GRAIN ANGLE EFFECTS ON ACOUSTIC EMISSION CHARACTERISTICS OF SOUTHERN YELLOW PINE COLUMNS UNDER COMPRESSION

Abstract

This study investigated the influence of wood grain angle (0, 10, 20, 30, 45, 60, 75, and 90 degrees) on acoustic emission (AE) characteristics of southern yellow pine columns subjected to compressive loading. Four AE parameters considered were counts, cumulative counts, count rate, and amplitude. The main conclusion was that AE cumulative counts versus time curves can be characterized with three distinct stages in terms of AE count rates: initiation, growth, and acceleration. The initiation stage had a constant mean count rate of 0.33 counts/s compared to the growth stage mean count rate of 19.10 counts/s, while the acceleration stage had a mean count rate of 608.40 counts/s. Within each stage, count rates increased as grain angle increased from 0 to 30 degrees, then dropped as grain angle further increased to 90 degrees. Maximum AE counts and total cumulative AE counts all increased as grain angle increased from 0 to 30 degrees and decreased as grain angle further increased to 90 degrees. Higher AE amplitudes were observed in the yield and failing stages of tested wood columns according to their stress-strain curves plotted together with their corresponding amplitude-time curves. Maximum amplitude increased as grain angle increased from 0 to 20 degrees, then had a decreasing trend as grain angle increased to 45 degrees, followed by an increasing trend as grain angle increased to 75 degrees. These differences in AE characteristics suggested that AE “signatures” in terms of AE signals do exist for timber materials when subjected to compressive loading.