Modelling component cost in compression moulding of thermoplastic composite and sandwich components

Thermoplastic composite and sandwich materials offer a potential of reducing component weight and improving recyclability while at the same time enhancing process economy through reduced manufacturing cycle time. The economical aspects of compression moulding of three different thermoplastic composite and sandwich material systems are modelled herein and are compared to compression moulding of a thermoset sheet moulding compound and stamping of sheet metal. A program has been developed which predicts component cost for different component sizes and complexities. It is found that raw material cost strongly dominates component cost for compression moulding of composite components, while in sheet metal stamping component cost is dominated by equipment costs.The model shows that thermoplastic composites are cost competitive for small to medium sized components and short production series of large components. The sandwich concepts offers a potential of further reducing component cost compared to composites, thus making the concept interesting for larger components, but still for short to intermediate production series, which is illustrated by calculating component cost for compression moulding of a sandwich tailgate.     

Progressive damage modelling of SMC composite materials

The present work deals with the modelling of damage behaviour for sheet moulding compound (SMC) composite materials using a finite element analysis package. Specifically, a comparison is made between the results obtained experimentally for a three-point bending test, and those obtained from numerical simulation using a material model already implemented. The simulation has been performed for the material models available within the PAM-CRASH software. The simulation results are compared and validated with respect to experimentation.     

Effects of defects in hybrid sheet moulding compound – Evaluation of defects and the impact on mechanical properties

Sheet moulding compound is a widely used fibre‐reinforced material. Generally, it consists of discontinuous glass fibres in a thermoset matrix system. Due to the finite fibre length, mechanical properties of structural components are limited. To overcome this drawback, sheet moulding compound is locally reinforced with a unidirectional carbon fibre sheet moulding compound material in the approach presented in this contribution. The manufacturing of this hybrid material consisting of discontinuous glass fibre sheet moulding compound and continuous carbon fibre sheet moulding compound can result in different defects, such as folds or fibre misalignments. These defects may affect mechanical properties of the hybrid material. Consequently, this article deals with the investigation and analysis of defective hybrid sheet moulding compound components, which were examined by means of tensile tests. Results point out that investigated defects have different effects on mechanical properties. However, independent from the type of defect, mechanical properties were reduced. With a reduction of 68.86 %, folds have one of the greatest influences on tensile strength. In addition, depending on the angle deviation, even greater reductions can occur. Furthermore, the reduction of the mechanical properties can be identified clearly with increasing angle deviation.     

Low-cost tooling for the hot press moulding of glass fibre-reinforced polyester: a case study

Glass fibre-reinforced polyester, with its high strength to weight ratio, offers great potential as a structural material for use in the civil engineering industry. One application in which it has shown particular promise is in the form of repeatable basic units that can be assembled together to form a structure. This paper describes the manufacture of a moulding tool to enable a limited number of glass fibre-reinforced polyester components to be manufactured economically by the hot press moulding of sheet moulding compound. It outlines the manufacture of the tool and the difficulties encountered at all stages in the production of the final article. The paper also illustrates a structural model to one-fifth scale which has been fabricated from the final composite sheet moulding compound units and which will be tested to destruction. The results of this test and those for small tensile coupons will be the subject of a further paper.     

片状模塑料模压流动仿真分析

本文采用有限元分步计算方法,对酚醛片状模塑料(P-SMC)在模压过程中的流动变形情况进行了计算机仿真模拟,与试验结果做了对比。编制了相应的有限元计算与后处理软件,分析了模压料在封闭模具中充满模腔的过程、在一定合模速率下的充模时间以及在一定粘度下的模压成型压力。对SMC模压时模具的设计以及优化成型工艺参数具有一定的理论指导意义。     

The effect of processing parameters on the mechanical properties of kenaf fibre plastic composite

This paper investigates the effects that processing parameters, including temperature and speed, have on the mechanical properties of kenaf fibre plastic composite. Kenaf fibre was used to fabricate a composite material along with polypropylene (PP) as a binding material. The composite was manufactured using a newly developed compression moulding machine. Tensile and impact tests were performed on the PP/kenaf composite to characterise its mechanical properties. The tensile properties of PP/kenaf composite increased by 10% after the addition of unidirectional kenaf fibre (UKF). However, its impact properties simultaneously deteriorated. Dynamic mechanical analysis (DMA) was carried out to examine the material properties. Results show that the storage modulus (E′) and loss modulus (E″) increase with the addition of UKF. However, its addition decreases the tan δ amplitude. The fracture surface of PP/kenaf composite was investigated by SEM. The newly invented compression moulding machine illustrates a new trend in processing parameters of long kenaf fibre plastic composite.     

Investigation of the dimensional stability of carbon epoxy cylinders manufactured by resin transfer moulding

The prediction of process-induced dimensional variability and residual stresses occurring during the manufacturing of composite structures is critical to produce parts where tight tolerances are required. Therefore, the development of material constitutive models and processing properties, and the validation of these models, are two essential steps in order to accurately simulate the behaviour of the materials involved. In this paper, the material constitutive models of a one-part epoxy resin were implemented in a three-dimensional finite element software based on the ABAQUS/COMPRO platform to investigate the dimensional stability of a composite structure manufactured by resin transfer moulding (RTM). A simplified geometry was used as a representative structural component with different layup configurations. Both heat transfer analysis and stress analysis were conducted. Contact interactions were implemented in the stress analysis to simulate the tool–part interaction. The presented analysis predicted the angle variation and the composite debonding caused by the coefficient of thermal expansion mismatch between the mould and the composite part and the resin volumetric chemical shrinkage.     

模压工艺对玻璃纤维增强聚丙烯复合材料层合板力学性能的影响

利用热模压工艺制备玻璃纤维增强聚丙烯（GF/PP）复合材料层合板,通过差示扫描量热（DSC）法试验分析,确定相变参数,运用ANSYS有限元分析,将复合材料热力学参数与温度的非线性关系定义到材料特性中,研究模压成型过程中温度场变化情况,为模压成型工艺制度的确立提供理论指导和依据。以压缩强度、层间剪切强度和冲击韧性作为力学性能评价指标,采用响应曲面法探讨和分析制备工艺对GF/PP复合材料层合板力学性能的影响,得到最优模压工艺制备参数,获得最高复合材料层合板力学性能,为GF/PP复合材料自动铺放奠定铺放工艺基础。试验结果表明:模压加热工艺参数对复合材料层合板力学性能的影响度（从大到小）依次为:热压温度、热压时间、热压压力。较优的模压加热工艺参数为:热压温度228℃、热压时间6 min、热压压力1.1 MPa,在此工艺条件下制备的GF/PP复合材料层合板,层间剪切强度为31.12 MPa,压缩强度为100.96 MPa,冲击韧性为2.27 kJ/cm2。      

Downtime analysis for automatic moulding plants

In foundries with automatic moulding plants a complex system of different kinds of material flow exists. The multitude of technological constraints results in a dynamic and unstable production process. Therefore, small variances in process parameters may entail interruptions of a material flow and consequently cause downtime. Automatic moulding plants consist of rigidly chained units, so that to secure a high reliability corresponding expenditure is required. We present the results of an investigation of 21 automatic moulding plants in 15 German foundries. The analysis of the structure of downtime shows that the low efficiencies result not only from technical reasons, but also from missing materials and personnel, and technological disturbances due to planning and scheduling.     

Polyester moulding materials in automotive underbonnet environments

This paper describes investigations which have been carried out to characterize the behaviour of polyester moulding compounds when subjected to tests in environments encountered in automobile underbonnet situations. The tests contrast the behaviour of various polyester resin types in aqueous and hydrocarbon media; and show that the materials which best resist water and antifreeze exhibit the greatest degradation in petrol. The resistance of a range of polyester types to dry heat at 130°C and 180°C is discussed. Combinations of resin and glass fibre types have been tested in boiling water: the results show that the correct choice of resin and glass fibre can improve the onset of blistering from within one week to over 12 months. Single surface exposure of moulded plaques is shown to result in a far higher level of strength retention than total immersion of the material. A comparison has been made of the effect of different types of motor fuel, including methanol additives and ethanol, on the strength retention of dough moulding compound and sheet moulding compound throughout a 12 month ageing period.     

Preliminary study on cost optimisation of aircraft composite structures applicable to liquid moulding technologies

This paper details the initial development of a method for determining the associated recurring labour costs for the manufacture of a aircraft component that will form the basis for a computerised methodology for determining the optimum manufacturing method for a component design. The research focuses on the flow of process steps to manufacture an aircraft component for the vacuum-assisted resin transfer moulding and resin transfer moulding manufacturing process. The methodology developed is based on applying MIT cost equations to process steps from which cost variables and constants are established to represent an estimated costing of the aircraft structure. This research will assist in providing a swifter and more accurate conceptual design/manufacturing system that includes an analysis of cost and will assist the production of trade studies that consider the manufacture of aircraft components using cost-effective technologies, such as liquid moulding.     

Elastic moduli of randomly oriented,chopped-fibre composites with filled resin

An analytical method is developed to determine the effective elastic moduli of a filled resin reinforced by randomly oriented chopped fibres, a three-phase composite such as a filled sheet moulding compound (SMC). The analytical results compare well with experimental results for both filled (glass/calcium carbonate/polyester) and unfilled (glass/polyester) SMC composites. The numerical results also illustrate the important influence of the filler phase on the composite stiffness properties.     

An incremental 2D constitutive model accounting for linear viscoelasticity and damage development in short fibre composites

A model accounting for linear viscoelasticity and microdamage evolution in short fibre composites is described. An incremental 2D formulation suitable for FE‐simulation is derived and implemented in FE‐solver ABAQUS. The implemented subroutine allows for simulation close to the final failure of the material. The formulation and subroutine is validated with analytical results and experimental data in a tensile test with constant strain rate using sheet moulding compound composites. FE‐simulation of a four‐point bending test is performed using shell elements. The result is compared with linear elastic solution and test data using a plot of maximum surface strain in compression and tension versus applied force. The model accounts for damage evolution due to tensile loading and neglects any damage evolution in compression, where the material has higher strength. Simulation and test results are in very good agreement regarding the slope of the load–strain curve and the slope change. Copyright © 2005 John Wiley & Sons, Ltd.     

Mechanical analysis of fracture in an automotive radiator head produced from a nylon–glass fibre composite

The fracture during assembly of a radiator head produced from a nylon–short glass fibre composite is studied in the framework of complexities such as determining elastic constants and fracture stresses on the one hand and manufacturing problems such as distortion after moulding and deformations induced during assembly on the other. The combination of in situ measurements, SEM observation of fracture surfaces and reverse modelling of non-linear material properties permitted to make a sufficiently accurate estimate of the real mechanical behaviour of the material, as opposed to the properties mentioned in its data sheet. While the method was applied to solve a particular production problem, its applicability in process evaluation and redesign of injection-moulded short fibre composites is general.     

Fibre structure and anisotropy of glass reinforced thermoplastics

The fibre structure and orientation distribution of two commercially available glass mat thermoplastics reinforced by continuous glass fibre was studied to investigate the anisotropic behaviour under compression moulding and mechanical loading, and to investigate the influence of the fibre structure and orientation on the anisotropic behaviour. Circular samples were deformed into ellipses when moulded, due to the anisotropic fibre orientation. The fibre content and orientation were examined in different locations of the elliptically deformed specimens.X-ray pictures were taken of the material in order to develop images of the fibres, before and after compression moulding. In another procedure, the matrix was burned off and the fibre network structures were studied in each case. A CCD camera was used to scan the fibres as digital images to measure the orientation distribution functions of the fibres. The fibre orientation measuring process was facilitated by subroutines implemented in the source code of the public domain NIH-image analysis software using simulated Fraunhofer diffraction.     

Rheological characterisation of discrete long glass fibre (LGF) reinforced thermoplastics

Three experimental techniques have been employed to assess the rheological behaviour of discrete long glass fibre reinforced polypropylene and propylene/ethylene copolymers. A Carri Med cone and plate rheogoniometer has been used to determine shear viscosity as a function of strain rate and time at temperatures relevant to the extrusion and injection moulding processes. A bubble inflation test (BIT) has been designed and used to characterise the behaviour of these composites under the extensional flow fields typical of blow moulding and thermoforming. Finally a squeeze load test (SLT), similar to those developed for sheet moulding compounds (SMC) and glass mat thermoplastics (GMT), has been used to explore the rheological behaviour of the long glass fibre (LGF) materials under compression moulding conditions, in particular to assess the relative importance of shear and extensional flow.     

碳纤维增强聚合物复合材料方形蜂窝夹层结构水下爆炸动态响应数值模拟

基于ABAQUS有限元仿真软件,建立了不同夹芯相对密度的碳纤维增强聚合物（Carbon Fiber Reinforced Polymer,CFRP）复合材料方形蜂窝夹层结构在水中爆炸冲击波载荷作用下的仿真模型,分析了结构的变形过程、夹芯的压缩特性及结构的失效及破坏情况。数值模拟结果表明,CFRP复合材料蜂窝夹芯压缩量在前面板速度降至与后面板相同时达到最大; CFRP复合材料蜂窝夹芯的最大压缩量随着初始压力的增大呈先缓慢增大后快速增大的趋势,其增大趋势在夹芯接近完全压缩时又趋于缓慢; CFRP复合材料夹层结构失效随夹芯相对密度和初始压力的变化呈现不同的模式,且其防护性能优于等重的层合结构。研究结果可以为复合材料夹层结构在水中冲击波载荷防护中的应用提供参考。      

废纸纤维基包装材料的加工工艺与性能

介绍了一种以废纸纤维为原料,以淀粉为辅料,通过模压成型,利用玉米淀粉糊化后在纤维中的助流作用,使纸纤维-淀粉混合物在热压条件下,制成可用于承受重载荷的包装材料的方法。实验研究了瓦楞纸与新闻纸纤维配比、淀粉含量变化对复合材料力学性能的影响。     

Energy distribution in the squeezing of particles in concentrated suspension

In the present work, the squeeze flow geometry is used to investigate the properties of concentrated suspensions. The suspensions consist on hard glass spherical particles dispersed in a viscoplastic fluid. With such a material, following the solid volume fraction, the material rheological behaviour ranges from purely viscoplastic fluid to granular media. During the squeezing action, the material structure evolves with energy variation due to particle displacement and interaction. The goal of our study is to identify the effect of energy evolution on the flow properties of suspensions and detect granular contact evolution. The proposed study consists on an energy approach based on the analysis of the global squeeze force and sample height with time. The squeeze force is decomposed in a combination of an average force component and a fluctuating one. This local fluctuating component is investigated from Fourier analysis as a function of solid volume fraction and compression velocity. Results show the evolution of the energy distribution during compression and allow the flow regime modification to be evaluated.