Measurements of Elastic Constants and Internal Friction of Fiber-Reinforced Metal-Matrix Composites and Evaluation of Their Damage : Development of a New Noncontacting Ultrasonic-Measurement Method

在室温至873 K范围内，我们测定了具有横向各向同性的碳化硅纤维的所有五个独立弹性-刚度系数C_ij。首先，我们测量了仅用纤维和基体合金单向增强的钛合金基复合材料的C_ij。电磁声共振检测试件的自由振动共振频率，确定其C_ij。其次，我们应用微观力学计算从测量的复合材料和矩阵C_ij中推断出纤维C_ij。得到的光纤C_ij在温度导数上表现出较强的各向异性，光纤轴向的温度导数要小得多。此外，我们还开发了一种方法，可以在不使用任何有关弹性常数的预先信息的情况下推导出各向异性固体材料的精确弹性常数。结合位移分布。共振超声光谱（RUS）的测量。通常的…More RUS方法是测量固体的自由振动共振频率，并将其与计算结果进行比较，通过反计算找到最合适的弹性常数集。这种比较需要对测量的共振频率进行模式识别，这一直是困难的，而且从来没有摆脱过模糊性。采用激光多普勒干涉仪测量了安装在电感器上的振动试样表面的位移分布规律；将测量的位移分布与计算的位移分布进行比较，使我们能够正确地识别测量的共振频率，从而准确地确定弹性常数。由于位移模式几乎不受弹性常数的影响，因此即使在反算开始时采用不合理的弹性常数作为初始猜测，也一定能得到准确的结果。用一种铝合金和一种langasite晶体证明了该技术的有效性。少

We have determined all five independent elastic-stiffness coefficients C_ij of a silicon-carbide fiber with transverse isotropy from room temperature up to 873 K. First, we measured the C_ij of a Ti-alloy-matrix composite reinforced unidirectionally with the fibers and the matrix alloy alone. Electromagnetic acoustic resonance detected the free-vibration resonance frequencies of the specimens to determine their C_ij. Second, we applied a micromechanics calculation to deduce the fiber C_ij from the measured composite and matrix C_ij. The resulting fiber C_ij, show strong anisotropy in the temperature derivatives of the C_ij, the temperature derivatives for the fiber-axis-direction are much smaller than the others. Also, we developed a methodology to deduce exact elastic constants of an anisotropic solid material without using any advance information on the elastic constants by. incorporating a displacement-distribution. measurement into resonant ultrasound spectroscopy (RUS). The usual … More RUS method measures free vibration resonance frequencies of a solid and compares them with calculations to find the most suitable set of elastic constants by an inverse calculation. This comparison requires mode identification for the measured resonance frequencies, which has been difficult and never been free from ambiguity. This study then adopts a laser-Doppler interferometer to measure the displacement-distribution patterns on a surface of the vibrating specimen mounted on pinducers ; comparison of the measured displacement distributions with those computed permits us to correctly identify the measured resonance frequencies, leading to unmistakable determination of elastic constants. Because the displacement patterns are hardly affected by the elastic constants, an exact answer is surely obtained even when unreasonable elastic constants are used as initial guesses at the beginning of the inverse calculation. The usefulness of the present technique is demonstrated with an aluminum alloy and a langasite crystal. Less