Shear mechanical properties and fracturing responses of layered rough jointed rock-like materials

This study aims to investigate mechanical properties and failure mechanisms of layered rock with rough joint surfaces under direct shear loading.Cubic layered samples with dimensions of 100 mm×100 mm×100 mm were casted using rock-like materials,with anisotropic angle(α)and joint roughness coefficient(JRC)ranging from 15°to 75°and 2-20,respectively.The direct shear tests were conducted under the application of initial normal stress(σ_(n)) ranging from 1-4 MPa.The test results indicate significant differences in mechanical properties,acoustic emission(AE)responses,maximum principal strain fields,and ultimate failure modes of layered samples under different test conditions.The peak stress increases with the increasingαand achieves a maximum value atα=60°or 75°.As σ_(n) increases,the peak stress shows an increasing trend,with correlation coefficients R² ranging from 0.918 to 0.995 for the linear least squares fitting.As JRC increases from 2-4 to 18-20,the cohesion increases by 86.32%whenα=15°,while the cohesion decreases by 27.93%whenα=75°.The differences in roughness characteristics of shear failure surface induced byαresult in anisotropic post-peak AE responses,which is characterized by active AE signals whenαis small and quiet AE signals for a largeα.For a given JRC=6-8 andσ_(n)=1 MPa,asαincreases,the accumulative AE counts increase by 224.31%(αincreased from 15°to 60°),and then decrease by 14.68%(αincreased from 60°to 75°).The shear failure surface is formed along the weak interlayer whenα=15°and penetrates the layered matrix whenα=60°.Whenα=15°,as σ_(n) increases,the adjacent weak interlayer induces a change in the direction of tensile cracks propagation,resulting in a stepped pattern of cracks distribution.The increase in JRC intensifies roughness characteristics of shear failure surface for a smallα,however,it is not pronounced for a largeα.The findings will contribute to a better understanding of the mechanical responses and failure mechanisms of the layered rocks subjected to shear loads.

Acoustical properties of a 3D printed honeycomb structure filled with nanofillers:Experimental analysis and optimization for emerging applications

The novelty of this research lies in the successful fabrication of a 3D-printed honeycomb structure filled with nanofillers for acoustic properties,utilizing an impedance tube setup in accordance with ASTM standard E 1050-12.The Creality Ender-3,a 3D printer,was used for printing the honeycomb structures,and polylactic acid(PLA)material was employed for their construction.The organic,inorganic,and polymeric compounds within the composites were identified using fourier transformation infrared(FTIR)spectroscopy.The structure and homogeneity of the samples were examined using a field emission scanning electron microscope(FESEM).To determine the sound absorption coefficient of the 3D printed honeycomb structure,numerous samples were systematically developed using central composite design(CCD)and analysed using response surface methodology(RSM).The RSM mathematical model was established to predict the optimum values of each factor and noise reduction coefficient(NRC).The optimum values for an NRC of 0.377 were found to be 1.116 wt% carbon black,1.025 wt% aluminium powder,and 3.151 mm distance between parallel edges.Overall,the results demonstrate that a 3Dprinted honeycomb structure filled with nanofillers is an excellent material that can be utilized in various fields,including defence and aviation,where lightweight and acoustic properties are of great importance.

Acoustic Response and Micro-Damage Mechanism of Fiber Composite Materials under Mode-Ⅱ Delamination

Realizing the accurate characterization for the dynamic damage process is a great challenge. Here we carry out testing simultaneously for dynamic monitoring and acoustic emission （AE） statistical analysis towards fiber composites under mode-Ⅱ delamination damage. The load curve, AE relative energy, amplitude distribution, and amplitude spectrum are obtained and the delamination damage mechanism of the composites is investigated by the microscopic observation of a fractured specimen. The results show that the micro-damage accumulation around the crack tip region has a great effect on the evolutionary process of delamination. AE characteristics and amplitude spectrum represent the damage and the physical mechanism originating from the hierarchical microstructure. Our finding provides a novel aud feasible strategy to simultaneously evaluate the dynamic response and micro-damage mechanism for fiber composites.

Confined aquifer as wave-guide and its responses to geo-acoustic waves

On the basis of the hydro geological model of a confined aquifer, the propagation mechanism of geo acoustic waves along the confined aquifer outlined as a plate wave guide is proposed. The harmonic frequency equation for geo acoustic propagation along confined aquifer as waveguide is derived from Biot theory. The basic frequency of the confined aquifer with a deep well for geo acoustic observation, located at Juxian county, Shandong province, China, is 35.0 Hz. By Wigner distribution of geo acoustic signals observed at Juxian geo acoustic well, the frequencies of geo acoustics are basically the integral multiple of the basic frequency. The results show that the responses of the confined aquifer to geo acoustic waves are characterized by frequency selection and frequency dependence. Only the waves whose frequency f is the integral multiple of basic frequency can propagate as guide waves in the aquifer, that is , the aquifer responds to the waves.

Prepulse inhibition (PPI) of tactile startle response in recombinant congenic strains of mice:QTL mapping and comparison with acoustic PPI

Prepulse inhibition （PPI） of the startle response is a psychophysiological measure of sensorimotor gating believed to be cross-modal between different sensory systems. We analyzed the tactile startle response （TSR） and PPI of TSR （tPPI）, using light as a prepulse stimulus, in the mouse strains A/J and C57BL/6J and 36 recombinant congenic strains derived from them. Parental strains were significantly different for TSR, but were comparable for tPPI. Among the congenic strains, variation for TSR was significant in both genetic backgrounds, but that of tPPI was significant only for the C57BL/6J background. Provisional mapping for loci modulating TSR and tPPI was carried out. Using mapping data from our previous study on acoustic startle responses （ASR） and PPI of ASR （aPPI）, no common markers for aPPI and tPPI were identified. However, some markers were significantly associated with both ASR and TSR, at least in one genetic background. These results indicate cross-modal genetic regulation for the startle response but not for PPI, in these mouse strains.

Acoustic logging response law in shales based on petrophysical model

Shale acoustic logging response law is complex due to the multiple minerals and pores,which limits the application of acoustic logging in shale reservoir parameter evaluation,therefore clarifying the shale acoustic logging response law is of great importance.Different petrophysical models are adopted for the equivalence of organic matter,clay,matrix minerals,and fractures,in Wufeng-Longmaxi shale formation in the Jiaoshiba area.Finally,the self-consistent approximation model is used to combine different components,and a shale petrophysical model with a complex pore structure is constructed.The model verification results show it has good predictability for shale.Based on the model,the effect of different mineral compositions and different types of pores are studied.The results show that:1)The effect of clay and organic matter is very complex,and the variation laws of layered clay(organic matter)and dispersed clay(organic matter)on the acoustic wave are consistent.2)Layered clay or organic matter leads to the formation anisotropy increase,which makes the acoustic time difference greater than that of containing dispersed clay(organic matter).3)The fracture is the main control factor of anisotropy,and the anisotropy of gas-bearing fracture is higher than that of water/oil fracture.

2 kHz High Power Smart Transducer for Acoustic Sub-bottom Profiling Applications

In this study,a 2kHz Tonpilz projector was designed using a Terfenol-D and modeled in ATILA.For the purpose of modeling studies,it has been determined that a radiating head mass exhibits better transmitting current response（TCR） at 136 mm diameter,where the resonance occurs at 2.4kHz and the peak value of 118 dB re 1 μPa/A at 1 m occurs at 12 kHz.Also bolt at a 46mm distance from the center of the head mass offers resonance at 2.4kHz,and the peak value of 115.3 dB re 1 μPa/A at 1m occurs at 11.5kHz.This optimized design is fabricated and molded with polyurethane of 3mm thickness.The prototype was tested at the Acoustic Test Facility（ATF） of National Institute of Ocean Technology（NIOT） for its underwater performances.Based on the result,the fundamental resonance was determined to be 2.18kHz and the peak value of TCR of 182 dB re 1 μPa/A at 1m occurs at 14 kHz.The maximum value of the RS was found to be -190 dB re 1V/μPa at 1m at a frequency of 2.1kHz.

Experimental Research on the Load/Unload Response Ratio (LURR) Theory

Implementing acoustic emission experiments with large rock samples, LURR (Load/Unload Response Ratio) theory was studied. The loading conditions in the experiments were designed to simulate the complicated loading process of underground rocks. The damages emerging inside the rock samples were recorded by the acoustic emission technique during the loading process. The experimental results were consistent with prediction by LURR theory. Integrating the changing processes of LURR value Y and the location process of acoustic emission events showed agreement between the variation of LURR value Y and the damage evolution inside the rocks. Furthermore, the high value of Y emerged before the complete breakdown of materials. Therefore, the damage evolution of rock specimen can be quantitatively analyzed with LURR theory, thus the failure of the rock materials and the earthquake occurrence may be predicted. The experimental results gave a further verification of LURR theory.

Risk of Hearing Loss Caused by Multiple Acoustic Impulses in the Framework of Biovariability

We consider the hearing loss injury among subjects in a crowd with a wide spectrum of individual intrinsic injury probabilities due to biovariability. For multiple acoustic impulses, the observed injury risk of a crowd vs the effective combined dose follows the logistic dose-response relation. The injury risk of a crowd is the average fraction of injured. The injury risk was measured in experiments as follows: each subject is individually exposed to a sequence of acoustic impulses of a given intensity and the injury is recorded;results of multiple individual subjects were assembled into data sets to mimic the response of a crowd. The effective combined dose was adjusted by varying the number of impulses in the sequence. The most prominent feature observed in experiments is that the injury risk of the crowd caused by multiple impulses is significantly less than the value predicted based on assumption that all impulses act independently in causing injury and all subjects in the crowd are statistically identical. Previously, in the case where all subjects are statistically identical (i.e., no biovariability), we interpreted the observed injury risk caused by multiple impulses in terms of the immunity effects of preceding impulses on subsequent impulses. In this study, we focus on the case where all sound exposure events act independently in causing injury regardless of whether one is preceded by another (i.e., no immunity effect). Instead, we explore the possibility of interpreting the observed logistic dose-response relation in the framework of biovariability of the crowd. Here biovariability means that subjects in the crowd have their own individual injury probabilities. That is, some subjects are biologically less or more susceptible to hearing loss injury than others. We derive analytically the distribution of individual injury probability that produces the observed logistic dose-response relation. For several parameter values, we prove that the derived distribution is mathematically a proper density function. We further study the asymptotic approximations for the density function and discuss their significance in practical numerical computation with finite precision arithmetic. Our mathematical analysis implies that the observed logistic dose-response relation can be theoretically explained in the framework of biovariability in the absence of immunity effect.

Study and simulation on the characteristics of drill string channel for acoustic waves

Traditional wireless MWD telemetry systems such as mud pulse and electromagnetic telemetry are limited due to low carrier frequencies. The first acoustic telemetry system was studied as part of a drill stem testing system in 2000, but there are some problems limited it to using for information transmission in drilling. In the paper, we study and simulation on the drill string channel characteristics. Based on the transmission equation of longitudinal wave in periodic drill string channel, we get a geometrical model for drill string channel. Two aspects are studied. Firstly, the equation for dispersion is established analyze and simulate the influence of length and cross-section to dispersion. Secondly, we introduce finite-difference for analyzing of transient response. Simulate transient response of drill string channel by changing the geometrical-characters of drill string. The paper gets characteristics of channel dispersion and signal attenuation, and useful for the choosing of best passband for carrier frequency. It is valuable for the acoustic telemetry to use for drilling applications.

飞行器结构热声疲劳问题研究进展

高超声速飞行器表面结构,如发动机叶片、内涵道及其排气道等暴露在高温强噪声复合环境中,容易出现热声疲劳损伤问题,因此,结构热声疲劳问题引起了广泛关注。热声疲劳研究对增强这类结构的耐久性和可靠性具有重要意义。本文总结了国内外在飞行器结构热声疲劳领域的研究现状,阐述了在热声疲劳理论研究、仿真分析和试验技术方面所取得的进步。从时间维度回顾了国外自20世纪70年代至今在结构热声疲劳领域的研究情况;按研究单位分类介绍了国内科研院所和高等院校在该领域所开展的工作。在此基础上分析了飞行器结构热声疲劳研究所面临的技术难点问题,指出了尚需进一步研究的方向。

不同注液速率水力压裂多裂缝扩展规律研究

为了分析影响水力压裂效果的射孔参数,采用TCHFSM-I型大尺寸真三轴压裂渗流模拟装置,并配合声发射监测系统和高温-高压动态流量计,以均质水泥砂浆试件为研究对象,对不同注液速率下水力压裂多裂缝同步扩展规律进行研究。研究结果表明:随注液速率增大,射孔裂缝长度和宽度不同程度增加,缝间干扰程度减弱,应力阴影效应减小,射孔间距较大时裂缝扩展更加均衡,压裂效果更佳;随注液速率增大,射孔水力压裂裂缝起裂压力增大,起裂时间变短,受射孔间距影响较小;不同注液速率条件下各射孔注液流量分配差异显著,且受射孔间距影响明显,射孔间距为20 mm和60 mm时,中部射孔注液流量占比分别为7.31%、10.88%、16.12%和31.12%、32.69%、33.44%。

损伤岩石声发射演化特征及响应机制试验研究

岩石内部损伤演化是导致岩土工程灾害的原因之一,揭示岩石破裂过程中的关键参数响应特征可为岩石破坏后失稳状态识别提供依据,对于岩体工程灾害预警防控至关重要。通过循环加载-卸载(加卸载)试验制备不同损伤程度粉砂岩试样,利用损伤试样开展单轴加载试验,分析试样损伤程度与波速关系及声发射演化规律,探讨不同损伤程度岩石的声发射响应机制。结果表明:(1)损伤试样纵波波速随着损伤程度增加呈线性减小趋势,但声发射振铃计数由阶段性递增转变为加载全过程迅速增加,声发射能量在屈服阶段由小幅度突增转变为快速增加。(2)反映岩石内部不同尺度裂隙发展趋势的声发射b值峰值区由峰后破坏阶段向压密阶段转移,造成峰后破坏阶段失稳特征不明显,反映岩体内部声发射源集中程度和能量尺度的S值在压密至屈服阶段由低位中幅度波动转变为高位小幅度波动,表明岩石在峰前阶段产生非稳定破坏。(3)损伤试样破裂过程随着损伤程度增加由晶间滑移主导型转变为裂隙发育主导型,导致声发射高频低能(400~800 kHz、0~250 aJ)信号由零星出现转变为加载全过程密集分布,以及高频信号带变宽。(4)损伤岩石内部裂隙发育程度不同是导致声发射响应机制差异化的根本原因,岩石内部裂隙密度随着损伤程度增加而增大,造成其在受载过程中由渐进式稳定破坏模式向突发式非稳定破坏模式转变,同时加载过程中声发射信号活跃度及强度增强。研究获得了不同损伤程度岩石的声发射参数特征,可为工程岩体损伤程度识别提供理论依据。

秀丽隐杆线虫对声表面波刺激的行为响应

利用频率为8.8 MHz的声表面波,刺激位于压电基底上琼脂表面秀丽隐杆线虫,研究其对超声作用的行为响应。具体地,分析了超声刺激后线虫的转向和后退行为与声表面波辐照时长、基底振动幅度及脉冲重复频率的关系,发现线虫对高频声表面波脉冲刺激的响应与此前低频体波刺激所得规律一致,即类似于可感知脉冲重复频率的带通滤波器。通过比较温度感知缺陷突变体线虫与野生型线虫的行为,明确了机械振动在诱发线虫响应中占据主导地位,而超声热效应并非主要因素。在此基础上,尝试通过信号时-空分布的调节改变声场形态,研究线虫在声场中的趋避性,进而实现对线虫转向行为的初步干预。

平均听阈正常的听神经瘤患者临床及听力学特征分析

目的 分析平均听阈正常(PTA≤25 dB HL)的单侧听神经瘤患者的临床特征及听力学特征,为听神经瘤早期筛查及诊断提供参考。方法 选取平均听阈正常的单侧听神经瘤患者32例(32耳)作为试验组,选取与年龄、性别相匹配的平均听阈正常的耳鸣患者20例(32耳)作为对照组,试验组和对照组均在符合国家标准的隔声室行纯音测听、声导抗、听性脑干反应、畸变产物耳声发射检查,回顾性分析两组临床及听力学特征。结果 单纯耳鸣、耳鸣伴反复发作且可治愈的突发性听力下降为平均听阈正常听神经瘤患者常见的首发症状,占50.00%,多见于30~40岁人群。试验组听性脑干反应异常率为75.00%(24/32),畸变产物耳声反射异常率为78.12%(25/32),患耳的同侧镫骨肌声反射和健耳的交叉声反射异常率分别为28.13%、56.25%,健耳的同侧镫骨肌声反射和患耳的交叉声反射异常率分别为6.25%、62.50%。通过对比分析试验组和对照组听力学特征,两组听性脑干反应的波Ⅲ、波Ⅴ潜伏期、波Ⅰ-波Ⅲ波间期、波Ⅰ-波Ⅴ波间期,患耳的交叉声反射和健耳的交叉声反射(0.5、1、2、4 kHz)、患耳的同侧声反射(2 kHz),均存在统计学差异(P<0.05),两组间畸变产物耳声反射异常率未见统计学差异(P>0.05)。结论 听性脑干反应及镫骨肌声反射检测有助于听神经瘤早期诊断,DPOAE是敏感性高但特异性差的检测指标。对门诊平均听阈正常的单侧耳鸣,或伴有反复发作的、可治愈的突发性听力下降患者,建议联合应用听性脑干反应、镫骨肌声反射、畸变产物耳声发射综合评估,为听神经瘤的早期诊断提供依据。

基于信号重采样频移处理的宽带ADCP分层校准方法

针对宽带声学多普勒流速剖面仪(ADCP)现有校准方法无法有效实现流速分层校准的问题,提出基于信号重采样频移处理的声波应答校准方法,通过应答换能器组分别接收ADCP各波束换能器发射信号,经分段重采样、时间窗补偿等处理,产生包含多普勒频移信息的模拟回波信号,实现对宽带ADCP流速分层校准。为更符合真实水体散射情况,基于主动声呐方程建立了回波信号幅度计算模型。搭建了可适用于陆上和水下的宽带ADCP分层快速校准装置,对两个ADCP样机开展了校准实验,流速范围在0.01~10 m/s,测量不确定度优于0.3%v+5 mm/s(v为流速测量值)(k=2),并与水槽拖车法进行了对比验证。

不同水下爆炸参数下双层加筋圆柱壳结构响应研究

本文采用声固耦合方法模拟水下中远场爆炸产生的冲击波载荷和气泡脉动对双层加筋圆柱壳的冲击响应。从不同工况水下爆炸载荷下的鞭状运动和关键部位冲击响应2个方面,研究了药量、爆距、水深、爆炸方位等参数对双层加筋圆柱壳结构响应的影响。研究表明,在中远场水下爆炸作用下,双层加筋圆柱壳在不同药量和爆距下鞭状运动的位移响应幅值和冲击环境谱加速度幅值变化较大,但其鞭状运动的位移响应曲线的周期变化不大。双层加筋圆柱壳在不同水深下,鞭状运动受到水下载荷周期性影响显著,但谱加速度幅值变化不大。双层加筋圆柱壳在不同爆炸方位下鞭状运动变化和冲击环境谱加速度分布受其影响显著。这项研究旨在为水下中远场爆炸作用下,水下航行体结构的抗冲击特性研究提供数据及理论支撑。

砂土含水率对DAS振幅响应影响的试验研究

利用分布式声波传感(DAS)技术和地下通讯光纤网进行周界安防(入侵)监控、管道泄漏监测、交通状况评估等是城市安全动态监测的新方向。为探究DAS监测过程中暗光纤周围岩土介质含水率变化对DAS振幅响应特性的影响,设计了小球撞击圆盘与小球直接撞击砂土面二种激振方式下五种质量含水率0%、5%、10%、15%和20%砂土的DAS振幅响应试验。试验结果表明:(1)小球自由下落撞击砂土面激发的振动信号和传感光纤圆环布设可提高DAS信噪比,试验装置可靠性高、试验结果重复性好;(2)受砂土似黏聚力和声波传播衰减两个因素共同影响,DAS信号振幅随砂土含水率变化存在一个临界含水率。当砂土含水率小于临界含水率时,DAS信号振幅随含水率增大而减小,而当砂土含水率大于临界含水率时,DAS信号振幅随含水率增大而增大;(3)因砂土似黏聚力作用和小球撞击时能量转化的差异,小球与砂土的接触形式对DAS振幅响应有显著影响。研究结果为城市地下工程安全动态DAS精细监测提供理论依据。

掘进工作面煤岩动力灾害声电响应特征

为了监测、预警掘进过程中前方可能发生的危险,在掘进工作面布设声电监测预警系统,利用声发射技术和电磁辐射技术对掘进巷道进行动态实时监测和预警,通过对掘进过程中异常声电响应特征的研究得到突出危险发生的前兆规律特征,并根据现场实际情况进行了验证。结果表明,掘进过程中,声发射、电磁辐射强度整体变化趋势呈现3个阶段;煤与瓦斯突出危险发生时,声电强度参数响应剧烈,出现了明显的声增电降趋势,且声发射、电磁辐射强度与瓦斯浓度呈显著相关,瓦斯浓度突增与声电信号异常基本是同步发生的;声—电—瓦斯能够反映煤岩石动力演化过程中的变化情况,可将第一次声电异常波动定为瓦斯预警前兆开始时间,超前预警8 h左右。由此可以看出,通过研究声—电—瓦斯的异常响应,能够实现煤与瓦斯突出的预警预报。

板壳结构在声振联合试验下的振动响应耦合分析

目的研究具有工程实践意义的板壳组合结构在声振联合作用下的响应预测方法。方法在噪声试验、振动试验和声振联合试验响应曲线的基础上,分析板壳组合结构在噪声和振动同时激励下的响应耦合规律,并根据噪声试验和振动试验的响应极值包络法,来预测在声振联合试验作用下板壳结构的响应分布。结果声振联合试验响应曲线近似于噪声试验和振动试验的最大值包络线,噪声的面激励和随机振动的基础激励在不同的频率范围内对结构响应起着主要影响。试验件的噪声试验和振动试验响应曲线在给定的频率点出现相交,小于交越频率的声振联合试验响应与振动试验高度吻合,高于交越频率的响应则以噪声试验为主。结论在工程实际中,可以直接利用振动试验和噪声试验的响应数据对声振联合试验的响应进行预测。由于交越频率难以事先获得,因此响应叠加法在实践中更易于实现。