Key Engineering Materials Vols. 611-612

Abstract: Sandwich panel structures are increasingly used in applications where the most important demands are the weight saving and long service life. Utilizing sandwich panels, extremely light-weight, stiff and robust structures can be manufactured. In this study, sandwich panels were produced by specially designed cost-effective forming tools. Various kind of test materials were used for corrugated cores and skin plates: conventional low-carbon steel grade EN 10130 and ferritic stainless steel grade 1.4509 with plate thicknesses of 0.6 and 0.75 mm. A common S355 structural steel was used as a reference for bending strength comparison.For measuring the stiffness, MTS tensile and fatigue testing machine was selected to determine the bending resistance of the sandwich panels. The bending force, needed for yielding and fracture, related to the bending length and intensity was compared with the results from bending of the reference plates. Results showed that the bending force of the panels is significantly higher than that of a plate having similar intensity. The best results were obtained with the stainless steel (SS) panel that had 27% higher bending force at the yield point than 5 mm thick S355 plate having 3 times larger intensity. The carbon steel panel was approximately 40% weaker than the SS-panel and both panel types lost strength when loading direction was changed from transverse to 45 degree and further to 90 degree load (longitudinal).

Abstract: The main aim of the study was to develop forming tools for wide (over 1.2 meter) sandwich panels. Longitudinal laminating technology was selected for tool manufacturing due to its flexibility and cost efficiency. Laminating technology enables easy modification of the tool dimensions afterwards. The function to optimize or vary the dimensions of the tool was set as a secondary objective for the study. Forming tools for sandwich panels are usually complicated structures and joining of the plates can be difficult in some cases. Typically sandwich forming tools are capable to produce only narrow panels (less than 1 meter) and optimization must be done during designing of the tool. In this study, a rapid designing and manufacturing of a flexible sandwich panel forming tool was investigated. Sandwich panels are usually applied in light structures or voice covers due to their very low weight, high stiffness, durability and production cost savings. Designing of the forming tool was made by using a 3D CAD program. Conventional steel plates were used for the forming tool and the assembly was done by fixing the plate parts longitudinally together (laminating). Most important criterion for the forming tool was its capability to produce high quality geometry for the core. Laser welding assembly showed that the quality of the core was good enough for welding the lap joints properly. Both of the objectives were fulfilled: 1) forming tools were suitable for forming of wide cores (1.2 meter) and 2) the structure of the laminated tool enables to change or add new plate parts to change the dimensions of the final product.

Abstract: In the manufacturing of metal components both wear and corrosion have to be considered. In particular, corrosion is a primary problem in the aeronautic field, where the aluminium alloys are affected by several corrosion typologies. Furthermore, nowadays carbon fibre reinforced plastics (CFRP) are finding an increasing use, but they can induce galvanic corrosion phenomena when coupled with aluminium alloys. To overcome this problem, corrosion resistant coatings are used on aluminium components. On these premises, the realization of a titanium coating on aluminium components could allow the coupling of CFRP and aluminium alloys, improving the corrosion resistance. Cold Spray Deposition is a recent technology to realize these coatings. This technology allows the production of near fully dense coatings on metallic surfaces. In many applications the coated aluminium sheets have to be machined (cut or drilled). Machining with conventional cutting methods leads to both tool wear and damages in the coating. Laser cutting represents a promising alternative: it does not involve any mechanical cutting force or tool wear and, thanks to the small laser beam spot, it allows to realize complex shapes. In this paper, laser cutting of an Al alloy sheet (0.6 mm thick) coated with Ti Alloy, was studied. The adopted laser source was a 150 W, lamp pumped Nd:YAG, specifically developed for micro-machining operations on metals. During the tests, the process parameters (cutting speed, pulse duration and entrance side) were changed and the kerf geometry was analysed as a function of the process parameters.

Abstract: This study describes design and construction of a novel flexible heat treatment line for processing customer-oriented small batch steels. The induction heater (600 kW) developed is suitable for the sheet thickness in the range 3.2 30 mm and the width of 85 1250 mm. Sheets are fed using an electrical motor (1.5 kW) and a chain drive, the speed being in the range 0.3 7 m/min, depending on the power and the sheet dimensions. At this study, 4.5 (WR-1) and 10 mm (WR-2) thick wear resistant steels were tempered at different peak temperatures to compare the effect of rapid tempering on mechanical properties. Results showed that the heat treatment line is capable of producing tempered steel grades with adequate properties at industrial product rate. For example, 4.5 thick WR-1 tempered at 550 oC provided a yield strength (YS) over 1000 MPa with minimum bending radius of 6 mm (in the delivered condition YS = 1605 MPa and R_min = 12). Tempering of WR-1 at 700 oC provided YS of 762 MPa and R_min of 1 mm. Results were similar between two test materials, but the enhancement in bendability was slightly more effective with the thinner sheet.

Abstract: Additive Manufacturing technology offers almost unlimited capacity when manufacturing parts with complex geometries which could be impossible to get with conventional manufacturing processes. This paper is based on the study of a particular real part which has been redesigned and manufactured using an AM process. The challenge consists of redesigning the geometry of an originally aluminium made part, in order to get a new stainless steel made model with same mechanical properties but with less weight. The new design is the result of a structural optimization process based on Finite Element simulations which is carried out bearing in mind the facilities that an AM process offers.

Abstract: The injection over-moulding of 30wt% short glass fibre reinforced PA6 (SGF from Solvay Engineering Plastics) onto consolidated unbalanced (87/13) 70wt% glass fabric reinforced PA6 (Continuous Fibre Reinforced Thermoplastic (CFRT) from Solvay Engineering Plastics) was investigated with the objective to optimise the flexural and interlaminar shearing of the complex. Among the processing parameters, the temperature of the fabric before injection and the over-moulded melt temperature associated to the mould temperature (cooling rate of the complex) were revealed as the main parameters directing the mechanical properties of the complex. Moreover, the flexural modulus and the apparent interlaminar shear strength fall down critically in the main direction (chain direction of the fabric) under a CFRT temperature of 150°C. The effect of the SGF/CFRT interface was quantified in term of quadratic distance of diffusion through the interface. First, the 1D cooling of the complex was simulated according to the heat transfer module of COMSOL Multiphysics® in order to determinate the variation of the temperature field during the cooling stage of process. The calculations were achieved with an initial CFRT temperature of 23, 100, 150 and 200°C, the mould and SGF melt temperatures were kept constant. The diffusion theory has then been applied to calculate the variation of the auto-diffusion coefficient through the thickness during the complex cooling, the diffusion is supposed occurring only at a temperature above the PA6 crystallisation temperature (185°C). The calculation of the quadratic distance of diffusion through the thickness confirmed the mechanical results. Under a CFRT temperature of 150°C, the ability to the molecular diffusion at the interface becomes non-existent. The melt temperature of the SGF PA6 has to be sufficient to melt the CFRT PA6 interface, the time of diffusion directed by both the CFRT and mould temperatures (cooling rate) has to be long enough to allow the molecular diffusion from the material to the other.

Abstract: Hydroxypropyl methylcellulose (HPMC) constitutes one of the most dedicated polymers used in the production of film coatings for pharmaceutical applications (capsules, tablets …). In order to control the surface properties (adhesion, friction, wear) of HPMC films, additives are frequently incorporated during film formulation: these are in most cases hydrophobic lubricant (like fatty acids) or hydrophilic plasticizer. Hydrophilic plasticizer like polyethylene glycol (PEG) will determine the diffusion properties of water through the film and thus drug release but also its deformability as well as its surface softness. The main objective is to use dedicated analytical tools to access HPMC formulated film surface characteristics in terms of structuration, surface morphologies, surface phase separation, wettability, nano-adhesion and nano-friction properties. At nanoscale, Atomic Force Microscopy (AFM) in contact mode and in friction mode (FFM) is a powerful tool for studying nano-adhesion and nano-friction. The presented paper underlines the strong dependence of film surface properties on additive nature and concentration. It also shows that first the HPMC-additive compatibility seems to be an interesting factor behind the variation of surface properties of HPMC formulated films, and second that formulation is an effective way to tune surface properties of HPMC biopolymer films.

Abstract: The main objective of this study is the substitution of a part of virgin polypropylene with recycled polyolefin from part of End-of-Life Vehicle (ELV) to be used in automobile applications while respecting existing material specifications. First, the recycled plastic sources were characterized by ThermoGravimetric Analysis (TGA), Fourier Transform Infrared Spectrometry (FTIR), Differential Scanning Calorimetry (DSC) and X-ray Fluorescence. As the sources have almost the same properties, the one, with the easiest supply, was selected. During the second step, the study allows comparison of mechanical performance of several formulations with three specific additives made in two injection process conditions. A higher heat temperature and smaller dosage speed reduced the degradation of fibre glass during processing. Moreover, the additive improving the adhesion between the fibre and the polymeric matrix increased by 3% the flexural modulus. This study has enabled the elaboration of a global method coupling sampling methodology, formulation and process optimisation to substitute a virgin material with recycled plastics from ELV.

Abstract: Initial heating conditions and temperature effects (heat transfer with air and mould, self-heating, conduction) have important influence during the ISBM process of PET preforms. The numerical simulation of infrared (IR) heating taking into account the air convection around a PET preform is very time-consuming even for 2D modelling. This work proposes a simplified approach of the coupled heat transfers (conduction, convection and radiation) in the ISBM process based on the results of a complete IR heating simulation of PET sheet using ANSYS/Fluent. First, the simplified approach is validated by comparing the experimental temperature distribution of a PET sheet obtained from an IR camera with the numerical results of the simplified simulation. Second, we focus on the more complex problem of the rotating PET preform heated by IR lamps. This problem cannot be modeled in 2D and the complete 3D approach is out of calculation possibilities actually. In our approach, the IR heating flux coming from IR lamps is calculated using radiative laws adapted to the test geometry. Finally, the simplified approach used on the 2D plane sheet case to model the air convection is applied to the heat transfer between the cylindrical preform and ambient air using a simple model in Comsol where only the preform is meshed. In this case, the effect of the rotation of the preform is taken into account in the radiation flux by a periodic time function. The convection effect is modeled through the thermal boundary conditions at the preform surface using the heat transfer coefficients exported from the simulations of the IR heating of a PET sheet with ANSYS/Fluent. The temperature distribution on the outer surface of the preform is compared to the thermal imaging for validation.

Abstract: The hot press moldability of bamboo powder without additives was investigated in this study. Bamboo powder was hot pressed into self-bonded cylindrical moldings at temperatures of 160 to 200 oC and pressing times of 1 to 20 min at a punch surface pressure of 200 MPa. After pressing, the color, density and bending properties of the moldings were evaluated. The bending strength, bending elastic modulus and density were found to increase with an increase in temperature, and moldings having good mechanical properties were obtained at a temperature of 200 oC. With respect to the influence of hot pressing time on moldability, a maximum bending strength of 34 MPa was achieved for a time of 10 min at a temperature of 200 oC. In addition, we removed moldings from the mold after cooling to 100 oC or less in order to improve the surface texture and density of the moldings. The results showed a cooled molding had a good surface texture (resembling plastic) and a bending strength of 53 MPa.