S. Anand
Please Note
6 records found
1
Historically, preliminary crashworthiness analysis has relied on linkage-kinematic joint representation of the aircraft, with characteristic curves for the kinematic joints derived using experimental or numerical campaigns. Even the most recent multi-body and FEM-kinematic joint hybrid models still depend on characteristic curves derived through simulations or experiments. Consequently, while these models are fast and ideal for preliminary crashworthiness analysis, design exploration is limited by the amount of component level test/simulation data, highlighting a clear research gap for analytical/semi-analytical models that can inform such multi-body models on the go with material and geometry data as inputs.
This thesis addresses that gap by focusing on the two dominant energy absorption mechanisms in metallic fuselage structures: axial crushing and plastic bending. For axial crushing of closed-section metallic tubular structures, existing models are evaluated and a generalized expression for various cross-section shapes is proposed. For bending collapse, a semi-analytical framework combining spring-linkage based elasto-plastic stage prediction, transition algorithm, and Kecman model for collapse stage prediction is proposed to obtain complete force–displacement curves. Although aircraft structures commonly use open sections, the scope of the present work is limited to closed sections in order to establish a robust and consistent methodological foundation within the available time frame.
Finally, the bending framework is extended to hybrid materials, specifically GLARE (Glass Laminate Aluminium Reinforced Epoxy). A maximum strain-based damage model based on the spring-linkage method is proposed, the approach predicts stiffness degradation and progressive central cracking failure for GLARE laminates. The results demonstrate that analytical and semi-analytical models can be further extended to hybrid systems, enabling fast, early-stage crashworthiness evaluation of unconventional aircraft designs utilizing hybrid materials. ...
Historically, preliminary crashworthiness analysis has relied on linkage-kinematic joint representation of the aircraft, with characteristic curves for the kinematic joints derived using experimental or numerical campaigns. Even the most recent multi-body and FEM-kinematic joint hybrid models still depend on characteristic curves derived through simulations or experiments. Consequently, while these models are fast and ideal for preliminary crashworthiness analysis, design exploration is limited by the amount of component level test/simulation data, highlighting a clear research gap for analytical/semi-analytical models that can inform such multi-body models on the go with material and geometry data as inputs.
This thesis addresses that gap by focusing on the two dominant energy absorption mechanisms in metallic fuselage structures: axial crushing and plastic bending. For axial crushing of closed-section metallic tubular structures, existing models are evaluated and a generalized expression for various cross-section shapes is proposed. For bending collapse, a semi-analytical framework combining spring-linkage based elasto-plastic stage prediction, transition algorithm, and Kecman model for collapse stage prediction is proposed to obtain complete force–displacement curves. Although aircraft structures commonly use open sections, the scope of the present work is limited to closed sections in order to establish a robust and consistent methodological foundation within the available time frame.
Finally, the bending framework is extended to hybrid materials, specifically GLARE (Glass Laminate Aluminium Reinforced Epoxy). A maximum strain-based damage model based on the spring-linkage method is proposed, the approach predicts stiffness degradation and progressive central cracking failure for GLARE laminates. The results demonstrate that analytical and semi-analytical models can be further extended to hybrid systems, enabling fast, early-stage crashworthiness evaluation of unconventional aircraft designs utilizing hybrid materials.
This paper investigates 3-point bending failure of five different types of GLARE laminates (2A, 2B, 3, 4A and 4B). 73 configurations (419 specimens), with different stacking sequences and aluminum layer thicknesses are tested. Failure mechanisms, effect of stacking sequence, effect of aluminum rolling direction, effect of displacement rate and energy absorption are analyzed. Configurations with predominantly 0°glass fiber layers fail with delamination as the major failure mode, while configurations with predominantly 90°glass fiber layers fail with central cracking as the major failure mode. GLARE 3, with 1:1 ratio of 0°and 90°fibers, fail with an equal mix of delamination and central cracking. A semi-analytical framework that can be used to predict the force versus displacement curve for central cracking failure is proposed and validated.
Corrigendum to “Crashworthiness in preliminary design
Mean crushing force prediction for closed-section thin-walled metallic structures” [International Journal of Impact Engineering, Volume 188, June 2024, 104946](S0734743X24000708)(10.1016/j.ijimpeng.2024.104946)
The authors regret to inform that an error has been identified in the numerical dataset presented in the original paper (Appendix C.1) for square tubular structures. The mean force values were taken for the entire range (including the peak) instead of the plateau phase of the crushing due to a scripting error. This has an effect on some of the coefficient of determination values, error ranges in Table 2 and causes a change in the generalized equation. However, the coefficient of determination of the generalized model remains unchanged. This corrigendum presents the changes in text and the updated figures and tables. The authors would like to apologise for any inconvenience caused.
Crashworthiness in preliminary design
Mean crushing force prediction for closed-section thin-walled metallic structures
To design crash structures for disruptive aircraft designs, it is required to have fast and accurate methods that can predict crashworthiness of aircraft structures early in the design phase. Axial crushing is one of the key energy absorbing mechanisms during a crash event. In this study, various analytical models proposed for calculation of mean crushing force for thin-walled tubular structures are compared with a database of numerical and experimental values to ascertain their accuracy. Improvements to some of the models have also been proposed. Finally a generalized model based on the studied and improved analytical models for prediction of mean crushing force for closed section thin-walled tubular structures is introduced. The generalized model demonstrates high accuracy when compared against experimental/numerical dataset as evidenced by a high coefficient of determination (R2) value of 0.97 and can therefore be used to estimate the mean crushing force for closed-section thin-walled metallic tubular structures with various cross-sectional shapes and crushing modes early in the design phase.
This paper reviews analytical models proposed by Abramowicz et al.[1, 2] and Stefan et al.[3] for the axial crushing of metallic tubular structures with square and circular cross-sections. First, a database of experiments for square and circular tubes was created based on the literature. Subsequently, the predictions obtained using these analytical models were compared against the database of experiments to determine the accuracy of these analytical models. The database of experiments was also compared against some results generated using Finite-Element Method (FEM). Furthermore, the sensitivity of the analytical models to various material and geometrical parameters was studied to determine the influence of these parameters on the mean crushing force. Both models were found to be highly sensitive to the thickness of the tubular structures. It was observed that the models proposed by Abramowicz et al.[1, 2] showed better agreement with experimental results, although an over-prediction was observed for square tubular structures made of materials with a significant difference between the values of yield and ultimate stress. The model proposed by Stefan et al.[3] slightly over-predicted for square tubes and showed reasonable accuracy for circular tubes.