Comparative Analysis of the Elastic Constants Measured via Conventional, Ultrasound, and 3-D Digital Image Correlation Methods in Eucalyptus globulus Labill.

Abstract

The design of engineering high value-added products and timber structures analysis requires reliable elastic characteristics related to a theoretical model that describes the elastic behavior of wood material. The present research focuses on determining the elastic constants of Eucalyptus globulus Labill., which allow their implementation as input parameters in any numerical model. The great potential of this species for novel structural applications was considered due to its superior mechanical properties. Two different testing methods were applied to the same specimens to directly compare the results. These two tests were conventional mechanical compression and a non-destructive ultrasound procedure. In addition, two different strain measurement techniques were contrasted in the performance of the mechanical tests, namely the conventional strain gauges that give local measurements, and the 3-D fullfield optical system based on the principles of digital image correlation. The elastic values obtained via ultrasound are higher than those coming from mechanical testing using conventional gauges. Conventional gauges lead to underestimated values in comparison to the results from full-field strain measurements. Eucalyptus globulus shows greater longitudinal and transversal stiffness than the average values for other hardwoods, which verifies the good structural possibilities of this species.

Mechanical Properties of Small Clear Specimens of Eucalyptus globulus Labill

“…Strain gauges were located on the specimens' faces to measure strains and derive the modulus of elasticity for each direction (see Figure 1c). Further details on the compression setup can be found in a previous work by the authors [16] which had the objective of determining the orthotropic elastic constants of eucalyptus.…”

“…Previous research by the authors in small clear specimens of E. globulus L. reported the twelve elastic constants of orthotropy obtained from compression testing (longitudinal elastic moduli, shear moduli, and Poisson coefficients) [16] and fracture parameters [17][18][19]. However, to our knowledge there are no studies on this species reporting complementary information necessary for the development of numerical finite element models, such as strength to different stresses and directions or friction coefficients.…”

Measuring the Cohesive Law in Mode I Loading of Eucalyptus globulus

“…The orthotropic average values for the radial modulus of elasticity E R = 1820 MPa, the tangential modulus of elasticity E T = 821 MPa, the shear modulus of elasticity in the LR plane G LR = 1926 MPa, and the shear modulus of elasticity in the LT plane G LT = 969 MPa, are taken from [24] using Galician Eucalyptus globulus with a similar density to the boards used in this study. These parameters were obtained by compression tests coupled with a stereovision system (DIC 3D).…”

Rheological behavior of wood in stress relaxation under compression

“…The AVX measurements meet the accuracy requirements for ASTM E83 Class B1 and ISO 9513 Class 0.5 calibration standards (MTS ® 2017). The advantages of measuring strain with digital method compared to a conventional method based on a comparative analysis of elastic constants determined with different methods were discussed in Crespo et al (2017). In the experimental analyses at hand, 3 virtual strain gauges were placed in horizontal and 3 in vertical direction on the front surface of each tested specimen.…”