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Chiara Bisagni

Publications and source records attributed to Chiara Bisagni.

13 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2020

A Scaling Methodology Applied to Buckling of Sandwich Composite Cylindrical Shells

Studying buckling behavior of large shell structures through full-scale test articles can be complex and expensive. Therefore, reduced scale structures are often preferred to investigate the buckling behavior. However, designing reduced scale structures that are representative of the full-scale structure can be difficult. An analytical scaling methodology for compression-loaded sandwich composite cylindrical shells based on the nondimensionalization of the buckling equations is presented herein. The methodology is used to develop scaled configurations that show similar buckling responses to the full-scale baseline configuration. Finite element analysis results showed that both a baseline and a scaled configuration buckled similarly, when the nondimensional stiffness, defined as the ratio between the nondimensional load and nondimensional displacement, is matched between the different scale models. Limitations of the methodology are discussed and are believed to be a result of neglecting the flexural anisotropy and the transverse shear compliance. A preliminary failure assessment for the different scales is also considered.

Ines Uriol Balbin↗
NASA NTRSDate not supplied

Buckling and Failure Tests of a Subscale Composite Cylinder

A subscale solid laminate composite cylinder 31.5-in. diameter and 47.8 in. long with a [23/0/-23]4S layup known as NDL-1 was designed to fail in buckling and tested in axial compression to collapse twice. The proposed paper will focus on comparing the behavior of NDL-1 from the first test to failure (TTF-1) and the second test to failure (TTF-2). NDL-1 had a peak load of 466.3 kips during TTF-1 and a peak load of 390.4 kips, 15.5% lower, but with a similar stiffness, during TTF-2. Failure initiated at the 200º circumferential location in TTF-1, and at the 30º circumferential location in TTF-2. Though failure initiated at different locations, a similar radial deformation pattern was present just prior to collapse in TTF-1 and TTF-2. A shallow delamination occurred due to the initial failure event in TTF-1, and the damage had no influence on the response of NDL-1 during TTF-2. In the end, it was determined that NDL-1 failed in buckling during TTF-1 and TTF-2, and the second test to failure of NDL-1 highlighted interesting observations with respect to the effect of damage.

Buckling↗
NASA NTRSDate not supplied

Effect of Composite Stiffened Panel Design on Skin-Stringer Separation in Postbuckling

To design aeronautical composite multi-stringer panels that can safely operate in a postbuckled state, it is important to identify the parameters that can influence the different modes in which skin-stringer separation might occur. A methodology is under development to study the interaction between the skin-stringer separation and the postbuckling deformation. A simple criterion that can predict the initiation of skin-stringer separation is developed using the building block approach and single-stringer specimens. The criterion identifies whetherthe initiation is mainly due to bending or twisting deformations, so that these two possible modes can be studied separately. This procedure has the potential to reduce the overall development cost and allows the investigation of the design parameters that might precipitate or delay the skin-stringer separation.

Lucas J. Kootte↗
NASA NTRSDate not supplied

Buckling Testing of a Subscale Composite Cylinder

A subscale solid laminate composite cylinder with a 31.5-in. diameter, a 48.2-in. length, and a [23/0/-23]4S layup was designated NDL-1 and was designed to fail in buckling after a series of subcritical tests. NDL-1 was experimentally loaded in axial compression until buckling at 466.3 kips. Visual inspection of the test article after the test revealed that a shallow area of delamination occurred near the buckling initiation site. After a successful first buckling test, there was an opportunity to test NDL-1 in axial compression to failure a second time despite that the test article was not designed or analyzed for multiple buckling tests. During the second test to failure, NDL-1 reached a peak load of 390.4 kips, 16.3% lower than the first test. Buckling did not initiate in the same location during the second test to failure as the first test to failure. The second buckling event caused a large V-shaped crack that penetrated through the thickness of the barrel. Though buckling initiated at different locations, a similar radial deformation pattern was present just prior to buckling during the both tests. In the end, NDL-1 maintained a significant amount of its structural integrity and a similar prebuckling radial displacement pattern, even after the first buckling test.

Test↗
NASA NTRSDate not supplied

Effect of Composite Stiffened Panel Design on Skin-Stringer Separation in Postbuckling

To design aeronautical composite multi-stringer panels that can safely operate in a postbuckled state, it is important to identify the parameters that can influence the different modes in which skin-stringer separation might occur. A methodology is under development to study the interaction between the skin-stringer separation and the postbuckling deformation using the building block approach and single-stringer specimens. In particular, the methodology can identify whether the skin-stringer separation occurs due to bending or twisting, so that these two possible modes can be studied separately. For bending, a simple criterion that can predict the location of initiation is presented. This procedure has the potential to reduce the overall development cost and allows the investigation of the design parameters that influence the skin-stringer separation.

Lucas J. Koote↗
NASA NTRSDate not supplied

Scaling Methodology for Buckling of Composite Conical Shells in Axial Compression

Conical shells are commonly used as structural components for launch vehicles. The axial compression experienced during launch is one of the sizing load cases, because it can lead to loss of stability. As Because experimentally testing these large full-scale structures is cumbersome and expensive, it is studied how reduced-scale shells can be designed such that their buckling behavior is representative of the full-scale scale shell behavior. An analytical, sequential scaling procedure methodology is developed based on the nondimensional governing equations for composite conical shells with a symmetric, balanced layup and negligible flexural anisotropy. The buckling behavior of the shells of different size is compared using linear and nonlinear finite element analyses, and good comparisons . Accurate results are obtained for the considered shells in terms of buckling load, displacement, and mode. The inclusion of a geometric imperfections affects reduces the prediction accuracy, but it does not to the extent that the methodology is no longer valid cause the methodology to fail.

Buckling↗
NASA NTRSDate not supplied

Testing of a Composite Conical-Cylindrical Shell

Launch-vehicle shell structures, which can be comprised of both cylindrical and conical sections, are known to be susceptible to buckling due to their large radius-to-thickness ratios. The advancements in composite manufacturing and numerical methods have enabled designers to consider more nontraditional shapes, such as connecting the conical and cylindrical sections with a toroidal transition to create a single-piece conical-cylindrical shell. This single-piece construction eliminates the need for a heavy interface ring between sections and has the potential to save mass. To better understand the buckling behavior, a composite conical-cylindrical shell was designed, fabricated, and tested. Prior to test, a finite element model that included thickness variations and radial imperfections was created. The test article buckled elastically at 251.8 kN, approximately 8.8% higher than the predicted buckling load of 231.4 kN Continued research in conical-cylindrical structures has the potential to expand the design space for launch-vehicle structures and lead to improved designs and reduced weight.

Buckling↗
NASA NTRSDate not supplied

Test and Analysis of a Composite Conical-Cylindrical Shell

Launch-vehicle shell structures, which can be comprised of both cylindrical and conical sections, are known to be susceptible to buckling due to their large radius-to-thickness ratios. The advancements in composite manufacturing and numerical methods have enabled designers to consider more nontraditional shapes, such as connecting the conical and cylindrical sections with a toroidal transition to create a single-piece conical-cylindrical shell. This single-piece construction eliminates the need for a heavy interface ring between sections and has the potential to save mass. To better understand the buckling behavior, a composite conical-cylindrical shell was designed, fabricated, and tested. Prior to test, a finite element model that included thickness variations and radial imperfections was created. The test article buckled elastically at 251.8 kN, approximately 8.8% higher than the predicted buckling load of 231.4 kN Continued research in conical-cylindrical structures has the potential to expand the design space for launch-vehicle structures and lead to improved designs and reduced weight.

Buckling↗
NASA NTRSDate not supplied

Buckling Behavior of Conical-Cylindrical Shells and Design Considerations for Launch-Vehicle Applications

Traditionally, launch vehicles are constructed with a series of buckling-prone thin-walled cylindrical and conical shells, in which the buckling behavior of these shells has been well studied and buckling design guidance exists. Conical-cylindrical shell geometry is now being utilized for launch-vehicle stage adapters and payload adapters due to advances in manufacturing and numerical techniques, but there is no available buckling design guidance for this nontraditional combined geometry. In order to provide design recommendations, the buckling behavior and imperfection sensitivity of conical-cylindrical shells and how it differs from the conical and cylindrical components needs to be better understood. From this premise, it is possible to investigate whether or not the buckling knockdown factor guidelines for conical and cylindrical shells outlined in NASA SP-8019 and NASA SP-8007, respectively, are still applicable. The results in this paper will show that the current recommendations are not appropriate in some cases. In addition, it was observed that the large rotations and displacements near the transition between the cone and cylinder can have a larger effect on the buckling load than the presence of radial imperfections for conical-cylindrical shells, which is different than conical and cylindrical shells. More interesting is the fact that design modifications to increase the buckling capability of a conical-cylindrical shell such as adding reinforcement, which may add mass, will make the shell more sensitive to imperfections. The increased imperfection sensitivity may negate the increase in buckling capability that was thought to be achievable. In the end, it may be more beneficial to design a conical-cylindrical shell in which the buckling behavior is dominated by the more predictable geometric nonlinearity, which may lead to an overall lower buckling load, but a lower knockdown factor may be possible since it will not be as sensitive to the less-known radial imperfections.

Buckling↗