Fig.1 is the previous ex.riment, in addition to the small friction coefficient, the stability is good, Figure 2 uses the same material and the same experimental parameters, but increases the cold pressure. The purpose is to reduce the porosity of the material and increase the hardness. The hardness is increased by 10 HB. However, the noise is too large during the friction experiment, and the friction coefficient jitter is too obvious. After that, the experimental speed and time are reduced, and the experiment is barely completed. But why is the friction coefficient so sparse and fluctuates so violently ?