Stress experiments, data acquisition

Before data acquisition techniques for stress MS experiments are reviewed, the operation of the TOFMS is discussed briefly. Detailed discussions of the theory and principles of TOFMS operation are in the literature (19,20), The essential features of a TOFMS are shown in Figure 5. The elements A, B, C, E, and F provide a pulsed monoenergetic electron beam of fixed current which ionizes molecules in the ion-source... 

The essential data acquisition problem in stress MS experiments is to record the information displayed on the oscilloscope screen during the time that the sample undergoes stress and/or failure. Both cinematography and still photography of the oscilloscope screen have been used. 

Cinematography. This data acquisition technique is straightforward in principle but tedious in practice. A high-speed movie camera photographs the mass spectral display on the oscilloscope screen. When the camera operates at 400 frames per sec and the mass spectrometer at a repetition rate of 10 kHz, each frame of the film contains the information of 25 mass spectra. This arrangement permits time resolution of 2.5 msec. A 150-m film records data for approximately 50 sec which is adequate for most stress MS experiments. 

The range of experimental methods and data acquisition techniques for stress mass spectrometry experiments provide a way to obtain a great amount of data on the volatile compounds evolved from polymeric samples when subjected to a mechanical load. These data provide information concerning the events occurring in the polymer which produce the evolved volatile compounds. 

Although not all of the experiments needed to determine residual stresses have been completed, some useful data has been gathered. As temperature increased, the diffraction peaks shifted to lower two theta values, indicating an increase in d-spacing correlating to thermal expansion of the composite material.(Figure 5) Once analysis of the powder samples is complete, the inherent thermal expansion of each phase can be calculated, which will allow the strains to be determined for each phase in the composite material. The diffraction patterns from the experiments also provided evidence that the use of B to produce the parts made neutron diffraction possible. The patterns were visible within the first few minutes of data acquisition, which indicated the excellent scattering from the material. 

The experiments presented in this work were conducted on a laboratory-scale flow rig at the University of Huddersfield. For the ERT experiments, a total of2000 flames of data each consisting of 104 measurements were recorded in a period of 20 seconds. The results were compared with those fl om the weighing hoppers and the miniature conductivity probe, both of which require a considerably longer acquisition time, due to their mechanical nature. It is important to stress that the experiments involving the miniature probe and the ERT system were not conducted simultaneously, as different time scales were involved, hence, slight differences in results were expected. 

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