1633
journal of materials research and technology 2021;14:1630 e 1643
2.3.
Finite element modeling
To evaluate the results of the equivalent rigidity method, the specimens were modeled in the Ansys software [41], exploring the effects of each layer of the panel and the non-linearity of the material. Due to the panel ' s geometric characteristics (Fig. 3), the 3D SHELL181 element is formed by four nodes and suitable for modeling shell structures from thin to moderately thick having three degrees of translation and three degrees of rotation in each node, was used. Concerning the thickness of the panel, the option of multi-layer in the SHELL181 element enables considering the different properties for each layer of the composite. The modeling with multi-layer elements requires the assignment of the corresponding thickness and the mechan- ical properties for each of the oriented layers. For OSB panels formed by the three layers of strands through the thickness, two types of materials must be established to represent the properties due to the directions of the layers relative to the length of the specimens (direction X). For the SL specimen (Fig. 4(a)), representing the bending behavior of the panel ac- cording to the longitudinal direction, Material 1 was assigned to both outer layers and, Material 2 to the core layer. In the case of ST specimen modeling (Fig. 4(b)), Materials 1 and 2 must be applied to the core and both outer layers, respectively.
Fig. 2 e Test arrangements of specimens extracted from the OSB panels: (a) three-point static bending; (b) tension.
8,254,507.1 N mm 2 was obtained and the coefficient of varia- tion was 9.2%. The geometry of a specimen is properly of a wide-beam with the length of span ( Ls ) and cross-section defined by the width ( b ) and thickness ( h ). For each group of specimens (longitudinal and transverse), the specimen with the flexural rigidity ( I E ) closest to the average group value was chosen, and its measured dimensions were taken for modeling. For the longitudinal direction, the SL specimen with I E L - ¼ 34,193,390.0 N mm 2 , with its dimensions b ¼ 47.9 mm, h ¼ 10.8mmand Ls ¼ 220 mm, was used for analysis. For the transverse direction, the ST specimen was used its measured dimensions being 49.4 10.4 220mmand I E T equal to 8,291,020.8 N mm 2 . Based on these flexural rigidity values and the moment of inertia ( I ¼ b h 3 /12 mm 4 ), the moduli of elasticity were calculated, the results being E L ¼ 6812.3 MPa and E T ¼ 1796.8 MPa, for the longitudinal and transverse di- rections, respectively. The Poisson ' s ratios were determined based on the results of tension tests (Fig. 2(b)), with 10 specimens for each group (SP and ST) and standardized procedures [21]. These tests were performed on a universal testing machine (Emic, Brazil), with the load applied at a constant crosshead speed of the machine of 4 mm/min. The strain in the longitudinal and transverse directions was obtained with strain gages (Kyoa, KFG-20-120-C1-11, Japan), making it possible to calculate the mean value of Poisson ' s ratio for the longitudinal group ( n L ¼ 0.31) and the transverse group ( n T ¼ 0.13). In a study of OSB produced with strands of pine wood and phenol-formaldehyde resin, with the strands of the outer layers randomly distributed and the inner layer oriented along the length of the panel [43], was obtained, in tension, Poisson ' s ratios equal to 0.24 and 0.17, for the longitudinal and trans- verse directions of the panel, respectively. In the literature of the OSB panels, many other values can be found with varia- tions for the major and minor Poisson ' s ratios, such as the values: 0.36 and 0.13 [44], or 0.30 and 0.11 [45]. The authors state that the Poisson ' s ratios of wood vary greatly due to the great variety of this material. In addition, other factors must also be considered, such as the type of adhesive and the orientation of the strands.
2.4.
Constitutive models for OSB
To implement the stress versus strain model, the elastic property of the material defining the elastic-linear segment must first be known, which in turn is represented by moduli of elasticity equal to 6812.3 and 1796.8 MPa, for the longitudinal and transverse directions, respectively. Subsequently, to represent the behavior of non-linearity of the material, the yield point must be defined. Based on the results of the bending tests with SL and ST specimens (Fig. 5), it was found that this point can be fixed at 60% of the maximum bending load. As shown in other studies, for the non-linear model, the yield point was indicated at a rate of approximately 60% of the ultimate compression stress [44]. The elastic e plastic relationship was proposed by segments in a multi-linear model for the range of 60 e 100% of the ultimate stress in compression ( f cu ), from which and to, a suggested
Fig. 3 e Mesh discretized by SHELL181 elements, with the representation of the supports at the ends of the span and the load application on key points positioned in the middle of the span of the specimen.
Made with FlippingBook - Online magazine maker