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Background: Early fatigue mechanisms for various materials are yet to be unveiled for the (very) high-cycle fatigue (VHCF) regime. This can be ascribed to a lack of available data capturing initial fatigue damage evolution, which continues to adversely affect data scientists and computational modeling experts attempting to derive microstructural dependencies from small sample size data and incomplete feature representations. Objective: The aim of this work is to address this lack and to drive the digital transformation of materials such that future virtual component design can be rendered more reliable and more efficient. Achieving this relies on fatigue models that comprehensively capture all relevant dependencies. Methods: To this end, this work proposes a combined experimental and data post-processing workflow to establish multimodal fatigue crack initiation and propagation data sets efficiently. It evolves around fatigue testing of mesoscale specimens to increase da mage detection sensitivity, data fusion through multimodal registration to address data heterogeneity, and image-based data-driven damage localization. Results: A workflow with a high degree of automation is established, that links large distortion-corrected microstructure data with damage localization and evolution kinetics. The workflow enables cycling up to the VHCF regime in comparatively short time spans, while maintaining unprecedented time resolution of damage evolution. Resulting data sets capture the interaction of damage with microstructural features and hold the potential to unravel a mechanistic understanding. Conclusions: The proposed workflow lays the foundation for future data mining and data-driven modeling of microstructural fatigue by providing statistically meaningful data sets extendable to a wide range of materials.

Materials are either enabler or bottleneck for the vast majority of technological innovations. The digitization of materials and processes is mandatory to create live production environments which represent physical entities and their aggregations and thus allow to represent, share, and understand materials changes. However, a common standard formalization for materials knowledge in the form of taxonomies, ontologies, or knowledge graphs has not been achieved yet. This paper sketches the efforts in modelling an ontology prototype to describe Materials Science experiments. It describes what is expected from the ontology by introducing a use case where a process chain driven by the ontology enables the curation and understanding of experiments.

Wie muss eine Innovationszelle designed und an die bestehende Organisationsstruktur gekoppelt sein, damit ein Material-und Produktentwicklungsprozess radikal beschleunigt werden kann? Der Beitrag stellt ein Beispiel für eine gelungene Organisationsentwicklung vor: Eine Innovationszelle für die Produktentwicklung mit Programmierbaren Materialien, die es schafft, die Expertise mehrerer Fraunhofer-Forschungsinstitute, Industriepartner und Drittmittelgeber in effizienter Art und Weise zu bündeln und rasch marktfähige Produkte zu entwickeln.

The digitization of materials is the prerequisite for accelerating product development. However, technologically, this is only beneficial when reliability is maintained. This requires comprehension of the microstructure-driven fatigue damage mechanisms across scales. A substantial fraction of the lifetime for high performance materials is attributed to surface damage accumulation at the microstructural scale (e.g., extrusions and micro crack formation). Although, its modeling is impeded by a lack of comprehensive understanding of the related mechanisms. This makes statistical validation at the same scale by micromechanical experimentation a fundamental requirement. Hence, a large quantity of processed experimental data, which can only be acquired by automated experiments and data analyses, is crucial. Surface damage evolution is often accessed by imaging and subsequent image post-processing. In this work, we evaluated deep learning (DL) methodologies for semantic segmentation and different image processing approaches for quantitative slip trace characterization. Due to limited annotated data, a U-Net architecture was utilized. Three data sets of damage locations observed in scanning electron microscope (SEM) images of ferritic steel, martensitic steel, and copper specimens were prepared. In order to allow the developed models to cope with material-specific damage morphology and imaging-induced variance, a customized augmentation pipeline for the input images was developed. Material domain generalizability of ferritic steel and conjunct material trained models were tested successfully. Multiple image processing routines to detect slip trace orientation (STO) from the DL segmented extrusion areas were implemented and assessed. In conclusion, generalization to multiple materials has been achieved for the DL methodology, suggesting that extending it well beyond fatigue damage is feasible.

This paper presents analytical and reduced-order numerical solutions describing the non-linear response of slender, elastic struts (or plates) inclined relative to the loading direction. The solutions provide a highly efficient framework to predict post-buckling behaviors in cellular structures, including: stability regimes, peak strains during and after buckling, the work dissipated via cyclic loading, the impact of biaxial loading, and the role of geometric imperfections in the struts. Regime maps are presented that illustrate configurations that lead to snap-through, permanent deformation after unloading, strut failure, and enhanced hysteresis during cyclic loading. The maps illustrate that reversible snap-through events only occur within a very specific range of relative density (e.g. ̴0.25-0.4 for rhombic lattices). A highly efficient non-linear single degree-of-freedom dynamics model is derived from the statics solution, and is shown to be in excellent agreement with fully explicit, non-linear, dynamic finite element simulations for inclined struts. This simplified dynamics model is used to quantify the relationships between quasi-static responses, loading frequencies and energy dissipation during cycling loading. A key finding is that effective damping during cyclic loading is dramatically increased by non-linear behavior, even when the corresponding quasi-static result exhibits zero hysteresis. The implications for structured foams and the design of lightweight structural dampers is briefly discussed.

In this study, the uniaxial tension-tension fatigue behavior of fully nanotwinned magnetron sputtered Cu-6wt%Al, Cu-2wt%Al, and Cu-10 wt%Ni is presented. These alloys have average twin thicknesses ranging from 4 to 8 nm, average grain widths from 90 to 180 nm, and tensile strengths from 1 to 1.5 GPa. In the high cycle regime (103 to 107 cycles), the nanotwinned alloys exhibit fatigue strengths ranging from 210 to 370 MPa, which is higher than previously observed in nanotwinned Cu (fatigue strengths between 80 and 200 MPa). Fatigue strengths are normalized by tensile strength for Cu alloys with different microstructures to study the correlation between tensile and fatigue properties. Post-mortem analysis of the materials reveals a newly observed deformation mechanism, where localized detwinning leads to intergranular fracture between columnar grains. Overall, materials displaying detwinning as a deformation mechanism show lower normalized fatigue strengths in comparison to materials that deform with slip band like behavior.

The testing and manufacturing of lab-on-a-chip devices increasingly require lower lead times from conception to market. In order to supply a potential answer to this burgeoning demand, the work herein explores a design and prototyping process for biocompatible surfaces with designed wetting states ranging from slightly hydrophilic behavior to superhydrophobicity. Direct laser writing was used to fabricate geometrically parameterized base structures out of an acrylic photopolymer (IP-Dip) for eventual coating of samples with hexamethyldisiloxane (HMDSO) via plasma polymerization, with numerical methods validating candidate geometries. After manufacturing, samples were examined for structural and/or coating integrity via scanning electron microscopy and optical microscopy; subsequent wetting property evaluation was performed with a contact angle goniometer. Beginning with the slight hydrophilicity of the planar-coated base polymer, surfaces were shown displaying wetting behavior from the 'mushroomed' Wenzel state, the metastable Cassie-Baxter state, and superhydrophobicity with the non-wetting rolling predicted by literature. The combination of methods used in this work creates a parameter space for the rapid fabrication of 'designer' or 'programmable' surfaces, that is, the attainment of a specific wetting state through parametric variation with fast prototype processing times on the order of hours or days instead of weeks or months, and is typified by a presented microarray section. Of further specific relevance to the lab-on-a-chip community is the biocompatible nature of the HMDSO coatings. All structures presented in this work can be used as printed on any substrate or transferred for further processing into media more applicable for large-scale manufacturing.

The purpose of this discussion is to point out some similarities between a paper that was recently published by J.G. Zhu et al. [1] and a paper that we published earlier on the same subject [2]. The micro-scale FIB-DIC ring core technique was first proposed in 2009 [3]. The attraction of this method lies in its compatibility with well-established experimental facilities and interpretation procedures, and its applicability to stiff and compliant, crystalline and amorphous materials alike. The technique utilizes a combination of material removal and imaging capabilities of focused ion beam and dual-beam microscopes. This allows highly spatially resolved residual stress measurements to be performed with sub-micron lateral spatial resolution [4] and depth profiling with a resolution of ~100 nm [2].

Micro-powder injection moulding (PIM) is a promising mass manufacturing technique for the microsystem technology. Because typical applications - like sensors or actuators - need to withstand serious mechanical loadings, the investigations of the mechanical properties are of vital importance. Therefore, we implemented a small-scale testing setup that enables tensile and tension-tension-fatigue testing of freestanding micro-samples. This allowed for investigating tensile and fatigue properties of conventionally produced and PIM 17-4PH stainless-steel thin membranes. The conventionally produced samples were machined from bulk material and showed properties and lifetimes comparable with the best bulk samples. The PIM samples showed a weaker but more ductile behaviour, due to a ferritic phase and SiO2 inclusions. But their ultimate tensile strength of up to S-U=1021 +/- 48MPa and their relative fatigue strength of approximate to 46% S-U (R=-1) are still comparable with average bulk values. This indicates the high potential of PIM materials.

A novel high-temperature micro-tensile setup allows the characterization of the elastic and plastic as well as creep behavior of free-standing thin films at temperatures of up to 1000 °C. Correspondingly, a new layout for free-standing thin film tensile test structures has been developed, enabling accurate self-alignment upon loading. Furthermore, a differential optical strain measurement technique as well as optimizations of the optical path has been implemented, providing a strain resolution of well below 1 × 10-4 at 1000 °C. Two different polycrystalline SiC free-standing thin films have been investigated in tension to acquire stress-strain data and corresponding Young's modulus at up to 1000 °C. The high sensitivity of the strain measurement technique makes it also possible to identify creep strains in the high-temperature regime.

High-purity Cu samples containing parallel columns of highly aligned nanotwins with median spacing of 25 nm were subjected to tensioncompression cyclic loading by a high-throughput cyclic testing method. The methodology utilizes gradients in surface strain amplitude of a vibrating cantilever: one along the beam axis, with decreasing strain from the fixed to the free end of the beam, and the other through the foil thickness with decreasing strain from the surface to the neutral axis. Systematic microstructural investigations indicate that nanotwins are not stable under cyclic loading and that the applied strain amplitude has a strong influence on the resulting twin structure. In the highly stressed regions the detwinning process produces a twin free microstructure, allowing for subsequent extrusion and crack formation, and introduces fatal defects into structural parts.

In this work, the mechanical behaviour of millimetre-scale, bulk single crystalline, nanoporous gold at room temperature is reported for the first time. Tension and compression tests were performed with a custom-designed test system that accommodates small-scale samples. The absence of grain boundaries in the specimens allowed measurement of the inherent strength of millimetre-scale nanoporous gold in tension. The elastic modulus and strength values in tension and compression were found to be significantly lower than values measured with nanoindentation-based techniques and previously reported in the literature, but close to those reported for millimetre-scale polycrystalline samples tested using traditional compression techniques. Fracture toughness was found to be very low, in agreement with the macroscopic brittleness of nanoporous gold, but this is due to the localization of deformation to a narrow zone of ligaments, which individually exhibit significant plasticity and necking.

We investigate the mechanically induced local deformation effects in single crystalline Ni-Mn-Ga stripes by in situ Digital Image Correlation (DIC). Ni-Mn-Ga stripes of 100 and 200 mm thickness and lateral dimensions of 15 mm × 3 mm are fabricated by cutting and electropolishing a Ni-Mn-Ga bulk single crystal having a 10 M martensite structure. Application of tensile stress causes reorientation of martensite variants being associated with the formation and growth of local strain bands. The true strain in the bands is determined to be about 6% indicating complete local variant reorientation. The stress-strain characteristics are strongly affected by the mechanical boundary conditions. (1) Fixation or clamping the foil specimens during training in a magnetic field results in the formation of a stationary twin boundary (TB) being oriented by 45° with respect to the specimen edge. Subsequent tensile loading causes formation of a strain band with 45° orientation extending in both lateral directions through TB motion. The corresponding twinning stress is about 2 MPa. (2) Bending in out-of-plane direction causes formation of a stationary TB being oriented by about 84° with respect to the specimen edge. In this case, tensile loading causes formation of a strain band with 84° orientation. The corresponding twinning stress is reduced to about 0.7 MPa.