PSI - Issue 13

O.H. Ezeh et al. / Procedia Structural Integrity 13 (2018) 728–734 Author name / Structural Integrity Procedia 00 (2018) 000–000

733

6

4. Conclusions Not only by generating new experimental results, but also by considering a large number of data that are available in the technical literature, the present paper investigates the effect of raster direction and non-zero mean stresses on the overall fatigue strength of AM PLA. According to the re-analyses being discussed in the previous sections, it is possible to come to the two key conclusions reported below.  In terms of engineering design against fatigue, the effect of raster direction can be neglected without much loss of accuracy. Therefore, 3D-printed PLA manufactured by setting the in-fill level equal to 100% can be modelled as a homogenous and isotropic material, with this resulting in a great simplification of the fatigue assessment problem.  The effect of non-zero mean stresses on the overall fatigue strength of 3D-printed PLA can be modelled effectively by simply using the maximum stress in the cycle,  max .

Plain Specimens -  f =45 

Plain Specimens -  f =45 

10 11 12

10 12 14 16 18 20

R=-1

+2S D

R=-0.5

 A [MPa]

 MAX [MPa]

0 1 2 3 4 5 6 7 8 9

 MAX =12.7 MPa

R=0

Goodman's Straight Line Eq. (1)

R=0.3

-2S D

0 2 4 6 8

 UTS =42.9 MPa

N Ref =2  10

6 Cycles to Failure

N Ref =2  10

6 Cycles to Failure

0

10

20

30

40

50

-1

-0.5

0

0.5

1

R=  min /  max

 m [MPa]

(a)

(b)

Plain Specimens -  f =45 

100

Run Out

P S =10%

 max [MPa]

P S =90%

P S =50%

k=6.9

10

R=-1 R=-0.5 R=0 R=0.3

 MAX, 50% =11.1 MPa T  =1.604

N Ref =2  10 6

1

100

1000

10000

100000

1000000 10000000

N f [Cycles to Failure]

(c) Fig. 5. Amplitude of the endurance limit,  A , vs. the corresponding mean stress,  M (a); relationship between endurance limit determined in terms of maximum stress,  MAX , and load ratio, R, obtained by post-processing the results summarized in Figure 4 (b); fatigue scatter band in terms of  max determined by re-analyzing together the data we generated under R=-1, -0.5, 0, and 0.3 (c). References

Afrose F., Masood, S.H., Iovenitti P., Nikzad, M., Sbarski, I., 2016. Effects of part build orientations on fatigue behaviour of FDM-processed PLA material. Prog. Addit. Manuf. 1, 21-28.