Modern materials behave differently on a micro-scale level than in bulk applications. Therefore, with ever present miniaturization, the materials’ testing on a micron-level is gaining importance. 3D printing with a sub micron precision, such as direct laser writing by two-photon lithography, allows for relatively fast manufacturing of miniaturized specimens for micromechanical testing. In combination with precise loading by a nanoindenter tip, high throughput micromechanical testing is enabled. Presented research shows design process of miniaturized cantilever and push to pull device specimens for fracture mechanics testing, aided finite element modelling, together with high throughput testing of polymeric materials with varied printing parameters and loading conditions. Such in situ and ex situ experimental setup allows for systematic fracture mechanics testing on the small scale for common materials used in small-scale 3D printing.
EXTENDED ABSTRACT

The last few years have seen the development of several testing techniques at the micro-scale to characterize the mechanical properties of multi-scale materials. One such novel methods are micro-cantilever bending tests to assess mechanical properties of materials. Micro-cantilever tests allow for a variety of test configurations, including scaled chevron-notch geometry allowing controlled crack-growth prior to critical failure load. Chevron notches are convenient at such length scales since they allow for ex-situ measurements of crack length – avoiding the need to directly measure crack length, which could be a challenge at such scale. The test approach provides access to R-curve behavior for quasi-brittle materials on the micro-scale and opens the door to investigate more sophisticated topics, i.e., creep crack growth. Moreover, the technique complemented with visualization and scanning tools, such as Scanning Electron Microscopy and Microtomography, allows for a proper and extensive analysis of the crack growth phenomena.
The motivation of this work revolves around expanding currently available knowledge on multiscale characterization of cement-based materials with the focus on fracture testing at the micro- and mesoscale through the novel micro-bending technique. This test opens the door to understanding fracture, toughening mechanisms, and evolution of these properties regarding processing variables.
EXTENDED ABSTRACT

Understanding the mechanisms of creep deformation and damage (cavitation) in engineering components materials is important, but despite the significant research that has been conducted over the past 50 years, there is still a lack of understanding of the microstructural processes that influence and control the development of damage. To provide further insights into this, in the present work a novel small-scale constant load cantilever beam geometry test specimen is used. The materials selected for the tests are polycrystalline and bi-crystals of high purity copper. The copper provides a simple model material for exploring initiation and early growth of creep cavitation and allows comparison with crystal-based model predictions.
In this study, both creep deformation and creep cavitation were measured. For the latter, a range of higher spatial resolution techniques were adopted including scanning electron microscopy, electron backscattered diffraction and focused gallium ion beam serial section milling. Creep cavity number density and size measurements were made using advanced image analysis procedures. Polycrystalline and bi-crystal results are compared, with particular attention given to the role of Schmid factor and misorientation on the initiation and early growth of the creep cavities. These experimental results inform the development of microstructural based models of cavitation.
EXTENDED ABSTRACT

Multilayering of metal/ceramic combinations can help to achieve better strength and toughness than the individual material constituents. The effect of elastic-plastic mismatch in multilayers on the crack driving force and eventually on fracture resistance has been analyzed in this work. The enhancement in fracture toughness by decreasing layer spacing has been predicted from finite element calculations and verified by micro-cantilever fracture tests. Further, calculations have been carried out for a more stable clamped beam bend geometry to determine R-curve behavior in such multilayers.
EXTENDED ABSTRACT