Dynamic response of a material during a high-speed impact

Abstract

The material of an aircraft structure must resist a high-speed impact-an impact of a bird or hail at the flight speed (a bird strike or hail strike). The proof of this resistance can be provided in the experimental or numerical way. The recent development of numerical methods takes advantage of the numerical way. However, the necessity to verify the used numerical models creates new challenges for the experiments. The goal is to measure and record a great deal of data during the very short time of a high-speed impact. The use of high-speed load cells makes it possible to record the time-dependent force response of an impact event. However, the major difficulty of this approach is the existence of parasitic resonances. The experimental stand, the support of the studied specimen, exhibits an eigen dynamic response and in consequence, the final measured dynamic response is coupled with the stand-structure one. The objective of a stand design is therefore to minimize these parasitic resonances, occurring due to the stand-structure dynamics. In this way, special equipment for the experimental research of the dynamic response during a high-speed impact is designed and realized. The stand is to support the specimen during the impact of a projectile (a bird or hail) ejected from a pneumatic gun. The stand design enables an impact at any angle (from 0°to 90°), without changing the contact point. The dynamic-response measurement is realized by means of load cells. The equipment is designed and optimized by means of FEM numerical simulations with the aim to minimize the parasitic resonances of the stand structure. Keywords: high-speed impact, bird strike, hail strike, impact projectile, parasitic resonances, virtual-load-cell record Strukture iz materialov za letala morajo prenesti trke razli~nih predmetov, ki z veliko hitrostjo udarjajo vanje. To so lahko udarci ptic, to~e ali drugih delcev med potovanjem letala z veliko hitrostjo. Odpornost proti tak{nim udarcem lahko dolo~imo eksperimentalno ali numeri~no oz. z ra~unalni{kimi simulacijami, ki imajo z razvojem novih metod mnoge prednosti. Vendar pa je numeri~ne metode oz. modele potrebno eksperimentalno verificirati, kar predstavlja dolo~en izziv. Cilj je merjenje in zapisovanje velikega {tevila podatkov v zelo kratkem~asu, zelo hitrega udarca. Uporaba celic za merjenje hitrih obremenitev omogo~a zapisovanje odgovora~asovno odvisnih sil med trki. Vendar je pri tem glavna te`ava tega pristopa nastanek {kodljivih (parazitnih) resonanc. Izdelano eksperimentalno stojalo je bilo podpora za {tudiranje primerov z lastnimi vrednostmi dinami~nega odgovora in posledi~no kon~nimi izmerjenimi dinami~nimi odgovori v povezavi s strukturo stojala. Cilj oblikovanja stojala je zato zmanj{anje tak{nih {kodljivih resonanc zaradi dinamike strukture stojala. Na ta na~in so avtorji oblikovali in izdelali posebno opremo za eksperimentalne raziskave dinami~nega odgovora med udarjanjem zelo hitrih projektilov. Stojalo je prena{alo udarce razli~nih projektilov, ptic ali to~e, izstreljenih s pnevma...