Analysis of isogrid reinforced cylindrical vessels in the case of axially symmetric buckling

Isogrid structures are a configuration of stiffeners of different sections, which make up a lattice placed on thin plates, with the aim of increasing the buckling factor of the overall structure. Because of the major benefits of isogrid structures when applied to increase the buckling factor and to decrease the mass of the structures the isogrid is placed on, its use has intensified until it has become a complete design technique for building cylindrical vessels under high compressive forces. Unfortunately, the detailed geometry of isogrid structures cannot be easily modelled or computed using FEM software, due to the high number of elements required to reliably mesh such a structure and the large amount of time taken to compute the results. This paper attempts to mitigate this problem by considering an analytical approach of sectioning the cylindrical vessel into component modules. These modules, consisting of a thin plate with isogrid stiffeners attached to it, are approximated as an overall thin plate with modified properties. The analytical algorithm is then implemented in a computed algebra system, which will quickly compute approximate values for the buckling factor and mass of the structure

Temperature Effects on Damage Mechanisms of Hybrid Metal – Composite Bolted Joints Using SHM Testing Method

This paper presents the quasi-static thermo-mechanical loading effects on the progressive damage mechanisms and failure modes of the single-bolt, single-shear, hybrid metal-composite, bolted joints in aerospace applications. A three-dimensional finite element method (FEM) technique was used to model the countersunk head bolted joint in details, including geometric and frictional based contact full nonlinearities and using commercial software PATRAN as pre/post-processor. The progressive damage analysis (PDA) in laminated (CFRP/ vinyl ester epoxy) composite material including nonlinear shear behavior, Hashin-type failure criteria and strain-based continuous degradation rules for different values of temperatures was made using SOL 400 NASTRAN solver. In order to validate the numerical results and close investigation of the fracture mechanisms for metal-composite bolted joints by determining ultimate failure loads, experiments were conducted in temperature controlled chamber using SHM (Structural Health Monitoring) technique. The results show that the thermal effects are not negligible on failure mechanism in hybrid aluminum-CFRP bolted joints having strong different thermal expansion coefficients. The complex 3D FEM model using advanced linear continuum solid-shell elements proved computational efficiency and ability to accurately predict the various failure modes as bearing and shear-shear out, including the temperature effects on the failure propagation and damage mechanism of hybrid metal-composite bolted joints

Coherent solutions to roll damping derivatives evaluation for a generic rocket model

This paper presents a coherent approach to evaluate the roll damping derivatives for the standard Basic Finner Model. The study compares and analyses the results obtained through a range of techniques, including experimental testing, numerical simulations and semi-empirical models. The study aims to evaluate the reliability and accuracy of these methods and to identify the factors that contribute to their sensitivity. The paper concludes by summarizing the findings of the study and discussing the implications of the results for the design and operation of rockets. The experimental and numerical analysis used in this study provides a robust and comprehensive evaluation of the roll damping coefficient

Automated procedure for determination of friction grip and bearing joint strength used for space missions

This paper presents an algorithm that calculates the nominal torque for friction grip joints, followed by its implementation in a Microsoft Excel worksheet that is automated by a macro written in Visual Basic. The algorithm outputs not only the optimum nominal torque (the value for which the margin of safety is maximum) but also the interval of acceptable values so that the user can easily choose the torque according to his preferences

On the construction of numerical iterative schemes of any order of convergence for solving nonlinear systems of equations

This paper presents a methodology for constructing iterative schemes of any order of convergence for solving nonlinear systems of equations. It also provides formulas for the order of convergence of any iterative schemes constructed using the method proposed in this paper. A test case is conducted numerically for the second and third order of convergence using a computer algebra system called Maxima. The code used is listed at the end of the test case

Comparative Analysis Program for Experimental and Calculated Data

This article aims to provide an interactive in-house tool to quickly asses the stress in the critical points of the aeronautical structures. The software compares the results between the stress values obtained from the experimental tests using the resistive electrical tensometry technique (RET) and the stress values calculated with FEM software. RET refers to the stress and strains measured by strain gauges applied to the critical points of the structures. The finite element analysis was carried-out with MSC. PATRAN/ NASTRAN using shell and solid elements in order to identify the critical points based on the stress and strain results. The validation of the results obtained by the finite element modelling has been made experimentally using the resistive electrical tensometry method. The results from these two methods have been compared with the in-house software developed in Visual Basic with Excel interface. The program evaluates the relative error between the experimental and calculated data at critical points