Drop Tower Tests Research Articles

Testing Liquid Distribution in a Vane-Type Propellant Tank under Conditions of Microgravity Using a Drop Tower Test

Propellant management devices (PMDs) are a key component used to manage liquid propellant in a propellant tank under zero gravity conditions. A microgravity drop tower test system was established to investigate the performance of a PMD. A single module was used for the experiments, and the microgravity level was less than 3 × 10 − 3 g . Anhydrous ethanol was used as the simulate liquid. Different volume fractions of liquid were used to study the influence of the PMD on performance management. Experiments were conducted with the position of the container oriented in different directions. Changes in the gas-liquid interface were studied during the test. This kind of vane transports liquid through the rectangular area between the vane and the wall. The velocity flows along the vane of different liquid volume fractions in the tank were different at the beginning ( t < 0.8 s ) compared with the end of the test. The liquid relocation time was less than 0.8 s while the liquid volume fraction was larger than 25%. The liquid relocation time was prolonged when the liquid volume fraction was less than 25%. The liquid climbing height along the vane under microgravity increased as the volume fraction of liquid reduced. The climbing velocity of the liquid is half reduction when the liquid volume fraction is small. The time for the liquid transferred from the top of the tank to the liquid outlet can be obtained by climbing velocity. It shows that the maneuverability of the satellite decreases at the end of its life. The above results are applicable to all propellant tank with vertical vanes. These results provide a favorable reference for further optimized design of vertical vane-type propellant tanks.

Newly Developed Anti-Buckling Fixture to Assess the In-Plane Crashworthiness of Flat Composite Specimens

Despite superior specific mechanical characteristics of carbon-fiber-reinforced polymers (CFRPs), a lack of understanding of their fracture mechanisms under different impact conditions has limited the application of CFRP energy-absorbing structures. To avoid complex and expensive tests on the final structure, it is more convenient to test flat elements. To prevent catastrophic crushing due to the global buckling, flat specimens must be supported by a specific fixture. Previously developed fixtures had shortcomings like tearing of the specimen, jamming of the fixture, short crushable length, or they were specifically designed only for one failure mode. This newly designed fixture overcomes the limitations of previously published solutions. The final configuration includes cylindrical anti-buckling columns 10 mm in diameter and spaced 65 mm apart with adjustable heights. The fixture is designed for rectangular specimens with dimensions of 150 × 100 mm and different thicknesses up to 16 mm, like the ones mandated by the ASTM D7137 standard test method for compression after impact analysis. Other features of this new fixture are the possibility to study the effects of different defects on the crashworthiness of composites, higher crushing area, and integration with Instron drop tower and hydraulic testing machines.

Design and Fabrication of a Drop Tower Testing Apparatus to Investigate the Impact Behavior of Spinal Motion Segments.

The vertebral column is the second most common fracture site in individuals with high-grade osteoporosis (30-50%). Most of these fractures are caused by falls. This information reveals the importance of considering impact loading conditions of spinal motion segments, while no commercial apparatus is available for this purpose. Therefore, the goal was set to fabricate an impact testing device for the measurement of impact behavior of the biological tissues. In the present study, first, a drop-weight impact testing apparatus was designed and fabricated to record both force and displacement at a sample rate of 100 kHz. A load cell was placed under the sample, and an accelerometer was located on the impactor. Previous devices have mostly measured the force and not the deformation. Thereafter, the effect of high axial compression load was investigated on a biological sample, i.e., the lumbar motion segment, was investigated. To this end, nine ovine segments subjected to vertical impact load were examined using the fabricated device, and the mechanical properties of the lumbar segments were extracted and later compared with quasi-static loading results. The results indicated that the specimen stiffness and failure energy in impact loading were higher than those in the quasi-static loading. In terms of the damage site, fracture mainly occurred in the body of the vertebra during impact loading; although, during quasi-static loading, the fracture took place in the endplates. The present study introduces an inexpensive drop-test device capable of recording both the force and the deformation of the biological specimens when subjected to high-speed impacts. The mechanical properties of the spinal segments have also been extracted and compared with quasi-static loading results.

Eco-friendly sandwich panel based on bottle caps core and sustainable components: Static and dynamic characterisation

A sandwich structure made of sustainable components is investigated under quasi-static and dynamic conditions. The upcycled plastic bottle caps are used to manufacture a greener circular cell honeycomb core, based on a full factorial design. A recycled PET foil is used as skins, being compared to a classic panel with aluminium skins. The particle-reinforced adhesive is also tested by adding recycled rubber particles, from remoulded tyres, and cement particles. Three-point bending test and a low-velocity drop-tower test are performed on sandwich structures. Flexural modulus has a 19% increase with aluminium skins, while core shear modulus increases by 27% with cement-reinforced PET panels. Energy absorption in quasi-static tests increased by 26% with rubber inclusions in aluminium-based samples, while no significant effect is observed in low-velocity impact tests. Aluminium skins lead to increments of up to 198% for specific energy absorption and 298% for specific maximum load under impact. The satisfactory results of the static and dynamic characterisation of the bottle cap structure highlight the promising characteristic of the reuse of plastic waste in lightweight structural applications.

Combat helmet liner design for blunt impact absorption using multi-output Gaussian process surrogates

A finite element based computational model simulating the standard drop tower test for military helmets was created and used in conjunction with a multi-output Gaussian process surrogate to seek different designs of helmets for improved blunt impact performance. Experimental drop test results were used for the validation of the model’s ability to simulate impact. The influence of foam stiffness, impact velocity, strap tension, as well as pad placement and size on parameters on the peak linear acceleration (PLA) of the headform was investigated for the first time through a surrogate model trained by strategically choosing simulation points. Impact velocity was found to have the greatest effect. The strap tension and foam pad stiffness ranges examined within this sampling plan were found to have less of an effect on the performance of the helmet than the pad size and shape parameters examined. The surrogate modeling approach was used to quantify the influence of design parameters and can lead to not only improved helmet designs but also new data-driven design metrics and testing standards to accelerate the development of TBI-mitigating helmets.

Application of air-bubble cushioning to improve the shock absorption performance of type I industrial helmets

The industrial helmet is the most used and effective personal protective equipment to reduce work-related traumatic brain injuries. The Type I industrial helmet is a basic helmet model that is commonly used in construction sites and manufacturers. The purpose of the current study was to investigate if shock absorption performance of these helmets could be improved by using an air-bubble cushioning liner to augment the helmet’s suspension system. Drop impact tests were performed using a commercial drop tower test machine according to the ANSI Z89.1 Type I drop impact protocol. Typical off-the-shelf Type I industrial helmets were utilized in the study. The effects of the air-bubble cushioning on the helmets’ shock absorption performance were evaluated by comparing the original off-the-shelf helmet samples to the helmets equipped with an air-bubble cushioning liner. The air-bubble cushioning liner (thickness 5 mm) was placed between the headform and the helmet when being tested. The impactor had a mass of 3.6 kg and was free-dropped from different heights. The maximal peak transmitted forces for each of the tests have been evaluated and compared. Our results show that the shock absorption effectiveness of the air-bubble cushioning is dependent on the magnitude of the impact force. At lower drop heights (h<1.63 m), the air-bubble cushioning liner has little effect on the transmitted impact forces, however, at higher drop heights (h⩾1.73 m) the air-bubble cushioning liner effectively reduced the peak transmitted forces. At a drop height of 1.93 m (the highest drop height tested), the air-bubble cushioning liner reduced the peak transmitted force by over 80%. Our results indicate that adding an air-bubble cushioning liner into a basic Type I industrial helmet will substantially increase shock absorption performance for large impact forces.

Experimental and Numerical Impact Analysis of Automotive Bumper Brackets Made of 2D Triaxially Braided CFRP Composites.

The impact behavior of carbon fiber epoxy bumper brackets reinforced with 2D biaxial and 2D triaxial braids was experimentally and numerically analyzed. For this purpose, a phenomenological damage model was modified and implemented as a user material in ABAQUS. It was hypothesized that all input parameters could be determined from a suitable high-speed test program. Therefore, novel impact test device was designed, developed and integrated into a drop tower. Drop tower tests with different impactor masses and impact velocities at different bumper bracket configurations were conducted to compare the numerically predicted deformation and damage behavior with experimental evidence. Good correlations between simulations and tests were found, both for the global structural deformation, including fracture, and local damage entities in the impact zone. It was proven that the developed phenomenological damage models can be fully applied for present-day industrial problems.

Experimental investigation of liquid transport in a vane type tank of satellite with microgravity

Propellant tank is used to store the propellant in propulsion system of satellite. Propellant management device (PMD) is the key component in propellant tank to manage the liquid propellant under zero gravity. In this paper, a microgravity drop tower test system was established to investigate the performance of vanes and refillable reservoir separately. Single module is used for experiment tests, and the microgravity level is between 10−2 g0 and 10−3 g0. Vane is fixed in a plexiglas container which provide a visual windows for the inner flow distribution. The anhydrous ethanol is used as analogue liquid. Different kinds of vanes were used to study influence of the geometry on the transport performance. Experiment tests of refillable reservoir were performed with different direction of gravity. Changes of liquid-gas interface during the test are studied. The width of the vane is related to the velocity of the liquid flow along the vane. The liquid climbing height along vane under microgravity is proportional to the time t1/2. Experiment results show that the direction of microgravity has great effect on the expulsion efficiency of a vane type tank. Experimental results provide a favorable reference for further optimization design of vanes and refillable reservoir.

Predicting the low velocity impact damage of a quasi-isotropic laminate using EST

In this paper, the low velocity impact (LVI) on a quasi-isotropic laminate [45/0/–45/90]3s (QIL) is studied to predict the deformation response and damage state of the laminate. This stacking of a QIL is a benchmark case that results in a “rotating-fan” pattern of delamination damage due to the impact. Drop-tower tests were performed with an impact energy of 25 J and an impactor mass of 7.5 kg. 3D digital image correlation (3D DIC) was carried out to measure the in situ deformation of the laminate. Non-destructive inspection (NDI) including ultrasound C-scanning and X-ray micro computed tomography (micro-CT) were done to characterize the overall damage footprint and the internal detailed damage morphology. The computational model is an extension and refinement of the model developed in Refs. [74,76]. Enhanced Schapery Theory (EST) is used as the constitutive model and implemented with a user material subroutine in the commercial code Abaqus. The EST uses Schapery theory for pre-peak damage and the crack band model for post peak failure. The major contributions reported in this paper are as follows; in the experimental study, the damage mechanisms have been illustrated with high-resolution micro-CT scanning, while in the numerical study, the “rotating-fan” pattern, damage-free cone and damage modes interaction have been accurately and efficiently captured with a uniform, non-fiber-aligned mesh.

Homogenized shell element-based modeling of low-velocity impact response of stainless-steel wire mesh

In this study, we describe the development of a shell model-based macro-scale approach for a stainless steel 304 wire mesh using Hill’s yield criterion and elasto-plastic material behaviors. The constants for orthotropic elastic-material response and the parameters for non-linear behavior were determined from experimental tests. For validation and comparison, the results obtained using this macro-scale model were compared with the experimental data obtained from drop-tower impact tests and the simulation results from a meso-scale model. The comparison highlighted that the macro-scale model of the wire mesh is more suitable for large-size simulations.

Statistical study of performance properties to impact of Kevlar® woven impregnated with Non-Newtonian Fluid (NNF)

This investigative work was carry out through a factorial planning, using Design of Experiment (DoE) in order to evaluate the impact performance properties of Kevlar® woven structure impregnated with Non-Newtonian Fluids (NNF). Pull out and drop tower tests were performed. The pull out test showed that Kevlar® strength values with NNF composition 3 were better (10.55 N) when compared to others (1 and 2). The drop tower test showed that woven samples with highest concentration of NNF nanoparticles (3OR) exhibited the best behavior with respect to the penetration depth for P1 (19.5%) and S1 (48.0%) knife blade geometries. Thus, evidencing best residual energy dissipation when compared to the others. Results also showed that the composition (1, 2 and 3) of NNF as well as the orientation of the woven layers can be used to improve impact performance properties. Therefore, the impact protection performance depends on the friction between the yarns (pull out), the knife blade geometry and mainly the composition of the NNF which, in turn, is directly related to the nanoparticle and agent content of silane coupling present in the composition of the Non-Newtonian Fluid. Finally, this study also demonstrates that the use of statistical analysis promoted the improvement for obtaining and effectiveness of the behavior of lightweight impact protection textile structures.

Behaviour of reinforcement in drop tower beam tests

Drop tower tests help to gain understanding about the general behaviour of reinforced concrete members under impact loading and to analyse strains and strain rates occurring within their reinforcement. For this purpose, beam and slab specimens are usually employed. The main advantage of beams compared to slabs is that they are less complex due to the almost two-dimensional instead of three-dimensional wave propagation within them. To investigate the steel strains and strain rates, ten impact tests on beam specimens with various impact energies were performed. The impactor sizes and velocities were varied. The reinforcement bars of the beams were instrumented with semiconductor strain gauges. The measured data suggest that the occurring strains in beam tests are independent of the loading velocity. The same was found for the strain rates. The reason is that higher impact energies mostly influence the concrete damage due to spalling on the impact-facing side which happens after the maximum strains occurred. The strains in the reinforcement bars generally result from the overall deflection because of the impact, the spreading of longitudinal waves in the horizontal direction, and the localized cracking of the concrete due to the formation of a punching cone.

A numerical investigation of puddle jumping

The nearly step reduction in gravity arising in routine drop tower tests leads to numerous interesting large-length-scale capillary flow phenomena. For example, a liquid puddle at equilibrium on a hydrophobic substrate is observed to spontaneously jump from the substrate during such tests. Implementing a modified version of the open-source Gerris code, we numerically investigate such a puddle jump phenomenon for a variety of water puddles on flat substrates. We quantify a range of puddle jump characteristics including jump time, jump velocity, and free puddle oscillation modes for an unearthly range of drop volumes between 0.001 ml and 15 ml and substrate contact angles between 60° and 175°. A numerical regime map is constructed identifying no jump, standard jump, bubble ingestion, geyser formation, drop fission, and satellite puddle jump regimes. Favorable agreement is found between the simulations, experiments, simple theoretical models, and scaling laws.

Application of polyethylene air-bubble cushions to improve the shock absorption performance of Type I construction helmets for repeated impacts.

The use of helmets was considered to be one of the important prevention strategies employed on construction sites. The shock absorption performance of a construction (or industrial) helmet is its most important performance parameter. Industrial helmets will experience cumulative structural damage when being impacted repeatedly with impact magnitudes greater than its endurance limit. The current study is to test if the shock absorption performance of Type I construction helmets subjected to repeated impacts can be improved by applying polyethylene air-bubble cushions to the helmet suspension system. Drop impact tests were performed using a commercial drop tower test machine following the ANSI Z89.1 Type I drop impact protocol. Typical off-the-shelf Type I construction helmets were evaluated in the study. A 5 mm thick air-bubble cushioning liner was placed between the headform and the helmet to be tested. Helmets were impacted ten times at different drop heights from 0.61 to 1.73 m. The effects of the air-bubble cushioning liner on the helmets' shock absorption performance were evaluated by comparing the peak transmitted forces collected from the original off-the-shelf helmet samples to the helmets equipped with air-bubble cushioning liners. Our results showed that a typical Type I construction helmet can be subjected to repeated impacts with a magnitude less than 22 J (corresponding to a drop height 0.61 m) without compromising its shock absorption performance. In comparison, the same construction helmet, when equipped with an air-bubble cushioning liner, can be subjected to repeated impacts of a magnitude of 54 J (corresponding to a drop height 1.52 m) without compromising its shock absorption performance. The results indicate that the helmet's shock absorbing endurance limit has been increased by 145% with addition of an air-bubble cushioning liner.

Evaluation of bone excision effects on a human skull model-II: Finite element analysis.

Patient-specific computational models are powerful tools which may assist in predicting the outcome of invasive surgery on the musculoskeletal system, and consequently help to improve therapeutic decision-making and post-operative care. Unfortunately, at present the use of personalized models that predict the effect of biopsies and full excisions is so specialized that tends to be restricted to prominent individuals, such as high-profile athletes. We have developed a finite element analysis model to determine the influence of the location of an ellipsoidal excision (14.2 mm × 11.8 mm) on the structural integrity of a human skull when exposed to impact loading, representing a free fall of an adult male from standing height. The finite element analysis model was compared to empirical data based on the drop-tower testing of three-dimensional-printed physical skull models where deformations were recorded by digital image correlation. In this bespoke example, we found that the excision site did not have a major effect on the calculated stress and strain magnitudes unless the excision was in the temporal region, where the reduction in stiffness around the excision caused failure within the neighboring area. The finite element analysis model allowed meaningful conclusions to be drawn for the implications of using such a technique based on what we know about such conditions indicating that the approach could be both clinically beneficial and also cost-effective for wider use.

Impact protection of borosilicate glass plates with elastomeric coatings in drop tower tests

Drop tower testing was performed on borosilicate glass plates to determine the effectiveness of an elastomeric polyurethane/urea coating against impact and to improve our understanding of how the coating could be used to protect high voltage (HV) porcelain bushings against rifle damage [1,2]. Drop tower testing was found to be a very useful and practical tool for the prediction of failures of very brittle materials subjected to low energy impact as a function of coating thickness. The testing also improved our understanding of the impact behavior of the coatings and how to relate their low energy impact performance in drop tower tests to much higher energy impact situations, such as rifle bullet impact. By performing a series of drop tower tests on the plates with the coating thickness ranging from 1.3 to 5.6 mm, the effectiveness of the coating was determined from the critical contact force and from the critical impulse. These critical parameters were determined at the onset of catastrophic fractures of the uncoated and coated glass specimens. It was found that the coating protected the glass samples by a factor of 5.25 times with respect to the critical maximum contact force, and 9.31 times with respect to the critical impulse. Therefore, the overall coating effectiveness was estimated to be 7.28. It was also shown that the high effectiveness of the elastomeric coating can be achieved for a coating thickness as small as 1.3 mm, for a range of critical impact energies between 8.7 J and 22.7 J. Since the same coating with a thickness of 3 mm efficiently protected HV porcelain bushings against rifle impact at energies as high as 3.1 kJ [2], the very high effectiveness of the protection for small coating thicknesses could be independent of the impact energy within the range of energies considered. This therefore could be the main observation from the comprehensive work performed in this study and in [1,2].

Experimental investigation into static and dynamic axial crush of composite tubes of glass-fiber mat/PA6 laminates

In this paper, the results are present of an experimental investigation into quasi-static and dynamic crushing responses and crashworthiness characteristics of round-hat-shaped crash tubes made with glass long-fiber-mat/PA6 laminates of around 45 vol%. These characteristics were explored using a high-dynamic hydraulic test machine. The crash tubes failed by the progressive splaying mode except for some tubes in the quasi-static tests, which failed by the mid-length collapse mode. The specific energy absorption (SEA, 42.0 J/g) in the quasi-static tests increased to around 52 J/g in the dynamic tests. The increased energy absorption at the higher test speed was analyzed through the microscopic behavior of the small bending radius of the splayed laminar bundles and fragmentation of the lamina bundles. The drop-tower tests show that the dependency of the performance of the crash tubes on the test speed appears only at relatively low speed (1 m/s in the limited tests reported in this paper), but the performance becomes relatively steady at much higher impact speeds. The impactor mass and tube length had almost no effect on the crash characteristics of the mean crushing load, SEA, and peak load.

New Multiphase CP and DP 1000 MPa strength level grades for improved performance after hot forming

Pure martensitic steels have after hot forming limited performance in terms of rest ductility which limits the application in crash relevant parts. New steel grades were designed in the EU project HOTFORM including the corresponding process routes. These steel grades have ferritic-martensitic dual phase (DP) and martensitic-bainitic complex phase (CP) microstructures after hot forming process. The laboratory tests show an improved formability after hot forming. The basic concepts of the new alloys are explained. Furthermore, for validation of upscaling purposes a semi-industrial test is carried out and the results are discussed. The main application is for vehicle safety. This is evaluated by comparing the crash performance of these hot formed grades with cold rolled DP1000 and CP1000 for crash cans in a drop tower test.

Impact of thin‐walled square aluminum tubes

AbstractThin‐walled profiles are widely used as crash energy absorbers. In this paper thin‐walled square aluminum crash boxes under impact load are studied numerically. ABAQUS commercial software is used for simulating the CBes. The simulated model is validated experimentally using a drop tower test. Folding pattern of a CB has a significant effect on the energy absorption of it. In this study the effects of different parameters such as wall thickness and width on the dynamic behavior and folding pattern of the CB under impact load have been investigated.

Beyond density: Mesostructural features of impact resistant wood

Wood is a neglected impact-resistant biological material: despite its use in tools and weapons for millennia the dynamic properties and common features between species such as maple, live oak, and others are poorly understood. In this study, the impact resistance in the radial loading direction of nine tree species was studied using drop-tower testing, micro-computed tomography, and scanning electron microscopy. It was found that unlike in quasi-static conditions, density alone is a poor predictor of mechanical behavior in wood and that specific mesostructural features (interlocking grain, diffuse porous vessel distribution and intermittent rays) improved impact strength. A new, hierarchical failure of individual tracheids and the bulk fibers resembling progressive delamination of fiber-composites was observed in African mahogany, the most impact resistant tree species tested.