Predicting ultimate tensile and bending strengths of three finger-jointed tropical African hardwoods using acoustic emissions

Abstract

The acoustic emissions behaviour of finger-joints from three tropical African hardwoods, Obeche (Triplochiton scleroxylon), Makore (Tieghemella heckelii) and Moabi (Baillonella toxisperma) were examined with a view to establishing their potential usefulness for non-destructively predicting ultimate tensile and bending strengths. Stress at first acoustic emission event-count as well as the cumulative event-count at 80 percent of mean failure stress and the cumulative event-count at 80 percent of mean proportional limit stress for all specimens were separately correlated to finger-joint strengths. The correlation suggested that all three acoustic emission properties could be used to non-destructively predict the ultimate tensile and bending strengths of finger-joints from the three hardwoods. Correlation coefficients obtained for the prediction models developed were, generally, good and statistically significant (a = 0.05). Stress at first event-count seemed best correlated to ultimate tensile strength of finger-joints from the three species, whilst cumulative event-count at 80 percent of mean failure stress was best correlated to modulus of rupture. A logarithmic regression function seemed to fit the regression of acoustic emission event-counts on ultimate tensile strength and modulus of rupture better than a linear function. The acoustic emission technique seems applicable as a non-destructive testing method for predicting the tensile and bending strengths of finger-joints from the three tropical African hardwoods.