Effect of Overlay Material on the Flexural Properties of Commercial Particle Board

Stressed skin design theory is discussed with respect to flexural properties of overlaid particle board, the effects were tested experimentally and the data applied to practical design problems. Four particle board types were overlaid with five overlays and tested for flexural strength and stiffness by ASTM testing procedures. Similar sections of one 4 by 8 sheet of each particle board type (A–3/8-inch hammermill planer shaving, B–1/2-inch hammermill chip, extruded; C–3/8-inch sandwich, hammermill chip center and flake surface, D–1/4-inch large flake) were overlaid with each of the five overlays (1.–1/8-inch Douglas-fir veneer, grain parallel to span, 2.–same perpendicular to span; 3.–1/16-inch face and cross banded Douglas-fir veneer; 4.–1/8-inch hardboard; 5.–medium density masking overlay). Two specimens, 3-inches wide, were cut from each overlaid section; the length 2-inches greater than the span. Span-depth ratios of 24:1 and 48:1 were used for controls and boards with noted exceptions. Particle boards in ascending order of M/R and M/I were B, A, C, D. Overlays increased both properties, in ascending order of effectiveness 2, 5, 4, 3, 1. Overlays made greatest percentage increase in both properties of weakest particle board. Although the limited tests resulted in high variation, experimental confirmation of stressed-skin principals was obtained. Comparison with flexural properties of insulation board, gypsum board plywood, and lumber are shown graphically. A detailed sample calculation of allowable working stresses for overlaid particle board is presented. A 3/8-inch particle board core overlaid with 1/8-inch Douglas-fir veneer has a M/R of 2000 psi and a M/E of 300,000 Psi. Parallel to a 24-inch unsupported span it could 1) carry a uniform load of 61 lbs./sq.ft. with deflection to 1/240th of span and 2) carry a uniform load of 124 lbs./sq.ft. with safety factor > 3.

You must be logged in to download any documents. Please login (login accounts are free) or learn how to Become a Member