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Injury mechanisms of the lumbar spine under dynamic loading are dependent on spine curvature and anatomical variation. Impact simulation with finite element (FE) models can assist the reconstruction and prediction of injuries. The objective of this study was to determine which level of individualization of a baseline FE lumbar spine model is necessary to replicate experimental responses and fracture locations in a dynamic experiment. Experimental X-rays from 26 dynamic drop tower tests were used to create three configurations of a lumbar spine model (T12 to L5): baseline, with aligned vertebrae (positioned), and with aligned and morphed vertebrae (morphed). Each model was simulated with the corresponding loading and boundary conditions from dynamic lumbar spine experiments. Force, moment, and kinematic responses were compared to the experimental data. Cosine similarity was computed to assess how well simulation responses match the experimental data. The pressure distribution within the vertebrae was used to compare fracture risk and fracture location between the different models. The positioned models replicated the injured spinal level and the fracture patterns quite well, though the morphed models provided slightly more accuracy. However, for impact reconstruction or injury prediction, the authors recommend pure positioning for whole-body models, as the gain in accuracy was relatively small, while the morphing modifications of the model require considerably higher efforts. These results improve the understanding of the application of human body models to investigate lumbar injury mechanisms with FE models. [ABSTRACT FROM AUTHOR]

Background: Polyurethane foams have many uses ranging from comfort fitting seats and shoes to protective inserts in helmets and sports equipment. Current military helmet designs employ foam pads of varying densities and bulk material properties to help absorb energy from impacts ranging from quasi-static to ballistic level strain-rates. Objective: This study aims to analyze the thermomechanical uniaxial compression behavior of a high density liner foam pad and a low density liner foam pad used in the Advanced Combat Helmet. These experiments were conducted under strain-rates of 10 2 s - 1 and under temperature conditions ranging from -20 to 40 °C. This temperature range was chosen to simulate desert and arctic conditions, with a strain-rate regime chosen to represent loads that would occur often throughout the life of the helmet, such as drops, bumps from riding in a vehicle, or heavy collisions from falling. Method: Multiple experimental apparatuses were used in this study, including a Shimadzu TCE-N300 thermostatic chamber (used to create the varying temperature environments) and a custom-built drop-test system (used to induce intermediate strain-rates). Every experiment was paired with two accelerometers and a high speed camera used for Digital Image Correlation (DIC) to analyze sample deformation and resultant acceleration. The foam's mechanical response and energy absorption properties were investigated from the measured stress-strain curves. Additionally, each foam composition was analyzed with X-ray computed micro-tomography (XCT) to investigate microstructure properties pre and post-mortem. Results: Results show that temperature decreased the energy absorption of the low density composition by 48% ± 5% as temperature changed from -20 °C to 40 °C, while energy absorption increased by 53% ± 16% for the high density composition over the same temperature. Conclusion: A comparison between the loading response and the material's density characteristics revealed that the foam's mechanical properties are heavily dependent on strain-rate applications, as well as environmental factors including temperature. Several important characteristics surrounding each foam composition's deformation mechanics and damage tolerance as a result of temperature are discussed. [ABSTRACT FROM AUTHOR]

The investigation of multi-body dynamics (MBD) modeling for landing gear drop tests is a hot topic in the realm of landing gear design. The current results were primarily focused on the multi-rigid body simulation or a simple multi-flexible body simulation, with little regard for the correctness of longitudinal loads and their experimental confirmation, particularly wheel–axle loads. Based on a genuine oleo-pneumatic landing gear drop test of a large civil aircraft, enhanced multi-body dynamics simulation research is carried out, considering the structural flexibility and bearing support by adopting flexible multi-bodies modeling and rigid-flex coupling contacts. When compared to the test data, which purposefully measured the longitudinal wheel–axle loads, the simulation results show that the loads, shock absorber compression, and shock absorber inner pressures are all within good agreement. Furthermore, the influence of structural stiffness and bearing contact was investigated by adjusting the model settings to confirm their importance. [ABSTRACT FROM AUTHOR]

Payloads for light unmanned free balloons must meet several safety requirements such as being able to protect the inner electronics in order to extract scientific data and to reduce the chance of inflicting personal injury in case of an accidental fall. This article proposes a novel payload structure, which exhibits the form of a dodecahedron. The actual form was determined by carrying out theoretical drop tests on different polyhedrons using the finite element method (FEM). From the simulations, it could be deduced that the dodecahedron was the optimal choice, since the duration of the impact was longer, while the impact force was slightly lower. The payload was produced by additive technologies; therefore, after performing tensile tests on probable materials, PLA was selected as the optimal candidate. The theoretical results about the dodecahedron's ability were validated by laboratory and real-life drop tests, where the new payload was subjected to 56% less impact force under a 78% longer collision time compared to a classic, rectangular cuboid design. Based on these tests, it was demonstrated that the new structure is safer and it is applicable. [ABSTRACT FROM AUTHOR]

Lycium barbarum L. (L. barbarum) is an economic crop with high added value and profit. Vibration harvesting is a suitable mechanized harvesting method for L. barbarum. It bruises easily during harvesting due to the softness and vulnerability of fresh ripe fruit, resulting in economic losses. This study analyzed the fruit drop and collision during vibration harvesting. High-speed photography was used to obtain the impact speed and angle of the falling fruit, and a kinematic analysis of the collision with the collection surface was conducted. The majority of the fruit had an impact speed of 3-6 m/s and an impact angle of 30-90° with the collection surface. A drop test was conducted to assess fruit bruising, and the impact speed was converted to the drop height. An orthogonal rotation experiment was conducted, and mathematical model was established between the drop height, impact angle, and impact material, and the fruit bruise rate, maximum impact force, recovery coefficient, and impact time. The effects of the factors on the fruit bruise rate, maximum impact force, recovery coefficient, and impact time were analyzed. The test results show that a vibration harvesting device for L. barbarum should be designed to reduce the height between the fruit and the collection surface and utilize a tilted collection surface and high cushioning materials to reduce the fruit bruising. This study provides guidance for subsequent research on the bruising of L. barbarum during vibration harvesting and harvester design. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Copyright of Gazi Üniversitesi Fen Bilimleri Dergisi Part C: Tasarım ve Teknoloji is the property of Gazi University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

为保证包装产品的质量，通过对普通瓶型和加强筋瓶型PET瓶进行壁厚测定、抗压试验和跌落试验来比较瓶身结构对瓶子的抗压性能及标签完好性的影响。结果表明，加强筋瓶型的瓶子更厚，垂直抗压能力更好，对标签的保护程度优于普通瓶型的，且瓶子质量的改变不影响其性能。综上，选择加强筋瓶型的PET瓶更有利于保证包装产品的质量。In order to ensure the quality of the packaged products, through wall thickness measurement, compression test and drop test of ordinary PET bottle and reinforced PET bottle, the influences of bottle body structure on the compression performance of bottles and label integrity were compared. The results showed that the reinforced bottle was thicker, its vertical compression resistance and label protection were better than the ordinary bottle, and the change of bottle mass did not affect its performance. In conclusion, choosing reinforced PET bottle is more conductive to ensure the quality of the packaged products.

Cu-to-Cu direct bonding has been regarded as an important approach to achieve three-dimensional integrated circuit integration. This study aims to investigate the effects of microstructure and Xenon flash exposure on the direct bonding of copper deposits. Copper electrodeposits, along with a sputtered deposit, with various grain sizes, preferred orientations, as well as surface hardnesses, were prepared to clarify the influence of individual factors quantitatively. Experimental results show that joint strength and grain boundary density followed a positively linear relationship regardless of other microstructural differences, suggesting the dominating role of grain boundary diffusion. Grain refinement can effectively enhance bonding strength, even only one side of the directly bonded joints possessed fine grains. Considering the portable device applications which may suffer from drop shocks, drop testing of the packages comprising sputtered copper on Si chips joined with electroplated copper on Al2O3 substrates assembled by thermal compression bonding was performed for the first time. Noticeably, a proper flash irradiaiton prior to bonding brought about not only remarkable improvement in shear strength by up to 60 % but also drop resistance for direct-copper bonds. The resistance against drop shock for directly-bonded daisy chains subjected to an appropriate light exposure prior to bonding was superior than the joints bonded using impact-resistant solders.

With the increased stress in people’s daily lives, the secretion of sweat from the human body has steadily increased. Therefore, textile industries continue to introduce various products to meet consumers’ demands. Thus far, people use more cotton and polyester fabrics among other textile fabrics in their daily usage or total living period. Textile products, especially those made from cellulose fibers such as cotton, can promote the growth of microorganisms due to their high surface area and moisture retention. In contrast to cellulosic materials, polyester contains no chemically functional or hydrophilic groups. Therefore, it is necessary to ensure wearers’ protection as both cotton and polyester can create unwanted odors due to the decomposition of sweat by microorganisms. The application of chitosan on textile substrates is a useful approach for textile functionalization. Chitosan has been reported as a popular finishing agent due to its intrinsic properties, such as biocompatibility, biodegradability, non-toxicity, abundance in nature, antimicrobial, and antistatic ability, etc. In this study, the solution of chitosan was applied to 100 % cotton and polyester fabrics using a common pad-dry-cure technique. The resulting fabrics were characterized by drop-test, scanning electron microscopy (SEM), and color measurement. Thus, this study presents a small overview of the finishing using chitosan-containing recipes on both cotton and polyester fabrics.

The coefficient of restitution (COR) is used to estimate the equivalent free fall drop height of packaging during handling and transportation. Various experimental studies were designed to explore factors affecting the conversion of the COR to equivalent free fall drop height. These factors include the number of drops, drop height, drop orientation, drop base, temperature and humidity on the COR. The results indicate that the number of drops and drop orientation are the two most influential factors affecting COR values. As the package undergoes more drops, the COR increases. Among the various orientations, the COR is largest for flat drops, followed by edge and corner orientations. Within flat drops, a smaller impact area results in a smaller COR. Manufacturing joints and the flats, edges and corners adjacent to manufacturing joints tend to yield smaller COR values. A COR correction matrix was developed to correct the conventional COR calculation. This matrix allows engineers to refine COR values based on the number of drops and drop orientations in the field. The matrix‐corrected equivalent free fall drop heights demonstrated an average accuracy of 96%. Compared to the conventional COR calculation method, it effectively reduces errors by a factor of 2–3. [ABSTRACT FROM AUTHOR]

Purpose: The primary objective of this study is characterizing the anisotropic mechanical properties of corrugated cardboard and simultaneously simulating its drop cushioning dynamic effects under various drop conditions. Design/methodology/approach: Static and dynamic tests were conducted on corrugated cardboard to obtain adequate experimental data in different directions. An effective anisotropic constitutive model is introduced by developing the honeycomb materials model in ANSYS LS-Dyna, and an effective approach is established toward effectively determining the material parameters from the test data obtained. The model is validated by comparing simulation results with experimental data from five drop conditions, including bottom drop, front drop, side drop, 30° side drop and edge drop. Additionally, simulations are conducted to study the cushioning performance of the packaging by dropping the corrugated cardboard at different heights. Findings: The study establishes a fast and effective approach to simulating the drop cushioning performance of corrugated cardboard under various drop conditions, which demonstrates good agreement with experimental data. Originality/value: This approach is of value for packaging protection and provides guidance for stacking of packaging during transportation. [ABSTRACT FROM AUTHOR]

The aim of this article was to assess the behavior of polymer composites under low-velocity impact considering stress concentrators (two side holes at the point of impact) and determine the residual mechanical properties of these materials using FAI (Flexural After Impact). Analysis of residual properties ascertained the effects of damage and stress concentrators, assessing their individual influence in increasing the stress concentration factor (K). This analysis was conducted via tests that consider the separate effects of each case and a formulation that relates them. In addition, this paper also assessed the influence of void percentage on the impact and residual strength, developing two E-glass fiber fabric-based composites with different void percentage. The tests performed showed that impact damage increased the concentration factor of the material by 18%, but in samples tested with side holes, damage decreased residual strength by only 5%. [ABSTRACT FROM AUTHOR]

The investigation of multi-body dynamics (MBD) modeling for landing gear drop tests is a hot topic in the realm of landing gear design. The current results were primarily focused on the multi-rigid body simulation or a simple multi-flexible body simulation, with little regard for the correctness of longitudinal loads and their experimental confirmation, particularly wheel–axle loads. Based on a genuine oleo-pneumatic landing gear drop test of a large civil aircraft, enhanced multi-body dynamics simulation research is carried out, considering the structural flexibility and bearing support by adopting flexible multi-bodies modeling and rigid-flex coupling contacts. When compared to the test data, which purposefully measured the longitudinal wheel–axle loads, the simulation results show that the loads, shock absorber compression, and shock absorber inner pressures are all within good agreement. Furthermore, the influence of structural stiffness and bearing contact was investigated by adjusting the model settings to confirm their importance.

Landing impact load design is essential, but the process has rarely been fully described, and some designers have even neglected the differences between wheel-axle and ground-contact loads, as well as loads in the longitudinal direction, especially in experimental validations. In this paper, the entire design process of a nose landing gear is addressed, including a theoretical analysis of the unit and its experimental validation. In the theoretical analysis, a mathematical model of a two-mass system with four degrees of freedom was adopted, a computer simulation model was built accordingly, and a preliminary analysis was subsequently conducted to analyze the landing impact loads, verify the landing gear performance, and gauge the difference between the wheel-axle and ground-contact loads. For the experimental validation of the gear, a landing gear drop test was conducted in an optimized manner that emphasized pre-test preparation and during-test wheel-axle load measurement. The test results showed that both the vertical and less studied longitudinal loads, as well as the wheel-axle and ground-contact loads, had good agreement with the analysis; thus, the model, the tool, and the preliminary design were considered to be experimentally validated. [ABSTRACT FROM AUTHOR]

Purpose: Because of growing demand for slim, thin and cheap handheld devices, reduced-volume solder interconnects like land grid array (LGA) are becoming attractive and popular choices over the traditional ball grid array (BGA) packages. This study aims to investigate the mechanical shock and impact reliability of various solder alloys and BGA/LGA interconnect configurations. Design/methodology/approach: Therefore, this paper uses drop testing experiments and numerical finite element simulations to evaluate and compare the reliability performance of both LGA and BGA components when exposed to drop and impact loadings. Additionally, three common solder alloys, including 63Sn37Pb, SAC305 and Innolot, are discussed. Findings: The results of this study showed that electronic packages' drop and impact reliability is strongly driven by the solder configuration and the alloy type. Particularly, the combination of stiff solder alloy and shorter joint, LGA's assembled with SAC305, results in highly improved drop reliability. Moreover, the BGA packages' performance can be considerably enhanced by using ductile and compliant solder alloys, that is, 63Sn37Pb. Finally, this paper discussed the failure mode of the various solder configurations and used simulation results to explain the crack and failure situations. Originality/value: In literature, there is a lack of published work on the drop and impact reliability evaluation and comparison of LGA and BGA solders. This paper provides quantitative analysis on the reliability of lead-based and lead-free solders when assembled with LGA and BGA interconnects. [ABSTRACT FROM AUTHOR]

For dangerous goods packagings, drop testing onto an essential unyielding target can be used to assess the mechanical resistance to impact loads. Adopted regulations like Agreement concerning the International Carriage of Dangerous Goods by Road (ADR)/Regulation concerning the International Carriage of Dangerous Goods by Rail (RID) require that the impact surface provided shall be integral with a mass at least 50 times than that of the heaviest package to be tested. The problem is that many manufacturers do not possess impact targets that satisfy the required 50 times mass ratio for regulative drop tests during series production. The objective of this work is to verify existing and define improved criteria for impact target structures based on systematic investigations. Previous evidence highlights the relevance of other parameters in addition to the mass ratio. Therefore, in this research, a variation of drop test parameters was carried out experimentally. Furthermore, numerical vibration analysis was applied to investigate the deformability of the impact surface. The results conclude that the mass ratio of 1:50 cannot be defined as a decisive criterion. In order to determine the influence of further drop test parameters, the research findings were used to validate a parametric model that assesses impact target deflection. An approximation quality of over 90% was achieved. As a result, new evaluation criteria are proposed. First, a method for identifying critical impact target designs is provided. Second, a new comprehensive formula compares the approximated maximum deflection of a real impact target to the respective theoretical threshold derived from a worst‐case assumption. In practice, this leads to great advantages in the evaluation of already installed impact targets for dangerous goods packagings. [ABSTRACT FROM AUTHOR]

Article highlights Direction with protection most influenced by wrapping turns: parallel to tray surface and perpendicular to tray length. Acceleration profile and peak variance show when 3S package failed in fully suspended protection. Wrapping around the corners of the object greatly influences the 3S package performance in the tray length direction.

Payloads for light unmanned free balloons must meet several safety requirements such as being able to protect the inner electronics in order to extract scientific data and to reduce the chance of inflicting personal injury in case of an accidental fall. This article proposes a novel payload structure, which exhibits the form of a dodecahedron. The actual form was determined by carrying out theoretical drop tests on different polyhedrons using the finite element method (FEM). From the simulations, it could be deduced that the dodecahedron was the optimal choice, since the duration of the impact was longer, while the impact force was slightly lower. The payload was produced by additive technologies; therefore, after performing tensile tests on probable materials, PLA was selected as the optimal candidate. The theoretical results about the dodecahedron’s ability were validated by laboratory and real-life drop tests, where the new payload was subjected to 56% less impact force under a 78% longer collision time compared to a classic, rectangular cuboid design. Based on these tests, it was demonstrated that the new structure is safer and it is applicable.

Metal shock absorbers of nuclear spent fuel casks for storage have been developed. The shock absorbers are equipped at both ends of the cylindrical cask to reduce the impact force and maintain the safety functions of the cask in the event of an unexpected drop accident. As a countermeasure to meet long-term storage requirement (against material degradation), the shock absorber was designed with metal instead of usual wood and its energy absorption performance against 2.5 m height drop (maximum hypothetical handling height in nuclear power plants during storage) was evaluated. With the aim of reducing compression stiffness the metal shock absorber was designed from a perforated aluminum block. Two tests were done for static compression characteristics using cubic specimens and energy absorption capacity against 2.5 m drop using 1/4 scale mockup of metal shock absorber. In addition, a drop test using 1/10 scale mockup cask with metal shock absorbers confirmed that it could deform as assumed and reduce the applied acceleration on the cask to a safety level at crash. As a result of the finite element analysis of the cask with designed shock absorbers dropped from a height of 2.5 m that was verified by the drop test, the fitting portion between body and primary lid in the cask remained within elastic deformation thus confirming the design’s validity.

The modeling clay is an oil-based soft, flowable, and pliable material made from waxes and oils. Besides its primary use for making sculptures, the modeling clay is commonly used to evaluate bulletproof vests and simulate metal manufacturing processes by conformation. In ballistic tests, the clay is used to retain the deformation of the rear face of body armors; and in the study of metal forming processes, it is used as a physical model to provide information on the plastic flow. However, its mechanical dynamic behavior is not entirely understood. In this study, Plastilina Roma No. 1 modeling clay was mechanically characterized using the power-law constitutive model at medium strain rates (10 2 s − 1). The material parameters were determined using a penetration model based on the Cavity Expansion Theory and an inverse technique involving the comparison of the model with experimentation. The optimum set of constitutive parameters was found by reducing the difference of the calculated penetration profile and the measurements from a drop test. This optimization process was programmed on the MATLAB–Simulink environment. The determined material parameters were validated by comparing the results from a computational model with three test set-ups. Finite element model results show good concordance with experimental measurements. [ABSTRACT FROM AUTHOR]

To determine the damage characteristics of potato falling on the separating screen and their relationship with the vibration characteristics, it is expected to provide a reference for the structural optimization of potato harvesting related machinery. The vibration characteristics of the separating screen were theoretically analyzed and a forced vibration model of separating screen was developed. The effects of vibration model parameters on the damage volume of potatoes were studied by single‐factor experiments with fall height, potato mass, fall direction, and potato varieties as experimental factors. Especially, the changes of decay coefficient α and the potato damage volume with test factors were obtained: the attenuation coefficient α increased with increasing falling height and potato mass and showed a significant correlation with potato damage volume. The decay coefficient α becomes largest when the potato falls along the length direction and smallest when it falls along the thickness direction. The α decreased with increasing hardness of potato varieties and showed a significant negative correlation with potato damage volume. Fitting equations between the attenuation coefficient α and the damage volume for each effects were established to predict the potato damage under different height, mass, and variety, as follows: V1 = 498035α − 2516, V2 = 209646α − 286, and V3 = −84397α + 1149. Practical Applications: During the mechanized harvest process, severe potato damage occurred on the swing separation screen. This will seriously affect the quality and economic value of potatoes. At present, there are few studies on the vibration damage theory and experiment during potato harvest. Therefore, in order to clarify the vibration characteristics of the separation screen and its relationship with the potato damage characteristics, we studied the influence of the vibration characteristics on the potato damage through the drop test, and established the vibration model of the separation screen. The relationship between the model parameters and the potato damage volume was further explored, and a mathematical model was developed to predict the volume of potato damage. This study provides a reference for the study of the coupled vibration of the potato soil mixture and the optimization of the potato soil separation device. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ordnance Equipment Engineering is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Energy-absorbing rockbolts have been widely adopted in burst-prone excavation support, and their serviceability is closely related to the frequency and magnitude of seismic events. In this research, the split-tube drop test with varying impact energy was conducted to reproduce the dynamic performance of MP1 rockbolts under a wide range of seismic event magnitudes. The test results showed that the impact process could be subdivided into four distinct stages, i.e. mobilization, strain hardening, plastic flow (ductile), and rebound stage, of which strain hardening and plastic flow are the primary energy absorbing stages. As the impact energy per drop increases from 8.1 to 46.7 kJ, the strain rate of the shank varies between 1.20 and 2.70 s−1, and the average impact load is between 240 and 270 kN, which may be considered as constant. The MP1 rockbolt has a cumulative maximum energy absorption (CMEA) of 31.9–40.0 kJ/m, with an average of 35.0 kJ/m, and the elongation rate is 11.4%–14.7%, with an average of 12.7%, both of which are negatively correlated with the impact energy per drop. Regression analysis shows that energy absorption and shank elongation, as well as momentum input and impact duration, conform to the linear relationship. The complete dynamic capacity envelope of MP1 rockbolts is proposed, which reflects the dynamic bearing capacity, elongation, and distinct stages. This study is helpful to better understand the dynamic characteristics of energy-absorbing rockbolts and assist design engineers in robust reinforcement systems design to mitigate rockburst damage in seismically active underground excavations.

The determination of suitable testing and qualification procedures for fiber-reinforced polymer matrix composite structures is an active area of research due to the increased demand, especially in the field of aerospace. This research illustrates the development of a generic qualification framework for a composite-based main landing gear strut of a lightweight aircraft. For this purpose, a landing gear strut composed of T700 carbon fiber/epoxy material was designed and analyzed for a given lightweight aircraft having mass of 1600 kg. Computational analysis was performed on ABAQUS CAE® to evaluate the maximum stresses and critical failure modes encountered during one-point landing condition as defined in the UAV Systems Airworthiness Requirements (USAR) and Air Worthiness Standards FAA FAR Part 23. A three-step qualification framework including material, process and product-based qualification was then proposed against these maximum stresses and failure modes. The proposed framework revolves around the destructive testing of specimens initially as per ASTM standards D 7264 and D 2344, followed by defining the autoclave process parameters and customized testing of thick specimens to evaluate material strength against the maximum stresses in specific failure modes of the main landing gear strut. Once the desired strength of the specimens was achieved based on material and process qualifications, qualification criteria for the main landing gear strut were proposed which would not only serve as an alternative to drop test the landing gear struts as defined in air worthiness standards during mass production, but would also give confidence to manufacturers to undertake the manufacturing of main landing gear struts using qualified material and process parameters. [ABSTRACT FROM AUTHOR]

It is important to achieve high strength, high modulus of elasticity, good energy damping for lightweight armor materials. For this purpose, two or more similar or different materials are combined at the macro level. In this way, a new structure emerges that we call composite material. A composite is a new structure in which the good properties of the components in its structure become evident in the material. Research on the production and mechanical properties of composites that meet the needs of the developing technology continues. Military personnel, armored vehicles and many security elements are tested in the field with a lot of threats (such as mines, armor piercing ammunition, explosives etc.). Therefore, the armor used by security elements should be strengthened without compromising features such as lightness, cost and longterm use. This study covers the development of Kevlar's ballistic properties by impregnating Shear Thickening Fluid (STF). STF is composed of silica (AEROSIL 200) and polyethylene glycol (PEG 400). STF-impregnated Kevlar fibers have been subjected to impact testing at low and high speeds. Low-speed tests were carried out with a drop tower. High-speed tests were carried out according to NIJ 0101.06 Level II standards. The mass fraction of silica in the STF was determined as the research parameter. The change in the behavior of the materials with the change of silica ratio was investigated; Although improvements were observed in energy dissipation in low-speed impacts, it was noted that ballistic behavior improved up to a certain point, and then the improvement in behavior decreased. [ABSTRACT FROM AUTHOR]

The oil characteristics and inflation pressure inside the oil-air shock absorber will change with the ambient temperature,which will affect the cushioning performance of landing gear.In order to explore the effect of temperature on the cushioning performance of oil-air landing gear,a buffer environment temperature simulation method is proposed based on the landing gear drop shock test,and the cushioning performance of oil-gas landing gear buffer at ambient temperature from 20 to 80℃is studied.The results show that within the studied temperature range,the initial inflation pressure of the buffer is sensitive to the change of temperature.With the increase of temperature,the stiffness of the air spring in the buffer increases and the oil damping force decreases,the ground vertical load of the landing gear system increases and the efficiency coefficient of the buffer system decreases.The temperature has a significant impact on the performance of the oil-gas landing gear buffer.

A molded expanded polystyrene (EPS) cushion is a flexible, closed-cell foam that can be molded to fit any packing application and is effective at absorbing shock. However, the packaging waste of EPS cushions causes pollution to landfills and the environment. Despite being known to cause pollution, this sustainable packaging actually has the potential to reduce this environmental pollution because of its reusability. Therefore, the objective of this study is to identify the accurate design parameter that can be emphasized in producing a sustainable design of EPS cushion packaging. An experimental method of drop testing and design simulation analysis was conducted. The effectiveness of the design parameters was also verified. Based on the results, there are four main elements that necessitate careful consideration: rib positioning, EPS cushion thickness, package layout, and packing size. These parameter findings make a significant contribution to sustainable design, where these elements were integrated directly to reduce and reuse packaging material. Thus, it has been concluded that 48 percent of the development cost of the cushion was decreased, 25 percent of mold modification time was significantly saved, and 27 percent of carbon dioxide (CO2) reduction was identified. The findings also aided in the development of productive packaging design, in which these design elements were beneficial to reduce environmental impact. These findings had a significant impact on the manufacturing industry in terms of the economics and time of the molded expanded polystyrene packaging development. [ABSTRACT FROM AUTHOR]

Hydrogen, a clean and renewable energy fuel is termed the fuel of the future. Although the production of hydrogen is well-established, its storage is a major concern. The conventional metallic cylinders are bulky and cause difficulties in transportation and long-term sustenance, calling for the exploration of alternatives that are durable, lightweight and easy to fabricate. Composite high-pressure cylinders appear to be a promising solution for the storage of gaseous hydrogen. In this work, weight optimization of Type 1, Type 3 and Type 4 cylinders have been performed using lightweight materials such as Titanium, Acrylonitrile Butadiene Styrene (ABS) and Carbon fibre. The stability of these cylinders has been confirmed via structural analysis. In addition, explicit analyses such as drop and crash tests have also been carried out to evaluate the performance of the cylinder. Type 1 shows the least deformation, however, failed both the crash as well as drop tests. Whereas, the type 4 cylinder exhibits better performance in both structural and explicit simulations and is 39.2% lighter than the Type 1 cylinder. Such type 4 cylinders can revolutionize the energy storage sector and can advance mobility to a great extent in the near future. [Display omitted] • Cylinder modelled using Titanium, Acrylonitrile Butadiene Styrene and Carbon Fibre. • Weight Optimization of cylinder through structural analysis. • Evaluating explicit performance of the cylinder though drop and crash tests. • Influence of carbon fibre in absorbing shock during drop and crash tests. [ABSTRACT FROM AUTHOR]

Roma Plastilina No. 1 clay has been widely used as a conservative boundary condition in bulletproof vests, namely to play the role of a human body. Interestingly, the effect of this boundary condition on the ballistic performance of the vests is indiscernible. Moreover, back face deformation should be characterized by measuring the indentation in the deformed clay, which is important for determining the lethality of gunshots. Therefore, several studies have focused on modeling not only bulletproof vests but also the clay backing material. Despite various attempts to develop a suitable numerical model, determining the appropriate physical parameters that can capture the high-strain-rate behavior of clay is still challenging. In this study, we predicted indentation depth in clay using an artificial neural network (ANN) and determined the optimal material parameters required for a finite element method (FEM)-based model using an inverse tracking method. Our ANN-FEM hybrid model successfully optimized high-strain-rate material parameters without the need for any independent mechanical tests. The proposed novel model achieved a high prediction accuracy of over 98 % referring impact cases. [ABSTRACT FROM AUTHOR]

To investigate the ability of energy absorption of composite beams with corrugated web in the crash process, the drop tests of composite beams with corrugated web are carried out, and the morphology of fracture, load and energy history curves are obtained. Based on the ABAQUS/Explicit platform, a simulation analysis model is developed to simulate the impact collapse process of composite beams with corrugated web by secondary development. The improved Hashin criterion and Choi‑Chang criterion are used with Cohesive interface element. The anisotropy and progressive damage of composite laminates are implemented. Specific energy absorption (SEA) and average loads are obtained by numerical simulation, which is verified by experimental results. Based on this model, further studies on the energy absorption of composite beams with corrugated web are analyzed with different wavenumbers. The progressive damage of corrugated web beams under impact loads are simulated by the developed FE model. The relative errors of average crushing load are small, which verifies the validity of the FE model. When the wave length of web is defined, the length of corrugated web beams has influence on energy absorption under impact. The shorter beam with corrugated web is instability and ineffective in energy absorption. [ABSTRACT FROM AUTHOR]

This paper presents the evaluation process of a Recovery System developed for the ILR-33 AMBER suborbital rocket, designed for small payloads and capable of launching 10 kg to altitudes up to 100 km. The Recovery System allows for retrieval of the payload by means of highangle-of-attack motion with flat spin and a two-stage parachute system. After presenting the design of the Recovery System, this study focuses mainly on a subsonic drop test campaign that allowed the system to be qualified for the first version of the AMBER rocket vehicle. Analytical and numerical methods for the recovery phase development are presented and compared with the experimental results obtained from the drop tests. Overall, the drop tests proved to be indispensable for the successful development of the AMBER rocket platform, by providing essential load and spin data to feed back into the re-design processes, and also by confirming the viability of the concept of three-stage parachute recovery. [ABSTRACT FROM AUTHOR]

2-Azido-N,N-Dimethylethanamine (DMAZ) and tetramethylethylenediamine (TMEDA) are promising green propellants for hypergolic applications, and blending DMAZ with TMEDA can achieve short ignition delay time (IDT) and comparable specific impulse to hydrazine-based fuels simultaneously. There are reports of a synergistic effect between DMAZ and TMEDA, but its mechanism is not well understood. In this work, drop tests and gas-phase autoignition experiments were combined to provide insights of this synergistic effect from different aspects. The drop tests of DMAZ/TMEDA blends with white-fuming nitric acid were conducted in a confined transparent chamber with controlled O 2 concentration. Results show that the hypergolic ignition is much faster for blends with 20–40 wt% DMAZ under all O 2 concentration conditions, and higher concentration of O 2 in the environment significantly promotes the hypergolic ignition process. To further investigate the chemistry between DMAZ/TMEDA with O 2 , gas-phase IDTs were measured using a rapid compression machine and a shock tube in a wide temperature range of 500–1100 K and at pressure of 10 bar. TMEDA shows a higher reactivity at lower temperatures (<690 K), while the autoignition of DMAZ is much faster at higher temperatures (>690 K). A synergistic effect between DMAZ and TMEDA was also observed in the gas-phase autoignition, i.e., fuel blend with 30 % DMAZ showed equal or even lower IDTs than pure TMEDA at lower temperatures. The newly measured IDTs of DMAZ/TMEDA were further adopted to validate a previously developed chemical kinetic model for pure TMEDA and DMAZ, which exhibits good predictions for the blending effects nonetheless. Kinetic analyses reveal that the low-temperature reactivity contributed from the TMEDA can be enhanced by the heat release from DMAZ decomposition, causing the synergistic effect in gas-phase autoignition of DMAZ/TMEDA blends. [ABSTRACT FROM AUTHOR]

Landing impact load design is essential, but the process has rarely been fully described, and some designers have even neglected the differences between wheel-axle and ground-contact loads, as well as loads in the longitudinal direction, especially in experimental validations. In this paper, the entire design process of a nose landing gear is addressed, including a theoretical analysis of the unit and its experimental validation. In the theoretical analysis, a mathematical model of a two-mass system with four degrees of freedom was adopted, a computer simulation model was built accordingly, and a preliminary analysis was subsequently conducted to analyze the landing impact loads, verify the landing gear performance, and gauge the difference between the wheel-axle and ground-contact loads. For the experimental validation of the gear, a landing gear drop test was conducted in an optimized manner that emphasized pre-test preparation and during-test wheel-axle load measurement. The test results showed that both the vertical and less studied longitudinal loads, as well as the wheel-axle and ground-contact loads, had good agreement with the analysis; thus, the model, the tool, and the preliminary design were considered to be experimentally validated.

Rapid and precise reliability evaluation of electronic circuits plays a key role in the design stage of the electronic systems. The task becomes even more difficult when several major parameters contribute into the reliability evaluation. This paper proposes a neural network aided approach as a prediction tool for estimating the useful lifetime of the ball shaped solder joint as the most resistless part under accidental drops in the electronic devices. Several contributory factors including ball grid array (BGA) chip location, printed circuit board (PCB) thickness, solder alloy composition and solder ball volume are considered in our proposed rapid prediction model and their effects are investigated. 480 finite element simulations as well as 20 experimental tests are performed to obtain an enriched database for our neural network based prediction model. The accuracy of the proposed model is calculated as 97.55% in comparison with the finite element and the experimental results. Ability of considering multi contributory factors in the reliability evaluation of the BGA chip makes our proposed approach be a suitable candidate in design for reliability of the electronic systems.

Ionic liquids have a wide engineering application foresight due to their easy and safe storage and handling while are limited by the unclear mechanism of hypergolic ignition. In this study, three dicyanamide-based ionic liquids with different cations, 1-allyl-3-methyl imidazolium ([AMIm]), 1-ethyl-3-methylimidazolium ([EMIm]) and 1-butyl-3-methyl-imidazolium ([BMIm]), are prepared to react with white fuming nitric acid through drop tests. The diameter of ionic droplet is 2.2 ​mm, the impact velocities are controlled at 0.16/0.45/0.62/0.82/1.01 ​m ​s-1 by adjusting the dropping height, and the whole reacting process is recorded by three cameras to provide macroscopic, microscopic and infrared details. The promotion effect of impact velocity on hypergolic ignition probability is confirmed for all the ionic liquids, and the minimum impact velocity for successful hypergolic ignition of each ionic liquid was determined. The temperature evolution of hypergolic process shows a non-monotonic trend, and a four-stage process was performed to reveal the hypergolic mechanism. The experimental results indicate that short-chain alkyl and unsaturated substituents in cations are favored for hypergolic ignition, and the datasets are conducive for kinetic model construction.

In this study, ground tests of a lab-scale hybrid rocket motor were conducted to verify the feasibility of the hybrid propulsion system for lunar lander application. The primary goal is to assess the realizability of hybrid rocket by testing its throttleability and soft landing capability with a scale-down lunar module. A design thrust of 200 N was achieved by clustering four identical 50 N-class gaseous oxygen (GOX)/high-density polyethylene (HDPE) hybrid rocket motors with multi-port solid fuels. Ground tests were carried out via two main experiments: static test and drop test. Static test was focused on the overall performance of the clustering module such as cold injection, uniform oxidizer distribution, throttleability and simultaneous ignition of the four motors, while the drop test was performed to investigate the planned throttle behavior using a 1-D vertical drop test stand. The clustering module was controlled in an open-loop setup with a simple ballistic flight simulation input. The landing velocity of 1.01 m/s was achievable, confirming the possibility of soft landing missions on lunar surface using hybrid rocket motors.

The cylindrical airbag is widely used in the landing buffer field with a simple structure. It is a three-dimensional closed structure, so the folding model is difficult to establish. Because the modeling process of the existing methods is complex and these methods are difficult to use in the actual folding process, a new direct folding method was proposed in this paper. In the method, the two end faces of the cylindrical airbag are recessed inward, and the cylindrical surface is flattened into a sheetlike structure; then, its finite-element model is established. The folded cylindrical airbag was inflated, and the deployed shape was the same as that of the initial unfolded model after inflation. Moreover, the maximum errors of the equivalent cross-sectional diameter, maximum length, and volume of the inflated airbag were less than 4%, which shows that the method is reasonable and feasible. Based on this method, three finite-element models of cylindrical airbags in different folding states were established, and then the effects of folding mode, inflation rate, and ambient pressure on the deployment process of the folding airbag were studied. In the landing buffer analysis, this method was used to model the folded secondary airbag when establishing the finite-element model for the cushioning dynamic of the combined airbag. The simulation results are in good agreement with the drop test results, which also verifies the effectiveness of this folding method. [ABSTRACT FROM AUTHOR]