Notch (In)Sensitivity of Aluminum Matrix Syntactic Foams

Area of Science:

• Materials Science
• Mechanical Engineering
• Composite Materials

Background:

• Metal matrix syntactic foams (MMSFs) offer unique properties for structural applications.
• Understanding their fracture behavior is crucial for material design and performance prediction.
• Aluminum alloys (Al99.5, AlSi12) are common matrices for MMSFs, with Globocer filler providing the hollow sphere reinforcement.

Purpose of the Study:

• To investigate the notch sensitivity and fracture toughness of aluminum alloy-based MMSFs.
• To correlate fracture properties with matrix composition and filler-matrix bonding.
• To elucidate the influence of notch geometry on the mechanical response of MMSFs.

Main Methods:

• Production of MMSFs via pressure infiltration using Al99.5 and AlSi12 matrices with Globocer filler.
• Machining of notched samples with varying geometries.
• Three-point bending tests to record load-displacement and crack opening displacement.
• Determination of fracture energies and fracture toughness.
• Fractographic analysis of fracture surfaces.

Main Results:

• Fracture energies of MMSFs were found to be sensitive to notch geometry.
• Fracture toughness values were independent of notch geometry, depending solely on the matrix material.
• Strong chemical bonding was observed between hollow spheres and the Al99.5 matrix.
• Weaker bonding was noted for the AlSi12 matrix, leading to distinct crack propagation behaviors.

Conclusions:

• Fracture energy is a critical parameter for assessing MMSF performance under different stress concentrations.
• Fracture toughness is a more intrinsic material property, less influenced by external geometric factors.
• The choice of aluminum alloy matrix significantly impacts filler-matrix interfacial integrity and overall fracture mechanisms in MMSFs.