Large Cutouts Research Articles

Enhanced Fatigue Crack Detection in Complex Structure with Large Cutout Using Nonlinear Lamb Wave.

The large cutout structure is a key component in the bottom skin of an airplane wing, and is susceptible to developing fatigue cracks under service loads. Early fatigue crack detection is crucial to ensure structural safety and reduce maintenance costs. Nonlinear Lamb wave techniques show significant potential in microcrack monitoring. However, nonlinear components are often relatively weak. In addition, a large cutout structure introduces complex boundary conditions for Lamb wave propagation, making nonlinear Lamb wave monitoring more challenging. This article proposes an integrated data processing method, combining phase inversion with continuous wavelet transform (CWT) to enhance crack detection in complex structures, with phase-velocity desynchronization adopted to suppress the material nonlinearity. Experiments on a large cutout aluminum alloy plate with thickness variations were conducted to validate the proposed method, and the results demonstrated its effectiveness in detecting fatigue cracks. Furthermore, this study found that nonlinear components are more effective than linear components in monitoring closed cracks.

Evaluation of cutout factors with small and narrow fields using various dosimetry detectors in electron beam keloid radiotherapy.

The inherent problems in the existence of electron equilibrium and steep dose fall-off pose difficulties for small- and narrow-field dosimetry. To investigate the cutout factors for keloid electron radiotherapy using various dosimetry detectors for small and narrow fields. The measurements were performed in a solid water phantom with nine different cutout shapes. Five dosimetry detectors were used in the study: pinpoint 3D ionization chamber, Farmer chamber, semiflex chamber, Classic Markus parallel plate chamber, and EBT3 film. The results demonstrated good agreement between the semiflex and pinpoint chambers. Furthermore, there was no difference between the Farmer and pinpoint chambers for large cutouts. For the EBT3 film, half of the cases had differences greater than 1%, and the maximum discrepancy compared with the reference chamber was greater than 2% for the narrow field. The parallel plate, semiflex chamber and EBT3 film are suitable dosimeters that are comparable with pinpoint 3D chambers in small and narrow electron fields. Notably, a semiflex chamber could be an alternative option to a pinpoint 3D chamber for cutout widths≥3 cm. It is very important to perform patient-specific cutout factor calibration with an appropriate dosimeter for keloid radiotherapy.

On-line Updated Guided Wave-Based Gaussian Process Method for Damage Evaluation of Aircraft Structure

Accurate damage evaluation for an aircraft by using guided wave-based structural health monitoring (SHM) technology is in critical demand. An aircraft experiences various uncertainties during its service life, such as the time-varying environment, operational conditions, and different flight missions. Additionally, the actual aircraft structure involves complex structural forms such as varied thickness, stiffeners, ribs, and large cutouts, leading to a strong uncertainty of damage initiation and propagation. Consequently, when applied to an individual aircraft structure, the diagnosis model trained by prior data inevitably introduces errors, and the errors accumulate as the damage propagates, which brings challenges in engineering application. To achieve individual aircraft structure’s more accurate damage evaluation, an on-line updated guided wave-based Gaussian process (GP) damage evaluation method is investigated in this paper. Multi-source data from the design, service, and maintenance stages are utilized to continuously update and evolve the GP model, enabling its accurate evaluation throughout the long-term service life.

Analysis of the results adequacy of the fuselage finite-element modeling in the vicinity of a large cutout

The issues of ensuring the reliability of the finite element models (FEM) of the fuselage in the hatch cutout zone are considered at the early aircraft design stages. The purpose and tasks of research are formulated. To assess the reliability of mathematical models, the objects with standards were selected. The methods of experimental research and measuring instruments are discussed. The results of a comparative analysis of the numerical experiment with analytical solutions and full-size experiments data are presented. For the validation of FEM structures, the checkable characteristics and types of their verification are determined. The results of this research contain a discussion of the impact of finite element mesh details on a stress concentration factor, an adequacy of modeling the stress and strain field in the vicinity of the cutout and taking into account a nonlinearity in strength calculations of structures with stress concentration. This paper focuses on the analysis of modeling a framed cylindrical shell with a large rectangular cutout, for which full-size tests were conducted by TSAGI researchers. Strains of strong frames, limiting the cutout in a cylindrical shell, shearing and equivalent stress in the skin, normal stresses in stringers at the intersection with the strong frame, displacements of strong frames cross-sections at test points are analyzed. Based on the results of this research, the recommendations for modeling thin-walled fuselage structures in the vicinity of a large cutout, ensuring the performance of calculations with engineering accuracy were formulated.

Stress Analysis of Fuselage Stiffened Panel with and Without A Door Cutout

Aircraft is a complex engineering structure. The safety of the structure and the weight of the structure are the two important aspects to be kept in mind while designing the aircraft structure. It is an uphill task for an aircraft structural designer to bring out a safest structure with minimum weight. The current project deals with the stress analysis of the fuselage-stiffened panel with and without a large cutout for an emergency exit door. Cabin pressurization load case, which is one of the critical load cases used for the stress analysis. When the aircraft is flying above 40000 ft. altitude pressure is applied to fuselage inside cabin to create sea level atmospheric pressure . Stress analysis of the fuselage segment will be carried out to capture the global response of the fuselage under pressurization. A skin panel with fuselage frame and stringers representing the fuselage features will be considered for the local analysis to capture global response. An emergency exit door cutout will be introduced in the stiffened panel and analyzed for stress distribution around the cutout. Stress concentration factor and variation of stress from cutout edge towards the free edge of the panel will be obtained from the stress analysis results. Key Words: Transport aircraft, Fuselage, Bulkhead, Orthogonal stiffening, Finite element method, stress analysis, emergency exit door cutout, Stress concentration factor

Mode shape modification of irregular design of buildings

Earthquakes are the most unpredictable and devastating of all natural disasters. In view of the extensive damage it can cause, it is very much necessary to understand the seismic response of buildings under various conditions. One such situation is buildings with plan irregularity, and poses a challenge to structural engineers because of the damage it can cause. These torsional irregular buildings are subjected to large rotations about the vertical axis due to the eccentricity between centre of mass and with centre of rigidity. Table 5 of IS 1893(Part-1):2016 mentions re-entrant corners, large cut outs in the slabs, non-parallel lateral force system are some of the causes of torsional irregularity. These buildings will have torsional mode as the fundamental mode and will be subjected to extensive damage during seismic activity. In situations where the irregular shape is inevitable because of architectural and functional demands, the structural engineer has to find means to transform the fundamental mode shape from torsional mode to translational mode. Adding structural walls, bracings at the appropriate locations are a few of the viable solutions. In the present study, an attempt is made to investigate the appropriate location and geometry of structural walls for few torsional irregular buildings. Three-dimensional dynamic analysis (Response Spectrum Method) of 15 storied L and C- shape buildings is carried out as per IS 1893 (part 1) using ETABS. Response quantities like Time Periods, Base Shear, Storey Moments, Modal Participation factors, Joint displacements, Storey Drifts are evaluated. A comparative study is made to arrive at the optimum location of shear walls with minimum torsion displacement and where translational mode becomes the fundamental mode.

A Nested Eight-Channel Transmit Array With Open-Face Concept for Human Brain Imaging at 7 Tesla

Purpose: Parallel transmit technology for MRI at 7 tesla will significantly benefit from high performance transmit arrays that offer high transmit efficiency and low mutual coupling between the individual array elements. A novel dual-mode transmit array with nested array elements has been developed to support imaging the human brain in both the single-channel (sTx) and parallel-transmit (pTx) excitation modes of a 7 tesla MRI scanner. In this work, the design, implementation, validation, specific absorption rate (SAR) management, and performance of the head coil is presented.Methods: The transmit array consisted of a nested arrangement to improve decoupling between the second-neighboring elements. Two large cut-outs were introduced in the RF shield for an open-face design to reduce claustrophobia and to allow patient monitoring. A hardware interface allows the coil to be used in both the sTx and pTx modes. SAR monitoring is done with virtual observation points (VOP) derived from human body models. The transmit efficiency and coverage is compared with the commercial single-channel and parallel-transmit head coils.Results: Decoupling inductors between the second-neighboring coil elements reduced the coupling to less than −20 dB. Local SAR estimates from the electromagnetic (EM) simulations were always less than the EM-based VOPs, which in turn were always less than scanner predictions and measurements for static and dynamic pTx waveforms. In sTx mode, we demonstrate improved coverage of the brain compared to the commercial sTx coil. The transmit efficiency is within 10% of the commercial pTx coil despite the two large cut-outs in the RF shield. In pTx mode, improved signal homogeneity was shown when the Universal Pulse was used for acquisition in vivo.Conclusion: A novel head coil which includes a nested eight-channel transmit array has been presented. The large cut-outs improve patient monitoring and reduce claustrophobia. For pTx mode, the EM simulation and VOP-based SAR management provided greater flexibility to apply pTx methods without the limitations of SAR constraints. For scanning in vivo, the coil was shown to provide an improved coverage in sTx mode compared to a standard commercial head coil.

Buckling of axially compressed composite cylinders with geometric imperfections

Cylindrical shell structures buckle at service loads which are much lower than their associated theoretical buckling loads. The main source of this discrepancy is the presence of various imperfections which are created on the cylinder body during different processes as manufacturing, handling, assembling and machining. Many cylindrical shell structures are still designed against buckling based on the experimental data introduced by NASA SP-8007 as conservative lower bound curves. This study employed the numerical based Linear Buckling mode shape Imperfection (LBMI) method and modified it using a stochastic method to assess the effect of geometrical imperfections in more details on the buckling of cylindrical shells with and without the cutout. The comparison of results with those obtained from the numerical Simcple Perturbation Load Imperfection (SPLI) method for cylinders with and without cutout revealed a good correlation. The effect of two parameters of size and number of cutouts on the buckling load was investigated using the linear buckling and Modified LBMI methods. Results confirmed that in cylinders with a small cutout inserting geometrical imperfection using either SPLI or modified LBMI methods significantly reduced the value of the predicted buckling load. However, in cylinders with larger cutouts, the effect of the cutout is dominant, thus considering geometrical imperfection had a minor effect on the buckling loads predicted by both SPLI and modified LBMI methods. Furthermore, the modified LBMI method was employed to evaluate the combination effect of cutout numbers and size on the buckling load. It is shown that in small cutouts, an increasing in the cutout size up to a certain value resulted in a remarkable reduction of the buckling load, and beyond that limit, the buckling loads were constant against D/R ratios. In addition, the cutout number shows a more significant effect on decreasing the buckling load at small D/R ratios than large D/R ratios.

Design, manufacturing and testing of a fibre steered panel with a large cut-out

Variable stiffness composites, where fibre angles are spatially varied by steering the tows in curvilinear paths to optimise the structural response, have been a subject of intensive study. In this paper, experimental validation of the variable stiffness composite technology is carried out for a panel representing a wing lower-skin with a large access hole designed against material failure. An idealised flat panel with a large cut-out under tension or combined tension and shear is modeled using finite elements. In addition to a quasi-isotropic laminate, constant stiffness and variable stiffness laminates are designed to maximise the failure load using a multi-step optimisation framework. Three panels, one for each type of laminate, are built from thermoset prepreg material using automated fibre placement. All three panels are tested in pure tension. The failure loads, failure modes and weights of the tested panels are compared. The results indicate that the variable stiffness laminate is capable of sustaining significantly larger loads, before failure, than the constant stiffness and quasi-isotropic laminates of equal weight.

The Application of Biomimetic Lightweight Sandwich Panel to the Aircraft Structure with Large Cutout and Its Optimum Design

The Application of Biomimetic Lightweight Sandwich Panel to the Aircraft Structure with Large Cutout and Its Optimum Design

Deformation of Perforated Aluminium Plates under In-Plane Compressive Loading

Aluminium plates containing a single hole or multiple holes in a row are recently becoming very popular among architects and consultant engineers in many constructional applications, due to their reduced weight, as well as facilitating ventilation and light penetration of the buildings. However, there are still uncertainties concerning their structural behaviour, preventing them from wider utilization. In the present paper, local buckling phenomenon of perforated aluminium plates has been studied using the finite element method. For the purposes of the research work, plates with simply supported edges in the out-of-plane direction and subjected to uniaxial compression are examined. In view of perforations, circular cut-outs and the total cut-out size has been varied between 5 and 40% of the total plate area. Moreover, different perforation patterns have been investigated, from a single, central cut-out to a more refined pattern consisting of up to 25 holes equally distributed over the plate. Regarding the material characteristics, several aluminium alloys are considered and compared to steel grade A36 on plates of different slenderness. For each case the critical (Euler) buckling load and the ultimate resistance has been determined.A study into the boundary conditions of the plate showed that the restrictions at the edges parallel to the load direction have a large influence on the critical buckling load. Restraining the top or bottom edge does not significantly influence the resistance of the plate.The results showed that the ultimate resistance of aluminium plates containing multiple holes occurs at considerably larger out-of-plane displacement as that of full plates. For very large total cut-out, a plate containing a central hole has a larger resistance than a plate with equal cut-out percentage but with multiple holes. The strength and deformation in the post-critical regime, i.e. the difference between the critical buckling load and the ultimate resistance, differs significantly for different number of holes and cut-out percentage.

Review: Electronic Superhighway (2016–1966)

Electronic Superhighway (2016-1966) WHITECHAPEL GALLERY LONDON JANUARY 29-MAY 15, 2016 There is no escaping the gargantuan pair of women's buttocks greeting the visitor entering Electronic Superhighway (2016-1966). With a series of speech bubbles emerging from deep within, Olaf Breuning's wall-scale photograph Text Butt (2015) places onto the naked female body a fragmented smartphone conversation made up of unrelated questions and nonsensical replies, in which she is quite literally speaking out of her ass. Introducing the theme of the body's changing relationship to technology that curator Omar Kholeif described as the starting point of the show's exploration of art and the internet, this is just one of the (exclusively) female bodies chosen to map this connection. To the left sits Katja Novitskova's Innate Disposition 2 (2012), a large cutout print of a small furry animal, nestled in a pair of manicured women's hands. To the right, in James Bridle's Homo Sacer (2014), a projected holographic image of a smiling woman hovers behind a wooden desk. Reminiscent of the kind of hologram appearing in bureaucratic spaces such as airports and government buildings to provide depersonalized instructions, she is a virtual receptionist who flickers into life as each gallery-goer walks through the door. Quoting decontextualized extracts from various nations' citizenship legislation, her singsong intonation welcomes us in, at the same time drawing our attention to the ways in which our sense of belonging is fragile and might be revoked. It is not clear whether the gendered nature of this opening display was intentional or an unthinking coincidence, but it places the image of woman in interesting relation to the technology at the heart of the exhibition--as naked, sexualized body parts to be penetrated and overcome, or as a kind of gatekeeper, a guardian of the secrets that follow in all their noisy, brazen, and in places, trashy glory. Including over one hundred works by seventy artists, Electronic Superhighway takes us back through time, posing the question: How has the internet changed art? Broad in scope, the curated response encompasses a variety of media and approaches, from the latest social media platforms, net.art, and computer-generated drawing, to traditional oil painting, photography, sculpture, film, and video. It covers many thematic bases: appropriation and remediation, authenticity and digital manipulation, technology and identity, the deconstruction of modernist paradigms and traditions, surveillance, and resistant forms of political agency. It was perhaps unavoidable that many are treated with a light touch, and in the crowded spaces of the large ground floor galleries of contemporary work, the flashing colors and glaring screens create an experience that at times feels like a rapid frog-march through its various themes. There is a lot to see. Covering the ever-evolving platforms in which we engage with the internet today, all the way back to the pre-internet era in which the earliest digital stirrings presented an exciting prospect to artists of the 1960s, there is no shared artistic approach. But the fluctuating and often uncomfortable relationship that emerges as the human body adopts, incorporates, and at times resists technology is an enduring theme throughout. [ILLUSTRATION OMITTED] It's about the internet, so there's a lot of sex. As part of his examination of its role in the negotiation of contemporary masculinity, Egyptian artist Mahmoud Khaled's series Do You Have Work Tomorrow? (2012) stages a Grindr conversation between two men. Presenting a fictional narrative as a series of thirty-two prints of iPhone screen shots, the banality of the dialogue draws attention to technology's everyday mediation of sexuality, despite the background turmoil of the Arab Spring suggested by the conversation's date. A similar relationship between social media and sexuality is explored in Celia Hempton's portraits of men encountered in chat rooms--albeit in a wholly different format. …

English

English

Effect of in-plane boundary conditions on elastic buckling behavior of solid and perforated plates

In this work, finite element method is used to obtain elastic buckling loads and mode shapes of plates. The effect of four different in-plane boundary conditions on the elastic buckling load of simply supported plates subjected to in-plane uni-axial compressive loading is studied. Elastic buckling behavior of plates with cut-outs (circular and square with curved corners) is also studied to illustrate the effect of the size, shape and the eccentricity of the cut-out on buckling loads. Results of the study show that the in-plane boundary conditions affect the elastic buckling behavior of the plate to a significant extent. Aspect ratio influences both the mode shape and the elastic buckling load for perforated plates, whereas its influence is generally limited to mode shape only in case of a solid plate. Restraints on the in-plane movements of plate׳s unloaded edges have different influence on the elastic buckling behavior of the plate when the position of cut-out is changed along the x-axis (loading direction) and along the y-axis (normal to loading direction) of the plate. Also, results show that a large cut-out in the vicinity of edges makes the plate unstable at a much lower load compared to the plate with no cut-out. It is envisioned that the results of this study may provide insight to predict buckling loads in practical scenarios.

Fatigue experiments on circular hollow sections with CFRP reinforced cutouts

CHS members appear in a great many structural applications. These elements are in some cases exposed to cyclic loading. In a previous study (Ghanbari Ghazijahani et al., 2014) the authors conducted a series of fatigue experiments on perforated CHS members and found that large cutouts resulted in a significant reduction in fatigue life, while small cutouts provided stress relief to the base plate connection and increased life. This study focuses on recovering the fatigue life for larger cutouts by reinforcement with CFRP. Fatigue life was not only fully recovered with the CFRP reinforcement but dramatically increased relative to the unreinforced intact specimen.

Stress Analysis and Damage tolerance evaluation for wing structure with a large cutout in the bottom skin

Wings are the lift generating components in the airframe structure. Wings are also used as fuel tanks in the transport aircraft. From the functional requirements point of view, cutouts are introduced in the bottom skin of the wing structure. Bottom skin is under tension stress field during flight. Cutouts in the bottom skin will act as stress risers due to stress concentration effect. The current project includes the stress analysis of a wing box with large cutouts in the bottom skin to identify the critical location for fatigue crack initiation. Damage tolerance evaluation includes the stress intensity factor calculations at crack tip. This is carried out by simulation of the crack in the finite element model. Stress intensity factor (SIF) at different crack lengths will be calculated using Modified Virtual Crack Closure Integral (MVCCI) method.

Stress Analysis and Damage tolerance evaluation for wing structure with a large cutout in the bottom skin

Stress Analysis and Damage tolerance evaluation for wing structure with a large cutout in the bottom skin

Perturbation-based imperfection analysis for composite cylindrical shells buckling in compression

A numerical investigation was conducted into a perturbation-based analysis approach for assessing the imperfection sensitivity of composite cylindrical shells buckling under compression loading. The Single Perturbation Load Analysis (SPLA) approach was applied, which uses a single lateral load to introduce a realistic, worst-case and stimulating imperfection pattern. Finite element analysis was conducted for cylinders of both monolithic composite laminate and sandwich construction, with and without small and large cutouts. It was found that using a perturbation displacement equal to the shell thickness provides a suitable technique for estimating the reduction in buckling load caused by imperfections. Predictions of buckling knockdown factors using the SPLA approach showed advantages over the use of eigenmodes as the SPLA approach provides a clear design point and does not require experimental data for calibration. The effect of small and large cutouts was analogous to the effect of small and large perturbation loads. The location of the perturbation load influenced the buckling knockdown factors for both small and large cutouts, and worst-case locations were identified for both configurations.

Reinforcement Design for Composite Laminate with Large Cutout by a Genetic Algorithm Method

A dual-zone reinforcement ply stacking sequence optimization method used for comosite laminate with large cutout is present. The optimization method utilized a new Genetic Algorithm. The new Genetic Algorithm introduced a new strategy which can improve the efficiency of the traditional Genetic Algorithm and overcome the shortages of the worse convergency and prematurity of the Simple Genetic Algorithm. In the new Genetic Algorithm, the selection probability and the mutation probability are self-adaptive. Compared with the Simple Genetic Algorithm, the new Genetic Algorithm method shows good consistency, fast convergency and practical feasibility. By using the new Genetic Algorithm, the reinforcement ply stacking sequence optimization method got reasonable symmetric and balance stacking sequence which could meet the design requirements.

SU‐E‐T‐113: Measurement of the Cutout Output Factor on Ortho‐Voltage Unit Using EBT‐2 Model GafchromicTM Film

Purpose: In this study, we evaluate feasibility of using EBT‐2 model GafchromicTM film to measure patient specific cutout output factors on an ortho‐voltage treatment machine. Methods: A Gulmay Orthovoltage D3225 unit was used to produce clinical beams in kV range from 50 kVp to 220 kVp. Previously established air kerma based radiochromic film dosimetry protocol for low energy x‐ray beams was used. A closed‐end applicator with 10 × 10 cm2 field size and SSD 50 cm was employed. Cutouts were made from a lead sheet of 1.8 mm in thickness. A 6‐cm thick slab of Solid WaterTM was used as a backscatter material for output factor measurement. In‐house made MatLab routines were used to analyze scanned images of exposed and unexposed films and a PTW 23342 parallel‐plate ion chamber (PP IC) was used to measure the cutout output factors for comparison. Results: Air‐Kerma based calibration curve was created in the 1–300 cGy range. Film dosimetic accuracy was verified for known doses to water of 1.00 and 2.00 Gy, respectively, with maximum observed difference of 0.4%. Two‐dimensional dose maps and dose profiles were obtained for various cutout sizes ranging from 0.8 cm diameter circle to 10 × 10 cm2 square. Comparisons of output factors between film and pp ion chamber measurements show that there are no differences for large cutouts but the chamber measurements are up to 11 % higher for small cutout size. Conclusions: We demonstrated that the air‐Kerma based radiochromic film dosimetry protocol using EBT‐2 model GafChromicTM film for low energy x‐ray beam is adequate for patient specific cutout output measurements on orthovoltage units, especially for small size cutout measurements, where IC measurements give higher output factor than films due to ICˈs over responses to electron contaminations from lead sheets.