Comprehensive review of the elastic constants of bamboo

Bamboo, which is a crucial industrial material, is characterized by its fast growth, excellent properties, and high transportation efficiency. Bamboo has many advantages as an engineering material; however, many obstacles hinder its practical application. One major obstacle is the lack of understanding regarding its elastic constants, including its elastic modulus, Poisson’s ratio, and shear modulus. Multiple parameters may be required to describe the stress–strain relationship of an anisotropic material. Bamboo is an anisotropic material, and its culm has a hollow structure; therefore, bamboo has many elastic constants that are difficult to measure. Accordingly, this review has three objectives: (1) to examine existing approaches for measuring the elastic constants of bamboo and the difficulties involved in these approaches, (2) to review existing results on the elastic constants of bamboo, and (3) to identify the factors affecting the elastic constants of bamboo. According to this review, several elastic constants of bamboo, especially those in the radial and transverse directions, are currently unknown. However, the vascular bundles in bamboo mostly have a unidirectional arrangement similar to that observed in transverse isotropic materials and consist of high-stiffness vascular bundle sheaths and isotropic ground tissue. Thus, approaches used for measuring the elastic constants of unidirectional fiber-reinforced polymers can be used to measure those of bamboo. This review indicates the direction of research with respect to the elastic constants of bamboo and consolidates existing results on these constants, which can be used as a reference in the industrial application of bamboo.