Test frame misalignment effect on CFRPs mechanical properties

Abstract

Traditionally, major aircraft manufacturers have shown great interest in ensuring a high degree of alignment in the load train of test machines that determine the mechanical properties of the CFRP materials being tested. This is manifested in the definition of stringent requirements as far as alignment is concerned in the actual testing regulations of these manufacturers, being the main reference standard ASTM E1012. This standard establishes different categories or classes, depending on the deformation recorded on a test piece instrumentalized with strain gauges. Specifically, the standard defines classes 5, 8 and 10, and it is common to establish class 5 for static tests on CFRPs, whereas these same tests on metallic materials usually require class 10. The present work aims to quantify the influence of the misalignment of the test frames on the mechanical properties of CFRPs subjected to static tensile testing (maximum tensile strength and modulus). In addition, the influence on the mechanical properties of the application of corrections of the test specimen has been studied when determining the degree of alignment based on the reference standard ASTM E1012. This last aspect is currently being studied by aeronautical manufacturers in the discussion forum of the NADCAP accreditation program, in its NMMT commodity. The present work shows the methodology used, as well as the results obtained for its discussion.