Feasibility Investigation of Utilizing the Internal Friction Damping Nondestructive Evaluation Technique (IFD-NDE) for Measuring the Degree of Fatigue in Mobile Bridge Structures.
DAEDALEAN INC WOODBINE MD
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This report discusses a nondestructive test technique which has the potential for measuring the degree of fatigue in military bridge structures. The physical property that is monitored in IFD-NDE is the rate at which an energy impulse imparted to a material or structure decays due to the internal friction of the material. A change in rate of decay reflects changes in the basic chemical andor mechanical properties of the material due to an accumulation of subtle material variables. These material variables include grain size, chemical compositions, interstitial elements, dislocations, precipitate particles, strain rate effects, etc. It has been shown in some materials to be possible to predict the remaining fatigue life before failure occurs by proper monitoring of the accumulation of these variables. This program sought to adapt the IFD-NDE technique to military bridges by first identifying the characteristic damping coefficient versus fatigue life curve for bar specimens of the materials used in bridges. Results generally show that for 6061 and 7075 aluminum alloys, the damping coefficient remains fairly constant until a point of approximately 30 remaining material life where a noticeable spike occurs in the data. Afterwards the damping coefficient returns to a nominal value. For the 7005 aluminum alloy, no correlation was found between the remaining fatigue life and damping capacity.
- Civil Engineering