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Dynamic mechanical analysis (DMA) is an essential procedure for characterizing the performance of composites and effectively simulate with the real-world applications. This research work aims to characterize the dynamic mechanical (DM) properties of sisal fiber reinforced polyethylene terephthalate (PET) composites as a factor of fiber content and fiber surface modification. The effect of elevated processing temperature (>260°C) on the thermal degradation of sisal fibers is also analyzed. To study the effect of sisal fiber loading, PET composite specimens; one with 25% by weight fraction of raw sisal fiber (w/w), abbreviated as 25% RSC and the other with 40% by weight fraction (w/w) of raw sisal fiber, hereafter abbreviated as 40% RSC, were prepared by injection molding. Similarly, to analyze the impact of fiber surface modifications, PET composite samples containing 40% by weight fraction (w/w) of alkali-treated sisal, hereafter abbreviated as (40% Al-SC), and 40% by weight fraction (w/w) of a combined alkali/acetylation-treated sisal, hereafter abbreviated as (40% Al-ASC), were prepared. It was found that the fiber volume fraction and fiber surface modifications affected the DM properties of the produced composites. The improved storage module and glass transition temperature (Tg) with minimized damping has been demonstrated by increasing fiber content. With the same 40% fiber content, the composites produced from modified fibers enhanced the storage modulus and Tg values. However, with increasing temperature, the storage modulus decreased, the loss modulus increased, and the damping factor increased with composites containing higher fiber content and surface modified fibers. This indicates the low thermal stability of the sisal fiber and the interface damage at elevated temperatures.

Bridging the gap between the material and geometrical aspects of a structure is critical in lightweight construction. Throughout the history of structural development, shape rationalization has been of prime focus for designers and architects, with biological forms being a major source of inspiration. In this work, an attempt is made to integrate different phases of design, construction, and fabrication under a single framework of parametric modeling with the help of visual programming. The idea is to offer a novel free-form shape rationalization process that can be realized with unidirectional materials. Taking inspiration from the growth of a plant, we established a relationship between form and force, which can be translated into different shapes using mathematical operators. Different prototypes of generated shapes were constructed using a combination of existing manufacturing processes to test the validity of the concept in both isotropic and anisotropic material domains. Moreover, for each material/manufacturing combination, generated geometrical shapes were compared with other equivalent and more conventional geometrical constructions, with compressive load-test results being the qualitative measure for each use case. Eventually, a 6-axis robot emulator was integrated with the setup, and corresponding adjustments were made such that a true free-form geometry could be visualized in a 3D space, thus closing the loop of digital fabrication.

The stickiness of prepregs (tack) is considered a decisive material property for the success of high‐quality composite manufacturing by automated lay‐up processes such as automated fiber placement (AFP) or automated tape laying (ATL). Adverse control of prepreg tack can easily result in laminate defects or machine breakdown, which are highly undesirable considering the tremendous machinery and material costs of these processes. Prepreg tack is governed by a complex interaction of adhesive and cohesive phenomena that are influenced by machine and environmental parameters of the production process as well as by intrinsic properties of the prepreg material itself. This review aims at providing a condensed insight into the current state of research on prepreg tack. Therefore, experimental studies including the discussion of utilized tack measurement methods as well as model approaches to prepreg tack are reviewed. The findings are discussed against the background of fundamental mechanisms, the strong interdependency of influencing parameters and the challenge of translating measured tack data into an enhanced AFP/ATL process stability by process adjustment.

Natural fibers are increasingly being used as composite reinforcement for both thermoplastic and thermoset resin, mainly for automotive application. Due to their hydrophilic nature, natural fibers have certain limitations during composite manufacture especially owing to their poor resin wettability, weak fiber–polymer interface, high moisture absorption, and being affected by high temperature in case of thermoplastic resin. This work investigates the impact of sisal fiber modification techniques on moisture absorption, thermal, and mechanical properties of the fiber. Four sisal fiber samples were prepared; untreated, alkaline treated, acetylated, and a combined alkaline-treated/acetylation samples. The samples were evaluated for their hygroscopic nature, thermal stability, and tensile properties. It is found that acetylation resulted in a reduction of moisture absorption of sisal fiber as the acetylated and alkaline-treated/acetylated samples recorded a decrease of 42% and 28%, respectively. Alkaline treatment increased the absorbency owing to the removal of hemicellulose and lignin. The thermogravimetric result revealed that alkaline treatment improved the thermal stability as the alkali-treated and alkali-treated/acetylated samples showed improvement in thermal properties. The acetylated sample resulted in a significant reduction in tensile strength. But, the results from tensile tests of the alkaline-treated samples showed an insignificant decrease in tensile strength and improvement in the modulus for all treated samples. Fourier-transform infrared and scanning electron microscopic analysis were included in the study to supplement the results with structural and microstructural changes. The effect of those treatments on the sisal–PET composite properties was studied and will be submitted in part 2 of the study.

A closer look was taken at a spray binder and the properties of the preforms made with said binder and non-crimp carbon fiber textiles. First the spray process was analyzed, then T-peel and three point flexural tests were carried out to compare the spray binder to other binder systems. While the spray binder showed higher peel strength than most binders found in literature, the measured flexural strength was lower than the values found for powder.

The constitution of prepreg tack in automated fiber placement (AFP) is affected by a sensitive balance between adhesive interfacial bond strength and cohesive strength of the prepreg resin. In an effort to explore the role of interfacial liquid-solid interaction on the tack of commercial aerospace-grade epoxy prepreg, a surface wetting analysis was performed on AFP-related substrates. The standard test liquid combination water/diiodmethane and extracted neat epoxy resin were used for contact angle measurement employing the sessile drop method and the Owens-Wendt-Rabel-Kaelble (OWRK) model. Additional rheological and topographical analyses were carried out to account for viscous resin flow on surfaces of different roughness. The results from the material characterization are discussed against the background of tack measurement by probe tack testing utilizing a rheometer. Significant differences between the investigated surfaces in terms of both the maximum tack level and the onset temperatures of adhesion were found as a function of test parameters relevant for contact formation. General agreement with the experimental tack results was observed employing a topographically extended version of the Dahlquist criterion. For each substrate, a temperature-dependent critical storage modulus could be determined that conforms to the onset temperature of tackiness. Contact angle measurements revealed a correlation between the thermodynamic work of adhesion and maximum tack and, moreover, the tack onset in the adhesive regime when additionally incorporating surface topography. Matching ratios of polar and dispersive surface free energy and surface tension components were found to favor the molecular interaction at the interface between prepreg resin and substrate.

Selectively adjusting the tackiness of epoxy pre-impregnated carbon fibers is considered mandatory in terms of process stability of automated lay-up and draping. This experimental study investigates the influence of crucial process and material parameters such as temperature, compaction force, debonding rate and ageing on prepreg tack using a rheometer as a test apparatus. Accompanying material characterization is conducted in terms of cure kinetics and rheology to establish a profound understanding of tack-determining mechanisms and material behavior. Two evaluated tack indicators are found to be sensitive to temperature and steadily increased as a function of compaction stress. The maximum tack plateau of progressively aged prepreg shifts towards higher temperatures. Material is still processable after tack life with tack properties exceeding the adhesive performance of fresh prepreg when being processed at elevated temperatures. Tackiness of impregnated tape for automated draping and aerospace epoxy prepreg differs in both quantitative extent and pivotal mechanisms.

Schalenformige Bauteile zeichnen sich durch ein sehr groses Verhaltnis von Breite oder Lange zur Wanddicke aus. Durch die geringe Wandstarke kommt der Einleitung von Lasten in derartige Strukturen eine besondere Bedeutung zu. Hierfur werden haufig spezielle Lasteinleitungselemente (Inserts) in die Struktur eingebracht, die als Anbindungspunkte dienen. Die Kombination von metallischem Lasteinleitungselement und CFK-Struktur wird anhand drei verschiedener Teilprojekte untersucht. Im Projekt „Multilayer-Inserts – Intrinsische Hybridverbunde zur Krafteinleitung in dunnwandige Hochleistungs-CFK-Strukturen“ wurde ein Lasteinleitungselement fur automatisiert gefertigte Faserverbundstrukturen entwickelt. Das Projekt „Grundlagenuntersuchungen intrinsisch gefertigter FVK/Metall-Verbunde – vom eingebetteten Insert zur lasttragenden Hybridstruktur“ untersucht die faserschonende, intrinsische Herstellung von FVK/Metall-Verbunden im RTM-Prozess anhand verschiedener Hybridisierungsansatze. Im Projekt „Einfluss, Detektion und Vorhersage von Defekten in grosserientauglichen Hybridverbunden fur Metall/CFK-Leichtbautragstrukturen“ wurde ein neuartiges Anbindungskonzept fur Metall-CFK-Hybridstrukturen mit thermoplastischer Zwischenkomponente entwickelt. Im Rahmen dieses Kapitels werden die Ergebnisse der Teilprojekte detailliert vorgestellt und erortert.

Conventional engineering design approach is to solve a structure for its strength. On the other hand, natural shapes and structures are more free-form, using stiffness and flexibility whenever and wherever necessary. Form-finding approaches for structural design draws inspiration from different trades of nature. In this work, an attempt is made to generate free-form structures using biological forms like growth of a plant. Generative design strategy within constrained design space was developed, and behavior of such solutions under different loading are discussed. Thus a structure is evolved (and adapted) via bottom-up approach, and not constructed (and optimized) as top-down process.

Plastics reinforced by natural fibers attract growing attention, particularly in the automotive industry. The properties and performance of these composites are usually determined before application. However, many mechanical tests of composite materials are destructive, expensive, time-consuming, and can cause operator fatigue. The objective of this research is to model the tensile properties of sisal fiber reinforced polyethylene terephthalate (PET) composites and compare the model outcomes with the results of experimental tests. For the experiment, PET was reinforced with 25% wt. of sisal fiber and composite samples were produced by compounding and injection molding processes. Modeling and simulation have also been carried out with ABAQUS/CAE software. The outputs on the tensile properties of the experiment and the model were statistically compared to see the accuracy of the model against the experimental results. The two-sample t-test indicates that, at 95% confidence interval, the mean differences for the stress, strain, and modulus for the experimental tests and the model results are not significantly different from zero. The research shows that the experiment can be effectively modeled with ABAQUS-based modeling and simulation techniques by linking with appropriate mathematical predictive models.

The use of thermoplastics (TPs) for natural fiber composites is restricted to commodity ones like polypropylene and polyethylene However, using engineered TPs such as polyethylene terephthalate (PET) will benefit from its technical and economic advantages. The research aims to characterize injection molded PET composites reinforced with sisal fibers treated differently. Polyethylene terephthalate composites containing 40 wt.% of untreated, alkaline-treated, and alkali/acetylation treated sisal fibers were prepared using compounding and injection molding processes and then characterized. It has been found that production of sisal-PET composites by compounding and injection molding has been shown to be possible. Thermal damage to sisal fiber was noticed during composite production. Based on the thermogravimetric analysis analysis, a net weight loss (excluding water loss) of 11.1%–14.0% was observed at the operating temperatures of the two processes. The addition of 40 wt.% of sisal to the PET matrix improved the tensile modulus by 137%. Further improvement by 179% was observed when alkali-treated sisal fiber was used. The combined alkali/acetylation treatment of sisal yields more enhancement by 233%. This is a significant advancement because modulus is the most influential parameter during the design and service of an engineering product. Generally, compared to the raw sisal composite (RSC) the interfacial, mechanical, thermal, and water absorption properties of the alkali treated sisal composite (Al-SC) and alkali/acetylated sisal composite (Al-ASC) specimens recorded an improvement. Relative to the natural fiber reinforced thermoplastic composites that were commercialized in the automotive industry, the produced sisal–PET composites resulted in a considerable improvement of 66.6%–190% in flexural strength and by 110.5%–410.0% in flexural modulus, depending on sisal fiber treatment and the composite to be compared. Thus, the studied composites can be recommended for various parts of automobiles.

Textile permeability is one of the dictating factors in the fabrication of fibre-reinforced polymer composites. However, reproducibility of experimental in-plane permeability characterization is still a challenging task due to the lack of standardized test and evaluation procedures. The paper at hand addresses two major sources for discrepancies when characterizing in-plane permeability through optical observation of radial flow experiments: digital image processing and data evaluation algorithms. A digital image processing strategy is presented, which robustly handles varying lightning conditions, optical properties of the materials under test and image occlusions caused by mechanical elements of the test setup. The strategy is of universal validity and independent of the choice of reinforcing material and impregnating fluid. An experimental analysis compares two approaches for fitting elliptic geometry models to data points detected along the fluid flow front. The study reveals the impact of the fitting strategy on the resulting permeability data and the benefit of forcing the ellipse centre to that of the injection opening. The computation algorithm of Chan and Hwang, widely used for calculating in-plane permeability values from experimental data, is critically discussed. A correction of the algorithm is proposed which avoids a violation of isotropic data characteristics while adding robustness to the data reduction. An experimental analysis compares anisotropic in-plane permeability values obtained with different evaluation algorithms. The study highlights the impact of the computational algorithm on the permeability data and reveals discrepancies of up to 6%, which is considerable compared to the scatter typically reported for in-plane permeability data.

The project “Multi-Layer Inserts” (MLI) proposes a new design for inserts used in thin-walled CFRP structures. The proposed inserts consist of multiple thin metal sheets and is build up simultaneously with the laminate in an intrinsic hybridization process, eliminating time-consuming post-processing steps. Furthermore, at equal weight, such inserts greatly increase the bonding area between metal and CFRP in comparison to conventional inserts. This results in a significant increase of the loads that can be transmitted into the CFRP. The present work discusses how the shape of the metal sheets which the proposed inserts consist of influences the mechanical properties of the surrounding laminate. This influence is investigated by measuring the strain distribution during tensile tests by means of digital image correlation. The strain distributions around the following three different MLI design approaches are compared: An elliptical metal sheet, which is expected to be ideal in terms of mechanical performance of the overall structure; a cross-shape metal sheet representing a production-driven simplification which only requires the ability to perform cuts in individual tows perpendicular to the laying direction and can be performed by state-of-the-art AFP systems; and lastly, a compromise between manufacturability and achieved mechanical performance, a decagonal metal sheet design, which requires angled cuts of the fiber tows. It is shown, that the decagon is able to evenly spread the strain over a larger area and is therefore able to significantly reduce the maximum strain values compared to a cross-shape metal sheet, while still being automatable.

The research presented here attempts to assess the potential for re-using carbon fibre (CF) fabrics recovered from recycling infusible acrylic thermoplastic carbon fibre reinforced polymer composites (CFRPs) in a universal manner, i.e. by combining with a wide variety of matrices to manufacture 2nd generation composite laminates by resin infusion. The 2nd generation composites have been compared in terms of bulk and interfacial properties against counteparts processed with virgin carbon fibre fabric infused with the same matrices. Generally, an increase in damping (tanδ) was observed in all 2nd generation composites, which can be attributed to a residual thin thermoplastic layer present on the recovered fibres. The interfacial adhesion of the 2nd generation composites was investigated by shear tests and scanning electron micsoscopy, and also appears to be less influenced by the type of matrix.

In this work, a closed loop recycling process is investigated, which allows polymerised bulk thermoplastic matrix (Elium 150) from production waste (also referred to as recyclate) to be reused as additive in composite manufacturing by vacuum assisted resin infusion (VARI) of virgin Elium 150 monomer. It is shown that this process can save up to 7.5 wt% of virgin material usage in each processing cycle. At the same time, the thermal stability and stiffness of the composite increases with the proportion of recyclate introduced. Contemporarily, the shear and bending properties have also been observed to improve. Gel permeation chromatography (GPC) showed that the changes observed are due to an increase in molecular weight with the recyclate content. In particular, a correlation between the molecular weight and the shear properties of the composite was discovered using single fibre push-out tests.

During recycling of waste paper from private households different fractions containing plastics and polluted paper fibers are received. Those polluted fibers cannot be recycled in the common paper manufacturing process or for energy recovery like in waste incinerating plants due t o economic reasons. Current research at the Institute of Polymer Materials and Plastics Engineering at Clausthal University of Technology evaluated the use of this waste paper recyclate as a substitution for natural fibers as fillers and reinforcements in polypropylene. Special attention was given to the mechanical properties of the composites. Additionally the influence of maleic anhydride grafted polypropylene (MAPP) as an adhesive was investigated.

During recycling of waste paper from private households different fractions containing plastics and polluted paper fibers are received. Current research at the Institute of Polymer Materials and Plastics Engineering at Clausthal University of Technology showed that the use of waste paper as filler and reinforcement in polypropylene leads to nearly the same mechanical properties as natural fibers like flax, sisal and hemp. The present investigations focus on the chemical cleaning of the paper recyclate to treat the fiber surface and to solve foreign plastics like polystyrene. For this purpose Soxhlet extraction with different solvents is used. The received extracts are examined via infrared spectroscopy, as well as the treated and the untreated fibers. Afterwards, the cleaned paper is incorporated into polypropylene. The received composites are investigated regarding their mechanical properties by tensile testing and Charpy impact testing.During recycling of waste paper from private households different fractions containing plastics and polluted paper fibers are received. Current research at the Institute of Polymer Materials and Plastics Engineering at Clausthal University of Technology showed that the use of waste paper as filler and reinforcement in polypropylene leads to nearly the same mechanical properties as natural fibers like flax, sisal and hemp. The present investigations focus on the chemical cleaning of the paper recyclate to treat the fiber surface and to solve foreign plastics like polystyrene. For this purpose Soxhlet extraction with different solvents is used. The received extracts are examined via infrared spectroscopy, as well as the treated and the untreated fibers. Afterwards, the cleaned paper is incorporated into polypropylene. The received composites are investigated regarding their mechanical properties by tensile testing and Charpy impact testing.

This article discusses modeling aspects of fiber circumplacement around a hole using continuous functions. Here, spatially inhomogeneous transversal isotropy is formulated on the basis of patches using B-spline approaches generating the fiber orientation. For this purpose, experiments with different fiber orientations and “hole”-concepts are provided for both the identification of material parameters as well as for model validation. The validation examples are a plate with uniform fiber distribution, where the hole is drilled after the production process, and a plate with circumplacement around the hole, where the fibers are bypassed before the matrix material is injected. The entire numerical problems are treated using finite elements. Furthermore, the material parameters are identified using – within a least-square approach – the combination of finite element simulations and optical results of a digital image correlation system.

In order to exploit full potential of hybrid materials, it is necessary to develop optimized load-dependent component designs, new manufacturing processes and joining technologies. Structural integrity concerning the interfaces between the single materials of the hybrid component poses a key factor to success. In this case, adhesion often constitutes the limiting factor for the maximum transferable load. In this investigation, a load-oriented innovative concept to increase the structural integrity of hybrid plastic-metal parts was developed. Local mechanical undercuts on the metal surface were created to generate an additional mechanical interlocking effect between the join partners. The aim is to find the best surface structure geometry to enhance mechanical bonding. Therefore, metal samples were structured by a new process and transferred to hybrid specimens by injection molding. For comparison, specimens with adhesive bonding (epoxy resin) of metal and plastic were prepared. The join partners aluminum AlCuMg1-2017 and PA6 as well as PA6GF30 were investigated. The evaluation of an increase in the structural integrity was determined using tensile tests. A significant improvement in joint strength compared with direct joining using adhesive bonding was achieved.

Flammability behavior of natural fiber polymer composites (NFPC) is an essential factor to define their scope of application. It was of great importance to quantitatively optimize the quantities of the flame retardants (FR) with respect to the corresponding mechanical properties as well as the flame retardance behavior. Flax/polypropylene (PP) system was selected in this study due to its diverse applications. Aluminium trihydroxide (ATH) which was an inorganic hydrate was used as a FR and smoke suppresser because of its environmentally–friendly nature. Flax and PP in the presence of a coupling agent were extruded together. Flax loading with respect to the host polymer was studied at 30% and 50%. Afterward, the compounds were mixed with three grades of ATH namely Apyral 32, 40CD, and 60CD which were loaded at different amounts ranging from 30 to 60 wt%. The synergetic effect of zinc borate (ZB) and ammonium polyphosphate Exolit AP-422 was also investigated. Both mechanical and flammability behavior were assessed with respect to ATH and its synergists. It was found that 40 wt% of Apyral 60CD was enough to reach V-0 level with a marginal loss of tensile strength namely 12.5% and 7% for samples of 30% and 50% flax, respectively. Higher loading of ATH at 60% results in strength reduction by 37%–40%. Cone calorimetry results proved the reduction of both heat release rate (HRR) and smoke release. Synergism with both additives improved the UL94 rating and decreased the HRR as well. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

An enhanced Vacuum Assisted Resin Transfer Molding (VARTM) process was studied for the manufacturing and characterization of bipolar plate with textile reinforced polymer composites. Rapid qualitative evaluation and quantitative characterization were conducted respectively to achieve an optimal manufacturing process design. The influence of process variables including pre-compaction cycle, post-filling time, curing pressure, etc., on the geometrical and mechanical properties of the textile reinforced polymer composites were investigated. The empirical optimized process design was then adapted for manufacturing of bipolar plate. The electrical properties of the bipolar plate were characterized by measuring its bulk (in-plane) conductivity according to the conventional four probe method. The influence of process conditions, carbon fabric design and nanofillers on the electrical properties of the bipolar plate were considered. The results show that the bipolar plate has a flexural strength in the range of 166.6–188.3 MPa, which is a great improvement in comparison with the one based on highly filled or cut fibres reinforced polymer composites. However, the maximum bulk conductivity achieved is limited at 5902 Sm−1 in this study, suggesting that further development effort is required for bipolar plate manufactured by textile reinforced polymer composites.

The aim of this work is to develop a new generation of nanoparticle-reinforced natural sisal fibres, which are also provided with several polymeric coating materials namely natural latex, polylactide and polyurethane. The improvement in the modified sisal fibres is validated by measuring the moisture content, mechanical properties by single fibre tensile testing and the thermal stability using the TGA through individual fibre tests. In addition, pull-out test is performed to examine the fibre/matrix adhesion. Further investigations of surface morphology are carried out using the optical microscope. Distribution of nanoparticles on the surface of fibres and in between the bundles as well as the polymer sleeving around the fibres are investigated by scanning electron microscopy (SEM). Furthermore, from this new type of natural fibre, a technical textile is made, which is processed through a common resin infusion process for production of fibre-reinforced composites. The analysis of the produced sleeved nanoparticle reinforced sisal fibre bundle samples proved a significant reduction in moisture absorption by 50% from the starting value. SEM investigations show uniform distribution of the injected nanoparticles between the fibrils and on the surface of the fibre bundle. Tensile strength of the single composite fibre increases by around 50% in comparison to the original unmodified sisal fibre for the latex sleeving. The change in the modulus of elasticity of the modified fibres follows a trend which complies with the properties of the applied sleeving material. Thermal stability of the composite fibre is positively improved where the decomposition temperature increased by 20 °C after fibre modification. The fibre/matrix bonding of imbedded modified sisal fibres in the epoxy resin is also dramatically enhanced especially in PLA and Latex sleeving cases as no matrix de-bonding as failure aspect is reported out of the pull-out test. Microscopic investigations of the laminate produced from the modified fibres show very uniform surface profile enhanced by the latex sleeve around the single fibres.

This work studies the possibility of compounding natural fibres (flax) into engineering plastics (PA6 and PB6) and comparing the results with counterpart glass fibre composites. The problem in compounding is the difficulty to compound the fibres with such polymers of high melting temperatures without decomposing the natural fibre thermally. Preliminary experiments are tried to define the possible processing window using the kneader namely temperature, compounding time and shear rate. Fibre content is tried in range of 0–50 wt.% with 10% step. The mixing temperature covers the range around the melting temperature ‘Tm’ [Tm−20, Tm+20]°C. The use of pre-melting temperature in compounding would utilise the energy evolving by fibres mutual rubbing. Compounding time is optimised at the minimum level. Shearing rate is tried at 25, 50, 75 and 100 rpm. Optimum conditions are defined to be 210–230 °C and 200–210 °C for PBT and PA6 respectively. Shearing rate is also defined to lie within 25–50 rpm. Two different additives of non-organic mineral and organic phosphate flame retardants are tried with the prepared composites either alone or in combination with each other. The loading of flame retardants is limited to 20 wt.% in order to leave a space for natural fibres as well as the polymer and to keep in turn the overall composite mechanical properties. A mix of 1:1 ratio between the both types of retardants is needed to reach V0 flame retardation level. Mechanical properties are even improved 30% in E-modulus and 4% in strength with respect to composites without flame retardants. However, the injection moulding is reported to be difficult because of the high viscosity and the parameters should be optimised regarding the desired flame retardance level and the required mechanical properties as well as keeping the fibres not damaged.

This study contributes to the understanding of the mechanism behind thermo chemical aspects related to the resin transfer moulding manufacturing process of a composite part. The aim is to comprehend the phenomena, to identify related parameters and to get knowledge-based methods for the process development. Therefore, the first part of this study is an experimental study about the behaviour of material properties during the manufacturing process of the single component and the composite. It concludes with constitutive equations for single-process parameters and their associated homogenisation approach for the composite properties. During the manufacturing process, material values of the matrix are changing and influenced by a high number of effects. In the second part, a simulation strategy is been derived. This developed material model integrates a dependency of the time–temperature–polymerisation and fibre volume content. The model is validated in a test case of a manufacturing process of an aircraft component, a fuselage frame.

A novel process is proposed for cost effective manufacturing of Fiber Metal Laminate (FML) with textile reinforced pCBT composites and aluminum alloy. To improve the adhesive bonding, prepregs with excellent impregnation quality and highly adhesive resin was introduced as interlayer for a 2/1 preform configuration, which is composed of two layers of dry carbon fabrics and one layer of aluminum alloy in between. The preform is impregnated by cyclic butylene terephthalate (CBT) resin melt in resin infusion process under isothermal molding conditions. After manufacturing, the FML was subjected to mechanical characterizations, including interlaminar shear test and Charpy impact test. The influence of various surface treatment methods on the Interlaminar Shear Strength (ILSS) was investigated for evaluation and enhancement of the novel process. Several comparisons between the novel process and the traditional autoclave process were performed to assess the performance of the novel process. The results indicate that the mechanical performance of the FML manufactured with the novel process could be even better than the one fabricated with traditional autoclave process, when the appropriate surface treatment and molding conditions were applied.

Multi-material design is a key technology for lightweight design and calls for combining different materials such as steels, light metals and composites like carbon fiber reinforced plastics (CFRP) into load-bearing structures. Due to the minor chemical affinity of such materials and contact corrosion aspects, the design of an appropriate interface is a current challenge. Aiming on highly performant single-stage manufacturing processes, the paper presents investigations on several surface treatment techniques like a laser pretreatment, the use of primers and a sol-gel coating. Beside investigations on the achievable joint strengths, the corresponding joining concepts to facilitate the in-mould assembly of hybrid structures are validated. In this case the intrinsic manufacturing methods of the Resin Transfer Moulding (RTM) and the Automated Fiber Placement (AFP) technology are presented. Furthermore corrosion protection measures for CFRP and aluminum are analyzed via immersion and salt spray tests.

As an index of viscosity, flowability of natural fiber polypropylene composites is assessed by spiral mold test using injection molding machine. The effect of the processing parameters like the injection temperature at 180-220°C, injection pressure at 500-1000 bar and the mold temperature of room temperature and 80°C on flowability is studied. The investigated parameters are the fiber shape (Non branched straight cellulose versus low flexural stiffness and branched hemp fibers), fiber length (0.5 versus 1.5 mm chopped cellulose fibers) and fiber content Wf (10 versus 30 wt%). The results show that the most significant parameters in a descending order are the pressure, temperature and the mold temperature. Another aspect of the product quality is the homogeneity of the fiber content through the whole injected spirals. Therefore samples are taken out at even distances along the spiral. The cut samples are dissolved to extract fibers and calculate the fiber content. Fiber content definition along the injecte...

Illusions and facts about aspect ratio and the corresponding mechanical properties of the polypropylene flax are studied in this work. Selection of extruder elements controls significantly the fiber final dimensions. Hence, the load transfer efficiency can be improved. Different extruder layouts are tried. First and second trials investigate the mixing degree effect using kneading elements with eight and four kneading elements, respectively. The third and fourth trials keep four kneading blocks but differentiate in using multiprocessing element MPE and toothed elements, respectively. All the four configurations are tested at different shearing rates namely 100, 200, and 300 rpm and different fiber loadings 10, 20, and 30 wt %. Polypropylene (PP) with high flowing properties and slivers flax natural fibers are used. The output extruded strands are mechanically tested. The third and fourth configurations showed superiority to the normal kneading profiles regarding the mechanical properties. Samples of composites are withdrawn after each processing extruder element to study the effect of this element on the fiber dimension. Measurement of extracted fibers is carried out by two methods namely dynamic image analysis machine and secondly normal microscopic investigation. Weibull distributions are defined for fiber geometry distributions for the different locations on the extruder configuration. Also, the effect of the shear rate and the extruder configuration on the final dimensions of the fibers extracted from the composite. The results show the correlation between extruder configuration and fiber aspect ratio and hence the composite overall strength. However, further processing like injection molding erases the pre-extrusion effect. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40435.

The presented study investigates the flow length and the corresponding fiber content distribution in the injection-moulded natural fiber reinforced thermoplastics and its relation to fiber type and processing parameters such as injection pressure, temperature, injection rate and mould tempering by increasing die temperature. In this research, polypropylene compounds with nominally 30 wt % hemp and sisal fibers are investigated. The influence of the injection pressure (500 and 1000 bar), melt temperature (180°C, 200°C, and 220°C), and die temperature (23°C and 80°C) on the fiber content distribution all over the sample is investigated. An increasing linear trend of fiber content along the spiral length is observed as an evidence of a fiber/polymer multiflow system. A pattern for fiber content distribution with respect to the fiber length along the injected spiral can be distinguished, where the longer fibers are usually found at the end of the injected part and the shorter fibers remain near mould entrance point. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39861.

At the present time, environmental protection and efficient energy and resource usage are key topics in the industrial sector. In contrast, the desire for comfort, mobility and protection increases progressively and leads to an immense weight gain. Particularly, in the automotive and aerospace industry, strong efforts are made to ensure an efficient manufacturing of lightweight structures. Thereby, an upcoming trend is represented by the application of hybrid structure manufactured by innovative procedures. One of these is the resin transfer moulding procedure, which ensures a highly automated one-step manufacturing of hybrid structures consisting of metal and carbon fibre-reinforced plastics (CFRP). In many cases, the generation of a strong and durable connection between the dissimilar materials is one of the major challenges. In this study, the influence of various surface pretreatment methods on the shear strength of the hybrid structures out of aluminium or steel and CFRP is investigated. In order to eliminate the influence of bending moments and specific material properties, shear edge tests, which enable a pure shear load, are carried out. Furthermore, the failure behaviour is analysed. It is shown that the shear edge test represents an excellent benchmark test to obtain precise interface properties such as shear-stress and fracture work. These properties can be significantly enhanced using surface pretreatment methods.

Digital speckle pattern photography is applied to the measurement of light deflection profiles of inhomogeneous transparent objects by transmission of a He–Ne laser speckle field through the object. The speckles are recorded with a CCD camera, and the local displacements are evaluated by comparison of the deflected speckle field with the undeflected field by a digital cross-correlation technique. In this way a complete two-dimensional deflection field can be obtained from a single pair of CCD records. The basic technique and two experimental setups suitable for objects with a size larger than that of the CCD chip are described. These novel techniques are applied to determine profiles of the refractive index of a free-burning arc in air. In addition, a cinematographic setup is described, which allows the investigation of transient objects by means of a video tape recorder.

A linear θ-pinch discharge without preionization is investigated in Helium within that range of density, in which the mean free path of electrons between two elastic collisions diminishes to such a low value that the electrons cannot gain the ionization energy in the induced electric field over this distance. Compared to the well known observations at low densities in this high density range the instant of the first breakdown in the discharge tube is found to be shifted to later halfcycles with increasing initial pressure. In addition, the further development of the discharge at high initial densities shows a very different structure compared to the low density behaviour. Comparison of optical observations with measurements of the current density distribution obtained by means of magnetic probes (using a special difference method on account of the very small plasma currrents) shows the following result: In the half cycle immediately following the breakdown, a typical shock wave pinch is produced at high densities. The regions near the axis are heated only by an ionizing shock, while the contraction of the current sheath, which initially started the shock, is stopped very early in far outer regions. During the following half-cycle quite a different behaviour of the discharge is observed on account of the enhanced electrical conductivity: The contraction runs much faster and therefore the separation between the shock front and the driving current sheath decreases.

A coil for the theta pinch was developed, which consists of two copper cylinders, one within the other, with countercurrently slanting slots. They are joined together at one end by a massive copper ring, while at the other end they are isolated from each other by a circular projecting disk. (M.C.G.)