Punch-Shear Test for Evaluating Properties of Hardboard

Nailhead pull-through tests using three types of 6d nails, and similar tests using a punch tool, were made on samples of embossed hardboard siding. Half of the samples were soaked and the remainder were conditioned at 68?F and 65 percent relative humidity. Nailhead area was calculated from average diameter. Stresses were calculated for loads at the center of each sample face and at 1/2 inch and 3/8 inch from an edge. A multiple regression analysis related stress to a number of independent variables, including MC, SG, nail type, panel, and caliper. The following conclusions were drawn from this study: Specific gravity had a mean of 0.75, a standard deviation of 0.11, and a significant positive effect on stress. The mean caliper was 0.46.077 inch. Caliper had no significant effect on stress. The mean MCs were 33.52.77 percent for the soaked specimens and 6.19.50 percent for the conditioned specimens. The mean nailhead pull-through values for the soaked specimens were 5,160 psi and 5,350 psi for the conditioned specimens. The difference between mean stresses was significant (p<.05). The mean adjusted stresses for the three test locations were 6,030, 5,180, and 4,560 psi for the center, 1/2-inch, and 3/8-inch locations, respectively. The differences were significantly different and were attributed to the support given by the edge of the opening provided in the tool. The mean area for the heads of the aluminum nails was about 9 percent smaller than that for the steel nail and the area for the galvanized nail was 4 percent smaller. The head area for the steel nails also was more variable than those for other types tested. Stresses measured with the punch were somewhat more precise than those measured by the nail pull-through test. SG, MC, and caliper each affected stress significantly as determined with the punch.

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