1、 259The 10th International Conference of the Slovenian Society for Non-Destructive Testing Application of Contemporary Non-Destructive Testing in Engineering September 1-3,2009,Ljubljana,Slovenia,259-265NONDESTRUCTIVE TEST TECHNOLOGY FOR THE COMPOSITES Keynote lecture B.Boro Djordjevic Materials and
2、 Sensors Technologies,Inc.798 Cromwell Park Drive;Suite C;Glen Burnie,MD 21061 USA bbdmast- ABSTRACT When manufacturing composite structure,material and structural components are created concurrently.Thus,for composite materials in critical structural applications,it is more important than ever to i
3、ndependently assure structural integrity.Complexity of the advanced composite materials manufacturing and composite in service maintenance represents challenges in developing optimized nondestructive tools and tests.Traditional metals based NDT methods are inappropriate and often misleading when app
4、lied to anisotropic and inhomogeneous composite materials.In advanced technology applications such as aerospace and with industrial emphasis on economics and safety,it is critical to use and develop robust and practical composites NDT methods.Composite NDT encompasses a range of modified traditional
5、 and new tools including ultrasonic,x-ray,acoustic emission,thermal,optical,electrical and a variety of hybrid methods.This paper provides overview of the current use of the NDT tools in the composite applications.Key words:NDT,NDE,composites 1.Introduction There are enormous mechanical advantages f
6、or using composite materials.Table 1 and Figure 1 illustrate the specific properties benefits of the composites structural use over traditional industrial materials.Fiber reinforced organic matrix composite materials specific-properties can double or triple the load carrying capacity over the tradit
7、ional metals.This materials benefit enables structural designs that outperform the conventional application limitations commensurately improving system performance such as reducing weight,increasing fuel efficiency or increasing speed.1,2,3 260Table 1:Illustration of specific strength values for the
8、 composite materials in comparison to traditional materials.Fig.1:Graphic comparison of the composite materials properties to traditional materials.Additionally,composite have better specific stiffness and their anisotropic character can be customized to the structural load requirements.The use of c
9、omposites is acceleration and now spans transportation industry applications including next generation aircraft such as new Boeing 787.Composites are in wide use for marine applications and have been revolutionary in sporting applications such as skiing,tennis rackets or golf clubs.2612.Composite Ma
10、terials and Testing Background Composite structures are often complex and formed by layers of dissimilar materials.Figure 2 illustrates complexity of the composite cross-sections.For weight-performance sensitive applications such as aerospace,composite materials are now common in critical structural
11、 components.3 Fig.2:Typical cross-sections of the composite materials.Composite mechanical damage is typically in the form of delaminations or disbonds(laminate-to-laminate or laminate-to-core),broken fibers due to impact,fatigue damage that affects the zone of composite material via micro cracking,
12、fiber delaminations,fiber breaks and overall loss of mechanical modulus,or can be caused by thermal damage from prolonged exposure to heat above resin cure temperatures as well as combination of effects due to extreme operational conditions.The detection and evaluation of damage in composites is com
13、pounded by the fact that damage is not visible to the naked eye and can occur in many different forms Table 2 shows a list of possible defects and damage found in composite materials.It should be noted that although the composite materials have been used for a long time,including in critical structu
14、ral applications,the effects of defects,damage mechanisms,fatigue and failure mechanisms are not mature and well understood.Connection between NDE/NDT/NDC information and mechanical performance is also not well established.Table 3 is a listing of the nondestructive testing and evaluation methods tha
15、t are applicable to composite materials and structures.262Table 2:Listing of typical defects and damage found in the composite materials.Table 3:Listing of the nondestructive testing and evaluation practices for the composite materials.Composite materials structural integrity can be compromised via
16、many mechanisms including presence of discontinuities or loss of mechanical properties.Because of composite materials complexity,complexity of the part geometry and often a limited part access,materials damage and materials condition sensing cannot be achieved via conventional NDT/NDE/NDC methodology.Of all nondestructive methods,only ultrasonic methods are directly sensitive to mechanical changes 263and can be used to directly assess the mechanical condition and integrity of the composite struc
