Safe Bending Radii for Curved Laminates

Investigation was conducted to determine minimum safe radii of curvature for woods commonly used in the U.S. Navy’s ship building program. Little information has been published about the ability of wood to be bent in a dry, unheated state. The work covered in this study was limited to clear straight grain lumber. Six species were included in the study: Douglas-fir (Pseudotsuga taxifolia), white oak (Quercus spp.), African mahogany (Khaya spp.), Philippine mahogany (Shorea spp.), Honduras mahogany (Swietenia macrophylla), and red oak (Quercus spp.) treated with Tanalith and pentachlorophenol. Seven thicknesses of white oak and four of Douglas-fir and African mahogany were tested. Only one thickness of each of the three remaining species was examined. On the basis of this study, the following woods are listed numerically according to their ability to be bent to severe curvature: 1) Red oak treated with Tanalith and pentachlorophenol, 2) White oak, 3) African and Honduras mahogany, 4) Philippine mahogany, 5) Douglas-fir. Within the range of thickness practical for laminating curved ship timbers, 1/4 to 1 inch, the relationship between board thickness and proportional limit radius was approximately linear for all species studied. “Safe curvature” formulas were developed from empirical data obtained in the study. These formulas assure that laminations will not fail on being bent to curvature but they do allow some boards to be bent beyond proportional limit.

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