Search

This paper focuses on investigating the forming behaviour of sandwich materials composed of steel sheets and glass fibre-reinforced polyamide 6 (GF-PA6), i.e., thermoplastic-based fibre metal laminates (FML). Stretching and forming limit curve (FLC) determination of FML with different cover/core layer thickness ratios at various forming temperatures, i.e., at room temperature (RT), 200 and 235 °C, are the main approaches for characterizing their formability. In addition, the formability of mono-materials and non-reinforced sandwich materials is investigated as a reference. For a successful test and reliable results, several technical issues are considered, such as the suitable lubrication configuration and digital image correlation at elevated forming temperatures. The results revealed that the formability of non-reinforced sandwich materials with different core layer thicknesses exhibited compared formability to their monolithic steel sheet and no remarkable improvement in their formability with increasing the temperature up to 200 °C. Conversely, the formability of FML shows significant improvement (approx. 300%) with increasing temperature with a forming depth of about 33 mm at 235 °C compared to only 12 mm at RT.

This study was carried out during the two successive seasons of both 2018 and 2019 on 5-year-old Flame Seedless grapevines in a private vineyard located at Kom Hamada - Beheira Governorate, Egypt. The trees were spaced at 1.5 x 3 m apart and irrigated by drip irrigation system and received similar cultural practices adapted in the orchard. The present investigation aimed at study yield and quality of table grapes cv. "Flame seedless" as affected by bud break and pre-harvest treatments. This experiment consisted of sixteen treatments arranged in factorial experiment in Randomized Complete Block Design (RCBD) with four replicates for each treatment and one tree for each replicate. The experiment consisted of 16 treatments (Control, Garlic oil at 1 %, Urea at 2 %, Dormex at 4 %, Abscisic acid at 400 mg/ l, Ethrel at 250 mg/ l, Gibberelic acid 250 mg/ l, Garlic oil at 1 % + ASA at 400 mg/l , Garlic oil at 1 % + Ethrel at 250 mg/l, Garlic oil at 1 % + GA3 at 250 mg/l, Urea at 2 % + ASA at 400 mg/l, Urea at 2 % + Ethrel at 250 mg/l , Urea at 2 % + GA3 at 250 mg/l, Dormex at 4 % + ASA at 400 mg/l , Dormex at 4 % + Ethrel at 250 mg/l and Dormex at 4 % + GA3 at 250 mg/l . Results revealed that spraying dormex at 4%, recorded the best values of cluster weight and yield/plant, physical characters i.e. (berry length, berry diameter, weight of100 berry, size of 100 berry and fruit firmness), and all chemical compositions i.e. (total sugars, reducing sugars, anthocyanin content and vitamin c), also, abscisic acid 400 mg/l gave the highest mean values of cluster weight, yield/plant and anthocyanin content, while Ethrel at 250 mg/l recorded the maximum values of physical characters i.e. (berry length, berry diameter, weight of100 berry, size of 100 berry and fruit firmness), and all chemical compositions i.e. (total sugars, reducing sugars, and vitamin c), as compared with the control treatment which recorded the minimum values of this studied characters, during both seasons.

This study was carried out during two successive seasons 2016 and 2017 on six years old ‘Wonderful’ pomegranate trees (Punica granatum L.). Trees were grown on sandy loam soil conditions in a private orchard located at Burg El-Arab, Alexandria governorate, Egypt. The trees were spaced 4x5 m apart and irrigated by drip irrigation system and received similar cultural practices adapted in the orchard. The effect of some growth regulators, nutrient elements and kaolin on cracking and fruit quality of pomegranate ‘Wonderful’ cultivar was studied. The experiment was designed as randomized complete block design with five replicates. Each block contained 11 treatments (control, naphthalene acetic acid (NAA) at 25 and 50 mg/l, gibberellic acid (GA3) at 100 and 150 mg/l, boric acid at 0.1% and 0.3%, calcium chloride at 1% and 2% and kaolin at 4% and 6%). Results revealed that, boric acid at 0.3% gave the highest mean values of fruit set (%), number of fruits/tree, yield (kg/tree) and anthocyanin; while, naphthalene acetic acid at 50 mg/l recorded the maximum mean values of fruit weight, fruit diameter, volume and grain weight, and gave the minimum mean values of fruit drop and fruit cracking (%). On other hand, gibberellic acid (GA3) at 150 mg/l gave the maximum yield (kg/tree), in the second season and the minimum fruit cracking (%), whereas, calcium chloride at 2% gave the best results of TSS (%), acidity (%), and vitamin C, total and reducing sugars were higher than the control for all treatments. Finally, kaolin at 6% gave the lowest percentage of sunburn and the highest percentage of juice, as compared with the control and other treatments during both seasons.

International audience

In this article, we continue the investigations on the forming behavior of the steel/polymer/steel (SPS) sandwich composites as introduced in Part 1 [1]. In this paper, the main focus lies on bending conditions, validated by analytical and numerical methods. A wide variety of SPS layer configurations and thicknesses were tested under three-point bending conditions considering different bending angles (60, 90 and 150°) and different punch radii (1.5, 3, 6 and 12 mm). The results are validated in terms of the bending forces, springback degree, strain field distribution, and thickness reduction, where a good matching between the numerical and analytical results with the experimental ones was reached.

Metal-polymer-metal sandwiches can find promising applications in the automotive field thanks to their lightweight and formability . The paper focuses on the effect of low velocity impacts on the residual mechanical behavior. Experimental stepwise tests are run on undamaged and impacted specimens with different combinations of thickness and grade for the outer steel skins and the inner polymeric core. Surface temperature evolution is thermally monitored during the tests with the aim to characterize the induced damage and to identify a parameter able to quantify the residual strength of the panel. Several approaches have been considered. The analysis of the thermal amplitude trend with the lock-in thermography evidences a variation in the thermal behavior of the specimens, defining a corresponding damage stress σD. We found a 20% σD difference between undamaged and damaged specimens. Moreover, impacted specimens experience a temperature and stress concentration at the impact area dependent on the indentation . Based on these results, we evidence the possibility to relate impact indentation with the damage stress estimated by thermography and with the stress concentration factor induced by the impact. Therefore, thermography is a useful and valid tool for post-impact damage detection, monitoring and quantification of these multi-layer sandwich materials.

Recently, the applicability of thermoplastic fibre-metal-laminates (FMLs) in the automotive and aerospace fields has gained more attention due to their lightweight potential and improved flexural stiffness. Therefore, this study deals with investigating the structural properties of FMLs top-hat crashboxes under quasi-static and highly-dynamic bending conditions. Accordingly, the energy absorption characteristics and failure modes including the arisen microscopic defects are identified. For improved structural integrity, the hat structures were produced using a one-step thermoforming process, in which the forming and bonding of the FMLs layers take place simultaneously. Different metallic skin sheets (aluminium and steel) combined with glass fibre reinforced polyamide cores with different fibre orientations and thicknesses were considered. Also, finite element analysis using LS-Dyna™ was carried out on the Al-based FMLs to calculate the energy absorption behaviour and analyse the failure modes. To characterize the monomaterials and FMLs, tensile tests at different temperatures and strain rates were performed. The results state that with the thermoforming process, arbitrary FMLs material combinations and thicknesses can be processed. Varied thicknesses in the different hat structure regions are expected due to the flow of the polyamide matrix. Moreover, increasing the core thickness and utilizing the 0°/90° fibre orientation can improve the bending stiffness. Several defects such as delamination, plastic deformation and fibre cracking arose during the bending test. Finally, the simulation results revealed good agreement with the experimental ones. Due to the model simplifications, some failure modes could not be replicated in the simulation. This requires further studies.

Crash structures consisting of metal/polymer/metal (MPM) sandwich structures with a thermoplastic core exhibit a sufficient energy absorbing effectiveness, comparable or even better than metallic crash absorbers. In general, the crash structures have an unfavorable absorbing behavior at the beginning of the crash, which is indicated by high forces and small displacements. Because of this, the influence of inserted crash initiators (triggers) on the buckling mechanism was investigated using quasi-static and dynamic tests with different trigger geometries. As a result, a slit of 4 mm width decreased the peak force with about 50 % in the dynamic testing regime. A slit of 1 mm was found to be the most effective one for decreasing the peak force. The way the trigger works on the structure transferring it in a progressive buckling mechanism needs further investigation, due to a recorded double peak in the peak force area, which was not reproducible in different samples.

In part 1, a fundamental study on mechanical properties and deep drawing of a steel/polymer/steel sandwich (SMs) combination was accomplished investigating one type of reinforced SMs (R-SMs). In this part, the effect of reinforcements (REs) with different geometries, sizes, materials and locations on stretching and deep drawability is introduced. Additionally, the influence of reinforcing SMs with different mechanical properties and skin/core thicknesses is considered. Therefore, a deep drawable steel grade with thicknesses 0.49 mm and 0.24 mm was utilized. For the core polyolefin (PP-PE) foils with thicknesses of 0.3 mm and 0.6 mm were used. Substantial reduction of the deep drawability was found if the RE is located in the forming region (close to the punch), however, only locally if located in the flange area. Inserting the RE in the flange has no remarkable effect on the drawing force but on the forming potential represented by the cup height at failure. The stretching results show that increasing the RE size reduces the forming potential. The RE creates a sharp interface with the neighbour core layer accelerating failure. A negligible effect of the RE geometry was found, however solid REs show reduced forming limits compared to the mesh-like ones.

Recently, increasing development efforts of components made of fibre metal laminates (FMLs), with thermoplastics due to their numerous advantages are remarkable. One-step adhesion and forming approach is an innovative solution to process such laminates reducing the cycle time and delivering failure-free components simultaneously. Hat shaped sections were the chosen geometry in this paper. This process is described considering the temperature, pressure and time progress in addition to the temperature distribution inside the FMLs in different locations. In order to describe the structural behaviour of the hat profiles, top-hat crashboxes were produced and tested via quasi-static three-point bending tests. The investigations were carried out by experimental and finite element simulation. Several parameters are discussed in detail, the top layer (steel and aluminium), the core layer thickness (0.5 and 1.0 mm) and glass fibre orientations (0°/90° and ±45°). The results revealed that by doubling the core thickness, the forming forces and accordingly the absorbed deformation energy were doubled at reduced weight increase. Comparing the experimental and numerical results for the Al-based FMLs, a good agreement regarding the energy absorption deformation mode and the force–displacement progress was reached.

Since years, metal/polymer/metal sandwich sheets (MPM) are in the focus of research, not only because of their lightweight potential, but also for their arbitrary customization in aviation as well as automotive applications fields. Because of the limited forming potential of the MPM containing thin metallic skin sheets in combination with epoxy resins, improving their shaping ability is a challenge. In this paper, studies on forming of MPM sheets by electromagnetic forming (EMF), a die less, high strain rate, free-forming process were carried out. EMF bending tests at different bending radii and complex forming process (comparable to stretch forming) were attempted at different energy discharges. The results revealed that forming the MPM sheets is possible with EMF with improved results in terms of the strain values and forming depth compared to the conventional stretch forming process with fixed tools. In the EMF bending tests, several damage types could be observed due to the inappropriate selected energy level and coil/sample size ratio. These parameters have to be optimized in a follow-up study to define a proper process window.

Steel/polymer/steel sandwich structures have a high potential in weight reduction at high stiffness values. The aim of this study is to investigate the adhesion properties of galvanized steel/Polyamide 6 sandwich composites, which are produced by hot pressing following a parametric design of experiments plan at varied temperatures, times and pressures. One of the most interesting phenomenon hindering a good adhesion strength was the formation of sub-millimeter sized bubbles during the hot pressing. Possible reasons and methods to avoid these bubbles were investigated using scanning electron microscopy, X-ray photoelectron spectroscopy , thermogravimetric analysis , ultraviolet photoelectron spectroscopy, metastable induced electron spectroscopy and X-ray diffraction. The proposed solution is to apply a heat treatment on the galvanized sheet prior to pressing, where varied treating regimes were applied. To improve the adhesion quality , mechanical/physical treatments were utilized as well. Furthermore, a compatible adhesive agent was applied in combination with the different surface treatments, where the lap shear strength reached at least 23 MPa, high enough for a delamination-free shaping afterwards.

The development of biocompatible implants is remarkably increased by designing new alloys; mainly on the basis of titanium (Ti) and magnesium (Mg) for permanent and biodegradable alloys, respectively. Polymer-based composite structures were also developed and tested to match the conditions of human bones. In this paper, a sandwich material (SM) approach is introduced to tailor the biomechanical properties, mainly the elastic modulus (E) and the biocompatible properties. The sandwich material is composed of Ti grade 1 (Ti Gr. 1) cover sheets and a polypropylene copolymer (PP-PE) core (PP-polypropylene, PE-polyethylene). An epoxy resin is used as an adhesive agent. This type of sandwich material has the potential to replace commercially used laminates in aerospace and automotive industry in cases of the need of a formable lightweight product, too. The mechanical properties were characterized for different core thicknesses via tensile testing. The mechanical properties exhibited a good matching with the estimated values according to the rule of mixtures. On this basis, sandwich material can be tailored to give the appropriate density, elastic modulus and strength as well by varying the ratio of thickness between the partners. The forming behavior was examined under deep drawing conditions, where the Ti-sandwiches exhibit a good drawing capability; cups can be drawn close to the limits of the mono-metal sheet. 3-[4,5-dimethylthiazol-2-y1]-2,5-diphenytetrazolium bromide (MTT) cell viability assay was used to examine the behavior of human osteosarcoma MG-63 cells on metal and polymer components of sandwich material. Cell viability was much higher for Ti/PP-PE/Ti sandwiches compared to 316L/PP-PE/316L ones. Die Entwicklung biokompatibler Implantate fokussiert sich derzeit mit der Zielsetzung der Anpassung an die mechanisch-biologischen Anforderungen neben dem Einsatz von Werkstoffen auf keramischer oder auch polymerer Basis weiterhin auf die funktionsgerechte Auslegung metallischer Werkstoffe wie Titan oder Magnesium und ihren Legierungen. In diesem Bericht wird ein Sandwichverbund (sandwich material) vorgestellt, der eine masgeschneiderte Anpassung der biomechanischen Eigenschaften ermoglicht, hier besonders der mechanischen Eigenschaften – wie den Elastizitatsmodul E – und Berucksichtigung der Biokompatibilitat. Die untersuchten Sandwichverbunde sind 3-Schichtverbunde, bestehend aus Titandeckblechen (Ti Gr. 1) und einem Polypropylen-Copolymer (PP-PE)-Kern (PP-Polypropylen, PE-Polyethylen). Als Haftvermittler zwischen den Schichten dient ein Epoxidharz. Neben dem Einsatz im biomedizinischen Bereich hat ein derartiger Titan-Sandwichverbund auch das Potenzial, eine Vielzahl kommerzieller Laminate im Bereich der Luftfahrtindustrie oder sogar auch im Automotivbereich zu ersetzen. Die mechanischen Eigenschaften wurden fur unterschiedliche Kernschichtdicken im Zugversuch ermittelt. Die Ergebnisse waren in guter Ubereinstimmung mit nach der Mischungsregel vorausberechneten Werten. So lassen sich durch Variation der Schichtdicken untereinander bedarfsangepasste Sandwichverbunde mit gezielt eingestellten Kennwerten wie Dichte, E-Modul und Festigkeit erzeugen. Das Umformverhalten dieser Sandwichverbunde wurde mit Hilfe von Standardtiefziehversuchen, das wohl haufigste Verfahren zur Formgebung blechformiger Bauteile, beschrieben. Die Sandwichverbunde zeigen ein gutes Umformverhalten, das nur leicht unter dem des Monometalls liegt. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromid (MTT) wurde zur Untersuchung der Zellviabilitat menschlicher Osteosarcoma MG-63 Zellen auf den Metall- und Polymerkomponenten der Sandwichverbunde benutzt. Die Viabilitat war fur die Ti/PP-PE/Ti Sandwiche, verglichen mit der Variante eines Sandwichverbundes mit Stahldeckblechen 316L/PP-PE/316L, deutlich hoher.

Steel/polymer/steel sandwich materials (SMs) with varying core thickness were produced using the roll bonding technology. At constant skin thickness, the effect of the core thickness change on the mechanical properties, particularly their specific stiffness and strength, was investigated. Additionally, the SMs were locally reinforced with steel inlays to improve their behaviour against dimension changes or the degradation of the core in case of local loading or joining. The effect of the reinforcement (RE) on the strain distribution under deep drawing conditions was studied. Strains were measured using photogrammetry. To take into account the influence of anisotropy in this sense, an essential anisotropy evaluation was carried out for the SMs to assess their forming behaviour. The results revealed an adequate agreement between the measured mechanical properties of SMs and the estimated values following the rule of mixtures. Up to a core volume fraction of approx. 0.37, the specific stiffness and strength values of the SMs are only slightly reduced compared to the monolithic steel material. The deformation analysis shows a significant influence of the inserted REs on the strain distribution and failure and consequently the position of cracking, occurring at the bottom/edge region in front of the RE.

In the present study, coating of some magnesium alloys including AZ31 and AZ91 were studied using different techniques namely anodizing, electroless and hot press cladding. AZ91 alloy was coated using anodizing process using three types of environmental friendly electrolytes; the first based on sodium silicate, the second based on sodium hydroxide-boric acid-borax and the third on sodium silicate-potassium hydroxide-sodium carbonate-sodium tetra borate. Characterization of the anodizing layer was achieved by determination of surface morphology, microstructure, phase analysis, coat thickness, adhesion and corrosion resistance. It was found that the anodic film thickness increases with increasing the current density, anodizing voltage and deposition time until the deposition stops due to the formation of a thick anodic film. The range of the anodic film thickness is 28 42 µm.Optimization of the anodizing conditions - current density and deposition time was determined for each electrolyte. A corrosion efficiency ranging from 94% to 97% was reached; the highest value corresponding to the third electrolyte. Another study is the electroless Ni plating technique with zinc pre-treatment applied on several magnesium alloys and the effect of pre-treatment and post heat treatment on the coat characteristics. The surface morphology, surface roughness, thickness of the layer, EDX analysis, adhesion, hardness and corrosion resistance are covered in this part. The electroless layer thickness is about 6 µm. The results showed good bond quality of the coat maintaining good corrosion behaviour of electroless Ni-P based on potentiodynamic polarization tests in chloride solution where it was improved after heat treatment process. On the other hand, AZ31 was covered by a commercial pure aluminum sheet by hot pressing. The influence of the applied pressure, holding time and temperature on the bond characteristics was studied. The experimental investigation has revealed a good bond quality due to the effective mutual diffusion of Mg and Al. The phase analysis resulted in the formation of two equilibrium phases namely; Mg17Al12and Mg2Al3. The corrosion resistance of AZ31 is enhanced as a results of this process by 98.6%. Further points will be covered.Keywords: Magnesium alloys; Coating; Anodizing; Electroless; Hot press cladding; environmental friendly electrolytes; corrosion

Composite materials are widely used in different industrial fields, because of their good formability and their high strength to weight ratio. In the present work a triple-layered sandwich composite is investigated. Experimental tests at room temperature are carried out for the materials constituting the composite. A finite element model of a deep-drawing process of the composite is performed, where a finite strain constitutive model for the metal part, with material parameters calibrated to uniaxial tensile tests, has been implemented. Experimental results are compared to the numerical simulations in view of validation purposes. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Steel/polymer/steel sandwich materials (SMs) are considered an innovative substitute to the commercial steel sheets in the automotive industry due to weight-saving potential and enhanced damping properties. Deep-drawing steel and thermoplastic core are used as the skin and core sheets, respectively. The mono-materials and SMs were characterized via tensile test, deep drawing and flow limit curves (FLC) determination. The mechanical properties of the tested SMs showed a good matching with the mixture rule regardless the skin/core sheet thickness. Varying the skin/core sheet thickness has a remarkable effect on the thinning behavior under deep drawing; the core thickness increases the cracking probability. In case of using SMs with different skin-thickness, it is better to position the thin skin sheet in contact with the punch. The core thickness exhibited no significant effect on the FLC results. The thicker-core SMs are subjected to failure at lower strains in the stretching region of the FLC.