This work presents a numerical approach for predicting damage evolution in aerospace structures s... more This work presents a numerical approach for predicting damage evolution in aerospace structures subject to impact through the use of an explicit finite element code coupled with a micromechanics damage analysis module. Soft body impact, in the form of bird strike on an F16 canopy, is simulated using this Progressive Failure Dynamic Analysis (PFDA) approach. First, bird impact on a canopy is studied for three finite element modeling approaches: (1) Lagrangian, (2) Arbitrary Lagrangian-Eulerian, and (3) Smoothed Particle Hydrodynamics. From these results, one method is chosen for incorporation into the PFDA methodology. Validation of results is performed by comparing against test data for the canopy deformation versus time and canopy failure at different bird impact velocities. The completed methodology clearly identifies impact failure mechanisms and their percent contribution to the multisite structural failure in order to guide aerospace design efforts.
A number of structural optimization methods have been applied over the years to aid in the design... more A number of structural optimization methods have been applied over the years to aid in the design process for structural components. The design criteria are often based on stress, strain, or displacement allowables which can be easily calculated with any finite element analysis model. For composites, the design criteria are often based on more detailed failure models at the constituent level which attempt to evaluate interlaminar shear and tension, matrix crazing and shear yielding, and fiber fracture. This paper looks at methods to be able to incorporate advanced composite failure models, including commercial codes and in-house proprietary models, into the optimization process to further improve the optimization results. A few case studies will be reviewed with a discussion on the challenges and potential solutions to incorporating these methods in a simple and efficient manner.
Composite simulation software has been enhanced to compute the shape changes and durability of pi... more Composite simulation software has been enhanced to compute the shape changes and durability of piezoelectrically controlled airfoil structures. The GENOA Progressive Fracture Analyzer (PFA) is now developed to simulate and validate probabilistic design methodology to identify composite shape changes as well as damage progression due to piezoelectric control of composite airfoils in engine applications. The software identifies probabilistic design parameters and choices of sandwich structure and piezo-composite architecture that will be compatible with the shape control needs. The piezoelectrically controlled composite airfoil structure is optimized based on minimum weight, minimum damage, and maximum performance requirements. Nomenclature εc = composite strains εpi = piezoelectric initial strains {εli} = ith lamina strain vector [d] = piezoelectric properties matrix E = piezoelectric voltages [Ec] = composite stiffness matrix [Eli] = lamina stiffness matrix Em = matrix modulus ν = P...
A computational structural/material analysis and design tool which would meet industry's futu... more A computational structural/material analysis and design tool which would meet industry's future demand for expedience and reduced cost is presented. This unique software 'GENOA' is dedicated to parallel and high speed analysis to perform probabilistic evaluation of high temperature composite response of aerospace systems. The development is based on detailed integration and modification of diverse fields of specialized analysis techniques and mathematical models to combine their latest innovative capabilities into a commercially viable software package. The technique is specifically designed to exploit the availability of processors to perform computationally intense probabilistic analysis assessing uncertainties in structural reliability analysis and composite micromechanics. The primary objectives which were achieved in performing the development were: (1) Utilization of the power of parallel processing and static/dynamic load balancing optimization to make the complex...
Design Framework for Optimized Multifunctional Coatings
An ICME (Integrated Computational Material Engineering) and lifing model/method is developed for ... more An ICME (Integrated Computational Material Engineering) and lifing model/method is developed for optimizing multifunctional coatings Atmospheric Plasma Spray (APS) process of metallic TBC (Thermal Barrier Coating) system. Optimized TBC performance was achieved by minimizing thermal conductivity and residual stresses/strains during APS utilizing multiphysics-based multi-objective topology optimization methodology, and virtual design of experiment (DOE), surrogate meta modeling methodology. Thermal conductivity and residual strains were minimized 41% and 27%, respectively, for APS 8YSZ TBC with MCrAlY bond over Waspaloy substrate considering as variables yttria (mol.%), number of layers, total thickness, substrate initial temperature, and coating initial temperature. Durability and Damage Tolerance (D&DT) analysis of Metallic bonded TBC dogbone specimen was performed using Multi-Scale Progressive Failure Analysis (MS-PFA). The objective was to determine the Remaining Useful Life (RUL) of Metal/TBC (8YSZ, Bond, Inconel-718) system under Low Cycle Fatigue (LCF) in-service loading at 900°C. The multi-scale multi-layer TBC modeling considered Thermal Growth Oxidation (TGO) in bond coat, and recession of top coat. Prediction was validated by Rig testing; TGO measurement Progressive damage analysis revealed that failure is due to tension and out of plane shear, delamination growth due to when recession penetrates bond. The results showed that predicted fatigue life compared well to experimental observations.
Additive manufacturing (AM) process methods such as powder bed fusion (LPBF) of metal powder laye... more Additive manufacturing (AM) process methods such as powder bed fusion (LPBF) of metal powder layers can produce layered material systems with designed microstructures, which may exhibit scatter in mechanical properties (e.g., lower yield and lower failure strain), corrosion due to porosity and print anomalies. This study shows the development of AM process simulation to predict As-built material characteristic and their scatter comparing with experimental test data. ICME (Integrated Computational Materials Engineering) was used to simulate yield, ultimate, strain, and reduction of the area of sample AM. The method was extended to predict oxidation and damage of as-built parts. The samples were fabricated horizontally and vertically in multiple and scatter directions to find the effect on the mechanical properties such as ultimate tensile strength (UTS) and yield strength (YS). The probabilistic sensitivities show that in order for the next-generation technology to improve the streng...
Damage tolerant composite design principles for aircraft components under static service loading using multi-scale progressive failure analysis
Journal of Composite Materials, 2016
The overall objective of this effort was to provide theoretical prediction for damage development... more The overall objective of this effort was to provide theoretical prediction for damage development for a set of laminated composites using Alpha STAR Corporations’ commercial code GENOA (GENeral Optimization Analyzer) for the Air Force Research Laboratory program entitled “Damage Tolerance Design Principles (DTDP)”. Damage progression and prediction for advance composite benchmarks were done under static and fatigue service loading using test data from Lockheed Martin Aeronautics and Air Force Research Laboratory. In the current paper, the results for the static analysis are presented. Emerging and innovative multi-scale (MS) modeling using computational structural mechanics and progressive failure analysis were proven to address the Air Force’s vision to perform predictive evaluation of composite materials using a building block validation strategy and certification process. Three layups were tested in tension and compression for unnotched and openhole configurations. Calibration of...
Traditionally engineers have tested materials and coupons in various forms in order to obtain the... more Traditionally engineers have tested materials and coupons in various forms in order to obtain the necessary “material allowable”, consider scatter in composite material laminates, and support scale up according to the “Building Block Testing Approach”. Unfortunately, the cost of testing per the Building Block approach is costly, because it requires a robust or reduced sampling of ASTM coupons. The determination of strength allowable by means of testing, even if the material is produced at one facility, is costly and time consuming, as a large number of samples needs to be tested at different environments. A new methodology is required to develop, qualify and introduce advanced composite materials into the mainstream of future applications within a shorter time span by determining A-B Basis allowables: 1) number of required tests, cause of scatter from material and manufacturing process. The proposed paper validates IM7-8552 material system using multi-scale progressive failure integrated with probabilistic and statistical approach that consists of: a) Constituent variation method (CVM) and Bayesian statistics; and b) generic basis strength values for polymer composites using NIAR. Its purpose is aimed at reducing tests and risk associated with the use of composites in aerospace structures. This is achieved by lowering the probability of failure of primary structures through the use of A-basis or B-basis strength allowables as design values considering (i) the composite scale up, (ii) use of different facilities and (iii) structural redundant load carrying capability. The methodology combines probabilistic methods with advanced multi-scale multi-physics progressive failure analysis and Bayesian statistics to reduce the number of tests needed for determination of strength allowables. The test reduction analysis process produces random variable vectors of fiber/matrix/lamina properties and fabrication variables such as fiber content, void, and ply thickness. The random variables are then fitted to normal distribution and distribution parameters are computed. Cumulative distribution functions, probabilistic sensitivities, and A and B Basis Allowables for unidirectional and several soft, quasi, and hard mixed layups (10/80/10, 25/50/25, and 50/40/10) in tension and compression for un-notched, open-hole and filled-hole are validated with physical testing for HEXCEL 8552 IM7 tape. All simulations are within an acceptable amount of error.
Study of Interlaminar Fracture Properties of Ceramic Matrix Composites at Room and Elevated Temperatures
Volume 6: Ceramics; Controls, Diagnostics and Instrumentation; Education; Manufacturing Materials and Metallurgy, 2017
Interlaminar fracture properties play an important role in predicting failure of structural compo... more Interlaminar fracture properties play an important role in predicting failure of structural components for CMC materials. In engine applications, components are subject to large thermal gradients which induce interlaminar stresses. One of the main challenges in evaluating interlaminar fracture toughness at room and elevated temperatures is the development of an experimental setup that provides ease for testing and allows for in-situ monitoring of the interlaminar crack growth. Therefore, a wedge-loaded DCB testing method is developed. The method utilize electrical resistance to monitor crack growth and was applied to a woven polymer infiltrated pyrolysis (PIP) SiC/SiNC composite. Post-testing inspection was carried out using optical microscopy of polished cross-sections, showing crack morphology. It was found that crack growth rate at room temperature is double the one at 815 °C for initial tests in this composite system. Estimates of Mode I energy release rate suggests flat R-curve...
Development of ASTM Test Standards for the Mode I Interlaminar Fracture Toughness (GIc--Crack Growth Resistance) of Ceramic Matrix Composites
Ceramic matrix composite (CMC) materials are targeted for high temperature application in aircraf... more Ceramic matrix composite (CMC) materials are targeted for high temperature application in aircraft and power turbines, because of their low density and high-temperature thermo-mechanical properties, compared to conventional nickel super alloys. New test methods are needed for the assessment of the effects of delamination cracks on the structural integrity and life of CMC components. The ASTM C28 Fracture Toughness (Crack Growth Resistance – CGR) Working Group has drafted a standard test method for the “Mode I Interlaminar Fracture Tougness (GIc – Crack Growth Resistance) of Fiber-Reinforced Ceramic Matrix Composites (CMC) by Wedge Loading of a Double Cantilever Beam at Ambient Temperatures” The wedge loading method was developed to avoid the problems of high temperature bonding of loading blocks and hinges. The ASTM test standard details the scope, use, and application of the test method, interferences, test equipment, specimen geometry and preparation, test procedures, data interpretation and calculation, and reporting requirements for the new CMC CGR test method.
Diagnostic/prognostic health monitoring system and evaluation of a composite bridge
Smart Structures and Systems, 2009
Composite bridges offer many advantages compared to current steel and aluminum bridges. This pape... more Composite bridges offer many advantages compared to current steel and aluminum bridges. This paper presents the results of a comprehensive on-going research program to develop innovative Diagnostic Prognostic System (DPS) and a structural evaluation of Composite Army Bridge (CAB) system. The DPS is founded on three technologies: optical fiber sensing, remote data transmission, and virtual testing. In developing this system, both laboratory and virtual test were used in different damage scenarios. Health monitoring with DPS entailed comparing live strain data to archived strained data in various bridge locations. For field repairs, a family of composite chords was subjected to simple ramp loads in search of ultimate strength. As such, composite bridge specimens showcased their strengths, heralded the viability of virtual testing, highlighted the efficacy of field repair, and confirmed the merits of health monitoring.
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Papers by Frank Abdi