Methods to estimate the length effect on tensile strength parallel to the grain in Japanese larch

Abstract

To find a desirable method for estimating the length effect on tensile strength (σt), we used three methods to analyze the σt, data from a Japanese larch (Larix kaempferi) small, clear specimen. These methods included a nonparametric method, the projection method of Hayashi, and a proposed method. The estimated length effect parameters (g) by the nonparametric method were 0.0237 and 0.0626 for 50th and 5th percentile σt, distributions, respectively. The projection method requires a standard Ef level (E*: dynamic Young's modulus), arbitrarily chosen for calculating the g value. The g values from the projection method were 0.1122 for low E*, 0.0898 for average E*, and 0.0759 for high E*. The estimated g values by the proposed method using selected σt, data were 0.1020 and 0.1838 for the 50th and 5th percentiles, respectively. Among the three methods, the nonparametric method did not consider the different distribution of Young's modulus among specimens, and the estimated length effect parameters (g) by this method were small. The projection method reduced the influence of Young's modulus, but the length effect parameters varied with the E* level. The proposed method minimized the dependence on Ef distributions among specimens. We believe the latter method is desirable for estimating the length effect on tensile strength.