PSI - Issue 28

Yifan Li et al. / Procedia Structural Integrity 28 (2020) 1148–1159 Author name / Structural Integrity Procedia 00 (2019) 000–000

1153

6

3.3. Fatigue test of single struts A servo-hydraulic testing machine (Instron 8872) with a 1 kN maximum load capacity sensor was used for the single strut fatigue tests. The frequency of fatigue loading was 10 Hz, and the load ratio R was equal to 0.1. All experiments were force controlled and performed at room temperature. The F ar -N curve was constructed by testing at least two struts at each load amplitude. Each single strut with five knots (i.e. strut joints) was cut from lattice specimen and glued between small aluminium plates to be clamped by test machine grips, as shown in Fig. 6. All of the single strut specimens broke between the connective point near the knots, indicating that the clamping method did not influence the measured strut fatigue life.

Fig. 6. Extraction of a single strut specimen from a 2D aluminum triangular lattice plate for fatigue testing.

From the fatigue tests, the relationship between fatigue life and the force amplitude was obtained; Fig. 7 shows the fitted curve. The fatigue life of single strut shows variations because of non-homogeneity in material properties, variations in the surface roughness and inconstant strut width, etc. The relationship between equivalent force amplitude and cycles can be expressed as: �� � �� ������ � ��� � � �������� (6)

Test results Fit line of test data

2.37

2.34

2.22 Load amplitude (log F ar ) 2.25 2.28 2.31

2.19

4.0

4.4

4.8

5.2

5.6

6.0

Number of cycles (log 2N)

Fig. 7. Fatigue lives at a range of load amplitudes for single struts of aluminium alloy 1050A taken from a water jet cut 2D triangular lattice.