Study on compressive stress relaxation behavior of beech based on the finite element method

Wen Gang Hu,Hui Yuan Guan

doi:10.4067/s0718-221x2019005000102

Abstract

The compressive stress relaxation behaviors in three directions of beech (Fagus orientalis) were studied by experiments, and predicted by mechanical model and finite element method. Firstly, short-term (3 hours) compressive stress relaxation experiments were carried out in longitudinal (L), radical (R) and tangential (T) directions of beech, and then the experimental data was fitted by mechanical model with two single Maxwell bodies in parallel connection. Secondly, the method of predicting the long-term (12 hours) stress relaxation behaviors of beech based on the finite element method was studied using the experimental data of short-term stress relaxation. Finally, the long-term stress relaxation behaviors in three directions of beech were investigated by experiments, mechanical model and finite element method respectively, and the results of them were compared. The results showed that stress relaxation behaviors of beech were different in three directions, and the short-term stress relaxation in L was much smaller than those in R and T directions under the same load. Besides, the mechanical model with two single Maxwell bodies in parallel connection was able to be predict the short-term relaxation behaviors of beech in three directions with correlation coefficients beyond 0.99, but it did not work in long-term relaxation. In addition, the errors of FEM were smaller than those of the mechanical model compared with the results of experiments in the long-term stress relaxation, and the errors of the FEM were approximately 8% in L and 20% in R and T directions, which were all accepted in the field of wood engineer. This study will contributes to predict the long-term relaxation behaviors of wood products and wooden structures based on the FEM. Keywords: Fagus orientalis, Maxwell model, mechanical properties, modulus of elasticity, wood structures

Highlights

Wood is a natural biomass material, which has complex physical and mechanical properties, including the elasticity of solid and of viscosity of fluid, so it is called viscoelastic material
The viscoelasticity of wood plays an important role in durability of solid wood structures and wood products, which leads to decrease the strength of wood beam and wood joints (Figueroa et al 2012, Daniela et al 2013)
They were fitted with mechanical model with two single Maxwell bodies in parallel connection by Origin software, and the correlation coefficients were all beyond 0,99

Summary

Introduction

Wood is a natural biomass material, which has complex physical and mechanical properties, including the elasticity of solid and of viscosity of fluid, so it is called viscoelastic material. Creep and stress relaxation are two main parts of viscoelasticity, there is relation between them. The stress relaxation can be regarded as creep in different stress levels (Zhou et al 2001). There are many factors influencing the viscoelasticity of wood, such as temperature (Peng et al 2017a), humidity (Jiang et al 2017) and stress levels (Peng et al 2017b, Zhang et al 2017). It is difficult to evaluate long-term viscoelastic behavior of wood for it is time consuming. Many researchers have been studying how to predict the long-term creep and stress relaxation of wood by Maderas.

Objectives

Methods

Results

Conclusion