This paper demonstrates that the crack‑growth rate under non‑proportional loading can be effectively characterized using a relatively simple stress indicator, the synthetic stress amplitude. The experimental results are presented in a clear and concise manner, giving the impression that the authors have organized their findings very effectively.
The study also proposes a practical method for predicting crack‑growth life that does not require the use of digital image correlation, which is often labor‑intensive. By estimating the effective synthetic stress range solely from non‑proportional loading conditions and predicting crack‑growth life using the proposed formula, the method appears feasible for engineers to apply in practice. It is also commendable that the evaluation metrics and predictive expressions are formulated to minimize the use of material‑specific parameters.
If engineers were to use the prediction method proposed in this paper, it would likely be in maintenance operations. For example, during routine inspections, a crack may be found in equipment that is otherwise operating normally. In such cases, the equipment is subjected to highly complex loads during operation, and engineers must determine whether the crack will continue to grow and, if so, when repairs should be scheduled.
On the other hand, in design and development work, strength design is generally not performed based on crack‑growth life, so the proposed method may not be directly necessary for that context.