Multiscale Investigation of Shape Memory Alloy Fatigue

Shape memory alloys (SMAs) are functional materials with two remarkable properties: superelasticity and the shape memory effect. The reversible, solid-to-solid ("martensitic") phase transformations that enable these useful material responses also complicate their durability predictions. SMAs are used extensively in biomedical devices such as stents and root canal files, and also have promising applications for important frontiers, such as weight-saving actuators, active structures for aerospace systems, and damping components for civil structures. Before SMAs can be widely adopted for these new applications, however, their response to cracking and failure must be understood. Complexities from martensitic phase transformations in SMAs confound many existing predictions of damage, fatigue, and fracture mechanics (including Schmid's Law and linear/elastoplastic fracture mechanics). Furthermore, this work's findings could extend to other emerging materials with phase transformations, such as Heusler alloys for high-efficiency magnetocaloric refrigeration. To address these knowledge gaps, this work provides new observations and insights on the role of phase transformation during cracking and failure of SMAs. Additionally, new experimental frameworks were developed to characterize cracks in structural materials for unprecedented breadth and precision between the millimeter and nanometer length scales. The early part of this work optimized full-field deformation measurements to enable the high-precision experiments of the later part of this work. Also, it advanced techniques in the broader experimental mechanics community. First, a new method was developed to enhance measurements from digital image correlation (DIC), a powerful technique for measuring material deformation. Also, clear guidelines were presented for optimizing an important sample preparation step for optical DIC ("speckle patterning" with paint) The latter part of this work established new insights into SMA cracking by examining the effects of grain size, crystallographic texture, and temperature. There are two types of fatigue in SMAs: functional fatigue (degradation of the phase transformation, especially from reduction in the recovered strain during superelastic cycling), and structural fatigue (the typical fatigue response of metals, with crack initiation and growth). Despite the dramatic enhancement of NiTi's functional fatigue resistance with grain size reduction to the nanoscale, there was no improvement in structural fatigue resistance with respect to grain size. Rather, the largest grain size studied had the slowest crack growth rate, which was attributed to roughness-induced crack closure (not observed in the other grain sizes). For all grain sizes, the macroscopic fatigue crack growth correlated well with microscopic crack tip observations: the grain sizes with relatively fast macroscopic crack growth rates exhibited large crack displacements at the microscale, and vice versa. Next, the effects of crystallographic texture on NiTi's functional and structural fatigue were characterized. Unlike the grain size study that was complicated by roughness-induced crack closure differences, the three texture conditions had similar fracture surface. Furthermore, there were clear connections between functional and structural fatigue. During cyclic tension, there was about three times as much residual strain accumulation in the sheet's rolling direction (RD) compared to the transverse direction (TD), and the crack growth rates of the RD condition were consistently faster than the 45 and TD conditions. Finally, fatigue experiments as a function of temperature characterized the role of martensitic phase transformation on cracking. The slowest crack growth rates were measured in the stable martensite and thermal R-phase martensite.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/146027/1/wlepage_1.pd

Applied Metaheuristic Computing

For decades, Applied Metaheuristic Computing (AMC) has been a prevailing optimization technique for tackling perplexing engineering and business problems, such as scheduling, routing, ordering, bin packing, assignment, facility layout planning, among others. This is partly because the classic exact methods are constrained with prior assumptions, and partly due to the heuristics being problem-dependent and lacking generalization. AMC, on the contrary, guides the course of low-level heuristics to search beyond the local optimality, which impairs the capability of traditional computation methods. This topic series has collected quality papers proposing cutting-edge methodology and innovative applications which drive the advances of AMC

Entropy in Image Analysis II

Image analysis is a fundamental task for any application where extracting information from images is required. The analysis requires highly sophisticated numerical and analytical methods, particularly for those applications in medicine, security, and other fields where the results of the processing consist of data of vital importance. This fact is evident from all the articles composing the Special Issue "Entropy in Image Analysis II", in which the authors used widely tested methods to verify their results. In the process of reading the present volume, the reader will appreciate the richness of their methods and applications, in particular for medical imaging and image security, and a remarkable cross-fertilization among the proposed research areas

Animal vision and colour change for camouflage

Camouflage is a well-studied form of antipredator defence. A key issue is how animals ensure camouflage effectiveness when the visual environments many camouflage strategies rely on vary. Phenotypic plasticity allows animals to adjust coloration to best match such environmental variation. It is assumed that vision is used in identifying this variation and guides changes in colour. However, questions still exist regarding the opportunities and limitations afforded from vision-guided changes for camouflage. Carcinus maenas, the green shore crab, already a widely used species to investigate a variety of questions regarding camouflage, was used to test the assumption that vision is directly responsible for guiding (and limiting) colour change for camouflage. In the first chapter, tests of spectral sensitivity and colour discrimination were performed, which were then compared to colour change responses. Following this, crabs’ spatial resolution was tested and compared to pattern change responses on uniform and patterned backgrounds. Finally, crabs’ brightness change responses to varying illumination and substrate brightness conditions were recorded to examine directional light’s role in substrate perception for plasticity. My results indicate that C. maenas colour change for camouflage is determined and limited by their vision. First, spectral and colour discrimination results indicate C. maenas cannot perceive differences in colour. This aligns with colour change results, with crabs only showing significant achromatic change despite apparently possessing the chromatophores needed for chromatic change. Following this, crab’s changed patterning by increasing pattern contrast proportionate to background pattern size, without changing pattern shape or size. This change in patterning is indicative of a shift from uniform background matching to disruptive markings. Finally, C. maenas colour change corresponds to the relative reflectance of substrates, accounting for illumination. This indicates some level of assessment of directional light, likely dependent on the differential stimulation of an eye perceiving light from multiple directions at once. These results indicate that while species’ vision can limit colour change for camouflage, effective improvements in camouflage are still capable within these limits

Applied Methuerstic computing

For decades, Applied Metaheuristic Computing (AMC) has been a prevailing optimization technique for tackling perplexing engineering and business problems, such as scheduling, routing, ordering, bin packing, assignment, facility layout planning, among others. This is partly because the classic exact methods are constrained with prior assumptions, and partly due to the heuristics being problem-dependent and lacking generalization. AMC, on the contrary, guides the course of low-level heuristics to search beyond the local optimality, which impairs the capability of traditional computation methods. This topic series has collected quality papers proposing cutting-edge methodology and innovative applications which drive the advances of AMC

Novel Research in Sexuality and Mental Health

Sexuality is considered as a great human value related to happiness and satisfaction, but unfortunately, when affecting mental disorders, they tend to be associated with second level human functions. Nevertheless, sexual dysfunction often accompanies psychiatric disorder, intensely influencing compliance, quality of life and human relationships. Sexuality could be influenced either by a mental disorder itself, difficulties to get and maintain couple relationships or by the use of psychotropic treatments. Treatment-related adverse events are unfortunately under-recognized by clinicians, scarcely spontaneously communicated by patients, and rarely investigated in clinical trials. The most frequent psychotropic compounds that could deteriorate sexuality and quality of life include antidepressants, antipsychotics and mood regulators. There are important differences between them related to some variations in mechanisms of action including serotonin, dopamine and prolactin levels. Little is known about the relevance of sexuality and its dysfunctions in chronic and frequent mental and neurological disorders, such as psychosis, mood disorders, anxiety, phobias, eating disorders, alcohol or drug dependencies, epilepsy and childhood pathology. Poor sexual life, low satisfaction and more frequent risky sex behavior than in the general population are associated with severe mental diseases. There is a need for increasing research in this field, including epidemiological, psychological, neurophysiological, neuroanatomical and genetic variables related to sexual life to get a better understanding of the implicated mechanisms. To increase the sensibility of clinicians, the identification and management of sexual disturbances after the onset of any mental disorder should be highlighted. This would avoid unnecessary suffering and deterioration of quality of life

An Energy-Efficient and Reliable Data Transmission Scheme for Transmitter-based Energy Harvesting Networks

Energy harvesting technology has been studied to overcome a limited power resource problem for a sensor network. This paper proposes a new data transmission period control and reliable data transmission algorithm for energy harvesting based sensor networks. Although previous studies proposed a communication protocol for energy harvesting based sensor networks, it still needs additional discussion. Proposed algorithm control a data transmission period and the number of data transmission dynamically based on environment information. Through this, energy consumption is reduced and transmission reliability is improved. The simulation result shows that the proposed algorithm is more efficient when compared with previous energy harvesting based communication standard, Enocean in terms of transmission success rate and residual energy.This research was supported by Basic Science Research Program through the National Research Foundation by Korea (NRF) funded by the Ministry of Education, Science and Technology(2012R1A1A3012227)