Entity

Time filter

Source Type

Long Beach, CA, United States

DorMohammadi S.,AlphaSTAR Corporation | Rais-Rohani M.,Mississippi State University | Rouhi M.,Concordia University at Montreal
Composite Structures | Year: 2015

A hierarchical framework for multilevel analysis and design of composite material and structural systems is presented. The micro- and macro-level material models are integrated with structural analysis to evaluate the response characteristics of the loaded structure affected by both the nanofiber enhancements and continuous fiber reinforcements in the polymer matrix. Besides the nanofiber waviness, the nanofiber-matrix interphase is also included in evaluation of the homogenized stiffness properties of the matrix. To take advantage of the design features at different length scales, a multilevel optimization approach based on analytical target cascading is developed and applied to material-structural analysis and design optimization of a rectangular composite sandwich plate under in-plane loading conditions. The design variables include the volume fractions of the nanofibers and continuous fibers along with the thicknesses of the core and facesheet plies. Multiple failure modes in the form of global buckling, shear crimping, intracell buckling, and face sheet wrinkling are included as design constraints. Different edge loads are applied to study the effect of loading on optimum design. Besides the significant computational efficiency in the multilevel approach, the analysis detail and the results of the multilevel sandwich plate optimization problem are presented and discussed. © 2015 Elsevier Ltd. Source


Samajder H.,University of California at Los Angeles | Baid H.,AlphaSTAR Corporation | Ricci F.,University of Naples Federico II | Mal A.,University of California at Los Angeles
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

Composite materials are being used increasingly in advanced aircraft and aerospace structures. Despite their many advantages including high strength to weight ratio, formability and low coefficient of thermal expansion, composites are often susceptible to hidden damage that may occur during their manufacturing and/or service of the structure. Safe operation of composite structures requires careful monitoring of the initiation and growth of such defects before they grow to a critical size resulting in possible catastrophic failure of the structure. Ultrasonic methods using guided waves offer a reliable and cost effective method for defects monitoring in advanced structures due to their long propagation range and their sensitivity to defects in their propagation path. In this paper some of the useful properties of guided Lamb type waves are investigated in an effort to provide the knowledge base required for the development of viable defects monitoring systems in composite structures. Some of our recent research in this area is presented in this paper. The research includes laboratory experiments using a pitch catch method in which a pair of moveable transducers are placed on the outside surface of the structure for generating and recording the wave signals. The recorded signals are analyzed to construct the dispersion and other relevant properties of the guided waves. Theoretical simulations using analytical and numerical methods are carried out and compared with the experimental results. The specific cases considered include an aluminum plate, a woven quasi-isotropic composite panel and an aluminum honeycomb panel with woven composite face sheets. The agreement between the experimental and theoretical results are shown to be excellent in certain frequency ranges, but not for others, providing a guidance for the design of effective inspection systems. © 2013 SPIE. Source


Siddens A.J.,Virginia Polytechnic Institute and State University | Bayandor J.,Virginia Polytechnic Institute and State University | Abdi F.,AlphaSTAR Corporation
Journal of Aircraft | Year: 2014

This work presents a numerical approach for predicting large deflections and damage evolution in aerospace structures subject to soft impact. The explicit finite-element code LS-DYNA is coupled with the micromechanics damage-analysis code GENOA, which is capable of predicting failure progression in a range of isotropic and orthotropic materials. The impact event studied was a bird strike on an F-16 canopy concept. Bird models were developed using three distinct finite-element modeling approaches: 1) Lagrangian, 2) arbitrary Lagrangian- Eulerian, and 3) smoothed particle hydrodynamics. Each model was studied by simulating impact at a speed that induced a large-deflection, elastic response in the canopy. Deflections at the impact location were compared against experimental data; from these results, the Lagrangian bird model was chosen for incorporation into a bird-impact progressive failure dynamic analysis methodology. Impact at velocities below and above that which induced failure were simulated and compared with test results. The completed methodology is able to accurately match the elastic deflection response and predict damage initiation and progression at higher velocities. Additionally, the progressive failure dynamic analysis methodology clearly identifies failure mechanisms and their percent contribution to multisite failure and can help guide the design process for parts that must withstand soft impacts. Copyright © 2014 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Source


Baid H.,AlphaSTAR Corporation | Schaal C.,University of California at Los Angeles | Samajder H.,University of California at Los Angeles | Mal A.,University of California at Los Angeles
Ultrasonics | Year: 2015

Composite materials are increasingly being used in advanced aircraft and aerospace structures. Despite their many advantages, composites are often susceptible to hidden damages that may occur during manufacturing and/or service of the structure. Therefore, safe operation of composite structures requires careful monitoring of the initiation and growth of such defects. Ultrasonic methods using guided waves offer a reliable and cost effective method for defects monitoring in advanced structures due to their long propagation range and their sensitivity to defects in their propagation path. In this paper, some of the useful properties of guided Lamb type waves are investigated, using analytical, numerical and experimental methods, in an effort to provide the knowledge base required for the development of viable structural health monitoring systems for composite structures. The laboratory experiments involve a pitch-catch method in which a pair of movable transducers is placed on the outside surface of the structure for generating and recording the wave signals. The specific cases considered include an aluminum plate, a woven composite laminate and an aluminum honeycomb sandwich panel. The agreement between experimental, numerical and theoretical results are shown to be excellent in certain frequency ranges, providing a guidance for the design of effective inspection systems. © 2014 Elsevier B.V. All rights reserved. Source


Ricci F.,University of Naples Federico II | Monaco E.,University of Naples Federico II | Baid H.,AlphaSTAR Corporation | Mal A.,University of California at Los Angeles
Structural Health Monitoring 2013: A Roadmap to Intelligent Structures - Proceedings of the 9th International Workshop on Structural Health Monitoring, IWSHM 2013 | Year: 2013

Damage identification using ultrasonic nondestructive evaluation (NDE) requires a good understanding of the properties of the various types of waves that can be transmitted in the structure in presence or absence of damage. For successful application of these techniques to locate and estimate the severity of the damage, it is extremely important to understand the propagation characteristics of ultrasonic waves in these structures. Wave propagation in composites is extremely complex due to material inhomogeneity and anisotropy, where characteristics of the waves depend on the laminate layup, direction of wave propagation, frequency, and interface conditions. When elastic waves are generated by surface sources in a plate, they experience repeated reflections at the top and bottom surfaces alternately. The mutual interference of the reflected waves results in propagation guided by the plate surfaces. In this paper a specific structure will be analyzed with different levels of complexities as far as the wave propagation characteristics are concerned. The structure is a sandwich plate composed of two carbon-epoxy face sheets with an aluminum honeycomb core with hexagonal cells. The work is carried out using theoretical analysis, numerical models and experimental verifications. Numerical (Finite Element) models are used for more practical cases, for which the geometric and material complexities of actual structures present practical difficulties in direct analysis of wave propagation data using theoretical constructs only. Source

Discover hidden collaborations