provide a summary and critical review highlighting its main contributions and challenges (based on the authors’ description and/or your own judgment).

Critical Review

For the article please provide a summary and critical review highlighting its main contributions and challenges (based on the authors’ description and/or your own judgment). The review of each article should be completed in one or two pages and may include a figure, plot, equation, etc. from the article if it assists general understanding. The figure or plot Should NOT encompass the entire review.

Topic is about, Meso/Lab Scale (>1mm and <1m) Composite (material).

Paper Title: Include the title of the paper before the review

Paper Summary: Summarize the key concepts of the paper. Be Concise!

Observations, Discussion, & Critical Review: Give examples of the observations found in the paper and discuss these results. Keep in mind the details of the experimental method and try to think critically about the conclusions drawn by the authors. Discuss why they make sense or not and give examples of how the work could be continued.

Paper: Include a copy of all the papers attached at the end of the review


Review Example

Crystallographic analysis for fatigue small crack growth behaviors of nickel-based single crystal by in situ SEM observation [1]

As discussed previously, significant research has been conducted into the damage tolerance for design or remaining life prediction. The models have expressed the need for modeling appropriate microscale features to accurately predict the fatigue life. This paper examines, in a Scanning Electron Microscope (SEM), the propagation of a fatigue crack in a nickel base superalloy.

Summary: A nickel based superalloy single crystal was used to create a notched dog-bone specimen. The specimen was cut so that the notch would have two different crystal orientations for comparison during observation in the SEM. The load was applied in a sinusoidal manner with a maximum stress of 500MPa, frequency of 10Hz, various temperatures, and a stress ratio of 0.3 or 0.1 depending on the particular specimen. Specimen 1-3 tested at room temperature, and specimen 1-5 tested at 300°C showed a different fatigue growth pattern than specimens 1-6 and 3-2 both tested at 600°C. Table 2 summarizes the experiment parameters. A sample of the crack growth paths can be found in Figs. 14 and 15. When loading at higher temperatures there is a shift from non-crystallographic to crystallographic crack growth. Specimens 1-3, 1-5, and 1-6 are oriented in the same direction with regard to the loading direction while specimen 3-2 is oriented differently. Trends between the crack growth rate and the equivalent stress intensity factor support the different crack propagation mode that appears when tested at 600°. Furthermore, the critical resolved shear stress values on all possible slip planes were calculated with cracks growing along 4 possible directions for both crack propagation modes. The results show highest stress on the slip plane that is visually seen inside the SEM for the higher temperature specimens. Finally, the crack surfaces were examined post mortem for all the specimens where some show a step structure indicative of failure along slip planes that is not seen in the specimens tested at room temperature or 300°C.

Figure 1 Fatigue crack growth behaviors for specimen 1-5 at 300°C [6]

Figure 2 Fatigue crack growth behavior for specimen 1-6 at 600°C [1]

Observation, Discussion & Critical Review: The crack initiates on a slip plane oriented at 45° for specimens 1-3 and 1-5; however, beyond that there seems to be no dependence on the direction of the slip systems. Specimens 1-6 and 3-2 initiate from the dominant slip plane and continue to grow on along slip planes. Specimen 1-6 is found to have high critically resolved shear stresses on multiple planes and the crack is observed to grow along the dominant one while occasionally switching to a secondary slip plane before returning to the original resulting in a “zigzag” type crack. Specimen 3-2, which has a different orientation, has one clear dominant slip plane and the crack propagates along it with no deviation. Specimen 3-2 has a different orientation that specimen 1-6, yet they have a similar crack propagation whereas specimens 1-3 and 1-5 have the same orientation, but a lower temperature and a different method of propagation. This suggests that the temperature has a direct effect on the crack propagation than the crystal orientation. This work verifies that different crack propagation modes exist for specimens at higher temperatures than for specimens at lower temperatures. The result being that the Paris Law cannot sufficiently characterize small cracks under non-crystallographic propagation since it does not take into account the effect of the micro-mechanisms such as slip. The SEM observations match the predicted slip plane for specimens tested at 600°C. The corresponding maximum resolved shear stress intensity parameter is used to characterize small crack propagation in crystallographic crack growth more reliable then possible using the Paris Law.


[1] Y. Zhang, H.-J. Shi, J. Gu, C. Li, K. Kadau, and O. Luesebrink, “Crystallographic analysis for fatigue small crack growth behaviors of a nickel-based single crystal by in situ SEM observation,” Theoretical and Applied Fracture Mechanics, vol. 69, pp. 80-89, 2014.