Residual Strength Prediction of Fuselage Structures with Multiple Site Damage

This paper summarizes recent results on simulating full-scale pressure tests of wide body, lap-jointed fuselage panels with multiple site damage (MSD). The crack tip opening angle (CTOA) fracture criterion and the FRANC3D/STAGS software program were used to analyze stable crack growth under conditions of general yielding. The link-up of multiple cracks and residual strength of damaged structures were predicted. Elastic-plastic finite element analysis based on the von Mises yield criterion and incremental flow theory with small strain assumption was used. A global-local modeling procedure was employed in the numerical analyses. Stress distributions from the numerical simulations are compared with strain gage measurements. Analysis results show that accurate representation of the load transfer through the rivets is crucial for the model to predict the stress distribution accurately. Predicted crack growth and residual strength are compared with test data. Observed and predicted results both indicate that the occurrence of small MSD cracks substantially reduces the residual strength. Modeling fatigue closure is essential to capture the fracture behavior during the early stable crack growth. Breakage of a tear strap can have a major influence on residual strength prediction

Exact Boundary Derivative Formulation for Numerical Conformal Mapping Method

Conformal mapping is a useful technique for handling irregular geometries when applying the finite difference method to solve partial differential equations. When the mapping is from a hyperrectangular region onto a rectangular region, a specific length-to-width ratio of the rectangular region that fitted the Cauchy-Riemann equations must be satisfied. In this research, a numerical integral method is proposed to find the specific length-to-width ratio. It is conventional to employ the boundary integral method (BIEM) to perform the conformal mapping. However, due to the singularity produced by the BIEM in seeking the derivatives on the boundaries, the transformation Jacobian determinants on the boundaries have to be evaluated at inner points instead of directly on the boundaries. This approximation is a source of numerical error. In this study, the transformed rectangular property and the Cauchy-Riemann equations are successfully applied to derive reduced formulations of the derivatives on the boundaries for the BIEM. With these boundary derivative formulations, the Jacobian determinants can be evaluated directly on the boundaries. Furthermore, the results obtained are more accurate than those of the earlier mapping method

On Computer-Aided Instruction Tools for Teaching College Engineering Mechanics Related Courses

In this research, questionnaires are designed to survey among teachers and students the current situation of applying Computer-Aided Instruction (CAI) tools to teaching and learning of college engineering mechanics related courses in Taiwan. The needs for CAI tools for teaching these mechanics related courses are investigated in the survey. Several prototypes of interactive multimedia tools are designed and implemented using information technologies. The applicability and effectiveness of these tools on assisting teaching of engineering mechanics related courses are discussed and evaluated. Moreover, a website for managing and sharing collected and developed CAI resources is constructed

A Miniature System for Separating Aerosol Particles and Measuring Mass Concentrations

We designed and fabricated a new sensing system which consists of two virtual impactors and two quartz-crystal microbalance (QCM) sensors for measuring particle mass concentration and size distribution. The virtual impactors utilized different inertial forces of particles in air flow to classify different particle sizes. They were designed to classify particle diameter, d, into three different ranges: d < 2.28 μm, 2.28 μm ≤ d ≤ 3.20 μm, d > 3.20 μm. The QCM sensors were coated with a hydrogel, which was found to be a reliable adhesive for capturing aerosol particles. The QCM sensor coated with hydrogel was used to measure the mass loading of particles by utilizing its characteristic of resonant frequency shift. An integrated system has been demonstrated

Atomistic Simulation and Investigation of Nanoindentation, Contact Pressure and Nanohardness

[[abstract]]Atomistic simulation of nanoindentation with spherical indenters was carried out to study dislocation structures, mean contact pressure, and nanohardness of Au and Al thin films. Slip vectors and atomic stresses were used to characterize the dislocation processes. Two different characteristics were found in the induced dislocation structures: wide-spread slip activities in Al, and confined and intact structures in Au. For both samples, the mean contact pressure varied significantly during the early stages of indentation but reached a steady value soon after the first apparent load drop. This indicates that the nanohardness of Al and Au is not affected by the indentation depth for spherical indenters, even at the atomistic scale.[[notice]]補正完

(15) Multiscale Materials Modeling

Chuin-Shan David Chen, PhD ‘99Professor of Computer-Aided Engineering, Department of Civil Engineering, National Taiwan UniversityFracturing processes occur at different materials length scales and naturally call for multiscale modeling. In this talk, I will present my journey on multiscale materials modeling, descended from my Ph.D. and Postdoc research association with Professor Anthony R. Ingraffea. Two critical length scales and modeling techniques will be addressed: one at the dislocation level and the other at the materials grain level. At the dislocation level, I will emphasize on the large-scale atomistic simulation: a new paradigm to study mechanics of materials in which mechanisms and properties are emerged directly from the fundamental evolution of atoms. At the grain level, a micromechanics model to simulate inter-granular fracture will be addressed.1_ch9rlb0

(16) Multiscale Materials Modeling (slides)

Fracturing processes occur at different materials length scales and naturally call for multiscale modeling. In this talk, I will present my journey on multiscale materials modeling, descended from my Ph.D. and Postdoc research association with Professor Anthony R. Ingraffea. Two critical length scales and modeling techniques will be addressed: one at the dislocation level and the other at the materials grain level. At the dislocation level, I will emphasize on the large-scale atomistic simulation: a new paradigm to study mechanics of materials in which mechanisms and properties are emerged directly from the fundamental evolution of atoms. At the grain level, a micromechanics model to simulate inter-granular fracture will be addressed

On the Selection of a Better Radial Basis Function and Its Shape Parameter In Interpolation Problems

A traditional criterion to calculate the numerical stability of the interpolation matrix is its standard condition number. In this paper, it is observed that the effective condition number (κeff) is more informative than the standard condition number (κ) in investigating the numerical stability of the interpolation problem. While the (κeff) considers the function to be interpolated, the standard condition number only depends on the interpolation matrix. We propose using the shape parameter corresponding to the maximum (κeff) to obtain a small error in RBF interpolation. It is also observed that the (κeff) helps to predict the error behavior with respect to the type of the RBF, where the basis function with a higher effective condition number yields a smaller error. In the end, we conclude that the effective condition number links to the error with respect to the selection of a radial basis function, choosing its shape parameter, number of collocation points, and test function. To this end, ten test functions are interpolated using the multiquadric, Matern family, and Gaussian basis functions to show the advantage of the proposed method