Assessment of low-velocity impact damage in composites by the measure of second-harmonic guided waves with the phase-reversal approach

Abstract

Structural strength and integrity of composites can be considerably affected by the low-velocity impact damage due to the unique characteristics of composites, such as layering bonded by adhesive and the weakness to impact. For such damage, there is an urgent need to develop advanced nondestructive testing approaches. Despite the fact that the second harmonics could provide information sensitive to the structural health condition, the diminutive amplitude of the measured second-order harmonic guided wave still limits the applications of the second-harmonic generation–based nonlinear guided wave approach. Herein, laminated composites suffered from low-velocity impact are characterized by use of nonlinear guided waves. An enhancement in the signal-to-noise ratio for the measure of second harmonics is achieved by a phase-reversal method. Results obtained indicate a monotonic correlation between the impact-induced damage in composites and the relative acoustic nonlinear indicator of guided waves. The experimental finding in this study shows that the measure of second-order harmonic guided waves with a phase-reversal method can be a promising indicator to impact damage rendering in an improved and reliable manner.

Dual-frequency acousto-ultrasonic sensing of impact damage in composites for mitigating signal instability

“…Thus, a linear fit, which is extensively used, can be applied to describe the decrease in amplitude with an increase in the impact number. 35,36 Then, the linear slope, k , was calculated to evaluate the sensitivity to the impact number at different frequencies. The k values for three cycles were −0.0064, −0.0097, and −0.02, respectively, at 150, 250, and 350 kHz.…”

Advances in theoretical, experimental and applied studies on second-harmonic generation of ultrasonic Lamb waves

“…金属高温损伤/老化，宏观上表现为机械性能的退化，微观上则体现为微组织的改变。Xiang等 [50,51] 研究 了微观组织结构与非线性超声之间相互作用的理论模型，建立了材料性能退化与非线性超声参量之间的定量 关系。在机理研究的基础上，Xiang等 [52] 开展了基于兰姆波二次谐波的奥氏体Fe-Cr-Ni不锈钢材料的高温损伤 评价。研究表明，兰姆波二次谐波和材料高温损伤程度之间存在一个"上升-平稳-下降"的关系，如图 4 所 示。据此，他们构建了兰姆波二次谐波与工程材料高温热损伤之间的映射关系。 图4 奥氏体不锈钢老化过程与非线性兰姆波之间的关系 [52] Figure 4 Correlationship of the austenite steel aging process versus nonlinear Lamb waves [52] 3.4 基于兰姆波二次谐波的塑性评价 A c c e p t e d https://engine.scichina.com/doi/10.1360/TB-2021-0723 金属材料在疲劳裂纹形成之前存在塑性变形阶段。材料初期的塑性变形不足以引起传播的超声兰姆波线 性声学参数的变化，但金属塑性变形的程度直接对应于金属材料微损伤的积累，而材料内部的微损伤对兰姆 波二次谐波发生效应有显著的影响。Pruell等 [35,36] 利用满足相匹配条件的兰姆波模式，研究了材料的累积塑性 变形对兰姆波非线性效应的影响。他们利用疲劳拉伸实验改变不同金属板构件的塑性变形程度，使用1个未变 形试件作为参考和5个塑性变形程度不同的试件，其中最大程度的塑性变形都远低于试件发生紧缩所达到的塑 性变形，因此塑性变形被认为均匀分布于整个试件。研究结果证实，积累塑性变形导致兰姆波的二次谐波幅 度逐渐增大。该研究证实了兰姆波二次谐波可用于检测由塑性变形诱发的材料微损伤。 3.5 基于兰姆波二次谐波的材料蠕变损伤评价 在材料高温老化早期阶段，由于析出相的作用使位错形成大角度弯曲，此时可用共格模型予以分析。随 着析出相的逐渐变多，析出相和基体位错之间的错配程度加剧，导致材料微组织缺陷增多 [52] 。Xiang等 [53] 将表 征材料微观组织变化的参数变化量引入非线性超声兰姆波的表达式，构建了超声兰姆波二次谐波与材料微观 组织相互作用的理论模型，并通过对奥氏体Fe-Cr-Ni不锈钢的高温损伤、Ti60钛合金的蠕变损伤的兰姆波二次 谐波测量，验证了兰姆波二次谐波和材料高温损伤程度之间存在关系，如图5所示。研究结果证实，兰姆波二 次谐波可以有效检测材料高温热损伤、蠕变损伤。 图5 理论和实验获得的兰姆波非线性系数与蠕变损伤程度曲线 [53] Figure 5 Theoretical and experimental results of Lamb wave nonlinearity versus creef life fraction [53] 3.6 基于兰姆波二次谐波的复合材料板热疲劳和冲击损伤的检测 复合材料板具有比强度、比刚度高，抗疲劳性、耐腐蚀性好，材料力学性能可设计，易于整体成形等优 点，被广泛应用于各类工业结构件中。但是，复合材料结构由于不同材料的热膨胀系数差异，热疲劳载荷会 导致复合材料结构内部出现微损伤(如纤维断裂、分层、脱粘等) 。此外，即使低速、低能的冲击，也会导致 复合材料基体开裂、纤维断裂等内部微损伤。复合材料热疲劳或冲击损伤演化过程中，宏观缺陷与损伤形成 之前通常经历材料微观结构变化以及微损伤的起始积累，复合材料结构中微损伤的扩展具有所谓的"突然失 效"特征。开展兰姆波二次谐波对复合材料评价研究，可有效检测复合材料早期损伤。Li等 [54,55] 开展了利用兰 姆波二次谐波对复合材料热疲劳和冲击导致的微缺陷的早期检测研究。如图6所示，在碳纤维/环氧树脂复合材 料中引入不同周期的热疲劳，实验测量复合材料板不同热疲劳周期下的兰姆波非线性系数的变化。研究结果 证实，兰姆波线性声学参数(群速度和衰减系数)对复合材料热疲劳早期阶段是不敏感的，而兰姆波二次谐 波可以有效表征复合材料热疲劳损伤的早期阶段。 Rauter等 [56] 在碳纤维复合材料板中引入低速、低能冲击，随着冲击能量的增加，兰姆波非线性参数也随 之明显增加。研究结果证实，利用该方法检测复合材料试件，相比于超声兰姆波幅值衰减的线性测量方法， 非线性方法对损伤的检测分辨率更高。 A c c e p t e d https://engine.scichina.com/doi/10.1360/TB-2021-0723 图6 不同复合材料热疲劳周期下线性及非线性兰姆波系数变化 [54] Figure 6 Linear and nonlinear acoustic parameters of Lamb waves in composites under different thermal fatigue cycles [54] 4 问题讨论…”

Defects Inspection in Wires by Nonlinear Ultrasonic-Guided Wave Generated by Electromagnetic Sensors

“…Sci. 2020, 10, 4479 3 of 14 certain distance, the underlying frequency wave is distorted to produce a higher harmonic [15][16][17][18][19][20][21]. For guided wave, the acoustic nonlinearity can be written as shown in Equation (1).…”