Damage identification in fiber reinforced titanium matrix composites using acoustic emission

https://doi.org/10.1016/j.jallcom.2020.153928Get rights and content

Highlights

  • AE signals of multiple damage modes were identified by tensile tests.

  • AE signals were analyzed by waveform, frequency and time-frequency distribution.

  • The effects of propagation media on signal characteristics were studied.

Abstract

The fundamentals of acoustic emission behavior in SiC fiber reinforced titanium matrix composites were investigated. In order to obtain preferred damage modes and provide insight into damage identification, the acoustic emission responses in the fiber tensile test, the matrix tensile test, the longitudinal tensile test and the transverse tensile test for the single fiber composite were studied respectively. Extracted signals of fiber fracture, matrix deformation, matrix fracture, fiber fragmentation, fracture of the fiber-matrix reaction layer and interface debonding were analyzed by waveform pattern, frequency contents and time-frequency distribution. The signal characteristics with respect to amplitude, waveform shape, frequency centroid and wave modes were given for different damage modes. Furthermore, the generation and propagation mechanisms of multiple signals were also discussed with the assistance of theoretical models.

Introduction

Owing to the increasing demand for high-strength and lightweight materials in the aerospace industry, the metal matrix composites (MMCs) are widely accepted as promising candidate materials because of their high specific strength and high specific stiffness at elevated temperatures [[1], [2], [3]]. One of the most prospective MMC material systems is the continuous SiC fiber reinforced titanium matrix composite (TMC) [4,5]. For rotating components in the compressor of gas turbine engines [6], such as driving shafts and bladed rings [7], significant weight savings of 30–70% can be achieved by replacing monolithic alloys (such as Ti-6242) with TMC materials [8]. However, the innovation proceeds forwards slowly because of insufficient understanding of damage behavior for composite materials in these structural components. It is essential to ensure that these TMC components of aero engines operate with high safety during service, thus insightful investigation of damage monitoring in TMCs is required.

Acoustic emission (AE) offers a powerful real-time nondestructive method in damage detection [[9], [10], [11]]. It is applied to monitor and locate the damage behavior by detecting the sudden release of energy in the loading process [12,13]. Intensive investigation of damage identification is performed on fiber reinforced polymer matrix composites [14] and ceramic matrix composites [15]. The correlations between damage modes (including matrix cracking, fiber breakage and fiber-matrix debonding) and signal characteristics (including waveform parameters and frequency contents) have been extensively discussed [16]. However, investigation of damage identification in MMCs shows fewer prosperities due to more complexity. The metal matrix, different from brittle resins or ceramics, exhibits strong AE activity due to plastic deformation (slipping and twinning) [17]. Many researchers have discussed the relationship between deformation mechanisms and AE activity for metal materials [18]. The strong AE activity caused by the matrix has also been found in MMCs [19]. Thus the strong background AE activity of the metal matrix significantly increases the difficulty of classifying damage signals in MMCs [20]. Besides, the fiber-matrix reaction layer [21], easily introduced in the fabrication process at high temperatures, also affects AE behavior. Although previous researchers have discussed the characteristics of AE events during damage growth in TMCs under different loading conditions, few efforts are made in refined research concerning damage identification of multiple signals [22]. Insufficient understanding of precise signal classification confines the use of AE technique in health monitoring of TMCs, thus a more precise classification of multiple damage signals in TMCs is desired to be obtained by comprehensive analysis of AE signals and profound understanding of signal propagation.

The purpose of the paper is to identify damage modes precisely in a SiC fiber reinforced Ti–6Al–2Sn–4Zr–2Mo-0.1Si composite system using AE technique. Firstly, the AE responses in the fiber tensile test, the matrix tensile test, the longitudinal tensile test and the transverse tensile test of the single fiber composite were studied respectively to obtain AE signals of fiber fracture, matrix deformation, matrix fracture, fiber fragmentation, fracture of the fiber-matrix reaction layer and fiber-matrix interface debonding. Then the signal waveform, fast Fourier transform (FFT) and continuous wavelet transform were used to extract signal characteristics. Moreover, the generation and propagation mechanisms of AE signals were also analyzed. Fractographic examinations were also conducted to validate the result using a scanning electron microscope (SEM).

Section snippets

Material

The SiC fibers were manufactured by a two-step chemical vapor deposition process in Institute of Metal Research, Chinese Academy of Sciences. The SiC layer was firstly deposited on 14 μm diameter tungsten wires from a gas mixture of chlorosilane and hydrogen, then 2 μm thick carbon coating was deposited from a gas mixture of acetylene and hydrogen. The total diameter of the SiC fiber is about 100 μm. The ultimate strength of the SiC fiber is about 3800 MPa and the elastic modulus is about

AE response in the fiber tensile test

Fifty fiber specimens were used to carry out tensile tests. All AE signals were collected to analyze the amplitude distribution of fiber fracture. The typical AE behavior during the fiber tensile test is shown in Fig. 3a. No AE event is detected before the final fracture in the fiber tensile test. The fiber fracture produces a strong AE event with amplitude above 99 dB. The amplitude distribution of fiber fracture is plotted in Fig. 3b. The amplitude range of fiber fracture in the test is

Waveform analysis

Typical AE waveforms of fiber fracture, matrix fracture, matrix deformation, fiber fragmentation, fracture of the reaction layer and interface debonding are shown in Fig. 12. The AE signal by matrix fracture shows longer duration and slower attenuation, as shown in Fig. 12b. The ductile fracture of the matrix generates AE signals with duration of over 3 ms. The rise time, defined as time interval between the first threshold crossing and the peak value of the signal, is different for multiple

Conclusions

The AE signals generated by fiber fracture, matrix deformation, matrix fracture, fiber fragmentation, fracture of the reaction layer and interface debonding are obtained by the tensile tests. The characteristics of AE signals are analyzed by waveform, power spectrum and time-frequency distribution. The generation and propagation of AE signals are also investigated. The main conclusions are as follows:

  • (1)

    The SiC fiber fracture only produces one AE event with high amplitude of 100–110 dB. The power

Data availability

The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study. However, the data that support the findings of this paper are available from the corresponding author on reasonable request.

CRediT authorship contribution statement

Xu Kong: Conceptualization, Methodology, Investigation, Writing - original draft. Yumin Wang: Conceptualization, Writing - review & editing. Qing Yang: Resources, Validation. Xu Zhang: Resources, Formal analysis. Guoxing Zhang: Visualization, Formal analysis. Lina Yang: Visualization. Ying Wu: Visualization, Validation. Rui Yang: Supervision, Writing - review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The first author thanks Mr. Hui Guan and Mr. Ningbo Shang for the support of the tensile test.

References (32)

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