Abstract:
A controlled failure rope and method of making the same. The controlled failure rope comprises first and second portions. The first portion is formed of a first material having a first set of tension failure characteristics. The second portion is formed of a second material having a second set of tension failure characteristics. The first and second sets of tension failure characteristics differ such that, when the rope is subjected to tension loads above a tension threshold, the first portion of the rope begins to fail before the second portion of the rope, therefore providing a prior indication of possible rope failure before the rope becomes completed separated.

Description:
RELATED APPLICATIONS 
   This application claims priority of U.S. Provisional Patent Application Ser. No. 60/530,131, which was filed on Dec. 16, 2003. 

   TECHNICAL FIELD 
   The present invention relates to rope systems and methods and, in particular, to rope systems in which the failure of the rope under predetermined failure conditions is controlled and to methods of making such rope. 
   BACKGROUND OF THE INVENTION 
   The characteristics of a given type of rope determine whether that type of rope is suitable for a specific intended use. Rope characteristics include breaking strength, elongation, flexibility, weight, abrasion resistance, and coefficient of friction. The intended use of a rope will determine the acceptable range for each characteristic of the rope. The term “failure” as applied to rope will be used herein to refer to a rope being subjected to conditions beyond the acceptable range associated with at least one rope characteristic. 
   The present invention primarily relates to the performance of rope when the rope fails due to excess tension loads. When a rope is subjected to excess tension loads, the rope fails over time in what will be referred to as a tension failure sequence. For the purposes of the following discussion, it will be assumed that a constant tension load is applied to the rope throughout the tension failure sequence. However, a rope of the present invention may be used in situations in which the tension load varies or is eliminated during the tension failure sequence. 
   The tension failure sequence varies from rope to rope and from environment to environment. In general, a rope or portion of a rope breaks when all of the fibers of the rope separate or break apart at a given location on the rope. If the fibers are all identical, it is conceivable that all of the fibers will break at the same time. Typically, however, individual fibers differ from each other based on such factors as manufacturing variations and wear on the fibers during use of the rope. Accordingly, when the failure sequence begins, the lower elongating fibers will break first, transferring the load to the remaining fibers. As the entire tension load is transferred to the remaining higher elongating fibers, these also begin to break. When all of the fibers have broken at a given location, the rope is broken. 
   In a conventional rope, the tension failure sequence typically begins with elongation of the rope. After a certain amount of elongation, the rope breaks, marking the end of the tension failure sequence. At the end of the tension failure sequence, the rope exceeds the acceptable range of elongation and eventually breaks. When the rope breaks, potential energy within the rope is converted into kinetic energy that can cause unpredictable movement of the ends of the rope on either side of the break. 
   The need thus exists for improved ropes that, when subjected to excess tension loads, fail in a controlled manner; the need also exists for systems and methods for controlling the failure of rope and for producing such improved ropes. 
   SUMMARY OF THE INVENTION 
   The present invention is a controlled failure rope and method of controlling the failure of a rope. A controlled failure rope of the present invention comprises first and second portions. The first portion is formed of a first material having a first set of tension failure characteristics. The second portion is formed of a second material having a second set of tension failure characteristics. The first and second sets of tension failure characteristics differ such that, when the rope is subjected to tension loads above a tension threshold, the first portion of the rope begins to fail before the second portion of the rope. 
   The present invention may also be embodied as a method of making a controlled failure rope comprising the following steps. Initially, first and second materials are provided. The first and second materials define first and second sets of tension failure characteristics, respectively. The materials are combined to form a rope comprising first and second portions, where, when the rope is subjected to tension loads above a tension threshold, the first portion of the rope begins to fail before the second portion of the rope. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a somewhat schematic, perspective view of a controlled failure rope constructed in accordance with, and embodying, the principles of the present invention; 
       FIG. 2  is a side elevation view of a second example of a controlled failure rope of the present invention; 
       FIG. 3  is a radial cross-section of the controlled failure rope depicted in  FIG. 2 ; 
       FIG. 4  is a close-up view of a portion of  FIG. 3 ; 
       FIG. 5  is a side elevation view of a third example of a controlled failure rope of the present invention; 
       FIG. 6  is a radial cross-section of the controlled failure rope depicted in  FIG. 5 ; 
       FIG. 7  is a close-up view of a portion of  FIG. 6 ; 
       FIG. 8  is a side elevation view of a fourth example of a controlled failure rope of the present invention; 
       FIG. 9  is a radial cross-section of the controlled failure rope depicted in  FIG. 8 ; and 
       FIG. 10  is a close-up view of a portion of  FIG. 9 . 
       FIG. 11  is a side elevation view of a fifth example of a controlled failure rope of the present invention; 
       FIG. 12  is a radial cross-section of the controlled failure rope depicted in  FIG. 11 ; 
       FIG. 13  is a close-up view of a portion of  FIG. 12 . 
       FIG. 14  is a side elevation view of another example of a controlled failure rope of the present invention; 
       FIG. 15  is a radial cross-section of the controlled failure rope depicted in  FIG. 14 ; and 
       FIG. 16  is a close-up view of a portion of  FIG. 15 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring initially to  FIG. 1  of the drawing, depicted therein is a controlled failure rope  20  constructed in accordance with, and embodying, the principles of the present invention. The rope  20  comprises at least a first portion  22  of a first material having a first set of tension failure characteristics and a second portion  24  of a second material having a second set of tension failure characteristics. 
   The first and second portions  22  and  24  are physically combined such that the rope  20  does not fail in a single stage when subjected to excess tension loads. Instead, the properties of the first and second materials and the manner in which the first and second portions  22  and  24  are combined to cause the rope  20  to fail in at least two stages under excess tension loads. As will be described in further detail below, the rope  20  thus has improved performance when failing under excess tension loads as compared to conventional synthetic ropes. 
   In the rope  20  constructed according to the principles of the present invention, a first stage of the tension failure sequence begins with elongation of the first portion  22 . Before or when the first portion  22  breaks, the second portion  24  of the rope  20  elongates, marking the end of the first stage and the beginning of a second stage of the tension failure sequence. When the second portion  24  breaks, the second stage of the tension failure sequence ends. 
   In the rope  20  comprising only the first and second portions  22  and  24  comprising first and second materials, the end of the second stage marks the end of the entire tension failure sequence. However, it may be possible to employ a third and/or additional portions, each comprised of a material having different tension failure characteristics. In this case, the tension failure sequence may comprise three or more stages. 
   The term “tension failure characteristics” is used herein to refer to the detectable or measurable changes associated with the tension failure sequence. The tension failure characteristics include:
         Load Threshold: the load at which the tension failure sequence begins;   Elongation: the amount of elongation that occurs after the Load Threshold is exceeded and before the rope breaks (axial direction);   Tension Failure Duration: the duration of the tension failure sequence; and   Tension Failure Geometry: changes in shape and/or diameter (radial direction) of the rope or its constituent parts during the tension failure sequence.       

   When the terms Load Threshold, Elongation, Tension Failure Duration, and Tension Failure Geometry are used without further explanation, these terms refer to tension failure characteristics of a rope as a whole. A rope typically comprises a plurality of individual components, and the terms Load Threshold, Elongation, Tension Failure Duration, and Tension Failure Geometry may also be applied to these individual components or groups of components. 
   In the example rope  20 , the first set of tension failure characteristics meets the operational requirements defined by the intended use of the rope  20 . The second set of tension failure characteristics may or may not meet the operational requirements of the rope  20  but differ from first set of tension failure characteristics in at least one aspect. 
   In particular, in a rope  20  constructed in accordance with the principles of the present invention, the first and second portions  22  and  24  are formed and combined such that the first portion  22  will bear most or all of the tension loads under normal operating conditions. As the tension load on the rope  20  exceeds the Load Threshold associated with the first set of tension failure characteristics, the first portion  22  of the rope  20  begins to deform, marking the beginning of the first stage of the tension failure sequence. Typically, this deformation takes the form of elongation of the first portion  22 . 
   As the first portion  22  of the rope begins to deform, the tension load on the rope  20  is eventually at least partly borne by the second portion  24 , and the second portion  24  of the rope also begins to deform. Typically, the deformation of the second portion  24  of the rope  20  also takes the form of elongation. 
   The first material is selected such that the first portion  22  will break before the second portion  24 . The breaking of the first portion  22  marks the end of the first stage and the beginning of the second stage of the tension failure sequence. 
   After the first portion  22  breaks, the entire tension load on the rope  20  is borne by the second portion  24 . At this point, the rope  20  has not completely failed, and the still intact second portion  24  continues to deform. After further deformation, the second portion  24  of the rope  20  eventually also breaks, marking the end of the tension failure sequence. 
   When the first portion  22  breaks at the end of the first stage of the tension failure sequence, at least a portion of the potential energy introduced into the rope  20  by the tension load is converted to kinetic energy. However, the intact second portion  24  prevents the rope  20  from breaking entirely. In addition, the second portion  24  of the rope  20  absorbs at least a portion of the kinetic energy associated with the breaking of the first portion  22 . 
   The deformation of the second portion  24  of the rope  20  will also increase the Tension Failure Duration of the tension failure sequence associated with the rope  20 . Depending upon the size and composition of the rope  20  and the tension load applied thereto, the tension failure sequence can be increased as compared to a conventional rope by from a fraction of a second to ten seconds or more. The look and performance of the tension failure sequence of the rope  20  will thus be significantly different from that of a conventional rope. 
   The first material forming the first portion  22  of the rope  20  is the lower elongating material and may be any one or more yarns with tenacity greater than approximately 15 grams per denier (gpd) to serve as the strength component. Surface modifications may be accomplished through the blending of other fiber or fibers with the high tenacity strength component to obtain the desired surface characteristics. 
   The second material forming the second portion  24  of the rope  20  is the higher elongating material and may be any one or more yarns having an elongation that is at least three times greater than the elongation of the yarns forming the first portion  22 . 
   As generally discussed above, the first material  22  bears most of the primary tension loads during normal use (i.e., when the tension loads are below the Load Threshold). The second material  24  thus increases weight of the rope without significantly contributing to the performance of the rope during normal use. Accordingly, the amount of the second material  24  used should be kept as low as possible while still functioning properly during the tension failure sequence. 
   In particular, the second material  24  should be within a first preferred range of approximately between 1 percent and 40 percent by weight of the rope  20 . The second material  24  should be within a second preferred range of approximately between 5 percent and 30 percent by weight of the rope  20 . 
   The following discussion will describe several particular example ropes constructed in accordance with the principles of the present invention as generally discussed above. 
   EXAMPLE I 
   Referring now to  FIGS. 2 ,  3 , and  4 , those figures depict an example of a controlled failure rope  30  constructed in accordance with the principles of the present invention. As shown in  FIG. 2 , the controlled failure rope  30  comprises a core  32  and a jacket  34 .  FIG. 2  also shows that the core  32  and jacket  34  comprise a plurality of strands  36  and  38 , respectively.  FIG. 4  shows that the strands  36  and  38  comprise a plurality of yarns  40  and  42  and that the yarns  40  and  42  in turn each comprise a plurality of fibers  44  and  46 , respectively. 
   The fibers  44  and  46  are the elemental components of the rope  30 . The example yarns  40  and  42  are formed of fibers  44  and  46  made of synthetic materials. The fibers  44  and  46  are combined to form the yarns  40  and  42  using any one or more of a number of techniques. The strands  36  and  38  are formed by the combining the yarns  40  and  42 , also by using any one or more of a number of techniques. The techniques for combining fibers to form yarns and combing yarns to form strands are or may be conventional and will not be described herein in detail. 
   The exemplary core  32  and jacket  34  are formed from the yarns  40  and  42  using a braiding process. The example rope  30  is thus the type of rope referred to in the industry as a double-braided synthetic rope. 
   The example rope  30  comprises first and second portions, which are analogous to the first and second portions  22  and  24  described above. The first and second portions of the example rope  30  are formed using any one or more of several different arrangements. The following Table A lists some of the configurations of the first and second portions of the example rope  30 : 
   
     
       
             
             
             
           
             
             
             
           
         
             
               TABLE A 
             
             
                 
             
             
               Configuration 
               first portion 
               second portion 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               1 
               core 32 
               jacket 34 
             
             
               2 
               jacket 34 
               core 32 
             
             
               3 
               some of the strands 36 of 
               some of the strands 36 of 
             
             
                 
               the core 32 
               the core 32 and the jacket 
             
             
                 
                 
               34 
             
             
               4 
               the core 32 and some of the 
               some of the strands 38 of 
             
             
                 
               strands 38 of the jacket 34 
               the jacket 34 
             
             
               5 
               some of the yarns 40 of the 
               some of the yarns 40 of the 
             
             
                 
               strands 38 
               strands 38 and the jacket 
             
             
                 
                 
               34 
             
             
               6 
               the core 32 and some of the 
               some of the yarns 42 of the 
             
             
                 
               yarns 42 of the strands 38 
               strands 38 
             
             
               7 
               some of the strands 36 of 
               some of the strands 36 of 
             
             
                 
               the yarns 40 and some of 
               the yarns 40 and some of 
             
             
                 
               the strands 38 of the yarns 
               the strands 38 of the yarns 
             
             
                 
               40 
               40 
             
             
               8 
               the core 32 and some of the 
               some of the fibers 46 of the 
             
             
                 
               fibers 46 of the jacket 34 
               jacket 34 
             
             
               9 
               some of the fibers 44 of the 
               some of the fibers 44 of the 
             
             
                 
               yarns 40 
               yarns 40 and the jacket 34 
             
             
               10 
               some of the fibers 44 of the 
               some of the fibers 44 of the 
             
             
                 
               yarns 40 and some of the 
               yarns 40 and some of the 
             
             
                 
               fibers 46 of the yarns 42 
               fibers 46 of the yarns 42 
             
             
                 
             
           
        
       
     
   
   In the configurations in Table A, the strands  36  and yarns  40  may be substantially identical in size and composition. However, strands  36  and yarns  40  of different sizes and compositions may be combined to form the core  32 . Similarly, the strands  38  and yarns  42  of the jacket  32  may be substantially identical in size and composition, although strands  38  and yarns  42  of different sizes and compositions may be combined to form the jacket  34 . 
   EXAMPLE 2 
   Referring now to  FIGS. 5 ,  6 , and  7 , those figures depict another example of a controlled failure rope  50  constructed in accordance with the principles of the present invention. As perhaps best shown in  FIG. 6 , the controlled failure rope  50  comprises a plurality of strands  52 .  FIG. 7  further illustrates that each of the strands  52  comprises a plurality of yarns  54  and that the yarns  54  in turn comprise a plurality of fibers  56 . 
   The fibers  56  are the elemental components of the rope  50 . The fibers  56  are combined to form the strands  52  using any one or more of a number of techniques. The example yarns  54  are formed of fibers  56  made of synthetic materials. The strands  52  are formed by combining the yarns  54  using any one of a number of processes. The exemplary rope  50  is formed from the strands  52  using a braiding process. The example rope  50  is thus the type of rope referred to in the industry as a twelve-strand braided synthetic rope. 
   The example rope  50  comprises first and second portions, which are analogous to the first and second portions  22  and  24  described above. The first and second portions of the example rope  50  are formed using any one or more of several different arrangements. The following Table B lists some of the configurations of the first and second portions of the example rope  50 : 
   
     
       
             
             
             
           
         
             
               TABLE B 
             
             
                 
             
             
               Configuration 
               first portion 
               second portion 
             
             
                 
             
           
           
             
               1 
               some of the strands 52 
               some of the strands 52 
             
             
               2 
               some of the yarns 54 
               some of the yarns 54 
             
             
               3 
               some of the fibers 56 
               some of the fibers 56 
             
             
                 
             
           
        
       
     
   
   In the configurations in Table B, the strands  52  forming the rope  50  may be substantially identical in size, but at least some of them must be different in composition. However, strands  52  of different sizes may be combined to form the rope  50 . One form of the example rope  50  may comprise eighty percent by weight of the first portion and twenty percent by weight of the second portion. 
   EXAMPLE 3 
   Referring now to  FIGS. 8 ,  9 , and  10 , those figures depict yet another example of a controlled failure rope  60  constructed in accordance with the principles of the present invention. As perhaps best shown in  FIG. 8 , the controlled failure rope  60  comprises a plurality of strands  62  and  64 .  FIG. 9  further illustrates that each of the strands  62  and  64  in turn comprises a plurality of yarns  70  and  72 , respectively, and that the yarns  70  and  72  are in turn comprised of a plurality of fibers  74  and  76 , respectively. 
   The fibers  74  and  76  are the elemental components of the rope  60 . The example strands  62  and  64  are formed of fibers  74  and  76  made of synthetic materials. The fibers  74  and  76  are combined to form the yarns  70  and  72  using any one or more of a number of techniques. The yarns  70  and  72  are in turn combined into the strands  62  and  64  using known techniques. The exemplary rope  60  is formed from the strands  62  and  64  using a twisting process. The example rope  60  is thus the type of rope referred to in the industry as an eight-strand twisted rope. 
   The example rope  60  comprises first and second portions, which are analogous to the first and second portions  22  and  24  described above. The first and second portions of the example rope  60  are formed using any one or more of several different arrangements. The following Table C lists some of the configurations of the first and second portions of the example rope  60 : 
   
     
       
             
             
             
           
             
             
             
           
         
             
               TABLE C 
             
             
                 
             
             
               Configuration 
               first portion 
               second portion 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               1 
               the strands 62 
               the strands 64 
             
             
               2 
               some of the strands 62 
               some of the strands 62 
             
             
                 
                 
               and the strands 64 
             
             
               3 
               the strands 62 and some of 
               some of the strands 64 
             
             
                 
               the strands 64 
             
             
               4 
               some of the strands 62 and 
               some of the strands 62 
             
             
                 
               some of the strands 64 
               and some of the strands 
             
             
                 
                 
               64 
             
             
               5 
               the strands 62 and some of 
               some of the yarns 72 
             
             
                 
               the yarns 72 
             
             
               6 
               some of the yarns 70 
               the strands 64 and some 
             
             
                 
                 
               of the yarns 70 
             
             
               7 
               some of the yarns 70 and 
               some of the strands 70 
             
             
                 
               some of the yarns 72 
               and some of the yarns 72 
             
             
               8 
               the strands 62 and some of 
               some of the fibers 76 
             
             
                 
               the fibers 76 
             
             
               9 
               some of the fibers 74 
               the strands 64 and some 
             
             
                 
                 
               of the fibers 74 
             
             
               10 
               some of the fibers 74 and 
               some of the fibers 74 and 
             
             
                 
               some of the fibers 76 
               some of the fibers 76 
             
             
                 
             
           
        
       
     
   
   In the configurations in Table C, the strands  62  and  64  forming the rope  60  may be substantially identical in size, but at least some of them must be different in composition. However, strands  62  and  64  of different sizes may be combined to form the rope  60 . One form of the example rope  60  may comprise eighty percent by weight of the first portion and twenty percent by weight of the second portion. 
   EXAMPLE 4 
   Referring now to  FIGS. 11 ,  12 , and  13 , those figures depict still another example of a controlled failure rope  80  constructed in accordance with the principles of the present invention. As perhaps best shown in  FIG. 12 , the controlled failure rope  80  comprises a plurality of strands  82  and  84 .  FIG. 13  further illustrates that each of the strands  82  and  84  in turn comprises a plurality of yarns  90  and  92 , respectively, and that the yarns  90  and  92  are in turn comprised of a plurality of fibers  94  and  96 , respectively. 
   The fibers  94  and  96  are the elemental components of the rope  80 . The example strands  82  and  84  are formed of fibers  94  and  96  made of synthetic materials. The fibers  94  and  96  are combined to form the yarns  90  and  92  using any one or more of a number of techniques. The yarns  90  and  92  are in turn combined into the strands  82  and  84  using known techniques. The exemplary rope  80  is formed from the strands  82  and  84  using a braiding process. The example rope  80  is thus the type of rope referred to in the industry as an eight-strand braided synthetic rope. 
   The example rope  80  comprises first and second portions, which are analogous to the first and second portions  22  and  24  described above. The first and second portions of the example rope  80  are formed using any one or more of several different arrangements. The following Table D lists some of the configurations of the first and second portions of the example rope  80 : 
   
     
       
             
             
             
           
             
             
             
           
         
             
               TABLE D 
             
             
                 
             
             
               Configuration 
               first portion 
               second portion 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               1 
               the strands 82 
               the strands 84 
             
             
               2 
               some of the strands 82 
               some of the strands 82 
             
             
                 
                 
               and the strands 84 
             
             
               3 
               the strands 82 and some of 
               some of the strands 84 
             
             
                 
               the strands 84 
             
             
               4 
               some of the strands 82 and 
               some of the strands 82 
             
             
                 
               some of the strands 84 
               and some of the strands 
             
             
                 
                 
               84 
             
             
               5 
               the strands 82 and some of 
               some of the yarns 92 
             
             
                 
               the yarns 92 
             
             
               6 
               some of the yarns 90 
               the strands 84 and some 
             
             
                 
                 
               of the yarns 90 
             
             
               7 
               some of the yarns 90 and 
               some of the strands 90 
             
             
                 
               some of the yarns 92 
               and some of the yarns 92 
             
             
               8 
               the strands 82 and some of 
               some of the fibers 96 
             
             
                 
               the fibers 96 
             
             
               9 
               some of the fibers 94 
               the strands 84 and some 
             
             
                 
                 
               of the fibers 94 
             
             
               10 
               some of the fibers 94 and 
               some of the fibers 94 and 
             
             
                 
               some of the fibers 96 
               some of the fibers 96 
             
             
                 
             
           
        
       
     
   
   In the examples in Table D, the strands  82  and  84  forming the rope  80  may be substantially identical in size, but at least some of them must be different in composition. However, strands  82  and  84  of different sizes may be combined to form the rope  80 . One form of the example rope  80  may comprise eighty percent by weight of the first portion and twenty percent by weight of the second portion. 
   EXAMPLE 5 
   Referring now to  FIGS. 8 ,  9 , and  10 , those figures depict yet another example of a controlled failure rope  120  constructed in accordance with the principles of the present invention. As perhaps best shown in  FIG. 14 , the controlled failure rope  120  comprises a plurality of strands  122  and  124 .  FIG. 15  further illustrates that each of the strands  122  and  124  in turn comprises a plurality of yarns  130  and  132 , respectively, and that the yarns  130  and  132  are in turn comprised of a plurality of fibers  134  and  136 , respectively. 
   The fibers  134  and  136  are the elemental components of the rope  120 . The example strands  122  and  124  are formed of fibers  134  and  136  made of synthetic materials. The fibers  134  and  136  are combined to form the yarns  130  and  132  using any one or more of a number of techniques. The yarns  130  and  132  are in turn combined into the strands  122  and  124  using known techniques. The exemplary rope  120  is formed from the strands  122  and  124  using a twisting process. The example rope  120  is thus the type of rope referred to in the industry as a four-strand twisted rope. 
   The example rope  120  comprises first and second portions, which are analogous to the first and second portions  22  and  24  described above. The first and second portions of the example rope  120  are formed using any one or more of several different arrangements. The following Table C lists some of the configurations of the first and second portions of the example rope  120 : 
   
     
       
             
             
             
           
             
             
             
           
         
             
               TABLE E 
             
             
                 
             
             
               Configuration 
               first portion 
               second portion 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               1 
               the strands 122 
               the strands 124 
             
             
               2 
               some of the strands 122 
               some of the strands 122 
             
             
                 
                 
               and the strands 124 
             
             
               3 
               the strands 122 and some 
               some of the strands 124 
             
             
                 
               of the strands 124 
             
             
               4 
               some of the strands 122 
               some of the strands 122 
             
             
                 
               and some of the strands 
               and some of the strands 
             
             
                 
               124 
               124 
             
             
               5 
               the strands 122 and some 
               some of the yarns 132 
             
             
                 
               of the yarns 132 
             
             
               6 
               some of the yarns 130 
               the strands 124 and some 
             
             
                 
                 
               of the yarns 130 
             
             
               7 
               some of the yarns 130 and 
               some of the strands 130 
             
             
                 
               some of the yarns 132 
               and some of the yarns 132 
             
             
               8 
               the strands 122 and some 
               some of the fibers 136 
             
             
                 
               of the fibers 136 
             
             
               9 
               some of the fibers 134 
               the strands 124 and some 
             
             
                 
                 
               of the fibers 134 
             
             
               10 
               some of the fibers 134 and 
               some of the fibers 134 and 
             
             
                 
               some of the fibers 136 
               some of the fibers 136 
             
             
                 
             
           
        
       
     
   
   In the configurations in Table C, the strands  122  and  124  forming the rope  120  may be substantially identical in size, but at least some of them must be different in composition. However, strands  122  and  124  of different sizes may be combined to form the rope  120 . One form of the example rope  120  may comprise eighty percent by weight of the first portion and twenty percent by weight of the second portion. 
   Given the foregoing, it should be clear to one of ordinary skill in the art that the present invention may be embodied in other forms that fall within the scope of the present invention.