Search

A survey of structural problems on offshore rigs indicates a need for a better understanding of fatigue loading produced by dynamic effects initiated by the oceanic environment. For general design purposes a valid loading spectra might be produced by measuring elastic strain cycles in selected oceanic areas, over extended periods. Examination of a typical strain sensor output shows that the record can be handled as counts of cyclic loading at preselected magnitudes. These indicate the loading spectrum for that particular area, and also can be used, in association with Miner’s cumulative damage hypothesis, to provide an estimate of the damage produced by the loading history. A simple instrument is described which will count the number of times particular strain levels have been exceeded. Numbers of counts can be printed out automatically for periods of up to 8 weeks, and can also be read manually at any time. Special provision is required if long term variation in mean strain is to be corrected.

A new type of thin-film strain sensor has been conceived. This sensor is a p-n heterojunction diode utilizing polycrystalline semiconductor layers obtained by vacuum evaporation onto an insulating substrate. The device exhibits large shifts in its forward I-V characteristic when subjected to a mechanical strain, and thus functions as a low output impedance voltage source.

Several simple pressure transducers have been built by using heterode strain sensors evaporated directly onto a pressure diaphragm. The performance of these units indicates that pressure transducers are a feasible area of application for the heterode strain sensor, and that such transducers are potentially inexpensive and easily adapted to a variety of pressure ranges.

Using a new device concept, a unique semiconductor strain sensor has been demonstrated in the laboratory. It is a p-n heterojunction diode which is fabricated by vacuum evaporation techniques directly onto flexible substrate. This sensor's mechanical input properties are controlled by the choice of substrate, and it has a low-impedance voltage source output characteristic.