Análise de influências da inclusão de descontinuidades em corpos de prova para o ensaio de tração paralela às fibras

Abstract

Wood is a natural composite material which, due to its complex anatomical composition, is generally modeled as an orthotropic material, exhibiting distinct properties depending on the direction of analysis. Among the various mechanical properties of interest, the behavior of wood under tensile loading is particularly relevant. In this condition, wood presents an elasto-brittle response, characterized by the absence of significant plastic deformations prior to failure. The tensile failure process may occur through different modes, which introduces substantial uncertainties in determining the tensile strength parallel to the grain. This difficulty arises because the irregularity and randomness of the failure plane make the concept of average normal stress less representative for accurately estimating the actual strength values. In this context, the main objective of this research was to evaluate the influence of introducing lateral notches into standardized specimens, aiming to induce preferential failure planes in the central region. Four species of hardwoods from tropical forests were studied (Erisma uncinatum, Goupia glabra, Hymenolobium petraeum e Bagassa guianensis), thereby encompassing distinct anatomical and mechanical features. Notches were introduced in different orientations: aligned (0°) and inclined (30° and 45°). This approach sought to verify how the presence of such discontinuities would affect the failure modes observed during tensile tests parallel to the grain, as well as the magnitude and variability of the measured tensile strength values. The investigation combined experimental tests with numerical analyses based on the finite element method, allowing for a more comprehensive assessment of specimen behavior. The results demonstrated that the use of aligned notches in the standardized Brazilian specimen configuration led to a significant reduction in result dispersion, by consistently inducing fracture in the central region of the tested samples. In this case, an average reduction of 0.893 in tensile strength was observed compared to unnotched specimens. However, this decrease was accompanied by a reduction in variability and uncertainty associated with the estimation of tensile strength parallel to the grain, thus providing more consistent and representative results regarding the actual behavior of the material. Therefore, it can be concluded that the introduction of aligned notches represents an effective strategy to improve the reliability of tensile strength measurements in wood, contributing to methodological advances in the mechanical characterization of this natural and heterogeneous material.