Abstract
The low cycle fatigue strength properties of the additively manufactured Ti-6Al-4V alloy are experimentally investigated under proportional and nonproportional multiaxial loading. The fatigue tests were conducted using hollow cylinder specimens with and without heat treatments, at room temperature in air. Two fatigue tests were conducted: one for proportional loading and one for nonproportional loading. The proportional loading was represented by a push-pull strain path (PP) and the nonproportional loading by a circle strain path (CI). The failure lives of the additively manufactured specimens were clearly reduced drastically by internal voids and defects. However, the sizes of the defects were measured, and the defects were found not to cause a reduction in fatigue strength above a critical size. The fracture surface was observed using scanning electron microscopy to investigate the fracture mechanisms of the additively manufactured specimens under the two types of strain paths. Different fracture patterns were recognized for each strain paths; however, both showed retention of the crack propagation, despite the presence of numerous defects, probably because of the interaction of the defects. The crack propagation properties of the materials with numerous defects under nonproportional multiaxial loading were clarified to increase the reliability of the additively manufactured components.
Highlights
Additive manufacturing (AM) has enabled the fabrication of complex geometrical parts, reducing weight and shortening the processing time as a result of the creation of subsequent thin cross-sections of a component
Few tension torsion fatigue tests have been conducted under nonproportional multiaxial conditions that have focused on internal defects on the failure lives of AM materials
The total strain amplitudes and the failure lives are presented. It is clear from the results of the pull strain path (PP) NHT that a defect-size range of three times leads to scatter in the failure lives of the factor of three
Summary
Additive manufacturing (AM) has enabled the fabrication of complex geometrical parts, reducing weight and shortening the processing time as a result of the creation of subsequent thin cross-sections of a component. Molaei et al [22] performed uniaxial and multiaxial fatigue tests of notched AM materials, and clarified the effect of stress concentration on the failure lives of AM materials. Few tension torsion fatigue tests have been conducted under nonproportional multiaxial conditions that have focused on internal defects on the failure lives of AM materials.
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