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"Fatigue (materials)"
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Ultralow-fatigue shape memory alloy films
Functional shape memory alloys need to operate reversibly and repeatedly. Quantitative measures of reversibility include the relative volume change of the participating phases and compatibility matrices for twinning. But no similar argument is known for repeatability. This is especially crucial for many future applications, such as artificial heart valves or elastocaloric cooling, in which more than 10 million transformation cycles will be required. We report on the discovery of an ultralow-fatigue shape memory alloy film system based on TiNiCu that allows at least 10 million transformation cycles. We found that these films contain Ti₂Cu precipitates embedded in the base alloy that serve as sentinels to ensure complete and reproducible transformation in the course of each memory cycle.
Journal Article
Fatigue Testing and Analysis - Theory and Practice
This book is a summary of experimental and analytical techniques that are essential to students and practicing engineers for conducting mechanical component design and testing for durability. There is a serious need for engineers to have an overview on the entire methodology of durability testing and reliability to bridge the gap between fundamental fatigue research and its durability applications.
eBook
On the accuracy of spectral solvers for micromechanics based fatigue modeling
A framework based on FFT is proposed for micromechanical fatigue modeling of polycrystals as alternative to the Finite Element method (FEM). The variational FFT approach (de Geus et al. in Comput Methods Appl Mech Eng 318:412–430,
2017
; Zeman et al. in Int J Numer Methods Eng 110:903–926,
2017
) is used with a crystal plasticity model for the cyclic behavior of the grains that is introduced through a FEM material subroutine, in particular an
Abaqus umat
. The framework also includes an alternative projection operator based on discrete differentiation to improve the microfield fidelity allowing to include second phases. The accuracy and efficiency of the FFT framework for microstructure sensitive fatigue prediction are assessed by comparing with FEM. The macroscopic cyclic response of a polycrystal obtained with both methods were indistinguishable, irrespective of the number of cycles. The microscopic fields presented small differences that decrease when using the discrete projection operator, which indeed allowed simulating accurately microstructures containing very stiff particles. Finally, the maximum differences in the fatigue life estimation from the microfields respect FEM were around 15%. In summary, this framework allows predicting fatigue life with a similar accuracy than using FEM but strongly reducing the computational cost.
Journal Article
Fatigue Testing of Transversely Prestressed Concrete Decks
In the Netherlands, slab-between-girder bridges with prestressed girders and transversely prestressed decks in between the girders require assessment. Static testing showed that compressive membrane action increases the capacity of these structures and that the decks fail in punching shear. The next question is if compressive membrane action also increases the capacity of these decks under repeated loads. Therefore, the same half-scale bridge structure as used for the static tests was subjected to repeated loads at different fractions of the maximum static load, different loading sequences, and for single- and double-concentrated loads. A relationship between the load level and number of cycles at failure (S-N curve) for the assessment of these bridges is proposed, but the influence of the loading sequence was not successfully quantified yet. The conclusion of the experiments is that compressive membrane action enhances the punching capacity of transversely prestressed thin decks subjected to repeated loads. Keywords: bridge evaluation; compressive membrane action; concrete bridges; fatigue; fatigue testing; laboratory testing; prestressed concrete; punching shear.
Journal Article
Aircraft Fuselage Corrosion Detection Using Artificial Intelligence
Corrosion identification and repair is a vital task in aircraft maintenance to ensure continued structural integrity. Regarding fuselage lap joints, typically, visual inspections are followed by non-destructive methodologies, which are time-consuming. The visual inspection of large areas suffers not only from subjectivity but also from the variable probability of corrosion detection, which is aggravated by the multiple layers used in fuselage construction. In this paper, we propose a methodology for automatic image-based corrosion detection of aircraft structures using deep neural networks. For machine learning, we use a dataset that consists of D-Sight Aircraft Inspection System (DAIS) images from different lap joints of Boeing and Airbus aircrafts. We also employ transfer learning to overcome the shortage of aircraft corrosion images. With precision of over 93%, we demonstrate that our approach detects corrosion with a precision comparable to that of trained operators, aiding to reduce the uncertainties related to operator fatigue or inadequate training. Our results indicate that our methodology can support specialists and engineers in corrosion monitoring in the aerospace industry, potentially contributing to the automation of condition-based maintenance protocols.
Journal Article
Compression Fatigue Properties of Pervious Concrete
To promote the application of pervious concrete (PC) in heavy-duty pavement engineering, a thick plate (approximately 50 to 100 cm) paving structure can be used, and its failure form mainly by fatigue compression. Therefore, compressive fatigue tests were carried out under fatigue loads in four stress levels (S): 0.6, 0.7, 0.8, and 0.9, at three loading frequencies of 10, 15, and 20 Hz. The results showed that the fatigue life (N) and fatigue residual strength are controlled by S, while loading frequency showed no statistically significant effect on them. The fatigue failure of PC will not occur under a stress level of 0.6. The survival rate of PC and the fatigue life of uniaxial compression obey a Weibull distribution with two parameters. The material constants of uniaxial compression fatigue of PC are 0.0464 to 0.052, which are similar to ordinary concrete. There are two forms of fatigue failure: one is the shearing along the vertical central axis and the other is shear failure at an angle of 15 to 30 degrees with the vertical central axis. Keywords: fatigue deformation characteristics; fatigue life equation; fatigue properties; fatigue residual strength; loading frequency; pervious concrete (PC).
Journal Article
Punching Capacity of Prestressed Concrete Bridge Decks Under Fatigue
Previous research showed that the capacity of existing slab-between-girder bridges is larger than expected based on the punching shear capacity prescribed by the governing codes, as a result of compressive membrane action. A first series of fatigue tests confirmed that compressive membrane action also acts under cycles of loading. However, a single experiment, in which first a number of cycles with a higher load level and then with a lower load level were applied, seemed to indicate that this loading sequence shortens the fatigue life. This topic was further investigated in a second series of fatigue tests with three static tests and 10 fatigue tests. The parameters that were varied were the sequence of loading and the effect of a single or a double wheel print. The results show that the sequence of load levels does not influence the fatigue life. Keywords: bridge evaluation; compressive membrane action; concrete bridges; fatigue; fatigue testing; laboratory testing; prestressed concrete; punching shear.
Journal Article
Fatigue Resistance of Steel Fiber-Reinforced Concrete Deep Beams
An investigation of the fatigue resistance of small-scale steel fiber-reinforced concrete deep beams with steel fiber-volume ratios of 0, 0.75, and 1.5% is reported. The behavior of steel fibers in enhancing the fatigue life of deep beams and reducing the congestion of reinforcement in concrete is studied, and the possibility of obtaining optimized structural sections that are cost-effective using steel fiber-reinforced concrete is verified. Evolutions and inclinations of average principal strains and bond strength between concrete and steel reinforcing bars within the shear spans were also observed. The use of steel fibers, especially with a volume ratio of 1.5%, was observed to reduce the progressive strain values in concrete and steel reinforcing bars, hence resulting in enhanced fatigue life. No significant evolution profile was observed for the inclination of the principal directions, while the use of adequate anchorage preserved the bond strength between concrete and steel reinforcement. In all specimens, fracture of the longitudinal reinforcing bars occurred at failure, and fiber pullout was more prevalent than fiber breakage. Keywords: deep beam; fatigue; steel fiber; strain evolution; strength; wind turbine foundations.
Journal Article