Fracture control for composite structures

A fracture control technique for composite structures is presented which takes advantage of the unique capability of composite materials to be tailored in stiffness and fracture toughness. Crack arrestment is achieved through the use of integral ‘buffer’ strips in the primary load-carrying laminate. Experimental uniaxial tension data obtained from damaged laminates containing such buffer strips indicate residual strength capacity in excess of the limit design stress for the selected laminate.     

A study of the differential scheme for composite materials

The overall moduli of a 2-phase linearly elastic composite are estimated by the differential scheme. The phases may be arbitrarily anisotropic and 1 phase is regarded as similar ellipsoidal inclusions at any concentration embedded homogeneously in a matrix. For an isotropic dispersion of spheres and for a fibre reinforced material it is shown that the estimates of the overall moduli lie between their Hashin-Shtrikman bounds. Also some known exact results are reproduced using this scheme.     

质子交换膜燃料电池复合材料双极板的研究

以高分子预聚物为粘合剂，天然或人造石墨为导电骨料，通过模压一次成型制备质子交换膜燃料电池双极板。研究了导电骨料的组分、树脂的种类及其含量，成型温度、成型压力对双极板性能的影响。结果表明：1)导电骨料的组分、树脂的种类及其含量对制品的性能影响较大；成型温度、成型压力对制品的性能影响较小。2)人造和天然两种石墨混合组分为导电骨料的制品，其导电性能明显高于单一石墨组分的制品；乙烯基树脂为粘合剂的性能优于以邻苯基树脂为粘合剂的双极板的性能。3)使用质量分数为16％～18％的乙烯基树脂作粘结剂，在成型压力为10MPa～20MPa，成型温度为150℃～200℃时制备的复合材料双极板的电导率＞300S／cm，抗折强度＞30MPa，空气透气率为10^-7cm^2／S。     

A study on the composite screw rotors for superchargers

In this work, the screw rotors for superchargers were manufactured with chopped carbon fiber epoxy composite materials by resin transfer molding process. The manufactured composite screw rotors were tested in different combinations such as the male composite and female composite rotors, the male composite and female aluminium rotors, and the male aluminium and female composite rotors. The temperature and pressure increases of the air at the outlet and the required torque of the supercharger were measured with respect to the angular velocities.     

Feasibility study to control fiber distribution for enhancement of composite properties via three-dimensional printing

The distribution of fibers in the composite (which takes into account both their locations and orientations) is one of the important factors that affect the mechanical properties of FRCs. However, this parameter depends on various factors during composite fabrication, and controlling the distribution of fibers in the produced material represents a significant challenge. In this study, the applicability of three-dimensional (3D) printing technique for controlling fiber distributions was evaluated. The fibers fabricated using a 3D printer were placed inside a mold to produce cementitious composites. Three-point bending tests were conducted and the results of the experiment were discussed.     

Model-assisted feedback control for liquid composite molding

A model-assisted feedback control algorithm, a type of generic model control, is implemented to control cure in resin transfer molding. This control algorithm calculates an apparent temperature of reaction based on the cure data input form a sensor, and this temperature is used to compare the actual rate of reaction to the desired rate and to calculate the mold set-point temperature. The model input into the control algorithm is an empirical cure model of a pre-ceramic polymer with an Arrhenius temperature dependence from 55 to 95 °C. In this work, the effect of varying control parameters is evaluated through cure simulations and experiments. Also, the effect of noise on the controller robustness is evaluated through simulation and experiment. Control parameters are evaluated for 55 and 95 °C.     

A general software module for CAMAC,equipment and composite variable control

Current PS controls application software has a strong hierarchical structure of software modules which translate user-friendly commands into the intricacies of hardware devices. Starting from the most elementary hardware level, these are: (i) the “interface module” (IM), which hides the various CAMAC commands so as to provide a standard access to each type of CAMAC module; (ii) the “equipment module” (EM) presents a simple standard software interface of each process equipment. There is one EM for each type of equipment and all process equipment is accessed through EMs via IMs; (iii) the “composite variable module” (CVM) provides control of abstract beam variables. It involves control of several and possibly different kinds of equipment. Setting a CVM results in appropriate setting of all relevant equipment through calls to their EMs.For the LEP Preinjector (LPI) a new generation of application software is being implemented based on the experiments with the current system and the technological evolution since its conception. The logical levels of IM, EM and CVM are kept, but their managerial and housekeeping functions are merged into a single module: the “General Module” (GM).This paper represents the characteristics of the GM, its decomposition into housekeeping and management activities ones to supervise device specific controls, and its structuring into logic and data modules. This results in a unique frame for all modules in the application hierarchy. It is transparent to the programmes so that the development of specific IMs, EMs and CVMs reduces to editing appropriate data tables, developing specific codes or re-using existing ones. This new generation of application software follows modern ideas on conceptual modelling by data abstraction and object-oriented programming.     

化学复合镀Ni-P-PTFE-SiC的研究

在化学镀Ni-P-PTFE与Ni-P-SiC的基础上，成功获得了Ni-P-PTFE-SiC复合镀层。同时对镀层进行了X射线衍射和SEM分析，并着重研究了镀层的耐磨－减摩性能。发现Ni-P-PTFE-SiC的加入使镀层硬度显著降低，但其耐磨性远优于NiP,Ni-P-PTFE和Ni-P-SiC镀层。     

A study of the tribological properties of cobalt-titania composite

The frictional and wear behaviour and hardness of cobalt and cobalt-titania (anatase) particulate composites, developed by sediment electro-codeposition method, were studied. Frictional and wear studies, performed on a disc-on-disc type machine, show that the microhardness of the composite increases as the titania content in the composite increases. A decrease in both the coefficient of friction and specific wear rate was observed for the composites with increasing titania content in the cobalt matrix. The effect of sliding velocity and load on the coefficient of friction and specific wear rate of cobalt and cobalt titania composites was also investigated. The optical microphotographs and X-ray diffractogram reveals that the tribo-deformation is oxidation dominated for cobalt. A probable mechanism is discussed.     

A study on the low-velocity impact response of laminates for composite railway bodyshells

This paper presents a study on the low-velocity impact response of woven fabric laminates for the composite bodyshell of a tilting railway vehicle. In this study, low-velocity impact tests for the three laminates with size of 100 mm × 100 mm were conducted at three impact energy levels of 2.4 J, 2.7 J and 4.2 J. Based on these tests, the impact force, the absorbed energy and the damaged area were investigated according to different energy levels and stacking sequences. The damage area was evaluated by visual inspection and C-scan measurement. The test results showed that the absorbed energy of [fill]₈ laminate was highest whereas [fill₂/warp₂]_s laminate was lowest. The [fill]₈ laminate had the largest delamination area because of the highest impact energy absorption.     

Embedded flaws for crack path control in composite laminates

An experimental investigation was conducted on using small flaws purposefully introduced into composite laminates to control growth of interlaminar cracks and through-thickness crack branching. Mode I crack growth specimens were used to study branching through 0°, 90° and 45° plies. The results showed that crack growth through 0° plies could be promoted by a ply gap, but this was not as controllable as combining a ply gap with a pre-crack to create a “crack branch flaw”. Crack branching through 45° plies could be controlled using crack branch flaws, and also promoted controllably using ply gaps. Crack branching through 90° plies was seen without any flaws, but was better controlled with embedded delaminations. Using these outcomes, crack branching through two quasi-isotropic laminates was demonstrated. The results have application to improved damage tolerance and fracture toughness, by taking advantage of high toughness crack growth mechanisms.     

A numerical study of adhesively bonded composite panel-flange joints

A geometrical non-linear numerical analysis for two-dimensional models of adhesively bonded composite panel-flange joints is presented to investigate the peel and shear stress redistribution in the joints when the panels buckle. The maximum stress failure criterion is used to predict failure loads and the associated failure modes induced by the buckled panels. Parametric studies for a variety of geometric configurations are carried out to show the effect of the relative stiffness and length ratios of the panel and flange on the redistribution of the peel and shear stresses as well as the failure loads and the associated modes. It is also shown that flexible joints provide higher joint efficiency.     

Behaviour control of modern composite structures

Numerical and experimental assessment of modern composite structures provided with knowledge‐based joints for their behaviour control is treated in the present paper. Special connection strip, joining composite materials, is adopted. The wave approach of the back propagation neural network in micro‐ and macromechanical modelling is used for the numerical analysis of the problem. Some numerical and experimental results are given in order to demonstrate the efficiency of the control joint suggested. Copyright © 2004 John Wiley & Sons, Ltd.     

Behaviour control of slender composite structures

Numerical and experimental assessment of a new connecting strip for the behaviour control of modern composite structures is treated in the present paper. The wave approach of the back‐propagation neural network in micromechanical modelling is used for the numerical analysis of the problem. Some numerical and experimental results are submitted in order to demonstrate the efficiency of the connecting strip developed. Copyright © 2006 John Wiley & Sons, Ltd.     

Shape control of NITINOL-reinforced composite beams

The shape of composite beams is controlled by sets of flat strips of a shape memory nickel–titanium alloy (NITINOL). The strips are embedded in the composite fabric of these beams inside sleeves, which are placed on the neutral axes. Prior to their insertion inside the beams, the NITINOL strips are thermally trained to provide and memorize controlled transverse deflections. Proper activation of the shape memory effect of the appropriate strips is utilized to produce controlled shapes of the NITINOL-reinforced beams.

A mathematical model is developed to describe the behavior of this class of SMART composites. The model describes the interaction between the elastic characteristics of the composite beams and the thermally induced shape memory effect of the NITINOL strips. The effect of various activation strategies of the NITINOL strips on the shape of the composite beams is determined.

The theoretical predictions of the model are validated experimentally using a fiberglass composite beam made of 8 plies of unidirectional BASF 5216 prepregs, which are 9.75 cm wide and 21.20 cm long. The beams are provided with four NITINOL-55 strips, which are 1.2 mm thick and 1.25 cm wide. The time response characteristics of the beam are monitored and compared with the corresponding theoretical characteristics. Close agreement is obtained between the theoretical predictions and the experimental results. The obtained results suggest the potential of the NITINOL strips in controlling the shape of composite beams without compromising their structural stiffness.     

A composite model for superplasticity

A composite model for superplasticity, based on the joint influences of both the behaviour of a composite boundary and creep, is proposed. In this model, superplasticity is considered as a combination of two mechanisms: grain-boundary sliding and dislocation creep, which occur either together or sequentially. Applied to experimental data, it can describe the logarithmic stress versus strain rate curves observed for superplastic materials showing regions I, II and III.     

锂二次电池SnO2-MCMB复合负极材料的研究

用直接沉淀法将氧化锡颗粒沉积在中间相碳微球(MCMB)核心上,制备了一种锂离子电池用的新型复合负极材料.用X射线衍射(XRD)和扫描电镜(SEM)对材料的结构及形貌进行了表征.通过恒流充放电、交流阻抗等测试手段对该材料的嵌脱锂特性进行了研究,循环20周后其比容量仍然保持在420mAh/g以上.电化学测试表明,此种复合物可以作为一种锂离子电池新型负极材料.     

A composite cost model for the aeronautical industry: Methodology and case study

This paper presents a novel composite production cost estimation model. The strength of the model is its modular construction, allowing for easy implementation of different production methods and case studies. The cost model is exemplified by evaluating the costs of a generic aeronautical wing, consisting of skin, stiffeners and rib feet. Several common aeronautical manufacturing methods are studied. For studied structure, hand layup is the most cost-effective method for annual volumes of less than 150 structures per year. For higher production volumes automatic tape layup (ATL) followed by hot drape forming (HDF) is the most cost-effective choice.