Fatigue crack growth behavior of 2124/SiC/10 p functionally graded materials
- PDF / 2,487,991 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 17 Downloads / 185 Views
gineering applications require that components perform multiple functions or exhibit characteristics not attainable by any single engineering material currently available. For example, a component may require high surface hardness, for wear resistance, combined with high interior toughness. It is known that abrupt transitions in composition and properties within a component, as are found in most coating systems, often result in sharp local concentrations of stress that can lead to failure. In recent years, development of a new series of materials, known as functionally graded materials (FGMs),[1] has opened new fields for material design for effective applications in industrial situations. This is because FGMs offer attractive advantages over their conventional counterparts, such as adjusted thermal mismatching,[2] relaxation of stress at the interface,[3,5] increased fracture toughness,[5–8] and crack retardation.[6,7] Bulk FGMs with radial graded cores based on the 2124/ SiC/10p composite system can be fabricated by hot extrusion.[7,9–11] They have both high surface hardness, because of the SiC particulate reinforced Al-2124 matrix annulus, and high interior toughness, due to the introduction of an unreinforced Al-2124 central core.[5,8–10] Crack propagation is impeded by the presence of the more ductile core
H. UZUN, Associate Professor, is with the Department of Metal Education, Sakarya University, 54188 Ozanlar, Sakarya, Turkey. T.C. LINDLEY and R.D. RAWLINGS, Professors, and H.B. McSHANE, Doctor, are with the Department of Materials, Imperial College of Science, Technology, and Medicine, The University of London, London SW7 2BP, United Kingdom. Manuscript submitted August 12, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS A
within the bulk FGM as the crack reaches successive interfaces. These FGMs give some warning of component failure by exhibiting graceful failure instead of the catastrophic failure of conventional composites. Thus, FGMs could be more acceptable for critical applications than their conventional metal matrix composite counterparts. Most of the previous studies on FGMs have dealt with their physical, particularly their thermal, properties, but until recently, little attention has been paid to their mechanical properties. In particular, the authors are not aware of publications on the fatigue of FGMs. In order to use FGMs in critical structural applications, a clear understanding of the fatigue crack growth behavior of these materials is required. Consequently, during a comprehensive study of the powder metallurgy processing of FGMs, the opportunity was taken to carry out a preliminary investigation into the fatigue crack growth behavior of extruded bulk FGM rods based on the 2124/SiC/10p composite system. The effects of the radial graded structure of the bulk FGMs on fatigue crack propagation was investigated using a constant nominal stress intensity range, ⌬K, and constant amplitude tests. Testing was carried out with the fatigue crack propagation from a brittle region to a ductile region an
Data Loading...
