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Research

Active Projects

Project Principal Investigator Abstract
Administration of the FAA Center for Excellence for Advanced Materials in Transport Aircraft Structures (AMTAS) Mark Tuttle, Ph.D.
UW Dept. of Mechanical Engineering, tuttle@u.washington.edu
Link to abstract
Improving Adhesive Bonding of Composites through Surface Characterization Brian Flinn, Ph.D.
UW Dept. of Materials Science & Engineering, bflinn@u.washington.edu
Link to abstract
Failure of Notched Laminates Under Out-of-plane Bending John Parmigiani, Ph.D.
OSU Dept. of Mechanical Engineering, parmigjo@engr.orst.edu
Link to abstract
Effect of Surface Contamination on Composite Bond Integrity and Durability Dwayne McDaniel, Ph.D.
FIU Applied Research Center
mcdaniel@fiu.edu
Link to abstract
Development and Evaluation of Fracture Mechanics Test Methods for Sandwich Composites Dan Adams, Ph.D.
Utah Dept. of Mechanical Engineering
adams@mech.utah.edu
Link to abstract
Certification of Discontinuous Composite Material Forms for Aircraft Structures Mark Tuttle, Ph.D.
UW Dept. of Mechanical Engineering, tuttle@u.washington.edu

Paolo Feraboli, Ph.D.
UW Dept. of Aeronautics and Astronautics, feraboli@aa.washington.edu

Link to abstract
Analysis of Disbond and Delamination Arrest Features in Laminated Composite Structures Kuen Lin, Ph.D.
UW Dept. of Aeronautics and Astronautics, lin@aa.washington.edu
Link to abstract
Durability of Adhesively Bonded Joints For Aircraft Structures Dan Adams, Ph.D.
Utah Dept. of Mechanical Engineering
adams@mech.utah.edu
Link to abstract
Composite Thermal Damage Measurement with Hand Held FT-IR Brian Flinn, Ph.D.
UW Dept. of Materials Science & Engineering, bflinn@u.washington.edu
Link to abstract
Development of an Active Flutter Suppression Research Plan Eli Livne, Ph.D.
UW Dept. of Aeronautics and Astronautics, eli@aa.washington.edu
Link to abstract
Durability of Bonded Aerospace Structures Lloyd Smith, Ph.D.
WSU School of Mechanical & Materials Engineering, smith@mme.wsu.edu
Link to abstract

UW = University of Washington
WSU = Washington State University
EdCC = Edmonds Community College
FIU = Florida International University
Utah = University of Utah


Abstracts

Administration of the FAA Center for Excellence for Advanced Materials in Transport Aircraft Structures (AMTAS)

In December 2003 the Federal Aviation Administration (FAA) announced a joint award to the University of Washington and Wichita State University to create a new Air Transportation Center of Excellence for Advanced Materials (JAMSCOE). This award established a center led by the UW and named the FAA Center for Advanced Materials in Transport Aircraft Structures (AMTAS). Academic members of AMTAS include the UW, Washington State University, Oregon State University, and Edmonds Community College. As lead institution of AMTAS, the UW is responsible for overall administration of AMTAS, oversight of AMTAS projects conducted by all academic members, and hosting of an annual AMTAS Conference. This proposal requests FAA funding necessary to administer AMTAS. As in all other AMTAS proposals, the FAA funding requested will be matched on a 1:1 basis from non-federal sources.

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Improving Adhesive Bonding of Composites through Surface Characterization

The purpose of this research is to determine the effect of atmospheric pressure plasma treatment on Mode I strain energy release rate (GIC) and failure mode of bonded peel ply prepared carbon fiber reinforced polymer composites. Previous research showed that Toray T800/3900 carbon fiber reinforced epoxy composites prepared with Precision Fabrics Group 52006 nylon peel ply and bonded with MetlBond 1515-3M structural film adhesive failed in adhesion at low fracture energies when tested in the double cantilever beam (DCB) configuration. Other research suggested that plasma treatment could be able to activate these “un-bondable” surfaces and result in good adhesive bonds. Nylon peel ply prepared 177°C cure carbon fiber reinforced epoxy laminates were treated with atmospheric pressure plasma after peel ply removal prior to bonding. Surface characterization methods, including contact angle (CA), Fourier transform infrared (FTIR) spectroscopy, and x-ray photoelectron spectroscopy (XPS) were used to determine how plasma treatment changed nylon peel ply prepared surfaces. CA can be used to measure surface energy of a composite prepared for adhesive bonding. This information can help understand one requirement of adhesion: surface wetting of the adherend by the adhesive. FTIR and XPS can be used to measure composite surface chemistry, which can help understand another requirement of adhesion: the formation of chemical bonds between the adherend and adhesive. FTIR and XPS can also be used for the identification of contaminants, which can inhibit adhesive bonding. DCB specimens were bonded with MetlBond 1515-3M and tested to determine failure mode and GIC. Plasma treated samples had acceptable failure modes and fracture energies that were triple that of peel ply only samples. It was demonstrated that atmospheric pressure plasma was able transform poor bonding surfaces to good bonding surfaces.

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Failure of Notched Laminates under Out-of-plane Bending

The design of aircraft structures made of composite materials is heavily influenced by damage tolerance requirements. The problem of predicting failure in notched laminates has been the subjected of numerous studies. In general, these investigations have focused on the response of laminates to in-plane tension, compression or shear. In spite of the fact that out-of-plane bending, twisting, or shear can be an important load situation, very little research has been devoted to this topic. The overall goal of this research is to develop analysis techniques that are useful for the design of composite aircraft structure subjected to general out-of-plane loading. For this project we will limit ourselves to the out-of-plane bending case and focus on some very basic experiments and modeling efforts involving simple structures (center-notched, unstiffened laminates) under pure bending. In partnership with the Boeing Commercial Airplane Company, we will determine the modes of failure of the laminates and evaluate the capability of some currently existing analysis techniques for predicting these failures. Accomplishing our objective will require both experimental and computational efforts.

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Effect of Surface Contamination on Composite Bond Integrity and Durability

Previous research has shown that surface contamination plays a key role in the initial bond strength of adhesively composite joints (ABCJ’s). Advancements in experimental methods to capture changes in bond strength are of significant relevance in predicting ABCJ’s performance. This study presents an experimental method to evaluate the effects of contamination on the durability of ABCJ’s. Bonded double cantilever beam (DCB) specimens were manufactured with laminates that were contaminated prior to bonding. Surface characterization of the laminates prior to bonding was conducted using ECS, FTIR and water contact angle measurements techniques. After manufacturing, specimens were environmentally exposed to a high humidity environment or cyclically loaded to challenge the bond with an accelerated aging process. DCB testing of the specimens provided the fracture toughness and mode of failure for each group of conditioned specimens. Results were compared with previous tests where no contamination was introduced but a similar accelerated aging process was utilized. Additionally, the moisture absorption of contaminated and non-contaminated specimens in unstressed conditions was used to obtain the equilibrium saturation point over a period of time. Future studies will include evaluating contaminated specimens that have been subjected to a high moisture environment and cyclic loading simultaneously.

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Development and Evaluation of Fracture Mechanics Test Methods for Sandwich Composites

Whereas the development of test methods for fracture mechanics of composite laminates has reached a high level of maturity in recent years, relatively little attention has been given to the development of fracture mechanics test methods for sandwich composites. Of the limited number of investigations performed to date, a majority have emphasized a particular sandwich material or the effects of specific environmental conditions. In general, the test methods proposed for fracture mechanics of sandwich composites have been found to be problematic due to problems in testing, crack propagation, and the analysis of test data. Emphasis in this research project grant will be focused on the development of fracture mechanics test methods for sandwich composites. The ultimate goal of the proposed research is to establish draft ASTM standards for both Mode I and Mode II fracture toughness of sandwich composite materials.

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Certification of Discontinuous Composite Material Forms for Aircraft Structures

Polymeric composites based on discontinuous fiber reinforcement are being used in primary and secondary structures in modern transport aircraft. A prime example is HexMC, a composite material system developed by Hexcel that is being used to produce several structural components within the Boeing 787, for example the window frames. Some of the major advantages of the HexMC material system include ease of manufacturing, near in-plane quasi-isotropic mechanical properties and low notch sensitivities.

The overall objective of the proposed project is to study the technical issues important to the development, certification and production of discontinuous composite material parts for primary aircraft structures. HexMC will be used as the model material form throughout the study.

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Analysis of Disbond and Delamination Arrest Features in Laminated Composite Structures

An accurate and efficient analysis method is critically needed for the damage tolerant design of bonded composite structures.  In this proposal, sponsored by Boeing research and Technology, a technical approach to the disbond/delamination arrest problem has been presented. Major tasks to be accomplished during the six months period have been identified and discussed. These tasks include: development of analytical capability for the analysis of disbonds and delaminations as well as performing sensitivity studies on the effects of stacking sequence and the fastener dimensions and properties.  Results of this research will contribute directly to the integrity and safety of aircraft structures made of bonded materials.

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Durability of Adhesively Bonded Joints for Aircraft Structures

The objective of this recently-initiated research investigation is to revisit and revise the ASTM D 3762 metal wedge crack durability test. While considered to be a reliable method for investigating adhesive bond durability, the existing standard provides little guidance regarding the conditions and requirements that constitute an acceptable metal bonded joint. Of particular concern is the reduction in strength of the bonded metal joint over time due to hydration. Thus a need exists to revise the existing test standard such that it provides specific guidance on how to successfully develop criteria for the wedge crack durability test. Possible revisions to the standard include proposed exposure environments, and pass/fail criteria with regards to both crack growth extension and failure modes. This research project will initially focus on reviewing the literature and identifying stakeholders associated with the test method. Test results and proposed additions and revisions to the ASTM D 3762 standard will be communicated regularly to ASTM Committee D14 on adhesives. In addition to proposing revisions to this standardized test method, research results from this investigation will be disseminated through an FAA technical report and journal publications. Expected benefits to aviation include an improved adhesive bond durability test method for use in assessing the reliability of adhesively bonded aircraft structures.

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Composite Thermal Damage Measurement with Hand Held FT-IR

The purpose of this research is to determine if Fourier transform infrared (FTIR) spectroscopy can be used to quantify incipient thermal damage (ITD) in aerospace composites. ITD is the early stages of thermal damage that cannot be detected by visual or ultrasonic methods but can lead to significant reductions in matrix-dominated properties of the composite. This project involves the detection of thermal damage with FTIR and performing a simulated repair guided by FTIR. The first task is the development of calibration curves for FTIR data on short-beam strength (SBS) samples with varying levels of ITD. This effort focuses on constructing calibration curves from SBS samples that have varying levels of ITD using an ExoScan FITR configured with diffuse reflectance. The SBS samples are 177 °C cure carbon fiber reinforced epoxy laminates that were carefully heat soaked to achieve uniform ITD in the samples. FTIR spectra and calibration curves relating the FTIR spectra to levels of ITD are reported and compared to previous results. These calibration curves will be used to guide mapping of thermal damage both on the surface and during the scarfing repair process with localized heat damage.

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Development of an Active Flutter Suppression Research Plan

The utilization of active control systems for gust alleviation, load redistribution, flight control, and ride comfort improvements has matured over the last two decades to levels of reliability and safety that allow implementation and certification on both military and civil aircraft. Active Flutter Suppression (AFS) – the reliance on active control systems to stabilize flutter-unstable vehicles throughout their flight envelopes – while studied extensively and demonstrated in theoretical, numerical, wind tunnel tests, and flight tests, is not approved for wide spread implementation, mainly because of the catastrophic nature of vehicle response to the failure of such systems. This paper and talk will present a general introduction to active flutter suppression in the context of flight vehicle aeroelasticity and aeroservoelasticity. First steps taken in the effort to assess the state of the art and the implementation level of readiness of the technology will be described.

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Durability of Bonded Aerospace Structures

This work is concerned with understanding mechanisms contributing to the mechanical durability of adhesively bonded joints. To that end, the response of coupons bonded with brittle and toughened adhesives are compared under quasi-static and repeated load environments. Since this phase of the work considers adhesive response (rather than adherend failure), the adherends are made of 2024-T3 aluminum. The testing regime is designed to study the effects of peel (double cantilever beam coupons) and shear (wide area lap shear coupons and scarf joints) stress on bond strength and durability. The coupons are bonded using brittle and toughened adhesives (FM-300, FM73, EA9696) so that effects of adhesive strength and toughness may be independently considered.

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