Experimental Drop Tests Research Articles

Multi-body Model Validation of a Landing Gear System for a General Aviation Aircraft

The present work is aimed to numerically validate the experimental drop test results, related to the landing gear of a general aviation aircraft, in order to define an appropriate simulation methodology able to save time, costs and risks due to structural design and experimental test campaign required in the certification phase. The aircraft selected for this research activity is the AP-68TP-300 Spartacus, an Italian nine-seat, twin-engined, high wing monoplane, realized by Vulcanair S.p.a.. The multi-body approach has been developed through the MSC Adams software, starting from a simplified 1D model up to a more detailed 3D one. The comparison between numerical and experimental results in terms of load factors has been carried out in accordance with CS-23 (Certification Specifications for Normal, Utility, Aerobatic and Commuter Aeroplanes), and it has shown a good correlation, especially for the 3D model, since it better fits the real behaviour of the entire system. Keywords: Landing Gear, Drop Test, Multi-body Systems, MSC Adams.

Rigid-Object Water-Entry Impact Dynamics: Finite-Element/Smoothed Particle Hydrodynamics Modeling and Experimental Validation

A numerical study on the dynamic response of a generic rigid water-landing object (WLO) during water impact is presented in this paper. The effect of this impact is often prominent in the design phase of the re-entry project to determine the maximum force for material strength determination to ensure structural and equipment integrity, human safety and comfort. The predictive capability of the explicit finite-element (FE) arbitrary Lagrangian-Eulerian (ALE) and smoothed particle hydrodynamics (SPH) methods of a state-of-the-art nonlinear dynamic finite-element code for simulation of coupled dynamic fluid structure interaction (FSI) responses of the splashdown event of a WLO were evaluated. The numerical predictions are first validated with experimental data for maximum impact accelerations and then used to supplement experimental drop tests to establish trends over a wide range of conditions including variations in vertical velocity, entry angle, and object weight. The numerical results show that the fully coupled FSI models can capture the water-impact response accurately for all range of drop tests considered, and the impact acceleration varies practically linearly with increase in drop height. In view of the good comparison between the experimental and numerical simulations, both models can readily be employed for parametric studies and for studying the prototype splashdown under more realistic field conditions in the oceans.

Dynamic Response and Damage Mechanism of Two-Core Composite Sandwich Panels under Low-Velocity Impact

Dynamic response and damage mechanism of two-core sandwich panels with foam and honeycomb cores and glass fiber/epoxy composite sheets under low-velocity transverse impact are investigated. The emphasis is focused on the contact force response and crash mechanism of the two-core sandwich panels. Effects of configurations, impact energy levels and types of the cores on the dynamic response are investigated. A modified drop-test experiment is carried out to obtain contact force history of the two-core sandwich structures under different impact energies. The experimental results show that the 10:10 configurations for both honeycomb and foam core sandwich structures under lower impact energy absorb more impact energy than the other two structures. However, under higher impact energy, the honeycomb core sandwich structures of 15:5 configuration absorbs a little more impact energy than the other two, while for the foam core sandwich structures the 5:15 configuration shows a little better impact resistance. Results also show that when impact energy is low foam core sandwich structures do better in absorbing impact energy than the honeycomb ones.

Investigation into the Hypergolic Ignition Process Initiated by Low Weber Number Collisions

The processes leading to the hypergolic ignition of monomethyl hydrazine and red fuming nitric acid have been the subject of several studies. Whereas drop test experiments provide the scale necessary for detailed observations, they typically rely on the impact of a fuel droplet moving at its terminal velocity and an oxidizer pool contained within a crucible. By controlling the kinetic energy and the size of the fuel droplet, effectively varying the Weber number of the fuel droplet, precise amounts of reactants can be made to react at a defined location, thus, increasing the repeatability of the experiment. With an unrestrained oxidizer pool, the reaction can be made to resemble that occurring in a combustion chamber. In this study, the collisions of fuel droplets, limited to a Weber number below 12, with unrestrained red fuming nitric acid pools within a dry nitrogen environment were observed. The postprocessing of high-speed visible and infrared movies revealed that, under most conditions, explosion events precede the ignition of the propellants. The explosions result in vigorous secondary atomization, creating micron-sized drops that evaporate rapidly and serve as ignition sources. The presence and behavior of these micron-sized drops is believed to play a critical role in ignition.

Drop-Shock Failure Prediction in Electronic Packages by Using Peridynamic Theory

Peridynamic (PD) theory is used to investigate the dynamic responses of electronic packages subjected to impact loading arising from drop-shock. The capability of the PD theory to predict failure is demonstrated by simulating a drop test experiment of a laboratory-type package. The failure predictions and observations are exceptionally similar. For the drop test simulation of a production-type package, the finite element method (FEM) and PD theory are coupled via a submodeling approach. The global modeling is performed using the FEM while the PD theory is employed for the submodeling and failure prediction. The analysis yielded the outermost solder joint as the critical joint, with failure at the interface between the solder and copper pad on the printed circuit board side.

Issues on Viscoplastic Characterization of Lead-Free Solder for Drop Test Simulations

Reliable drop test simulations of electronic packages require reliable material characterization of solder joints. Mechanical properties of lead-free solder were here experimentally investigated for both monotonic and cyclic loading at different strain rates. With regards to the observed complex material behavior, the nonlinear mixed hardening Armstrong and Frederick model combined with the Perzyna viscoplastic law was chosen to fit the experimental data. This model was subsequently implemented into a commercial finite element code and used to simulate drop tests. Actual drop test experiments were conducted in parallel and experimental results were compared to simulations. Prediction discrepancies were analyzed and explanations suggested.

Mechanical assessment within type B packages approval: application of static and dynamic calculation approaches

This paper demonstrates exemplarily how numerical and experimental approaches can be combined reasonably in mechanical assessment of package integrity according to the IAEA regulations. The paper also concentrates on the question about how static mechanical approaches can be applied, and what their problems are in relation to dynamic calculation approaches. Under defined impact tests, which represent accident transport conditions, the package has to withstand impact loading, e.g. resulting from a 9 m free drop onto an unyielding target in sequence with a 1 m puncture drop test. Owing to the local character of the interaction between the puncture bar and the cask body, it is possible to develop a dynamic numerical model for the 1 m puncture drop which allows an appropriate simulation of the interaction area. Results from existing experimental drop tests with prototype or small scale cask models can be used for verification and validation of applied analysis codes and models. The link between analysis and e...

Dynamic Damping Properties of Thermoplastic Elastomers Based on EVA and Recycled Ground Tire Rubber

Recycling waste tires being important for both economical and environmental reasons, ground tire rubber can be blended with other polymers, modifying their properties. In order to characterize and explain these modifications, an experimental study was carried out concerning the improvement in the dynamic damping properties when adding recycled ground tire rubber (GTR) fillers to an elastomeric matrix (ethylene vinyl acetate, EVA).To evaluate the influence of both the GTR and the porosity in a GTR/ EVA composite, three samples have been elaborated by injection:the EVA matrix alone, a GTR/EVA composite, and a GTR/EVA porous composite. Dynamic measurements of the samples were performed using dynamic mechanical thermal analysis. The Young’s modulus and loss factor of these materials are estimated using the frequency—temperature equivalence introduced by Williams—Landel—Ferry expanding the measurement of the dynamic properties over a wider range of frequencies. This method showed that in low-frequency bandwidth, the loss factor has been improved by the addition of GTR to the EVA matrix. The α-relaxation study showed lower activation energy for both the GTR-filled composites leading to the conclusion that the mobility of the polymer chains has been improved by addition of GTR. The impact behavior study carried out using a weight drop test experiment also concluded to better impact energy absorption for the GTR-filled composites at the expense of a larger maximum displacement.

Drop Test Simulation of Table Grapes (Vitis vinifera L.) with Finite Element Method

Table grapes is a second industry in viticulture in Turkey and have been grown in primarily Mediterranean region a popular fruit for local consumption and export to many European and Asian countries as a fresh dessert and for this reason this product has to be transport so long distances for marketing. This simulated drop test experiment with Alphonse Lavallee and Antep Karasi (Vitis vinifera L.) table grape cultivars grown in Konya province was conducted in lab condition Selcuk University Faculty of Agriculture. To produce main knowledge, and to improve the application of resources used to produce, pack, transport, and merchandise Turkish table grapes by increasing efficiency, controlling cost and managing risk throughout the supply chain. This study focuses on the deformation behavior of the grape berries under drop case. In the drop test the mechanical parameters such as maximum force, deformation, Poisson ratio, modulus of elasticity and deformation energy of grape berries were determined. These parameters were used in the drop test packaged program of Solidworks 2010. For modeling the grape berry; a three dimensional scanner and high speed camera were used. Eventually, the important parameters as stress and displacement were determined according to finite element results. The results of this study shed light on new investigations of mechanical parameters of fruits by using finite element method.

Mechanical design assessment approaches of actual spent fuel and HLW transport package designs

In recent years, BAM Federal Institute for Materials Research and Testing finalised the competent authority assessment of the mechanical and thermal package design in several German approval procedures of new spent fuel and high level waste package designs. The combination of computational methods and experimental investigations in conjunction with materials and cask components testing is the most common approach to mechanical safety assessment. The methodology in the field of safety analysis, including associated assessment criteria and procedures, has evolved rapidly over the last years. The design safety analysis must be based on a clear and comprehensive safety evaluation concept, including defined assessment criteria and constructional safety goals. In general, for new package designs, the implementation of experimental package drop tests in the approval process should be obligatory. Additionally, preand post-test calculations as well as components or material testing could be important. The extent to which drop tests are necessary depends on the individual package construction, the materials used and identified safety margins in the design.

A Combined Zinc/Cadmium Sensor and Zinc/Cadmium Export Regulator in a Heavy Metal Pump

Heavy metal pumps (P1B-ATPases) are important for cellular heavy metal homeostasis. AtHMA4, an Arabidopsis thaliana heavy metal pump of importance for plant Zn(2+) nutrition, has an extended C-terminal domain containing 13 cysteine pairs and a terminal stretch of 11 histidines. Using a novel size-exclusion chromatography, inductively coupled plasma mass spectrometry approach we report that the C-terminal domain of AtHMA4 is a high affinity Zn(2+) and Cd(2+) chelator with capacity to bind 10 Zn(2+) ions per C terminus. When AtHMA4 is expressed in a Zn(2+)-sensitive zrc1 cot1 yeast strain, sequential removal of the histidine stretch and the cysteine pairs confers a gradual increase in Zn(2+) and Cd(2+) tolerance and lowered Zn(2+) and Cd(2+) content of transformed yeast cells. We conclude that the C-terminal domain of AtHMA4 serves a dual role as Zn(2+) and Cd(2+) chelator (sensor) and as a regulator of the efficiency of Zn(2+) and Cd(2+) export. The identification of a post-translational handle on Zn(2+) and Cd(2+) transport efficiency opens new perspectives for regulation of Zn(2+) nutrition and tolerance in eukaryotes.

Development of Empirical Equations for Metal Trace Failure Prediction of Wafer Level Package Under Board Level Drop Test

Accompanying the increasing popularity of portable and handheld products, high reliability for board level drop test becomes a great concern for semiconductor and electronic product manufacturers. Meanwhile, for design purpose, a reliable impact life prediction model is also a must in estimating the performance of packages subjected to drop impact. In this study, a stress-buffer-enhanced package is proposed to meet the high drop test performance requirement. Both the drop test experiment and numerical simulation were performed. The experimental drop test results showed that a different failure mode, the broken metal trace at package side, was observed in the stress-buffer-enhanced package. Several drop test simulations were conducted to elucidate the mechanical behavior of the test board and packages during the blink of impact. Based on the simulation results, a metal trace impact life prediction model is then developed for the novel stress-buffer-enhanced package to forecast the number of drops. Unlike the thermal cycle test, the dynamic response of the drop impact is irregular and not cyclic. As such, the concept of cumulative damage is considered in the life prediction model. Several characteristics of the metal trace dynamic response, the cumulative fatigue life, the cumulative plastic strain, and the cumulative effective plastic deformation, were studied during the development of the life prediction model. The results showed that the cumulative plastic strain of the metal trace could accurately predict impact life.

Scale modelling of aircraft fuselage: an innovative approach to evaluate and improve crashworthiness

Scale modelling of an aircraft fuselage and its measure of accuracy was investigated and determined with 1/5th, 1/10th, 1/15th and 1/20th times scaled models of an aircraft fuselage. Non-linear Finite Element Method (FEM) solver LS DYNA 3-D has been employed to analyse the experimental 1/20th scale aircraft fuselage model. The results were validated with the experimental scaled drop test model. The focus of this paper is to evaluate the scaling concept and its possible incorporation into the crashworthiness evaluation of fuselage as a potential crashworthiness evaluation tool. The impact design requirement for the 1/20th scale model fuselage section is to maintain 500 g floor-level acceleration for a 30 ft/s vertical impact velocity onto a rigid surface. This impact requirement corresponds to 25 g floor-level acceleration for a geometrically and constitutively similar full-scale fuselage section. Sub-floor concepts were then evaluated by conducting dynamic tests and confirmed with analytical calculations by performing finite element analysis using LS-DYNA. Finally, an assessment of model accuracy is provided with suggestions for improvements to achieve a better correlation result. These tests are carried out to determine the fuselage crashworthiness level and safe limit loads prescribed by the Federal Aviation Administration (FAA), and to satisfy the design goals for improved crashworthiness. A thorough investigation has been made on the existence of scaling effects and to demonstrate the application of scale model technology in the development of a new feasible methodology to evaluate the crashworthiness of the transport aircraft fuselage. Percentage error linearity of scaling is a major achievement of this study. This innovative and cost-effective crash test technique has a great potential to play a major role in the cost-saving methodology to evaluate the structure crashworthiness of the aircraft fuselage. The 1/20th scale model was built, tested and simulated with the LS-DYNA FEM package and the results were validated with the experimental drop test.

Solder joint and trace line failure simulation and experimental validation of fan-out type wafer level packaging subjected to drop impact

Accompanying the popularization of portable and handheld products, high reliability under board level drop test is a great concern to semiconductor manufacturers. In this study, a stress-buffer-enhanced package with fan-out capability is proposed to meet the high requirement of drop test performance. Both drop test experiment and numerical simulation were performed. The results showed the first failure of proposed package passed over 100 drops (mean-life-to-failure over 240 drops). Moreover, the failure of broken trace metal in the stress-buffer-enhanced package which is different from the solder joint failure in the conventional wafer level package was observed both in experiments and dynamic simulations. Simulation results were validated with experimental data and explained how the proposed stress-buffer-enhanced package improved drop test performance.

Board Level Drop Test Analysis Based on Modal Test and Simulation

Solder joint reliability in drop test is crucial for handheld systems, such as mobile phone, digital camera, and MP3 player. In recent years, a lot of experiments and simulations have been carried out by researchers to study board level drop test, and many useful results have been obtained. Regarding mechanical simulation and analysis, there are still two challenges: How to design drop test printed circuit board (PCB) based on dynamic simulation and analysis? How to get accurate elastic modulus of PCB, especially damping parameters, as property inputs for drop test simulation? In this study, an approach based on systematic modal tests and analyses is used to address these two challenges. First, modal dynamic simulation is used to design the test board to meet drop test requirements. Second, modal tests are conducted on drop test board in order to validate dynamic simulation and measure structural damping parameters and overall board elastic modulus as well. Adopted directly in drop test simulation, the measured damping parameters and elastic modulus are proved to be accurate. It is verified through comparison between the finite element simulation and real drop test results. With the modal tests and simulation method established here, drop simulation becomes very simple and accurate, and test board design and characterization are also simplified. Thus, considerable drop test experiment and simulation fine tune, and validation work can be saved.

Identification of a Non-Linear Landing Gear Model Using Nature-Inspired Optimization

This work deals with the application of a nature-inspired optimization technique to solve an inverse problem represented by the identification of an aircraft landing gear model. The model is described in terms of the landing gear geometry, internal volumes and areas, shock absorber travel, tire type, and gas and oil characteristics of the shock absorber. The solution to this inverse problem can be obtained by using classical gradient-based optimization methods. However, this is a difficult task due to the existence of local minima in the design space and the requirement of an initial guess. These aspects have motivated the authors to explore a nature-inspired approach using a method known as LifeCycle Model. In the present formulation two nature-based methods, namely the Genetic Algorithms and the Particle Swarm Optimization were used. An optimization problem is formulated in which the objective function represents the difference between the measured characteristics of the system and its model counterpart. The polytropic coefficient of the gas and the damping parameter of the shock absorber are assumed as being unknown: they are considered as design variables. As an illustration, experimental drop test data, obtained under zero horizontal speed, were used in the non-linear landing gear model updating of a small aircraft.

Assessing Behind Armor Blunt Trauma in Accordance With the National Institute of Justice Standard for Personal Body Armor Protection Using Finite Element Modeling

To assess the possibility of injury as a result of behind armor blunt trauma (BABT), a study was undertaken to determine the conditions necessary to produce the 44-mm clay deformation as set forth in the National Institute of Justice (NIJ) Standard 0101.04. These energy levels were then applied to a three-dimensional Human Torso Finite Element Model (HTFEM) with soft armor vest. An examination will be made of tissue stresses to determine the effects of the increased kinetic energy levels on the probability of injury. A clay finite element model (CFEM) was created with a material model that required nonlinear properties for clay. To determine these properties empirically, the results from the CFEM were matched with experimental drop tests. A soft armor vest was modeled over the clay to create a vest over clay block finite element model (VCFEM) and empirical methods were again used to obtain material properties for the vest from experimental ballistic testing. Once the properties for the vest and clay had been obtained, the kinetic energy required to produce a 44-mm deformation in the VCFEM was determined through ballistic testing. The resulting kinetic energy was then used in the HTFEM to evaluate the probability of BABT. The VCFEM, with determined clay and vest material properties, was exercised with the equivalent of a 9-mm (8-gm) projectile at various impact velocities. The 44-mm clay deformation was produced with a velocity of 785 m/s. This impact condition (9-mm projectile at 785 m/s) was used in ballistic exercises of the HTFEM, which was modeled with high-strain rate human tissue properties for the organs. The impact zones were over the sternum anterior to T6 and over the liver. The principal stresses in both soft and hard tissue at both locations exceeded the tissue tensile strength. This study indicates that although NIJ standard 0101.04 may be a good guide to soft armor failure, it may not be as good a guide in BABT, especially at large projectile kinetic energies. Further studies, both numerical and experimental, are needed to assist in predicting injury using the NIJ standard.

HMA1, a New Cu-ATPase of the Chloro plast Envelope, Is Essential for Growth under Adverse Light Conditions

Although ions play important roles in the cell and chloroplast metabolism, little is known about ion transport across the chloroplast envelope. Using a proteomic approach specifically targeted to the Arabidopsis chloroplast envelope, we have identified HMA1, which belongs to the metal-transporting P1B-type ATPases family. HMA1 is mainly expressed in green tissues, and we validated its chloroplast envelope localization. Yeast expression experiments demonstrated that HMA1 is involved in copper homeostasis and that deletion of its N-terminal His-domain partially affects the metal transport. Characterization of hma1 Arabidopsis mutants revealed a lower chloroplast copper content and a diminution of the total chloroplast superoxide dismutase activity. No effect was observed on the plastocyanin content in these lines. The hma1 insertional mutants grew like WT plants in standard condition but presented a photosensitivity phenotype under high light. Finally, direct biochemical ATPase assays performed on purified chloroplast envelope membranes showed that the ATPase activity of HMA1 is specifically stimulated by copper. Our results demonstrate that HMA1 offers an additional way to the previously characterized chloroplast envelope Cu-ATPase PAA1 to import copper in the chloroplast.

Initial water impact of a wedge at vertical and oblique angles

This paper examines initial asymmetric wedge-impact flows with horizontal as well as vertical impact velocity. The method of two-dimensional vortex distributions is employed to model the initial-boundary-value problem. The numerical analysis involves discretization of the body surface and an iterative solution technique. Experimental drop tests of a prismatic wedge were performed to gain understanding and provide data for comparison of initial water impact when asymmetry and horizontal impact velocity are present. The experimental investigation of initial flow separation off the wedge vertex (i.e., keel) during impact is described. Initial separation-ventilation of the flow from the vertex due to asymmetric impact or horizontal-vertical impact velocity is examined in relation to the present theory. Agreement between the data and the numerical predictions was demonstrated for small degrees of asymmetry and small ratios of horizontal to vertical impact velocity. The initial flow detachment from the vertex also revealed interesting hydrodynamic characteristics.

Numerical simulation of the drop impact response of a portable electronic product

The ability of portable electronic products like cellular phones and personal digital assistants to withstand accidental impacts and shock is a valuable attribute consumers expect and manufacturers desire. Usually, manufacturers conduct expensive experimental drop tests to determine the fragility of such products during the product design cycle. An alternative to conducting drop tests is to perform numerical simulation. This paper examines the feasibility of studying the drop impact response of an electronic pager using a finite element software, ABAQUS/Explicit. Experimental drop test results are then used to compare with that of numerical simulation. Parameters examined include surface strains on pager housing and impact force. Comparisons show good correlation between experimental and numerical results. Finite element computation allows critical impact orientations and drop heights to be identified so that selective experimental drop tests can be performed to determine the actual physical robustness of these products.