The new forming limit diagram (FLD) of a laser tailored blank, which includes independent forming limit curves (FLCs) of a welded zone and constituent base metals, is introduced. To obtain the forming limits of a welded zone, hemispherical dome tests are performed with various widths of symmetric and asymmetric specimens. Together with the know-how to find specific strain conditions for the FLC of a welded zone, the experimental experience is discussed. The dome height at the fracture associated with various specimen widths in the same and different thickness combinations is also investigated in order to examine the formability of a laser tailored blank. In order to see the reliability and applications for the new FLD, the measured strains of a squared cup drawing and the simulated strains of a door inner panel stamping are compared with their FLDs. The successful prediction of the fracture with a new FLD reveals that the forming limits of a welded zone and constituent base metals should be found separately for the accurate evaluation of the formability and workability of the laser tailored blank.
Abstract. Composite pressure tanks are rapidly expanding in their range of use. However, for high pressure flammable or toxic gases, there is less confidence about their reliability. In this study, fiber Bragg grating (FBG) sensors embedded into a filament wound composite pressure tank monitored strain and detected damage. The sensor heads and fiber optic lines were protected with an acrylate recoating, adhesive films, and PVC tubes with Teflon ® to survive under the harsh environment of the filament winding process. During the quasi-static loading test, the internal strain was measured with embedded FBG sensor arrays. Simultaneously, acoustic emission (AE) signals from matrix cracks and delaminations were detected with both an embedded FBG sensor and an attached piezoelectric sensor. The signal characteristics from the sensors were then compared. For the feasibility test of active sensing, impacts were applied on 3 different positions in each side by an impact hammer. The difference between damaged and undamaged sides in impact response was analyzed. A FBG interrogation system using a wavelength-swept fiber laser (WSFL) was used for the strain measurement, and an EDFA source with a tunable Fabry-Perot filter was used for the high frequency vibration.
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