The effect of stringer design and leading-edge design on the strength characteristics of wooden pallets
Impact shear and static flexure tests were performed on pallet stringers notched with six different fillet radii. These notches were cut with a band-saw or a stringer-notcher. Attempts were made to reduce the incidence of stringer fracture between the notches (a) by nail-reinforcing the stringers adjacent to the inner notch ends and (b) by retarding longitudinal moisture movement through the notch ends by notch coating. The leading-edge design of the paIlet was studied by determining its impact resistance if fabricated with leadboards and stringers of different species and specific gravities.
The impact shear resistance and the flexural strength of notched pallet stringers increased with increasing notch fillet radii. The optimum fillet radius was one inch. No performance difference was found between the band-sawn and machine-shaped notches. Nail-reinforcing slightly increased the immediate flexural strength at initial failure of green stringers; did not increase the delayed flexural strength of seasoned stringers; and increased their immediate and delayed ultimate flexural strength. Notch-coating progressively increased the delayed ultimate flexural strength during the seasoning period.
Leadboard and stringer specific gravity effected the leading-edge impact resistance of wooden pallets. It increased more rapidly if the leadboard specific gravity was increased. An increase in the stringer specific gravity did not necessarily increase the leading-edge impact resistance. Optimum leading-edge impact resistance should be attained by using high-density lumber assembled with a supplementary nai I driven through the leadboard into the center stringer, provided lumber splitting is avoided.