Abstract:
The invention relates to a collar for measuring the lateral deformation of a test piece during uniaxial or triaxial compression tests. According to the invention, the collar includes a metal hoop or a hoop that is made from composite materials, which can clasp the test piece and which is open. The free ends thereof are separated by a distance Δ. The inventive collar also includes a mechanism for directly or indirectly measuring the distance Δ. Between the free ends of the hoop, the mechanism includes at least one strain gauge.

Description:
CROSS-REFERENCE TO RELATED U.S. APPLICATIONS 
   Not applicable. 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not applicable. 
   NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT 
   Not applicable. 
   REFERENCE TO AN APPENDIX SUBMITTED ON COMPACT DISC 
   Not applicable. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention concerns a collar for measuring the lateral deformation of a test piece during compression tests, in particular uniaxial or triaxial. 
   It will find a particular application in a polyvalent triaxial test cell for sample geomaterials of rock, of soil, of cimentitious materials or of fabricated materials, on the sampling sites, in laboratory test conditions. Such samples, also called test pieces, cylindrical in shape, may be subjected to different pressure, load, temperature, and drainage conditions, wherein said parameters may be controlled using pressure, temperature, internal or external displacement sensors. The pressure stresses may be directed axially and/or to the lateral face of the sample. 
   2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98. 
   Document FR-2.566.531 divulges a lateral displacement sensor, in the form of a collar, formed of a plurality of parallel rolls, hinged together, and capable of clamping the sample held by a spring-loaded system. Such collar enables to measure the lateral deformation of the sample while measuring the spacing of both last rolls. 
   Document FR-2.663.121 divulges a polyvalent triaxial test cell for geomaterials. Such cell includes a pressure chamber inside which is placed the cylindrical test piece. It includes at least one compression jack capable of exerting uniaxial thrust longitudinally to the test piece. A lateral pressure, and more particularly radial, is exerted on the test piece while subjecting the lateral face of said cylindrical test piece to the pressure of a fluid. A hydraulic compensation system enables moreover to balance the longitudinal and radial loads. 
   Also, the sample is immersed in a fluid, such as oil, and is protected from said fluid by means of a sheath in the form of a sleeve formed of an elastic diaphragm. In order to measure the lateral deformation of the sample, a collar of known type, formed of rolls, is placed around the sheath while hugging it. 
   Nevertheless, such a collar proves little satisfactory, since these rolls have a tendency to impress in the elastic wall of the diaphragm, thereby disturbing their displacement by rolling around the periphery of the sleeve. 
   Moreover, it has been noticed that the elasticity of the wall of the diaphragm twists the measurement, wherein the collar measures the lateral deformation of the sample, but also the lateral deformation of said diaphragm. 
   Moreover, the collar known aforementioned, formed of rolls, proves relatively cumbersome and requires a test cell whereof the pressure chamber is sufficiently large, in particular in width, to be installable. 
   BRIEF SUMMARY OF THE INVENTION 
   The aim of the present invention is to provide a collar measuring the lateral deformation of a test piece which remedies the shortcomings aforementioned, thereby enabling to increase the accuracy of the measurements. 
   Another aim of the invention is to provide a measuring collar, simple in its design and at low cost. 
   Another aim of the invention is to offer a protective sheath for specific test piece, suited to be used with a collar according to the invention. 
   Other aims and advantages of the present invention will appear from the following description, given solely by way of example and without being limited thereto. 
   The invention relates first of all to a collar for measuring the lateral deformation of a test piece during compression tests, in particular uniaxial or triaxial. The collar is formed of a metal ring or a ring made of composite materials, capable of clamping said test piece and being open. The free ends are spaced apart by a distance A, said collar exhibiting moreover means for measuring; directly or indirectly, the spacing  4  of said free ends of the ring, formed by at least one stress gauge. 
   The invention also relates to a sheath, intended for being used in a test cell, in order to protect a test piece, in particular mineral, rock and/or soil, or concrete. The sheath is formed by an elastic sleeve and is capable of cooperating with a measuring collar in particular according to the invention. 
   According to the invention, the sleeve exhibits, in its wall, at least two hard spots spread regularly on the circumference of said sleeve, being capable of forming resting points for said collar. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The invention will be understood better when reading the following description accompanied by the appended drawings. 
       FIG. 1  is a perspective view of a measuring collar according to the invention. 
       FIG. 2  is a diagrammatical top plan view of the measuring collar as illustrated on  FIG. 1 . 
       FIG. 3  is a perspective view of a protective sheath according to the invention. 
       FIG. 4  is a horizontal sectional view IV-IV, as illustrated on  FIG. 3 . 
       FIG. 5  is a detailed sectional view as illustrated in the frame V-V. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The invention relates first of all to a collar for measuring the lateral deformation of a test piece during compression tests, in particular uniaxial or triaxial. 
   By lateral deformation is meant a deformation of the test piece in a plane perpendicular to the longitudinal axis of the cylindrical test piece. 
   According to the invention, the collar  1  is farmed of a metal ring or a ring made of composite materials, capable of clamping said test piece. The ring  2  is open. The free ends  3  of the ring are spaced apart by a distance A. Said collar  1  exhibits moreover means  5  for measuring; directly or indirectly, the spacing A of said free ends  3  of the ring  2 , the means being formed by at least one stress gauge  6 . 
   The stress gauge, also called extensometric gauge, is an apparatus enabling to follow the deformation of materials subjected to stresses, by means of resistance variations of an electric conductor. 
   The metal ring, being made of composite materials, can be composed of a single-piece or two adjoining portions, for instance joined by welding, in particular rigid or semi-rigid. It enables the test piece to be clamped by hugging. 
   In an embodiment, the means  5  for measuring the spacing of said free ends of the ring are formed by four stress gauges. 
   In a particular embodiment, illustrated on  FIG. 1  or  2 , the measuring means  5  are formed, on the one hand, by a resilient blade  7  fitted with said at least one stress gauge  6 . The resilient blade  7  is pre-stressed and slaved to one of the free ends  3  of the ring  2 . On the other hand, with a contact finger  8 , the resilient blade  7  is slaved to the other end of the ring, being capable of causing the flection of the resilient blade during the deformation of the collar. 
   The free ends of the ring  3  are each spaced apart by a material protrusion, substantially parallel to one another. 
   As illustrated on  FIG. 1  or  2 , said resilient blade  7  is arranged at an end  3  of the collar  1 , held substantially perpendicular to the plane of the collar by one of its ends. 
   The stress gauge(s) are instrumented, according to a technique known, with an electric measuring device, capable of measuring the resistance variations of the gauge. Such a device, after calibration, enables to retrieve the deformation of test piece. 
   Advantageously, the resilient blade is pre-stressed, i.e. stressed even when the collar is at rest, so that the values measured by the electrical measuring device are reliable and continuous. 
   The stress gauge(s) may be slaved to the resilient blade by gluing. 
   In an embodiment, the contact finger  8  is arranged substantially perpendicular to the resilient blade  7 . The collar exhibits a first means for adjusting the position of the contact finger relative to said resilient blade. 
   As illustrated on  FIGS. 1 and 2 , the contact finger  8  is threaded, in particular in the form of a screw, and capable of co-operating with the internal screw thread of a bore provided at one of the free ends  3  of the ring  2 . The contact finger  8  is then screwed, mounted as a through-piece at a flank  15  extending upwards from such a protrusion forming such a free end  3 . 
   In an embodiment, one of the free ends  3  of the ring  2  exhibits a clamping jaw  9 , capable of maintaining said resilient blade  7 . 
   As illustrated on  FIG. 1 , such a material protrusion, forming such a free end  3 , shows a shoulder against which a cheek  16  clamps the resilient blade  7 , at the lower end thereof, in particular by means of a locking screw  17 . 
   A cover (not illustrated) may be provided to protect the resilient blade  7 . The cover may be provided removable, in particular slaved to the cheek  16  of the clamping jaw  9 . The cover extends upwards over the whole height of the blade  7  and shows an internal volume inside which the blade  7  may be clamped during the deformation of the collar. 
   In an embodiment, the free ends  3  of the ring  2  are connected by extended resilient means  10 . The resilient means  10  enable advantageously to pre-stress the resilient blade  7 . The collar may exhibit moreover means for adjusting the recall force of the resilient means  10 . 
   The resilient means  10  may in particular be in the form of an extended spring or in the form of an O-ring. 
   Both free ends  3  of the ring  2  may be connected by resilient means  10  at two catching points  11 ,  12 , wherein the collar exhibits moreover second means  13 ,  14  for adjusting the position of a catching point  12  relative to one of the free ends  3  of the ring  2 . 
   Said second setting means are illustrated for instance on  FIGS. 1 and 2 . For easier illustration, said second setting means have been illustrated below the free ends  3  of the collar on  FIG. 1  and in the extension of said free ends  3  on  FIG. 2 . 
   Also, advantageously, a catching point  13  is formed by an element mounted slidingly, along the longitudinal direction of the resilient means, at such a free end  3  of the ring. Such element is tapped, to be traversed by a positioning screw  14 , capable of bearing upon one side of such a free end  3 . 
   In a non-illustrated embodiment, both free ends  3  of the ring are, in particular, traversed by a guiding rod, in particular at a bore running through said free ends  3 . 
   This guiding rod, mounted slidingly at least as such a free end  3 , sees to it that the collar  1  deforms in a controlled fashion, in particular without any twist, so that said free ends  3  are kept substantially opposite to one another. 
   However, the invention also relates to a sheath  20 , intended for being used in a test cell, such as that for instance described in document FR-2,663.121, in order to protect a test piece  21 , in particular mineral, rock, soil, or concrete. The sheath  20  is formed of a resilient sleeve  22 , being capable in particular of co-operating with a measuring collar according to the invention. 
   According to the invention, the sleeve  22  exhibits in its wall at least two hard spots  24 , spread regularly on the circumference of said sleeve  22  and capable of forming resting points for said collar  1 . The sleeve can be realized from an elastic diaphragm in particular from of an elastomer. 
   As illustrated on  FIG. 4 . The sleeve exhibits, according to an embodiment, four points spread regularly on the circumference of said sleeve at 90°. 
   Such hard spots will be advantageously formed by a material exhibiting a stiffness greater than the diaphragm and a stiffness greater than the sample so that their deformation is negligible relative to the deformation of the test piece. Such hard spots might be formed in particular of a metal matter. 
   According to an embodiment, each hard spot  24  is formed of an insert, of thickness substantially equal to the thickness of the wall of the sleeve, and flush with both sides of said wall. The insert exhibits moreover interlocking means  25 ,  26  for retaining said insert to the sleeve. 
   The interlocking means might be formed by a lateral lug  25 , capable of extending, along the wall of the sleeve, as shown on  FIG. 4 , inside a mortice  26  arranged in said wall so as to form a baffle providing for the tightness of the sleeve to fluid. 
   Advantageously, as illustrated as a dotted line on.  FIG. 3 , the lateral lug is continuous on the periphery of the insert. 
   Thus, as illustrated on  FIG. 5 , during the deformation of the diaphragm, the lug  25  is capable of sliding in the mortice  26  arranged in the diaphragm providing for the tightness function even during deformations. 
   The insert can be advantageously arc-shaped by a curving radius substantially equal to the curving radius of the wall of the sleeve. 
   Advantageously, the lateral lug is advantageously arc-shaped similarly. 
   The sleeve can be in particular made of silicon. The sleeve is advantageously compound-filled in a mold where the inserts are pre-positioned. For instance, the molding operation is performed under vacuum to prevent the occurrence of inclusions, in particular bubbles. 
   Naturally, other embodiments, understandable to the man of the art, could have been contemplated without departing from the framework of the invention.