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A quasi-continuum (QC) method based on the embedded atom method (EAM) potential was employed to investigate the fatigue crack growth and expansion characteristics of single-crystal Fe and Ni under cyclic loading modes I and II. In particular, the crack growth and expansion characteristics of Fe and Ni under cyclic loading were evaluated in terms of atomic stress fields and force–distance curves. The simulation results indicated that under cyclic loading, the initially damaged area of the crack will coalesce again after compression or shear to the initial geometry leading to a strengthening of the material. If no coalescence appears, the crack spreads rapidly and the material breaks. Moreover, under the cyclic loading of shear at any orientation, the slip dislocation observed in the materials considerably affects the release of stress.

Rationale: Greenstick fractures most commonly occur in the pediatric population, especially in those under 10 years of age. Greenstick fractures are “extremely” rare in adults. This report presents the case of a greenstick fracture of the ulnar shaft in an adult following physical therapy for a radial neck fracture and ulnar shaft fracture post-internal fixation. Greenstick fracture can occur during physical therapy near the drill holes created during surgery. Patient concerns: A 23-year-old man without any past medical history had sustained a greenstick fracture of the ulnar shaft after rehabilitation for a left radial and ulnar fracture that had been previously treated with internal fixation. Diagnoses: Five months after removal of the implants, the patient complained of left elbow tenderness and a “breaking” sound that occurred during physical therapy. The results of a subsequent X-ray revealed a greenstick fracture of the left ulnar shaft. Interventions: Splinting of the fracture. Outcomes: After 2 months of splint fixation, the pain and range of motion in the affected arm were improved, and sequential X-rays showed callus formation and increased density of the ulnar shaft. Lessons: Greenstick fractures occur not only in children but also in adults in specific circumstances. The cortex of long bones may be further weakened by drill holes created during surgery, and fractures may occur during physical therapy. During treatment, physicians, and therapists should pay more attention to the patient who has undergone implant removal to avoid greenstick fractures, especially in the locations near drill holes.