Sandwich Sheets Research Articles

Tailored Sandwich Structures in the Focus of Research

The aim of the investigations is to deliver the necessary data for modelling and simulation adapted and designed sandwich structures. Therefore, in the first step three-layer sandwich sheet, 316 L/polypropylene–polyethylene/316 L (316 L/PP-PE/316 L) with and without local reinforcement, were processed by roll bonding at 260°C of two steel sheets with a pre-rolled polypropylene-polyethylene–core sheet. Stretch test, deep drawing, and bending tests had been done to investigate mechanical and forming behavior of the parts. In order to analyze the polymer-metal interface SEM observations were done.

Development of application technique of aluminum sandwich sheets for automotive hood

Objective of this study was to develop basic techniques in order to apply aluminum sandwich sheets for an automotive hood part. The aluminum sandwich sheet is the material fabricated by adhering two aluminum skins to one polypropylene core. When it has the same bending stiffness as a steel sheet, it is 65% lighter than the steel sheet and 30% lighter than an aluminum alloy sheet. Therefore, it is notified exclusively as good substitutive materials for a steel body to improve the fuel efficiency. Through aluminum sandwich sheet, however, it has relatively lower formability than that of the steel sheet for automotive application. In this study, we developed application techniques of the aluminum sandwich sheet for automotive hood. The various formability evaluations were carried out in order to secure the fundamental data for the measurement of sheet metal forming and the establishment of optimum application conditions of the sandwich sheet. From these results, it was found that the sandwich sheet could reduce the weight and maintain the flexural rigidity simultaneously comparing to the steel sheet.

Finite Element Analysis of Heterogeneous Sandwich Sheets During Rolling

Three-dimensional DEFORMTM finite element simulations are performed to analyze the plastic deformation of heterogeneous sandwich sheets during rolling. The finite element code is based on a rigid-plastic model and the simulations assume that the rollers are rigid bodies and that the deformation-induced change in temperature during rolling is sufficiently small to be neglected. The rolled product is assumed to comprise a central sheet of either A3003 or A6063 aluminum alloy sandwiched between upper and lower sheets of A1100 aluminum alloy. The simulations examine the effects of the sheet thickness and reduction ratio on the maximum effective stress, maximum effective strain, Y-direction load, and maximum damage induced within the rolled product. The simulation results for the final thicknesses of the three layers in the rolled sandwich sheet are compared with the experimental measurements. Overall, the results presented in this study provide a useful insight into the deformation mechanisms involved in the rolling of heterogeneous sandwich sheets.

FLD determination of AL 3105/Polypropylene/AL 3105 sandwich sheet using numerical calculation and experimental investigations

Sandwich structures are gaining increase application in aeronautical, marine, automotive and civil engineering. Since such sheet can be subjected to stamping processes and their deformation limited by various defects, knowing beforehand the limiting amount of deformation is very important. For achieving this goal, sandwich sheet of Al 3105/Polymer/Al 3105 were prepared using thin film hot melt adheres. FLD of sandwich sheet was predicted using simulations by considering GTN damage model. Also FLD of prepared sheets evaluated through experimental investigations.

Formability of Aluminum 5182-Polypropylene Sandwich Sheet for Automotive Application

The AA5182/polypropylene/AA5182 (AA/PP/AA) sandwich sheet is the material fabricated by adhering two aluminum skins to one polypropylene core. When it has the same flexural rigidity as a steel sheet, it is 65% lighter than the steel sheet and 30% lighter than an aluminum alloy sheet. Therefore, it is notified exclusively as good substitutive materials for a steel body to improve the fuel efficiency. Through AA/PP/AA sandwich sheet, however, it has relatively lower formability than that of the steel sheet for automotive application. In this study, we developed formability evaluation techniques in order to apply AA/PP/AA sandwich sheet for an automotive parts. For this purpose, newly adopting formability evaluations (using limit dome height and plane strain test) were carried out in order to secure the fundamental data for the measurement of sheet metal forming and the establishment of optimum forming conditions of the sandwich sheet. The results showed that there were in good agreements between the old formability evaluation method and the new one which was more simplified than that of the old one. From the results of these formability evaluations, the formability of sandwich sheet was higher than that of aluminum alloy sheet alone which was the skin component for the sandwich sheet. In addition, it was found that sandwich sheet could reduce the weight and could have the same flexural rigidity simultaneously when it was compared to the automotive steel sheet.

Numerical and experimental investigations on HYLITE sandwich sheets as an alternative sheet metal

Current developments show that in the field of sheeting alternative material concepts are successfully applied. In this context metal plastic sandwiches, which are composed of two thin metallic surface layers and a polymer core, represent an interesting group of semi-finished products. Compared to conventional sheet metal materials the structural modification caused by sandwich design provides an increased specific flexural rigidity. Extensive experimental and numerical investigations were carried out for the characterisation of this still young group of semi-finished products. The evaluation of suitable calculation methods represents a crucial step to a broad application of semi-finished metal plastic sandwiches within bulk production processes.

Resistance welding of thin stainless steel sandwich sheets with fibrous metallic cores: experimental and numerical studies

This paper concerns resistance spot welding (RSW) of two types of thin stainless steel sandwich sheet. The cores of these materials, made of stainless steel fibres, are highly porous (> around 85 vol.-%) and have low thermal and electrical conductivities. However, these conductivities change during the compression and heating associated with RSW. A sequentially coupled finite element model has been developed, in which the crushed core is treated as a continuum, with properties which vary throughout the process. It is shown that a constitutive relationship of the type commonly used for crushable foams can be successfully employed to simulate the deformation of the sandwich sheets. The thermoelectrical part of the model incorporates the effects of the associated phase transformations and changes in interfacial conductance. It is shown that the predictions are broadly consistent with data obtained during welding experiments. The model is used to explore the effects of welding parameters on weld characteristics (weld pool formation and weld nugget shape).

The Influence of Temperature on the Forming Behavior of Metal/Polymer Laminates in Sheet Metal Forming

The influence of temperature on the forming behavior of an aluminum/polypropylene/aluminum (APA) sandwich sheet was studied. Shear and tensile tests were performed to determine the mechanical properties of the laminate and the component materials as a function of process temperature. The forming limit diagram (FLD) of the laminate was established for two different temperatures, and its springback behavior was examined in four-point bend and channel bend tests. Cup forming tests were performed at various test temperatures to determine the limiting drawing ratio (LDR) and the tendency for wrinkling at these temperatures. Although there was only a minor influence of temperature on the mechanical properties and the FLD values of the laminate, the bend test results reveal that springback can be reduced by forming at higher temperature. The decreasing strength of the core material with rising process temperature led to an increased tendency of the laminate to wrinkle in the heated cup drawing tests.

Tensile properties of stainless steel sandwich sheets with fibrous cores

The unnotched and notched tensile properties of flocked and brazed stainless steel sandwiches with fibrous cores were examined. The tensile stress–strain responses show that the fibres do not carry any load in the flocked sheets and that the load transfer is better facilitated in the brazed sandwich sheets. Notched strength results show that the flocked sheets are notch-insensitive whereas the brazed sheet’s strength is highly sensitive to short notches.

P-30 Formability of Aluminum 5182-Polypropylene Sandwich Sheet for Automotive Application

The AA5182/polypropylene/AA5182 (AA/PP/AA) sandwich sheet is the material fabricated by adhering two aluminum skins to one polypropylene core. When it has the same flexural rigidity as a steel sheet, it is 65% lighter than the steel sheet and 30% lighter than an aluminum alloy sheet. Therefore, it is notified exclusively as good substitutive materials for a steel body to improve the fuel efficiency. Through AA/PP/AA sandwich sheet, however, it has relatively lower formability than that of the steel sheet for automotive application. In this study, we developed formability evaluation techniques in order to apply AA/PP/AA sandwich sheet for an automotive parts. For this purpose, newly adopting formability evaluations (using limit dome height and plane strain test) were carried out in order to secure the fundamental data for the measurement of sheet metal forming and the establishment of optimum forming conditions of the sandwich sheet. The results showed that there were in good agreements between the old formability evaluation method and the new one which was more simplified than that of the old one. From the results of these formability evaluations, the formability of sandwich sheet was higher than that of aluminum alloy sheet alone which was the skin component for the sandwich sheet. In addition, it was found that sandwich sheet could reduce the weight and could have the same flexural rigidity simultaneously when it was compared to the automotive steel sheet.

Serration Phenomena of AA5182/Polypropylene/AA5182 Sandwich Sheets

It has been reported that the 5182 aluminum sheet shows Lüders band because of dissolved Mg atoms that cause fabrication process problem, especially surface roughness. The examination of serration phenomena has been made after the tensile deformation of the AA/PP/AA sandwich sheets as well as that of the 5182 aluminum. All sandwich sheets and the 5182 aluminum skin showed serration phenomena on their flow curves. However, the magnitude of serration was significantly diminished in the sandwich sheet with high volume fraction of the polypropylene core. According to the results of the analysis of the surface roughness after tensile test, Lüders band depth of the sandwich sheet evidently showed lower than that of the 5182 aluminum skin. The strain rate sensitivity, m-value, of the 5182 aluminum skin was -0.006. By attaching these skins to the polypropylene core, which has relatively large positive value of 0.050, m-value of the sandwich sheets changed to the positive value.

피라미드 코어를 가진 샌드위치 판재의 두께 방향 압축 특성에 대한 연구

Sandwich sheet with inner structure is expected to find many applications because of high stiffness to mass ratio. However, low resistance to the compressive pressure in the thickness direction is a dominating factor in the formability of sandwich sheet. In this study, sandwich sheet with pyramid type core is considered. For the compressive characteristics in the thickness direction, experiments and finite element simulations are carried out. In the experiment, deformation behavior is observed and discussed as the compression proceeds. It is shown that a corresponding finite element simulation can give a reasonable agreement with experiment in terms of maximum pressure. However, simulation shows some discrepancy from the experiment in terms of compressive pressure-displacement characteristics. The reasons for this discrepancy are studied in the geometrical imperfectness of sandwich sheet. It is also observed that most of deformation is dominated by buckling mode of pyramid legs.

SERRATION BEHAVIOR OF AA5182/POLYPROPYLENE/AA5182 SANDWICH SHEETS

The examination of serration behavior has been made after the tensile deformation of the AA/PP/AA sandwich sheets as well as that of the 5182 aluminum skins. All sandwich sheets and the 5182 aluminum skin showed serration behavior on their flow curves. However, the magnitude of serration was significantly diminished in the sandwich sheet with high volume fraction of the polypropylene core. According to the results of the analysis of the surface roughness following the tensile test, Lüders band depth of the sandwich sheet evidently showed lower than that of the 5182 aluminum skin. The strain rate sensitivity, m-value, of the 5182 aluminum skin was -0.006. By attaching these skins to the polypropylene core, which has relatively large positive value of 0.050, m-value of the sandwich sheets changed to a positive value. The serration reduction of the sandwich sheets was quantitatively investigated with respect to the effect on polypropylene thickness variation, that on the strain rate sensitivity and that on the localized stress state. It was found that the serration reduction degree from the experimental results of the sandwich sheet was higher than from the calculated values by the rule of mixture based on the volume fraction of the skins and the core.

Joining of lightweight sandwich sheets to aluminium using self-pierce riveting

Lightweight sandwich sheets are a novel alternative lightweight material for automotive vehicle body manufacture. This paper presents the results from an investigation into the joining of this material to aluminium using self-pierce riveting. Comparative trials conducted on similar thickness bulk aluminium joints show that whilst this material combination can be joined using SPR with a variety of die profiles, joining lightweight sandwich sheets to aluminium shows greater sensitivity to changes in this parameter, with the result that substrate defects occur within the joint.

Correlation between Protein Stability Cores and Protein Folding Kinetics: A Case Study on Pseudomonas aeruginosa Apo-Azurin

This paper reports a combined computational and experimental study of the correlation between protein stability cores and folding kinetics. An empirical potential function was developed, and it was used for analyzing interaction energies among secondary structure elements. Studies on a beta sandwich protein, Pseudomonas aeruginosa azurin, showed that the computationally identified substructure with the strongest interactions in the native state is identical to the "interlocked pair" of beta strands, an invariant motif found in most sandwich-like proteins. Moreover, previous and new in vitro folding results revealed that the identified substructure harbors most residues that form native-like interactions in the folding transition state. These observations demonstrate that the potential function is effective in revealing the relative strength of interactions among various protein parts; they also strengthen the suggestion that the most stable regions in native proteins favor stable interactions early during folding.

Forming Limit of Electrodeposited Nickel Coating in the Left Region

A uniform nickel (Ni) coating was bilaterally electrodeposited on the low-carbon steel substrate for the application of advanced battery shells. Its forming limit was investigated by Hill localized necking theory coupled with finite element simulation and scanning electron microscopy. The effective stress and effective strain in the Ni coating and steel substrate are deduced using Hill’s anisotropic yield function. The localized necking condition is derived by sandwich sheet analysis, and the forming limit strains are obtained by solving the nonlinear equation of the localized necking condition. Extensive calculations are carried out using the proposed model. This study exhibits the nickel coating thickness and the normal anisotropic coefficients of the coating and substrate have little influence on the forming limit curve (FLC) in the left region of the coated sheet, but the strain hardening exponents of the coating and substrate have much effect on it. The calculated result matches well with the measured data in uniaxial tension. This investigation is useful for the preparation of the electrodeposited Ni coating and helpful for the forming operation of the battery shells.

Multi-scale finite-strain plasticity model for stable metallic honeycombs incorporating microstructural evolution

This paper deals with the development of a mechanism-based two-scale constitutive model for thick-walled metallic honeycombs in sandwich applications. The mechanical response of metallic honeycomb sandwich sheets subject to large in-plane normal loading and out-of-plane shear loading is investigated using a detailed finite element model of the honeycomb microstructure. Based on the simulation results, a simple micro-mechanical system is proposed and used to develop the macroscopic constitutive model. The finite-strain constitutive model accounts for microstructural evolution due to geometrical changes and strain hardening at the microscale. The macroscopic model has been validated for various loading conditions. Furthermore, the evolution of the macroscopic yield surface for pure out-of-plane shear is discussed in detail.

On the Crashworthiness of Shear-Rigid Sandwich Structures

Abstract This paper deals with the evaluation of the crashworthiness of thin-walled sandwich box structures for automotive applications. Quasi-static crushing simulations are carried out to estimate the energy absorption of prismatic box columns made from sandwich sheets. The sandwich sheets have perforated cores of different densities with staggered holes perpendicular to the panel faces. It is found that the specific energy absorption of columns made of sandwich sheets is approximately the same as that of conventional columns composed of homogeneous sheets of the same total wall thickness. Furthermore, theoretical analysis indicates that by increasing the core thickness, sandwich structures could be up to 50% lighter while providing the same mean crushing force. However, these gains may not be achieved in practical applications since increasing the core thickness also increases the likelihood of premature face sheet fracture during crushing.

접합판재의 전단 변형거동에 관한 연구

In order to improve the quality of the sheared surface in cutting of inner structure bonded sheet metal the cut-off operation is mainly investigated, which is the typical shearing process in sheet metal forming technology. The sandwich sheet metals considered have inner structure which is constructed in the form of crimped expanded metal and woven metal. The inner structure is bonded between solid sheet by resistance welding or adhesive bonding. The shearing process is visualized by the computer vision system installed in front of the cut-off die and the sheared surface is measured and quantitatively compared with the help of the optical microscope after cut-off operation. From test results we found that the influence of sheared position can be observed and explained clearly and this result can be utilized to get the better sheared surface.

Development of Formable All‐Metal Sandwich Sheets for Automotive Applications

This paper describes the development of thin all‐metal sandwich sheets. Sandwich sheets are used in various engineering applications, but the lack of formability and weldability has prevented their wide spread use in the automotive industry. The failure modes of state‐of‐the‐art sandwich sheets in forming operations have been analyzed in detail. Based on theoretical analysis, a formable prototype sandwich sheets has been designed. A draw bending experiment has been performed to demonstrate the formability of this prototype sheet.