The present invention relates to a high tensile wire structure including an outer sleeve of a fiber-reinforced resin material enclosing an elongated light guide the form of an optical fiber. The latter makes it possible to monitor optically the tensile stress, breakage or bending stress applied to the wire. The wire structure of this invention is applicable for example as a bracing wire for reinforced concrete.
From the German publication DE-OS No. 3,016,009 a method of producing fiber-reinforced resinous structures is known in which fibers drawn in one direction through a manufacturing apparatus are first impregnated with resin, then provided in warm air with a gel-like upper surface, and finally guided through a bath of molten metal having a temperature between 95.degree. C. and the decompostion temperature of the resin. The fed-in resin has a composition which becomes cross-linked and hardened by the applied heat and which is kept in liquid condition at ambient or increased temperatures. The heat-hardening resin can be of various kinds, such as epoxy resins, polyamides, polyesters, phenolformaldehyde resin, silicon resins, and the like. This known method can be employed in connection with all known fibrous materials, such as for example glass fibers, steel fibers, Aramid fibers (registered trademark), graphite fibers and the like. These fibers can also enclose other fibers which in turn are coated with different protective layers, such as for instrance soft metal fibers (copper) or optical fibers. These structures can be of an arbitrary cross section and can include electrical conduits, light guides, fluid conduits, and the like, which are surrounded by the fiber-reinforced outer resin structure and whose form is determined by forming nozzles or matrices.
In this known method, it is possible to employ an optical fiber (light guide) as a center fiber on which the surrounding reinforcing fibers are run, whereby the light guide is coated with a separating agent in which the resin does not adhere. In this manner the light guide is surrounded by more or less loosely applied resinous cage of reinforcing fibers which cab be withdrawn from the light guide without any breakage of adhesive connections between the resin and the light guide.
A high tensile fiber-compound material in which glass fibers oriented in one direction are bound with polyester resin is commercially available from Bayer AG of Leverkusen, Germany, under the registered trademark Polystal. This material, in connection with a light guide, has been hitherto employed as a protective material for optical communications cables only. In the latter cables, care is always taken that the light guide be loosely inserted in its outer jacket, so that outer stresses be minimized, and in addition that the different expansions between the light guide and the jacket be compensated. An example of such an application is disclosed in the German publication DE-OS No. 3,112,422.
Furthermore, it is also known how to employ a light guide for monitoring component parts exposed to a tensile stress. For example, in German publication DE-OS No. 2,937,824 a method is described in which the light guide is cemented on or inserted into a component part to be monitored, the cementing being used preferably for metal parts and the insertion is used for component parts of a plastic material or of concrete. In this priorart method the inlet and outlet ends of the light guide are connected to an instrument for testing the light throughput, so that the light conduction or attenuation is continuously or intermittently monitored to serve as a measure of expansion or the danger of breakage of the associated component.