Effects of heat treatment and minor additional elements Cr or Zr on mechanical and SCC properties of 7075 based cast alloys fabricated with a newly developed rheocast method were investigated. SCC tests were conducted by SSRT slow strain rate tensile technique using a round bar tensile specimen under a constant strain rate 8.3ϫ10 Ϫ7 /s in 3.5%NaCl aerated solution. Similarly with a rolled alloy 7075, the rheocast alloy with temper of underaging or peak-aging T6 showed a high susceptibility to SCC, while the alloy with temper of overaging, T73 or T77 exhibited a less elongation in tensile property, although together with an improved resistance to SCC. On the other hand, the alloy direct-quenched into an oil bath at 433 K from solution temperature, followed by aging for 86.4 ks, represented a superior combination among strength, elongation and SCC resistance, and the alloy with 0.2 mass% Cr addition showed a more improved combination. The improvement was attributed to a repression of hydrogen embrittlement caused by coarsening of precipitates in gain matrix and along grain boundary, and further by a relief for planar slip due to fine distribution of Cr dispersoides within grains.
We have developed a functional distributed fiber-optic stress sensor by synthesis of the optical coherence function (SOCF). The technique determines the location of stress-induced polarization mode coupling in a polarizationmaintaining fiber (PMF) by measuring the optical path difference (OPD) between the fast mode and the slow mode in PMF with SOCF. By modulating the frequency of the lightwave from a super-structure-grating distributed Bragg reflector laser diode (SSG-DBR-LD) in a stepwise waveform, the coherence function is synthesized into a series of periodical peaks in the meaning of time-integration. The period is controlled to allow only one coherence peak enter the range of the PM fiber under test. Then we can measure the polarization mode coupling at the position corresponding to the peak. The position of the peak is adjusted by using a phase modulation proportional to the frequency modulation. Therefore, polarization mode coupling distribution along the fiber can be obtained. Up to date, one end of the sensing fiber is used as the input end, and the other as the output end. This scheme is generally not convenient for remote applications. In this presentation, we report two new effective methods that unify the input and the output to one end of the fiber. In one scheme, a mirror plus a polarizer is attached to the far end of the PM fiber. The other scheme employs a polarization beam splitter (PBS) attached to the far end of the PM fiber. The light beam output from the PBS in one polarization direction is fed back into the fiber through the PBS in the perpendicular polarization direction. Experimental demonstrations for both schemes are presented.
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