Tensile properties of earlywood and latewood from loblolly pine (Pinus taeda) using digital image correlation

Abstract

The goal of this research was to measure the elastic properties and strength of earlywood and latewood from two growth-ring positions of loblolly pine.Because of the small specimen size, a contactless strain measurement was applied using a microscope with an appropriate field of view.The tensile properties of the earlywood and latewood were calculated from load data from a Minimat tester coupled with elastic strain data from a digital image correlation technique.Incremental loading was applied until specimen failure occurred.Elastic modulus, Poisson ratio, and strength generally increased as the growthring numbers increased, except for the strength of latewood that slightly decreased.Elastic properties and strength were significantly different for different growth-ring positions and intraring layers.The elastic modulus for earlywood and latewood were best fitted by Weibull distributions regardless of growth-ring positions, whereas Poisson ratios were best fitted by Weibull distributions for earlywood 1 -10 and latewood 11 -20 groups, and gamma distributions for earlywood 11 -20 and latewood 1 -10 groups.Strain distribution analysis showed nonuniform strain distributions for the four groups and also showed more resistance to load for earlywood and latewood from a higher growth-ring position.