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Author : Pascal Casari
Results 1 - 3 of 3
New Methodology of Bending Fatigue Test and Slamming Test on PVC Foam Core Sandwich with GFRP Faces
The purpose of this study is to investigate the influence of a spatially moving load and edge effects on the fatigue life of the foam-cored sandwich structures. A spatially moving load can be observed in structures subjected to slamming. A new geometry of specimen is developed to reduce the influence of edge effects in the test specimen. Numerical model results of the new geometry are presented. This study confirms that edge effects are leading to early failures and shear stress concentrations are significantly reduced near the edges, improving ASTM C393 standard.
Updated Fatigue Test Methods for Structural Foams and Sandwich Beams
Foam-cored sandwich yacht hulls are subjected to high core shear stresses during slamming events. As slamming is
repetitive by nature, failures observed on boats may be due to fatigue. This study aims to investigate possible improvements to
fatigue testing of both foam core materials and sandwich specimens. In general test set-up induces differences between the ways a
material behaves in a test coupon and in a real application. One such difference is “edge effect”, as the material behaviour can change
close to a free edge. For example, the micro-structure may have been affected by the specimen machining, which may influence
failure initiation. This is exacerbated if the test set-up induces stress concentrations close to the edge. Another difference is that in a
standard core shear fatigue testing by 4 point bending, the stress field is spatially static, when in a slamming event the stress field is
spatially variable. Does the material react differently to a static and moving stress field? This study aims to develop a core shear test
method replicating a moving stress field, free of edge effect. This paper presents the finding of the initial steps of this study: The
edge effect has been investigated using modified loading fixture. The moving stress field has been investigated with a modified 4-
point bending test using asynchronous loading. The differences in test results between the modified test methods and the relevant
standard test methods indicate that both aspects affect measured fatigue life.
Adhesive Bonding for Structural Marine Applications
In order to make the structural junction in a sailing boat, for example between the shell and the bulkheads, many nautical
builders use overlap joints. This technique is expensive and could be replaced by direct adhesive junction without
overlap. Structural adhesive bonding has been tested on three boats prototypes : a motor boat of 5.75 m long, and two
sailing boats one of 5.5 m long and one of 10 m long. The originality of those boats is the measurement device using
strain gages included on some of the junctions during the boats construction. Gages and sensors have also been placed
on the shell, the keel and the rigging: the stress state of the bonded junctions under sailing in different conditions can
then be qualified. Therefore, testing has been managed on specimens. A coupled loads tests (bending + compression) on
tee samples seems more pertinent to qualify tee junction for shipbuilding applications.