Damage Evolution of Metal Matrix Composites Under Dynamic Impact Loading
Xianghong Li
Department of Engineering Mechanics
University of Nebraska
Lincoln, NE
M.S. Advisors: Dr. Wei Tong and Dr. Kevin Murphy
Date: Friday, April 25, 1997
Time: 12:30 p.m.
Place: 306 Bancroft Hall
Numerous works have been done on the deformation and failure processes of PMMCs under quasi-static or cyclic loading condition. With the graduate acceptance and widespread prospective usage of PMMCs in automotive, aeronautics, and aerospace industry, there is an increasing need for the understanding and evaluation of mechanical behavior of PMMCs under dynamic impact loading. But little about some unique effects of dynamic loading on damage initiation and growth in PMMCs is known.
In this study, an experimental technique was developed to investigate the damage and fracture behavior of particulate reinforced metal matrix composites subjected to dynamic impact loading. Titanium-based metal matrix composites reinforced by three different ceramic particles TiC, SiC, and B4C respectively were evaluated in this study. Dynamic loading conditions were achieved by means of a split Hopkinson pressure bar (SHPB). Four types of testing configurations, i.e., uniaxial compression, disk splitting, ball indentation, and disk bending, were performed on all three materials on both dynamic and quasi-static loading. The quasi-static tests were carried out for comparison purpose. Specimens after tests were recovered and the damages of each sample were characterized by optical and scanning electron microscopy. For fractured specimens, the fracture surfaces were also examined by scanning electron microscope (SEM). Finite element codes DYNA2D and DYNA3D were used to analyze the stress wave propagation within the loading bars and stress and strain fields within the samples.
As results, the mechanical behavior and damage evolution of titanium-based PMMCs under dynamic loading are different from quasi-static loading conditions. While reinforcement damage modes are still mainly particle cracking and particle/matrix interfacial debonding, the degree of damage is more serious in dynamic loading case. Also, the degree of damage of particle reinforcement depends on the porosity existing inside the tested material and the bonding strength of particle/matrix interface.
