Search

In space, surface tension plays an important role and liquid behaviour is much different from that on the ground. The static capillary surfaces in the annular space between two coaxial cones under microgravity are studied in this paper. Theoretical expressions of the capillary surfaces are derived and a procedure is developed to predict the capillary surfaces based on the expressions. By considering various liquid contact angles, liquid volumes, and container geometries, numerical simulation with the volume of fluid method is carried out and microgravity experiments in Beijing Drop Tower are performed. The numerical and experimental results are in good agreement with theoretical predictions. Furthermore, capillary surfaces in an annulus with constant cross-section and in a spherical tank with a central column are also discussed. z ¯ 3 will decrease obviously with the increase of the liquid contact angle. The theoretical models and findings will be great helpful for liquid management in space and the evaluation of propellant residue. [ABSTRACT FROM AUTHOR]

Drop tower is an important facility for conducting microgravity experiments on the ground. Since the Beijing drop tower was put into operation in 2003, a large number of scientific experiments have been carried out in the fields of microgravity fluid physics, combustion, materials science and fundamental physics. The drop tower has two operation modes: single capsule falling and double capsule falling, with the microgravity levels reaching 10−2g ~ 10−3g and 10−5g respectively. In order to meet the demand of multi-level microgravity levels in ground microgravity experiments, a double capsule microgravity level control system based on the cold-gas micro thruster is developed. The micro thrusters are mounted in the inner capsule of the double capsule system. During the fall of the double capsule, the cold-gas micro thrusters thrust in the opposite direction of the movement of the structure, which increases the resistance of the inner capsule to realize the control of microgravity level. The measurement results of the high-precision accelerometer show that the 10–3 ~ 10−5g microgravity level can be controlled by this system. [ABSTRACT FROM AUTHOR]

The tuning of the structural batteries for various applications of transportation is an ambitious target. The pollutant emission and mostly the process for battery recycling and recovery are peculiar aspects to consider for new designs. The goal is to reduce the weight. In this frame, taking into account that the traditional battery packs do not contribute to the structural performance, it is worth to underline the solution of the structural batteries allows to increase the mechanical properties as they are integrated into the primary structure. The paper establishes the response of a composite structural battery model subjected to low-velocity impact tests. The process used to manufacture the structural battery model is described, and the experimental activities are performed by a customized drop tower and finally replicated numerically by explicit code to enhance the comprehension of the structural dynamics. Differences with respect to a carbon fiber laminate are highlighted both for the force released at the impact and dart displacement, for the same levels of energy. [ABSTRACT FROM AUTHOR]

During spaceflight, humans experience a variety of physiological changes due to deviations from familiar earth conditions. Specifically, the lack of gravity is responsible formany effects observed in returning astronauts. These impairments can include structural as well as functional changes of the brain and a decline in cognitive performance. However, the underlying physiological mechanisms remain elusive. Alterations in neuronal activity play a central role in mental disorders and altered neuronal transmission may also lead to diminished human performance in space. Thus, understanding the influence of altered gravity at the cellular and network level is of high importance. Previous electrophysiological experiments using patch clamp techniques and calcium indicators have shown that neuronal activity is influenced by altered gravity. By using multi-electrode array (MEA) technology, we advanced the electrophysiological investigation covering single-cell to network level responses during exposure to decreased (micro-) or increased (hyper-) gravity conditions. We continuously recorded in real-time the spontaneous activity of human induced pluripotent stem cell (hiPSC)-derived neural networks in vitro. The MEA device was integrated into a custom-built environmental chamber to expose the system with neuronal cultures to up to 6 g of hypergravity on the Short-Arm Human Centrifuge at the DLR Cologne, Germany. The flexibility of the experimental hardware set-up facilitated additional MEA electrophysiology experiments under 4.7 s of high-quality microgravity (10-6 to 10-5 g) in the Bremen drop tower, Germany. Hypergravity led to significant changes in activity. During the microgravity phase, the mean action potential frequency across the neural networks was significantly enhanced, whereas different subgroups of neurons showed distinct behaviors, such as increased or decreased firing activity. Our data clearly demonstrate that gravity as an environmental stimulus triggers changes in neuronal activity. Neuronal networks especially reacted to acute changes in mechanical loading (hypergravity) or de-loading (microgravity). The current study clearly shows the gravity-dependent response of neuronal networks endorsing the importance of further investigations of neuronal activity and its adaptive responses to micro-and hypergravity. Our approach provided the basis for the identification of responsiblemechanisms and the development of countermeasures with potential implications on manned space missions. [ABSTRACT FROM AUTHOR]

Testing was performed in a partial gravity centrifuge drop vehicle in the Zero Gravity Research Facility with cast PMMA rods in concurrent axial buoyant stagnation flow to determine flammability limits as a function of partial gravity level. The partial gravity levels studied varied from 0.04 g to a simulated 1g for ambient oxygen concentrations from 13.2 % to 15.2 % O 2 by volume at an average 57.6 kPa (8.4 PSIA) ambient pressure, which is very close to the anticipated Lunar habitat pressure. The PMMA flammability boundary as a function of oxygen concentration and gravity level has been determined at five gravity levels. Coriolis effects appear to be minimal in the stagnation region where the flame is stabilized while the tips of the flame do show some bending at the higher gravity levels. Lunar gravity levels are near the minimum in the oxygen - gravity level flammability boundary. This suggests that fire is a significant safety risk for future exploration missions to the Moon since materials are screened in normal gravity to evaluate their safe use in space. If normal gravity screening is not conservative, a material derating method will need to be applied to ensure the material is not flammable on the Moon. Since the blowoff boundary appears to be linear with forced flow velocity, it may be possible to conduct elevated forced flow blowoff testing that could then be extrapolated down to effective Lunar gravity levels to provide an oxygen delta between 1g and Lunar flammability limits to derate the material. • Partial gravity centrifuge tests were performed to evaluate the effect of gravity on the flammability of PMMA rods. • Flammability of PMMA rods is enhanced in partial gravity with a maximum flammability near Lunar gravity levels. • Enhanced Lunar flammability has fire safety implications for future exploration missions to the Moon. [ABSTRACT FROM AUTHOR]

During spaceflight, humans experience a variety of physiological changes due to deviations from familiar earth conditions. Specifically, the lack of gravity is responsible for many effects observed in returning astronauts. These impairments can include structural as well as functional changes of the brain and a decline in cognitive performance. However, the underlying physiological mechanisms remain elusive. Alterations in neuronal activity play a central role in mental disorders and altered neuronal transmission may also lead to diminished human performance in space. Thus, understanding the influence of altered gravity at the cellular and network level is of high importance. Previous electrophysiological experiments using patch clamp techniques and calcium indicators have shown that neuronal activity is influenced by altered gravity. By using multi-electrode array (MEA) technology, we advanced the electrophysiological investigation covering single-cell to network level responses during exposure to decreased (micro-) or increased (hyper-) gravity conditions. We continuously recorded in real-time the spontaneous activity of human induced pluripotent stem cell (hiPSC)-derived neural networks in vitro. The MEA device was integrated into a custom-built environmental chamber to expose the system with neuronal cultures to up to 6 g of hypergravity on the Short-Arm Human Centrifuge at the DLR Cologne, Germany. The flexibility of the experimental hardware set-up facilitated additional MEA electrophysiology experiments under 4.7 s of high-quality microgravity (10–6 to 10–5 g) in the Bremen drop tower, Germany. Hypergravity led to significant changes in activity. During the microgravity phase, the mean action potential frequency across the neural networks was significantly enhanced, whereas different subgroups of neurons showed distinct behaviors, such as increased or decreased firing activity. Our data clearly demonstrate that gravity as an environmental stimulus triggers changes in neuronal activity. Neuronal networks especially reacted to acute changes in mechanical loading (hypergravity) or de-loading (microgravity). The current study clearly shows the gravity-dependent response of neuronal networks endorsing the importance of further investigations of neuronal activity and its adaptive responses to micro- and hypergravity. Our approach provided the basis for the identification of responsible mechanisms and the development of countermeasures with potential implications on manned space missions.

Background: Damping elements made of elastomer materials are used in almost every mechanical system to prevent damage to components caused by impact-like excitations and the resulting high-frequency, large-amplitude oscillations. The dynamics of these operating conditions exceed the performance limits of conventional experimental testing methods, impeding validated predictions of the damper's transmission behaviour. Objective: A method is proposed to directly investigate the influence of impacts on the transmission behaviour of elastomeric dampers by impact testing. Methods: Torsional-loaded elastomer dampers were experimentally investigated using a drop tower. During the experiment, a mass is brought into impact contact with a lever arm connected to the tested coupling. Measurements on resulting torsional oscillations and a comparison of the measurement results with a simple analytical model of the system allow for determining the coupling parameters stiffness and damping ratio. Results: The characteristic parameters stiffness and damping ratio of the elastomer damper were mapped as a function of excitation-amplitude and frequency. A comparison of drop-tower test results with servo-hydraulic measurements validated the determined parameters. Conclusions: Determining the transmission behaviour of elastomeric dampers from highly dynamic and impact-induced oscillation states proved to be a good approach to supplement established testing methods. [ABSTRACT FROM AUTHOR]

Gravity affects colloidal dispersions via sedimentation and convection. We used dynamic light scattering (DLS) to quantify the mobility of nanoparticles on ground and in microgravity. A DLS instrument was adapted to withstand the accelerations in a drop tower, and a liquid handling set-up was connected in order to stabilize the liquid temperature and enable rapid cooling or heating. Light scattering experiments were performed in the drop tower at ZARM (Bremen, Germany) during a microgravity interval of 9.1 s and compared to measurements on ground. Particle dynamics were analyzed at constant temperature and after a rapid temperature drop using a series of DLS measurements with 1 s integration time. We observed nanoparticles with average gold core diameters of 7.8 nm and non-polar oleylamine shells that were dispersed in tetradecane and had an average hydrodynamic diameter of 21 nm. The particles did not change their diameter in the observed temperature range. The particle dynamics inferred from DLS on ground and in microgravity were in good agreement, demonstrating the possibility to perform reliable DLS measurements in a drop tower. [ABSTRACT FROM AUTHOR]

Traumatic Brain Injury (TBI) is a significant public health and financial concern that is affecting tens of thousands of people in the United States annually. There were over a million hospital visits related to TBI in 2017. Along with immediate and short-term morbidity from TBI, chronic traumatic encephalopathy (CTE) can have life-altering, chronic morbidity, yet the direct linkage of how head impacts lead to this pathology remains unknown. A possible clue is that chronic traumatic encephalopathy appears to initiate in the depths of the sulci. The purpose of this study was to isolate the injury mechanism/s associated with blunt force impact events. To this end, drop tower experiments were performed on a human head phantom. Our phantom was fabricated into a three-dimensional extruded ellipsoid geometry made out of Polyacrylamide gelatin that incorporated gyri-sulci interaction. The phantom was assembled into a polylactic acid 3D-printed skull, surrounded with deionized water, and enclosed between two optical windows. The phantom received repetitive low-force impacts on the order of magnitude of an average boxing punch. Intracranial pressure profiles were recorded in conjunction with high-speed imaging, 25 k frames-per-second. Cavitation was observed in all trials. Cavitation is the spontaneous formation of vapor bubbles in the liquid phase resulting from a pressure drop that reaches the vapor pressure of the liquid. The observed cavitation was predominately located in the contrecoup during negative pressure phases of local intracranial pressure. To further investigate the cavitation interaction with the brain tissue phantom, a 2D plane strain computational model was built to simulate the deformation of gyrated tissue as a result from the initiation of cavitation bubbles seen in the phantom experiments. These computational experiments demonstrated a focusing of strain at the depths of the sulci from bubble expansion. Our results add further evidence that mechanical interactions could contribute to the development of chronic traumatic encephalopathy and also that fluid cavitation may play a role in this interaction. [ABSTRACT FROM AUTHOR]

Fibre metal laminates (FMLs) are lightweight structures with high structural performance and are suitable for many industrial applications. This work describes the impact behaviour of novel sisal fibre-reinforced aluminium laminates (SiRAL) and their dependence upon the orientations of the fibres, the composite core used and the surface treatment of the metal skins. A cold-pressing technique is used to produce SiRALs in six configurations. The FMLs here also have treated or untreated aluminium skins (2024 T3) and three different types of core materials (0°/90° fabric, ±45° fabric and random matt). The ±45° core treated SiRAL provides the highest energy absorption and deflection properties. The pre-treatment of aluminium skins using sandpaper, deep cleaning and primer significantly affects the delamination of the panels under bending impact. The findings reveal that the SiRAL concept is a promising multifunctional FML suitable for different applications that require lightweight, bending and impact performance, together with sustainability characteristics. [ABSTRACT FROM AUTHOR]

Traumatic Brain Injury (TBI) is a significant public health and financial concern that is affecting tens of thousands of people in the United States annually. There were over a million hospital visits related to TBI in 2017. Along with immediate and short-term morbidity from TBI, chronic traumatic encephalopathy (CTE) can have life-altering, chronic morbidity, yet the direct linkage of how head impacts lead to this pathology remains unknown. A possible clue is that chronic traumatic encephalopathy appears to initiate in the depths of the sulci. The purpose of this study was to isolate the injury mechanism/s associated with blunt force impact events. To this end, drop tower experiments were performed on a human head phantom. Our phantom was fabricated into a three-dimensional extruded ellipsoid geometry made out of Polyacrylamide gelatin that incorporated gyri-sulci interaction. The phantom was assembled into a polylactic acid 3D-printed skull, surrounded with deionized water, and enclosed between two optical windows. The phantom received repetitive low-force impacts on the order of magnitude of an average boxing punch. Intracranial pressure profiles were recorded in conjunction with high-speed imaging, 25 k frames-per-second. Cavitation was observed in all trials. Cavitation is the spontaneous formation of vapor bubbles in the liquid phase resulting from a pressure drop that reaches the vapor pressure of the liquid. The observed cavitation was predominately located in the contrecoup during negative pressure phases of local intracranial pressure. To further investigate the cavitation interaction with the brain tissue phantom, a 2D plane strain computational model was built to simulate the deformation of gyrated tissue as a result from the initiation of cavitation bubbles seen in the phantom experiments. These computational experiments demonstrated a focusing of strain at the depths of the sulci from bubble expansion. Our results add further evidence that mechanical interactions could contribute to the development of chronic traumatic encephalopathy and also that fluid cavitation may play a role in this interaction.

Surface tension tanks exploit the liquid surface tension in liquid transport and gas–liquid separation to provide gas-free propellant for the thruster. High transport efficiency of deflectors can ensure liquid relocation in the microgravity environment within a short period of time, which is helpful for providing gas-free propellant. This paper explores transport efficiency of deflectors through drop tower experiments and numerical simulations with the volume of fluid method. The experimental and numerical results show that both the liquid flow speed and the mass flow rate along deflectors increase as the widths of deflectors increase. Besides, a new type of propellant management device, which consists of four deflectors and four anti-sloshing baffles, is verified with numerical simulations and drop tower experiments. Moreover, long-term conditions are predicted by using similarity theories. These results can provide important references for the design of plate tanks. [ABSTRACT FROM AUTHOR]

In the following article impact experiments from experimental and numerical point of view will be described. In order to keep the number of parameters to be varied manageable, the focus was firstly on similar plain concrete plates. The experiments were carried out with the aim to collect reference values and to simulate these experiments as basis for further investigations. The only parameter that has been changed was the impact velocity. The experimental part of the publication deals with manufacturing of the specimens, the experimental setup, the execution of the experiments, the measured values, and a brief evaluation of the results. The numerical part of the publication deals with the computation of experimental results using the simulation program LS‐Dyna. In this context, it will be explained how the model was created and which boundary conditions and material models were used. Furthermore, the calibration of the materiel law is described. Subsequently, a comparison between the experimental and simulated results is carried out. The focus of the further investigations will be the consideration of concrete layers reinforced with textiles under impact load. The work presented here deals with the matrix material of the textile reinforced concrete and thus laid the foundation for these investigations. [ABSTRACT FROM AUTHOR]

This study presents the performance of carbon textile reinforcement used as strengthening layers for reinforced concrete (RC) slabs under repeated impact loads. In order to reveal the contribution of carbon textile reinforcement to the behavior of RC slabs under impacts, five identical RC slabs with the dimensions of 1.5 m × 1.5 m × 0.20 m were manufactured and tested at the Technische Universität Dresden. To understand failure mechanisms of RC slabs under impact loadings, two specimens were kept unstrengthened and tested under different impact velocities. The rest of the specimens was strengthened with three different carbon textile reinforcements embedded in an additional 2 cm fine‐grained concrete layer and subjected to impact loads with the same striker velocity. The results observed from the tests revealed that the carbon textile reinforcement is very effective at increasing the impact capacities of the specimens. Additionally, displacement–time histories and crack profiles are highly affected due to the carbon textile reinforcement types and ratios during the impact loadings. [ABSTRACT FROM AUTHOR]

This study aims at examining the impact behavior of hybrid carbon and glass fibers woven-ply reinforced PolyEther Ether Ketone (PEEK) thermoplastic quasi-isotropic laminates. An instrumented Charpy pendulum is specifically designed to estimate its capability to perform low velocity impact tests. Through the comparison of different impact methods (Quasi-static indentation tests, Charpy and drop tower impacts), the influence of impact velocity on the impact behavior of this hybrid composite material is investigated. From the obtained results, it appears that the macroscopic impact response is similar in terms of force-displacement response. Indeed, the impact velocity is significantly higher (2.5 times higher) with falling weight impact testing. In PEEK-based laminates whose mechanical behaviour is time-dependent, slow loading rates (e.g. Charpy impact testing) are instrumental in ruling the dissipated energy (+20% at 35 and 40J) as well as in increasing the permanent indentation (1.6 times higher) that is always higher than the Barely Visible Impact Damage.

Fibre metal laminates (FMLs) are lightweight structures with high structural performance and are suitable for many industrial applications. This work describes the impact behaviour of novel sisal fibre-reinforced aluminium laminates (SiRAL) and their dependence upon the orientations of the fibres, the composite core used and the surface treatment of the metal skins. A cold-pressing technique is used to produce SiRALs in six configurations. The FMLs here also have treated or untreated aluminium skins (2024 T3) and three different types of core materials (0°/90° fabric, ±45° fabric and random matt). The ±45° core treated SiRAL provides the highest energy absorption and deflection properties. The pre-treatment of aluminium skins using sandpaper, deep cleaning and primer significantly affects the delamination of the panels under bending impact. The findings reveal that the SiRAL concept is a promising multifunctional FML suitable for different applications that require lightweight, bending and impact performance, together with sustainability characteristics.

This paper refers to studying the effect of microgravity on the friction behavior of friction units and to further analyzing the influencing mechanism. The potential factors affecting the friction behavior of the moving joints of space mechanisms in microgravity environment were analyzed. A friction apparatus was designed and manufactured by reducing the complexity and costs. A microgravity test program was designed and performed using the Beijing Drop Tower platform with designing three positioning styles for the friction apparatus by changing the relationship between the normal load and gravity. For each positioning style of the friction apparatus, the friction behavior of friction unit in gravity and microgravity environment was compared. It was found that microgravity can not only change the value of friction, but also affect its dynamic characteristics. For different positioning styles of the friction apparatus, the influencing mechanism of microgravity on friction behavior was different. The normal load or the relative position between the connected bodies of the friction unit could be changed by microgravity, resulting in that the friction behavior was different from that in gravity environment. [ABSTRACT FROM AUTHOR]

A series of experiments were conducted in the 3.6-s microgravity drop tower and normal gravity to investigate the effect of solid fuel curvature, conduction, and reradiation on the flame extinction of spherical polymethyl methacrylate (PMMA). In the semi-quiescent microgravity environment, flame extinction was observed if the PMMA diameter was larger than 40 mm, because of a smaller flame conductive heating in larger diameter (i.e., the curvature effect). Compared to the droplet combustion with a low evaporation point and fast heat convection in the liquid phase, the solid fuel has a high pyrolysis point and large transient heat conduction. Thus, the large surface reradiation effectively cools down the fuel surface to promote extinction. Also, as the initial burning duration increases, the conductive cooling into the solid fuel decreases, which delays or prevents the flame extinction in microgravity. The extinction criterion for microgravity flame is explained by the critical mass flux and mass-transfer number. This work helps to understand the curvature effect of solid fuel on flame extinction and the material fire safety in the microgravity spacecraft environment. [ABSTRACT FROM AUTHOR]

The study is devoted to the flames instabilities that occur during the transition from the normal gravity to zero one. The experiments were carried out at the Bremen Drop tower. A stoichiometric methane-air flame was investigated during the first second after the capsule release. High amplitude oscillations with periodic flame flashback inside the burner and detaching of the hot spots during the transition period were found. The similarity of oscillation spectra for stoichiometric flames with different flow rates was observed. The coincidence of the first and second fundamental harmonics of the oscillations frequencies for all the studied flows indicates instability mechanism independence from the Reynolds number for the investigated range of Re: 600–2000 (laminar and weak turbulent regimes). It was found that the oscillations logarithmic decrements for all flow Reynolds numbers under investigation have a similar value. Based on a linear approximation, the hydrodynamic instability of a flame was considered and it was shown that the transition from conditions of normal terrestrial gravity to microgravity leads to the flame instability region extension which was confirmed experimentally. A following instability occurrence model was proposed. The buoyant motion of Kelvin-Helmholtz vortices arising at the air/combustion products interface slows down due to gravity decrease. Therefore the vortices deform not only the flame front tip but side part as well, leading to flame front deformations and constrictions, forming separating hot spots. • Flame instability occurs during the transition from normal gravity to zero one. • High amplitude oscillations and hot spots detaching are found. • The first and second harmonics of the oscillations are independent on flow rate. • Oscillations logarithmic damping decrements are constant for various flow velocities. [ABSTRACT FROM AUTHOR]

A test series of 15 reinforced concrete (RC) plates was carried out in the drop tower of the Otto Mohr Laboratory of Technische Universität Dresden. In these tests, the structural behavior of RC plates of different thicknesses was investigated under impact load. Within this report, the investigated specimen and the used drop tower facility are introduced. Furthermore, the experimental program and the experimental results will be shown. Following, the influence of different thicknesses and impact velocities are presented and discussed. The different damage levels of the RC plates influenced by the specific variation of the impact speed form a very good basis for further investigations in this scientific field. Especially the view into the plates, which was made possible by saw cuts, extends the understanding of the impact behavior considerably. [ABSTRACT FROM AUTHOR]

The objective of the present paper is to investigate the overall impact performance of various riot helmets in a comparative study. The National Institute of Justice (NIJ-0104.02) and the Canadian Standards Association (CS A-Z611-02) standards regulate the use of riot helmets in North America. Both sets of standards have a number of requirements for impact performance. Impact tests carried out with the use of a drop tower apparatus compliant with NIJ test protocols demonstrated large differences in impact attenuation level among the helmets from six manufacturers in terms of frontal and lateral impacts to the shell, and face-shield deflection. For instance, the impact energy yielding a headform acceleration of 300 g's was measured for each helmet for frontal impacts on the helmet shell. Values ranging from 69 J up to 171 J were obtained. The energy levels of typical crowd-control threats, e.g., baton blows and projectiles, were quantified and compared with the impact energy values used in the standards. It is observed that the NIJ face-shield deflection requirement is low as compared to actual riot threats, whereas the CSA requirements are more in line with these threats. A novel method was devised to objectively assign a global impact performance score to each helmet. This method takes into account the frontal and lateral impacts to the shell as well as the face-shield deflection tests. It is based on the directional origin of the threat and the geometry of the helmets (frontal percentage area of the visor). From these global performance scores, it is possible to obtain a ranking of the various riot helmets used in the present comparative study. Based on the analysis of the global scores, it was found that appropriate protection of the face (through an impact resistant visor) is the key feature for a helmet that will be used in riot environments. [ABSTRACT FROM AUTHOR]

Experiments were conducted to measure the flame propagation rate of a plug-flow flame through a combustible matrix of randomly oriented cubes of polyurethane foam in microgravity and normal gravity as a function of the forced air flow. The experiments in microgravity were conducted at the Japan Microgravity Center (JAMIC) drop tower, which provides 10s of microgravity. The normal gravity experiments were simulations of the microgravity experiments, and by comparison, were used to determine the effect of gravity on the flame propagation process. The experiment was conducted in a cylindrical geometry. Ignition was accomplished by means of a hot-surface igniter brought into direct contact with the foam at one end of the sample holder. The other end of the sample was sealed to a fan drawing air through the sample, which was adjustable using a variable DC power supply. In this configuration the flame propagation is flow-assisted. The flame propagation rate was determined by means of the temperature histories provided by thermocouples placed along the centerline of the sample. It is found that, both in normal and microgravity, as the air flow rate is increased the flame propagation velocity increases. Comparison between the normal and microgravity experiments shows that the microgravity combustion is greatly influenced by the ignition period. In microgravity the time to initiation of flame propagation is significantly longer than the corresponding time in normal gravity. This is due to the contribution of the buoyant flow that assists the forced flow during the initiation period in normal gravity. A simplified analytical model is presented for correlation of the velocity data.

The aim of the study was to compare the physical and mechanical properties of known prostheses for cranioplasty: knitted Codubix based on polypropylene and Modela-cryl resin based on PMMA. It was expected that the study would allow to check whether it is possible to combine their properties, which should enable the preparation of a new material with properties combining the best features of both components. Physico-chemical and mechanical properties were evaluated. It was found that the two materials meet the requirements for chemical purity, ensuring the safety of their use. Regarding the mechanical properties, the energy of impact diffusion for two types of prostheses was determined applying the Drop Tower technique. The polymerisation heat of Modela-cryl resin was determined in real time using the DSC technique. [ABSTRACT FROM AUTHOR]

Strain rate sensitivity has been widely recognized as a significant feature of the dynamic mechanical properties of lithium-ion cells, which are important for their accurate representation in automotive crash simulations. This research sought to improve the precision with which dynamic mechanical properties can be determined from drop tower impact testing through the use of a diaphragm to minimize transient shock loads and to constrain off-axis motion of the indenter, specialized impact absorbers to reduce noise, and observation of displacement with a high speed camera. Inert pouch cells showed strain rate sensitivity in an increased stiffness during impact tests that was consistent with the poromechanical interaction of the porous structure of the jellyroll with the liquid electrolyte. The impact behaviour of the inert pouch cells was similar to that of an Expanded Polypropylene foam (EPP), with the exception that the inert pouch cells did not show hysteretic recovery under the weight of the indenter. This suggests that the dynamic mechanical behaviour of the inert pouch cells is analogous to a highly damped foam.