INFLUENCE OF FATIGUE ON BENDING OF Pinus caribaea WOOD

André L Christoforo,Tulio H Panzera,Diego H De Almeida,Francisco A R Lahr,Thaina Q Barbosa

doi:10.1590/1809-4430-eng.agric.v40n2p238-242/2020

Abstract

ABSTRACT This research aimed to evaluate the effect of the number of fatigue cycles (NC, 0 – reference, 450, 4500, 45000, and 90000) for frequencies (Fr) of oscillation equal to 0.5 and 1.0 Hz on the modulus of elasticity (Em) and operating stress (σm) in the static bending of Pinus caribaea wood. Em and σm were determined taking into account three specimens (SPEC) manufactured for reference condition and another three for each of the four NC levels and each Fr level, resulting in 27 SPEC. Sixty experimental determinations were obtained, being the approximate total time of sample exposure to fatigue of 350 hours. The same specimens used to determine Em and σm for the reference condition were also used (via non-destructive tests) to obtain these properties for all fatigue cycles. The frequency and number of cycles significantly influenced both investigated properties. Reductions in Em and σm values were observed after 45000 cycles. The progressive increase in the number of fatigue cycles caused more marked reductions in mechanical properties when compared to the increase in the frequency of oscillation.

Highlights

Wood is a material widely used in the manufacture of building components, such as partition panels, doors, frames, wainscoting, ceilings, and floors
To collaborate with useful information for the project of wooden structures in Brazil, which can be incorporated together with the results of correlated national surveys in new versions of the Brazilian standard ABNT NBR 7190, this study aimed to evaluate the effect of the number of fatigue cycles (0 – reference, 450, 4500, 45000, and 90000) for frequencies of oscillation equal to 0.5 and 1.0 Hz on the mechanical properties modulus of elasticity and operating stress in the static bending of Pinus caribaea wood
Woods of Pinus caribaea were properly stored at the facilities of the Laboratory of Woods and Wood Structures (LaMEM) of the São Carlos Engineering School (EESC) of the University of São Paulo (USP), with a moisture content close to 12%, which consists of the equilibrium moisture established by the Brazilian standard ABNT NBR 7190 (1997)

Summary

Introduction

Wood is a material widely used in the manufacture of building components, such as partition panels, doors, frames, wainscoting, ceilings, and floors. Such employment has been growing despite some well-known prejudices inherent to wood, especially related to the insufficient dissemination of technological information already available about its properties under different operating conditions, and due to the almost systematic lack of specific projects developed by qualified professionals (Nogueira et al, 2018). In Brazil, the project of wooden structures, as well as the methods and premises for obtaining physical and mechanical properties, are regulated by the Brazilian standard ABNT NBR 7190 (1997), named as “Project of Wooden Structures.”. For dynamic and/or cyclical stresses, such as structures of bridges, silos, and others, in which the effect of mechanical fatigue is appreciable, the Brazilian standard does not present information regarding the variation of strength and stiffness properties of the wood due to fatigue cycles, which motivates the development of research on this subject

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Conclusion