Malin ÅkermoKTH Royal Institute of Technology | KTH
Malin Åkermo
PhD
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59
Publications
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1,323
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Introduction
Additional affiliations
January 2012 - January 2018
October 2001 - present
Publications
Publications (59)
This work investigates the role of fiber orientation on interply friction. Interply friction tests were performed on a novel snap-cure unidirectional (UD) carbon/epoxy prepreg for five fiber orientations over a broad range of normal pressures and sliding speed. The test method used closely mimicked the actual processing condition of the prepreg pri...
Composite cure tools are preferable to metal tools regarding in-plane thermal expansion, quicker part processing using the tool and potentially lower cost. However, durability is often questioned and moisture in the tool is often assumed to be a negative factor. In order to increase understanding of the durability of composite cure tools sorption a...
Fatigue strength dictates life and cost of welded structures and is often a direct result of initial manufacturing variations and defects. This paper addresses this coupling through proposing and applying the methodology of predictive life-cycle costing (PLCC) to evaluate a welded structure exhibiting manufacturing-induced variations in penetration...
A non-isothermal vacuum assisted hot-forming process using tailored laminate temperature is introduced. By using process simulation and manufacturing experiments, improved laminate quality is achieved compared to the standard hot-forming process. Furthermore, it is also shown that the manufacturing time in the clean room can be reduced to one tenth...
The influence from moisture on shape distortion of curved thermoset composite laminates is investigated experimentally. The objects of study are L-shaped carbon/epoxy specimens with a quasi-isotropic layup and a thickness varying between 1 and 12 mm. The effect on the shape distortion is quantified by means of angle measurements vs. accelerated moi...
The cure tool is a key factor for successful composite part manufacturing since the tool shape is directly reflected in the moulded part. A composite cure tool is an alternative to metal tools. Lead time is often lower and rate tools less expensive. The recurring cost per produced part in the tool is often also lower, for instance from faster autoc...
In this article, tailored temperature zones are used to obtain improved quality during rapid, high pressure forming of multi-stacked unidirectional prepreg. Particularly in aerospace applications, commonly used forming processes for multi-stacked unidirectional prepreg are often considered a bottleneck in production since the forming cycle requires...
The design of a composite material structure is often challenging as it is driven by the trade-off between lightweight performance and production costs. In this paper, the boundaries of this design trade-off and its implications on material selection, geometrical design and manufacturability are analysed for a number of design strategies and compos...
Self‐reinforced polymer composites are thermoplastic materials for design of recyclable lightweight components. The combination of sheet forming and subsequent overmolding from these materials allows an efficient manufacturing process with function integration. This article investigates how temperature exposure during an overmolding cycle influence...
This paper presents a novel recyclate value model derived from the retained mechanical performance of retrieved fibres in fibre-reinforced composites. The proposed recyclate value model was used to perform an economic analysis for establishing the future closed-loop material usage of fibre-reinforced composite materials. State-of-the-art recycling...
In this article, the opportunities of fast forming of multistacked UD prepreg when using high‐pressure forming were examined in an experimental study. Forming is often considered a bottleneck in manufacturing of composite aircraft parts and speeding up the process is, therefore, of great interest. A Quintus Flexform fluid cell press was used to cre...
This paper presents the results and analysis of an experimental study of laminate thickness effects on the spring-in and shape distortion of thermoset composite L profiles. The primary objective is to achieve a broader understanding of how shape distortion is affected by laminate bending stiffness and part thickness of L-shaped laminates whose thic...
To enable shimless composite part assembly it is desired to manufacture composite spars in concave, female tools. However, due to restricted access this process is often associated with a high degree of manual operations or expensive highly specialized production equipment. This study investigates a sequential manufacturing operation where the mate...
This paper investigates shape distortion and tensile properties of hot consolidated Self-reinforced poly(ethylene terephthalate) (SrPET) by evaluating the influence from stretching before consolidation and annealing after consolidation. Spring-in angle and warpage is measured from V-shaped samples that are hot consolidated from a woven fabric that...
Self-reinforced poly(ethylene terephthalate) laminates were prepared from woven fabric by compression moulding. The fabric was stretched to different degrees during heating before hot consolidation to simulate a manufacturing process where the material is stretched through forming. High tenacity poly(ethylene terephthalate) fibres with different de...
The aim of this paper is to experimentally study how forming behaviour can be changed by local manipulation of prepreg interfacial characteristics. Different methods for surface modification are examined, however all were aimed at enabling significantly increased interply friction. The paper shows that by using increased friction in between layers,...
This paper presents a cost-efficiency study of part integration with respect to reduced assembly effort within aeronautical composite structures. The study is performed through the use, and continuous improvement upon, a previously developed cost model. Focus are on the assembly and basic inspection a wing box, part of a section of a full wing, whe...
A screening environmental life cycle analysis (LCA) of the novel self-reinforced poly(ethylene therephthalate) (SrPET) is presented in this paper. A truck exterior panel is used as case study where a concept design made by SrPET is assessed and compared to a glass fibre reinforced composite and a thermoplastic blend that are currently used for the...
Carbon nanotubes offer the potential for improved or changed matrix properties, thereby enabling the creation of novel, multifunctional composite materials. By using highly aligned, multiwall, carbon nanotubes (MWCNT) with thermoset resins, good dispersion and distribution of nanotubes is obtained. To date, research has mainly focused on improving...
When manufacturing composite aircraft components consisting of uni-directional prepreg laminates, Hot Drape Forming (HDF) is sometimes used. One issue with HDF is that, in contrast to hand lay-up where normally only one ply is laid up at a time, multiple plies are formed together. This limits the in-plane deformability of the stack, thus increasing...
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 c...
To make carbon fiber composites not only weight but also cost effective in high volume production the different cost drivers need to be addressed and new design philosophies considered. This study analyzes integral and differential design approaches when partitioning large complex composite structures. The influence of different partition philosoph...
The introduction of carbon fibre composites into the high volume automotive sector challenges the design process, since these components not only need to be light but also producible in a cost-efficient manner. One way forward is to introduce manufacturing constraints into the design process, but such constraints affect the freedom of design and op...
In this work experimental measurements of the permeability of fully interlaced 3D-woven carbon fibre preforms are performed using the unsaturated parallel flow method. The effect on the permeability from three different parameters is studied by altering the architecture of woven preforms and varying mould sizes in a duct flow set-up. Influences fro...
One disadvantage of multi-layer forming of unidirectional (UD) prepreg tape is the risk of out-of-plane wrinkling. This study aims to show how mixed ply material properties affect global wrinkling behaviour.
An experimental study was performed using pre-stacked UD prepreg on a forming tool with varying cross sections. Parameters studied include loc...
Various modelling aspects of the permeability of three-dimensional (3D) woven textile preforms are studied using computational fluid dynamics (CFD). The models are built using a recently developed technique able to generate close to authentic representations of 3D textile arrangements. One objective of the study is to investigate how parameters suc...
A method for the early concept phase is proposed, which is aimed at limiting the financial and performance-related risks when designing a carbon fibre composite automotive body structure. The method manages the structural requirements imposed on the complete body structure and analyses the suitability of different carbon fibre material systems and...
In order to decrease the weight of the automotive body structure and increase the energy efficiency of future cars, attention is now turning towards structural composites, mainly carbon fibre-reinforced plastics. Composites have several advantages such as their excellent weight-specific properties and the possibility to be manufactured in large int...
The effect of various parameters on the overall permeability of a two dimensional dual scale fibrous structure is studied employing computational fluid dynamics. The permeability of the structure is computed using two models; one resolved and one with homogenised porosity. The homogenised porous tow model is compared with the resolved model to the...
Self-reinforced poly(ethylene terephthalate) composite laminates were manufactured from fabric using a hot press. Fabric was either allowed to shrink or exposed to stretching during different phases of the manufacturing process. Composite macrostructure, crimp, was investigated and results showed that shrinkage affects fibre crimp more than stretch...
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 in...
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...
During the manufacturing process of composite structural parts, layer of fabrics or unidirectional prepreg may have to be cut in order to fulfil production requirements. From a general mechanical point of view, cutting fibres in a composite part has a large negative impact on the mechanical properties. However, such interventions are necessary in p...
A general problem when forming quasi-isotropic, multilayer unidirectional (UD) prepreg over a double curved geometry is out-of-plane wrinkling. The presented study aims to show the existence of compression in the laminate in a recess area that is globally under tension during forming. Further it aims to investigate the influence of compression on t...
Tensile and compression properties of self-reinforced poly(ethylene terephthalate) (SrPET) composites has been investigated. SrPET composites or all-polymer composites have improved mechanical properties compared to the bulk polymer but with maintained recyclability. In contrast to traditional carbon/glass fibre reinforced composites, SrPET composi...
The work presented herein aims to investigate the in-plane properties of cross-plied unidirectional prepreg using the bias extension method. The study considers different generations of carbon fibre/epoxy material systems, and testing is performed at elevated temperatures to enhance the deformability. Using digital image correlation, the specimen d...
Shape distortions are generally considered influenced by several factors including thermal contraction, curing kinetics, fibre content, lay-up (balanced / unbalanced) and anomalies developed during manufacturing. In this work influences from forming on the shape distortion of a C-shaped composite spar with a recess area on one side is investigated....
Thermoplastic composite materials have some advantages over thermoset resin based composites, such as fast processing, recyclability, reparability etc. In the present study commingled Carbon/Polyamide 12 (PA12) is analyzed as dry yarn and after heating the matrix fibers above the melting temperature and applying ambient pressure. The results are pr...
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...
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 a...
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 structu...
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...
The compression molding process is studied with the aim of modeling the instantaneous degree of face-core bonding in all-thermoplastic sandwich components during molding. The theory of bonding is briefly discussed and it is concluded that for most thermoplastic materials, processing is performed at temperatures where full bond strength is seemingly...
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 here...
The compression molding process for manufacturing of all-thermoplastic honeycomb core sandwich components is studied with the aim of verifying a previously proposed model describing the instantaneous face-core bonding during molding. Experiments are performed with glass/polypropylene (PP) faces and PP honeycomb core and experimental data are compar...
Compression molding of sandwich components made from a novel material combination, glass/polypropylene faces and expanded polypropylene foam core, has been experimentally investigated. The aim of the study was to determine the processing window for this material concept in terms of shear, transverse tensile and flexural properties of compression mo...
A model to predict the bond strength between thermoplastic faces and rigid, closed-cell foam cores in structural sandwich components is presented. The model is based on the assumption that the bond strength is proportional to the amount of resin that flows during manufacturing into the open surface cells of the core to bond the constituents to each...
The all-thermoplastic sandwich concept offers an opportunity to meet today's demands of recyclability and rapid processing. The concept refers to the combination of fibre reinforced faces and either honeycomb or foam core, where the same polymer is used throughout the sandwich. The faces are fusion bonded to the core requiring careful control of th...