Abstract:
A wire rope pre-failure indicating device that can be installed at any location along a length of conventional wire rope of the character used in many industrial applications. The indicating device reliably functions to provide a pre-failure warning that the wire rope has been loaded beyond a specified magnitude. The indicating device also provides a pre-failure warning that the swaged fittings, which interconnect the indicator to the wire rope, have undesirably slipped.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates generally to safety devices. More particularly, the invention concerns a wire rope pre-failure indicating device and method of using the same that can be installed at any location along a length of conventional wire rope that provides a pre-failure warning that the wire rope has been loaded beyond a specified magnitude. 
         [0003]    2. Discussion of the Prior Art 
         [0004]    Flexible wire rope of various sizes is commonly used in various types of industrial applications, including cranes and similar lifting equipment. Wire rope is also extensively used in automotive and aircraft running gear, in marine halyards and in various other types of mechanical control systems. 
         [0005]    In many prior art applications, the flexible wire rope is exposed to wear and potential damage as a result of being threaded through various pulleys and sheave configurations and of being wrapped upon and unwrapped from storage drums. 
         [0006]    Less flexible wire rope of various sizes is more often used in more static applications such as stays to support construction elements, crane booms, towers, telephone poles, construction masts, and marine rigging. 
         [0007]    In virtually all of the prior art applications the wire rope is installed into the load path by one of two techniques. In one technique the wire rope is wrapped around a thimble with the free end of the wire rope clamped to itself using either a mechanical clamp or a lead lug that is crimped onto the wire rope with a crimping tool. The second technique typically involves the step of swaging a designed eye or clevis end fitting onto the wire rope by extruding a section of the fitting into the twisted strands of the wire rope using a hydraulic die. 
         [0008]    When dynamic tension is applied to the wire rope during any of the aforementioned applications, the wire rope can become overstressed. If the overstressed condition of the wire rope is not promptly discovered and the situation promptly corrected, the overstressed wire rope will fail resulting in serious and, on occasion, catastrophic damage or injury. The thrust of the present invention is to solve this serious prior art problem by providing an easy-to-use, highly reliable wire rope pre-failure indicating device that can be installed at any location along a length of conventional wire rope of the type used in a common industrial application and will function to provide a pre-failure warning that the wire rope has been overstressed and that corrective action must be taken. 
         [0009]    U.S. Pat. No. 5,466,082 issued to Sherar, which is directed to an in-line safety shackle for a cable system, is primarily directed to a safety device for use in the logging industry. The Sherar device comprises a first member adapted to engage a first cable, and a second member adapted to engage a second cable, wherein the second member releasibly inter-fits with the first member. At least one safety cable is provided for substantially permanently securing the first member to the second member. The device also comprises means releasibly connecting the first member to the second member, the means being provided with a pre-determined shear force sufficient to release the first member from the second member before the first or second cable breaks due to the dynamic tension placed on the cables. The Sherar patent also describes an in-line safety shackle device for a cable system that includes a first cable and a second cable comprising a first member adapted to releasibly engage the first cable. The first member includes a first cable shaft and a first shear pin shaft. The first member further includes at least one safety cable shaft for receiving a first end of a safety cable. The device further comprises a second member adapted to releasibly engage the second cable. The second member includes a second cable shaft and a second shear pin shaft, wherein the second member is adapted to releasibly inter-fit with the first member. The shear pin is provided with a designed shear strength which is less than the tensile force of the safety cable. 
         [0010]    The prior art patent to Ellis, et al., U.S. Pat. No. 5,400,868, concerns a shock-load indicator for use with a safety cable, and more particularly to a shock-load indicator for use with retracting life line devices. The Ellis, et al., shock-load indicator comprises a casing surrounding a section of the cable, having severable top and bottom sections connected through a shearing means. The casing normally supports the weight of the user of the cable, and encloses a length of the cable such that, when the cable is extended as a result of the severance of the casing due to a fall induced shock-load, the top and bottom sections separate by a pre-determined distance indicating that the cable has been subjected to a shock-load. 
       SUMMARY OF THE INVENTION 
       [0011]    By way of brief summary, the wire rope pre-failure indicating device of the invention, which is of a simple, easy-to-use construction, can be installed at any location along a length of conventional wire rope of the character used in many industrial applications and reliably functions to provide a pre-failure warning that the wire rope has been loaded beyond a specified magnitude. The device also provides a pre-failure warning that the swaged fittings, which interconnect the indicator to the wire rope, are in jeopardy of slipping. In use, the device is typically swaged onto the wire rope in the same manner as eye-and-clevis end fittings are swaged onto the wire rope. When a specified tensile load in the wire rope is exceeded, the indicator uniquely provides a visible indicator that an overload condition has occurred. When the overload condition occurs, the indicator automatically transfers the load from the indicator body to the wire rope so as to maintain the integrity of the load path. In one form of the invention the body is locally work-hardened to provide specific material failure characteristics. In another form of the invention the body is provided with strategically spaced-apart gauge marks that can be used to determine that an overload condition has occurred. 
         [0012]    In the preferred form of the invention, the wire rope pre-failure indicator device comprises a generally cylindrically shaped, machined body having a central section and tapered end portions. A concentric, longitudinal bore of a diameter to fit a specific wire rope size is machined through the entire length of the device. A lateral slot slightly wider than the diameter of the longitudinal bore is machined proximate the central one third of the device and may be locally work-hardened to remove the ductility or otherwise adjust the material properties of that material in the failure section. A circumferentially extending, circular groove is then machined proximate the mid-point of the slot. 
         [0013]    In using the device of the invention, the wire rope is first threaded through the entire length of the device and the device is strategically positioned along the length of wire rope at the desired location. With the device located in the desired position, the wire rope is pushed towards the center of the device in a manner to form a small arc, or slack in the rope. This done, the end portions of the device are swaged onto the wire rope in a conventional manner well known in the art. The swaged length at each end section of the device is of less length than the swaged length of typical eye-clevis end fittings. It is to be appreciated that with the construction thus described, the section of the wire rope that is disposed within the slotted center portion of the device (the tension-free section) will support no tensile load. 
         [0014]    As a tensile force is applied to the wire rope, the force will be transferred from the leading swaged section of the device to the outer center section or outer body of the device. The tensile force in the outer body of the device will then be transferred back into the wire rope as it continues through the swaged section at the opposite end of the device. As previously mentioned, that portion of the wire rope with the slight circular arc or slack in the center of the lateral slot supports no load. 
         [0015]    It is to be observed that the section perpendicular to the longitudinal axis of the device at the groove location is the critical cross section of the device due to the stress concentration created by the reduced cross-sectional area at the groove location. It is apparent that if the axial load placed on the device becomes excessive, the device will fail at this groove cross section. 
         [0016]    With the forgoing in mind, the primary function of the device of the invention is to fail at a specified tensile load magnitude for the size of the particular wire rope to which the device is interconnected. For example the device may be designed to fail at a designated percent, for example 60%, of the breaking load of the particular wire rope. When this load is exceeded, the outer body of the device will fail and the load will be transferred back into the tension-free, or arcuate section of the wire rope causing it to visibly straighten. 
         [0017]    In the design of the device, the elastic properties of both the device and the wire rope are considered so that shock-loading of the wire rope is minimized during device failure. In this regard, the failure characteristics of the material within the tension-free-slot may be adjusted by local work hardening before the reduced area is machined. If the device has failed in the reduced area section as indicated by the visible straightening of the arcuate section of the rope, then the wire rope system has been overloaded and should be replaced. 
         [0018]    For a wire rope system that is repeatedly loaded and unloaded longitudinally spaced gauge marks may be added to the body portion of the device on either side of the reduced area section. These important gauge marks can be used to track the load history of the wire rope by measuring the distance between the gauge marks each time the wire rope is unloaded and recording any increase in the distance between the gauge marks caused by excessive loading of the system. 
         [0019]    With the foregoing in mind it is an object of the present invention to provide a wire rope pre-failure indicating device, which is of a simple, easy-to-use construction, can be installed at any location along a length of conventional wire rope and functions to provide a readily visible pre-failure warning that the wire rope has been loaded beyond a specified magnitude. 
         [0020]    Another object of the invention is to provide a device of the aforementioned character that also provides a readily visible pre-failure indicator that the swaged sections, which interconnect the fuse to the wire rope, have slipped and thus suggesting that other swaged sections of greater length within the system may also be in jeopardy of slipping. 
         [0021]    Another object of the invention is to provide a device as described in the preceding paragraphs that includes a viewing portal that enables the status of the device to be conveniently and frequently checked by relatively unskilled observers. More particularly, the viewing portal enables observers to easily see on a real time basis the pre-failure warnings that occur when the wire rope has been loaded beyond a specified magnitude. 
         [0022]    Another object of the invention is to provide a wire rope pre-failure indicating device that includes a central body portion upon which longitudinally spaced-apart gauge marks are provided that can be conveniently used to track the load history of the wire rope by measuring the distance between the gauge marks each time the wire rope is unloaded and recording any increase in the distance between the gauge marks caused by excessive loading of the system. 
         [0023]    Another object of the invention is to provide a device of the character described in the preceding paragraph in which the body portion of the device is locally work-hardened in order to more accurately control the failure load and to minimize shock-loading of the wire rope during system failure. 
         [0024]    Another object of the invention is to provide a wire rope pre-failure indicating device of the character described that is approximately the same size and appearance as that of conventional prior art eye-or-clevis end fittings. 
         [0025]    Another object of the invention is to provide a wire rope pre-failure indicating device that can be interconnected with the wire rope by relatively unskilled workers using a skill level and type and quality of equipment that is comparable to that used to interconnect standard prior art end fittings with wire cables. 
         [0026]    Another object of the invention is to provide a wire rope pre-failure indicating device that is designed to fail at a pre-selected percent of the breaking strength of the wire rope with which it is being used. More particularly, for a selected wire rope size, the indicating device can, by way of example, be designed to fail at 50%, 60%, 70%, or even 80% of the breaking load of the wire rope with which it is being used. 
         [0027]    Another object of the invention is to provide a wire rope pre-failure indicating device that includes a conventional eye fitting that can be conveniently swaged on the end of a wire rope. 
         [0028]    Another object of the invention is to provide a wire rope pre-failure indicating device that includes a conventional clevis fitting that can be conveniently swaged on the end of a wire rope. 
         [0029]    The foregoing as well as other objects of the invention can be achieved by the indicating device described in greater detail in the paragraphs which follow. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  is a generally isometric view of one form of the wire rope pre-failure indicating device of the invention. 
           [0031]      FIG. 1A  is a side-elevational view of the wire rope pre-failure indicating device shown in  FIG. 1 . 
           [0032]      FIG. 1B  is a cross-sectional view taken along lines  1 B- 1 B of  FIG. 1A . 
           [0033]      FIG. 2  is a generally isometric view similar to  FIG. 1 , but showing the device as it appears after the loading of the wire rope has exceeded a specified magnitude and the frangible central portion of the device has been broken. 
           [0034]      FIG. 2A  is a side-elevational view of the wire rope pre-failure indicating device shown in  FIG. 2 . 
           [0035]      FIG. 2B  is a cross-sectional view taken along lines  2 B- 2 B of  FIG. 2A . 
           [0036]      FIG. 3  is a generally isometric view similar to  FIG. 1 , but showing the device as it appears after the loading of the wire rope has caused one of the swaged end portions of the device to slip relative to the rope, but has not caused the frangible central portion of the device to fail. 
           [0037]      FIG. 3A  is a side-elevational view of the wire rope pre-failure indicating device shown in  FIG. 3 . 
           [0038]      FIG. 3B  is a cross-sectional view taken along lines  3 B- 3 B of  FIG. 3A . 
           [0039]      FIG. 4  is a generally isometric view of an alternate embodiment of the invention that has another type of central frangible portion. 
           [0040]      FIG. 5  is a generally isometric view of still another embodiment of the invention showing yet another type of central frangible portion. 
           [0041]      FIG. 6  is a generally isometric view of yet another embodiment of the invention showing still another type of central frangible portion. 
           [0042]      FIG. 7  is a generally isometric view of still another embodiment of the invention showing yet another type of central frangible portion. 
           [0043]      FIG. 8  is a generally isometric view similar to  FIG. 7 , but showing the device of  FIG. 7  as it appears after the loading of the wire rope has exceeded a specified magnitude. 
           [0044]      FIG. 9  is a generally isometric view similar to  FIG. 7 , but showing the device of  FIG. 7  as it appears after the device has been disabled due to the wire rope slipping within one of the swaged section at ends of the device. 
           [0045]      FIG. 10  is a generally isometric view of yet another form of the invention which includes a conventional eye fitting that has been swaged on the end of a wire rope. 
           [0046]      FIG. 11  is a generally isometric view of still another embodiment of the invention which includes a conventional clevis fitting that has been swaged on the end of a wire rope. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0047]    Referring to the drawings and particularly to  FIGS. 1 ,  1 A,  2  and  2 A, one form of the pre-failure indicating device of the invention is there shown and generally designated by the 14. The indicating device  14  is specifically designed for use with a length of wire rope “R” that will fail in tension upon applying a load of a first magnitude to the wire rope. In the present form of the invention the indicating device  14  comprises a generally cylindrical casing  16  that surrounds a portion of the wire rope in the manner illustrated in  FIGS. 1 and 1B . As shown in  FIGS. 1 ,  1 A and  1 B, casing  16  is provided with a longitudinal wire rope receiving bore  18  therethrough for receiving the uninterrupted length of wire rope “R”. Additionally, casing  16  is provided with a viewing portal, here shown as a longitudinally extending slot  19 , for viewing the length of wire rope. Casing  16  here includes first and second spaced-apart end portions  20  and  22  that are swaged sections connected to the wire rope and a central body portion  24  that is disposed between the first and second end portions. Disposed between central body portion  24  and first end portion  20  is a tapered portion  25 . Similarly, disposed between central body portion  24  and second end portion  22  is a tapered portion  27 . Preferably, end portions  20  and  22  are interconnected with the wire rope by swaging these sections as well as the terminal portions  20   a  and  22   a  to the wire rope in a conventional manner. However, as illustrated in  FIGS. 1 and 1B , after the sections  20  and  20   a  have been swaged to the wire rope, and prior to the portions  22  and  22   a  being swaged to the wire rope, the wire rope is urged inwardly in a manner to form within the central portion  24   a  ( FIG. 1B ) of body  24  an arc, or slack portion designated in the drawings as “R- 1 ”. After the swaging operation is complete, this important slack portion “R- 1 ” is readily visible through the viewing portal, or longitudinally extending slot  19  formed in the central portion of the casing. 
         [0048]    As previously mentioned, a primary function of the indicator device of the invention is to fail at a specified second tensile load magnitude for the size of the particular wire rope to which the device is interconnected. Accordingly, an important feature of the device of the present invention resides in the provision of a central body frangible portion that will fail in tension upon applying a load of a second magnitude to the wire rope. This central body frangible portion can take various forms, but in the form of the invention shown in  FIGS. 1 and 2  is uniquely provided in the form of a circumferentially extending, reduced diameter portion, or groove  26 . As indicated in  FIGS. 2 ,  2 A and  2 B of the drawings, when a load of a second pre-determined magnitude, which is less than the load of a first magnitude, is placed on the wire rope the central body frangible portion will fail resulting in a separation of portions  24   a  and  24   b  of central body  24 . 
         [0049]    As the central body frangible portion  26  fails, the tensile force being applied to the wire rope will be transferred from the leading swaged sections  22  and  22   a  of the device to the outer body section  24   b . The tensile force will then be transferred back into the wire rope as it continues through the swaged sections  20  and  20   a  located at the opposite end of the device. As the tensile force is transferred back into the wire rope, the arcuate portion “R- 1 ” of the wire rope will automatically visibly straighten (indicated as R- 2 ) thereby providing a readily observable warning that the load on the wire rope has exceeded an acceptable magnitude (see  FIGS. 2A and 2B ). If the device has failed in the reduced diameter portion  26 , as indicated by the visible straightening of the arcuate section of the rope, then the wire rope system has been overloaded and should be replaced. 
         [0050]    Another important feature of the invention is to provide a wire rope pre-failure indicating device that is designed to fail at a pre-selected percent of the breaking strength of the wire rope with which it is being used. By way of example of, the indicating device can be designed to fail at 40%, 50%, 60%, or even 70% of the breaking load of the wire rope with which it is being used. 
         [0051]    The device illustrated in  FIGS. 1 ,  1 A,  1 B,  2 ,  2 A and  2 B of the drawings is specifically designed to fail at 60% of the breaking load of the wire rope “R”. Accordingly, when this load is exceeded, the outer body of the device will fail in the manner described in the preceding paragraph and the load will be transferred back into the tension-free, or arcuate section of the wire rope causing it to visibly straighten. 
         [0052]    In the design of the device, the elastic properties of both the device and the wire rope are considered so that shock-loading of the wire rope is minimized during device failure. In this regard, the failure characteristics of the material within the tension-free-slot may be adjusted by local work hardening before the reduced area is machined. 
         [0053]    For a wire rope system that is repeatedly loaded and unloaded another novel means for determining overstressing of the wire rope is provided. In this regard, after the reduced area  26  has been machined into the body of the device, two small indentations  30  and  32  (see  FIG. 1 ) are symmetrically machined into the top surface of the body  16 . These small indentations, which comprise gauge marks, are preferably located precisely 0.750 inches on either side of the center of the reduced area  26  to provide a gauge mark having a length of 1.500 inches. When the indicator device is in the unloaded state, the gauge mark length can be accurately measured with a linear caliper to be 1.500 inches. In the situation where the frangible portion of the device has not failed and the gauge mark length measures greater than 1.500, then the wire rope has been overstressed to some degree. By making frequent measurements of the spacing between the gauge marks, the load history of the wire rope can be definitively recorded and maintained. 
         [0054]    Therefore, in accordance with one form of the method of the invention, these important gauge marks are used to track the load history of the wire rope by measuring the distance between the gauge marks each time the wire rope is unloaded and recording any increase in the distance between the gauge marks caused by excessive loading of the system. 
         [0055]    Turning to  FIGS. 3 ,  3 A and  3 B of the drawings, it is to be noted that the reduced area section  26  has not broken and is identical to the appearance of the device as shown in  FIG. 1  drawings. However, the curvature, or slack in the wire rope shown in  FIGS. 1 and 1B  is no longer present. This can only mean that one or both of the swaged sections  20  and  20   a  or  22  and  22   a  has slipped thus straightening the wire rope portion “R- 2 ” within the tension-free slot  19 . This slippage has occurred at a load less than the specified magnitude since the frangible portion, or reduced area section  26  has not failed. With the device in the configuration shown in  FIGS. 3 ,  3 A and  3 B it is apparent that the device has been disabled due to one of the swaged sections slipping. Since one or both of the swaged sections  20  and  20   a  or  22  and  22   a  has slipped, the other swaged section has become extremely suspect and, therefore, the indicator device needs to be replaced. 
         [0056]    Referring to  FIG. 4  of the drawings, an alternate form of the pre-failure indicating device of the invention is there shown and generally designated by the numeral  34 . This form of the invention is similar in many respects to that shown in  FIGS. 1 through 3  of the drawings and like numerals are used in  FIG. 4  to identify like components. The primary difference between this latest form of the invention and that earlier described resides in the fact that the frangible portion of the device comprises a transverse bore  36  rather than a reduced diameter portion. The pre-failure indicating device  34  here comprises a generally cylindrical casing  38  that surrounds a portion of the wire rope in the manner illustrated in  FIG. 4 . As before, casing  38  is provided with a longitudinal wire rope receiving bore  18  for receiving the uninterrupted length of wire rope “R”. Additionally, casing  38  is provided with a viewing portal, here shown as a longitudinally extending slot  40 , for viewing the length of wire rope. Casing  38  also includes first and second spaced-apart end portions  20  and  22  that are connected to the wire rope and a central body portion  42  that is disposed between said first and second end portions. End portions  20  and  22  are interconnected with the wire rope by swaging these sections as well as the terminal portions  20   a  and  22   a  to the wire rope in a conventional manner. As was the case with the earlier described embodiment of the invention, after the sections  20  and  20   a  have been swaged to the wire rope, and prior to the portions  22  and  22   a  being swaged to the wire rope, the wire rope is urged inwardly in a manner to form within the central portion  42   a  of body  42  an arc, or slack portion designated as “R- 1 ”. After the swaging operation is complete, this important slack portion “R- 1 ” is readily visible through the viewing portal, or longitudinally extending slot  40  formed in the central portion of the casing. 
         [0057]    As was the case with the embodiment of  FIGS. 1 and 2 , when a load of a second pre-determined magnitude, which is less than the load of a first magnitude, is placed on the wire rope the central body portion  42  in the area of the transverse bore  36  will fail resulting in a separation of portions  42   b  and  42   c  of central body  42 . 
         [0058]    As the central body frangible portion fails, the tensile force being applied to the wire rope will be transferred from the leading swaged section  22   a  of the device to the outer body section  42   b . The tensile force will then be transferred back into the wire rope as it continues through the swaged sections  20  and  20   a  located at the opposite end of the device. As the tensile force is transferred back into the wire rope, the arcuate portion “R- 1 ” of the wire rope will automatically visibly straighten thereby providing a readily observable warning that the load on the wire rope has exceeded an acceptable magnitude. If the device has failed in the reduced diameter portion, as indicated by the visible straightening of the arcuate section of the rope, then the wire rope system has been overloaded and should be replaced. 
         [0059]    Turning now to  FIG. 5  of the drawings, still another form of the pre-failure indicating device of the invention is there shown and generally designated by the numeral  44 . This embodiment of the invention is substantially identical in construction and operation to that shown in  FIG. 4  of the drawings save that the frangible portion of the device is a different configuration. Once again, like numerals are used in  FIG. 5  to identify like components. As indicated in  FIG. 5 , the frangible portion of device  44  comprises generally vertically extending slots  46  that are formed substantially at the center of the body portion  48  of the device casing. As before, the casing is provided with a longitudinal wire rope receiving bore  18  for receiving the uninterrupted length of wire rope “R”. When a load of a second pre-determined magnitude, which is less than the load of a first magnitude, is placed on the wire rope the central body portion  48  in the area of the transverse bore will fail resulting in a separation of portions  48   a  and  48   b  of central body  48 . As the central body frangible portion fails, the tensile force being applied to the wire rope will be transferred from the leading swaged sections  22  and  22   a  of the device to the outer body section  48   b . The tensile force will then be transferred back into the wire rope as it continues through the swaged sections  20  and  20   a  located at the opposite end of the device. As the tensile force is transferred back into the wire rope, the arcuate portion “R- 1 ” of the wire rope will automatically visibly straighten thereby providing a readily observable warning that the load on the wire rope has exceeded an acceptable magnitude. If the device has failed in the reduced diameter portion, as indicated by the visible straightening of the arcuate section of the rope, then the wire rope system has been overloaded and should be replaced. 
         [0060]    Referring to  FIG. 6  of the drawings, yet another form of the pre-failure indicating device of the invention is there shown and generally designated by the numeral  50 . This embodiment of the invention is also substantially identical in construction and operation to that shown in  FIG. 4  of the drawings save that the frangible portion of the device is a different configuration. As before, like numerals are used in  FIG. 6  to identify like components. As illustrated in  FIG. 6 , the frangible portion of the device  50  here comprises transversely spaced-apart slots  52  that are generally oval in cross-section and are located substantially at the center of the body portion  54  of this embodiment. Once again, the casing is provided with a longitudinal wire rope receiving bore  18  for receiving the uninterrupted length of wire rope “R”. When a load of a second pre-determined magnitude, which is less than the load of a first magnitude, is placed on the wire rope the central body portion  46  in the area of the transverse bore will fail resulting in a separation of portions  54   a  and  54   b  of central body  54 . As the central body frangible portion fails, the tensile force being applied to the wire rope will be transferred from the leading swaged sections  22  and  22   a  of the device to the outer body section  54   b . The tensile force will then be transferred back into the wire rope as it continues through the swaged sections  20  and  20   a  located at the opposite end of the device. As the tensile force is transferred back into the wire rope, the arcuate portion “R- 1 ” of the wire rope will automatically visibly straighten thereby providing a readily observable warning that the load on the wire rope has exceeded an acceptable magnitude. If the device has failed in the reduced diameter portion, as indicated by the visible straightening of the arcuate section of the rope, then the wire rope system has been overloaded and should be replaced. 
         [0061]    Referring next to  FIGS. 7 ,  8  and  9  of the drawings, yet another form of the pre-failure indicating device of the invention is there shown and generally designated by the numeral  56 . This embodiment of the invention is somewhat similar in construction and operation to that shown in  FIG. 4  of the drawings save that, once again, the frangible portion of the device is a different configuration. Because of the similarity between the latest form of the invention and that shown in  FIG. 4 , like numerals are used in  FIGS. 7 ,  8  and  9  to identify like components. As indicated in  FIGS. 7 and 8 , the frangible portion of device, like that of  FIG. 4  comprises a generally vertically extending bore  58  that is formed substantially at the center of the body portion  60  of the device casing. An indicator pin  62 , which is slidably received within bore  58 , requires the wire rope “R” to be threaded around the pin in the manner shown in  FIG. 7 . This assures that a pre-determined amount of slack will be formed in the portion of the wire rope “R- 1 ” that resides within the tension-free slot  64 . With this construction, when a load of a second pre-determined magnitude, which is less than the load of a first magnitude, is placed on the wire rope the central body portion  60  in the area of the transverse bore  58  will fail resulting in a separation of portions  60   a  and  60   b  of central body  60  (see  FIG. 8 ). 
         [0062]    As the frangible portion fails, indicator pin  62  will be ejected from bore  58 . This failure of the frangible portion and the straightening of the wire rope portion “R- 2 ” along with the ejection of indicator pin  62  provides a clear visible indication that, for the reasons previously described, the load on the wire rope has exceeded a specified magnitude. 
         [0063]    If desired, to provide even a more pronounced visible indication of the overloading of the wire rope, the indicator pin  62  can be constructed in the form of a thin walled, sealed cylinder that contains a colored liquid dye. With such a construction, when the frangible portion of the device fails and the indicator pin is ejected, or when one of the swaged sections  20  and  20   a  or  22  and  22   a  slips and the indicator pin  62  is deformed in the manner shown in  FIG. 9  of the drawings, the colored dye within the indicator pin will flow from the failed pin thereby providing a further visible indication that the load on the wire rope has exceeded a specified magnitude. 
         [0064]    Turning to  FIG. 9  of the drawings, it is to be noted that the frangible area of the central body portion  60  has not broken. However, the curvature, or slack in the wire rope shown in  FIG. 7  is no longer present if the indicator pin  62  has been deformed. This can only mean that one or both of the swaged sections  20  and  20   a  or  22  and  22   a  has slipped thus straightening the wire rope portion “R- 1 ” within the tension-free slot  64 . This slippage has occurred at a load less than the specified magnitude since the frangible portion has not failed. With the device in the configuration shown in  FIG. 9 , it is apparent that the device has been disabled due to one of the swaged sections slipping. Since one or both of the swaged sections  20  and  20   a  or  22  and  22   a  has slipped, the other swaged section has become extremely suspect and, therefore, the indicator device needs to be replaced. 
         [0065]    Turning next to  FIG. 10  of the drawings, still another form of the pre-failure indicating device of the invention is there shown and generally designated by the numeral  68 . This embodiment of the invention is substantially identical in operation to the embodiment shown in  FIG. 1  of the drawings. However, as indicated in  FIG. 10 , unlike the embodiment of  FIG. 1 , a conventional eye-end fitting  70  is connected to the free end of the wire rope “R”. Once again, like numerals are used in  FIG. 10  to identify like components to those of the embodiment shown in  FIG. 1 . The frangible portion is provided in the form of a circumferentially extending, reduced diameter portion, or groove  26 . When a load of a second pre-determined magnitude, which is less than the load of a first magnitude, is placed on the wire rope the central body frangible portion will fail resulting in a separation of portions  24   a  and  24   b  of central body  24 . As the central body frangible portion  26  fails, the tensile force being applied to the wire rope will be transferred from the leading swaged sections  22  and  22   a  of the device to the outer body section  24   b . The tensile force will then be transferred back into the wire rope as it continues through the swaged sections  20  and  20   a  located at the opposite end of the device. As the tensile force is transferred back into the wire rope, the arcuate portion “R- 1 ” of the wire rope will automatically visibly straighten thereby providing a readily observable warning that the load on the wire rope has exceeded an acceptable magnitude. 
         [0066]    Referring to  FIG. 11  of the drawings, yet another form of the pre-failure indicating device of the invention is there shown and generally designated by the numeral  72 . This embodiment of the invention is also substantially identical in operation to the embodiment shown in  FIG. 1  of the drawings. However, as indicated in  FIG. 10 , unlike the embodiment of  FIG. 1 , a conventional clevis end fitting  74  is connected to the free end of the wire rope “R”. Once again, like numerals are used in  FIG. 11  to identify like components to those of the embodiment shown in  FIG. 1 . The frangible portion is provided in the form of a circumferentially extending, reduced diameter portion, or groove  26 . As before, when a load of a second pre-determined magnitude, which is less than the load of a first magnitude, is placed on the wire rope the central body frangible portion will fail resulting in a separation of portions  24   a  and  24   b  of central body  24 . As the central body frangible portion  26  fails, the tensile force being applied to the wire rope will be transferred from the leading swaged sections  22  and  22   a  of the device to the outer body section  24   b . The tensile force will then be transferred back into the wire rope as it continues through the swaged sections  20  and  20   a  located at the opposite end of the device. As the tensile force is transferred back into the wire rope, the arcuate portion “R- 1 ” of the wire rope will automatically visibly straighten thereby providing a readily observable warning that the load on the wire rope has exceeded an acceptable magnitude. 
         [0067]    Considering next the methods of the invention for pre-determining the failure of an uninterrupted length of wire rope that will fail in tension upon applying a load of a first magnitude to the wire rope. In conducting one form of the method of the invention, a device such as that depicted in  FIGS. 1 ,  1 A,  1 B,  2 ,  2 A and  2 B of the drawings is used. In carrying out this method, once the device casing has been appropriately formed from a metal, such as steel, and the longitudinally extending central bore has been machined to a diameter slightly larger than a diameter of the wire rope with which the device is to be used, the wire rope is threaded through the longitudinally extending bore. This done, the wire rope is pushed inwardly on either side of the device to form in the central body portion of the device a generally arcuate-shaped slack in rope such as that shown in  FIGS. 1A and 1B  of the drawings. Next, the first and second end portions of the casing are securely connected to the wire rope as by conventional swaging. With the device of the invention thusly connected to the uninterrupted length of the wire rope, a load can be applied to the rope. With the wire rope under load, the slack portion of the wire rope is periodically viewed through the viewing portal until the slack portion straightens. This will indicate either that the central body portion of the device has failed in tension due to the application of the load to the wire rope of a second predetermined magnitude less than the magnitude at which the wire rope will fail (see  FIGS. 2 ,  2 A and  2 B), or alternatively, that one of the swaged end fittings has failed (see  FIGS. 3 ,  3 A and  3 B). In either case, this provides a clear indication that the wire rope has been overstressed and must be replaced. 
         [0068]    In carrying out another form of the method of the invention using an indicating device having longitudinally spaced-apart gauge marks machined into the body of the device (see  FIG. 1 ), the distance between the spaced-apart gauge marks is measured using a conventional caliper or like device to obtain a first distance. Next, following the application of the load to the wire rope, the distance between the spaced-apart gauge marks is periodically re-measured to determine a second distance. If the second distance is greater than the first distance, the observer must conclude that the body portion of the device has experienced over-stressing due to an over-stressing of the wire rope and replacement of the device and replacement of the wire rope must be considered. 
         [0069]    Having now described the invention in detail in accordance with the requirements of the patent statutes, those skilled in this art will have no difficulty in making changes and modifications in the individual parts or their relative assembly in order to meet specific requirements or conditions. Such changes and modifications may be made without departing from the scope and spirit of the invention, as set forth in the following claims.