Device for detecting an applied compressive load

A one-shot compressive-load sensitive electrical circuit element which changes from an electrically non-conductive condition to a conductive condition when a compressive load of predetermined magnitude is applied thereto, comprising:

• a first and a second electrically conductive metallic member, the first of said members being made of material which is harder and less ductile than the material of the second member, a first substantially planar face on the first member, a second substantially planar face on the second member, a wall receding from the first planar face at an angle thereto, said wall at least partially defining an open region adjacent to the first face, a substantially flat insulation layer between the faces, the faces being opposed to and facing one another across the insulation layer, and being contiguous thereto, the faces being the closest portions of the members to one another so as to function to hold the members apart in a compressive substantially non-yielding stack while the insulation layer remains unbroken at said second planar face adjacent to the wall, and said insulation layer extending beyond the wall and over the open region, the material of the insulation layer being hard and brittle, and of such thickness that, when the members are pressed toward each other by a compressive load, the insulation layer remains unbroken until said predetermined load, whose magnitude depends at least in part on the physical strength of the insulation layer, is applied, whereupon the insulation layer abruptly fractures adjacent to the wall, and a portion of one of the members moves axially toward the other member, displacing in a shear-like axial movement that portion of the insulation layer which is bounded by the wall, whereby to bring insulation-free metal of both members into contact with each other and thereby to make an electrically conductive contact as a consequence of the application of said load, said members being adaptable to connection into an electrical circuit.