Dynamic Drop Test Research Articles

Subject-Specific Geometry of FE Lumbar Spine Models for the Replication of Fracture Locations Using Dynamic Drop Tests.

For traumatic lumbar spine injuries, the mechanisms and influence of anthropometrical variation are not yet fully understood under dynamic loading. Our objective was to evaluate whether geometrically subject-specific explicit finite element (FE) lumbar spine models based on state-of-the-art clinical CT data combined with general material properties from the literature could replicate the experimental responses and the fracture locations via a dynamic drop tower-test setup. The experimental CT datasets from a dynamic drop tower-test setup were used to create anatomical details of four lumbar spine models (T12 to L5). The soft tissues from THUMS v4.1 were integrated by morphing. Each model was simulated with the corresponding loading and boundary conditions from the dynamic lumbar spine tests that produced differing injuries and injury locations. The simulations resulted in force, moment, and kinematic responses that effectively matched the experimental data. The pressure distribution within the models was used to compare the fracture occurrence and location. The spinal levels that sustained vertebral body fracture in the experiment showed higher simulation pressure values in the anterior elements than those in the levels that did not fracture in the reference experiments. Similarly, the spinal levels that sustained posterior element fracture in the experiments showed higher simulation pressure values in the vertebral posterior structures compared to those in the levels that did not sustain fracture. Our study showed that the incorporation of the spinal geometry and orientation could be used to replicate the fracture type and location under dynamic loading. Our results provided an understanding of the lumbar injury mechanisms and knowledge on the load thresholds that could be used for injury prediction with explicit FE lumbar spine models.

Rolling droplets and partial discharges in AC electric field

High-voltage silicone insulators can be used in climatic conditions such as rain or fog since they are hydrophobic. However, water droplets lead to discharges, which reduces hydrophobicity of the silicone rubber which is, in turn, is a first step to failure of an insulator. To increase the resistance of the rubber to the discharges, it is necessary to study the discharges between droplets in detail.The present work is devoted to the study of the loss of hydrophobicity of silicone rubber due to rolling droplets and discharges between them on the inclined silicone rubber sample under AC voltage of 35 kV. An experimental setup used in the work has been developed based on Dynamic Drop Test (DDT) and makes it possible to study discharges only between droplets, and avoid contact of droplets with the electrodes.Simultaneous observation of droplets and discharges made it possible to distinguish characteristic events and to divide the loss of hydrophobicity into stages. Experiments showed that the behavior of the droplets changed gradually, while the discharges were observed only at the last stage. Presumably, the resistance of rubber to discharges is not the only factor that determines the time of loss of hydrophobicity. The very beginning of the process of loss of hydrophobicity should be investigated further.

Quasi-static and impact behaviour of foam-filled graded auxetic panel

Cellular structures (in general) and auxetic topologies (in particular) have excellent energy-dissipation characteristics and can be used as lightweight impact-energy absorbers. This paper aims to experimentally and computationally examine the behaviour of novel re-entrant auxetic graded aluminium panels filled with polyurethane foam in an auxetic pattern. The performance is compared with 3 non-graded, 1 graded and 2 foam-filled graded panels. The 6 compared auxetic panels share the same basic geometry but vary in the sheet thickness and the addition of polyurethane foam. The auxetic panels were built by corrugating and gluing 12 aluminium sheets. The material properties of the used aluminium sheets and foam were determined with standard mechanical testing. Detailed quasi-static and dynamic drop tests were conducted and compared with a non-linear computational model. The stress-strain relationships, deformation patterns, specific energy absorption, crash force efficiency and Poisson's ratio were comprehensively evaluated. Foam-filled panels revealed higher specific energy absorption and more stable deformation than non-filled panels. The developed computational models successfully describe mechanical and deformation behaviour and can be used for future virtual testing of other configurations.

Suitable Ultra-Thin Asphalt Binder Achieved the Energy Equilibrium

The tensile behaviour of asphalt binder films confined between aggregate particles as an adhesive was investigated to evaluate the direct adhesion bond between asphalt binder and surface of aggregate utilizing several laboratory experiments. The results were interrogated in terms of the mechanical, chemical and surface free energy theories. The preformed tests include dynamic shear rheometer (DSR), sessile drop and direct tension tests. The experimental results demonstrated a strong relationship between the internal work represented by bond energy and the external work represented by the practical work required to fracture from the direct tension test that can be used to estimate asphalt binder-aggregate combinations performance. A simulation for the adhesion behaviour using a static model in terms of external work and internal work to predict the suitable asphalt binder thickness required to prevent fatigue and rutting failures was proposed as a new design criterion for asphalt pavement. Keywords: Internal and external bonding work, asphalt binder, SFE, fracture work, direct tension test, DSR.

Experimental investigation of a flow-oriented throttleable injector designed for throttleable hybrid rocket motor

Easily achieving thrust throttling is a significant advantage of hybrid rocket motor. To achieve more stable combustion and reduce the pressure of the upstream feed system during the thrust throttling, it is necessary to control the injection conditions while controlling the oxidizer mass flow rate. In view of this, a flow-oriented throttleable injector that can control the injection pressure drop during the thrust throttling was designed, fabricated and tested. In order to verify the feasibility and obtain the injection pressure drop characteristics, cold flow tests of the flow-oriented throttleable injector were performed, including static injection pressure drop tests with/without back pressure and dynamic injection pressure drop tests with/without back pressure. Then, the steady-state hot test and thrust throttling hot tests of the throttleable hybrid rocket motor with the flow-oriented throttleable injector were conducted, in which the 98%H2O2/PE were adopted as the propellant combination and the controllable cavitating venturi was used to control oxidizer mass flow rate. In thrust throttling tests, the achieved maximum of the thrust throttling ratio was 8.65 under the condition that the change ratio of oxidizer mass flow rate was 7.19. During the thrust throttling, the motor worked stably, and the combustion chamber pressure, thrust and injector pressure drop varied approximately linearly with the linear variation of the oxidizer mas flow rate. The variation of injection pressure drop of the flow-oriented throttleable injector was much less than that of the conventional fixed structure injector, of which the injection pressure drop is proportional to the square of the oxidizer mas flow rate.

Lightweight and maintainable rotary-wing UAV frame from configurable design to detailed design

Rotary-wing unmanned aerial vehicles (UAVs) are widespread in both the military and civilian applications. However, there are still some problems for the UAV design such as the long design period, high manufacturing cost, and difficulty in maintenance. Therefore, this paper proposes a novel design method to obtain a lightweight and maintainable UAV frame from configurable design to detailed design. First, configurable design is implemented to determine the initial design domain of the UAV frame. Second, topology optimization method based on inertia relief theory is used to transform the initial geometric model into the UAV frame structure. Third, process design is considered to improve the manufacturability and maintainability of the UAV frame. Finally, dynamic drop test is used to validate the crashworthiness of the UAV frame. Therefore, a lightweight UAV frame structure composed of thin-walled parts can be obtained and the design period can be greatly reduced via the proposed method.

Mechanical and Thermal Properties of Carbon/Basalt Intra-ply Hybrid Composites. I. Effect of Intra-ply Hybridization

The effects of intra-ply hybridization on mechanical and thermal properties of carbon/basalt fibers reinforced epoxy composites were experimentally investigated. Combination of superior mechanical properties of carbon fiber, good thermal stability and basalt fiber toughness is the main purpose of designing of these composites. Three types of homogeneous carbon fiber reinforced polymer (CFRP), basalt fiber reinforced polymer (BFRP) and intra-ply hybrid of carbon/basalt reinforced polymer (CBFRP) composites were fabricated by using vacuum assisted resin infusion molding (VARIM) method. All fabricated composite plates were cut according to ASTM standard. The effect of incorporation of basalt fiber with carbon fiber on mechanical properties, such as modulus of elasticity, tensile strength, flexural modulus, flexural strength and inter laminar shear strength (ILSS) were studied by bending, tensile and short beam shear (SBS) experiments. Measurement of thermal conductivity, dynamic mechanic analyze (DMA), thermogravimetric analyze (TGA) tests were also carried out for thermal characterization of fabricated homogeneous and hybrid composites. Furthermore, dynamic drop test (DDT) was used to evaluate hybridization effect on hydrophobicity of composites. The results indicated that the CBFP hybrid composites perform a moderate mechanical performance between homogeneous CFRP and BFRP composites. On the other hand, incorporation of basalt fiber in the structure of carbon fiber composite not only enhances the thermal stability of composites but also moderates the fabrication price by alternating cheaper basalt fiber with expensive carbon fiber.

Investigation on leakage current, erosion, and hydrophobic performance ofhigh-voltage insulator coatings of different thicknesses

Room-temperature vulcanizing (RTV) silicone rubber is used as a high-voltage insulator coating to enhance the pollution performance of conventional insulators, and the electrical performance of RTV coating depends on the several parameters. The present study shows the effects of the thickness on the leakage current, erosion, and hydrophobic performance of high-voltage insulator coating. Several different thicknesses of RTV silicone rubber were taken into consideration on porcelain substrates. Erosion and leakage current performances of the samples were evaluated by using inclined-plane tests (IPTs) based on the IEC 60587 standard. Eroded masses and fundamental and harmonic components of the leakage currents were investigated with respect to coating thicknesses. On the other hand, hydrophobic features of the samples were evaluated by using dynamic drop tests (DDTs) with regard to CIGRE TB442 documentation. Time to loss of hydrophobicity and the level of the leakage currents were investigated in DDTs considering the thicknesses.

On the effectiveness of incorporating shear thickening fluid with fumed silica particles in hip protectors

The objective of this research is to develop a smart hip protector by incorporating shear thickening fluid (STF) into conventional foam hip protectors. The shear thickening properties of fumed silica particles dispersed in liquid polyethylene glycol (PEG) were determined from rheological tests. Dynamic drop tests, using a 4 kg drop platen at 0.5 m drop height, were conducted to study how STF improves energy absorption as compared to unfilled foam and PEG filled foam. The results show that PEG filled foam reduces the mean peak force transmitted by a further 55% and mean peak displacement by 32.5% as compared to the unfilled foam; the STF filled foam further reduces mean peak force and displacement by 15% and 41% respectively when compared to the PEG filled foam. At a displacement of 22 mm, the STF filled foam absorbs 7.4 times more energy than the PEG filled foam. The results of varying the drop mass and drop height show that the energy absorbed per unit displacement for STF filled foam is always higher than that of PEG filled foam. Finally, the effectiveness of a prototype of hip protector made from 15 mm thick STF filled foam in preventing hip fractures was studied under two different loading conditions: distributed load (plate drop test) and concentrated load (ball drop test). The results of the plate and ball drop tests show that among all hip protectors tested in this study, only the prototype can reduce the mean peak impact force to be lower than the force required to fracture a hip bone (3.1 kN) regardless of the type of loading. Moreover, the peak force of the prototype is about half of this value, suggesting thinner prototype could have been used instead. These findings show that STF is effective in improving the performance of hip protectors.

Optimization of the reefed parachute using genetic algorithm

PurposeThe purpose of this paper is to find optimal reef parameters to minimize the maximum instantaneous opening load for a reefed parachute with geometry and environmental parameters given in the model.Design/methodology/approachThe dynamic model Drop Test Vehicle Simulation (DTVSim) is used to model the inflation and descent of the reefed parachute system. It is solved by the fourth-order Runge–Kutta method, and the opening load values are thereby obtained. A parallel genetic algorithm (GA) code is developed to optimize the reefed parachute. A penalty scheme is used to have the maximum dynamic pressure restricted within a certain range.FindingsThe simulation results from DTVSim fit well with experimental data from drop tests, showing that the simulator has high accuracy. The one-stage and two-stage reefed parachute systems are optimized by GA and their maximum opening loads are decreased by 43 and 25 per cent, respectively. With the optimal reef parameters, two of the peaks in the opening load curve are almost equal. The velocity, loiter time and flight path angle of the parachute system all change, but these changes have no negative effect on the parachute’s operational performance.Originality/valueAn optimization method for reefed parachute design is proposed for the first time. This methodology can be used in the preliminary design phase for a reefed parachute system and significantly improve design efficiency.

Dynamic stability drop tests with capsule shaped model

Dynamic stability drop tests with capsule shaped model

Contact angles at the water–air interface of hydrocarbon-contaminated soils and clay minerals

Contact angles at the water–air interface have been measured for triturated preparations of clays and soils in order to assess changes in their hydrophobic properties under the effect of oil hydrocarbons. Tasks have been to determine the dynamics of contact angle under soil wetting conditions and to reveal the effect of chemical removal of organic matter from soils on the hydrophilicity of preparations. The potentialities of static and dynamic drop tests for assessing the hydrophilic–hydrophobic properties of soils have been estimated. Clays (kaolinite, gumbrine, and argillite) have been investigated, as well as plow horizons of soils from the Republic of Tatarstan: heavy loamy leached chernozem, medium loamy dark gray forest soil, and light loamy soddy-calcareous soil. The soils have been contaminated with raw oil and kerosene at rates of 0.1–3 wt %. In the uncontaminated and contaminated chernozem, capillary water capacity has been maintained for 250 days. The contact angles have been found to depend on the degree of dispersion of powdered preparation, the main type of clay minerals in the soil, the presence and amount of oxidation-resistant soil organic matter, and the soil–water contact time. Characteristic parameters of mathematical models for drop behavior on triturated preparations have been calculated. Contamination with hydrocarbons has resulted in a reliable increase in the contact angles of soil preparations. The hydrophobization of soil surface in chernozem is more active than in soils poorer in organic matter. The complete restoration of the hydrophilic properties of soils after hydrocarbon contamination is due to the oxidation of easily oxidizable organic matter at the low content of humus, or to wetting during several months in the absence of the mazut fraction.

Evaluation of the retention and recovery of hydrophobicity of insulating materials in high voltage outdoor applications under AC and DC stresses with the Dynamic Drop Test

This paper shows the results of the development of a test procedure to quantify dynamic properties of hydrophobicity, focusing on the retention and the recovery of hydrophobicity. The Dynamic Drop Test (DDT) has proven to be a suitable test method and the investigations are intended to improve the test with respect to repeatability and reproducibility. The results include an overview on the investigations for determining suitable test parameters and test conditions in the DDT at two independent test laboratories. Parameters like the volume conductivity, the flow rate of the electrolyte, test voltage and magnitude, as well as the definition of a physically determined failure criterion are analysed for a variety of polymeric insulating materials used in electrical applications. The recovery of hydrophobicity is evaluated by using the DDT with a so called interval testing. This procedure enables a defined evaluation of the recovery of hydrophobicity compared to the test method previously used. The interval testing covers resting and stressing periods under ac and dc stresses.

High Dynamic Measurement of Strain and Acceleration Using a Multichannel Measuring System with Single Cable Serial Connection

Strain and acceleration measurement during high dynamic drop tests, e.g., of containments for dangerous goods is performed using high speed multichannel measuring systems. So far established and operated systems need a cable connection of every strain gauge and acceleration sensor with the measuring device, often counting up to a number of more than 100 cables, corresponding to the number of applied sensors. The result is a massive cable harness consisting of all single cables, which is difficult to handle and causes a number of practical problems. An innovative approach is proposed by using a single cable measuring system, consisting of measuring modules with data bus connection and local data acquisition. Promising results were presented in a previous study. This paper follows up with additional results from full-scale testing of a further enhanced single cable system for the application in drop tests.

Development of the second generation Berry Impact Recording Device (BIRD II).

To quantitatively measure the impacts during blueberry harvesting and post-harvest handling, this study designed the second generation Berry Impact Recording Device (BIRD II) sensor with a size of 21 mm in diameter and a weight of 3.9 g, which reduced the size by 17% and the weight by 50% compared to the previous prototype. The sensor was able to measure accelerations up to 346 g at a maximum frequency of 2 KHz. Universal Serial Bus (USB) was used to directly connect the sensor with the computer, removing the interface box used previously. LabVIEW-based PC software was designed to configure the sensor, download and process the data. The sensor was calibrated using a centrifuge. The accuracy of the sensor was between −1.76 g to 2.17 g, and the precision was between 0.21 g to 0.81 g. Dynamic drop tests showed that BIRD II had smaller variance in measurements than BIRD I. In terms of size and weight, BIRD II is more similar to an average blueberry fruit than BIRD I, which leads to more accurate measurements of the impacts for blueberries.

Recurrent Plot Analysis of Leakage Current in Dynamic Drop Test for Hydrophobicity Evaluation of Silicone Rubber Insulator

In order to reduce electrical accidents caused by aging of polymer insulators, hydrophobicity evaluation is one of the essential methods to monitor the practical performance of insulators. This paper presents recurrent plot (RP) analysis of leakage current (LC) to evaluate the hydrophobicity of the silicone rubber insulator. Experiments were carried out according to the dynamic drop test method. Dynamic behaviors of water droplets and the induced discharge phenomena were captured by using a high-speed camera fixed vertically to the specimen surface. LC was measured and extended to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$m$</tex></formula> -dimensional phase space by using a phase-space reconstructed method. The RP of LC was obtained to reflect the underlying mechanism of surface discharges in relation to the insulator hydrophobicity. The results indicate that the RP technique can give a visual method for the hydrophobicity evaluation. The increasing tendency in RP indicators can reveal the decrease of hydrophobicity.

Design and Analysis of UAV Fuselage

The objective of this paper is to design and analyze a UAV fuselage. The UAV considered in this paper is designed for short-term use and light-weight with mass carrying capacity of 2kg. Firstly, the shape is considered for aerodynamics. Then, the internal system installation, cargo positioning and fuselage structure are designed. Finite element analysis is used for the stress analysis under the landing condition of static model with 3.5g acceleration. The short-term use is specified to be 20 life cycles and the model is verified by the dynamic drop test. The result from finite element analysis shows that the maximum stress is less than the material’s strength with safety factor of 1.1. From the dynamic drop test, the fuselage can safely support the structure under the required life cycles. Therefore, it can be concluded that UAV fuselage can achieve the requirements.

Characterization of surface discharge as indicator for hydrophobicity evaluation of silicone rubber insulators

A Dynamic drop test (DDT) has been employed for hydrophobicity evaluation, which has proven the occurrence of different discharge phenomena in relation to the hydrophobicity variation. In this paper, based on DDT method, the characterization of surface discharges, including the discharge magnitude, pulse number, adjacent discharge magnitude and adjacent time interval, have been analyzed to evaluate the surface hydrophobicity of silicone rubber insulator. It is found that with the decrease of hydrophobicity, these characteristics apparently show an increasing tendency. The characteristic pattern of discharge pulse and discharge magnitude presents a twin-peak shape, in which both the increase of the discharge magnitude and the discharge pulse number of higher magnitude reflect the decrease of surface hydrophobicity. The characteristic pattern of adjacent discharge magnitude and discharge magnitude emerges to be an 'X' shape composed by the discharge spots, in which the larger value in both the spot density and the shape expansion reveals the decreasing hydrophobicity. The characteristic pattern of next time interval and discharge magnitude demonstrates the frequency of surface discharges increases with the decrease of surface hydrophobicity. Furthermore, the comparability between the discharge characteristic methods and the contact angle method is analyzed to obtain the higher similarity coefficients. Obtained results indicate that the characteristic of surface discharge in DDT method can be utilized to the hydrophobicity evaluation.

Crumb rubber in concrete: Static and dynamic evaluation

In this study, six different concrete mix designs containing various amounts of coarse and fine crumb rubber were tested for properties important to concrete safety barriers. Eighteen samples – three of each mix design – were tested under static compression to determine the compressive strength and elastic modulus values. Another eighteen samples were subjected to dynamic drop tests to assess the effect of rubber on energy dissipation. Test results show that increasing the amount of rubber decreases the compressive strength and elastic modulus of the concrete, while significantly increasing impact time and energy dissipation capacity. It was determined that replacing 20–40% of aggregates with crumb rubber creates concrete mixes that would be useful for concrete safety barriers in locations where strength, fracture resistance and energy dissipation are required. Finally, concrete mixes with greater than 60% of aggregates replaced by crumb rubber would be useful for concrete impact attenuators in locations where low impact severity is of ultimate importance, and fracture or fragmentation upon impact is acceptable.

Hydrophobicity evaluation of silicone rubber insulator using PD-induced electromagnetic wave

Silicone rubber insulators are widely used as outdoor insulation due to their excellent surface performance. However, the decrease even the loss of hydrophobicity will take place under various environments, which causes the essential concern on the hydrophobicity evaluation. Dynamic dropping test (DDT) method is proposed as one of the evaluation methods. In this paper, based on DDT method the PD-induced electromagnetic wave is investigated for the hydrophobicity evaluation. An antenna is utilized to receive the high-frequency electromagnetic wave produced by the surface discharges, which are associated with the hydrophobicity variation. The electromagnetic signals are analyzed by a signal-processing system based on the wavelet-transform theory. The obtained 3-D images of surface discharges contain the relationship among the frequency, the time and the amplitude, which can reveal different ageing condition of the insulators. Based on the 3-D images, the fractal dimension (FD) and the lacunarity of 2-D contour line spectra are discussed to quantitatively give the complexity of surface discharges. It is found that the distribution range of discharge becomes wider and the frequency increases with the ageing time in the 3-D images, and the FD value shows the increasing tendency with the increase of ageing level. Therefore, the PD-induced electromagnetic wave can recognize the characteristics of the surface discharges, which can be utilized to evaluate the hydrophobicity of silicone rubber insulators.