Drop impact analysis of TSV-based 3D packaging structure by PSO-BP and GA-BP neural networks

Particle swarm algorithm(PSO) and genetic algorithm(GA) were used to optimize the back propagation(BP) artificial neural network for predicting the dynamic responses of the through silicon via(TSV) based three-dimensional packaging structures.A finite element model of the TSV packaging structure with a strain-rate dependent constitutive model for solder joints was created to simulate the drop impact due to a free fall of 0.8 m to the rigid ground to investigate the structural dynamic responses during the whole impact process.The spatial coordinates of the solder joints were used as the input parameters of the hybrid neural network model for the drop impact responses,while the maximum Von Mises stress and PEEQ(plastic strain) values are identified the output parameters.The correlation coefficient(R),the mean absolute percentage error(MAPE) and the training time were used as the measures to validate and compare the proposed PSO-BP and GA-BP neural networks.The results show that both the PSO-BP model and the GA-BP model can achieve high accuracy predictions with strong generalization capability.Apparently,both optimized algorithms outperform the original BP model,but the PSO-BP model is slightly more superior than the GA-BP model.It is also demonstrated that the proposed optimized algorithms efficiently predict the drop impact responses of TSV packaging structures by greatly saving the computational and experimental cost of drop impact tests.

Effect of viscosity on motion of splashing crown in high speed drop impact

A splashing crown is commonly observed when a high-speed drop impacts a liquid film. The influence of the liquid viscosity on the crown＇s evolution is not yet clear. We review several existing theories of this problem, and carry out a series of numerical simulations. We find that a three-segment model can describe the crown＇s motion. In the very early stage when the crown is barely visible, the influence of viscosity is small. Later, a shallow water approach used in most existing models is applicable as long as the initial conditions are formulated properly. They depend on viscous dissipation in the intermediate period. Preliminary estimation based on a dissipation function is proposed to characterize the influence of viscosity in this problem.

Correlating solder interconnects failure with PCBs response during board level drop impact test

Solder interconnects reliability during drop impact is important for portable electronic products. In this paper, board level drop impact tests were conducted according to the standard of the Joint Electronic Devices Engineering Council （JEDEC）. Solder failure drop numbers were recorded and solder failure analyses were carried out. A high speed data acquisition system was constructed to measure the printed cireuit board （ PCt~ ） dynamic response during the impact. Measured response data were used to characterize the loading feature of the impact. The relatioT~~hip between solder failure features and PCB dynamic response was correlated. Solder failure mechanisms were discussed. The correlation of PCB strain data with the solder failure life indicates that the solder damage accumulated during drop impact is dependent on both strain amplitude and modes contribution of the PCB. Compared with high strain amplitude loading condition, lower strain amplitude with higher mode can even produce more severe damage to the solder interconnects. Repeated impact loadings to the solder induce the combination failure mechanism of both impact and fatigue. Failure analyses results provide convincing verification for the complexity of the failure mechanisms.

Drop impact on substrates with heterogeneous stiffness

Previous studies of drop impact mainly focus on homogeneous substrates while heterogeneous substrates remain largely unexplored. A convenient preparation strategy of stiff heterogeneous substrates is presented in this work, and the drop impact on such a stiffness-patterned substrate consisting of soft spirals surrounded by a rigid region is systematically investigated. The results show that the splash behavior of a drop on a stiffness-patterned substrate exhibits distinct characteristics from those on a homogeneous substrate. Prompt splash is more likely to occur on the substrate with the greater heterogeneity of stiffness, which is reflected in the lower critical impact velocity. Moreover, the splash velocity of emitted droplet is significantly larger on the heterogeneous substrate than that on a corresponding homogeneous substrate,especially at a higher impact velocity of the drop, indicating a stronger splash intensity on the heterogeneous substrate.The difference in drop splashing between homogeneous substrate and heterogeneous substrate is largely due to the stiffness heterogeneity, rather than the variation of overall stiffness of the substrate. The use of spiral shape provides a feasible solution for introducing stiffness heterogeneity of substrate. This study is conducive to the understanding of drop impact research beyond uniform substrates, reveals the potential of using stiffness-patterned substrates to control splash, and may find useful applications in industries related to drop impact and splash.

Impact response and energy absorption of metallic buffer with entangled wire mesh damper

An innovative metallic buffer consisting of series-connected hat-shaped entangled wire mesh damper(EWMD)and parallel springs are proposed in this work to enhance the reliability of engineering equipment.The impact response and the energy dissipation mechanism of hat-shaped EWMD under different quasi-static compression deformations(2-7 mm)and impact heights(100-200 mm)are investigated using experimental and numerical methods.The results demonstrate distinct stages in the quasi-static mechanical characteristics of hat-shaped EWMD,including stiffness softening,negative stiffness,and stiffness hardening.The loss factor gradually increases with increasing compression deformation before entering the stiffness hardening stage.Under impact loads,the hat-shaped EWMD exhibits optimal impact energy absorption when it enters the negative stiffness stage(150 mm),resulting in the best impact isolation effect of metallic buffer.However,the impact energy absorption significantly decreases when hat-shaped EWMD enters the stiffness hardening stage.Interestingly,quasi-static compression analysis after experiencing different impact loads reveals the disappearance of the negative stiffness phenomenon.Moreover,with increasing impact loads,the stiffness hardening point progressively shifts to an earlier stage.

Numerical simulation of drop weight impact sensitivity evaluation criteria for pressed PBXs

A thorough understanding of drop-weight impacted responses for polymer-bonded explosives(PBXs)is significant to evaluate their impact sensitivity.The characteristics of the drop-weight impacted pressed PBXs including deforming,fracturing,forming a local high-temperature region and igniting,were simulated using a coupled mechanical-thermo-chemical model integrating micro-defects evolution.A novel evaluation method for impact sensitivity is established using the relation between the input kinetic energy and the output energy due to deformation,crushing energy,local hot spot energy and ignition.The effects of impact velocity on sensitivity were analyzed and the critical local ignition impact velocity is determined as 4.0-4.5 m/s.The simulated results show that shear-crack friction heating is the dominant ignition mechanism.The region along the boundary of PBXs sample is the most hazardous regions where ignition first occur.The propagation of stress wave in PBXs causes shear-crack hotspot and bulk temperature exhibiting an approximate 45°direction evolution path,which is the main reason that dominated damage-ignition region transits from the boundary to the central of sample.

A LATTICE BOLTZMANN METHOD FOR SIMULATION OF A THREE-DIMENSIONAL DROP IMPACT ON A LIQUID FILM

A single-phase free surface tracking model based on the Lattice Boltzmann Method （LBM）, which has capability of simulating liquid-gas system with the assumption that the gas phase has only negligible influence on the liquid phase, is utilized to simulate the flow of a drop impacting on a liquid film. Three typical outcomes in the flows, i.e., deposition, crown and splash, which have been observed in the previous experiments, are obtained in the present three dimensional numerical simulations. The numerical results are consistent with the experimental and analytical results available.

Droplet impact on regular micro-grooved surfaces

We have investigated experimentally the process of a droplet impact on a regular micro-grooved surface. The target surfaces are patterned such that micro-scale spokes radiate from the center, concentric circles, and parallel lines on the polishing copper plate, using Quasi-LIGA molding technology. The dynamic behavior of water droplets impacting on these structured surfaces is examined using a high-speed camera, including the drop impact processes, the maximum spreading diameters, and the lengths and numbers of fingers at different values of Weber number. Experimental results validate that the spreading processes are arrested on all target surfaces at low velocity. Also, the experimental results at higher impact velocity demonstrate that the spreading process is conducted on the surface parallel to the micro-grooves, but is arrested in the direction perpendicular to the micro-grooves. Besides, the lengths of fingers increase observably, even when they are ejected out as tiny droplets along the groove direction, at the same time the drop recoil velocity is reduced by micro-grooves which are parallel to the spreading direction, but not by micro-grooves which are vertical to the spreading direction.

Impact of Drops on Non-wetting Biomimetic Surfaces

We have carried out an experimental study of liquid drop impact on superhydrophobic substrates covered by a carpet of chemically coated nano-wires.The micro-structure of the surface is similar to some biological ones(Lotus leaf for example).In this situation the contact angle can then be considered as equal to 180 degrees,with no hysteresis.Due to its initial inertia,the drop experiences a flattening phase after it hits the surface,taking the shape of a pancake.Once it reaches its maximal lateral extension,the drop begins to retract and bounces back.We have extracted the lateral extension of the drop,and we propose a model that explains the trend.We find a limit initial velocity beyond which the drop protrudes into the nano-wire carpet.We discuss the relevance of practical issues in terms of self-cleaning surfaces or spray-cooling.

Oblique Drop Impact on Deep and Shallow Liquid

Numerical simulations using CLSVOF(coupled level set and volume of fluid)method are performed to investigate the coalescence and splashing regimes when a spherical water drop hits on the water surface with an impingement angle.Impingement angle is the angle between the velocity vector of primary drop and the normal vector to water surface.The effect of impingement angle,impact velocity and the height of target liquid are carried out.The impingement angle is varied from 0o to 90o showing the gradual change in phenomena.The formation of ship pro like shape,liquid sheet,secondary drops and crater are seen.Crater height,crater displacement,crown height and crown angle are calculated and the change in the parameters with change in impingement angle is noted.

Cavity dynamics of water drop impact onto immiscible oil pool with different viscosity

In this work,we numerically study the impact of a water droplet onto a deep oil pool.Two fluids are immiscible and the viscosity of the pool liquid is changed systematically.We focus on the cavity dynamics during the impact and especially the effects of the pool liquid viscosity and the impacting velocity.For the parameter range explored,we identify the regime where splashing occurs with corolla breaking into droplets,and the regime where no splashing is observed.Similarity is found for the time evolution of cavity depth for fixed impact velocity and different viscosity,if the cavity depth and time are nondimensionalized by the maximal depth and the time when the maximal depth is reached.Effective power-law scalings are also proposed to describe the dependence of the maximal cavity depth and the corresponding time on the impact velocity and pool liquid viscosity,in the term of Froude and Reynolds numbers.

Effect prediction of stiffened-ring cylindrical shells subjected to drop mass impact

This study focuses on the effect of lateral mass impact on ring-stiffened thin-walled cylindrical shell.Cylindrical shells were fabricated to validate the numerical modeling and analytical techniques,and drop tests were performed using a rigid spherical indenter.Next,stiffened-ring cylindrical shells with various structural size parameters were simulated using ABAQUS software.The relationships between the impact force,deformation displacement,and rebound velocity were established,on the basis of impact mechanics theory and simulation results.It derived fitting functions to analyse the relationship between the maximum load and maximum displacement of ring-stiffened cylindrical shell under dynamic mass impact.Based on the validation of the simulation model,the fitting function data were compared with the simulation results,and the functions showed a good accuracy.Besides,the parameters,mass ratio and stiffened-ring mass ratio were used to reflect the effect of the mass change in the ring-stiffened cylindrical shell.Furthermore,parametric studies on ring-stiffened cylindrical shell models were conducted to analyse the progressive impact responses.

Experimental investigations of mechanical and reaction responses for drop-weight impacted energetic particles

Low-velocity drop-weight impact experiments on individual and multiple Cyclotetramethylene tetranitramine (HMX) energetic particles were performed using a modified drop-weight machine equipped with high-speed photography components. Multiple particles experienced more severe burning reactions than an individual particle. Comparisons between impacted salt and HMX particle show that jetting in HMX is mainly due to the motion of fragmented particles driven by gaseous reaction products. Velocity of jetting, flame propagation, and area expansion were measured via image processing, making it possible to quantify the chemical reaction or mechanical deformation violence at different stages.

Analysis of Pipeline Damage to Impact Load by Dropped Objects

Marine pipeline damage subjected to dropped objects from platforms or supply vessels is analyzed to introduce an easy and applicable approach to investigating the damage induced by impact load from drop weight. A practical engineering example was presented and analyzed using the commercial program 'ANSYS/LS-DYNA', which is a powerful tool with an explicit dynamic solver. And rational agreement of the results with previous works was obtained. The suggested procedure might be taken as a checking analysis of the protection measures of pipelines in addition to the general risk assessment method.

CFRP加固损伤钢筋混凝土梁抗冲击性能试验研究

对采用碳纤维增强复合材料(CFRP)加固的不同损伤程度的钢筋混凝土梁进行落锤冲击试验,以冲击高度、加固层数为试验参数分析CFRP加固损伤试件的裂缝发展、破坏形态及抗冲击性能,并研究试件在冲击荷载下的动力性能。结果表明:试件损伤程度越高,其斜向裂缝发展越密集,试件的破坏程度越严重;落锤冲击高度越高,裂缝发展越趋近于跨中局部化;当采用多层CFRP布加固损伤试件时,试件在落锤冲击作用下保持较好的完整性,仅外部混凝土粉碎掉落;随着CFRP布粘贴层数的增加,试件整体产生弯剪破坏,损伤试件加固修复后的抗冲击能力及刚度相较于完好试件得到显著提升,提升幅度为70%~72%,但增加CFRP布粘贴层数对试件的加固修复效果提升作用有限,且加固效果与抗冲击能力并非呈线性关系;基于有效应变计算的结果可知,采用CFRP布加固修复不仅仅具有加固补强的作用,同时能够在一定的程度上改善试件的整体抗冲击性能。

不同钢纤维掺量全轻混凝土梁落锤冲击试验研究

由于全轻混凝土结构抗剪承载力较低,因此有必要探究钢纤维的加入对全轻混凝土梁动力性能的影响。设计钢纤维体积掺量为0%、1%、2%共3根适筋梁,对其跨中区域进行落锤冲击试验,并利用LS-dyna有限元软件进行数值模拟,对比分析各试件破坏形态、冲击力时程曲线、跨中位移时程曲线。试验结果表明:在相同冲击荷载作用下随着钢纤维体积掺量的增加抑制裂缝产生和发展的现象越显著,并且裂缝相对更加集中于梁跨中区域,支座处裂缝相对减少。钢纤维的加入不影响试件冲击力最大值,但随着钢纤维体积掺量的增加,各试件冲击力第二峰值与最大值之比增加14%和26%,跨中位移最大值与残余位移分别降低3、8mm与3、7mm。经研究得出钢纤维的加入显著提高全轻混凝土梁抗冲击性能。

舰载飞机着舰撞击载荷实测技术研究

针对国内飞机起落架载荷测量中普遍存在的静标动测问题,从理论和机理上分析了静标定的应变法实测动态载荷存在问题的原因。同时,考虑到舰载飞机因定点着舰方式遭受严重的动态载荷,重点研究了舰载飞机着舰撞击载荷的静标动测问题。通过动态落震试验模拟飞机着舰过程,根据测力平台的实测载荷分析,获取了应变法实测载荷精度受动态影响的程度,提出一种改进的惯性修正方法,即:通过落震试验数据辨识质量矩阵,通过辨识的质量矩阵和实测加速度修正应变法的实测载荷。试验结果表明,改进的惯性修正方法进一步提高了垂向载荷的测量精度,显著提高了航向和侧向载荷的实测精度。

粗骨料纤维充填体的力学特性与能量损伤演变规律

为提升充填体的抗拉性能、抗裂性能和韧性,通过抗压、巴西劈裂和落锤冲击试验研究了聚丙烯纤维对充填体强度特征、变形特征、抗冲击性能和能量演变的影响。结果表明:随着纤维掺量增加,充填体强度先增大后减小,弹性模量逐渐降低;掺入纤维后,充填体总耗能增加,达到峰值后释放动能减小,摩擦内能增加,可促进弹性应变能转变为耗散应变能;随着纤维掺量增加,充填体冲击耗能、延性比和韧性系数先增大后减小,终裂形态由“开裂即碎”演变为“裂而不碎”;掺入0.10%纤维的充填体抗拉强度、韧性和抗冲击等性能最优。强化机制主要是充填体内纤维“筋网结构”延缓裂纹产生、抑制裂纹扩展和提升能量吸收上限。研究成果有助于提升采场充填体顶板的稳定性,保障矿山生产作业安全。

增幅冲击下钢筋混凝土板的抗冲击性能

钢筋混凝土板在服役期间可能承受落物多角度连续撞击等多次冲击荷载作用,钢筋混凝土板抵抗多次冲击的能力、多次冲击作用下钢筋混凝土板的性能演化和剩余性能评估等问题至关重要,其中,多次冲击的加载制度是研究钢筋混凝土板抗冲击性能的重点。为研究多次冲击下钢筋混凝土板的抗冲击性能,利用落锤和摆锤试验研究钢筋混凝土板在增幅冲击下的抗冲击性能,获得钢筋混凝土板在历次冲击过程中的冲击力时程曲线以及历次冲击后的整体变形和凹陷变形特征,分析钢筋混凝土板的吸能特性和累计损伤演化规律,研究钢筋混凝土板受冲击后的残余性能。结果表明:冲击角度对钢筋混凝土板的变形有显著影响,斜向冲击对钢筋混凝土板安全性能的影响更大;增幅冲击降低钢筋混凝土板的吸能能力,提高其破坏率,钢筋混凝土板的冲击响应相对于恒重重复冲击更加稳定。

液滴撞击柔性基底研究进展

液滴撞击固体基底现象广泛存在于自然界、日常生活及工业生产中.在多数液滴撞击场景中,固体基底可以近似地视为理想刚性基底.然而在一些场景中,具有较小杨氏模量或者几何结构为薄壁或细长类的固体基底在受到液滴撞击后会产生明显的变形,而固体基底的形变反过来又会影响液滴的动力学行为.相比于刚性基底情况,液滴与柔性基底的耦合作用可能会引发新的动力学现象和机制.因此,柔性基底液滴撞击动力学的研究很有意义,也成为一些学者当前关注的研究焦点之一.根据几何结构的特点,柔性基底可以分为柔性体、柔性面和柔性杆3种类型.文章据此分类介绍与这3类柔性基底相关的液滴撞击动力学的研究进展.柔性基底的可变形性是导致其液滴动力学与刚性基底液滴动力学存在差异的根本原因.现有的研究表明,基底柔性对液滴撞击的接触时间、最大铺展因子、气泡捕获、回弹和溅射等方面均存在着影响,其中关于接触时间及溅射方面的结论可能为制造防水、抗冰和防溅射材料提供新思路.