Our safety, comfort and peace of mind are heavily dependent upon our capability to prevent, predict or postpone the failure of components and structures on the basis of sound physical principles While the external loadings acting on a material or component are clearly important, There are other contributory factors including unfavourable materials microstructure, pre-existing defects and residual stresses Residual stresses can add to, or subtract from, the applied stresses and so when unexpected failure occurs it is often because residual stresses have combined critically with the applied stresses, or because together with the presence of undetected defects they have dangerously lowered the applied stress at which failure will occur Consequently it is important that the origins of residual stress are understood, opportunities for removing harmful or introducing beneficial residual stresses recognized, their evolution in-service predicted, their influence on failure processes understood and safe structural integrity assessments made, so as to either remove the part prior to failure, or to take corrective action to extend life This paper reviews the progress in these aspects in the light of the basic failure mechanisms

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Residual stress and its role in failure

A methodology for performing uniaxial compression tests on samples having micron-size dimensions is presented. Sample fabrication is accomplished using focused ion beam milling to create cylindrical samples of uniform cross-section that remain attached to the bulk substrate at one end. Once fabricated, samples are tested in uniaxial compression using a nanoindentation device outfitted with a flat tip, and a stress–strain curve is obtained. The methodology can be used to examine the plastic response of samples of different sizes that are from the same bulk material. In this manner, dimensional size effects at the micron scale can be explored for single crystals, using a readily interpretable test that minimizes imposed stretch and bending gradients. The methodology was applied to a single-crystal Ni superalloy and a transition from bulk-like to size-affected behavior was observed for samples 5 μm in diameter and smaller.

A methodology to investigate size scale effects in crystalline plasticity using uniaxial compression testing

Measuring the toughness of brittle coatings has always been a difficult task. Coatings are often too thin to easily prepare a freestanding sample of a defined geometry to use standard toughness measuring techniques. Using standard indentation techniques gives results influenced by the effect of the substrate. A new technique for measuring the toughness of coatings is described here. A precracked micro-beam was produced using focused ion beam (FIB) machining, then imaged and loaded to fracture using a nanoindenter.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400084016

Measuring fracture toughness of coatings using focused-ion-beam-machined microbeams

This article discusses applications of focused ion beam micro- and nanofabrication. Emphasis is placed on illustrating the versatility of focused ion beam and dual-platform systems and how they complement conventional processing techniques. The article is divided into four parts: maskless milling, ion beam lithography, ion implantation, and techniques such as in situ micromanipulation.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0883769400007296

Focused Ion Beam Micro- and Nanoengineering

Microcantilevers were first introduced as imaging probes in Atomic Force Microscopy (AFM) due to their extremely high sensitivity in measuring surface forces The versatility of these probes, however, allows the sensing and measurement of a host of mechanical properties of various materials Sensor parameters such as resonance frequency, quality factor, amplitude of vibration and bending due to a differential stress can all be simultaneously determined for a cantilever When measuring the mechanical properties of materials, identifying and discerning the most influential parameters responsible for the observed changes in the cantilever response are important We will, therefore, discuss the effects of various force fields such as those induced by mass loading, residual stress, internal friction of the material, and other changes in the mechanical properties of the microcantilevers Methods to measure variations in temperature, pressure, or molecular adsorption of water molecules are also discussed Often these effects occur simultaneously, increasing the number of parameters that need to be concurrently measured to ensure the reliability of the sensors We therefore systematically investigate the geometric and environmental effects on cantilever measurements including the chemical nature of the underlying interactions To address the geometric effects we have considered cantilevers with a rectangular or circular cross section The chemical nature is addressed by using cantilevers fabricated with metals and/or dielectrics Selective chemical etching, swelling or changes in Young's modulus of the surface were investigated by means of polymeric and inorganic coatings Finally to address the effect of the environment in which the cantilever operates, the Knudsen number was determined to characterize the molecule-cantilever collisions Also bimaterial cantilevers with high thermal sensitivity were used to discern the effect of temperature variations When appropriate, we use continuum mechanics, which is justified according to the ratio between the cantilever thickness and the grain size of the materials We will also address other potential applications such as the ageing process of nuclear materials, building materials, and optical fibers, which can be investigated by monitoring their mechanical changes with time In summary, by virtue of the dynamic response of a miniaturized cantilever shaped material, we present useful measurements of the associated elastic properties

/pdf/measurement-of-mechanical-properties-of-cantilever-shaped-4sjli2d1sl.pdf

M Becker

Papers

FIB micromachined submicron thickness cantilevers for the study of thin film properties