Assessing the density and mechanical properties of ancient timber members based on the active infrared thermography

Abstract

The objective of this study was to assess the density and mechanical properties of ancient timber members based on the active infrared thermography (IRT). Based on the unsteady heat transfer theory, the cooling constant (Ve) was proposed and the relationship between Ve and density as well as the mechanical properties of timber was analyzed. The cooling tests were conducted on 50 small clear specimens of ancient timber members to obtain the Ve and the cooling law of specimens. In addition, the effect of heating on the dynamic modulus of elasticity (Eus) and color of ancient timber members was investigated. At the same time, static mechanical tests and density measurement test were carried out to analyze the relationship between Ve and density as well as mechanical properties. The results indicated that there was unobservable influence on Eus and color parameters (L*, a* and b*) of specimens with its heating process in evaluation of the density and mechanical properties based on active IRT. Meanwhile, the initial excess temperature θ0 and initial temperature T0 had no influence on the cooling constant Ve as well as the relationship between τ and θ in the cooling process of specimens. Moreover, Ve had a strong negative correlation with density, modulus of elasticity (MOE), modulus of rigidity (MOR) and compressive strength parallel to grain (CSPG) of specimens (R2 = 0.9768, 0.8493, 0.8714 and 0.8865). In addition, the validation test result show that there is satisfactory predictive ability for density, MOE, MOR and CSPG of ancient timber members based on the prediction models established.