Numerical simulation of hypervelocity impact on CFRP/Al HC SP spacecraft structures causing penetration and fragment ejection

A representative carbon fiber reinforced plastic/aluminum honeycomb sandwich panel (CFRP/Al HC SP) spacecraft structure has been modeled in the hydrocode AUTODYN using the state-of-the-art ADAMMO material model [Riedel W, Harwick W, White D, Clegg R. Advanced material damage models for numerical simulation codes. ESA CR(P) 4397, 2003] to study the performance of the structure during impact events that cause perforation and fragment ejection. A new procedure combining a series of existing theoretical methods has been developed and applied to derive a full set of coarse material data. The data set has been implemented in AUTODYN, and the results of the numerical simulation have been compared to experimental impact test data. For impact tests performed near the structural ballistic limit, quantitatively accurate results were obtained over a range of impact velocities and angles. A further increase in the projectile size resulted in significant destruction of the sandwich panel front face-sheet and diversion from the experimental damage measurements. Inspection of the numerical model has shown non-localized propagation of inter-laminar delaminations, possibly caused by an under-prediction of the laminate dynamic inter-laminar tensile strength. The effects of the delamination propagation occur over an extended time scale and were not found to affect the state and trends of the fragment cloud ejected into the satellite interior. Accordingly, experimental trends of fragment cloud dispersion have been qualitatively reproduced.     

Impact between fluids and solids. Comparison between analytical and FEA results

Theoretical and numerical analyses of the dynamic force acted on structures by fluid-like debris flows (d.f.) or fluids are presented. Current analyses of the interaction between d.f. and structures usually take into account a modified hydrodynamic pressure or a multiple of the hydrostatic pressure, to determine the impact force. A close examination of analytical and experimental results, mainly pertaining to hydraulic and coastal engineering, regarding the impact of water waves against coastal facilities, however, reveals that these simplified assumptions are not supported by rational presumptions. Numerical (FE) analyses have been therefore carried out and their results compared to the available theoretical and numerical results in the literature. The importance of the impulsive phase of the impact phenomenon, especially if a planar d.f. front face is parallel to the impacted structure, is put into evidence. Proposed FEA results highlight the role of fluid's speed, density and compressibility in the general problem of the impact of fluids against structures.     

Flight model performance test results of a helium dewar for the soft X-ray spectrometer onboard ASTRO-H

ASTRO-H is a Japanese X-ray astronomy satellite, scheduled to be launched in fiscal year 2015. The mission includes a soft X-ray spectrometer instrument (SXS), which contains an X-ray micro calorimeter operating at 50 mK by using an adiabatic demagnetization refrigerator (ADR). The heat sink of the ADR is superfluid liquid helium below 1.3 K. The required lifetime of the superfluid helium is 3 years or more. In order to realize this lifetime, we have improved the thermal performance from the engineering model (EM) while maintaining the mechanical performance. Then, we have performed a thermal test of the flight model (FM). The results were that the heat load to the helium tank was reduced to below 0.8 mW in the FM from 1.2 mW in the EM. Therefore, the lifetime of the superfluid helium is more than 3 years with 30 L of liquid helium.In this paper, the thermal design and thermal test results are described.     

Viscoelastic impact between a cylindrical striker and a long cylindrical bar

Axial impact between a cylindrical striker of finite length and a long cylindrical bar, both of linearly viscoelastic materials, is considered. General results are derived for the impact force, the particle velocity and the strain in the bar in terms of closed-contour integrals. Such results are derived also for the transfer of momentum and energy from the striker to the bar. Numerical results for a striker and a bar made of the same material but with different cross-sectional areas are compared. In viscoelastic impact, unlike elastic impact, the duration of contact may be finite and larger than two transit times for a wave front through the striker due to the formation of a tail of finite length after the main pulse. Furthermore, multiple contacts and separations of the striker and the bar may occur within a range of striker-to-bar characteristic impedance ratios. In the case of viscoelastic impact studied numerically, the duration of contact is at least as long and the momentum and energy transferred are at most as large as in elastic impact. Strains measured at three locations of a polymethyl methacrylate (PMMA) bar impacted by strikers of the same material as the bar agree well with the theoretical results.     

Analogies and differences between quasi-static indentation and hypervelocity impact morphologies on thin solar cells

Morphologies produced by quasi-static indentation on thin Hubble Space Telescope (HST) solar cells show remarkable similarities to much of the hypervelocity damage sustained by the HST solar array whilst in orbit. Quasi-static indentation tests carried out with blunt and sharp indentors reveal analogies between static and dynamic (hypervelocity) indentation indicating similar fracture mechanics processes over the energy range evaluated. Understanding the static case assists to characterise better the dynamic process and bridge the intervening gap.     

International comparison of a standard voltage transformer between Ukraine and Germany

Results are provided for international comparisons of a standard voltage transformer performed in Ukraine and Germany. Algorithms are given for the equivalence of national standards taking account of expanded uncertainty. __________ Translated from Izmeritel’naya Tekhnika, No. 11. pp. 57–58, November, 2007.     

Evolution and calibration of a numerical model for modelling of hybrid-fibre ECC panels under high-velocity impact

A material model for hybrid-fibre engineered cementitious composites (ECC) under impact loading is developed and calibrated in this paper, and size effect, appropriate erosion criteria and strain rate effect are investigated and accounted for in the model. Employing the new material model, a numerical model and modelling technique are developed to model the impact behaviour and impact process of hybrid-fibre ECC panels using LS-DYNA commercial software. The material model and the numerical model developed in this paper are validated against the experimental results.     

Investigation of the response to low velocity impact and quasi-static indentation loading of particle-toughened carbon-fibre composite materials

This work investigates damage caused by low velocity impact and quasi-static indentation loading in four different particle-toughened composite systems, and one untoughened system. For impact tests, a range of energies were used between 25 and 50 J. For QSI, coupons were interrupted at increasing loading point displacement levels from 2 to 5 mm to allow for monitoring of damage initiation and propagation. In both loading cases, non-destructive inspection techniques were used, consisting of ultrasonic C-scan and X-ray micro-focus computed tomography. These techniques are complemented with instrumentation to capture force–displacement data, whereby load-drops are associated with observed damage modes. Key results from this work highlight particular issues regarding strain-rate sensitivity of delamination development and an earlier onset of fibre fracture associated with particle-toughened systems. These issues, in addition to observations on the role of micro-scale events on damage morphology, are discussed with a focus on material development and material testing practices.     

An experimental and modeling study of the thermomechanical behavior of an ABS polymer structural component during an impact test

An experimental and modeling study of the thermomechanical behavior of an ABS polymer structural component during an impact test is presented. The structural component was a heel of a woman's shoe made of ABS polymer material reinforced or not by a pin. Kinematics and thermal full field measurement techniques were used to observe the material and structural component during preliminary experimental tensile and impact tests. With the kinematic fields it was possible to identify the stress–strain response, which takes the necking localization into account. Positive volume variations were also observed during these tensile tests, which were associated with the crazing damage mechanisms in this type of polymer. The thermal fields measured during these tests showed high temperature variations (a few K to 25 K) in the zone where strain was localized.     

Investigation of dissolution behavior of diclofenac sodium extended release formulations under standard and biorelevant test conditions

Background: Dissolution characteristics of four extended release (ER) generic formulations of diclofenac sodium were examined. Aim: The aim of this study was to compare the drug dissolution behavior of diclofenac ER generics to clarify whether the products are characterized by comparable dissolution characteristics under the applied test conditions. Methods: The investigations were performed in the USP apparatus 2 and in the new biorelevant dissolution stress test device. Results: The experiments yielded striking differences between the generic formulations. Applying USP apparatus 2 it was noticed that the dissolution profiles of the products were distinctly affected by the stirring rate. Using the biorelevant dissolution stress test device susceptibility of the products to biorelevant stresses was observed. Change of pH within the experiments reduced the dissolution rates of all formulations and distinctly influenced their dissolution characteristics. Conclusion: The study demonstrates clearly the divergences in the dissolution behavior among the generic ER formulations of diclofenac sodium. The observed susceptibility of the tested dosage forms toward biorelevant stress bears in our interpretation the risk to cause unwanted fluctuations in drug plasma concentration profiles.     

一种新型楔形膜在真空中的制作方法及测试结果

提出了一种新型楔形膜在真空中的制作方法,可以替代白光干涉位移传感器中的关键元件.该方法采用两层复制技术,用有机材料SU8胶作为楔形膜中间的材料.同时,搭建了白光干涉位移传感器系统,对制作的楔形膜进行了测量.实验结果表明,该解调系统具有较好的稳定性及较高的测量精度.     

Experimental investigation of bond characteristics between CFRP fabrics and steel plate joints under impact tensile loads

In recent years, the use of adhesively-bonded fibre-reinforced composite materials has attracted widespread attention as a viable alternative for the retrofitting of civil infrastructure such as buildings and bridges. This has been particularly the case for concrete structures. The retrofitting of metallic bridges and buildings with FRP materials, however, is still in its early stages. In real life, these structures are subjected to dynamic loads. Therefore, it is necessary to understand the bond behaviour between steel and the strengthening materials for both static and dynamic loads. To examine the bond between steel plates and carbon fibre-reinforced polymers (CFRP) fabrics, this paper describes the experimental procedures and results of double strap steel joints loaded at different loading rates (2 mm/min, 3.35, 4.43 and 5 m/s). In this test program, ultimate load-carrying capacity, effective bond length, failure mechanism and strain distribution were examined for all loading rates. Different numbers of CFRP layers with different bond lengths were investigated. Experimental findings reveal that the maximum improvement in joint capacity occurs at a rate of 3.35 m/s. It was observed that the effective bond length is insensitive to loading rate for both joints. The failure modes and strain distributions, however, exhibit little difference between static and dynamic conditions.     

Correlation between the bond dissociation energies and impact sensitivities in nitramine and polynitro benzoate molecules with polynitro alkyl groupings

The geometries of nine CHNO nitro-contained explosive molecules were fully optimized employing the B3LYP method of density functional theory with the 6-31G* basis set. The bond dissociation energy (BDE) for removal of the NO(2) group in nitroamine molecules with nitro alkyl, and benzoate with nitro alkyl were calculated at the same level. The calculational results of B3LYP/6-31G* and B3P86/6-311G* levels showed that the strength of C-NO(2) is weaker than that of N-NO(2) bond in nitroamine molecules with nitro alkyl. The weakest bond is the C-NO(2) in these computed molecules. The relationship between the impact sensitivities and the weakest C-NO(2) bond dissociation energy values was examined. The results indicate a nearly linear correlation between the impact sensitivity and the ratio of the BDE value to the molecular total energy.     

史密斯预估补偿控制与PID控制的比较研究

比较了两种工业过程控制中的控制器,PID控制器和史密斯预估补偿控制器.介绍了四种PID参数的整定方法,分别为试凑法确定PID调节参数、Ziegler-Nichols参数整定方法、最优PID整定算法、运用Matlab/simulink中的NCD Outport(非线性控制设计输出端口模块)模块对PID参数进行最优整定.史密斯预估补偿控制器主要用于工业控制中的大延时系统控制,以提高系统的阶跃响应性能.在理论上,史密斯预估补偿控制器提供了一个有效的方法来提高控制效果.运用Matlab/Simulink仿真方案对前述两种控制方法进行了仿真比较,结果表明,在有较大延时情况下,史密斯预估补偿控制能获得比PID控制更好的结果.     

Dialysate saving by automated control of flow rates: comparison between individualized online hemodiafiltration and standard hemodialysis

Cost reduction and quality improvement seem to be conflicting issues. However, online hemodiafiltration (oHDF) with new automatic functions offers a cost‐efficient therapy compared to hemodialysis (HD). Seven dialysis centers conducted a randomized clinical trial with cross‐over design: high‐flux HD vs. postdilutional oHDF with functions coupling both dialysate and substitution flow rates to blood flow rates. During the 6 weeks of the study, all treatment parameters remained unchanged for HD and oHDF, apart from dialysate and substitution flow rate. Treatment data were recorded during each treatment, and predialytic and postdialytic concentrations of urea were recorded at the end of each study phase. The analysis involved 956 treatments of 54 patients. The mean dialysate consumption was 123.2 ± 6.4 l for HD and 113.4 ± 14.9 l for oHDF (p < 0.0001), the mean dialysis dose was 1.42 ± 0.23 for HD and 1.47 ± 0.26 for oHDF (p < 0.0001); oHDF resulted in a lower dialysate consumption (8.0% less) and a slightly increased dialysis dose (Kt/V 3.5% higher) compared to HD. oHDF with the investigated automatic functions offers substantial savings in dialysate consumption without decreasing dialysis dose.     

Conductivity in carbon nanotube polymer composites: A comparison between model and experiment

Carbon nanotubes (CNTs) demonstrate remarkable conductive behaviour, which suggests promising applications. Their outstanding properties have been used in the development of CNT–polymer composites as possible alternative materials for various applications, such as flexible electrodes, antistatic coatings and piezoresistive sensors. In our study we focused our attention on the evaluation and modelling of CNT-filled epoxy resin electrical conductivity. We discuss the results with regard to the influence of CNTs dimensions and content. Exploiting the Dijkstra algorithm, we implemented a simulation code which determines the shortest route between electrodes in the polymer. The longer the path inside the polymer, the more non-conductive the composite becomes, since polymer resistivity is orders of magnitude higher than that of CNTs. We compared these simulated results with experimental data obtained at several wt% and found a good correspondence between modelling and experimental results.     

A new soft-particle DEM model of micro-particle impact integrated adhesive,elastoplastic and microslip behaviors

Micro-particle impact is a problem of solid mechanics that is common in many applications. To address this problem, a new soft-particle DEM model of micro-particle impact is proposed, which incorporates adhesive, elastoplastic and microslip behaviors. The normal force model is developed as two contiguous loading stages: the elastic stage and the elastoplastic stage in which the transition is from the elastic deformation to fully plastic deformation. Most innovative in unloading, the normal force model is also evolved into two contiguous stages: unloading under elastic loading and unloading under elastoplastic loading in which it combines Hertz elastic model and Mesarovic-Johnson plastic model. The normal force model is further assumed as the one-way coupling with pressure-based Maw tangential model with the micro-slip behavior. Further model validations are performed by employing the experimental results in literatures. The validation results indicate that model predictions agree with the experimental data, and are demonstrated to be incredibly accurate than other models, particularly for restitution coefficients and critical sticking velocity. Furthermore we can find that the smaller size particle has a longer period of nonlinear loading, while the larger size particle has a longer period of linear loading. For tangential restitution coefficient at the small incident angle, a down trend may be due to the oscillation of the tangential force.