Drop Impact Analysis Research Articles

Structural design and experimental verification of a thin-walled plastic chairs based on the finite element method

This study focuses on the design and preparation of a thin-walled plastic chair, and its mechanical properties were investigated by high load, cyclic load and drop impact. The finite element method (FEM) was employed to accurately evaluate the chair’s safety under these forces. Additionally, the effects of important structural parameters on the loading process in different states were investigated. Furthermore, a solid plastic chair prototype was created for experimental analysis. The findings revealed that increasing the thickness of the key structural parameters enhanced the safety properties of the chair under various load conditions. Optimal results were obtained when both dimensions were set to 5 mm. The deformation errors in FEM, experimental strength analysis, fatigue analysis, and drop impact analysis were measured at 3.7%, 3.6%, and 11.7%, respectively. Similarly, the stress errors were determined to be 5.9%, 5.2%, and 6.5%. These results suggest that the structural design of the chair demonstrates excellent reliability. Studying the crucial structural parameters of a plastic chair can provide valuable insights for the scientific design and safety evaluation of thin-walled furniture.

Development of simplified fuel assembly model for nuclear fuel transportation

To evaluate the integrity of spent nuclear fuel (SNF) during transportation, the vibration and drop impact analysis requires a transport cask model loaded with a significant amount of SNF and performing a dynamic analysis in the time domain. A cask model with a three-dimensional fuel assembly (FA) model requires substantial time. Therefore, simplified hexahedral-shaped FA models with equal weights have been used. However, FAs interact with the cask and account for a significant portion, affecting the mechanical response behavior of the transport cask and FA. Therefore, a dependable FA model must be used to obtain accurate cask and FA mechanical responses. Herein, we developed a simplified equivalent beam FA model to address the above issues. The guide tubes and fuel rods were modeled as a single equivalent beam, and the spacer grids were simplified to a shell shape by removing springs and dimples supporting the fuel rods. Rotational springs were implemented at the locations of spacer grids and nozzles to simulate the static bending and dynamic vibration of FA. The simplified FA model was compared with mechanical test results, and the results correlated well. Therefore, this model can be used for FA transportation and will be crucial in predicting the reliable mechanical responses of FA and transport cask.

Analysis of high-speed drop impact onto deep liquid pool

The present work is devoted to the analysis of drop impact on a deep liquid pool, focusing on the high-energy splashing regimes caused by large raindrops at high velocities. Such cases are characterized by short time scales and complex mechanisms, thus they have received very little attention until now. The BASILISK open-source solver is used to perform three-dimensional direct numerical simulations. The capabilities of octree adaptive mesh refinement techniques enable capturing of the small-scale features of the flow, while the volume of fluid approach combined with a balanced-force surface-tension calculation is applied to advect the volume fraction of the liquids and reconstruct the interfaces. The numerical results compare well with experimental visualizations: both the evolution of crown and cavity, the emanation of ligaments, the formation of bubble canopy and the growth of a downward-moving spiral jet that pierces through the cavity bottom, are correctly reproduced. Reliable quantitative agreements are also obtained regarding the time evolution of rim positions, cavity dimensions and droplet distributions through an observation window. Furthermore, simulation gives access to various aspects of the internal flows, which allows us to better explain the observed physical phenomena. Details of the early-time dynamics of bubble ring entrapment and splashing performance, the formation/collapse of bubble canopy and the spreading of drop liquid are discussed. The statistics of droplet size show the bimodal distribution in time, corroborating distinct primary mechanisms of droplet production at different stages.

Free fall drop impact analysis of board level electronic packages

The electronic failure from accidental dropping event of modern handheld electronic devices may result from various failure modes such as cracking of PCB, solder joint etc. In this work, the dynamic response characteristics of electronic packages when subjected to board level drop impacts are investigated. Initially, board level drop tests are conducted on a custom made PCB as per JEDEC standard using a drop test apparatus. A Finite Element model of the free fall drop phenomenon is developed and numerical simulation is carried out using ANSYS 16.0 software based on two simplified Finite Element (FE) methods (Input-G method and Support Excitation Scheme) reported in the literatures are compared with experimental results to identify the most suitable FE method in terms of accuracy of the results produced. Using the identified FE method, the dynamic responses of PCBs with three different support configurations commonly used are analyzed to identify the best possible support configuration that can with stand drop impact loads better.

Drop Impact Analysis of Outside Cooling Unit Package of System Air-Conditioner and Experimental Verification

Drop Impact Analysis of Outside Cooling Unit Package of System Air-Conditioner and Experimental Verification

Blue Gene/L上での携帯電話の大規模落下衝撃解析 : SC06ゴードンベル賞ファイナリストに選ばれた研究の紹介(インダストリアルマテリアル)

Blue Gene/L上での携帯電話の大規模落下衝撃解析 : SC06ゴードンベル賞ファイナリストに選ばれた研究の紹介(インダストリアルマテリアル)

Study on Board-Level Drop Impact Reliability of Sn–Ag–Cu Solder Joint by Considering Strain Rate Dependent Properties of Solder

Board-level drop reliability test and analysis require dynamic characterization of the high strain-rate properties of the solder, along with solder joint failure tests. Relying on just the drop impact analysis of board-level dynamic response (i.e. G-levels and board bending strains) and an oversimplification of deformation response of solder joints (i.e., assuming elastic stress criteria) can lead to misleading conclusions in the physics-of-failure understanding in drop impact tests. In this paper, impact tests were conducted with a split Hopkinson pressure bar test system to study the dynamic response of bulk solder materials. A finite-element analysis of drop impact was conducted by considering different solder constitutive models such as the elastic and strain rate-dependent plastic model to investigate the effect of the solder constitutive model on the dynamic response of the solder joint. The important finding of this study is that the constitutive model used has a major impact on the dynamic response of solder joint stress and strain results. Theoretically, it is predicted that the strain rate-dependent plastic model gave better correlation results than the simple elastic model. A solder joint reliability characterization using the drop impact test with a clamped–clamped boundary condition was investigated for a plastic ball grid array assembly with Sn–Ag–Cu solder and two board surface finishes. In order to assess drop reliability of solder joint with different surface finishes, Charpy test was conducted to evaluate the dynamic strength of the soldered specimen using Sn–Ag–Cu solder and with or without Ni/Au plating.

GS0501-214 非連成解析による多層塗膜の動的損傷力学シミュレーション

In this research we use uncoupled analysis to evaluate the impact resistance of multi-layer coatings. We conduct high strain-rate simulation by ANSYS. Then the results of stress and strain are in put to damage analysis program which employs the elasto-viscoplastic damage constitutive equation based on continuum damage mechanics. Both of tensile fracture analysis and drop impact analysis have almost agreed well with the corresponding experimental results. Uncoupled analysis for dynamic damage mechanics problems can be expected to be used as a computational tool for the evaluation and the design of multi-layer coatings.

DROP IMPACT ANALYSIS OF PLATE-TYPE FUEL ASSEMBLY IN RESEARCH REACTOR

In this research, a drop impact analysis of a fuel assembly in a research reactor is carried out to determine whether the fuel plate integrity is maintained in a drop accident. A fuel assembly drop accident is classified based on where the accident occurs, i.e., inside or outside the reactor, since each occasion results in a different impact load on the fuel assembly. An analysis procedure suitable for each drop situation is systematically established. For an accident occurring outside the reactor, the direct impact of a fuel assembly on the pool bottom is analyzed using implicit and explicit approaches. The effects of the key parameters, such as the impact velocity and structural damping ratios, are also studied. For an accident occurring inside the reactor, the falling fuel assembly may first hit the fixing bar at the upper part of the standing fuel assembly. To confirm the fuel plate integrity, a fracture of the fixing bar should be investigated, since the fixing bar plays a role in protecting the fuel plate from the external impact force. Through such an analysis, the suitability of an impact analysis procedure associated with the drop situation in the research reactor is shown.

Fabricating superhydrophobic aluminum: An optimized one-step wet synthesis using fluoroalkyl silane

In this paper we present a simple but effective procedure to impart superhydrophobicity to aluminum through a one-step wet chemistry synthesis. The synthesis is performed in one step, thanks to simultaneous etching with NaOH and grafting with fluoroalkyl silane (FAS) molecules, which allow aluminum surface functionalization. By optimizing the proper amount of reagents, controlling the reaction batch temperature and particularly by allowing pre-activation of the solution, we showed that the process can be used turn into water repellant superhydrophobic surfaces four aluminum samples in sequence, using the same reaction batch. Also, if FAS is further added to the solution the procedure can impart superhydrophobicity to further aluminum samples. The synthesis with the optimized parameters is green and cost effective, since it was developed to minimize the use of both base and fluorinated molecules. In addition, it is easy to scale up to large area treatments and to industrial application, because the procedure is one-step, is reproducible, and allows multiple use of the same reaction batch, for the treatment of multiple samples. Finally, we show that not only the surfaces show excellent non-wetting properties in quasi-static conditions, with contact angles ∼150̊ and with very low contact angle hysteresis, ∼4̊, but also in dynamic conditions, as proved by means of drop impact analysis up to Weber number of 690.

Observation and analysis of drop impact on wetted spherical surfaces with low velocity

The phenomenon of liquid drop impact on wetted spherical surfaces with low impact velocity is observed using a high speed digital camera at 10000 frames per second. Drop rebound, partial rebound and spreading are observed and analyzed, considering the effect of viscosity. Influences of the sphere diameter, impact velocity and viscosity on the spreading characteristic parameter are discussed quantitatively. The experimental observations show that the drop rebound and partial rebound phenomena may occur at large viscosity and low impact velocity, which cannot be observed at small viscosity. The spreading area can be increased by increasing impact velocity. The results also reveal that the spreading factor increases with viscosity decreasing. At the sphere diameters ranging from 4 mm to 20 mm, it is found that with the increase of the sphere diameter, the spreading factor will be increased.

A numerical analysis of drop impact on solid surfaces by using smoothed particle hydrodynamics method

In this paper, we present a numerical simulation of a single liquid drop impacting onto solid surface with smoothed particle hydrodynamics (SPH). SPH is a Lagrangian, meshfree particle method, and it is attractive in dealing with free surfaces, moving interfaces and deformable boundaries. The SPH model includes an improved approximation scheme with corrections to kernel gradient and density to improve computational accuracy. Riemann solver is adopted to solve equations of fluid motion. An new inter-particle interaction force is used for modeling the surface tension effects, and the modified SPH method is used to investigate liquid drop impacting onto solid surfaces. It is demonstrated that the inter-particle interaction force can effectively simulate the effect of surface tension. It can well describe the dynamic process of morphology evolution and the pressure field evolution with accurate and stable results. The spread factor increases with the increase of the initial Weber number. The numerical results are in good agreement with the theoretical and experimental results in the literature.

Drop Impact Analysis of Cushioning System with an Elastic Critical Component of Cantilever Beam Type

In some electronic products and sculpture crafts, there are possibly vulnerable elements that can be idealized as cantilever beam type, failure of which will certainly lead the whole product to lose function. Based on the critical component of cantilever beam type, a nonlinear coupling dynamics model between the critical component and the item was established. The computing procedure of the model was designed using finite difference scheme. A numerical example shows that the acceleration changes notably with the length of the critical component, and the cantilevered end of the critical component is liable to be damaged, because the dynamic stress there is the largest. In this case, the maximum acceleration just cannot serve as the damaged criterion of the packaged goods, only with the maximum stress value. In order to avoid making a mistake, it is necessary to consider the critical component as an elastic element. The maximum stress of the cantilever beam surpasses the proportional limit of elastic components or is not an effective structural strength to determine whether the product loses its functions.

A numerical analysis of drop impact on liquid film by using a level set method

Splashing and spreading of a liquid by drop impact on liquid film depends on the impact velocity, drop size, drop properties and liquid film thickness. These parameters can be summarized by three main dimensionless parameters: Weber number, Ohnesorge number and non-dimensional film thickness. Upon impact of a drop on liquid film, these parameters influence the shape of the splash and the forma- tion and propagation of the crown. In the present study, the splashing and spreading resulting from drop impact on liquid film has been numerically investigated by using a Level Set method for the interface tracking of the two-phase flow simulation. For various dimen- sionless parameters, characteristics of the crown formation and spreading were predicted, and the results were found to show good agreement with available experimental data in the earlier stage of crown formation and show some discrepancies in the later stage of crown spreading due to the present 2D axi-symmetric computation, which cannot predict the secondary drops.

OLED 모듈의 충격시험용 표준 지그 개발

이동전화기의 낙하 충격 시 디스플레이 모듈의 파손은 이동전화기의 재료, 강성 및 형상에 의하여 많은 영향을 받는다. 이동전화기 개발의 초기 단계에서는, 디스플레이 모듈의 내구성을 판단하기 위하여 모듈을 지그에 장착하여 낙하시험을 수행한다. 본 연구에서는 OLED 모듈의 충격 시험을 수행하기 위한 지그를 개발하였다. 지그의 재료, 두께 및 리브의 개수와 방향 등을 설계변수로 고려하여 실제 이동전화기가 낙하할 때 OLED 모듈이 받는 충격 응력과 가장 유사한 응력이 발생하도록 지그를 개발하였다. ABAQUS/Explicit를 사용한 1.5m 높이 충격 해석에서, 개발된 지그에 장착된 OLED 모듈의 유리에서 발생하는 최대주응력은 이동전화기에 장착된 동일 모듈의 유리에서 발생하는 최대주응력과 유사함을 확인할 수 있었다. The failure of display modules in cellular phones due to drop impact depends on the materials, stiffnesses and shapes of the phones. In the early development stage of cellular phones, the behavior of the display modules due to drop impact is tested using jigs where the display modules are installed. In this study, jigs of cellular phones for drop impact test of OLED modules were designed. The material, thickness and number and orientation of ribs were considered as design variables. Jigs were designed in a way that responses of modules due to drop impact were similar to those of modules in cellular phones. The maximum principal stresses at the upper glasses of modules were considered as responses, which were analyzed using a commercial software ABAQUS/Explicit. The drop impact analysis at the height of 1.5 meters showed that the responses of OLED module in the developed jig were in a good agreement with those in cellular phone.

A Comprehensive Review of Drop Impact Modeling on Portable Electronic Devices

This article is dedicated to the review of publications on drop impact analysis performed on consumer electronic devices such as cellular phones and two-way radios in the past decade. Prior to the highlights of this review, the scope and motivation behind this work will be briefly explained. A comprehensive survey on published literatures devoted to the methodologies established to analyze the reliability of electronic products exposed to the event of drop impact is presented. The scope of the review is extended beyond product level analysis to also include drop impact study at board level. This type of review is novel and has not been published in the past. The focus will be on the different analytical and numerical modeling approaches and the current status of finite element method in predicting the drop impact performance of electronic devices. Of equal interest is the methodology adopted in past work to establish a correlation between numerical and experimental results. This article serves as a reference to all intended future work which could be an extension from the current known art of drop impact analysis on electronic devices. The time frame of this review is up to year 2010.

드럼 세탁기 포장재 낙하해석 및 완충 특성

대형 드럼세탁기의 낙하 충격에 대한 포장재의 동적 거동 분석을 수행하였다. 해석에는 충격 해석에 널리 쓰이고 있는 LS-DYNA 를 사용하였으며, 자유 낙하 시의 충격 가속도와 유효 응력, 그리고 고속 카메라를 통한 포장재 압축 변형 비교를 통해 해석 결과의 신뢰성을 검증하였다. 완충 특성 및 포장재 구조 에 대한 파라미터 분석을 통해 기존 포장 구조에 대한 설계 개선안을 도출하였으며, 유통 시험을 통해 유효성을 검증하였다. 본 연구에서 사용한 해석 기법 및 분석 방법 등을 통해, 향후 드럼 세탁기의 완충 성능 및 재료비 개선에 효과적으로 기여할 수 있을 것으로 기대된다.

Strain Rate Effects and Rate-Dependent Constitutive Models of Lead-Based and Lead-Free Solders

As traditional lead-based solders are banned and replaced by lead-free solders, the drop impact reliability is becoming increasingly crucial because there is little understanding of mechanical behaviors of these lead-free solders at high strain rates. In this paper, mechanical properties of one lead-based solder, Sn37Pb, and two lead-free solders, Sn3.5Ag and Sn3.0Ag0.5Cu, were investigated at strain rates that ranged from 600 s−1 to 2200 s−1 by the split Hopkinson pressure and tensile bar technique. At high strain rates, tensile strengths of lead-free solders are about 1.5 times greater than that of the Sn37Pb solder, and also their ductility are significantly greater than that of the Sn37Pb. Based on the experimental data, strain rate dependent Johnson–Cook models for the three solders were derived and employed to predict behaviors of solder joints in a board level electronic package subjected to standard drop impact load. Results indicate that for the drop impact analysis of lead-free solder joints, the strain rate effect must be considered and rate-dependent material models of lead-free solders are indispensable.

Superhydrophobic Aluminum Surfaces by Deposition of Micelles of Fluorinated Block Copolymers

Superhydrophobic surfaces are generated by chemisorption on aluminum substrates of fluorinated block copolymers synthesized by reversible addition-fragmentation chain transfer in supercritical carbon dioxide. In an appropriate solvent, those block copolymers can form micelles with a fluorinated corona, which are grafted on the aluminum substrate thanks to the presence of carboxylic acid groups in the corona. Water contact angle and drop impact analysis were used to characterize the wettability of the films at the macroscale, and atomic force microscopy measurements provided morphological information at the micro- and nanoscale. The simple solvent casting of the polymer solution on a hydroxylated aluminum surface results in a coating with multiscale roughness, which is fully superhydrophobic over areas up to 4 cm(2).

Drop impact analysis of smart unmanned aerial vehicle (SUAV) landing gear and comparison with experimental data

AbstractThe dynamic behavior of the landing gear is very important, because it absorbs kinetic energy of the vertical load and reduces aircraft impact at touchdown. In this study, drop impact analyses have been conducted for SUAV’s landing gear using the explicit finite element code LS‐DYNA®. The landing gear was modeled as a flexible body and the analyses were focused on the dynamic behavior of the shock absorber, the deformation of the tire, energy analysis and the reaction load on the impact surface. Experimental results were compared with the analytical results.