The study of palm‐oil‐based bio‐polyol on the morphological,acoustic and mechanical properties of flexible polyurethane foams

The focus of this paper was to explore the acoustic properties of flexible polyurethane (FPU) foam modified by palm‐oil‐based polyol (POP). The presence of POP showed a marked influence on the microstructure and mechanical properties of FPU foam. A smaller mean pore diameter can be observed at lower POP content. Indeed, the introduction of POP caused a higher closed pore ratio and an increased air‐flow resistivity, which consequently improved the sound absorption coefficient and transmission loss. In particular, the acoustic performance of the all bio‐based FPU foam was enhanced at low frequency, and the density was lower than that of the reference foam. Additionally, the addition of POP also improved the compressive strength. Conversely, the tensile strength of FPU foam declined with increasing POP content. From this study, the outstanding acoustic ability of bio‐based FPU foam has been proved, with additional advantages of lower density and higher compressive strength. © 2019 Society of Chemical Industry     

运载火箭管道微泄漏声发射检测仪

目前,传统的运载火箭总对接管路系统气密性检测方法为皂泡法,该方法在检测过程中存在耗时长、容易发生误判和漏判问题。为解决传统皂泡法的缺陷问题,进行了便携式气密性检测声发射检测仪的研究。首先进行检测设备各个部件的设计与选型,然后对火箭管道进行了检漏试验,进一步分析了泄漏信号的时域和频域特征,最后确定了通过拟合频率段包络面积来判别泄漏等级的算法。结果表明,通过设计、开发和测试验证的手持式声发射检测仪新设备,能够对火箭管道的泄漏等级进行更加高效、精准的评估。     

岩石破坏声发射与裂纹尺度增长试验研究

选取内蒙古哈不沁铁矿花岗岩为试验对象,进行了岩石单轴压缩声发射试验,研究采用声发射参量预测岩石破坏裂纹尺度增长的可行性。花岗岩的全应力-应变曲线和声发射各参量曲线分析结果表明,应变的逐渐增加加快了岩石内部聚集的弹性变形能的释放,随着弹性变形能的释放,声发射的幅度、振铃计数、能量等越来越频繁地跳跃,当进入岩石破坏阶段时,声发射参量呈现突发性增长。对比分析了在声发射参量下预测裂纹尺度与实测裂纹尺度的相关性,结果表明,径向破坏裂纹尺度是轴向位移的2倍,且预测值与实测值非常吻合,预测的裂纹尺度能够反映岩石的损伤破裂过程,也能够描述岩石应变的发展过程。     

Installation and commissioning of a cryogen distribution system for the TPS project

A cryogen distribution system was installed and commissioned to transfer liquid nitrogen (LN₂) and liquid helium (LHe) from storage dewars to superconducting radio-frequency (SRF) cavities for the 3-GeV Taiwan Photon Source (TPS) project. The cryogen distribution system comprises one distribution valve box (DVB), four control valve boxes (CVB) and seven sections of multichannel transfer line (MCL). The DVB distributes the LHe and LN₂ to the CVB, and then to the SRF cavities through independent vacuum-jacketed transfer lines. The vaporized GHe and GN₂ from the cryomodules are collected via the MCL. The cryogen distribution system was installed and commissioned from October 2014 to the end of March 2015. This paper presents the installation, pre-commissioning and commissioning of the cryogen distribution system, and describes the heat load test. Thermal acoustic oscillation (TAO) was found in the GHe process line; this phenomenon and its solution are also presented and discussed.     

Measurement of vertical and horizontal vibrations of a probe for acoustic evaluation of food texture

Two‐dimensional (vertical and horizontal) vibrations of a wedge‐type probe upon food rupture were evaluated separately using two accelerometers placed perpendicular to a guide rod of a swing‐arm device for texture evaluation of the flesh of three varieties of apples and three types of potato chips. Voltage signals from the accelerometers were filtered using a half‐octave band‐pass filter. The energy texture index (ETI), based on kinetic energy of the vertical or horizontal probe vibrations, was calculated over low to high frequency bands (no. 1–21). The spectra for the flesh of the three varieties of apples included two common peaks for vertical ETI at band no. 11 (1,120–1,600 Hz) and 19 (17,920–25,600 Hz) and horizontal ETI at band no. 1 (0–10 Hz) and 15 (4,480–6,400 Hz). The spectra for the three types of potato chips had a common ETI peak at band no. 11 (1,120–1,600 Hz) for horizontal ETI and at no. 15 (4,480–6,400 Hz) for vertical ETI. The three apple varieties gave rise to different intensities of vertical and horizontal ETIs while the two peaks were maintained. The thick potato chip type had higher vertical and horizontal ETIs than the thin and soft varieties in most bands; however, the thin type had the highest vertical ETIs only in lower bands (0–200 Hz). The soft type had the lowest vertical and horizontal ETI. The above results suggest that different food textures can be distinguished by two‐dimensional vibration analyses of probe insertion into a food sample based on frequency bands.     

Optical fiber distributed acoustic sensing based on the self-interference of Rayleigh backscattering

In order to detect the weak underwater acoustic signal, a Distributed Acoustic Sensing (DAS) scheme based on the self-interference of Rayleigh backscattering is presented. Rayleigh backscattered light which contains a phase change induced by acoustic signal along the sensing fiber which is a standard telecom single-mode fiber is split and fed into an imbalance Michelson interferometer. With the self-interference of two Rayleigh backscattered beams, the phase change is amplified theoretically compared with phase-sensitive OTDR. We designed an experiment to prove the scheme, and successfully restored the acoustic information, meanwhile, the DAS system has preliminary realized around the acoustic phase sensitivity of −151 dB (re rad/μPa) at 600 Hz, and the minimum detectable acoustic pressure of 6 Pa in the experiment.     

Acoustic emission characterization of steel in H2S solution subjected to tensile load

Abstract

This paper investigates the characteristics of acoustic emission (AE) signals generated from hydrogen induced cracking (HIC) and sulfide stress corrosion cracking (SSCC) for a medium strength steel in hydrogen sulfide (H₂S) solution. The experiments performed in this study include the constant load test (CLT) and the constant extension rate test (CERT).

From the results of the CLT, the AE count rate caused by SSCC was found to be much higher than that resulted from the HIC; and the increase of the AE count rate was observed to be approximately proportional to the increase of the applied loading. In addition, the AE frequency distribution diagrams obtained from these tests were found to contain potential information for distinguishing the mechanisms of HIC and SSCC. From the results of CERT, the AE signals detected from the specimens tested in the H₂S solution were compared with those obtained from the specimens tested in the air. In addition, the AE count rate detected from the tensile specimens was studied according to the different deformation stages of the specimens. From this study, the variation of the AE count rate in each deformation stage was described.     

Biomechanics of fibrous proteins of the extracellular matrix studied by Brillouin scattering

Brillouin light scattering (BLS) spectroscopy is a technique that is able to detect thermally excited phonons within a material. The speed of propagation of these phonons can be determined from the magnitude of the Brillouin frequency shift between incident and scattered light, thereby providing a measure of the mechanical properties of the material in the gigahertz range. The mechanical properties of the extracellular matrices of biological tissues and their constituent biopolymers are important for normal tissue function and disturbances in these properties are widely implicated in disease. BLS offers the prospect of measuring mechanical properties on a microscopic scale in living tissues, thereby providing insights into structure–function relationships under normal and pathological conditions. In this study, we investigated BLS in collagen and elastin—the fibrous proteins of the extracellular matrix (ECM). Measurements were made on type I collagen in rat tail tendon, type II collagen in articular cartilage and nuchal ligament elastin. The dependence of the BLS spectrum on fibre orientation was investigated in a backscattering geometry using a reflective substrate. Two peaks, a bulk mode arising from phonon propagation along a quasi-radial direction to the fibre axis and a mode parallel to the surface, depending on sample orientation relative to the fibre axis, could be distinguished. The latter peak was fitted to a model of wave propagation through a hexagonally symmetric elastic solid, and the five components of the elasticity tensor were combined to give axial and transverse Young''s, shear and bulk moduli of the fibres. These were 10.2, 8.3, 3.2 and 10.9 GPa, and 6.1, 5.3, 1.9 and 8 GPa for dehydrated type I collagen and elastin, respectively. The former values are close to those previously reported. A microfocused BLS approach was also applied providing selection of single fibres. The moduli of collagen and elastin are much higher than those measured at lower frequency using macroscopic strains, and the difference between them is much less. We therefore believe, like previous investigators, that molecular-scale viscoelastic effects are responsible for the frequency dependence of the fibre biomechanics. Combining BLS with larger-scale mechanical testing methods therefore should, in the future, provide a means of following the evolution of mechanical properties in the formation of the complex structures found in the ECM.