NDT (Thử nghiệm không phá hủy): Hướng dẫn đầy đủ

Nguyên tắc:

Acoustic Emission Testing is based on the principle that materials under stress release energy in the form of elastic waves or acoustic emissions. These emissions occur due to the rapid release of strain energy resulting from various phenomena, such as crack propagation, plastic deformation, material failure, or structural changes. The acoustic waves are detected by sensors and analyzed to identify and characterize the source of the emissions.

Thủ tục:

1. Sensor Placement: Acoustic emission sensors, typically piezoelectric transducers, are strategically placed on the surface of the material being tested. The number and location of sensors depend on the material, the expected defect locations, and the test objectives.

2. Stress Application: The material is subjected to a controlled stress or loading condition, which could be mechanical, thermal, or a combination thereof. The stress level is gradually increased or maintained at a constant level, depending on the test requirements.

3. Acoustic Emission Detection: As the material undergoes stress, internal changes or defects generate acoustic emissions. The sensors detect these emissions in the form of high-frequency waves and convert them into electrical signals.

4. Signal Amplification and Filtering: The electrical signals from the sensors are amplified and filtered to remove unwanted noise and interference, enhancing the quality of the acquired data.

5. Data Acquisition and Analysis: The amplified signals are recorded and analyzed using specialized instrumentation or software. Various parameters, such as amplitude, duration, rise time, energy, and waveform characteristics, are evaluated to identify and classify the acoustic events.

6. Event Localization: By analyzing the time differences in the arrival of acoustic waves at different sensors, the location of the emission source within the material can be estimated.

7. Interpretation and Evaluation: The collected data is interpreted by trained analysts or automated algorithms to determine the nature, location, and severity of the detected emissions. Comparison with pre-established criteria or standards helps in evaluating the material’s integrity.

Ứng dụng:

Acoustic Emission Testing is used in a variety of industries for the detection and monitoring of defects, structural changes, and material behavior, including:

• Pressure vessel and storage tank inspections: AE can detect corrosion, leakage, cracks, and other defects in pressure vessels and storage tanks.

• Structural health monitoring: It is used for monitoring the integrity and stability of structures, such as bridges, dams, pipelines, and buildings, by detecting crack growth or deformation.

• Composite material inspections: AE helps in identifying delamination, fiber breakage, and other defects in composite materials used in aerospace, automotive, and wind energy industries.

• Weld inspections: AE can detect defects, such as lack of fusion, incomplete penetration, and cracks in welded joints.

• Fatigue and creep testing: It is employed to study the behavior of materials under cyclic loading or prolonged exposure to high temperatures, detecting the onset of fatigue cracks or creep deformation.

Thuận lợi:

• Can detect internal defects and changes in materials.
• Real-time monitoring and detection of abnormalities.
• Can be used on various materials, including metals, composites, and concrete.
• Non-intrusive technique that does not require material removal.
• Provides information on defect growth, behavior, and failure mechanisms.

Hạn chế:

• Requires controlled stress application, which may not be feasible in all situations.
• Noise and interference can affect the accuracy of the acquired signals.
• Localization accuracy may be limited, especially in complex geometries or heterogeneous materials.
• Interpretation and analysis of the data require expertise and experience.

Acoustic Emission Testing is a valuable non-destructive testing method that provides insights into the behavior and condition of materials and structures. It is particularly useful for monitoring critical components, detecting defects, and assessing the integrity of various industrial systems.