The Deflection of Composite Furniture Panels Under Constant Bending Stress

Experiments were performed to determine the elastic and inelastic behavior of veneered particleboard and its individual components using a commercial brand particleboard and walnut veneers of various thicknesses. The grain direction of the face veneers was parallel to the length of the specimens. The initial and creep deflections were reduced by more than half under all conditions by the application of 1/36-inch veneer on the particleboard surfaces; thereafter the reduction of initial and creep deflections was not proportional to further increasing of the veneer thickness. In all cases, the creep deflection was greatest at 90 percent humidity; also the effect of high humidity on the creep overshadowed the effect of load. The least creep deflection in the particleboard occurred at 65 percent humidity. From the creep data for short-term creep tests between 10 and 100 minutes, .a. technique was found that was satisfactory for predicting long-term creep for a period up to 30 days. This technique is suitable for adoption as a routine creep quality-control method in the manufacturing of furniture panels. Based on a creep rate of 0.0005 inch per day, the best approximation of the ultimate bending and creep deflections as functions of shelling ratio, load level, moisture content, and time conditions of, the composite panels can be accurately predicted by the use of multivariable regression equations: with a R2 value of 0.99. Based on the best estimated ultimate bending deflections of the composites in terms of the initial (elastic) deflection (ratio = 1.0) of solid walnut at normal (65 percent) humidity, a ratio of 7.6 was found for the particleboard at intermediate humidity, 12.5 at low humidity, and 49.3 at high humidity. For the 1/36-inch walnut veneered particleboard, a ratio of approximately 3.0 was found at low and intermediate humidities, and a ratio of 13.0 was found at high humidity. The ratios for 1/8-inch and 3/16-inch veneered composites were all below 2.5 at low and intermediate humidities, and all below 4.5 at high humidity. Ratios of 1.3, 1.6, and 3.1 were found for solid walnut at low, intermediate, and high humidities, respectively. The load at the creep limit in bending corresponds to approximately 60 percent of the load at the proportional limit, or 20-30 percent of the load at the ultimate bending strength in the static bending tests for all specimens of various designs in this experiment.

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