Weston-Bartholemew, Winston (1972) Materials evaluation using ultrasonic surface waves. PhD thesis, University of Warwick.

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Abstract

The investigation reported in this thesis was prompted by the desire to develop an easy and reliable nondestructive method of testing to monitor changes in elastic properties of metals when they are subjected to creep, fatigue, and case hardening.

The possibilities of the useful application of such a test will be invaluable to the aircraft industry. It was 'therefore suggested that the specimens used should be made from the type of materials
Used in the aircraft industry. These were made of high strength alloys.

The method of nondestructive testing was to excite ultrasonic surface waves on the surface of the specimens, and measuring the changes in surface wave velocity, when the material (specimens) are subjected to creep, fatigue, and case hardening. An ultrasonic goniometer was designed and constructed and, using the goniometer; critical angle reflectometry was used to excite the surface waves on the surface of the specimens.

For the measurements during fatigue ,specimens were fatigued at high stress levels and low cycles. Constant amplitude alternating stresses with the specimen remaining in tension during the whole program type of loading was used. Most of the specimens were made of titanium (Ti230) but some work was also done on mild steel.

The specimens used for creep were made from C263 Nickel alloy and Titanium 230. Each specimen was subjected to creep to a certain degree. The case hardened specimens were made of steel with carburized case.

It was found that using ultrasonic surface waves it was possible to determine the depth of case hardening. Using a calibration curve drawn from the results obtained of the change in surface wave velocity for specimens with known case depths, it was possible to predict the case depths of specimens of unknown case depths; by measuring their surface wave velocities. Also, a frequency effect was observed whereby lower frequencies were found to better for detecting larger. case depths

When specimens which were subjected to creep were considered, it was found that ultrasonic surface waves can detect early stages of creep. This was the case for both materials studied. A difference was observed in' the response to the surface waves for the two materials studied. In both cases a frequency effect was observed in that higher frequencies were better for detecting early creep.

For both materials studied during fatigue, most of the change in surface wave velocity occurred during the very early stages of fatigue life. During the latter stages of fatigue life the rate of change was very much lower. No pattern was observed for the change in surface wave velocity with the number of fatigue cycles for either material.

Lastly, measurements were done on brass, copper, aluminium, stainless steel and mild steel bar specimens, at the critical angle of incidence. For all the specimens it was found that the surface wave velocity changed with frequency.

Item Type:	Thesis (PhD)
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Library of Congress Subject Headings (LCSH):	Ultrasonic waves, Nondestructive testing, Surface waves
Official Date:	1972
Dates:	Date Event 1972 Submitted
Institution:	University of Warwick
Theses Department:	School of Engineering
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Crecraft, D. I.
Sponsors:	Ministry of Technology (Great Britain) ; University of Warwick
Extent:	145 leaves : illustrations
Language:	eng

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