Isogrid Panel Research Articles

Compression behavior of 3D printed isogrid cylindrical shell structures using experimental and finite element modeling

AbstractLattice structures have been widely used in aircraft and automobile industries due to their excellent mechanical properties namely high specific strength, specific stiffness, and energy absorption capability. On the other hand, additive manufacturing that is considered as an essential for Industry 4.0 offers incredible opportunities for product development and production flexibility. Previous research on 3D printed isogrid structures focused on isogrid panels and their buckling behavior, whereas isogrid lattice cylindrical shells garnered less attention. This work reports the effect of short carbon fiber reinforcement with polyamide three‐dimensional printing material on the compression response of isogrid lattice shell structures by experimental and numerical modeling. Isogrid cylindrical shells were three dimensionally printed using fused deposition modeling. Initially, test coupons were printed using polyamide and carbon fiber reinforced polyamide and their mechanical properties were found using uniaxial tensile testing. The obtained tensile properties were given as an input to the numerical modeling performed using LS‐DYNA®. The peak load and the maximum displacement of the printed isogrid lattice shells subjected to axial compression loads were experimentally evaluated. The numerical findings were compared with those produced using experimental methods. The error in estimating the peak load of lattice cylinders through numerical modeling was limited to 5.35%. The effect of geometric parameters namely rib width (helical and hoop), shell thickness, helical angle of ribs on the buckling strength was also studied.

Effect of Geometric Parameters and Moisture Content on the Mechanical Performances of 3D-Printed Isogrid Structures in Short Carbon Fiber-Reinforced Polyamide

The present paper aims at studying the effect of geometric parameters and moisture content on the mechanical performances of 3D-printed isogrid structures in short carbon fiber-reinforced polyamide (namely Carbon PA). Four different geometric isogrid configurations were manufactured, both in the undried and dried condition. The dried isogrid structures were obtained by removing the moisture from the samples through a heating at 120 °C for 4 h. To measure the quantity of removed moisture, samples were weighted before and after the drying process. Tensile tests on standard specimens and buckling tests on isogrid panels were performed. Undried samples were tested immediately after 3D printing. It was observed that the dried samples are characterized by both Young modulus and ultimate tensile strength values higher than those provided by the undried samples. Similar results were obtained by the compression tests since, for a given geometric isogrid configuration, an increase in the maximum load of the dried structure was detected as compared to the undried one. Such discrepancy tends to increase as the structure with the lowest thickness value investigated is considered. Finally, scanning electron microscopy was carried out in order to analyze the fractured samples and to obtain high magnification three-dimensional topography of fractured surfaces after testing.

Buckling behavior of 3D printed composite isogrid structures

Different 3D printed composite isogrid structures in polyamide reinforced with 20% in weight of short carbon fiber were manufactured by means of fused deposition modeling process. Six configurations were realized varying the rib width and the rib thickness of the structures. The isogrid panels were tested under compressive load in order to investigate the effect of geometric parameters on the buckling behavior, in terms of strength and specific strength. Different failure modes were identified, depending on geometric parameters: global and local buckling. Finally, optical microscopy was carried out in order to analyze the fractured ribs after buckling. It was demonstrated that the configurations which result in the highest strength are not the same of those providing the highest specific strength.

Manufacturing of Isogrid Composite Structures by 3D Printing

In this research, isogrid panels in polyamide reinforced with short carbon fibers were manufactured by means of a 3D printing fused filament fabrication process. Before printing, the composite material was dried for 4 hours at 120°C in order to remove the humidity adsorbed by the polyamide. Then, during the printing process, the spool was kept at 70°C. The extrusion was performed at 240°C, with an infill density equal to 100%. The effect of geometric parameters, in terms of rib thickness and cell height, on the compressive strength and buckling behavior of the isogrid panels was investigated by means of compression tests carried out at room temperature on a servohydraulic testing machine. It was shown that the specific maximum compressive load at the onset of buckling increases with rib thickness. Furthermore, the isogrid panel characterized by the lowest cell height exhibits the highest specific maximum compressive load. Finally, the analysis of the isogrid panels after testing showed that failure is caused by global buckling failure mode; this suggests that the structure slenderness is higher than that of the ribs.

Design and mechanical properties of hierarchical isogrid structures validated by 3D printing technique

Based on general lattice structure, a hierarchical isogrid (isotropic grid) structure with T-ribs was designed to enhance the buckling resistance and plastic performance, and manufactured by three-dimensional (3D) printing technique. It is proposed that under edgewise compression, the latticed panel has three structural failure modes, including material failure, global buckling and local buckling. Hierarchical topology simultaneously improves the out-of-plane and in-plane rigidity of the lattice ribs, as T-ribs balance the global bending rigidity and the local rib bending rigidity, endowing the panel higher buckling resistance. In the stage of post-failure plastic bending, the T-rib lattice shows good load-carrying ability and deforming ductility. Based on three failure modes, a multi-failure theory was built and verified by experiments and finite element method (FEM). A plastic model for the hierarchical isogrid panels was built to predict the post-failure deformation. The failure mode map method was proposed, providing reference for further optimal design.

Fabricating patch antennas within complex dielectric structures through multi-process 3D printing

In this work, a 3D printed patch antenna is fabricated within a complex dielectric structure relevant to the construction of satellites – an isogrid panel. The antenna was fabricated via a multi-process, hybrid, additive manufacturing system that included polymer material extrusion enhanced with complementary manufacturing capabilities of foil placement and patterning, wire integration and component placement. The antenna design targeted the commercial frequency of Bluetooth communication at 2.4 GHz by introducing a rectangular conductor of precise width, height and thickness from ground plane for the specific resonance. The measured reflection and gain coefficients were reasonable, however, two challenges were identified with the fabrication related to (1) imperfections typical of material extrusion additive manufacturing processes including unintentional porosity and (2) the insecure mechanical bonding between the output connector and substrate. Porosity impacted the dielectric features (permittivity) of the substrate and consequently introduced error in final antenna resonance (2.13 GHz versus the target of 2.4 GHz). The bonding affected mechanical reliability and caused changes in input impedance which affected signal quality for some orientations depending on cable flexing. Several remediations were identified, all of which included reinforcing the connector during embedding with a bonding agent. In the end, the antenna was compared to a commercial dipole antenna and the signal-to-noise ratios were within 6%.

Parametric optimization of grid-stiffened composite panels for maximizing their performance under transverse loading

The main focus of this paper is the optimization of geometry to maximize the specific energy absorption of E-glass/polypropylene isogrid composite panels under transverse quasi-static and dynamic impact loading using finite element analysis. The behavior of some of these grid-stiffened composite panels was also analyzed experimentally under high velocity impact loading, and the fluctuations observed in the load–time response during the impact event were attributed to structural resonances of the impactor, the isogrid panel or both combined. Parametric studies of varying the geometry (rib width and thickness; center-to-center distance between rib joints and skin thickness) to maximize specific energy absorption were performed. This study will help in recommending isogrid composite panels for the design and use in applications where impact energy absorption is important, such as in the side doors of automobiles.

알루미늄 lsogrid 패널의 좌굴시험 및 비선형 해석

There are many methods to reinforce the cylindrical structure for light weight design like skin-stringer and semi-monocoque. Isogrid is one of the reinforced structures to improve buckling load. Isogrid has many advantages for complex load case, internal pressure and concentrated load.In this paper, compressive buckling test and non-linear FE analysis of the isogrid panel are described. Diameter of panel is 2.4m and thickness of plate is 11.43mm. The angle which the panel accomplish is about 70 degrees and, its height is about 660mm. Local buckling, global buckling and variation of stiffness after local buckling were observed during buckling test of the panel. MSC/MARC is used for non-linear FE analysis. When analysis, initial imperfection of panel which occurred during plastic forming is considered. The results of analysis for buckling mode and buckling load have good agreements with test.ጊ缀Ѐ㘰〻Ԁ䭃䑎䷙3㠵㬅K䍄乍쐗ጊ谀Ѐ㌸㠻Ԁ䭃䑎䶯᜜፭

Instability of thin composite isogrid panel during autoclave cure cycle

This paper describes the analyses performed to determine why nominally flat composite isogrid panels designed for the Clementine I satellite were warping during the autoclave cure cycle. Analytical models indicated that the largest factor was the mismatch in the coefficient of thermal expansion of different parts of the tooling. The next most important factor was the coefficient of thermal expansion mismatch between the skin and rib materials of the composite isogrid itself. A new tooling design eliminated the first factor, producing a rib-only panel with no warping. An analytical model was developed, which predicted that warping caused by the rib/skin mismatch would be 3.31 mm over a length of 147.32 cm. A panel with the skin was manufactured and found to have a warp of 3.80 mm. Further improvements in producing flat panels will depend on finding appropriate materials for the rib and skin.