Thermoforming of closed cell polymer foam and its residual compressive mechanical properties

QC 20120514</p

On the interply friction of different generations of unidirectional prepreg materials

With the aim of reducing cost of prepreg composite components, manufacturing methods are developed and refined. An automatic tape laying machine can shorten the process cycle by stacking prepreg flat and thereafter allow for forming into desired shapes. Forming of stacked prepreg requires knowledge about the uncured properties of prepreg, such as viscosity of the matrix, intra- and interply deformation properties. This study focuses on the interply friction, i.e. the friction at the prepreg-prepreg interface, and how this affects the forming. The conclusions presented here show that the difference between prepreg material systems is significant. Further, it is concluded that the prepreg-prepreg friction is governed by a combination of Coulomb and hydrodynamic friction, where different mechanical phenomena dominate depending on the test conditions.QC 20101015Kostnadseffektiva kompositer (KEKS

In-plane deformation of multi-layered unidirectional thermoset prepreg - Modelling and experimental verification

Sheet forming of unidirectional prepregs is gaining increased interest as a cost efficient alternative manufacturing method. Its potential lies within the use of automatically and efficiently stacked flat prepregs, which in a second step can be formed. A successful forming requires understanding of the properties of the uncured material. Here, the in-plane deformation behaviour of two different unidirectional thermoset prepregs is investigated. Experimental measurements are performed, showing the importance of stacking sequence and its effect on the forming behaviour of stacked prepreg. Finite element models are developed, using material models calibrated from bias extension tests and interlaminar friction tests. The method developed can be used to predict the reaction force and fibre reorientation during in-plane forming of thermoset prepreg, for one of the considered material systems. Further, it enables prediction of the effect of stacking sequence, which is promising for future full-scale forming simulations.QC 20140131. Updated from submitted to published.</p

On the interply friction of different generations of carbon/epoxy prepreg systems

Using pre-stacked material that is formed as a first step in the manufacturing process offers reduced process cycle time for production of complex structural components. The forming is achieved by forcing layers to deform by e.g. intraply deformation and interply slippage, where the latter is the scope of this study. The prepreg-prepreg friction is experimentally determined for four unidirectional carbon/epoxy prepreg systems. The materials differ considering volume fraction of fibres, fibre stiffness and phase of thermoplastic toughener (solved or particles). The study shows large individual differences between the tested materials, where the material systems with particle tougheners seem to obey a boundary lubrication friction, while the other materials show hydrodynamically dominated friction. A large difference between the high and low friction materials, almost a factor of 10, correlates to trends seen in the herein performed surface roughness measurements. Vacuum as well as autoclave consolidated materials are tested.QC 20110128.  Uppdaterad från submitted till published 20110816.NFFP PriceXPRE

Material Selection for a Curved C-Spar Based on Cost Optimization

A case study for the cost optimization of aircraft structures based on the operating cost as an objective function is presented. The proposed optimization framework contains modules for estimation of the weight, manufacturing cost, nondestructive inspection cost, and structural performance; the latter is enhanced by a kinematic draping model that allows the fiber angles to be simulated more realistically. The case study includes five material systems: aircraft-grade aluminum, two types of resin-transfer molded noncrimp fabric reinforcements, and two types of M21/T800 prepreg. The results are compared in relation to each other, and it is shown that (depending on the estimated fuel burn share of the component) a different material system is favorable when optimizing for low-operating cost.QC 20110907</p

Cost/weight optimization of composite prepreg structures for best draping strategy

The application of hand-laid carbon fiber prepreg is very expensive from a labor perspective. Therefore the manufacturing cost should be included in the design process. In this work, we propose a novel optimization framework which contains a draping simulation in combination with a detailed cost estimation package and the calculation of the structural performance based on FE. We suggest applying the methodology in two steps. First, a draping knowledge database is generated in which combinations of seed points and reference angles are evaluated in terms of fiber angle deviation, scrap, ultrasonic cuts and material shear. Second, a cost/weight optimization framework picks the best sets of plies during the subsequent optimization. The methodology is tested by means of a curved C-spar which is designed using plain weave and unidirectional prepreg. Different objectives in the generation of the draping database lead to different design solutions.Uppdaterad från submitted till published: 20100723 QC 20100723European Framework Program 6, project ALCAS, AIP4-CT-2003-516092Nationella flygtekniska forskningsprogrammet (NFFP) 4, project kostnadseffektiv kompositstruktur (KEKS

In-plane properties of cross-plied unidirectional prepreg

Sheet forming of thermoset composites is a promising method to achieve reduction in manufacturing time and therefore cost. The behaviour of weaves has been thoroughly investigated and the PJN assumption is widely used. Cross-plied UD prepreg may initially show similar behaviour to weaves; however, the complete deformation is more complex, including slippage. Thus, the forming of cross-plies can offer a possibility of increased drapability compared to woven fabrics, but imposes difficulties in predicting forming limits and final fibre angles. The work presented herein aims to characterise the in-plane properties of cross-plied UD prepreg with the bias extension test method. Understanding the deformation modes and its limits could reduce the number of iterations from idea to component in production. The forming of a preplied stack depends on many parameters. The study shows that a higher crosshead rate consequently results in a higher load response. In addition, the type of deformation mode changes due to both speed and temperature.QC 20150624</p

INTEGRAL OR DIFFERENTIAL DESIGN FOR A COST EFFECTIVE COMPOSITE AUTOMOTIVE BODY STRUCTURE

The business case needs to be improved in order to make carbon fibre composites useful for the automotive industry. It is often claimed that one of composite greatest advantages over metals is the ability to be manufactured in large complex integral geometries. By reducing the number of tools and avoiding or minimising the assembly processes, an integral solution is commonly seen as more cost effective. In high volume manufacturing these claimed advantages might be questioned. This paper presents an investigation of how complexity and size of a structure affect the manufacturing design choice between integral and differential design. The study is based on a conceptual cost model with a part cost and assembly module for carbon fibre composite manufacturing. The result shows that an integral design solution is not necessary the most cost effective option. Instead, dependent of the size and complexity of the part a divided structure may both minimise total material cost and tool cost.QC 20150410</p