In this study, anisotropic stiffness tensors were reconstructed based on fiber orientation distributions obtained from X-ray computer tomography (xCT). A preform was manufactured via a big area additive manufacturing (BAAM) system with carbon fiber (CF) filled acrylonitrile butadiene styrene (ABS). The tailored preform from additive manufacturing (AM) was used in the compression molding (CM) process to produce a low-void high-performance thermoplastic composite panel. An xCT technique was employed to detect the fiber orientations in CF/ABS composites manufactured via three different methods: AM from BAAM, extrusion compression molding (ECM), and AM-CM. The anisotropic stiffness tensor was obtained from the composite panel manufactured via the three manufacturing methods (AM, ECM, and AMCM). A micromechanics theory was used to obtain the orthotropic stiffness tensors of the composite panels and compared with the experimental values. The predicted stiffness tensors of AM and AM-CM composite panels were used to study the deformation characteristics of a steering wheel during airbag deployment by performing finite element analysis (FEA). The approach developed in this study can be utilized for evaluating high-performance composites.
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.
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.
Non-destructive testing of critical structural components is time consuming, while necessary for maintaining safe
operation. Large aerospace structures, such as the vertical stabilizers of aircraft undergo inspection at regular intervals
for damage diagnostics. However, conventional techniques for damage detection and identification before repair can be
scheduled are conducted off-line and therefore can take weeks. The use of guided ultrasound waves is being investigated
to expedite damage detection in composites. We measure the frequency dependent loss of ultrasonic guided waves for a
structure comprising a boron-nitride composite skin sandwiching an aluminum honeycomb. A wide range of ultrasound
frequencies propagate as measured using PZTs, with the lowest attenuation observed about 200-250 kHz. These
measurements are confirmed using optical fiber Bragg grating arrays used as ultrasound transducers.
Advanced composites are being used increasingly in state-of-the-art aircraft and aerospace structures. In spite of
their many advantages, composite materials are highly susceptible to hidden flaws that may occur at any time during
the life cycle of a structure, and if undetected, may cause sudden and catastrophic failure of the entire structure. This
paper is concerned with the detection and characterization of hidden defects in composite structures before they
grow to a critical size. A methodology for automatic damage identification and localization is developed using a
combination of vibration and wave propagation data. The structure is assumed to be instrumented with an array of
actuators and sensors to excite and record its dynamic response, including vibration and wave propagation effects. A
damage index, calculated from the measured dynamical response of the structure in a previous (reference) state and
the current state, is introduced as a determinant of structural damage. The indices are used to identify low velocity
impact damages in increasingly complex composite structural components. The potential application of the approach
in developing health monitoring systems in defects-critical structures is indicated.
Advanced composites are being used increasingly in state-of-the-art aircraft and aerospace structures. In spite of their
many advantages composite materials are highly susceptible to hidden flaws that may occur at any time during the life
cycle of a structure and if undetected, may cause sudden and catastrophic failure of the entire structure. An example of
such a defects critical structural component is the "honeycomb composite" in which thin composite skins are bonded
with adhesives to the two faces of extremely lightweight and relatively thick metallic honeycombs. These components
are often used in aircraft and aerospace structures due to their high strength to weight ratio. Unfortunately, the bond
between the honeycomb and the skin may degrade with age and service loads leading to separation of the load-bearing
skin from the honeycomb (called "disbonds") and compromising the safety of the structure. This paper is concerned with
the noninvasive detection of disbonds using ultrasonic guided waves. Laboratory experiments are carried out on a
composite honeycomb specimen containing localized disbonded regions. Ultrasonic waves are launched into the
specimen using a broadband PZT transducer and are detected by a distributed array of identical transducers located on
the surface of the specimen. The guided wave components of the signals are shown to be very strongly influenced by the
presence of a disbond. The experimentally observed results are being used to develop an autonomous scheme to locate
the disbonds and to estimate their size.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.