Environmentally assisted fatigue response of Al-Cu-Mg-Mn with SiC particulate metal matrix composites
Başlık çevirisi mevcut değil.
- Tez No: 400988
- Danışmanlar: PROF. DR. W. J. EVANS
- Tez Türü: Doktora
- Konular: Metalurji Mühendisliği, Metallurgical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1999
- Dil: İngilizce
- Üniversite: University of Wales
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 268
Özet
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Özet (Çeviri)
Experimental research has been carried out with the purpose of evaluating llic tensile properties, stress and strain control fatigue properties and, crack propagation behaviour of a particulate reinforced metal matrix composite. Practographic examination has also been undertaken of the powder metallurgy processed 2124 Alalloy with two volume fractions (17 and 25vol%) and different paiticle sizes. (2.5|jm and' 15pm) silicon carbide particles (SiCp). The present study shows that teipile properties of composites significantly improve with the incorporation of hard, brittle ceramic particles. The composite materials were cyclically deformed over a range of constant stress amplitudes at R=0.l and R^O.S using a variety of notch geometiics in air and elevated temperatures. Results indicated that for a given aged condition (T4), load controlled fatigue lives of the composites are significantly improved compared with the unreinforced base alloy. However the severity ol a notch, i.e. increased stiess concentration factor and elevated temperatures shiR down the S-N curves of the 2124 2^vol% SiCp (AMC225) composite material. l^he effects of particle size and volume fraction on strain controlled fatigue behaviour were evaluated for a variety of composite materials at different strain range levels. An increased volume fraction of particles reduces fatigue lives due to the lower monotonic ductility of the AMC225 composite which showed some degree of softening at R=-l, but stable behaviour at the R-0 conditions under strain loading. At R=0.5 the composite cyclically hardened. On the basis of these results, fatigue life predictions for the notch geometries have been made by using a critical strain approach. Fatigue crack growth results show that increasing volume fraction and particle size gave the slowest crack growth rates at R=0.1 in air. An increase in the R ratio resulted in faster crack growth rates in the AMC225 composite material ^ and unreinforced material. The influence of salt solution was crucial at low R ratios where track closure mechanisms may play an important role. The AMC225 composite material showed superior crack growth resistance than the base alloy at R^O.l in air and S'dlt solution environment. Fracturc surfaces revealed that fatigue cracks often initiated at detectable microstmctural features, such as hard and brittle coarse particles due to the high dislocation density and local intense stress concentration at these large detects. The fracture mode of the composites combined ductile failure of the matrix and local brittle fracturc of SiC particlcs. Fractured, debonded and pulled out particles were observed during a variety of fatigue conditions.
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