Size Effect Characterization for Nanostructured Material in Nanoindentation Test
- PDF / 854,163 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 86 Downloads / 188 Views
L8.2.1
SIZE EFFECT CHARACTERIZATION FOR NANOSTRUCTURED MATERIAL IN NANOINDENTATION TEST Yueguang Wei, Ying Du, Siqi Shu, Chen Zhu LNM, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100080, P.R. China ABSTRACT Based on the microscopic observations and measurements, the mechanics behaviors of the nanostructured material (the surface-nanocrystallized Al-alloy material) at microscale are investigated experimentally and theoretically. In the experimental research, the hardness-indent depth curves or relations are measured by using both the method of randomly selecting loading points on the specimen surface and the continuous stiffness method. In the theoretical simulation, based on both the material microstructure characteristics and the experimental features of the nanoindentation, the microstructure cell model is developed and the strain gradient plasticity theory is adopted. The material hardness-indent depth curves are predicted and simulated. Through comparison of the experimental results with the simulation results, the material parameters and the model parameters are determined. INTRODUCTION Resent researches have displayed that the high-strength nano-structured materials can be fabricated by using some advanced techniques. For example, by using the severe plastic deformation (SPD) method, one can fabricate the nanocrystalline materials [1-3]. The adopted SPD methods include the large torsion method [1], the large pressing method [2] and the ultrasonic shot peening (USP) method [3], etc. Usually, the microstructure cell size is from tens to hundreds of nanometers, even to microns. Within this length scale, solids use to display a strong size effect. On the research of the size effect, many investigators have focused their attention on the nanoindentation problems for single crystal metals. Through theoretical and experimental researches for the nanoindentation size effect, one has found that as the indent depth decreases, the hardness curve displays a obviously going up trend, i.e., the size effect. The size effect was described by using the strain gradient theories [4,5], and the simulation results were consistent with the experimentally measured results. The researches have showed that the microscale length parameter for single crystal metals is in the order of one micron [4, 5]. However, the nanocrystalline material case investigated here will be very complicated, about which besides the size effect mentioned above, additionally the influences of both the crystal grain size and shape distributions on the material behaviors must be considered. In the author's previous research on the nano-polycrystal Al and the thin film/substrate system [6], the effect of both the crystal grain size and the shape distribution was called the geometrical effect for differing from the size effect described only by a single microscale parameter in strain gradient theories. Based on the microstructure cell model and the strain gradient plasticity theory, the size effect and geometrical effect have been studied. Throu
Data Loading...
