SAMPE Journal - November/December 2011 - (Page 46)

Feature Article Cost-Effective, Phase-Based Thermography Method for Ultrasonic Investigation of Defects in CFRP Structures M. Perterer, H. Baier Institute of Lightweight Structures, TU München, Germany F. Höchtl Department of Sports Equipment and Materials, TU München, Germany Abstract In recent years nondestructive inspection (NDI) methods have found their way into service in the aerospace and automotive industry. Reliable and sensitive NDI systems often represent high acquisition costs for small and medium-sized companies, which represent a significant fraction of aerospace and the majority of automotive suppliers as well as the whole area of high performance sports equipment. For this reason a new approach in thermographic testing is introduced in this work, which combines the advantages of a robust and cheap NDI system such as heat flow thermography with the defect sensitivity of a high performance NDI method such as Lock-In thermography. The data acquisition and excitation is separated, which together with the use of appropriate data management, analyzing software algorithms and cheap off-the-shelf components leads to an effective 2-D NDI system. A carbon fiber reinforced plastic (CFRP) test plate containing various kinds of defects (delaminations, inclusions, fiber cracks, resin accumulations, etc.) is used to compare this thermographic system with the results of a water-coupled ultrasonic system. It is shown that this system has comparable defect sensitivity and even shows advantages in the detection of overlapped defects while simultaneously reducing the total testing time. Furthermore large defect areas can be inspected very quickly. Introduction In the last decade fiber reinforced plastics and especially CFRP represent a growing percentage of modern high performance structures. In contrast to metallic structures, damage is often not seen from the outside by cracks or local deformation. This is the reason why this growing demand for CFRP structures implicates appropriate nondestructive testing equipment for characterizing the damage state of the structure. In order to guarantee a constant product quality and to detect manufacturing defects at an early stage, there is a special demand for affordable NDI systems, which can be used directly after fabrication at the facilities of the aerospace and automotive supplying industry. Furthermore there is a need for large-scale two-dimensional NDI systems that are able to inspect large structural parts in a short period of time. This is the reason why a new approach of a two-dimensional NDI technique is introduced in this work to provide an affordable system with a sufficient accuracy in order to detect relevant defects in CFRP structures. Thermographic Techniques The defect condition of a structure can be characterized by numerous NDI methods, which use the different physical properties (mechanical, thermal, acoustic, radiation properties, etc.) of damaged regions in comparison with the undamaged structure. Thermal NDI methods1,2 can be further divided into different techniques. This can be done by using the excitation method on the one hand and the measurement signal on the other hand3 as shown in Table 1. In this work focus is given on optically excited techniques. The introduced method combines transient one-time excited heat flow thermography, which offers low cost and fast inspection, with periodically exited Lock-In Thermography, which has a very high defect sensitivity and is not influenced by terms of varying emissivity coefficients or nonuniform heating. SAMPE Journal, Volume 47, No. 6, November/December 2011 Figure 1. Optical excited thermal Lock-In method4. 46

Table of Contents for the Digital Edition of SAMPE Journal - November/December 2011

SMPE Journal - November/December 2011
Table of Contents
President’s Message
Technical Director’s Corner
Life Cycle Structural Health Monitoring of Airframe Structures: Strain Mapping Using FBG Sensors
Europe News & Views
SAMPE Europe’s SEICO 2012, Paris
12th Japan International SAMPE Symposium and Exhibition – JISSE-12
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SAMPE 2012
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SAMPE Asia 2012|Kuala Lumpur, Malaysia
Cost-Effective, Phase-Based Thermography Method for Ultrasonic Investigation of Defects in CFRP Structures
Tech Tidbits
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SAMPE Journal - November/December 2011