This paper presents a summary of the tests performed within a VAMAS (Versailles Project on Advanced Materials and Standards) round robin to examine the measurement of mode II interlaminar fracture toughness using four different test methods based on: End Notched Flexure (ENF), Stabilised End Notched Flexure (SENF), End Loaded Split (ELS), and four point End Notched Flexure (4ENF) carbon fibre reinforced epoxy specimens. Tests were performed by members of ESIS (European Structural Integrity Society), JIS (Japan Industrial Standards group) and ASTM (American Society for Testing and Materials).
The viability of a method for determining the fatigue life of composite rotor hub flexbeam laminates using delaminafion fatigue characterization data and a geometric non-linear finite element (FE) analysis was studied. Combined tension and bending loading was applied to non-linear tapered flexbeam laminates with internal ply drops. These laminates, consisting of coupon specimens cut from a full-size S2/E7T1 glass-epoxy flexbeam were tested in a hydraulic load frame under combined axialtension and transverse cyclic bending. The magnitude of the axial load remained constant and the direction of the load rotated with the specimen as the cyclic bending load was applied. The first delamination damage observed in the specimens occurred at the area around the tip of the outermost ply-drop group. Subsequently, unstable delamination occurred by complete delamination along the length of the specimen.Continued cycling resulted in multiple delaminations.A 2D finite element model of the flexbeam was developed and a geometrically non-linear analysis was performed.The global responses of the model and test specimens agreed very well in terms of the transverse displacement.The FE model was used to calculate strain energy release rates (G) for delaminations initiating at the tip of the outer ply-drop area and growing toward the thick or thin regions of the flexbeam, as was observed in the specimens. The delamination growth toward the thick region was primarily mode II, whereas delamination growth toward the thin region was almost completely mode I. Material characterization data from cyclic double-cantilevered beam tests was used with the peak calculated G values to generate a curve predicting fatigue failure by unstable delamination as a function of the number of loading cycles. The calculated fatigue lives compared well with the test data.
Hat stringer pull-off tests were performed to evaluate the delamination failure mechanisms in the flange region for a rod-reinforced hat stringer section. A special test fixture was used to pull the hat off the stringer while reacting the pull-off load through roller supports at both stringer
The effects of a uniform temperature change, from cure, on the stresses, axial expan sion, and thermally-induced twist for four specific angle-ply tube designs are considered. The study was conducted in the context of using tubes as major structural components in space structures. The four designs are: ( + Ø/ - Ø/040/ - Ø/ + Ø); (+ Ø2/040/- Ø2) ( + Ø2/ - Ø2/040); and (0 40/ + Ø2/ - Ø2). All tubes have off-axis fibers for holding the axial layers together and for providing some measure of torsional rigidity. All four designs have the same volume fraction of off-axis layers. In addition to considering smgle material tubes made of P75s/934, hybrid tubes using T300/934 in the off-axis layers and P75s/934 in the axial layers are studied. The stresses and deformations in the tubes are studied as a func tion of the four designs, the off-axis angle, and as a function of single-material and hybrid construction. The torsional and axial stiffnesses of the tubes are also computed. The study concludes that tube design has a minor influence on the stresses, axial stiffness, and axial thermal expansion. These are more a function of off-axis angle and material selection. On the other hand, because of the position of the + Ø and - Ø layers, both relative to each other and relative to the center of the tube, tube design does influence thermally-induced twist and torsional stiffness. None of the above designs is free of thermally-induced twist. In addition to tube design, the off-axis angle and material selection also influence thermally-induced twist and torsional stiffness.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.