A thorough understanding of polymer behavior under asymmetric thermal loading is a prerequisite for assessing the fire resistance of polymer structures. Yet, despite the widespread use of both fiber-reinforced and unfilled thermoplastics, their performance under such conditions remains insufficiently studied. In the present study polyoxymethylene (POM) tensile test specimens are exemplarily studied, the high thermal load is applied by a laser. Whereas on the irradiated front side temperatures considerably above the melting temperature occurred, temperatures on the back side were below. Quasistatic uniaxial tensile tests at room temperature after cooling showed that the elongation at break is strongly reduced by the irradiation, for stiffness and strength only a minor decrease could be observed. The transient temperature field inside the specimens was simulated by finite element analysis. This temperature was used to introduce a temperature dependent damage thickness which describes the thickness of the zone assumed to be irreversibly damaged by the thermal load. Based on this, an empirical model for the decrease of elongation at break of the investigated POM specimens is proposed.

The Hydrodynamic Ram (HRAM) effect occurs when a high kinetic energy projectile penetrates a fluid filled area, e.g., a liquid filled tank. The projectile transfers its momentum and kinetic energy to the fluid, what causes a sudden, local pressure rise, further expanding as primary shock wave in the fluid and developing a cavity. It is possible that the entire tank ruptures due to the loads transferred through the fluid to its surrounding structure. In the past decades, additionally to experimental investigations, HRAM has been studied using various computational approaches particularly focusing on the description of the Fluid-Structure Interaction (FSI). This article reviews the published experimental, analytical and numerical results and delivers a chronological overview since the end of World War II. Furthermore, HRAM mitigation measures are highlighted, which have been developed with the experimental, analytical and numerical toolboxes matured over the past 80 years.

Continuous fiber reinforced structures used in lightweight aerospace, defense, and automotive applications may be subjected to impact loads while operating under varying temperature conditions. In order to accurately predict the behavior of these materials under these extreme conditions, a temperature chamber has been developed and implemented on a split Hopkinson Tension Bar. The new setup has been used to realize - for the first time - in-plane shear tests on the aerospace grade material IM7/8552 at a strain rate of approx. 1000 1/s and temperatures ranging from -54 degrees C to +121 degrees C. The test results are post-treated using different approaches and compared with results treating decoupled thermal and strain rate conditions available in the literature. The results showed that shear strength of the material decreases linearly with temperature and that corrected strength increases logarithmically with strain rate at all three temperatures in an equivalent manner. The conducted investigations enable to conclude that superposition of strain rate and temperature, as used in many simulation models, appears to be valid for the considered material. Finally Scanning Electron Microscope pictures give insights into the micro-scale failure mechanisms involved at the various testing conditions.

The increasing presence of drones seen on the battlefields in modern conflicts poses new threats to manned military aircraft or rotorcraft. In order to assess this potential threat, this manuscript first summarizes all confirmed and suspected collisions between drones and aerostructures and the damage resulting from these collisions. Furthermore, this manuscript reviews experimental and numerical investigations on collision of drones with aerostructures. Additionally, some light is shed onto current regulation for drone operations intended to avoid collisions between drones and aircraft. Whilst these regulatory measures can prevent commercial aircraft to collide with drones, the authors believe that there is an inherent threat for civil and military rotorcraft due to their structural design and the fact that it is not possible to completely separate the airspace between drone operations and rotorcraft operations, in particular in the context of rescue missions in an urban or hostile environment. Furthermore, the stealth capability of 5th generation fighters may be compromised by damage suffered from collision with drones.

Micromechanical simulation of fiber reinforced unidirectional composites typically relies on representative volume elements comprising fibers and matrix. In order to optimize the validity of the predictions at minimum computational effort, it is important to have an understanding on the required level of detail of the micromechanical simulation. Whilst it is clear, that for predicting the longitudinal properties of composite materials based on micromechanical simulation, it is sufficient to model a single fiber and the surrounding matrix with the appropriate fiber volume fraction and matrix volume fraction, for transverse properties, this is not sufficient. The distribution of fibers and their closest distance are relevant for the failure of composite materials under transverse loading. In order to assess the required number of fibers in the micromechanical simulation, this paper proposes image based statistical analysis of composite microstructures. A micrograph of a carbon fiber/ epoxy composite was digitized and subsets of variable size were analyzed and compared to the statistical fiber volume fraction and fiber distribution of the total micrograph. it was found that a subset including 36 fibers has the same statistical characteristics in terms of fiber distance and fiber orientation as a subset including 25,000 fibers. It is therefore concluded that a minimum of 36 statistically distributed fibers should be included in a representative volume element of a composite microstructure if transverse mechanical properties are to be predicted.

Due to the increasing availability of drones, collisions between privately piloted drones and aircraft are becoming increasingly probable. It is commonly accepted, that during a collision, drones pose a higher threat to the aircraft than birds of the same mass due to the higher strength and stiffness. This manuscript investigates collisions between drones and rotorcraft based on high-fidelity Finite Element simulations. For this purpose, a detailed simulation model of a battery pack, which is considered the most dangerous component for in collision scenarios, for a DJI MAVIC 2 Zoom drone (mass 2-lb) was developed for the explicit FE code LS-DYNA. The battery pack then virtually collided with the engine cowling of a high-speed rotorcraft. The predictions obtained from the high-fidelity finite element simulations indicate that the engine cowling suffers some amount of damage during the collision with the drone battery. However, for the collision scenarios investigated within this work, the battery did not penetrate the engine cowling.

Nanoparticles are known to enable the modification of the properties of the material they are integrated into. In the context of ballistic protection, previous works have demonstrated that graphene and Montmorillonite (MMT) particles included in high-density polyethylene (HD-PE) and used as a matrix enable an increase in the ballistic performance, of consolidated woven aramid fabrics. Furthermore, the ballistic performance has been reported to be influenced by the in-plane shear properties of the impacted materials. In this context, quasi-static and high-rate in-plane shear tests have been conducted on two types of reinforcements, aramid, and carbon woven fabrics, consolidated by a high-density polyethylene matrix enriched by graphene, MMT and a mix of graphene and MMT nanoparticles. The conducted investigations provide for the first time in the literature the results of high-rate in-plane shear tests on aramid woven reinforcement consolidated with nanoparticle-enriched and not enriched high-density polyethylene composites. Despite the use of the same reinforcement and enriched matrix material as in previous works of literature, no significant differences in terms of in-plane shear behavior have been observed for any of the different types of nanoparticles integrated into the matrix. Nevertheless, the obtained results demonstrate a clear strain rate sensitivity of the tested materials.Highlights Aramid and carbon fabrics were consolidated with nanoparticle-enriched HD-PE Quasi-static and high-rate in-plane shear tests were conducted No influence of the nanoparticles could be identified A clear strain-rate sensitivity could be identified for both composites Overview of the manufacturing and quasi-static as well as high-rate in-plane shear testing campaign of the aramid and carbon fiber woven composites featuring a nanoparticle-enriched high-density polyethylene matrix. The test results demonstrate no clear influence of the nanoparticules but a strong strain rate sensitivity of the materials. image

Drones operating in an urban environment pose a potential collision threat to rotorcraft. In this paper, the battery pack of the DJI MAVIC 2 ZOOM is analyzed since the battery is considered to be the greatest threat due to its high weight and stiffness. Following a pyramid-type building block approach, a high-fidelity model simulation was developed for LSDYNA based on a wide range of experiments, ranging from quasi-static material tests to quasi-static component tests up to high-velocity impact experiments. The high-fidelity model allows the prediction of damage in potential collision scenarios between a high-speed rotorcraft and the battery pack of the drone. For the particular impact configuration analyzed within this paper, the drone battery does not cause catastrophic failure of the windshield of the rotorcraft.

The recycling of composite materials is nowadays a major challenge as it is systematically associated with a downcycling due to the reduction of the fiber length. However, recent works demonstrated that the delamination-based recovery of the unitary layers of laminated structures with preserved mechanical properties is possible under dedicated loading conditions. The presented work aims at investigating this innovative process and in particular the interlaminar crack initiation from a straight notch milled in the material by using an impact loading; further crack extension to recover the complete lamina being the following step of the process. A Split Hopkinson Bar setup has been used in a Direct Impact configuration and a dedicated test setup has been implemented to impose translational and rotational kinematics to the impacted side of the tested specimens in order to enable crack initiation and propagation over a few millimeters. Imposing translational kinematics to the impacted side of the specimen has been shown to induce cracks in a reproducible manner. Numerical simulation results explain the more favorable conditions provided by the translational kinematic.

Additive manufacturing of topology optimized metallic parts has widened the design space for aerospace engineering, enabling near-net shape production of complex shaped parts, which could not be produced with conventional shape cutting, thus enabling weight savings and enhanced sustainability. This manuscript describes in detail our process chain including the draft phase, concept phase, construction phase and virtual process simulation for the example of a cargo door latch fitting. Subsequently, the latch fitting was manufactured in Scalmalloy (R) using an EOS M400 laser powder bed fusion (LPBF) machine and subsequently mechanically tested. The experimental results exceeded the expectations with respect to the strength of the latch fitting.

Additive manufacturing of topology optimized metallic parts has widened the design space for aerospace engineering, enabling near-net shape production of complex shaped parts, which could not be produced with conventional shape cutting, thus enabling weight savings and enhanced sustainability. This manuscript describes in detail the manufacturing process of a topology optimized cargo door latch fitting produced from Scalmalloy (R) using an EOS M400 laser powder bed fusion (LPBF) machine. The manuscript further details the life cycle inventory for the manufacturing process and the life cycle analysis of the caro door latch fitting. It was found that the additive production phase accounts for approximately 96% of the total carbon footprint of the manufacturing of the component. The production of the powder itself is responsible for more than 50% of the CO2 emissions encountered during the manufacturing process.

A structure's sustainability depends not only on its components, but also on the manufacturing process. The adhesive layer mostly increases the structural weight, reducing weight-specific properties, beside hindering its disassembly and sorting at end-of-life. This study investigates an alternative joining method based on ultrasonic welding for upcycled honeycomb core sandwich panels. Thermoplastic composite skins, reinforced with flax or glass fibres, are connected to an upcycled polyethylene core made from disposed bottle caps and tested under quasi-static and dynamic loads. A life cycle assessment evaluates the environmental benefits of skin/core welding compared with adhesive bonding. Welded panels made from similar skins and cores presented similar to higher weight-specific flexural properties of adhesive-bonded structures (up to 45 % increase), while specific energy absorption under impact is increased by up to 23 % with welded joints. Skin/core welding reduces the panel environmental damage by up to 71 %, with an increment of up to 130 % in its eco-mechanical efficiency.

View Video Presentation: https://doi.org/10.2514/6.2023-1841.vid In this manuscript, the cavity growth during a hydrodynamic ram scenario is studied using both, high-fidelity numerical simulations with ANSYS AUTODYN and a recently published analytical solution. As a reference case, well documented experiments from the literature were taken. It was found that the high-fidelity numerical simulation was capable of predicting the cavity growth with reasonable accuracy, whilst the analytical approach failed to predict cavity growth, especially during later stages of the hydrodynamic ram event.

The loading-rate mechanical response of the mode I delamination in composites and adhesively bonded joints was investigated. The tests were carried out using a recently developed Guided Double Cantilever Beam test method. Three different data reduction methods were proposed and assessed: a displacement-based formulation, a near-crack-tip displacement formulation, and a numerical assessment using the Virtual Crack-Closure Technique method. The methods account for the dynamic effects which may be present. While small differences between the three different methods can be seen, no rate-dependency higher than the uncertainty for the materials and the loading rates considered have been evidenced.

In the presented work, high velocity hail impact tests have been conducted on an instrumented rigid target. The synthetic hails, consisting of ice spheres with a nominal diameter of 48 mm and a mass between 50 and 55 g conditioned to temperatures in the range of-3,-20 and-50 degrees C were accelerated using a gas gun. The range of impact velocities was 46-314 m/s leading to maximal impact energies between 2000 and 3000 J which had not been investigated so far in the literature. Peak force and time to reach the peak force where extracted from the experimental tests. The obtained results were compared with results from the literature using empirical equations established in another publication from the literature. The obtained results confirm the trend reported in the literature in terms of dimensionless peak force versus dimensionless impact velocity. However, the dimensionless time to reach the peak force during the impact could not be compared successfully with previous results. The role of the target characteristics is estimated to be the reason for this difference.

In this manuscript, Current Component A lightning strike tests on three different types of carbon fiber reinforced composite panels are analyzed. The panels feature different levels of lightning strike protection: no protection, medium protection and heavy protection. In particular it was analyzed if there were any direct correlations between the peak electric current of the artificial lighting strike and the recorded velocities at the back surface of the composite panels. The existence of a master curve correlating the peak electric current, the mass of the composite panels and the measured back surface velocity was demonstrated. This finding implies that the back surface velocity correlates linearly to the inertia of the panel and the peak current of the lightning strike.

The in-plane shear strength of tri-axial braided composite materials was measured for three different braid angles (30°, 45°, and 60°) and two strain rates (0.001 s −1 ; 3 s −1 ) using the three-rail shear test. The in-plane shear strength was found to be sensitive to both—the braid angle and the strain rate. An increase of braid angle resulted in a reduction of shear strength, whilst an increase of loading rate resulted in an increase of shear strength of 8%–17%, depending on the braid angle.

Due to the increasing availability of drones, collisions between privately piloted drones and aircraft are becoming increasingly probable. It is commonly accepted, that during a collision, drones pose a higher threat to the aircraft than birds of the same mass due to the higher strength and stiffness. This manuscript presents experimental data recorded during quasi-static and high velocity impact experiments with critical components of the DJI Mavic 2 Zoom. Due to their high mass, strength and stiffness, the batteries were found to be the most critical component of a drone. The motors had higher strength and stiffness than the batteries, but due to their low weight (only about 10% of the battery), the motors are considered less critical. Cameras were deemed uncritical due to low strength, stiffness and mass. Under high velocity impact, the batteries showed a fluid-type flow behavior which has not yet been reported before and which might guide future simulation work for drone impact scenarios.