Experimental evidence of a common local mode II growth mechanism of fatigue cracks loaded in modes II, III and II + III in niobium and titanium. (November 2016)

• Record Type: Journal Article
• Authors: Vojtek, Tomáš; Hohenwarter, Anton; Pippan, Reinhard; Pokluda, Jaroslav
• Is Part Of: International journal of fatigue. Volume 92:Part 2(2016)
• Page Start: 470
• Page End: 477
• Publication Date: 2016-11
• Subjects: Shear loading modes -- Local mode II -- Growth mechanism -- 3D crack path -- Coplanar growth; Materials -- Fatigue -- Periodicals; Materials -- Fatigue; Periodicals; 620.1122
• DOI: 10.1016/j.ijfatigue.2016.02.042
• Languages: English
• ISSNs: 0142-1123

Abstract

Highlights: Experiments for closure-free shear-mode fatigue cracks in titanium and niobium. Convincing fractographic evidence of a common local mode II mechanism. Cracks in all shear modes II, III and II + III grew by local mode II advances. All cracks grew nearly in the direction of the applied shear stress. Cracks nucleated at geometrical irregularities of precrack fronts. Abstract: The paper is focused on an identification of the local mode II mechanism of fatigue cracks loaded under the remote mode III and the mixed mode II + III and presents a convincing experimental evidence of such a mechanism in materials with a nearly coplanar crack growth. Closure-free data were obtained by applying fatigue experiments in modes II, III and II + III in commercially pure titanium and niobium. The results revealed that the micromechanism of propagation of all kinds of shear-mode cracks can be described by a common model of advances of local mode II crack segments nearly in the direction of applied shear stress. These segments nucleated at spatial geometrical irregularities of the precrack front generating fibrous patterns at fracture surfaces.