PSI - Issue 83

Sze Pei Tan et al. / Procedia Structural Integrity 83 (2026) 28–40

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4.3. Fatigue crack propagation testing The results from fatigue crack propagation testing are presented and discussed in this subsection. The results include the fatigue crack growth rate ( da/dN ) versus the range stress intensity factors range ( Δ K ) and Paris’ constant ( C and n ) based on the Paris’ law. Furthermore, the fracture surface is also observed under optical microscope to identify the fractography. The fatigue crack propagation can be divided into three main regions, which are initiation region, propagation region or also known as Paris’ region and finally the fracture region. In this study, the focus is to obtain the da/dN following the Paris’ law. Following the Fig. 8 and Eq. (3), the material constant can be obtained in the second region by evaluating the slope ( n ) and the interception ( C ). In this study, the material constant is used as one of the material input parameters to compute the fatigue crack growth using S-version FEM.

Fig. 8. Fatigue crack growth stages

The relationship as suggested by[30] can be expressed by a mathematical relationship in Eq.(3).

(3) where the da is the crack propagation while dN is the crack life corresponding to the crack changes while the C and n are both representing material constant. Finally, during stage III the crack propagation is unstable while the SIF is approaching the . Hence, the component is expecting total failure upon this final stage. In this present study, the Paris’ model is used for predicting the fatigue crack growth in Part II of this research. Fig. 9 is presenting the fatigue crack growth rate result produced by DMLS using the AlSi10Mg material (as built) corresponding to the Paris’ region. The graph is plotted in logarithmic scales due to the number of cycles varying from hundred thousand to million for one millimeter of crack length. The scattered data is due to the automated method from the COD and the load transducer that is used by the Instron 100 kN. The crack growth rate can be determined by using the manual method which is visual measurement. However, the process needs the user to remove the specimen and measure it under the microscope before re-installing it back to the testing machine. From the fatigue crack propagation results, the evaluation for the value of C is 1.85 x 10 -9 while the n is 3.69. The tensile and fatigue life results when consider together, a clear relationship between monotonic strength and cyclic performance can be monitored. The heat-treated specimen sample showed higher ultimate tensile strength and