A positive value of the vertical load
denotes the compression force on the packed powder bed, and a
negative value denotes the powder weight subjected to the rotor
blade during the lifting process. If powder sticks to the blade,
the value of the negative load increases. The hysteresis area was
calculated and defined as the cohesive property value of the
powder samples. It was calculated by integrating the wave data
from 13 mm to 63 mm, as shown in Fig. 4(b).