Computational and Experimental Characterization of Indentation Creep
- PDF / 194,455 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 53 Downloads / 235 Views
U8.23.1
Computational and Experimental Characterization of Indentation Creep Ming Dao1, Hidenari Takagi2, Masami Fujiwara3 and Masahisa Otsuka4 1
Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. 2Graduate Student, Department of Mechanical Engineering, College of Engineering, Nihon University, Koriyama, Fukushima 963-8642, Japan. 3Department of Applied Physics, College of Engineering, Nihon University, Koriyama, Fukushima 963-8642, Japan. 4Department of Materials Science and Engineering, Faculty of Engineering, Shibaura Institute of Technology, Minatoku, Tokyo 108-8548, Japan. ABSTRACT Detailed finite-element computations and carefully designed indentation creep experiments were carried out in order to establish a robust and systematic method to accurately extract creep properties during indentation creep tests. Finite-element simulations confirmed that, for a power law creep material, the indentation creep strain field is indeed self-similar in a constant-load indentation creep test, except during short transient periods at the initial loading stage and when there is a deformation mechanism change. Self-similar indentation creep leads to a constitutive equation from which the power-law creep exponent, n, the activation energy for creep, Qc and so on can be evaluated robustly. Samples made from an Al-5.3mol%Mg solid solution alloy were tested at temperatures ranging from 573 K to 773 K. The results are in good agreement with those obtained from conventional uniaxial creep tests in the dislocation creep regime. INTRODUCTION Instrumented indentation has been gradually established as a convenient mechanical testing method that can extract mechanical properties both at ambient and high temperatures. Considerable efforts and significant progresses were made in extracting room temperature elastic as well as elasto-plastic properties [1-5]. At the same time, various studies were also carried out on indentation creep [6-15]. Noting that an indentation stress or strain field is a highly non-uniform field closely linked to the prior plastic deformation history, and an indentation creep test often involves transient periods, a number of fundamentally significant issues still require further research: (1) Whether the initial transient response (not self-similar) will result in the loss of self-similarity throughout the entire indentation creep test; (2) If a self-similar indentation creep test can be achieved, how long it takes to reach that stage; and (3) Whether one can extract accurately and robustly the creep properties using indentation creep tests. These questions can only be properly resolved via detailed numerical analyses together with careful experiments. THEORETICAL AND COMPUTATIONAL CONSIDERATIONS Assuming the material’s creep behavior obeys the well known creep law for uniaxial steady-state creep [16, 17], n
Qc σ exp − , E RT
ε& c = A 1
(1a)
U8.23.2
a constitutive equation was given for the self-similar indentation creep [1
Data Loading...
