Crack Propagation and Fracture Process Zone (FPZ) of Wood in the Longitudinal Direction Determined Using Digital Image Correlation (DIC) Technique

Ying Yu,Xiaohong Wang,Wen Liu,Weihang Zeng,He Zhang

doi:10.3390/rs11131562

Ying Yu, Xiaohong Wang + Show 3 more

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https://doi.org/10.3390/rs11131562

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Abstract

As a state-of-the-art method, the digital image correlation (DIC) technique is used to capture the fracture properties of wood along the longitudinal direction, such as the crack propagation, the strain field, and the fracture process zone (FPZ). Single-edge notched (SEN) specimens made of Douglas fir (Pseudotsuga menziesii) from Canada with different notch-to-depth ratios are tested by three-point-bending (3-p-b) experiment. The crack mouth opening displacements (CMOD) measured by the clip gauge and DIC technique agree well with each other, verifying the applicability of the DIC technique. Then, the quasi-brittle fracture process of wood is analyzed by combing the load-CMOD curve and the strain field in front of the preformed crack. Additionally, the equivalent elastic crack length is calculated using the linear superposition hypothesis. The comparison between the FPZ evolution and the equivalent elastic crack shows that specimens with higher notch-to-depth ratios have better cohesive effect and higher cracking resistance.

Highlights

As a green and natural engineering material, wood has been widely used in construction
Some inherent defects in wood produce stress concentrations and cause failure cracks in the material when it is under tension and bending
It is recognized that mode I fracture along the L direction is the most important failure mode in wood structures [3]

Summary

Introduction

As a green and natural engineering material, wood has been widely used in construction. Some inherent defects in wood produce stress concentrations and cause failure cracks in the material when it is under tension and bending. The fracture process zone (FPZ) is defined as the region ahead of the traction free crack tip [4]. This region contains lots of distribute microcracks, in which the mechanical behavior, such as stress transformation, are quite complicate. As a kind of quasi-brittle material, wood has FPZ in front of the crack tip [5]. FPZ is used in the analysis of boundary effect mode [8] and can be combined with the critical crack length to reveal the properties of the fracture [9]. The identification of FPZ evolution is essential to explain wood fracture [10,11]

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