共查询到19条相似文献,搜索用时 125 毫秒
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复合材料中孔隙的存在造成了材料性能的下降,因此,对材料孔隙的检测至关重要。本文利用异丙醇(IPA)添加量的不同,制备了不同层数、不同孔隙率含量的碳纤维(CF)布/环氧树脂层合板试件。采用脉冲反射法测试计算了CF布/环氧树脂层合板试件的超声衰减系数,通过金相显微分析对孔隙的分布、形状及尺寸进行了表征,运用MATLAB对金相显微图进行分析得到试件的孔隙率。讨论了孔隙率对材料的声速、声阻抗及超声衰减系数的影响规律,利用4组不同层数样本试件的孔隙率和超声衰减量的试验数据,给出了基于模型的孔隙率与材料层数、超声衰减量的拟合公式。结果表明,随着IPA添加量的增加, CF布/环氧树脂层合板(2 mm)孔隙率从1.09%增加到4.16%,材料的声速和声阻抗均下降,超声衰减系数从2.51 dB/mm增大到5.34 dB/mm。孔隙率为1%时,厚度从2 mm (8层)增加到5 mm(20层),衰减系数增大了0.54 dB/mm。 相似文献
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为提高碳纤维增强树脂基复合材料(Carbon Fiber Reinforced Plastic,CFRP)单向板弹性常数的超声表征精度,基于超声液浸背反射法开展了实验测量和数值模拟。首先,搭建了角度旋转测试装置,并结合信号互相关处理技术实现了不同方向上的延时测量和声速计算;然后,通过模拟退火优化算法反演声速数据,得到了5个独立弹性常数;最后,利用理论计算和CIVA软件模拟仿真对实验测量结果进行了验证。结果表明:1-3平面内准纵波和准横波声速随入射角度而变化,与1-2平面内的表现出明显差异,由此显示材料为横观各向同性的;独立弹性常数分别为12.88、6.39、126.83、4.85、2.97GPa;理论计算、CIVA软件模拟仿真及实验测量结果的声速偏差小于6.4m/s,实验数据波动范围小于0.33%,对应的弹性常数误差均小于0.47%。相关方法同样适用于其他正交各向异性介质的弹性常数测试。 相似文献
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用碳纤维填充尼龙1010制备了碳纤维增强尼龙复合材料,并对碳纤维增强尼龙复合材料的力学性能和摩擦学性能进行了实验研究。力学实验结果表明:碳纤维增强使尼龙复合材料的拉伸强度、表面硬度增大,碳纤维增强尼龙材料的拉伸强度在20%碳纤维含量时达到最大值;碳纤维表面处理对尼龙复合材料的拉伸强度有很大影响,碳纤维表面氧化处理提高了碳纤维增强尼龙复合材料的拉伸强度。摩擦磨损实验表明:碳纤维增强尼龙复合材料的摩擦系数和磨损率与其拉伸强度和硬度有密切关系。随着拉伸强度和硬度的提高,尼龙复合材料摩擦系数和磨损率降低;摩擦系数和磨损率与拉伸强度具有反比关系,与材料硬度具有二次方程关系,与碳纤维填充量之间存在负指数变化规律。 相似文献
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冰介质中的声速特性受温度、盐度、密度等因素影响,是一个随时间和空间变化的不稳定值。研究了冰介质中温度、盐度、密度三个物理量在垂直方向上的变化特性,引入孔隙率作为冰中声速特性的表征因子,利用孔隙率与温度、盐度、密度已有的函数关系,通过大量天然冰的实验数据,得到淡水冰中声速关于温度、盐度和密度的经验公式。进行了河冰声速测量的外场试验,验证了淡水冰中声速的经验公式的有效性,并利用该声速经验公式研究了淡水冰垂直方向上的声速剖面。文中所做的相关研究可为以后研究利用冰介质中的声速特性提供借鉴,为以后利用声学方法,在极地或我国北方高纬度地区进行冰层厚度监测,了解寒地冰层的更替、演化以及气候变迁等工作奠定研究基础。 相似文献
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H.C. Choi A.J. Gray C.L. Vicente J.S. Xia G. Gervais W.P. Halperin N. Mulders Y. Lee 《Journal of Low Temperature Physics》2005,138(1-2):107-115
No Heading We report our results of shear acoustic impedance measurements performed on superfluid 3He in 98% porosity silica aerogel. Experiments in high porosity aerogel provide unique opportunity to study the influence of disorder on a p-wave superfluid and compare the behavior with that of the well understood pure bulk. Our experiment is designed to detect acoustic signatures from both bulk liquid and liquid in aerogel. In the past, experiments on 3He in aerogel have been conducted in zero or low magnetic fields (< 1 tesla). We made measurements in magnetic fields as high as 15 tesla at 28.4 and 33.5 bars and observed a new phase in aerogel induced by magnetic fields splitting the superfluid transition into two.PACS numbers: 67.57Pq, 67.80Mg 相似文献
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Young R Harris P Dawson A 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2011,58(3):547-566
This paper presents a theoretical investigation of ultrasonic wave propagation in a fabricated porous aluminum plate whose microstructure consists of columnar pores oriented normal to the plate surface. Attention is restricted to the symmetric modes which are seen to be compatible with a plane wave source whose wavefronts are vertically incident on the plate. The analysis shows the existence of two fundamental modes, a fast mode and a slow mode, which together transmit energy through the microstructure. The reflectivity and impedance properties of the plate are determined, and it is shown how these vary with frequency, pore spacing, and porosity. By varying the latter during the manufacturing process, a material may be fabricated whose acoustic impedance can be set to any desired value between that of water and solid aluminum. 相似文献
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Effect of RC load on performance of thermoacoustic engine 总被引:2,自引:0,他引:2
Based on linear thermoacoustics, a symmetric standing-wave thermoacoustic engine connected with an acoustic resistance and acoustic compliance (RC) load was simulated to study the effect of the load impedance on the performance of the thermoacoustic engine. Experiments were performed to verify the simulation. Both the simulation and the experimental results show that there is a non-monotonic variation of the acoustic power delivered to the load with the acoustic resistance of the load and a maximal acoustic power may be obtained when the acoustic resistance equals to its compliance impedance. And a lower compliance impedance of RC load may lead to a higher acoustic power delivered to the load. 相似文献
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Golan G. Kenyon A.J. Griffel G. Pitt C.W. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1994,41(4):565-568
A novel scanning acoustic microscopy technique for achieving high resolution acoustic images by employing thermal effects and image subtraction has been studied and demonstrated. Experiments were performed on a perspex block patterned with a machined grid on the reverse surface, and on a buried channel in similar material. If was found that using the image subtraction technique, short periods of sample heating can lead to a stronger pattern selectivity, because of the strong temperature dependency of the elastic parameters of the polymer. In previous SAM techniques improvement in signal has been achieved through the use of special liquids as acoustic coupling media between the acoustic lens and the sample. The reported technique retains water as the coupling medium and the acoustic impedance matching is performed by varying the elastic parameters of the sample itself through direct heating. The temperature increase in the sample decreases the velocity of propagation of acoustic waves in the solid, and brings the acoustic impedance close to that of water. A theoretical model, including expressions for the acoustic aberrations, depth dependence and acoustic impedance matching has been derived. Examples of the results obtained are presented 相似文献
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对定加热温度下行波热声发动机驱动阻容负载进行了数值模拟,分析讨论了声阻和容抗对声功输出的影响。以氦气为工质,在充气压力为3 MPa、加热温度为923 K的条件下,对不同气库体积的热声系统进行了模拟;此外,还采用负体积气库模拟了阻抗虚部为正值的情况。计算结果表明,容抗值较大时,在负载相位角约为-45°(或45°)时,声功率存在一个极大值;当容抗值较小时,声功率会出现两个极大值和一个极小值,且在负载阻抗相位角约为-45°(或45°)时为极小值;此外,声功输出最大值与效率最大值对应的阻抗并不相同。 相似文献