Long Beach, CA, United States
Long Beach, CA, United States

Time filter

Source Type

News Article | December 16, 2015
Site: www.materialstoday.com

AlphaSTAR Corporation’s Genoa 3D printing simulation software has been selected as a winner of the 2015 R&D 100 Award. The competition, sponsored by R&D Magazine, recognizes advances in the impactful technologies worldwide and acknowledges the scientists and engineers who have led these efforts. AlphaSTAR has previously received the award for the core Genoa Multi-Scale Technologies as developed with NASA Glenn Research Center and Clarkson University in the year 2000. Genoa 3D printing simulation can accurately predict the deflection, residual stress, damage initiation and crack growth formation observed by various 3D printing machines. Its multi-scale progressive failure analysis (MS-PFA) methods are used to determine the entire 3D printing process at the material characterization level without the use of FEM as well as the structural MS-PFA that simulates the entire 3D printing process using FEM. With the ability to print directly from the printers G-Code file, engineers can simulate the entire printing process, taking into account material uncertainties and production defects. The software can also visualize damage in the printed structure, such as damages in the fiber and matrix with specific delamination types such as transverse shear, fiber crushing, fiber micro-buckling, relative rotation and out of plane shear stress. Damages can be traced directly to 3D printing variables, such as deposition speed, bead width, overall path, and bottom plate temperature & convection conditions. AlphaSTAR collaborated with Oak Ridge National Laboratory to develop the software’s simulation capabilities. This story is reprinted from material from AlphaSTAR, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.


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.


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

Composite structures require a rigorous program of nondestructive inspection and maintenance to detect and characterize hidden defects at an early stage of their occurrence so that preventive measures can be taken before the structure loses its load carrying capacity or suffers from catastrophic failure. Current methods for defects detection in large aircraft and aerospace structures are slow, labor intensive and costly. This is especially true for composite structures where conventional techniques are often ineffective. Ultrasonic guided waves offer an attractive complementary tool for improving inspection techniques in relatively large plate-like structural components due to their large propagation range and sensitivity to defects in their propagation path. Since the waves are affected by the geometrical structural features (e.g. stringers) as well as harmful defects (e.g. delaminations), the application of guided waves in the NDE or SHM of real structures requires a good understanding of these interaction effects. This will help identify the defects from their distinguishing features in the signal in structural components with complex geometry. In this paper a detailed study of the interaction of guided waves with defects in an aluminum plate and a honeycomb composite sandwich structure is carried out using numerical simulations and laboratory experiments. The simpler aluminum plate is used for model validation and understanding the basic characteristics of the interaction phenomena. The agreement between the simulated waveforms and those measured from the experiments are found to be excellent in both cases indicating the possibility of applying guided wave based techniques to more realistic structures. © 2013 SPIE.


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.


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.


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

Composite structures require careful monitoring to detect and characterize hidden defects at an early stage of their development so that preventive measures can be taken before the structure loses its load carrying capacity and suffers from catastrophic failure. Ultrasonic guided waves offer an attractive tool for inspecting relatively large plate-like structural components due to the waves' large propagation range and sensitivity to defects in their propagation path. Since such waves are affected by geometrical structural features (e.g. stringers) as well as defects (e.g. delaminations), the application of guided waves in real structures requires a good understanding of their interaction with the aforementioned discontinuities. In this paper, a detailed study of the interaction of Rayleigh surface waves with defects in a thick aluminum plate is carried out using numerical simulations and laboratory experiments. The simple aluminum plate is used to demonstrate and analyze the basic characteristics of the interaction phenomena, which are shown to partially result in Lamb wave conversion. Furthermore, the agreement between simulated waveforms and those obtained from experiments are shown, indicating the possibility of applying the techniques to more realistic structures and their use in damage detection systems. © 2015 Elsevier Ltd. All rights reserved.


DorMohammadi S.,AlphaSTAR Corporation | Rais-Rohani M.,Mississippi State University | Rouhi M.,Concordia University at Montréal
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.


Rouhi M.,Mississippi State University | Rouhi M.,Center for Advanced Vehicular Systems | Rais-Rohani M.,Mississippi State University | Rais-Rohani M.,Center for Advanced Vehicular Systems | And 3 more authors.
Composite Structures | Year: 2013

An enhanced thermoset polymer matrix with randomly distributed carbon nanofibers (CNFs) is combined with conventional long fibers to form a hybrid composite material for application to impact energy absorbing components. The multi-inclusion method in combination with functionally graded interphase is used for stiffness characterization and shear-lag theory combined with quasi-isotropic lamination approximation is used for strength prediction. Axial crush simulations are performed using MD Nastran with a micromechanics-based progressive failure analysis constitutive model. The stochastic uncertainties in the geometric and material properties of CNF as well as the three-dimensional, non-homogeneous CNF-matrix interphase are represented using probability theory. Through Monte Carlo simulations, these uncertainties are propagated to the homogenized macroscopic properties of the nano-enhanced matrix and subsequently to the stiffness and strength properties of the composite laminate as well as the energy absorbing characteristics of the crush tube. A probabilistic design optimization problem is formulated for minimizing the failure probability associated with the specific energy absorption of the composite tube. A dual surrogate modeling approach is used for approximating the failure probability and solving the optimization problem using sequential quadratic programming. The modeling approach, uncertainty analysis, and probabilistic optimization results are presented and discussed. © 2013 Elsevier Ltd.


Najafi A.,Mississippi State University | Najafi A.,AlphaSTAR Corporation | Rais-Rohani M.,Mississippi State University
Materials and Design | Year: 2012

A sequential coupled nonlinear finite element analysis framework is developed to investigate the effects of sheet-forming process and product design parameters on energy absorption characteristics of thin-walled, multicorner tubes made of a magnesium alloy. Coupling stems from the use of analysis results from one simulation to form the initial state in the subsequent simulation. High fidelity coupled process-performance simulations are used in design of computer experiments for developing analytical surrogate models of process and performance responses as functions of product geometry and process parameters. Rupture, thinning and springback are treated as the manufacturing responses whereas mean crush force, maximum crush force, and mass are used as structural performance measures. An integrated process-performance optimization problem is setup and solved using the multi-objective genetic algorithm approach. The results of coupled simulations show the importance of manufacturing effects on the crush response while the Pareto optimal set highlights the tradeoff among process and performance attributes. © 2012 Elsevier Ltd.


Chamis C.C.,NASA | Abdi F.,AlphaSTAR Corporation | Garg M.,AlphaSTAR Corporation | Minnetyan L.,Clarkson University | And 4 more authors.
Journal of Composite Materials | Year: 2013

As a part of a world-wide study, a commercial code (General Optimization Analyzer), based on multi-scale (micro-macro) progressive failure analysis (PFA), is used to provide theoretical predictions for damage development for a set of challenging 13 test cases proposed in the Third World-Wide Failure Exercise (WWFE-III). Multiple failure criteria were utilized aimed at tackling issues related to a wide range of damage modes, being addressed by the WWFE-III. The critical damage events/indexes predictions tracked translaminar and interlaminar composite failures, namely matrix cracking/crack density, damage initiation/propagation, delamination initiation/growth, and their interaction with fiber failure. The composite laminates analysed were both with and without a central hole and the predictions were made using constituent fiber properties and matrix properties based on materials data or identification from ply stress-strain curve inputs. Loadings included uniaxial tension or compression, biaxial, bending, thermal, and loading-unloading. © The Author(s) 2013.

Loading AlphaSTAR Corporation collaborators
Loading AlphaSTAR Corporation collaborators