NDT Techniques

1. A Study on Non-Destructive
Testing Techniques for
Structural Health Monitoring
By kiran

2. Contents
 Introduction
 Ultrasonic Pulse Velocity Method
 Acoustic Emission Technique
 References

3. Introduction
 SHM is an important aspect of the assessment of various structures
which involves inspection, monitoring, and maintenance.
 The detection or measurement of strain, load, displacement, impact,
moisture, vibration signatures, and presence of cracks can be done.

4.  Non-destructive Testing (NDT) Techniques are generally used for SHM.
 Non-destructive testing (NDT) is the process of evaluating the changes in
characteristics without destroying the system's serviceability.
 In this study, main focus is given to two of the commonly used NDT Techniques,
Ultrasonic Pulse Velocity (UPV) Technique and Acoustic Emission (AE) Technique.
 In UPV Technique ultrasonic waves are induced into the element and waves
received from the element are studied.
 AE Technique involves recording the elastic waves produced in a structure by
means of sensors and by analysing these signals to the information is extracted.

5. Ultrasonic Pulse Velocity Method
 This method can be used to detect defects that are present in sound conducting
materials.
 Transducers are used to transmit high frequency (>20Khz) Ultrasonic waves
into a specimen and receive pulses from them.
 Inhomogeneities like damages in the material induce changes to the
propagating waves.
 This method is mainly used to determine the position and size of defects.
 One of the most commonly used inspection techniques for steel structures is
pulse-echo ultrasonic.

6. Figure: UPV test equipment and setup.

7. Some types of Transducers

8. Advantages and Limitations of UPV Method
 Sensitive to both surface and subsurface discontinuities.
 Depth of penetration for flaw detection or measurement is superior to other
methods.
 Reliable results are obtained and this method has high sample rate.
 The UPV method can be used to determine concrete properties, including
strength, dynamic elastic constants, defects, porosity and curing time effects.
 Skill and training required is more compared to other methods.
 Requires generation of source signal.
 Real time detection of crack generation is not possible.

9. Acoustic Emission Technique
 Recently the application of AE has received more attention as it is a
real-time monitoring technique in engineering structures.
 AE waves arise from rapid release of energy inside material, for
example from crack initiation.
 AE wave can be recorded by sensors and then analysed to extract
information about the source of emission.
 AE has been used for monitoring of
1. Various types of bridge structures such as steel, concrete and masonry
bridges
2. RC slab and RC beam
3. Composite material

10. Figure: AE sensor and medium Regular piezoelectric sensor

11. AE Parameters
 Peak amplitude - The maximum of AE signal.
 Energy – Integral of the rectified voltage signal over the duration of the
AE hit.
 Duration – The time from the first threshold crossing to the end of the
last threshold crossing.
 Counts – The number of AE signal exceeds threshold.
 Average Frequency –Determines the average frequency in kHz over
the entire AE hit.
 Rise time - The time from the first threshold crossing to the maximum
amplitude.

12. Advantages and Limitations of AE Method
 It is highly sensitive.
 No need of generation of AE waves.
 It has been used for damage detection and assessment.
 Because of the use of the sensors AE Technique is more accessible than
UPV Technique.
 Background noises affect monitoring in large structures.
 High sampling rates generate large volume of data.

13.  Ultrasonic method is expensive and requires generation of source signal
and real time monitoring of crack generation is not possible
 AE technique is highly sensitive and no need to generate source signal.
Background noises affect monitoring in large structures and high
sampling rates generate large volume of data
 Using multiple sensors, fast and complete inspection is done by AE
technique
 Because of the use of the sensors AE Technique is more accessible than
UPV Technique
 This technique can generally used to determine how much damage is
contained in a structure, for obtaining size, depth and position of defect
Ultrasonic pulse velocity method is more reliable
 combination of different methodologies may used to improve accuracy
and obtain more parameters to improve measuring processes.

14. References
 Pedreros, L.; Cárdenas, F.; Ramírez, N.; Forero, E. NDT non-destructive test for quality
evaluation of concrete specimens by ultrasonic pulse velocity measurement. In
Proceedings of the IOP Conference Series: Materials Science and Engineering,
Cartagena, Colombia, 30 October–1 November 2019; p. 012041.
 Liu, L.; Miramini, S.; Hajimohammadi, A. Characterising fundamental properties of
foam concrete with a non-destructive technique. Nondestruct. Test. Eval. 2019, 34,
54–69.
 Stankevych, O.; Skalsky, V. Investigation and identification of fracture types of
structural materials by means of acoustic emission analysis. Eng. Fract. Mech. 2016,
164, 24–34.
 Noorsuhada, M. An overview on fatigue damage assessment of reinforced concrete
structures with the aid of acoustic emission technique. Constr. Build. Mater. 2016,
112, 424–439.
 Kot,P.;Muradov,M.; Gkantou, M.; Kamaris, G.S.; Hashim, K.; Yeboah, D. Recent
Advancements in Non-Destructive Testing Techniques for Structural Health Monitoring.
Appl. Sci. 2021, 11, 2750.
 Peter C. Chang and S. Chi Liu, Recent Research in Nondestructive Evaluation of Civil
Infrastructures. Journal of Materials in Civil Engineering, Vol. 15, No. 3, June 1, 2003.