Influence of surface roughness on thermography measurement Abstract: This University Bachelor’s Thesis was performed to explore the influence of surface roughness on the thermography measurement.Thermography is a non-destructive testing method which can be used to detect cracks. However, it is hard to define how the surface roughness influences the emissivity and the result of a thermography measurement, as well as how the angle of the excitation source influences the result. Therefore, this work aims to define how the heating angle and surface roughness influence the thermography measurement, define the relationship between surface roughness and emissivity for the same crack, and define the influence of the angles which composed of the heating source, the direction of crack and the direction of surface roughness on thermography measurement.
In this report, the theories of radiation and Signal-to-noise ratio (SNR) were explained, clearly. Also, two kinds of experiments were set up. One is focus on how the heating angle influence the thermography measurement, the other is focus on how the angle of the heating source, in relation to the crack direction and the direction of surface roughness, influence the SNR value.
The conclusions of these experiments are that the heating of a crack increases as the angle  decreases (from wide side to narrow side) and the angle of  increases (from horizontal to vertical). Moreover, the SNR value decreases as the surface roughness increases. For the same surface roughness, the SNR value increases with increased crack angle (0°, 45° or 90°) and with decreased sample position angle (horizontal, 45°or vertical). What is more, the higher surface roughness, the larger the influence of the crack angle and the sample position angle. Finally, when the surface is polish, the crack angle and the sample position angle does not have any influence.20209
Key Words: Emissivity; Surface roughness; thermography measurement; crack direction; direction of surface roughness
Preface
The author gratefully acknowledges University West for providing online library and the experimental equipment. The author thanks Per Henrikson who is working at GKN, for supplying the experimental samples. Specially, the author thanks Dr. Patrik Broberg for his technical assistance and guidance.
 Contents
Preface    ii
Symbols and glossary    iv
1    Introduction    1
1.1    Background    1
1.2    Objective    1
2    Theory    1
2.1    Surface crack detection    2
2.2    Radiation    2
2.3    SNR    3
3    Literature survey    4
4    Experimental methods    7
4.1    Test sample    8
4.2    Experimental setup    10
5    Results    13
5.1    The results of the first experiments    13
5.2    The results of the second experiments    15
6    Discussion    16
6.1    The first experiments    16
6.2    The second experiments    19
7    Conclusions and future work    20
References    22

Appendices
A.    Appendix A: The code for the first experiments
B.    Appendix B: The data from the first experiments
C.    Appendix C: The code for the second experiments
D.    Appendix D: the original data from the second experiments
 
Symbols and glossary Influence of surface roughness on thermography measurement:http://www.751com.cn/zidonghua/lunwen_11890.html