306 third authors applied a quick stroke with one or two hands on the handle of a handsaw that was attached to the dynamometer. Using a digital caliper (CD-6CS, Mitutoyo, Japan), the diame- ter of each rope was measured (while the 41 kg mass was attached) at the point of blade impact before and after cutting. The pre- and post-cut diameters were converted to “percent cut” by dividing their difference by the pre-cut diameter. For ropes that were com- pletely severed, percent cut equaled 100%. After cutting, ropes that were not completely severed were tested by applying an in- creasing tensile load [at a rate of 12.6 mm/min (0.5 in/min)] in a universal testing machine [133 kN (30,000 lbf) capacity; MTS, Eden Prairie, MN]. A piece of rope 1.0 m (3.3 ft) long was also cut past the section that was damaged during the cutting test, and its breaking strength measured as a control. Each end of the rope was tied with an anchor hitch to galvanized steel eyebolts [23.7 mm (0.93 in) diameter] attached to the testing machine. While tensile testing of climbing ropes typically follows the CI-1500 standard Kane et al.: Damage Inflicted on Climbing Ropes by Handsaws Figure 3. Blade in jig attached to pendulum. “X” marks the tooth that first made contact with the rope. (Anonymous 2006b), the described setup was used because it was readily available. In reality, most attachment points (d-rings, car- abiners, rope snaps) on a climber’s saddle are smaller than 23.7 mm in diameter. Since rope strength decreases with decreasing bend radius (McKenna et al. 2004), the values for rope strength are likely overestimates compared to actual field conditions. “Per- cent strength loss” was calculated the same way as “percent cut,” substituting breaking strength of cut and un-cut sections of rope. Aligning the blade with the same curvature in which it was attached to the pendulum during testing, the curvature of each blade was measured when traced on a piece of paper. The un-toothed edge of each blade was traced from a com- mon starting point on the blade (opposite the first tooth clos- est to the handle) and on the paper. Curved blades (F1, F3, IB, ZU) contacted the rope between one-half and two-thirds of the blade length, depending on the curvature of the blade. This was not true of the straight blade (F2), for which initial con- tact occurred at approximately one-quarter of blade length. The study authors expected to cut entirely through some ropes, but also measured horizontal acceleration of the pendulum (i.e., in the direction of its motion when the blade impacted the rope) throughout the test. Data were collected at 2048 Hz with a G-Link® accelerometer (Micro-Strain Inc., Williston, VT). Accelerations (m/s2) provide an estimate of the resistance en- countered by the blade as it contacted the rope. Large accelera- tions in the direction opposite the motion of the pendulum re- flect a rope that was harder to cut with a particular blade. The study used the acceleration of greatest magnitude for analyses. Using 3.3 m (11 ft) sections, each rope and blade com- bination were tested five times in a randomized complete block design, with ropes blocked in each blade. For ev- ery blade, except IB, the study randomly alternated between two individual blades; all ropes were tested on one IB blade. A two-way analysis of variance (ANOVA) was used to in- Figure 2. Pendulum attached to beam; the jig that held blades (see Figure 3) is attached to the pendulum with clamps visible just below the midpoint of the pendulum. ©2009 International Society of Arboriculture vestigate differences between ropes and blades for percent cut, percent strength loss, and acceleration. Levene’s test indicated the possibility of nonhomogeneous variance for each response variable, which remained after the study authors 1) removed the Zubat blade from the analysis (see following explanation), and 2) arcsine transformed the percent cut and percent strength loss data. To determine whether violating the assumption of homogeneity of variance invalidated the ANOVA, the analysis was repeated using a nonparametric permutation ANOVA (Anderson 2001). Although p-values differed slightly, significance levels from the
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