Articles you may be interested inInfluence of fiber orientation on the inherent acoustic nonlinearity in carbon fiber reinforced composites J. Acoust. Soc. Am. 137, 617 (2015); 10.1121/1.4906165Large and stable emission current from synthesized carbon nanotube/fiber network Acoustic emission characteristics on microscopic damage behavior of carbon fiber sheet reinforced concrete AIP Conf.ABSTRACT. Broad-band modal acoustic emission (AE) was used to characterize micromechanical damage progression in uniaxial IM7 and T1000 carbon fiber-epoxy (C/Ep) tows, and a helical and hoop-wrapped IM7 composite overwrapped pressure vessel (COPV). To expedite analysis, tows and the COPV were subjected to an intermittent load hold tensile stress profile. Damage progression in tow specimens was followed by analyzing the Fast Fourier Transforms (FFTs) associated with AE events. FFT analysis showed that damage was usually cooperative, consisting of several failure modes occurring at once, and was dominated by fiber breakage throughout the duration of the stress profile. Evidence was found for the existence of a universal damage parameter, referred to here as the critical Felicity ratio, or Felicity ratio at rupture (FR*), which had a value close to 0.96 for the tows and the COPV tested. The use of FR* to predict the burst pressure of the COPV is demonstrated.

As metal additive manufactured spaceflight hardware moves closer to use in upcoming missions, the need for appropriate nondestructive evaluation (NDE) procedures to qualify and certify parts becomes more pressing. Traditionally, the level and specificity of certification requirements for aerospace parts is linked to part criticality, which is determined by structural margin, consequence of failure, and part inspectability. Unfortunately, rule-level (performance-based) certification requirements often do not define specific or acceptable NDE procedures or requirements. This level of detail usually falls on the original equipment manufacturer (OEM), which is unwise in the case of new technology, such as additive manufacturing (AM). Instead, it is incumbent upon the end user to communicate risks and with the OEM and to provide oversight to ensure risks are controlled. These risks arise from many sources, including uncertainty about property optimization for rapidly evolving AM processes, lack of engineering experience, and limited operational histories. From the NDE perspective, the main risk arises from uncertainty in the NDE procedure to detect the requisite critical flaw type, size, and distribution. Because the level of criticality of AM aerospace parts is expected to increase, more effort is needed to characterize and understand fatigue and fracture properties of AM materials. Crack initiation resulting from the presence of AM flaws must be considered. This requires knowledge of the critical initial flaw size (CIFS) and the appropriateness of NASA-STD-5009 flaw sizes. Knowledge of the CIFS for a given AM flaw type will allow for the fracture control and NDE communities to evaluate risks and communicate recommendations regarding the acceptability of risk. Toward this goal, this paper discusses NDE-related activities at the National Aeronautics and Space Administration, Japan Space Exploration Agency, and European Space Agency. Current NDE best practices for AM hardware are discussed, along with tailoring NDE according to part criticality.

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