He. Nassini et al., Thermal expansion behavior of aluminum alloys reinforced with alumina planar random short fibers, J MATER SCI, 36(11), 2001, pp. 2759-2772
The thermal expansion behavior of two aluminum alloys (Al-4%Cu and Al-12%Si
) reinforced with alumina planar random short fibers has been studied, both
experimentally and theoretically. The metal matrix composites (MMCs) were
manufactured by pressure infiltration of molten metal into short fiber pref
orms with a planar random distribution of fibers. Dilatometric testing was
used to investigate the influence of fiber volume fraction and architecture
, and the effects of thermal cycling between 25 degreesC to similar to 560
degreesC. Thermal expansion measurements showed that, by increasing the fib
er content in the composites, both the thermal strains and the effective co
efficient of thermal expansion (CTE) were reduced in the whole temperature
range. Furthermore, the thermal strains of MMCs increased almost linearly u
p to a critical temperature, T(c)r, where the metallic matrix began to yiel
d macroscopically due to internal thermal stresses. For temperatures higher
than T(c)r the thermal strains of MMCs showed a marked hysteresis during h
eating/cooling cycles due to the elasto-plastic response of the metallic ma
trix. In this temperature range, the thermal expansion curves deviated appr
eciably from linearity and the planar (in the plane of fibers) and transver
se (normal to the plane of fibers) responses were very different: while the
planar CTE was strongly reduced, the transverse CTE increased sharply with
temperature, being even larger than the CTE of the unreinforced alloy. The
rmal cycling produced a net dimensional change of composites during the fir
st 2-3 cycles but, on the subsequent cycles, the permanent deformation disa
ppeared almost completely and the successive thermal expansion curves were
identical. Experimental results were compared to the theoretical prediction
s of an analytical model based on the Eshelby's equivalent inclusion method
, and an excellent agreement was obtained. (C) 2001 Kluwer Academic Publish
ers.