Experimental investigation on a fully thermoplastic composite subjected to repeated impacts

Abstract

In the last years, the spread of composite laminates into the engineering sectors was observed; the main reason lies in higher values of strength/weight and stiffness/weight ratios with respect to conventional materials. Firstly, the attention was focused on fibres reinforced with thermosetting matrix. Then, the necessity to move towards low density and recyclable solutions has implied the development of composites made with thermoplastic matrix. Even if the first application of thermoplastic composites can be found into no structural parts, the replacement of metallic structural parts with such material in areas potentially subjected to impact has become worthy of investigation. Depending on the field of application and on the design geometry, in fact, some components can be subjected to repeated impacts at localized sites either during fabrication, activities of routine maintenance or during service conditions. When composite material was adopted, even though the impact damage associated to the single impact event can be slight, the accumulation of the damage over time may seriously weaken the mechanical performance of the structure. In this overview, the capability of energy absorption of a new composite completely made of thermoplastic material was investigated. This material was able to combine two conflicting requirements: the recyclability and the lightweight. In particular, repeated impacts at low velocity, on self-reinforced laminates made of polypropylene (PP), were conducted by experimental drop dart tests. Repeated impacts up to the perforation or up to 40 times were performed. In the analysis, three different energy levels and three different values of the laminate thicknesses were considered in order to analyse the damage behaviour under various experimental configurations. A visual observation of the impacted specimens was done, in order to evaluate the damage progression. Moreover, the trend of the peak force interchanged between specimen and dart and the evolution of both the absorbed energy and of the bending stiffness with the impacts number were studied. The results pointed out that the maximum load and the stiffness of the specimens tended to grow increasing the number of the repeated impacts. Such trend is opposite compared to the previous results obtained by other researchers using thermosetting composites.

Impact fatigue, multiple and repeated low-velocity impacts on FRP composites: A review

“…When plastic deformation is caused by successive impacts, absorbed energy decreases, but when tape breaking begins, absorbed energy increases. This result is contrary to what was previously observed by researchers using thermosetting composites [85,86].…”

“…Thicker samples require more impacts in order to penetrate [92]. The flexural stiffness is defined both by thickness and panel dimensions, smaller sized impact samples can be combined with interlaminar shear strength determination tests to assess the post-impact strength retention properties [86].…”

Experimental investigation on the effects of stainless-steel mesh reinforcing layers on low-velocity impact response of hybrid thermoplastic glass fiber composites

“…[19][20][21] Boria et al performed a thorough empirical investigation of the mechanical properties of a PP-based composite laminate under repeated LVI scenarios. 22 It was concluded that modifying the resin materials can govern the impact perforation energy, damage propagation, and permanent after-impact deformation of composite plates. 23,24 Moreover, inspecting the impacted samples introduces the matrix plasticization and straining of the whole yarn as the primary energy-absorbing mechanisms within the thermoplastic-based Glass composites.…”

Experimental and Numerical Study of the Influence of Pre-Existing Impact Damage on the Low-Velocity Impact Response of CFRP Panels

“…Although repeated impacts are not uncommon in real-world applications of composites [9,10], there are not many studies in the literature addressing that, either numerically-or experimentally-based, as most focus on multiple hits at the same point [11]. The studies on the repeated impact behavior of composites mostly concern repeated impact at the same location by considering different impactor or target features, such as impactor geometry [12][13][14] and mass [15], reinforcement type [16][17][18][19], laminate thickness [17,20], and stacking sequence [21,22]. Atas et al [23] investigated the effect of thickness on the repeated low-velocity impact response of E-glass/epoxy composites reporting the energy profiling diagram and the perforation limit.…”