دکتر شهرام یوسفی

In order to measure the strain due to the shear force applied on a wing's spar, it is necessary to install a strain gauge on the neutral axis. In cases such as a circular hole on the neutral axis, it is impossible to install a strain gauge. Therefore, by installing strain gauges outside the cutting area of the hole, it will be useful to measure the shear load. Therefore, the main objective of this study is to investigate the effect of circular slices on the accuracy of strain gauge data acquired for calculating shear load. In this regard, the front spar structure of a lightweight aircraft with two sections are considered as strain gauge bridges. In the laboratory for each measurement section, a bridge is installed on the neutral axis and another two bridges with certain distances from the neutral axis are installed. Concentrated load at specific points has been applied by linear electromotor actuators equipped with S-type load cells. Using the calibration method of ground loads, the load equations are written and finally by using of strain gauge signals which extracted from the test, the concentrated loads are calculated. The forces are calculated in non-creep conditions and in spite of the cuts in the sections, and the differences between them are evaluated. Accordingly, the effect of circular slices on the accuracy of the output of the strain gauge bridges was determined. The results show the correctness of the tests and the accuracy of the load equations.

In this paper, an exact analysis of a axial compressor’s spool of a gas turbine engine has been presented to calculate stresses, strains and displacements. Spool analysis is investigated for both homogeneous and functionally graded material (FGM) states and spool is subjected to centrifugal force and uniform radial loadings at internal and external surfaces. In FGM state, materal properties including Young's modulus and density considered variable along the radius direction. Because the Poisson’s ratio variation ranges are insignificant, it considered constant for all states. Stresses, strains and displacements for both homogeneous and FGM with different non-homogeneous coefficients has been calculated. The results shown that using FGM material with suitable non-Homogeneous coefficient can lead to significant improvement in spool’s safety factor and reduction of displacements, strains and stresses in comparison with homogeneous state. On the other hand, using inappropriate FGM coefficients can lead to safety factor reduction and even structure failure. For particular investigated spool, calculated stresses in FGM with negative coefficients are less than homogeneous state and can cause failure in spool, while improvement in safety factor and displacements reduction observed using FGM with positive coefficients in comparison with homogeneous state.

In the wind tunnels, the balance measurement instrument is used to measure six components of force and moment on an airplane model. The balance of measurement consists of two parts of the balance structure and electronic equipment. In this research, a mechanism with flexible hinges is designed to achieve the desired configuration of the balance structure. In the process of designing the geometric structure of this mechanism, an effective arrangement has been implemented for the six load cell - flexure columns. The advantages of flexible hinges in comparison to conventional hinges are the absence of friction, compactness and its linear behavior. The reaction effects of the components of force and moment on each six load cell - flexure columns created the coupling errors. One of the main sources of this kind of error is related to the structure of the balance mechanism. The reason for this type of error is the inadequacy of the axial flexibility to the lateral flexibility of the columns. The aim of this research is to optimize the design of the flexible mechanism in order to achieve the minimum coupling error of the structure. For this purpose, hinge design considerations and analytical equations of the flexible mechanism have been extracted. The design of the balance mechanism is optimized by creating a structure coupling error matrix. To validate the analytic equations and results, the problem is compared with the finite element analysis. The results indicated that the measurement errors decrease in the measurement of six components of force and moment of balance.

Compression stiffened panel are the reinforced skins that are mainly subjected to axial compressive load and widely used in aerospace structures. Iterative design loops are the common methods for this type of structures. Design methodology based on structural index concept is a coupled design and analysis method. In this method detail design of the compression stiffened panel is fully accomplished based on the key parameters of structural index and material properties of the panel. The complete design is obtained in single stagein a analytical and explict manner. In this paper the design methodology of stiffened panel using structural index concept is analyzed that could be applied on selective configuration of compression stiffened panel (including selection of stiffener type and the type of the panel: integral or skin-stringer ones). The results extracted and modified from two different approaches to cope with the results of common iteration methods that currently used in the preliminary sizing of stiffened panel. This procedure could be regarded as a near optimum design and therefore would be more conservative with respect to common methods. Final results of the derived methodology are compared with reported and F.E.M results. The results could be regarded as an acceptable design further more they can be used as appropriate starting point in numerical optimization methods.