A low density composite (Shirasu Balloons Aluminum Composite: SBAC) of volcano glass microballoons (Shirasu Balloons: SB) and aluminum alloy (Al-12%Si) was investigated in terms of the effect of volume fraction (
VSB) of SB on tensile strength (σ
T), compressive strength (σ
C), shear modulus (
G), internal friction coefficient (
Q-1) and specific conductivity (
C) of SBAC. The value of
G decreased exponentially and monotonously with the increase in
VSB and showed good agreement with logarithmic mixture rule. The values of σ
T, σ
C and
C also decreased exponentially with the increase in
VSB, but their curves inflected sharply toward low values at about 50vol% of SB. On the other hand,
Q-1 value increased linearly with the increase in
VSB and the curve inflected sharply toward high value at about 50vol% of SB. The
VSB of their knee points (about 50vol%) seemed to be the volume fraction above which contact points of SB in SBAC markedly increased.
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