**3. Experimental results and discussion**

#### **3.1. Wear tests of bamboo specimens**

**Figure 3** illustrates the wear volume of the three types of bamboo specimens versus the normal load at 0.42 and 0.84 m s−1. It can be seen from **Figure 3** that the wear volume was dependent upon the normal load, the sliding velocity, and the relative orientation of bamboo fibers with respect to the friction surface. The wear volume and its difference between different types of specimens increased with the increase of normal load. The wear rate at 0.42 m s−1 velocity was lower than that at 0.84 m s−1. The N-type specimens presented excellent wear resistance. Although they had the same relative orientation of friction surface, PS -type specimens presented better wear resistance than P<sup>I</sup> -type specimens under identical experimental conditions, suggesting that the wear resistance of the outside layer of bamboo stem was higher than that of its inner layer.
