tailieunhanh - Failure Analysis Case Studies II Episode 9

Tham khảo tài liệu 'failure analysis case studies ii episode 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 268 B type hosepipe Fig. 1. Appearance of bursting hosepipes arrowheads aim at openings . 3. Dissection of hosepipes The hosepipes were dissected from the outer to the inner layers in order to study the characteristics of bursting hosepipes. The results showed that 1 The steel wire layer was intact. 2 In all A type hosepipes there was only one opening in the inner rubber layer. Similar results were obtained for most B type hosepipes except two where two openings were observed. 3 The opening in the inner rubber layer was situated in the outside of the bend near the metal elbow adapter. The distance between the opening and the metal core is about mm see Fig. 2 . 4 The openings in the inner rubber layer are circumferential as shown in Fig. 2. 5 No other defects were observed in the inner layers of the hosepipes. 269 A type hosepipe B type hosepipe Fig. 2. The openings in the inner rubber layer. 6 There were small openings in the outer surface of the inside middle layer in one B type hosepipe see Fig. 3 . 4. Fracture analysis of layers . Fracture analysis of inner layer Opening the fracture and inspecting by SEM it was found that the fracture surfaces in both A and B type hosepipes have the same characteristics showing flats and radiating ridges see Figs 4 and 5 . Fatigue markings in the later period of propagation could be clearly observed Fig. 6 . The 270 Fig. 4. The fracture appearance of an A type hospipe. fatigue cracks were possibly initiated at the interface between the cotton thread and the inner layer. Finally there were no obvious defects in the fatigue initiation zone Fig. 5 . Smaller cracks had similar fatigue characteristics Fig. 7 . . Fracture analysis of outer layer Opening the outer layer fractures and observing by SEM it was concluded that cracks initiated from the outer surface and propagated towards the inner surface. Multiple initiation sites and some fatigue striations were observed Fig. 8