Thermoplastic composites are ever more expanding their use in many engineering applications ranging from aerospace to automotive and marine fields. This success, mainly due to several peculiarities such as high vibration dampening, short processing times with respect to thermoset based ones and intrinsic recyclability, is still partially limited by some drawbacks such as the high cost of production tools and the limited capability to give complex shapes. Thermoplastic composites, nevertheless, are very interesting for their higher toughness. The impact behavior of thermosetting based laminates is one of the major concern in structural composites because damages, induced during the production process, in service or during maintenance, can seriously reduce the performances of composite systems, thus compromising their durability, even when their size is below a visible threshold. Hybridization approaches are a very effective way to balance stiffness and toughness of composite structures. Common hybridizations techniques combine different types of fibers (very stiff fibers alternated with ductile ones) distributed in different laminas or in the same one to form interply or intraply laminates, respectively. In this contribution, a new hybridization design, here cited as IGIS (Interfacial Graded Interlaminar Strength), is proposed. IGIS design is essentially based on the hybridization of the matrix instead of the reinforcing fibers, thus having the advantage of not affecting the reinforcement configuration. Specifically, with the awareness that a key role is covered by the interfacial strength between fibers and matrix, new laminate configurations have been investigated. They are based on polypropylene films (PP), neat (N) or previously compatibilized (C) by the inclusion of 2% by weight of a common coupling agent (polypropylene grafted with malheic anhydride), and glass fiber fabrics. Different samples have been developed by properly alternating N and C layers with glass fiber fabrics to obtain 3 symmetric (HNCN, HCNC and HX) and 2 asymmetric (HCN and HNC) configurations, characterized by different gradations of the interfacial strength along the laminate thickness. For comparison, two configurations based exclusively on neat or on modified layers of PP, respectively coded as NEAT and COMP, have been prepared and considered as reference materials. For each sample, plates constituted by 20 layers, symmetrically stacked with respect to the middle plane and coded as [(0/90)10]s, have been obtained by using typical film stacking and compression molding procedures. With the main purpose to highlight potentials of this new class of hybrid laminates, low-velocity impact tests were carried out using an instrumented drop weight machine at different levels of impact energy. These tests, properly integrated with both visual inspections of damaged zones and/or morphological analyses, could give useful insights on how to use such new hybridization approach to design new composites capable of exploiting complex failure mechanisms to maximize the impact resistance without significantly affecting the static mechanical response.
Low-velocity impact behavior of thermoplastic composites laminates with graded interface strength
P Russo;L Sorrentino
2016
Abstract
Thermoplastic composites are ever more expanding their use in many engineering applications ranging from aerospace to automotive and marine fields. This success, mainly due to several peculiarities such as high vibration dampening, short processing times with respect to thermoset based ones and intrinsic recyclability, is still partially limited by some drawbacks such as the high cost of production tools and the limited capability to give complex shapes. Thermoplastic composites, nevertheless, are very interesting for their higher toughness. The impact behavior of thermosetting based laminates is one of the major concern in structural composites because damages, induced during the production process, in service or during maintenance, can seriously reduce the performances of composite systems, thus compromising their durability, even when their size is below a visible threshold. Hybridization approaches are a very effective way to balance stiffness and toughness of composite structures. Common hybridizations techniques combine different types of fibers (very stiff fibers alternated with ductile ones) distributed in different laminas or in the same one to form interply or intraply laminates, respectively. In this contribution, a new hybridization design, here cited as IGIS (Interfacial Graded Interlaminar Strength), is proposed. IGIS design is essentially based on the hybridization of the matrix instead of the reinforcing fibers, thus having the advantage of not affecting the reinforcement configuration. Specifically, with the awareness that a key role is covered by the interfacial strength between fibers and matrix, new laminate configurations have been investigated. They are based on polypropylene films (PP), neat (N) or previously compatibilized (C) by the inclusion of 2% by weight of a common coupling agent (polypropylene grafted with malheic anhydride), and glass fiber fabrics. Different samples have been developed by properly alternating N and C layers with glass fiber fabrics to obtain 3 symmetric (HNCN, HCNC and HX) and 2 asymmetric (HCN and HNC) configurations, characterized by different gradations of the interfacial strength along the laminate thickness. For comparison, two configurations based exclusively on neat or on modified layers of PP, respectively coded as NEAT and COMP, have been prepared and considered as reference materials. For each sample, plates constituted by 20 layers, symmetrically stacked with respect to the middle plane and coded as [(0/90)10]s, have been obtained by using typical film stacking and compression molding procedures. With the main purpose to highlight potentials of this new class of hybrid laminates, low-velocity impact tests were carried out using an instrumented drop weight machine at different levels of impact energy. These tests, properly integrated with both visual inspections of damaged zones and/or morphological analyses, could give useful insights on how to use such new hybridization approach to design new composites capable of exploiting complex failure mechanisms to maximize the impact resistance without significantly affecting the static mechanical response.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
