th
                             The 10  International Conference of the Slovenian Society for Non-Destructive Testing  
                                  »Application of Contemporary Non-Destructive Testing in Engineering«  
                                           September 1-3, 2009, Ljubljana, Slovenia, 259-265
                         NONDESTRUCTIVE TEST TECHNOLOGY FOR THE 
                                                      COMPOSITES 
                                                       Keynote lecture 
                                                      B. Boro Djordjevic  
                                             Materials and Sensors Technologies, Inc. 
                                               798 Cromwell Park Drive; Suite C; 
                                                  Glen Burnie, MD 21061  USA 
                                                       bbd@mast-inc.com 
                                                           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  independently  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  applied  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 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 for 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 traditional 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]  
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        Table 1: Illustration of specific strength values for the 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 composites 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. 
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       2. Composite Materials 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 
       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,  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 compounded 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 structural 
       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 that are applicable to 
       composite materials and structures. 
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           Table 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  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 
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