Can microscale fracture tests provide reliable fracture toughness values? A case study in silicon
- PDF / 467,962 Bytes
- 13 Pages / 584.957 x 782.986 pts Page_size
- 97 Downloads / 175 Views
Christoph Kirchlechner Structure and Nano/Micro-mechanics of Materials, Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf 40237, Germany; and University of Leoben, Leoben 8700, Austria
Gerhard Dehma) Structure and Nano/Micro-mechanics of Materials, Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf 40237, Germany (Received 2 October 2014; accepted 17 December 2014)
Fracture toughness testing of materials at the micrometer scale has become essential due to the continuing miniaturization of devices accompanied by findings of size effects in fracture behavior. Many techniques have emerged in the recent past to carry out fracture toughness measurements at the relevant micro and nanolength scales, but they lack ASTM standards that are prescribed for bulk scale tests. Also, differences in reported values arise at the microscale due to the sample preparation technique, test method, geometry, and investigator. To correct for such discrepancies, we chose four different fracture toughness test geometries in practice, all of them micromachined in the focused ion beam (FIB), to investigate the fracture toughness of Si(100) at the micrometer scale. The average KIC that emerges from all four cases is a constant (0.8 MPa m1/2). The advantages and limitations of each of these geometries in terms of test parameters and the range of materials that can be tested are discussed.
I. INTRODUCTION
Device miniaturization and shrinking internal material length scales have pushed the mechanics community to investigate deformation and fracture behavior of materials at ever smaller length scales. The principal problem that crops up with reducing sample dimensions is that size effects cannot be accounted for by direct extrapolation of known properties at the macroscale. Two of the most widely known size effects pertaining to strength of materials deal with the extrinsic (smaller is stronger)1–3 and intrinsic (Hall–Petch like effects)4,5 material length scales, respectively. Although known as a characteristic material property, many reports on KIC for the same given materials show variations due to the geometry, sample dimensions, and preparation techniques. One example is that of pure single crystal silicon, Si(100), a homogeneous, and ideally elastic–brittle material. The reported KIC as found from tension, bending, and indentation experiments both at the bulk and smallscales for Si(100) shows a wide scatter, anywhere
Contributing Editor: George M. Pharr a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.2 J. Mater. Res., 2015
http://journals.cambridge.org
Downloaded: 26 Feb 2015
from 0.7 to 2.1 MPa m1/2.6–10 The largely agreed value though is between 0.7 and 1.3 MPa m1/2 for single crystal Si.11 One of the reasons for this scatter in reported values could be due to the inability at small length scales to strictly adhere to the ASTM standards, which prescribe exact sample dimensions and crack sizes for a valid fracture toughness test.12 As the sample dimensions become smaller, the relative
Data Loading...
