Comparison of structural model reduction methods applied to a large-deformation wing box

In this paper, the accuracy and practical capabilities of three different reduced-order models (ROMs) are explored: an enhanced implicit condensation and expansion (EnICE) model, a finite element beam model, and a finite volume beam model are compared for their capability to accurately predict the nonlinear structural response of geometrically nonlinear built-up wing structures. This work briefly outlines the different order reduction methods, highlighting the associated assumptions and computational effort. The ROMs are then used to calculate the wing deflection for different representative load cases and these results are compared with the global finite element model (GFEM) predictions when possible. Overall, the ROMs are found to be able to capture the nonlinear GFEM behaviour accurately, but differences are noticed at very large displacements and rotations due to local geometrical effects.

Determination of in situ detection efficiency for IM-NAA of non-standard geometrical samples

The k0-based internal mono-standard (IM) method was first proposed for the concentration analysis of samples of non-standard geometry in the 2000s. The method has demonstrated several advantages such as the elimination of gamma-ray self-attenuation and geometrical effects. On the other hand, the accuracy of the method principally depends on the in situ relative detection efficiency, which requires to be obtained in each measurement. Therefore, the relative detection efficiency is always under consideration for the improvement of the analysis results. The present paper describes a simple and automatic procedure for the determination of the relative efficiency using one or more activation products emitting gamma rays over a considered range of the spectrum. The procedure can be applied for INAA and PGNAA analysis.

Theoretical and Experimental Research of Viscoelastic Damping Limb-Like-Structure Device with Coupling Nonlinear Characteristics

The nonlinear characteristic of vibration control systems has attracted increasing attention for its advantage in improving structural performance. In this paper, a new type of viscoelastic damping limb-like-structure (VE-LLS) device is proposed by combing the viscoelastic (VE) damper and limb-like-structure (LLS) together, which possesses coupling nonlinearity characteristic caused by geometric and material factors, as well as a remarkable advantage in improving the control performance. First, to explore the nonlinear geometrical effects on the static stiffness of the VE-LLS device, a formula is derived from static stiffness, and the results are discussed. Second, dynamic analysis is performed of the proposed device considering the coupling geometrical and material nonlinearities in frequency domain, with the real-time effect of frequency and temperature on the mechanical properties of the viscoelastic damper considered in solving the nonlinear vibration equation. The harmonic balance method (HBM) is used to solve the nonlinear dynamic equation. Then, the displacement transmissibility of the VE-LLS device is calculated and assessed. The results indicate that the proposed device possesses excellent vibration isolation performance, and the geometric parameters of the viscoelastic damper have significant nonlinear effect on the performance. Finally, an experiment is carried out of the VE-LLS device to verify the accuracy of the static stiffness analysis. The results show that the theoretical results agree well the experimental ones, and that the theoretical results have high accuracy and reliability.

Evaluating the Degree of Nonlinearity by Applying the Nonlinear SPC-I Technique in the FEM Simulation of Materials With Breathing Cracks

Detecting internal defects such as fatigue cracks in their early stages is critically important to avoid catastrophic failures. However, detection of micro-scale defects poses a challenge to NDT/SHM (Non-Destructive Testing & Structural Health Monitoring) community. Conventional linear ultrasonic techniques that use absolute time of flight and attenuation to monitor damage progression encounter difficulty in detecting small defects. On the other hand, nonlinear ultrasonic techniques have been proven to be more reliable and sensitive to micro-scale defects. This study uses the nonlinear Sideband Peak Count Index (SPC-I) technique to evaluate the nonlinearity of the material. The problem is simulated using the finite element method (FEM). Fatigue cracks are simulated as breathing cracks. The problem is modeled as an infinite medium to minimize the geometrical effects such as reflections from the boundaries. A narrow band signal is excited and propagated through the material in a single sided excitation/detection setup. The degree of nonlinearity caused by breathing cracks is investigated for multiple configurations. First, the problem is modeled with no cracks to be taken as a reference condition. Then thick crack and thin crack (breathing crack) are modeled, analyzed, and compared. Finally, problems with different number of breathing cracks are simulated and analyzed. All simulated results are compared to investigate the dependence of the degree of nonlinearity on the density and orientation of the cracks.

Geometrical Effects on Ultrasonic Al Bump Direct Bonding for Microsystem Integration: Simulation and Experiments

This study employed finite element analysis to simulate ultrasonic metal bump direct bonding. The stress distribution on bonding interfaces in metal bump arrays made of Al, Cu, and Ni/Pd/Au was simulated by adjusting geometrical parameters of the bumps, including the shape, size, and height; the bonding was performed with ultrasonic vibration with a frequency of 35 kHz under a force of 200 N, temperature of 200 °C, and duration of 5 s. The simulation results revealed that the maximum stress of square bumps was greater than that of round bumps. The maximum stress of little square bumps was at least 15% greater than those of little round bumps and big round bumps. An experimental demonstration was performed in which bumps were created on Si chips through Al sputtering and lithography processes. Subtractive lithography etching was the only effective process for the bonding of bumps, and Ar plasma treatment magnified the joint strength. The actual joint shear strength was positively proportional to the simulated maximum stress. Specifically, the shear strength reached 44.6 MPa in the case of ultrasonic bonding for the little Al square bumps.