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Advanced transducer materials have become increasingly important with the rapid development of the internet of things and flexible electronics. Herein, fully transparent flexible polyvinylidene fluoride/polydimethylsiloxane (PVDF/PDMS) composite piezoelectric films are fabricated using scrape coating techniques based on electrospun PVDF nanofiber films. Compared to the electrospun PVDF, the PVDF/PDMS not only owns high transparency and a more uniform and stable structure but also has superior piezoelectric properties. Based on the electrospun PVDF and the PVDF/PDMS films, flexible piezoelectric sensors are developed, which can effectively detect weak mechanical signals including finger tapping and bending signals, radial artery pulses, and environmental sound signals. The PVDF/PDMS sensor performs better than the electrospun PVDF sensor and presents great potential for applications in flexible sensors and transducers. Especially, thanks to their high transparency, the PVDF/PDMS composite piezoelectric films lend themselves easily to application fields requiring transparent sensors such as imperceptible sensors and human‐machine interfaces, display devices, electronic skins, intelligent windows, etc. [ABSTRACT FROM AUTHOR]

It is known that fine granular area morphology is often formed around interior micro‐defect in the case of very high cycle fatigue failure of high strength steel. The mechanism of "fragmentation of martensitic laths and formation of dislocation cells" (Zhu's model), which revealed a microstructure‐dependent crack initiation and early growth for micro‐defect induced internal fatigue cracking, was discussed in several lathy martensitic or similar steels, verified under environmental fatigue, and applicable to white etching crack in rotating contact fatigue. A machine learning‐Z parameter integrated approach was developed for fatigue life, which is promising for design against fatigue of engineering structures for long life. Highlights: The FGA model of martensitic steels in air (Zhu's model) was illustrated.Zhu's model was confirmed in environmental media and similar steels.Zhu's model was applicable to white etching crack in rotating contact fatigue.Machine learning‐Z parameter was integrated for fatigue life prediction. [ABSTRACT FROM AUTHOR]

Finite element analyses on notched beams and axis‐symmetric pipes of power‐law creep materials subjected to combined primary and secondary loads are performed in this work. In view of the characteristics of time‐dependent strain energy density at notches under combined loads, a time‐dependent stress and strain estimation method to address the primary and secondary loads has been proposed by considering the stress ratio between the reference stress devoted by primary stress and the total reference stress. The applicability of the modified method to notched components with different geometrical configurations and load conditions is discussed. Good agreement between the results of inelastic analysis and the modified method is observed. [ABSTRACT FROM AUTHOR]

The nanomaterial effect on the interfacial properties between glass, carbon, and their 1:1 hybrid fiber‐bundle reinforced epoxy resin is evaluated based on fiber‐bundle pull‐out tests. Graphene and multi‐walled carbon nanotubes (MWCNT) are incorporated in the interfacial region. Three contents of nanomaterials that including 0.1, 0.3, and 0.5 wt% are considered, and the temperatures are set as 25 and 150°C during the pull‐out tests, respectively. The interfacial shear strength (IFSS) of graphene and MWCNT filled interfaces is compared. Results indicate that both the two nanomaterials can improve the IFSS and shear toughness effectively. The IFSS of 0.3 wt% MWCNT filled glass‐carbon/epoxy hybrid specimens is increased by 82% at 150°C, which is the largest among all the specimens. According to scanning electron microscope (SEM) morphologies of fiber surfaces, the IFSS improvements are ascribed to the efficient stress transfer by the enhanced bonding performance after filling nanomaterials in the interphase. POLYM. COMPOS., 39:E2370–E2380, 2018. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

ABSTRACT: The overall mechanical performance of glass–carbon hybrid fibers reinforced epoxy composites depends heavily upon fiber–matrix interfacial properties and the service temperatures. Fiber‐bundle pull‐out tests of glass (GF) and/or carbon fiber (CF) reinforced epoxy composites were carried out at room and elevated temperatures. Graphene nanoplatelets were added in the interfacial region to investigate their influence on the interfacial shear strength (IFSS). Results show that IFSS of specimens with fiber‐bundle number ratio of GF:CF = 1:2 is the largest among the hybrid composites, and a positive hybridization effect is found at elevated temperatures. IFSS of all the specimens decreases with the increasing of test temperatures, while the toughness shows a contrary tendency. As verified by scanning electron microscopy observations, graphene nanoplatelets on fiber surface could enhance the IFSS of pure glass/carbon and hybrid fibers reinforced epoxy composites at higher temperatures significantly. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46263. [ABSTRACT FROM AUTHOR]

Lamb waves provide sensitive and effective approach for nondestructive inspection of large‐scale composite structures. Traditionally in Lamb wave‐based damage detection systems, the piezoelectric (PZT) wafer transducers are attached on the surface of composite components. However, surface‐bonded PZT wafers are fragile, and they may lose serviceability when external load happens. In this paper, numerical and theoretical investigations are firstly carried out to analyze the Lamb wave features generated by PZT wafers that are located in the mid‐thickness of a thin‐walled plate. Subsequently, the authors integrate the PZT wafer arrays in woven glass fiber reinforced epoxy (WGF/epoxy) laminates with stacking sequence of [90°/0°]4. It is found that the approximate single S0 Lamb wave mode is generated by the built‐in PZT wafers. This makes the received signals very simple and easy to be interpreted. Utilizing the signals obtained by the built‐in and surface‐bonded PZT wafer transmitter‐receiver arrays, damage localization algorithms that considered the slowness profiles are compiled to help locating the defects. The compared results demonstrate that the built‐in PZT strategy has great potential for quantitative non‐destructive evaluation of composite structures. This paper presents a built‐in PZT wafer methodology to generate S0 mode dominant Lamb wave in WGF/epoxy composites. Symmetrical dominant waves are generated by the built‐in PZT method. In both the enhanced ellipse and probabilistic imaging algorithms, the damage localization errors are limited and are kept within the range of ±10%. The built‐in PZT method has higher damage detection sensitivity. [ABSTRACT FROM AUTHOR]

The long‐term durability of polymer composites serviced under moist, high‐temperature conditions is a major concern in many industries. As an attempt, we filled 0.3 wt % graphene in a fiber–matrix interfacial region between glass fibers, carbon fibers, glass–carbon hybrid fibers, and epoxy resin to enhance the mechanical performance of the composites under water‐immersion conditions. The mass increment was recorded periodically while the specimens were immersed in 25 and 70°C water. Axial compression tests were carried out to investigate the initiation behavior of the interfacial radial microcracks after immersion. The results show that the equilibrium moisture content and permeability of the graphene‐filled interfaces were larger than that of the virgin specimens. The interfacial radial crack initial stress decreased sharply after immersion; however, the addition of graphene in the fiber–matrix interface help to decrease this tendency in 70°C water. The observed rough surfaces of the graphene‐coated fibers after breakage in the compression tests verified the feasibility of this method. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47080. [ABSTRACT FROM AUTHOR]