In the industries today, metal components are increasingly being produced by powder
metallurgy (PM) method. The PM method is highly efficient in cost of production and
materials usage. However, PM components suffer from inhomogeneous density
variation and are more likely to have internal cracks. These deficiencies usually make
PM components prone to sudden fracture failure. A parameter that is known to define
the rate at which cracks grow in a material is fracture toughness. Unfortunately, the
fracture toughness of most metal powder compacts have not been determined due to
lack of suitable test technique. This study developed a notching device that has the
capability to provide uniform notches on the surfaces of powder compacts. The
effectiveness of the notching device enhanced the determination of mode I fracture
toughness (KIC) of two metal powder compacts; iron and copper. A method known as
the modified diametrical compression test technique (MDCTT) was also developed to
measure the mode II fracture toughness (KIIC) of the powder compacts. Finally, the
study examined the influence of density on the rate of crack propagation in the
compacts and developed mathematical relation that predicts fracture toughness from
the relative density of either the iron or copper powder compacts. Notched samples of
two types of metal powder; Hoaganas ASC100.29 iron powder and pure copper powder
were prepared by uniaxial compaction in a rigid die using universal testing machine.
The relative density of the powder compacts was determined as a fraction of the
density of the compact to their corresponding solid metal before the diametrical
compression test was carried out for each sample. The behavior of the cracks around
the tip of the notch was examined using scanning electron microscope (SEM). A new
equation was developed to calculate the values of KIIC from the MDCTT. The results of
KIC for the iron powder compacts showed close agreement with values mentioned in
the literature. The KIC values for copper powder compacts range from 0.32 to 0.58
MPa.m0.5 while the KIIC for the iron and copper powder compacts ranged from 0.30 to
0.57 MPa.m0.5 and 0.28 to 0.59 MPa.m0.5 respectively. The ratio KIIC/KIC for the iron
and copper powder compacts from this study showed good agreement with the
predicted values of 0.87 and 1.04 based on the maximum tangential stress (MTS) and
the minimum strain energy density (SED) criteria respectively. The agreement implies that the developed MDCTT is reliable and can be used to measure the KIIC of other
metal powder compacts. Furthermore, the results also show that the rate of crack
extension reduced as the density of the powder compacts increases. A generalized
mathematical expression that relates fracture toughness and relative density has been
successfully developed. This relationship will be beneficial for further analysis of crack
propagation within metal powder compact
