Resistance Strain Gages and Adhesives for Wood

A number of foil and wire strain gages along with nine different bonding adhesives were evaluated for their accuracy in strain measurement on sugar pine (Pinus lambertiana Douglas). In measuring strain parallel to the grain, readings accurate to 2 percent were easily obtainable. When measuring strains perpendicular to the grain, the best gage and adhesive system indicated strains that were 4 percent less in tension and 10 percent less in compression than were expected from bending deflection of a beam. The best gage system consisted of a free-filament hairpin-shaped length of strain-sensitive wire bonded with thinned nitro-cellulose adhesive. A flexibilized epoxy adhesive performed better than higher modulus ones. Errors in strain as great as 50 percent were indicated by some commonly used gage and adhesive combinations. Refinements suggested for obtaining better results perpendicular to the grain were to use smaller diameter annealed wire in free-filament type gages with a creep-resistant low-modulus adhesive.

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