Study On The Low Velocity Impact Behavior Of Composite Foam Sandwich Structures

With the extraordinary high strength and stiff to weight ratio, composite materials sandwich structures play an important role in the aeronautics, astronautics, transportation as well as facility fields. Sandwich structures can be produced in a variety of constructions based on different requirements, such as high strength, high modulus, impact resistance, protection structures and so on. Composite materials sandwich structures are susceptible to some impact, for example, the bird impact and the explosion impact etc. So it is urgent to improve the impact resistance for the development of sandwich structures. Nowadays, most of the studies are focused on the Z-direction strength and the strength after impact(CAI), however, few research are focused on the sandwich structures energy absorption abilities, which plays an important role for sandwich structure impact resistance. Based on this situation, this paper is mainly focused on how to improve the energy absorption abilities to increase sandwich impact resistance.In this study, we used vacuum assist resin infusion technology to produce woven roving laminates with and without surface mat and investigated the mechanical properties of laminates to prove the inter-laminar toughness effect. Besides, we used woven roving, unidirectional woven roving and multi-axial fabrics and surface mat to produce sandwich structures. We used the quasi-static indentation(QSI) force test and low velocity impact(LVI) test to measure different structures' energy absorption abilities and discussed the relationship between QSI and LVI. Finally we may draw some conclusions as follows:(1) Adding surface mat to woven roving can improve the energy absorption for the laminates. Besides, the surface mat can restrict the curvature of the fiber yarns which can reduce the stress between fibers and resin, and then reduce the failure area.(2) The different structures of the sandwich structure face sheet have a serious influence on the QSI tests: face sheet with surface mat can improve the ability of energy absorption; orthotropic lay-up structure using woven roving has the best energy absorption ability among all the orthotropic lay-up samples, while, using woven roving and multi-axial fabrics to produce the quasi-isotropic lay-up samples(woven roving is laid at the outermost layer) has the best ability of energy absorption contrast to the other quasi-isotropic counterparts.(3) The different structures of the sandwich structures face sheet have a serious influence on the LVI tests: inter-laminar toughing can avoid the delamination failing in the same layer and then increase the failure resistance, besides, the face sheet with surface-mat have bigger contact peak force and energy absorption efficiency compared to the specimens with the same thickness; increasing the thickness of face sheet does not influence the contact force, while this would decrease the energy absorption efficiency; the angle of the lay-up has different effects on different failure model specimens, that is for woven roving specimens, which are mainly failed through fiber breakage, the lay-up angle does not influence the energy absorption efficiency, however, for unidirectional woven roving specimens, which the failure model are mostly by delamination, the smaller angle between the adjacent layers, the smaller delamination area, which will decrease the energy absorption efficiency. Among the quasi-isotropic lay-up samples, woven roving specimens have the best energy absorption efficiency.(4) The failure mechanism for LVI and QSI test are different, so using QSI technology to predict or replace LVI test has some limits.