Assessment of Impact Damage in Kevlar{reg_sign}-epoxy, Filament-wound Spherical Test Specimens by Acoustic Emission Techniques
Assessment of Impact Damage in Kevlar{reg_sign}-epoxy, Filament-wound Spherical Test Specimens by Acoustic Emission Techniques

Author:

Publisher:

Published: 1996

Total Pages: 26

ISBN-13:

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The results of a study of the acoustic emission (AE) behavior of impact-damaged, spherical, composite test specimens subjected to thermal cycling and biaxial mechanical loading are presented. Seven Kevlar{reg_sign}-epoxy, filament-wound, spherical composite test specimens were subjected to different levels of impact damage. The seven specimens were a subset of a group of 77 specimens made with simulated fabrication-induced flaws. The specimens were subjected to two or three cycles of elevated temperature and then hydraulically pressurized to failure. The pressurization regime consisted of two cycles to different intermediate levels with a hold at each peak pressure level; a final pressurization to failure followed. The thermal and pressurization cycles were carefully designed to stimulate AE production under defined conditions. Both impacted and nonimpacted specimens produced thermo-AE (the term given to emission stimulated by thermal loading), but impacted specimens produced significantly more. Thermo-AE was produced primarily by damaged composite material. Damaged material produced emission as a function of both rising and falling temperature, but the effect was not repeatable. More seriously damaged specimens produced very large quantities of emission. Emission recorded during the static portion of the hydraulic loading cycles varied with load, time, and degree of damage. Static load AE behavior was quantified using a newly developed concept, the event-rate moment, and various correlations with residual strength were attempted. Correlations between residual strength, long-duration events, and even-rate moments were developed with varying degrees of success.

Summary of a Study to Determine Low-Velocity Impact Damage and Residual Tension Strength for a Thick Graphite/Epoxy Motor Case
Summary of a Study to Determine Low-Velocity Impact Damage and Residual Tension Strength for a Thick Graphite/Epoxy Motor Case

Author: National Aeronautics and Space Adm Nasa

Publisher: Independently Published

Published: 2018-10-11

Total Pages: 40

ISBN-13: 9781728673523

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Impacters of various shapes and masses were dropped from various heights onto 36 mm (1.4 in.) thick graphite/epoxy cylinders, which represented filament wound cases (FWC) for the booster motors of the Space Shuttle. Insert solid propellant was cast into some of the cylinders. The cylinders were impacted numerous times around the circumference and then cut into 51 mm (2.0 in.) wide tension specimens, each containing an impact site. Four indenters were used: a sharp corner, two hemispheres, and a bolt-like rod. The diameters of the hemispheres were 12.7 mm mm (0.5 in.) and 25.4 mm (1.0 in.), and the diameter of the rod was 6.3 mm (0.25 in.). Impacts with the rod were simulated by pressing the rod against the face of specimens. For the hemispheres, the damage initiated beneath the surface at a critical contact pressure and was not visible on the surface until an even larger pressure was exceeded. The damage consisted of matrix cracking and broken fiber. The rod an corner made visible surface damage in all tests. For the hemispheres, the tension strength was reduced considerably before the damage was visible on the surface, 30 percent for the 25.4 mm (1.0 in.) diameter hemisphere and 10 percent for the 12.7 mm (0.5 in.) diameter hemisphere. Analytical methods were used to predict the damage and residual tension strength. A factor of safety to account for nonvisible damage was determined. Poe, C. C., Jr. Langley Research Center RTOP 505-63-01-05

Optical Imaging Evaluation of Impact Damage Resistance Testing on Exterior Finishes
Optical Imaging Evaluation of Impact Damage Resistance Testing on Exterior Finishes

Author: Textile and Flexible Plastics Committee

Publisher:

Published: 2011

Total Pages: 0

ISBN-13:

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This SAE Recommended Practice covers a procedure for evaluating plastic and multiple-layer coatings exposed to gravelometer testing (as defined in SAE J400) with an optical imaging and analysis system. The intent of the procedure is to detect, count and characterize instances of damage in the coated surface that fracture the top coat layer or penetrate through multiple layers of the coating system. It may be possible to extend this methodology of coating damage evaluation to specimens that have undergone test procedures or exposures that produce similar, discrete damage sites in the coating system. If so applied, evaluation results must be interpreted with respect to the limitations and intent implied by the original evaluation procedure and its associated rating system, if applicable. The ISO method is designed only for exterior coatings material. SAE J2661 is a more comprehensive method that covers not only the exterior coatings materials but also exterior plastics, coatings, paints, plastic sheeting materials and so on. The ISO method is not comprehensive in its description of how the evaluation is performed. The SAE method describes details of performance not covered in the ISO method, base on the input of American automakers and their suppliers. The American automakers perform a slightly different type of stone chipping test (Gravelometer Test) compared to the rest of the world due to the road conditions in the U.S.SAE J2661 is technically equivalent to ISO 21227-2.

A Global Method for the Identification of Failure Modes in Fiberglass Using Acoustic Emission
A Global Method for the Identification of Failure Modes in Fiberglass Using Acoustic Emission

Author: V. Arumugam

Publisher:

Published: 2011

Total Pages: 13

ISBN-13:

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The various failure mechanisms in bidirectional glass/epoxy laminates loaded in tension are identified using acoustic emission (AE) analysis. AE data recorded during the tensile testing of a single layer specimen are used to identify matrix cracking and fiber failure, while delamination signals are characterized using a two-layer specimen with a pre-induced defect. Parametric studies using AE count rate and cumulative counts allowed damage discrimination at different levels of loading and Fuzzy C-means clustering associated with principal component analysis were used to discriminate between failure mechanisms. The two above methods led to AE waveform selection: On selected waveforms, Fast Fourier Transform (FFT) enabled calculating the frequency content of each damage mechanism. Continuous wavelet transform allowed identifying frequency range and time history for failure modes, whilst noise content associated with the different failure modes was calculated and removed by discrete wavelet transform. Short Time FFT finally highlighted the possible failure mechanism associated with each signal.