Development of experimental verification techniques for non-linear deformation and fracture on the nanometer scale.

Moody, Neville Reid ; Bahr, David F.

Sandia National Laboratories

关键词: Mechanical Properties;    Fractures;    Plasticity;    36 Materials Science;    Fracture (Mechanics);   

DOI  :  10.2172/876231
RP-ID  :  SAND2005-6885
RP-ID  :  AC04-94AL85000
RP-ID  :  876231

美国|英语

来源: UNT Digital Library

【 摘 要 】

This work covers three distinct aspects of deformation and fracture during indentations. In particular, we develop an approach to verification of nanoindentation induced film fracture in hard film/soft substrate systems; we examine the ability to perform these experiments in harsh environments; we investigate the methods by which the resulting deformation from indentation can be quantified and correlated to computational simulations, and we examine the onset of plasticity during indentation testing. First, nanoindentation was utilized to induce fracture of brittle thin oxide films on compliant substrates. During the indentation, a load is applied and the penetration depth is continuously measured. A sudden discontinuity, indicative of film fracture, was observed upon the loading portion of the load-depth curve. The mechanical properties of thermally grown oxide films on various substrates were calculated using two different numerical methods. The first method utilized a plate bending approach by modeling the thin film as an axisymmetric circular plate on a compliant foundation. The second method measured the applied energy for fracture. The crack extension force and applied stress intensity at fracture was then determined from the energy measurements. Secondly, slip steps form on the free surface around indentations in most crystalline materials when dislocations reach the free surface. Analysis of these slip steps provides information about the deformation taking place in the material. Techniques have now been developed to allow for accurate and consistent measurement of slip steps and the effects of crystal orientation and tip geometry are characterized. These techniques will be described and compared to results from dislocation dynamics simulations.