Simulation of the reinforcement compaction and resin flow during the complete resin infusion process

Resin infusion (a.k.a. VARTM) is one of the LCM processes, for which liquid resin is drawn into dry reinforcements. Significant cavity thickness changes occur during processing, due to the flexibility of the vacuum bag used as one side of the tool, and the complex stress balance within the laminate. While the magnitude of thickness change is often small, the influence is significant on reinforcement properties. Changes in permeability during filling and post-filling have the potential to significantly affect the process. To simulate this behaviour, it is important to accurately model compaction and unloading of reinforcement in dry and wet states. A series of tests were completed to determine compaction behaviour of an isotropic glass fibre mat. From these tests several non-linear elastic compaction models have been determined, and applied within a resin infusion simulation which addresses pre-filling, filling and post-filling. This simulation was then used to assess different post-filling strategies.     

Resin infusion under flexible tooling process and structural design optimization of the complex composite part

Employing optimum structural design strategies and accompanying optimal production processing while employing efficient and cost effective methods is a key for the expansion of composite structures in various industrial applications. Within this context, Resin Infusion under Flexible Tooling (RIFT) process has become a rapidly growing manufacturing approach for large scale and complex parts. In this study, replacement of automotive body parts with glass woven fabric/epoxy composite manufactured by RIFT Type I (RIFT I) process is investigated both experimentally and numerically to improve the mechanical characteristics with weight saving. The optimization of the laminate stacking sequence is the first step taken. Then the simulation of resin infusion for the optimum location of gates and vents in order to shorten the filling time, decrease dry spots and voids, and avoid costly and time consuming trial-and-error procedures. Numerical results of the filling time and fluid front position over time are assessed by comparison with the experimental data and good accuracy was obtained. Based on the results of the optimization, an automotive part with a complex geometry is fabricated with 50% weight saving relative to steel.     

Comparative binder efficiency modeling of dry granulation binders using roller compaction

Roller compaction parameters’ impact on granules and tableting properties of coprocessed Avicel^® DG [ADG], a physical mixture of the two components at the same composition present in ADG [PADCP], and microcrystalline cellulose and Kollidon^® VA-64 Fine physical mixture [KVA64] was quantified by analysis of variance (ANOVA) and multivariate methods. Roller force, roller gap, and roller speed levels were selected for evaluation. A 3³ full-factorial experimental design with three center points for roller force, roller gap, and roller speed was used. The response parameters studied were granule-to-fines (GF) ratio, compressibility index (CI), tablet thickness (TT), tablet friability (TF), tablet breaking force (TBF) and disintegration time (DT). A model acetaminophen tablet formulation was roller granulated and tableted at 10?kg scale. Principal component analysis of ADG and PADCP formulations were separated from KVA64 formulations, indicating different granule and tableting properties were binder dependent. This difference in binder performance was also confirmed by ANOVA. The ANOVA also showed that there were no statistical performance differences between coprocessed ADG and its comparable physical blend with the exception of TT. Principal component regression (PCR) analyses of ADG and PADCP revealed that these excipients exhibited a statistically significant negative effect on granules-to-fine (GF) ratio, TT, TBF, and DT. KVA64 demonstrated a positive effect on these parameters. The KVA64 physical mixture demonstrated an overall better performance and binding capability. This study strongly suggests that there is no performance advantage of coprocessed Avicel^® DG when compared to a physical mixture of the two components at the same composition.     

织物纤维干湿态压缩成型特性

对干态和湿态两种工况下的碳纤维和玻璃纤维织物进行了压缩成型特性实验,利用黏弹性理论模型,分析了上述两种工况下压缩、应力松弛和回弹阶段的黏弹性曲线和黏弹性模型参数。通过分析两种工况下织物纱线压缩成型3个阶段的变形机制,阐述了产生上述差异的原因。结果表明,对于织物压缩阶段,当达到相同的最大成型压力时,湿态织物的成型厚度比干态的成型厚度略大。湿态织物的压缩时间比干态的压缩时间短,且织物规格越小,相差时间越少。湿态织物压缩阶段的时间常数小于干态织物对应值。对于织物应力松弛和回弹阶段,介质较少渗入织物间隙,织物变形过程基本相同,织物在两种工况下的成型厚度差值与回弹厚度差值十分接近。因此,湿态下织物的回弹厚度比干态下的回弹厚度略大。应力松弛和回弹阶段的时间常数基本相同。上述研究结果对纤维增强树脂基复合材料的成型工艺具有了一定的指导意义。      

Calculation of a hypersonic flow over bodies of complex configuration on unstructured tetrahedral meshes using the AUSM scheme

An approach to solving the three-dimensional Navier-Stokes equations on tetrahedral computational meshes on the basis of splitting by physical processes is considered. An algorithm of numerical implementation of the suggested method for solving three-dimensional problems of aerothermodynamics of freeconfiguration hypersonic flying vehicles (HFVs) is elaborated. The finite-volume method is applied to approximate the gasdynamics equations. The fluxes on the boundaries of the computational elements are calculated using the AUSM scheme. A computer code aimed at numerical simulation of the three-dimensional aerothermodynamics of the structural elements and the integral configurations of the HFV on the basis of the Euler and Navier-Stokes equations is developed. The algorithms developed are tested using the benchmark problem of a viscous hypersonic perfect gas flow over a sphere. The results of comparison of the computational data found using the suggested approach on the unstructured different-size meshes with the numerical solutions found on structured grids with application of the computational code NERAT are presented. The computational model of the flow of viscous and inviscid perfect gas developed is applied to investigate the aerothermodynamics of a model of an unmanned experimental aircraft X-43 of complex configuration.     

Structural,electrical and electrochemical properties of ZnO nanoparticles synthesized using dry and wet chemical methods

The effect of particle size and morphological structure on the electrical and electrochemical properties of ZnO (nanowires, nanorods, and nanospheres) prepared by two various routes: soft-wet and dry methods were investigated. The electrochemical performance is analyzed by cyclic voltammetric and galvanostatic charge–discharge measurements in 1 M KOH, whereas their electrical conductivity, and dielectric constant are measured by electrochemical impedance spectroscopy in a temperature range 293–383 K and frequencies from 10² to 10⁷ Hz. All samples showed semiconducting behavior with conductivity values depending on the particle size and the morphological structure of the sample. The prepared samples showed supercapacitance behavior with capacitance values lie between 77 and 330 F g⁻¹ and depend upon the morphological structure. The nanowire's structure showed the highest capacitance and good cycling stability. The high performance depends on the nanocrystalline size and the high surface area of the nanowire sample.     

Analysis and modeling of 3D Interlock fabric compaction behavior

During the preforming stage in Liquid Composite Molding (LCM), fibrous reinforcements are compacted to obtain the specified fiber volume fraction. Numerous studies have been carried out to understand their compression behaviors. The first objective of this investigation is to study experimentally the influence of the weaving parameters on the compaction behavior of five different 3D Interlock fabrics. In parallel, composite parts were fabricated to perform a microscopic analysis of fabric deformation after compression. The second objective is to provide a model of the experimental results. Since there is no nesting in three-dimensional woven fabrics, the compaction behavior turns out to be easier to predict than for laminates. A model based on experimental observations was devised to connect the compaction behavior with the deformation modes of five fabrics investigated. The good correlation with experiments confirms the assumptions on the main factors governing the compaction and relaxation of 3D Interlock fabrics.     

铜基复合材料干湿条件下的摩擦学行为

采用粉末冶金技术制备铜基复合材料,在制动压力0. 5～1. 2 MPa 范围内,通过定速摩擦试验机研究了干、湿条件下,速度、压力与材料摩擦磨损性能的关系,结果表明:影响摩擦磨损性能的重要因素在于载荷性质和第三体状态。在干摩擦条件下,处于低摩擦速度范围时,摩擦力的静载荷性质使第三体呈疏松状态,这增加了微凸体间的啮合程度而使摩擦系数处于较高值。随第三体致密性增加,其润滑作用增强,微凸体间的机械啮合程度减弱,使材料的摩擦系数和磨损量降低。在高速摩擦时,微凸体间的冲击作用使处于摩擦表层的硬质颗粒容易发生粉碎性破损而弥散分布,这强化了表面强度而使摩擦系数有所增加。摩擦压力对高速摩擦性能影响明显,原因在于高负荷加剧了摩擦面的变形和损伤程度。湿摩擦条件下,水膜的润滑和流动具有降低摩擦系数和增加磨损率的作用主要体现在低速低压条件下。在高摩擦速度和高压力条件下,水分的高温蒸发与离心作用明显,破坏了水膜的存在条件,从而使材料的摩擦磨损性能与干摩擦状态相近。      

复合材料带筋壁板预成型体压缩性与渗透性对树脂流动的影响

以航空碳纤维增强树脂基复合材料典型结构件带筋壁板为研究对象,通过对U3160单向织物的组织结构进行分析,根据纤维束的受压变形状态对其压缩响应进行理论建模,然后以纤维束压缩模型为基础,预测了U3160单向织物按0°/45°/90°/-45°铺层时预成型体在压缩应力作用下厚度变化的响应行为。建立了压缩应力作用下纤维预成型体的渗透率解析模型:在织物压缩模型的基础上,建立了纤维束等效渗透率模型;根据张量理论,分别建立了0°、±45°和90°铺层织物等效渗透率模型;运用渗透介质串并联关系,建立了带筋壁板各特征区域渗透率综合表征模型。基于PAM-RTM流动模拟软件,进行分区渗透率定义,在充模过程中对树脂在带筋壁板预成型体中的流动行为进行模拟,优化工艺参数,确定出最终充模方案,并制作带筋壁板实验缩比件进行成型实验,验证了充模方案的合理性。研究结果为制件的成功制作提供理论依据,从而指导生产实践。      

Comparison of the wet and dry fatigue properties of all ceramic crowns

The purpose of this paper was to investigate the influence of fatigue on the fracture strength of In ceram, optimal pressable ceramic (OPCTM) and IPS Empress in both wet and dry environments. Twenty-six crown shapes 8 mm in diameter and 8.5 mm in height were fabricated for each ceramic system. For each ceramic system, ten specimens were tested for fracture strength without fatiguing. The second group was submitted to a fatigue and fracture test in a dry (eight specimens) and a third group in a wet (eight specimens) environment using an Instron testing machine. The results were statistically analysed using a Mann–Whitney test. The results indicated that: (i) the fracture strength for In ceram was significantly stronger than OPCTM and IPS Empress (p<0.05) – no difference was found between OPCTM and IPS Empress; (ii) fatiguing and fracture testing showed a significant decrease in the fracture strength for In ceram and IPS Empress in the wet environment and no difference was found in the dry environment – no difference was found for OPCTM; and (iii) when fatigued in a dry environment, In ceram crown shapes were significantly stronger than OPCTM and IPS Empress (p<0.05) – the same statistical differences were found when fatigued in a wet environment.     

Nano-scale sliding contact deformation behaviour of enamel under wet and dry conditions

The abrasion response of cross sectional areas of enamel was studied by sliding a rounded diamond conical nano-indenter tip across the surface. The nano-indenter tip (radius ~1,200 nm) was scanned over a specific squared area with a load of 400 μN. Two different environments were chosen: Hank’s balanced salt solution (HBSS) and atmospheric laboratory condition. SEM (Scanning Electron Microscopy) and AFM (Atomic Force Microscopy) were used to characterize the final abraded areas. In addition, single scratches with linear incremented load were performed. The normal load and displacement data were utilized in a complementary manner to support the proposed deformation mechanisms. Greater orientation dependence for the case of the single scratches in relation to the abrasion tests was found. The latter results are discussed in terms of plastic deformation effects. The abrasion mechanisms were found to be the same for both wet and dry measurements and similar to that described in a previous study (Guidoni et al., Wear 266:60–68, 2009; Guidoni, Nano-scale mechanical and tribological properties of mineralized tissues. PhD. Montan University Leoben, Leoben, Austria, 2008). However, scratch deformation under fluid measurements shows greater recovery effects and abrasion resistance.     

Sizing related kinetic and flow considerations in the resin infusion of composites

Fibres used in preforms of resin transfer moulded (RTM) composites are coated with sizings, binders, and/or finishes that serve multiple purposes, including facilitating handling, protection of the fibres from compaction and process induced damage (including notching), aiding in compatibility and wetting of the fibres by the resin, and overall enhancement of the behavioural response of the composites. In this investigation four different sizings applied to S2 glass fibres are shown to significantly affect two aspects of RTM processing - resin infusion, and cure. In both cases phenomena at the microscopic level are seen to affect response variables at the macroscopic level. On a microscopic level, the behaviour of a thermosetting resin based composite is affected by the formation of interphase regions that greatly affect the cure kinetics and hence the mechanical and physical properties of the composite, which are dependent on the inter-constituent variations in local properties such as modulus and glass transition temperature. Similarly fibre-sizing-resin interactions occurring during the infusion stage affect wet-out and local flow behaviour through the development of stoichiometric imbalances in local regions. It is shown that the molecular interactions between the constituents (as initiated by the sizing) are affected by processing conditions such as temperature and rate of resin flow, and that heat evolution and resin rheology may be affected by the stoichiometric imbalances resulting from interphasial level reactions. This revised version was published online in November 2006 with corrections to the Cover Date.     

Optimization of CFRP laminate dynamic properties using combinations of short/continuous fibres and stiff/flexible resin matrices

High volume fraction carbon fibre-reinforced plastics (CFRPs) have a stiffness-to-weight ratio much greater than some conventional metallic materials but the material damping is low. Damping may be increased by the use of short fibres or a matrix material with high dissipation. Experimental and theoretical studies are described which show that a lamina can be made which has high damping; the effects of lamina properties on those of the laminate have been investigated. The effects of fibre length, matrix type and fibre orientation have been assessed with the objective of optimizing the dynamic properties of laminated CFRP plates using combinations of short/continuous fibres and conventional/highly dissipative resin matrices.     

Modeling flow properties of fine dry powders using particle morphological properties and its effects on geometry of fly ash evacuation hoppers

This paper results from an ongoing effort to correlate the physical properties of powders at a fundamental level with their bulk behavior. Cohesion and unconfined yield stress are the measure of inter-particle forces of attraction in the bulk powder. The existing model for cohesion does not include important bulk properties, such as particle size distribution, tapped density, and prevailing applied stress. In the present paper, flow properties of 25 bulk solids (different cement and fly ash samples) have been evaluated using a ring shear tester and the products have been characterized according to their flowabilities. Models for cohesion and unconfined yield strength have been developed in this study by taking into account the effects of particle size distribution, tapped bulk density and pre-shear stress. The newly developed models have provided good fit to the experimental data. The effect of these flow properties on the design of hoppers have been investigated for fly ash samples collected from seven consecutive electrostatic precipitator (ESP) hoppers of a coal fired thermal power station. The results show that fly ash from the rear end ESP hopper would require higher amount of opening size compared to the first or second field of ESP to ensure proper mass flow condition is achieved at all the ESP hoppers.     

Fully coupled linear modelling of incompressible free‐surface flow,compressible air and flexible structures

Incompressible free‐surface flow is a common assumption for the modelling of water waves. Connected with the aim to develop very large floating platforms, air chamber supported floating structures have attracted considerable research interest in the past. Such structures are carried by air entrapped in chambers formed by stiff, vertical walls. In order to model these types of structures, the interactions between surface gravity waves and compressible air must be taken into account. If the payload requirements for air chamber supported structures are low enough, the air chambers may be formed by flexible membrane cylinders. In such systems, pressure variations can lead to considerable changes in chamber volume. Therefore, the flexibility of the bounding structures must be taken into account. We present a modelling strategy to tackle the fully coupled problem of compressible gas in a flexible chamber and incompressible free‐surface flow in an unbounded domain. The governing equations and boundary conditions are described and solved by the finite element method. A perfectly matched layer is used to obtain a solution for an unbounded domain. Finally, the numerical implementation is validated by various test cases. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of repeated compaction of tablets on tablet properties and work of compaction using an instrumented laboratory tablet press

The repeated compaction of Avicel PH101, dicalcium phosphate dihydrate (DCP) powder, 50:50 DCP/Avicel PH101 and Starch 1500 was studied using an instrumented laboratory tablet press which measures upper punch force, punch displacement and ejection force and operates using a V-shaped compression profile. The measurement of work compaction was demonstrated, and the test materials were ranked in order of compaction behaviour Avicel PH101?>?DCP/Avicel PH101?>?Starch?>?DCP. The behaviour of the DCP/Avicel PH101 mixture was distinctly non-linear compared with the pure components. Repeated compaction and precompression had no effect on the tensile fracture strength of Avicel PH101 tablets, although small effects on friability and disintegration time were seen. Repeated compaction and precompression reduced the tensile strength and the increased disintegration time of the DCP tablets, but improved the strength and friability of Starch 1500 tablets. Based on the data reported, routine laboratory measurement of tablet work of compaction may have potential as a critical quality attribute of a powder blend for compression. The instrumented press was suitable for student use with minimal supervisor input.     

Design of newly fabricated tribological machine for wear and frictional experiments under dry/wet condition

Nowadays, there is demand to evaluate tribological performance of new engineering materials using different techniques. Various laboratory tribo-machines have been designed and fabricated such as Pin-on-Disc (POD), ASTM G99, Block-on-Ring (BOR), ASTM G77 or G137-953, Dry Sand Rubber Wheel (DSRW), ASTM G655, Wet Sand Rubber Wheel (WSRW), ASTM G105, and sand/steel wheel test under wet/dry conditions (ASTM B611). A concept of integrating more than one tribo-technique at different contact mechanisms (line or area) working simultaneously under same test condition against same material is introduced in a current designed machine. Different wear modes (adhesive, two-body-abrasive, three-body-abrasive, under dry, lubricated, or slurry conditions) can be conducted on the same machine. Results of adhesive wear, friction and interface temperature of glass fibre reinforced polyester composite under wet/dry contact condition are reported at 50 N load for different sliding speeds (2.8–7.8 m/s) using the new machine. Weight loss and friction coefficient of the composite were substantially influenced by introducing water as lubricant. Additionally, the contact condition has the high influence key on the wear and frictional performance of the composite.