Acoustic Emissions (AE) has been successfully used with composite structures to both locate and give a measure of
damage accumulation. The current experimental study uses AE to monitor large-scale composite modular bridge
components. The components consist of a carbon/epoxy beam structure as well as a composite to metallic bonded/bolted
joint. The bonded joints consist of double lap aluminum splice plates bonded and bolted to carbon/epoxy laminates
representing the tension rail of a beam. The AE system is used to monitor the bridge component during failure loading to
assess the failure progression and using time of arrival to give insight into the origins of the failures. Also, a feature in
the AE data called Cumulative Acoustic Emission counts (CAE) is used to give an estimate of the severity and rate of
damage accumulation. For the bolted/bonded joints, the AE data is used to interpret the source and location of damage
that induced failure in the joint. These results are used to investigate the use of bolts in conjunction with the bonded
joint. A description of each of the components (beam and joint) is given with AE results. A summary of lessons learned
for AE testing of large composite structures as well as insight into failure progression and location is presented.
It has been well established that using viscoelastic damping materials in structural applications can greatly reduce the dynamic response and thus improve structural fatigue life. Previously these materials have been used to solve vibration problems in metallic structures, where the damping material is attached to the structure and then a stiff outer layer is attached to promote shear deformation in the damping material. More recently, these materials have been used successfully in expensive aerospace composite structures, where the damping material is embedded between plies of prepreg graphite/epoxy prior to being cured in a high-temperature, high-pressure autoclave. The current research involves embedding these damping layers into low-cost composite structures fabricated using the Vacuum Assisted Resin Transfer Molding (VARTM) process. The damping layers are perforated with a series of small holes to allow the resin to flow through the damping layer and completely wet-out the structure. Experimental fabrication, vibration testing, and stiffness testing investigate the effect of hole diameter versus hole spacing. Results show that the damping and stiffness can be very sensitive to perforation spacing and size. It is shown that for closely spaced perforations (95% damping area) that damping increases by only a factor of 2.2 over the undamped plate. However, for greater perforation spacing (99.7% damping area) the damping is increased by a factor of 14.3. Experimental results as well as practical design considerations for fabricating damped composite structures using the VARTM process are presented.
Forced Vibration testing of four different damage states of a full scale, six span, reinforced concrete bridge, were conducted by Utah State University. These tests were performed to characterize the bridge based on its dynamic characteristics and to determine any correlation that may exist between the dynamic properties of a structure and the location of the inflicted damage. The test structure was a mature bridge being prepared for demolition as part of the Interstate 15 reconstruction through Salt Lake City. An eccentric mass shaker was utilized to excite the structure at several different natural frequencies for which data was collected through an array of seismometers. This data was processed to determine the natural frequencies and mode shapes of the structure. Investigation showed a decrease in the natural frequencies of the structure as well as noticeable changes in the mode shapes of the structure as a result of localized damage to the structure.
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