to be moving; their response reflects figure/ground assignment, as the motion is perceived to be perceptually owned by the figural side of the boundary. We manipulated the shape and size of the bay, and the position of the probe (inside the bay or elsewhere along the contour). Subjects were significantly more likely to perceive the exterior as figural (that is, to invert the normal figure/ground assignment) when the probe was inside the bay than when it was outside, suggesting that the bay was indeed perceived as a “negative part.” Moreover the shape (convexity) of the bay influenced figure/ground assignment when the probe was inside the bay, but not when it was outside; that is, the figure/ground inversion was local to the negative part itself, resulting in a globally inconsistent figure/ground interpretation. Two followup studies suggest that this phenomenon involved a local inversion of perceived depth, not mere contour ownership. The results suggest that figure/ground interpretation is a dynamic and complex process in which local and global cues combine and compete to produce an ultimate percept that may not be globally consistent.

WE-D-BRB-03: Novel Plaques for Iris Melanoma I-125 and Pd-103 Brachytherapy

Purpose: To calculate three dimensional dose distributions in the eye region for novel plaques used in the treatment of iris melanoma at the Mayo Clinic and compare these with dose distributions for other plaques used in these treatments.Method and Materials: The EGSnrc user‐code BrachyDose is used to perform Monte Carlo simulations. Plaques and seeds are fully modeled. The Mayo Clinic plaques are based on the Collaborative Ocular Melanoma Study (COMS) 22 mm plaque design with a gold alloy backing, outer collimating lip, and silicone polymer insert. An inner collimating lip surrounds a 10 mm diameter cutout region at the plaque center. Plaques span 180, 270, and 360 degree arcs. Three‐dimensional dose distributions in the eye region are calculated and are compared via depth‐dose curves, tabulation of the dose at critical structures (cornea, sclera, lens, macula, optic disk), and isodose contours. Results: The inner lip reduces dose to the cornea and surrounding region by 30–45%. Doses at some points of interest (e.g. cornea) differ by as much as 60–70% compared to those calculated with the TG‐43 protocol. The outer lip collimates radiation and significantly reduces doses to neighboring tissues. Catering plaque arc length to tumor extent reduces doses to the anterior portion of the eye outside the treatment area. For the same prescription dose, Pd‐103 offers a lower dose to critical structures than I‐125, with the exception of the sclera adjacent to the plaque. Conclusion: The Mayo Clinic plaques offer a number of advantages compared to other plaques used in the treatment of anterior eye tumors.Dose is significantly reduced to regions outside the treatment area. Calculations achieving 2% statistical uncertainty on the prescription dose take a few minutes on a single CPU, making BrachyDose sufficiently fast for routine clinical treatment planning.

Progressive damage arrest mechanism in tailored laminated plates with a cutout

This study addresses the effectiveness of a simple stiffness tailoring concept to delay damage initiation, control damage progression, and improve residual strength in tensile-loaded composite plates with a central circular cutout. The tailoring concept is to simply reposit all axially oriented (0°) material into regions near the edge of the plate away from the cutout. This tailoring is done in a way so as not to affect the weight of the plate. This accomplishes several beneficial changes in the way that the plate resists loading with no increases in material cost or weight. Lowering the axial stiffness of the laminate surrounding the cutout lowers the stress concentration. Increasing the axial stiffness near edges of the plate attracts loading away from the vicinity of the cutout to further lower stresses in the critical cutout region. This study focuses on in-plane response including damage progression and residual strength as a function of the degree of tailoring and cutout size. Strength and stiffness properties typical of IM7/8551-7 preperg material were assumed and a modified version of the Hashin failure criteria was used to identify the local damage. Results show that tailoring can significantly increase the damage initiation load and the residual strength. In some cases, observed evidence shows that tailoring performs as a damage arrest mechanism.

Near-tip mode-I elastic fields in bimaterial layered systems

The micromorphic stress fields in the near-tip region of a Mode-I semi-infinite crack embedded in an infinite elastic bimaterial layered system are investigated. The local and global features of the micromorphic stresses in the heterogeneous near-tip domain are captured through an approximate analytical model vis-à-vis a two-dimensional plane strain finite element model. The studies are carried out within a heterogeneous cut-out region surrounding the physical crack-tip wherein alternating matrix and fiber layers are positioned perpendicular to the crack plane. The approximate analytical model is developed by postulating a general form of displacement field that is obtained by the superposition of the applied homogenized near-tip field and a family of kinematically admissible unit-cell micro-displacements. While preserving the aggregate response of the material, these micro-displacements take into account the effects of material micro-structure. The results indicate that the microstress field in the immediate vicinity of the crack-tip exhibits an r−½ singularity when the crack-tip is located entirely within the matrix phase and lies sufficiently away from the adjacent interfaces. The structure of the stress field in the matrix region surrounding the crack-tip corresponds to the universal isotropic field dominated by the tip stress intensity factor. In the farfield region (radial distance greater than one unit-cell thickness), the continuous stress components σxx and σxy are found to be dominated by the orthotropic stress intensity factor and found to be in good agreement with their homogeneous orthotropic counterparts. As expected, the discontinuous stress component σyy is found to exhibit strong dependency on the material heterogeneity. While σyy is dominated by the applied orthotropic stress intensity factor, it is described by a discontinuous spatial eigen-function which has been obtained with the aid of the analytical approximate model. Several parameter studies are presented and implications on the mode-I brittle fracture in layered systems are discussed.