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Aida Cameselle‐Molares Roohollah Sarfaraz Moslem Shahverdi Thomas Keller Anastasios P. Vassilopoulos 《Fatigue & Fracture of Engineering Materials & Structures》2017,40(12):2183-2193
A quasi‐static progressive damage model for prediction of the fracture behaviour and strength of adhesively bonded fibre‐reinforced polymer joints is introduced in this paper. The model is based on the development of a mixed‐mode failure criterion as a function of a master R‐curve derived from the experimental results obtained from standard fracture mechanics joints. Consequently, the developed failure criterion is crack‐length and mode‐mixity dependent, and it takes into account the contribution of the fibre‐bridging effect. Energy release rate values for adhesively bonded double‐lap joints are obtained by using the virtual crack closure technique method in a finite element model, and the numerically obtained strain energy release rate is compared to the critical strain energy release rate given by the mixed‐mode failure criterion. The entire procedure is implemented in a numerical algorithm, which was successfully used for predicting the strength and R‐curve response of adhesively bonded double‐lap structural joints made of pultruded glass fibre‐reinforced polymers and epoxy adhesives. 相似文献
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Dr. Mengjun Xue Prof. Roy A. Black Caitlin E. Cornell Prof. Gary P. Drobny Prof. Sarah L. Keller 《Chembiochem : a European journal of chemical biology》2020,21(19):2764-2767
A major challenge in understanding how biological cells arose on the early Earth is explaining how RNA and membranes originally colocalized. We propose that the building blocks of RNA (nucleobases and ribose) bound to self-assembled prebiotic membranes. We have previously demonstrated that the bases bind to membranes composed of a prebiotic fatty acid, but evidence for the binding of sugars has remained a technical challenge. Here, we used pulsed-field gradient NMR spectroscopy to demonstrate that ribose and other sugars bind to membranes of decanoic acid. Moreover, the binding of some bases is strongly enhanced when they are linked to ribose to form a nucleoside or – with the addition of phosphate – a nucleotide. This enhanced binding could have played a role in the molecular evolution leading to the production of RNA. 相似文献
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Many wind turbine gearboxes require repair or replacement well before reaching the end of their design life. The most common failure is bearing axial cracks, commonly called white etching cracks (WECs), which typically occur in the inner raceways of the high‐speed parallel‐stage rolling element bearings. Although the root causes of WECs are debated, one theory is that they are related to routine dynamic operating conditions and occasional transient events prevalent in wind turbines that can result in high bearing stress and sliding of the rolling elements. This paper examined wind turbine gearbox high‐speed shaft bearing loads and stresses through modeling and full‐scale dynamometer testing. Bearing outer race loads were directly measured and predicted using a variety of modeling tools in normal operations, misaligned conditions, and transient events particularly prone to bearing sliding. Test data and models of bearing loads were well correlated. Neither operational misalignment due to rotor moments nor static generator misalignment affected the bearing loads when compared with pure‐torque conditions. Thus, it is not likely that generator misalignment is a causal factor of WECs. In contrast, during transient events, the bearings experienced alternating periods of high stress, torque reversals, and loads under the minimum requisite at high rotating speeds while showing indications of sliding, all of which could be related to the formation of WECs. 相似文献
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Xing Zhao Xin Wang Zhishen Wu Thomas Keller Anastasios P. Vassilopoulos 《Polymer Composites》2019,40(6):2273-2283
In this study, the temperature effect on the static and tension–tension fatigue behavior of basalt fiber‐reinforced epoxy polymer (BFRP) composites is investigated. The S–N curves, energy dissipation, stiffness degradation, and displacement increment with lifetime under temperatures of −20, 0, 20, 40, and 60°C were derived to evaluate the BFRP fatigue performance under different environmental temperatures. The results showed that the static strength and fatigue life at a certain maximum stress increased with decreasing temperatures. This effect of temperature on the fatigue life was more pronounced at the low cycle fatigue regime. Life differences between the various temperatures became smaller with higher life. While energy dissipation was small for all specimens, the stiffness degradation and permanent displacement increment were sensitive to different temperatures, showing a greater lifetime stiffness loss and permanent displacement increment before failure at lower temperatures. POLYM. COMPOS., 40:2273–2283, 2019. © 2018 Society of Plastics Engineers 相似文献
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Sandra Keller Franziska Tschan Guido Beldi Anita Kurmann Daniel Candinas Norbert K. Semmer 《Ergonomics》2016,59(12):1541-1552
Noise peaks are powerful distractors. This study focuses on the impact of noise peaks on surgical teams’ communication during 109 long abdominal surgeries. We related measured noise peaks during 5-min intervals to the amount of observed communication during the same interval. Results show that noise peaks are associated with less case-relevant communication; this effect is moderated by the level of surgical experience; case-relevant communications decrease under high noise peak conditions among junior, but not among senior surgeons. However, case-irrelevant communication did not decrease under high noise level conditions, rather there was a trend to more case-irrelevant communication under high noise peaks. The results support the hypothesis that noise peaks impair communication because they draw on attentional resources rather than impairing understanding of communication. As case-relevant communication is important for surgical performance, exposure to high noise peaks in the OR should be minimised especially for less experienced surgeons.
Practitioner Summary: This study investigated whether noise during surgeries influenced the communication within surgical teams. During abdominal surgeries, noise levels were measured and communication was observed. Results showed that high noise peaks reduced the frequency of patient-related communication, but did not reduce patient-irrelevant communication. Noise may negatively affect team coordination in surgeries. 相似文献
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In numerous modern stream ciphers, the internal state consists of a large array of pseudo-random words, while the output key-stream is a relatively simple function of the state. It has been heuristically shown in several situations [3], [8], [9], [10], [11] and [14] that this structure may lead to distinguishing attacks on the cipher. In this note we present a more rigorous treatment of this structural attack. First, we present a rigorous proof of the main probabilistic claim behind it in the basic cases. We then apply it concretely to the cipher sn3 [12], and demonstrate that the heuristic assumptions of the attack are remarkably precise in more complicated cases. 相似文献