High-Strength-Cord高強(qiáng)度繩索

1、2000 International Technical Rescue SymposiumComparative Testing of High Strength CordTom MoyerPaul Tusting, Chris Harmston,( Tom Moyer)Complete test data for the results presented in this paper can be found at/tmoyer/testingChris Harmston and Paul Tusting are employees of Blac

2、k Diamond Equipment, the manufacturer of a product evaluated in this paper. All effort has been made to present the information here impartially. This paper presents the results of testing of many products. It does not represent the official position of Black Diamond Equipment.AbstractMany climbers

3、carry an 18-foot length of accessory cord called a cordelette for rigging anchors and as a tool for self-rescue situations. In the past, this cord was usually 7mm Nylon. In recent years, many climbers have changed to using one of a number of high-strength materials in smaller diameters. Vectran, Tec

4、hnora, Spectra, Kevlar, Kevlar/Spectra blends and Spectra/Nylon webbing are all used for these purposes along with Nylon cord and Nylon webbing. These materials all have different properties, and in some applications, dramatically different performance. This study tests and compares the strength of

5、different knots in these materials, in both static and dynamic loading, along with their resistance to cyclic flexing, in order to judge their suitability as tools for climbers and rescuers.BackgroundThe use of Kevlar, Spectra and Vectran fibers to make high-strength rope was pioneered by the sailin

6、g industry, to take advantage of their high tensile strength, low elongation, and low moisture absorption. These materials gradually moved into climbing applications, first as chock cord and more recently as cordelette material, prusik cord, and emergency rappel line. In the climbing world they have

7、 been surrounded by a lot of mythology and little hard data. It has been said that tying and untying chock cord weakens it severely, that double fishermans knots are not secure, triple fishermans are needed, that Kevlar-based cords will self-abrade and eventually weaken, and that knots will not hold

8、 in Spectra/Nylon webbing. In recent years, manufacturers have been combining and improving materials, and climbers have been expanding their applications. Have the materials improved? Are the myths true? And most importantly, are these materials strong enough to use in these applications? This test

9、ing will provide some answers to these questions.MaterialsKevlarKevlar was one of the first high-strength fibers to be used in rope. It still offers high tensile strength and very low elongation, but has poor fatigue properties. The fibers inside the rope abrade each other, offering little indicatio

10、n of the reduced strength until the rope breaks. Kevlar has a very high melting point, 500 C or 932 F. Kevlar-core ropes are sold as escape lines for firefighters - to be used once and discarded. Manufacturers have had some success at solving the self-abrasion problem by combining Kevlar with Spectr

11、a.TechnoraTechnora, like Kevlar, is an aramid, but with vastly improved fatigue properties. It shares Kevlars high tensile strength and high melting point.SpectraSpectra is a very high molecular density form of polyethylene - the same thing used to make grocery bags, six-pack carriers and milk jugs.

12、 The manufacturing process aligns the molecules, which vastly increases the strength of the material. It is twice as strong as hardened steel (per unit area) and one-tenth the density. Spectra has several difficult issues. The melting point is very low, 147 C or 297 F, not much warmer than boiling w

13、ater. The material is unbelievably slippery, which makes it difficult for manufacturers to form into a workable rope. And, while the modulus of the fibers is comparable to steel, they slowly elongate under a continuous load. This process is called creep. It is mostly irrelevant to climbers, but anno

14、ying to sailors. Spectra/Nylon is also known as Dyneema (a trade name of Beal Ropes) in Europe.1VectranVectran is a liquid crystal polymer - its properties are between those of crystalline solids and liquids. It has similar strength to Spectra, but without the creep problems. It has poor UV resistan

15、ce, which is not a problem when used as the core in kernmantel rope construction.Seven products were tested for this project. Sterling Vectran, Blue Water Titan, Black Diamond Gemini2, Maxim Spectra A, Mountain Tools Ultratape, Sterling 7mm Nylon accessory cord, and Liberty Mountain 1 inch Nylon Tub

16、ular Webbing.Sterling Vectran has a Vectran core and a Nylon sheath - it is sold in precut lengths labeled cordelette in addition to spools. Blue Water Titan has a braided Spectra/Nylon core and a Nylon sheath. Black Diamond Gemini2 has a Technora core and a polyester sheath. It is identical to the

17、product sold as Tech Cord by Maxim (New England Rope). The original Black Diamond Gemini was a different product, similar to Maxims Spectra-A, and has not been sold in several years. Spectra -A has a braided Spectra/Kevlar core and a polyester sheath. It has largely been replaced by Tech Cord, but i

18、s still sold, usually at cheaper prices. Ultratape is a Spectra/Nylon webbing, constructed to minimize the amount of Spectra on the outside surface. This helps protect the Spectra from UV damage, and lets knots hold better, since more Nylon is in contact.ApplicationsThe cordelette has become the fav

19、ored tool of climbers for a quick, convenient and redundant anchor, using a minimum of gear. It also doubles as an extremely useful self-rescue tool, or can be cut up and left as rappel anchors when retreating off a climb. Mountain Tools has introduced the concept of the Web-o-lette, a long runner,

20、with sewn eyes in each end. This makes the same 3 point tied-off anchor, but two of the pieces are clipped with only a single strand of webbing. This means the whole length of material can be reduced, which makes it lighter and less bulky on the harness.Cordelette AnchorWebolette Anchor(Karl Lew pho

21、to)Test MethodsSlow Pull TestsSlow pull tests were done on the 11,000-lb SATEC Apex 11 EMF universal test machine at Black Diamond. These were done on unknotted material over 4 diameter drums, on figure -eight knots, on loops tied with double fishermans, triple fishermans and water knots, and on a c

22、ordelette loaded on a single arm. Pull rates and fixtures were consistent with CEN standards. The material was not temperature and humidity conditioned, but all tests were done at 29% humidity 4% and at 71F 6. Five samples were tested in each material for each configuration and the results were aver

23、aged. One sample of various friction knots was also tested in each material on Black Diamond 10.5mm Cirrus dry-coated rope.2Keep in mind that an average breaking strength (the arithmetic mean) is not a good quantity to use to determine whether a component is strong enough. A minimum breaking strengt

24、h - three standard deviations below the mean- is much more appropriate. However, five samples are not sufficient to determine a meaningful statistical minimum, so average strength is presented here.Drop TestsDrop Tests were conducted at the Rocky Mountain Rescue Group drop tower in Boulder Colorado.

25、 The configuration modeled the UIAA and CEN drop test - a fall factor 1.71 fall on 2.8 meters of rope. A new section of 10.5mm Black Diamond Cirrus (nondry) rope was used for each test. This rope carries a UIAA rated impact force of 8.4 kN (1888 lb). The cordelette to be tested was placed at the loc

26、ation of the pivot edge, or the direction change anchor. The force at this point should theoretically be twice the rope tension because of the direction change. In reality, carabiner friction reduces this to around 170%. The load was applied to the cordelette with carabiners, as it would be in a cli

27、mbing fall. As in the slow pull tests, only one arm of the cordelette was clipped. In accordance with the CEN specifications, the weight was dropped once every five minutes until the cordelette had broken or sustained five falls without breaking.Flex Cycle TestA cyclic flex test was run to check the

28、 fatigue performance of the different materials. A sample of cord passed through a horizontal hole in the fixture, flexed 90 degrees over a steel edge, and was loaded with a 40 lb weight. The fixture was rotated back and forth 180 degrees by a pneumatic actuator for a specified number of cycles, wit

29、h all the flexing happening at the same point on the sample. The sample was then pull-tested over drums with the fatigued point in the free section to measure any reduction in tensile strength at that point.ResultsSlow Pull TestsThe Technora and Kevlar/Spectra cords live up to their billing as havin

30、g extraordinary tensile strength, but the story changes immediately when the cord is knotted. Knot efficiencies for a figure -eight knot ranged from 40% on the Gemini to 92% on the Nylon. For a double fishermans knot, Gemini and Titan share an interesting failure mode. The sheath breaks at the knot

31、and the slippery core unties, pulling through the sheath. When a triple fishermans knot is tied, this does not happen. The strength gain for the triple fishermans is not large, but it is enough to change the mechanism. The Ultratape - a Spectra/Nylon webbing - shows excellent strength in all of the

32、knots, contradicting the popular belief that knots will not hold in this type of material. Testing is needed on webbing with a more conventional Spectra/Nylon weave to see if that conclusion can be extended to other products.3Tensile Strength(lbs)6000Average Tensile StrengthStrengthManufacturers Rat

33、ed StrengthCEN Minimum for 7mm cord5000Single Strand40003000200010000NylonVectran(Spectra)(Technora) (Spectra/Kevlar) ToolsUltratapeWebbing7mmSterlingSterlingTitanGemini1TubularWaterBDSpectraAMtnBlueMaximFigure Eight Knot ComparisonkN2520151050Single Strand Strength (lbs)600025 kNAverage Tensile Str

34、ength40%Figure-Eight Knot(Knot Efficiency)500061%20400064%86%70%53%15300092%48%10200051000007mmVectran(Spectra)(Technora)(sewnTubularWebbing(Spectra/Kevlar)-8)NylonUltratape(figeye)SterlingSterlingWaterTitanBD GeminiAToolsUltratape1ToolsBlueMaximSpectraMtnMtn4Loop Knots (Bends) Comparison7000(lbs)Double FishermansWater Knot (Ring Bend)Triple FishermansStrength6000Sterling Spec for Vectran5000Loop40003000200010000NylonVectran(Spectra)(Technora) (Spectra/Kevlar) ToolsUltratapeW