Patent ID: 7694581

Claim:
A testing apparatus for measuring lateral deformation of a test piece during triaxial compression tests, the testing apparatus comprising: a collar formed of a single ring having free ends spaced by a distance, said single ring being formed of a metal material or a composite material, said collar having a means for measuring the distance between said free ends, said means for measuring comprising: a flexible blade fitted with at least one stress gauge, said flexible blade being pre-stressed and fastened to one of said free ends of said single ring; a contact finger fastened to the other of said free ends of said ring, said contact finger extending perpendicular to said flexible blade, said contact finger suitable for causing a bending of said flexible blade during a deformation of said collar; and a means for adjusting a position of said contract finger in relation to said flexible blade; and a sheath encircled by said single ring such that said single ring grips said sheath, said sheath suitable for protecting the test piece, said sheath having a flexible sleeve, said sleeve having at least a pair of hard spots evenly spaced from each other around a circumference of said sleeve so as to form support points for said collar, each of the hard spots being an insert having a thickness substantially equal to a thickness of a wall of said sleeve, said insert having sides flush with both sides of said wall of said sleeve, said insert having therein means for interlocking said insert on said sleeve.