This paper reports an application of phase shifted fiber Bragg grating (PS-FBG) intensity-type acoustic sensor in a
continuous and in-situ failure testing of an E-glass/vinylester top hat stiffener (THS). The narrow transmission channel
of the PS-FBG is highly sensitive to small perturbation, hence suitable to be used in an effective acoustic emission (AE)
assessment technique. The progressive failure of THS was tested under transverse loading to experimentally simulate the
actual loading in practice. Our experimental tests have demonstrated, in good agreement with the commercial
piezoelectric sensors, that the important failures information of the THS was successfully recorded by the simple
intensity-type PS-FBG sensor.
In this paper, we report our recent work in an application of fiber Bragg grating (FBG) sensors in progressive failure
monitoring of E-glass/vinylester top-hat stiffener (THS) composites. FBG sensor arrays were embedded at strategic
points within the THS to monitor the onset and progress of failure modes as the THS undergone a transverse loading.
Techniques to embed FBGs in-situ during composite structure fabrication are developed. Our experiments demonstrated
that key structural failure information can be obtained from the analysis and assessment of data, such as average strain,
strain gradient and full spectrum measurements, collected by the embedded FBG sensors.
Effects of apodization on distributed feedback fiber laser (DFB FL) output power and threshold gain are theoretically
investigated by employing the transfer matrix method. Three distinct types of profile are investigated: the gaussian, flat
or nonapodize, and sigmoid profile. The gaussian and sigmoid profiles are the two extreme cases examined; the former
has a strong profile around a centrally located phase shift, while the latter is with a weaker profile. Findings indicate that
the tradeoff between output power and higher order mode threshold performance are resulting from the interplay
between these profile shapes. The comprehensive results presented in this paper should assist the development of high
performance DFB FLs.