Abstract:
A testing fixture assembly induces a compound bend deflection in a test panel upon relative movement of opposing pressure applying parts. A panel holder has restraint members for receiving the edges of a test panel and a measuring device has an element for measuring the compound deflection induced in the panel. A liquid filled bladder formed of a pair of opposed pliant membranes is partitioned by a non-pliant plate and a bladder frame structure sandwiches the perimeter edge portions of the plate and membranes in tightly clamped relationship.

Description:
This invention claims the priority of U.S. provisional application Serial No. 60/324,657 filed Sep. 25, 2001 and relates to testing machines for measuring the effects of varied high pressure loadings on heavier gauge marine hull compositions and other rigid plate test panels. 
    
    
     FIELD OF THE INVENTION 
     BACKGROUND OF THE INVENTION 
     The present application is directed to a system of the general type described in U.S. Pat. No. 5,431,061 entitled DEFLECTION TESTING FIXTURE ASSEMBLY AND METHODS OF TESTING issued Jul. 11, 1995, which discloses and claims a system wherein the material being tested must withstand loads which:apply bends in the test panels in two dimensions along two axes simultaneously over a substantial area of surface. 
     While this machine has proven to work exceedingly well, it has not been possible to use it at much higher pressures to test heavier gauge marine hull multiple plywood and sandwich composite materials or to test more rigid and elongate test panels such as composite material bridge deck samples. 
     The present mechanism is particularly advantageous for testing the complex interactions between resin, fiber, and core that take place when a flat composite panel is forced to compoundly bend, or between resin and ply when a multi-ply wood sample is so flexed, and differs from the machine depicted in the patent mentioned in certain critical aspects and its ability to operate with more rigid materials. 
     SUMMARY OF THE INVENTION 
     The present invention is concerned with a machine which can utilize much higher pressures to test not only heavier gauge boat hull composites, but also a host of other rigid composites and other materials which may be used for such diverse purposes as, for example, bridge decks. Such decks may comprise spaced apart flat composite sheets with honeycomb or cellular cores bonding to them as an integral, part of them, and the test panels employed may be elongately rectangular in configuration. 
     Whereas, in the patent cited, the bladder or envelope was constructed of pliant membranes whose edges were joined in abutting relationship by a perimeter clamp frame, the present bladder incorporates a plate between the membranes with edges which separate the membrane edges and provide an edge composite assembly in which each membrane edge is tightly clamped against the intermediate plate in a manner to seal the bladder so liquid cannot escape, even when the bladder is subjected to pressures in the neighborhood of three times the pressures previously used. The plate stabilizes the clamp frame under these pressures and prevents the clamp frame from distorting out of its footprint and altering the shape of the distributed load during the test. 
     The prime object of the present invention is to retain the attributes of the previous testing machine, while permitting the machine to apply contact loads on more rigid materials to obtain the required load distributions over the contact areas. 
    
    
     Other objects and advantages of the invention will become apparent with reference to the accompanying drawings and the accompanying descriptive matter. 
     THE DRAWINGS 
     The presently preferred embodiment of the invention is disclosed in the following description and in the accompanying drawings, wherein: 
     FIG. 1 is a fragmentary schematic sectional end elevational view of the lower end of the testing machine frame; 
     FIG. 2 is a fragmentary schematic end elevational view showing only the upper portion of the machine upper frame; 
     FIG. 3 is a greatly enlarged, fragmentary, sectional end elevational view showing a test panel in position ready for initiation of the test; 
     FIG. 4 is an exploded schematic perspective view of the liquid filled bladder component parts; 
     FIG. 5 is a greatly enlarged schematic fragmentary sectional side elevational view showing the pressure tube or probe carried in the equalizing plate; 
     FIG. 6 is a top plan view illustrating the configuration of the probe groove in the equalizing plate; 
     FIG. 7 is a schematic sectional fragmentary side elevational view illustrating the manner in which shear forces react on the former prior art edge construction; 
     FIG. 7A is a sectional side elevational view illustrating shear forces reacting in the new edge clamping system; and 
     FIG. 8 is a schematic diagram identifying the various electronic components used in the test. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     It needs to be understood that the machine involved in the present invention may be an MTS system machine of the character previously used which is capable of applying the heavier pressures to test panels which require the heavier pressures to deflect them. 
     As such, the machine includes an upper cross head  10  supported on vertically disposed columns  11  extending to the base B of the machine. In the present instance, the vertically movable cross head  10  is used in vertically stationary position. The heavier pressure load cell which is connected to cross head  10  has hydraulic grippers  13  for supporting the T member  14 . 
     The member  14  supports the hollow pyramidal fixture  14   a , which has a cap  15  bolted to the T member  14  as at  16 . Below the fixture  14   a  is the MTS machine actuator plate or platen  17 , which is hydraulically powered by the MTS machine to move upwardly at a controlled rate toward load cell  12 . The actuator member  17  is supported by the base B on a support block  18  provided on the actuator  17  to receive a bladder or envelope, generally designated E, which, as illustrated, is of rectangular configuration. Upper and lower three ply rectangular membrane sections or sheets  19  and  20 , respectively, are provided to form the bladder and are made up of, for example, food service, polyester belting, as previously. This belting may comprise polyester fabric sheets embedded in a nitrile, polyvinyl chloride core, and may be characterized as both pliant and moderately stretchable or elastic. 
     As FIG. 3 particularly indicates, an equalizing and stabilizing plate SP is provided between the upper and lower membrane sections  19  and  20  to partition them to form an upper chamber UP and a lower chamber LP. The equalizing plate SP which has the rectangular configuration of membranes  19  and  20  may be a stainless steel plate of about ⅛″ in thickness, which is provided with liquid communicating openings O distributed in the pattern shown in FIG.  5 . Dependent on the testing being performed, the configuration of the bladder could be otherwise, such as square. Openings O assist in the liquid filling operation and maintain equal water pressures in the upper and lower chambers during testing procedures. The perimeter edges of the membrane sections  19  and  20  are tightly clamped to the perimeter edges of the plate SP by open or skeletal upper and lower rectangular frames made of metal (i.e., steel), the end and side rails  21  and end and side rails  22 , respectively having edge bolt openings x. The upper and lower frame rails  21  and  22  are tightly bolted together by closely spaced (i.e., one inch) bolts  21   a  secured by nuts  22   a , the bolts  21   a  extending snugly through edge openings  21   b  and  21   c  in the membrane sections  19  and  20 , respectively, and edge openings  21   d  in the stabilizing plate SP. It is essential that no leaks occur when the bladder or envelope E, which is filled with water or another incompressible liquid or substance, is subjected to the high pressures required. As FIG. 4 illustrates, the abutting pattern of the side and end bars  21  is different from the abutting pattern of the side and end bars  22  at each corner of the combined upper and lower frames so that upper and lower frame joints do not align and are not imbricated. The envelope or bladder E is completely filled and all air eliminated. In the present bladder, approximately five gallons of water is used. The water pressure can reach approximately 140 p.s.i. during testing, as opposed to 60 p.s.i. previously. 
     At one side of the equalizing plate SP, a recess or groove s, which diverges slightly as at  23   a  at its laterally inner end, as shown in FIG. 6, is provided to house and support a probe  23  which extends into the interior of the upper chamber of the envelope E from a pressure sensor device  24 . This device  24  may be the stainless steel probe part of the “Omega” pressure transducer sensor described in the aforementioned patent, which mounts to the frame rails  21  and  22  in the same manner as previously. The slot s accepts the open ended tubular probe  23  which may be adhesively secured in the slot s in a manner to leave its remote inner end open to the entrance of liquid. The slot s converges laterally in an outward direction so that if any of the adhesive should over time break away, it tends to only wedge back into the slot s. The slot s is positioned remotely from the corners of the plate SP and at an angle to diagonal lines connecting the corners. 
     For supporting the test panel TP in marine hull testing, a steel rod frame  26  may be used, as previously, along with the test panel holding frame assembly, generally designated  31 , which may again have inwardly extending flanges  32  with bead members  32   a  for holding the test panel TP. Provided on the side walls of the fixture  14   a  at the corners are the anchor blocks, generally designated  27 , which can have vertically extending openings  28  for receiving elongate bolt members  29 , which bear on washers  30  and secure the panel frame assembly  31  in proper position. A linear variable differential transformer LVDT may be provided as previously and incorporates a core probe  39 , which is normally maintained in extended position by the spring  40 . The LVDT unit may be the Schaevitz device identified in the aforementioned patent (incorporated herein by reference) wherein the core is at the center or null position before the actuator  17  is moved upwardly to bulge the test panel TP. While the system is depicted as utilizing only a single envelope E mounted on platen  18 , it is to be understood the platen shown may be readily altered to mount two or more side by side envelopes E to test elongate bridge deck test panels, for example. Also the MTS type machine may be arranged so that the test sample is under the envelope or envelopes, and the platen or actuator plate descends. 
     FIG. 8 portrays the various electronic components which are commonly employed in such testing systems. As previously, the signals from the pressure sensor  24 , the LVDT device and the load cell  12  are fed to the MTS machine controller/computer, which further controls the hydraulic motor for raising the actuator  17  at a controlled rate of speed. 
     THE OPERATION 
     For purposes of simplicity, it will be assumed that only a single bladder E is being utilized in the test. With a predetermined volume of water in the envelope E, the MTS machine actuator plate  17  is moved upwardly from the position shown in FIG. 1 to induce a compound bend in the test panel TP. When the actuator plate  17  moves upwardly, the pliant upper wall  19  of the envelope E assumes the shape of the deflected panel TP when the plate  17  begins to press the envelope E against the lower surface of the test panel. 
     The water inside the envelope E will adjust so that the applied load is transferred evenly to all of the contacted panel area. The widely distributed pressure applied to the test panel TP produces the bulge which raises the core probe  39  at the same time the increase of pressure in the liquid in bladder E is linearly sensed by the pressure sensor device  24 . The linear values recorded may be used to enable the production of graphs of the type shown in the previous patent. The system may also be well utilized in fatigue and failure testing operations. 
     When upward pressure or force is applied to the bladder E, the water pressure in the upper and lower bladder chambers remains equal. The plate SP is tensiley stressed, primarily in the directions of its corners. The side and end frame bars  21  and  22  brace against the flat equalizing plate SP and the membranes  19  and  20  are tightly pinched against the plate SP. The edge openings X,  21   b ,  21   c , and  21   d  are all tightly sized to the diameter of bolts  21   a , which may be quarter-inch bolts and closely spaced to cover the 12″×38″ footprint of the membrane clamping-edge frame. This is a typical size, but other sizes are, of course, possible. 
     Because the:membrane members  19  and  20  have some elasticity, they are subjected to shear forces as indicated by the arrows y in FIGS. 5,  7  and  7 A, as pressures in the envelope E increase during the testing procedure. This tends to produce the edge distortion or buckle z when the membrane edges  19  and  20  abut as in prior art FIG.  7 . When the edges membranes  19  and  20  do not abut and, rather engage the metal test plate SP, the split deflections z-1 are much decreased in amplitude. To avoid water reaching the bolts  21   a , a seal must occur substantially laterally inwardly of the bolts  21   a . In use, the deflections z or z-1 tend to pull on the membranes  19  and  20  and enlarge or stretch the openings  21   b  and  21   c  in a laterally inward direction. Under the shear forces imposed, the deflection buckle z, in FIG. 7, may be sufficient to induce a water leak in the FIG. 7 construction, while it would not be a problem under the same pressure in the FIG. 7A construction. Thus, the new envelope edge construction is clearly better suited to the high pressure testing which the present invention contemplates. 
     With considerably less shear deformation occurring with the FIG. 7A construction, the toll on the edge construction occurring over time with testing machine use is considerably less. In high pressure testing, it is important that both sides of each belting membrane  19  and  20  be engaged with a rigid surface to provide the improved pinching result. The bolts  21   a  are torqued in so as to be secured with the same pressure to provide uniformity around the edge construction perimeter. The prevention of shear displacement is further important in achieving uniformity in the distributed load fields during the test to avoid variables which would affect the test being carried out. While the contact area, of course, increases with the continued application of load, a stable pattern is desired throughout the range of loads utilized. It is important to maintain edge control and not alter the shape of the distributed load field under the higher pressures encountered. 
     The method of testing described herein has been successful in testing three by eight foot bridge deck sections made of reinforced concrete where the applied load was on the order of 55,000 pounds and the bladder pressure reached about 130 p.s.i. In other fracture tests a five inch thick slab of reinforced concrete was fractured by the device in a test to determine what loads would fracture the panel. 
     The disclosed embodiment is representative of a presently preferred form of the invention, but is intended to be illustrative rather than definitive thereof.