Fracture Properties and Residual Stresses in Small Dimensions: Fracture Testing Methodologies
Sponsored by: TMS Structural Materials Division, TMS Materials Processing and Manufacturing Division, TMS: Mechanical Behavior of Materials Committee, TMS: Nanomechanical Materials Behavior Committee
Program Organizers: Daniel Kiener, University of Leoben; Marco Sebastiani, Roma TRE university; Nagamani Jaya Balila, Max Planck Institut fuer Eisenforschung GmbH; William Gerberich, University of Minnesota; Siddhartha (Sid) Pathak, University of Nevada, Reno

Thursday 8:30 AM
March 2, 2017
Room: 21
Location: San Diego Convention Ctr

Session Chair: Nathan Mara, Los Alamos National Laboratory; Richard Vinci, Lehigh University


8:30 AM  Invited
SEM-based In-situ Fracture Measurements of Ceramics and Metals: Richard Vinci1; 1Lehigh University
    Fracture experiments performed at the micrometer scale within an SEM environment offer the opportunity to examine failures of specific features such as individual interfaces. They also make it possible to examine materials such as thin films that are difficult to probe using conventional macroscale techniques. However, issues such as plastic zone size and fracture mode must be taken into account in order to correctly interpret the measurement results. Several methods for performing in-situ tension and bending fracture tests will be reviewed, and examples will be presented representing brittle ceramics, ductile metals, and nanocrystalline metals that range in behavior from brittle to ductile.

9:00 AM  
In Situ Stable Fracture of Sapphire-Niobium Interfaces: Rui Hao1; Giorgio Sernicola2; Eduardo Saiz2; Finn Giuliani2; 1University of Illinois at Urbana−Champaign; 2Imperial College London
    There are many interesting mechanical properties that can be achieved with metal/ceramic multilayers. However, the deformation or fracture mechanisms can be complex. To simplify the problem, in this work we have concentrated on the effect of a single metal interlayer (30-200 nm thick) within a ceramic bi-crystal. The samples were produced by sputtering niobium on to sapphire substrates and then diffusion bonding the two coated crystals together. These were then orientated so the interface was vertical and a series of micropillars containing the niobium interlayer were cut. These were then loaded under displacement control with a wedge to form a double cantilever beam geometry in situ within an SEM. This allowed the evolution fracture energy with crack length along the interface to be calculated. The correlation of the fracture energy to the microstructure and thickness of the interface will then be discussed.

9:20 AM  
Measurement of the Fracture Toughness of Thin Films by Pillar Splitting: Effect of Materials Structure and Indenter Geometry: Matteo Ghidelli1; Marco Sebastiani1; 1University of Roma Tre
    The accurate knowledge of mechanical properties of micrometer sized materials has become fundamental for applications. Recently, a pillar splitting method has been applied for the determination of the fracture toughness. Micropillars are fabricated by focus ion beam and then indented up to failure. To date, this method has been applied only for a standard Berkovich tip and for a small number of materials. Here, we produce micropillars on different materials involving Si, SiO2, CrN, TiN, and BN, while studying the effect of the indenter geometry using 4 tips with angles ranging from 65.03° down to 35.3°. Finite element simulations (FES) are also performed accounting the effect the indenter geometries. We show that the fracture toughness can be easily extracted, while the splitting load decreases for sharper tips. Furthermore, FES carried out on different tip geometries enable an easy relationship between the failure load, pillar radius and fracture toughness.

9:40 AM  Invited
Enhancing Ductility of Metal-Metal (BCC-HCP) and Metal-Ceramic Multilayered Nanocomposites: Nathan Mara1; Siddhartha Pathak2; William Mook3; Youxing Chen1; Nan Li1; Jon Baldwin1; Jian Wang4; Irene Beyerlein1; 1Los Alamos National Laboratory; 2University of Nevada, Reno; 3Sandia National Laboratories; 4University of Nebraska, Lincoln
    In this work we explore the mechanical response of multilayered composites where one constituent phase has a low ductility, with a final goal of enhancing both the strength and ductility of the system. Using physical vapor deposition (PVD) techniques we synthesized two multilayered systems: a metal-ceramic (Cu-TiN and Al-TiN) nanocomposite (where the ceramic TiN is the brittle phase) and a hexagonal close-packed (HCP) – body-centered cubic (BCC) Mg-Nb system (where twinning in Mg leads to its lack of ductility), over a range of layer thicknesses ranging from 5 nm to 200 nm. We utilize a combination of nanoindentation, in-situ SEM compression testing of micro-pillars, in-situ SEM fracture toughness testing of 3-point bend micro-beams containing these multilayered nano-composites, and post-deformation TEM analysis to evaluate their deformation mechanisms. These results are analyzed as a function of decreasing layer thicknesses using the concepts of dislocation motion within the confined nanoscale layers.

10:10 AM Break

10:30 AM  
Indentation Fracture Experiments on Single Crystal Olivine from 300K to 1100K: David Armstrong1; Katie Kumamoto2; David Wallis1; Steve Roberts1; Angus Wilkinson1; Jessica Warren3; Lars Hansen1; 1University of Oxford; 2Stanford University; 3University of Delaware
    Olivine is the major constituent mineral of the lithospheric mantle and as such its mechanical behavior has significant influence over processes such as the formation of new tectonic plate boundaries. However, basic deformation mechanisms of olivine at relevant temperature ranges for plates (~300-1500K) are poorly characterized. In this study nano and micro-indentation experiments have been performed on single crystal olivine from room temperature to 1100K in vacuum. At room temperature cracks are seen around indentations after testing. Up to 800K little change in hardness is observed, above this temperature the hardness gradually decreases. Post indentation analysis shows that the degree of fracture seen around indents decreases above 800K. To understand fracture events FIB-SEM sectioning of indents was performed. This showed the cracks emanating from the indentations were shallow and can only be formed during the unloading process, with dislocation motion dominating the deformation during the sample loading at all temperatures.

10:50 AM  
Small-scale Testing Methodology to Study Fracture Toughness of Interfaces in Multilayered Systems: Adnan Ozekcin1; Richard Vinci2; Srinivasan Rajagopalan1; 1ExxonMobil Research and Engineering Company; 2Lehigh University
    Macroscopic mechanical properties of materials are determined by structure and composition at much smaller length scales. In multilayered systems, chemistry and structure of interfaces can also govern the overall fracture behavior. This study addresses the development of a small-scale (micro to nano-scale) test methodology to measure fracture toughness with high site specificity in a multilayered thin coating. Interfaces of interest were targeted for determination of fracture toughness, and compared against the intrinsic values of fracture toughness obtained for the layers themselves. Through determination of the interface and intrinsic properties, the approach allows for identification of key structure and chemistry parameters for further optimization and enhancement of overall coating and material performance. Finally, the applicability of the approach to determining site-specific material properties in other multiphase systems will be discussed.

11:10 AM  
Orientation Dependent Fracture Behaviour of LiTaO3 and LiNbO3 Single Crystals: Manuel Gruber1; Raul Bermejo1; Jeroen Bielen2; Peter Supancic1; Robert Danzer1; Daniel Kiener1; 1Montanuniversität Leoben; 2Epcos Netherlands B.V., A TDK Group company
    Single crystal piezoelectric materials such as LiTaO3 and LiNbO3 have found important application as surface acoustic wave filter substrates for high frequency data transfer. In order to optimize the functionality of the filters, a particular orientation and surface conditioning (e.g. grinding) of the crystal must be ensured. This can affect the mechnical response of the functional material to external thermo-mechanical loading.In this work, the strength and crack growth resistance (fracture toughness) of LiTaO3 and LiNbO3 materials were investigated macroscopically using biaxial bending and microscopically by miniaturized V-notched cantilevers in a SEM, respectively. It was found that the orientation of the notch, either parallel to the corresponding cleavage plane or with an angle, yields to a significant difference in the toughness values. As a consequence, the orientation of the grinding directions during flexural bending with respect to the cleavage planes showed a high impact on the strength for both materials.

11:30 AM  
Extraordinary Stability of Clamped Beam Fracture Toughness Specimen: Stress Intensity Factor Solutions and New Insights on Possibilities at Small Dimensions: Nagamani Jaya Balila1; Vikram Jayaram2; 1MPIE GmbH; 2Indian Institute of Science, Bangalore
    Edge notched clamped beam bending has been established as a viable fracture toughness test specimen at small length scales. Finite element modeling of this test geometry shows regions of crack length to width ratio where stable crack growth can be maintained both in load and displacement control which opens up possibilities of R-curve measurements and fatigue crack growth studies. Stable crack growth will also be experimentally demonstrated in a range of brittle and quasi-brittle materials. Stability diagrams of clamped beam bending will be compared to other ASTM standard geometries like SENT and SENB. Analytical stress intensity factor solutions have been derived from numerical simulations for a range of specimen dimensions and crack lengths, which will be presented along with a discussion on the advantages and limitations of this geometry.