Location

La Jolla, CA

Start Date

1-1-1991 12:00 AM

Description

The detection of cracks below fasteners in aircraft skin has been a longstanding challenge for the aviation industry. Among conventional NDE inspection methods, radiography is more suited to the detection of relatively large cracks, while eddy current techniques can achieve good probability of detection for small cracks [1], but requires the removal of the fasteners. Consequently, considerable effort has been focussed on the development of ultrasonic inspection methods [2]. Aircraft skins are constructed in various ways, and the possibility of ultrasonic inspection depends critically on the manner of construction. For example, many commercial aircraft skins are constructed with a thin outer layer of aluminum over a relatively thick inner layer. The two layers are fastened together with rivets and sealed to prevent moisture or fuel from penetrating. In this first case, the critical flaws occur in the inner layer. Ultrasonic inspection is hampered by reverberations in the outer skin and the need to penetrate the layer of sealant. On the other hand, some military aircraft have a thick structural outer skin fastened to an inner framework by bolts. Importantly, the critical cracks occur in the outer layer of metal. The possibility of ultrasonic inspection is greatly enhanced in this second case since there is no need to penetrate through a sealant to an inner layer. The possibility of inspecting skins of this second type with a high-angle, shear-wave pulse-echo technique is the subject of this progress report.

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

10B

Chapter

Chapter 7: Characterization of Materials

Section

Non-Linear Acoustic Properties

Pages

1891-1898

DOI

10.1007/978-1-4615-3742-7_98

Language

en

File Format

application/pdf

Share

COinS
 
Jan 1st, 12:00 AM

Ultrasonic Detection of Cracks below Bolts in Aircraft Skins

La Jolla, CA

The detection of cracks below fasteners in aircraft skin has been a longstanding challenge for the aviation industry. Among conventional NDE inspection methods, radiography is more suited to the detection of relatively large cracks, while eddy current techniques can achieve good probability of detection for small cracks [1], but requires the removal of the fasteners. Consequently, considerable effort has been focussed on the development of ultrasonic inspection methods [2]. Aircraft skins are constructed in various ways, and the possibility of ultrasonic inspection depends critically on the manner of construction. For example, many commercial aircraft skins are constructed with a thin outer layer of aluminum over a relatively thick inner layer. The two layers are fastened together with rivets and sealed to prevent moisture or fuel from penetrating. In this first case, the critical flaws occur in the inner layer. Ultrasonic inspection is hampered by reverberations in the outer skin and the need to penetrate the layer of sealant. On the other hand, some military aircraft have a thick structural outer skin fastened to an inner framework by bolts. Importantly, the critical cracks occur in the outer layer of metal. The possibility of ultrasonic inspection is greatly enhanced in this second case since there is no need to penetrate through a sealant to an inner layer. The possibility of inspecting skins of this second type with a high-angle, shear-wave pulse-echo technique is the subject of this progress report.