1. Introduction and overview 2. Film stress and substrate curvature 3. Stress in anisotropic and patterned films 4. Delamination and fracture 5. Film buckling, bulging and peeling 6. Dislocation formation in epitaxial systems 7. Dislocation interactions and strain relaxation 8. Equilibrium and stability of surfaces 9. The role of stress in mass transport.

Thin Film Materials: Stress, Defect Formation and Surface Evolution

We provide an overview of the basic concepts of scaling and dimensional analysis, followed by a review of some of the recent work on applying these concepts to modeling instrumented indentation measurements. Specifically, we examine conical and pyramidal indentation in elastic-plastic solids with power-law work-hardening, in power-law creep solids, and in linear viscoelastic materials. We show that the scaling approach to indentation modeling provides new insights into several basic questions in instrumented indentation, including, what information is contained in the indentation load-displacement curves? How does hardness depend on the mechanical properties and indenter geometry? What are the factors determining piling-up and sinking-in of surface profiles around indents? Can stress-strain relationships be obtained from indentation load-displacement curves? How to measure time dependent mechanical properties from indentation? How to detect or confirm indentation size effects? The scaling approach also helps organize knowledge and provides a framework for bridging micro- and macroscales. We hope that this review will accomplish two purposes: (1) introducing the basic concepts of scaling and dimensional analysis to materials scientists and engineers, and (2) providing a better understanding of instrumented indentation measurements.

Scaling, dimensional analysis, and indentation measurements

This paper reviews commonly used methods of analysing and interpreting nanoindentation test data, with a particular emphasis on the testing of thin films. The popularity of nanoindentation testing is evidenced by the large number of papers that report such measurements in recent years. Unfortunately, there appear to be several issues that are emerging as common sources of error in using this technique. The present paper is aimed at highlighting these errors for the benefit of those practitioners who wish to use the technique but are not fully conversant with the field.

Critical review of analysis and interpretation of nanoindentation test data

http://nanomechanics.mit.edu/sites/default/files/documents/Lu-et-al-ActaMat-March-05.pdf

Nano-sized twins induce high rate sensitivity of flow stress in pure copper

http://ece.uprm.edu/~msuarez/4001/doc/read_assign3_2ndSem0910.pdf

Nanoindentation studies of materials

http://web.mit.edu/durint/PDF/Dao_et_alFR.pdf

Computational modeling of the forward and reverse problems in instrumented sharp indentation

A systematic investigation of the fretting fatigue behavior of the titanium alloy Ti-6Al-4V in both the mill-annealed (MA) and the solution-treated and overaged (STOA) conditions was carried out. A sphere-on-flat fretting fatigue device was used that facilitated real-time control and monitoring of all the relevant parameters such as the contact geometry, contact (normal and tangential) loads, and bulk alternating stress. While different sets of experiments were conducted to examine the influence of the bulk stress, the tangential load, and the normal load, respectively, on fretting fatigue response, the effect of microstructure on fretting fatigue was explored with experiments on the acicular, Widmanstatten, and martensitic microstructures as well. In experiments where the contact loads were maintained constant and the bulk stress was varied, fretting reduced the fatigue strength of Ti-6Al-4V. For this case, the “strength reduction factor” was higher for the experiments with higher tangential loads. For cases where the bulk stress and the normal or the tangential loads were maintained constant, lower fretting fatigue lives were obtained at larger tangential loads and at smaller normal loads. Of all the microstructures studied, preliminary results on the martensitic structure suggest an enhanced fretting fatigue resistance, compared to the basic STOA or the MA microstructure. Using the measured maximum static friction coefficient for Ti-6Al-4V, the experimentally observed contact and stickzone radii were found to exhibit good agreement with analytical predictions. Furthermore, conditions for crack initiation were determined through the application of the recently developed adhesion model for fretting fatigue. The model predictions of weak adhesion and crack initiation were validated with experimental observations of stick-slip behavior and fretting fatigue failures, respectively.

An experimental investigation of fretting fatigue in Ti-6Al-4V: the role of contact conditions and microstructure

Reactive infiltration processing was used to fabricate bulk NiAl and fiber-reinforced NiAl composites. Homogenous, pore-free materials were obtained by chemical reaction between nickel and aluminum after complete infiltration with liquid aluminum of preforms of nickel wires (containing tungsten wires for the composites) with low surface-to-volume ratio, high permeability, and regular infiltration paths. Reactively-processed, monolithic NiAl exhibited compressive creep properties at 715 °C and 1025 °C in good agreement with those of conventionally processed NiAl. The compressive creep behavior of NiAl composites reinforced with 5 to 20 vol pct W was also characterized at the same temperatures. At 715 °C, the NiAl-W composites exhibited secondary creep with little primary and tertiary creep, while at 1025 °C, the composites displayed all three stages. Microstructurally, secondary creep was characterized by pure uniaxial compression of tungsten fibers. The measured composite secondary creep rates could be predicted reasonably well with the role-of-mixtures isostrain model developed for composites where both phases undergo creep deformation using tensile creep data measured on the as-received tungsten fibers.

/pdf/reactive-infiltration-processing-and-secondary-compressive-e0n55vsrkq.pdf

Reactive infiltration processing and secondary compressive creep of NiAl and NiAl-W composites

http://arc.nucapt.northwestern.edu/refbase/files/model-fiber.pdf

A model for the longitudinal primary creep of a long-fiber composite

The uniaxial compression-creep behavior of unidirectionally reinforced continuous-fiber composite materials was investigated for the case where both the matrix and the fiber underwent plastic deformation by creep. The creep behavior of NiAl composites reinforced with 5 to 20 vol pct tungsten fibers was characterized at 1025 °C. The NiAl-W composites exhibited a three-stage creep behavior, with distinct primary, secondary, and tertiary creep. Microstructurally, tertiary creep was characterized by one of the following fiber-deformation mechanisms: brooming, bulging, buckling, or kinking. The composite tertiary creep is modeled by solving for global or local kink-band evolution, with composite deformation contributing, respectively, to fiber buckling or kinking. The model predicts (1) the critical strain for the onset of the tertiary stage to be most sensitive to the initial kink angles, while being relatively insensitive to the initial kink-band heights and (2) the critical strain to vary inversely with the volume fraction of fiber in the composite. Reasonable agreement between model predictions and experiments is obtained.

/pdf/tertiary-compression-creep-of-long-fiber-composites-a-model-3tcct6dljj.pdf

T. A. Venkatesh

Papers

Computational modeling of the forward and reverse problems in instrumented sharp indentation

An experimental investigation of fretting fatigue in Ti-6Al-4V: the role of contact conditions and microstructure

Reactive infiltration processing and secondary compressive creep of NiAl and NiAl-W composites

A model for the longitudinal primary creep of a long-fiber composite

Tertiary compression creep of long-fiber composites : A model for fiber kinking and buckling