## 1 Introduction  
Advanced polymeric composites are playing a major role in designing high-performance and lightweight aircraft structures. However, a major challenge delaying the implementation of the advanced composites is the lack of accurate methods for material characterization [1]. Accurate measurement of three-dimensional mechanical properties of composites, stress-strain response, strength, fatigue, and toughness properties, is essential in the development of validated analysis techniques accelerating design and certification of composite structures [2; 3; 4]. In particular, accurate measurement of interlaminar tensile (ILT) strength is needed to capture delamination failure, which is one of the primary failure modes in composite aircraft structures. A major technical challenge to accurate measurement of ILT properties is their extreme sensitivity to manufacturing defects, including porosity, which could lead to unacceptable scatter in the test results. Unacceptable failure mode in standard test methods that use transverse tension specimens is another challenge to accurate measurement of the ILT properties. Currently, American Society for Testing and Materials (ASTM) D 6415 curved-beam (CB) method is a standard practice for measurement of the ILT strength [5]. However, large scatter typically found in ASTM D 6415 ILT strength raises doubts concerning the adequacy of the curved-beam test as a coupon independent test for measuring ILT material strength. Large scatter in the ILT strength test results may indeed reflect the manufacturing quality as much as materials properties. In particular, the ASTM D6415 CB strength is extremely sensitive to porosity/voids in the radius area. In [6], [PERSON] and [PERSON] observed a drastic (up to a factor of four) CB strength reduction in low-quality CB specimens due to large (macroscopic) voids detected based on a cross-section cut using a diamond saw. In [7], the authors of this work measured the ASTM D 6415 CB strength using high-quality 6.6 mm (0.26 inch) thick CB coupons manufactured from Hexcel IM7/8552 unidirectional tape and cured per manufacturer's specifications. ASTM D 6415 ILT strength values ranging between 37.7 MPa (5.5 ksi) and 94.6 MPa (13.7 ksi) were reported with a coefficient of variation higher than 26%. Similarly, typical high-quality IM7/8552 ASTM D 6415 CB specimens were tested in fatigue in [8] and showed large variation in fatigue life and correlated poorly with the power-law least-squares fit commonly used for description of the \(S\)-\(N\) curves of carbon-epoxy materials. CT scans of the CB specimens tested in [7; 8] revealed the presence of individual critical voids at ply interfaces that were correlated with the knockdown and large scatter found in the ASTM D 6415 CB strength and ILT CB fatigue life. It is worth noting that a test method that relies on extensive CT measurement may not be suitable for efficient characterization. Another method relevant to the assessment of the ILT strength is ASTM D 7291 [9], which applies a tensile force normal to the plane of the composite laminate using adhesively bonded thick metal end-tabs. It was noted in the ASTM Standard D 7291 that through-thickness strength results using this method will, in general, not be comparable to ASTM D 6415 since ASTM D 7291 subjects a relatively large volume of material to an almost uniform stress field, while ASTM D 6415 subjects a small volume of material to a non-uniform stress field. Also, characterization of ILT strength using ASTM D 7291 is perhaps even more challenging than ASTM D 6415 as the failure could occur not in the composite material but at the bond lines between the composite and the metal end-tabs used to transfer the load to the composite. Many of the challenges in standard testing of composite materials, including the difficulties mentioned previously in measurement of the ILT strength, stem from their inherent anisotropy and heterogeneous nature.