Isogrid Structures Research Articles

Neural network assisted for parameters uncertainty of isogrid tube under different load types

Isogrid structures offer an excellent balance between mass and rigidity, making them a crucial component in various industrial sectors. However, like all types of structures, isogrids are susceptible to performance degradation due to uncertainties in geometrical and material parameters arising from manufacturing errors and exposure to critical service environments. This paper addresses the effects of parameter uncertainty on the structural behavior of isogrid tube structures. To this end, a Sobol index is employed to assess the sensitivity of the tube’s natural frequency, axial buckling, torsional buckling, and overall mass to three geometrical and one material parameter, each subject to a 10% random variation. The data for this analysis were generated using a parametrized numerical model specifically developed for this purpose. To optimize computational costs further, an artificial neural network predictive model is proposed, which accurately replicates the behavior of the numerical model. The results indicate that the angle between helicoidal ribs is the most influential parameter.

Wall panel structure design optimization of a hexagonal satellite

Considering that it satisfies high strength and stiffness at a low weight, the grid structure is the ideal option for meeting the requirements for developing the wall panel structure for the satellite. The most attractive grid structures for the satellite wall panel industry are isogrid and honeycomb structures. The first part of this work involves studying the mechanical and dynamic performance of five designs for the satellite wall panel made of 7075-T0 Al-alloy. These designs include two isogrid structures with different rib widths, two honeycomb structures with different cell wall thicknesses, and a solid structure for comparison. The performance of these designs was evaluated through compression, bending, and vibration testing using both finite element analysis (FEA) with the Ansys workbench and experimental testing. The FEA results are consistent with the experimental ones. The results show that the isogrid structure with a lower rib thickness of 2 mm is the best candidate for manufacturing the satellite wall panel, as this design reveals the best mechanical and dynamic performance. The second part of this work involves studying the influence of the length of the sides of the best isogrid structure in the range of 12 mm–24 mm on its mechanical and dynamic performance to achieve the lowest possible mass while maintaining the structure’s integrity. Then, a modified design of skinned wall panels was introduced and dynamically tested using FEA. Finally, a CAD model of a hexagonal satellite prototype using the best-attained design of the wall panel, i.e., the isogrid structure with a 2 mm rib width and 24 mm-long sides, was built and dynamically tested to ensure its safe design against vibration. Then, the satellite prototype was manufactured, assembled, and successfully assessed.

Material choice to optimise the performance index of isogrid structures

Three key qualities should define the structures used in the aviation industry: they should be light, rigid, and strong. These goals can be met by selecting lightweight, high-performance materials like titanium alloy or composites, but careful structural design is also crucial to improve mechanical performance. The structures known as isogrids, which consist of a skin reinforced by a lattice frame, offer an effective way to meet the aforementioned specifications. The structural performances of isogrid-stiffened cylinders composed of various materials were compared in the current work. The structures under investigation were composed of titanium alloy, carbon fibre composite material, or a combination of both. A FEM model was proposed and validated by comparison with experimental results obtained from a composite material structure, and then it was used to simulate the behaviour of all the other structures. While there was some variation in the strength of the parts, it was discovered that the stiffness was almost uniform throughout all of the structures that were examined. But when the weight of the various constructions was taken into account, some very intriguing findings emerged: the composite material-only structure proved to be the most effective because it had the highest specific performances.

An efficient deep learning model to predict the structural response of CFRP isogrid tubes

Several sectors have increased the use of lattice structures due its great capacity to reduce the structural mass with reasonable rigidity loss. However, these structures can present complex mechanical behaviors, impossible to be determined analytically. Surrogate models obtained from design of experiments have been shown to be promising but insufficient. Numerical models using finite elements are computationally expensive when optimization model updating is considered. In order to solve these problems, in this paper a deep learning model is trained in order to predict 16 different structural responses (static, dynamic and stability) of a complex composite isogrid structure tube. All input data were generated from a numerical finite element model. The results demonstrated substantial capacity of the deep learning model to fit the isogrid physical behavior and also predict the structural responses. In addition, it was also to predict the design parameters of the isogrid structure from the desired results, also demonstrating the good performance (R2 > 90 %) of the artificial intelligence model to perform this prediction.

Behavioural Study of Truss Bridge using Isogrid Members

The search for lightweight and highly efficient structural components is a continuing process. Reducing the structural weight and improving the load carrying capabilities of these structures will allow designers to append additional capabilities while reducing cost. Isogrid is a lattice of stiffened ribs forming an array of contiguous equilateral triangles. This rib pattern forms triangular trusses by maintaining isotropic property. Ribs when arranged in 60? pattern are known as Isogrid. The highly redundant nature of Isogrid stiffening concept provides high efficiency distributing loads and is less susceptible to impact damage, delamination, and crack propagation. Isogrid structure is typically found in stiffness critical components that resist buckling. The behavior and performance of Isogrid deck slab in a Bridge supported by the truss girders is studied. Isogrid is modeled, analyzed and designed using commercial Finite Element (FE) software. In the present work, a truss bridge is designed for a span of 10.305 m. The bridge is designed using three different kinds of deck configuration, rectangular section without skin, inverted T section with skin, and I section with skin. Commercial FE software is used for computing deflections and stresses. It is found that the deck profile of I section with skin is more preferable than other configurations for Truss Bridge.

Examination of isotropy assumption in isogrid structures through analysis and experimentation on four isogrid variations

An isogrid is a lattice structure with a high strength to weight ratio making it an ideal structure for spacecraft. Isogrids were originally designed to yield isotropic properties; however, recent finite element analyses show that isogrids do not exhibit isotropic behavior. Isogrids are theorized to be isotropic because of the equal distribution of stresses induced by the structure’s geometry. To determine the isotropy of an isogrid, truss and finite element analyses are executed to predict failure among four various isogrid specimens. The isogrid specimens are 3D printed and vary in geometry to determine the effect of geometric parameters on the isotropy of the structure. In addition, experimental tests are conducted by applying compressive loads to the specimens using a universal testing machine (UTM) with digital image correlation (DIC) to measure strain. The analyses indicate that isogrids are not isotropic because of the observed unequal load distributions.

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.

Damage detection in Composite laminates by Fiber optic sensors

Fiber optic sensors, both FBG point sensors and distributed sensors based on OFDR, are accepted and validated as temperature and strain sensors, enjoy a high TRL and are already in use in many industrial applications. The determination of occurrence of damage from strain measures is a technique still not mature, its TRL can be 2-3. A local crack can greatly weaken a structure, it will be the point of initiation of the catastrophic failure, but until the failure has occurred, the crack only causes very small changes in the overall behavior of the structure (stiffness, natural frequencies, strain field, etc.). Therefore, and unless the position of the crack coincides with the predetermined position of the sensors, it is not easy to detect the existence of damage from strain measurements. In this work two parallel techniques, experimentally validated, are presented. The first one is to use distributed measurement, with an optical fiber placed in the area where the damage is expected. It is verified that a delamination causes residual strains in the delaminated area, of  significant value, and that will be detected by the fiber, if it crosses the delamination zone. The second technique is to compare the strains measurements obtained at different points, when the structure subjected to external loads. Although the changes are going to be very small, local damage causes a redistribution of the rigidity of the structure, and of the load paths, and therefore the strains readings, may be slightly different. Results of the application of the model are presented to actual composite elements, such as an isogrid structure, and a small wind turbine blade.

Effects of deposition - strategy - induced raster gaps and infill voids on the compressive strength of 3D printed isogrid structures

Additive Manufacturing (AM) parts are attractive for many applications. AM can produce parts of complex geometries in small batches with short lead times in a wide range of materials. While parts are commonly used in non-load bearing functions, improving mechanical properties can help expand their use in engineering applications. This work evaluates the effects that AM process conditions have on part strength. The relationship between design characteristics and path planning induced imperfections is discussed. The effects that raster gaps and internal voids have on the compressive strength of composites are analyzed based on the results of compressive tests and computer simulations.

Genetic algorithm based design optimization of crashworthy honeycomb sandwiched panels of AA7075-T651 aluminium alloy for aerospace applications

Crashworthiness studies, for decades have been an area of tremendous interest in aerospace and automotive sectors, as ensuring the safety of the occupants in the vehicle is a primary goal. Honeycomb sandwich panels are generally used for building floor, ceiling and other important fuselage parts in a commercial airliner to make the structures shock-resistant. In this work, optimization of the design of crashworthy sandwiched honeycomb structure was carried out using a non-dominated sorting genetic algorithm (NSGA) . The stated algorithm had actively monitored the variation of the geometric parameters. To study the shape effect of the cells which absorb impact energy, three cellular shapes namely hex-grid, ortho-grid and iso-grid structures were considered for analyzing their deformation behavior under impact loading. A multi objective function in the genetic algorithm was implemented in MATLAB, where the objectives were to minimize weight and to maximize the absorbed impact energy while constraining the maximum transmitted force and displacement due to crushing. Sandwiched aluminum (AA7075-T651) honeycomb structures were modeled in ABAQUS using python scripts , with the number of core cells and the wall thickness of each core cell being optimized through genetic algorithm in MATLAB using an interactive mechanism. Significant improvements were observed in terms of reduction of weight and increase in the ability to absorb the specific energy during crushing in the sandwiched panels after 450 iterations of optimization cycles. A novel methodology in the domain of crash analysis of aerostructures was established with design optimization of honeycomb sandwiched panels.

Performance index of isogrid structures: robotic filament winding carbon fiber reinforced polymer vs. titanium alloy

ABSTRACT The structures adopted in the aeronautic field should have three main characteristics: they must be strong, stiff, and light. These targets can be obtained by choosing high performance and low weight materials, as composite or titanium alloy, but also the wise design of the structure itself is important for enhancing the mechanical performances. The isogrid structures, that are composed of a lattice frame reinforcing a skin, represent a very interesting solution to fulfill the abovementioned requirements. In the present work, a comparative analysis of the structural performances of lattice-stiffened cylinders made of different materials was carried out. The studied parts were made of carbon fiber composite material or titanium alloy, while a FEM model was implemented and verified for this study. The cylinder made of composite material was produced through robotic filament winding, an innovative technology that allows the attainment of high-quality parts. It was found that the strength and the stiffness of the structures were almost the same for both the analyzed material, but very interesting results were determined by considering the weight of the different structures: the composite material one resulted to be the most performant since it had the highest specific performances.

Automated draping analysis of 3D printed flexible isogrid structures for textile applications

Fused filament fabrication (FFF) 3D printing can be used for manufacturing flexible isogrid structures. This work presents a novel draping analysis of flexible 3D printed isogrids from thermoplastic polyurethane (TPU) using image processing. A small-scale multi-camera automated draping apparatus (ADA) is designed and used to characterize draping behavior of 3D printed isogrid structures based on draping coefficient (DC) and mode. Circular specimens are designed and 3D printed that accommodate up to eight additional weights on their perimeters to enhance draping. Five infill patterns, three infill percentages, and three loading cases are explored to evaluate their impact on specimens’ draping coefficient and mode, resulting in 45 tests. The range of DCs in this study is 21.9% to 91.5%, and a large range of draping modes is observed. For the lowest infill percentage, specimen mass is not the sole contributor to the DC values and the infill pattern has a significant impact for the three loading cases. Considering draping modes, the maximum number of convex and concave nodes observed for 25% infill specimens with added weights is three. The draping behavior characterization developed in this study can be followed to design and 3D print new flexible isogrids with textile applications.

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.

Multiobjective design optimization of CFRP isogrid tubes using sunflower optimization based on metamodel

In this paper, the authors carried out the optimization of an isogrid structure considering six different responses: Tsai-Wu failure index under compression and torsion efforts; instability coefficient under compression and torsion efforts; mass and natural frequency. The response surface methodology was used to find the functions that describe the model from the data found by numerical analysis; and a new optimization algorithm called SunFlower Optimization (SFO) was used to find the best possible configurations. This paper shows something unprecedented in the literature to date when evaluating the compression, torsion, and modal performance of an isogrid tube. The simultaneous evaluation of several responses brings something more real to the scientific world, the results obtained here suggest that the optimal configuration for one response can be very bad for others and the use of a multi-objective optimization solved this problem.

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.

Environmental and buckling performance analysis of 3D printed composite isogrid structures

Additive manufacturing of composite materials is gaining important market shares, especially in the aerospace field, since it leads to a reduction of the environmental impacts while ensuring high product performances. Structures of particular interest are isogrids due to their high compression strength-to-weight ratio. In this research, isogrids and solid panels were 3D printed using carbon fiber reinforced polyamide. All the parts presented the same width, height and specific resistances but they differ in thickness, ribs dimensions and drying process after printing. A comparison between their environmental impacts and buckling loads have been conducted. The objective was to determine the configuration which leads to the best compromise between sustainability and mechanical performances.

3D printing and testing of composite isogrid structures

The present work aims at studying the effect of geometric parameters of isogrid structures on their buckling behavior. To this purpose, isogrid structures in polyamide reinforced with short carbon fibers, with different rib widths, rib thicknesses, and cell heights, were additively manufactured using the fused deposition modeling technology; then, they were subjected to compression test until the occurrence of buckling. It was observed that isogrid structures can undergo to different failure modes, local and global buckling, depending on the values of geometrical parameters. Furthermore, the geometrical parameters that lead to the highest strength are different to those providing the highest specific strength. However, the specific strength of the 3D printed composite material is higher than those of 1XXX and 3XXX aluminum alloys. Rib thickness was characterized by the highest effect on both strength and specific strength while the cell height results in the lowest contribution. Finally, optical and scanning electron microscopies were carried out in order to analyze the fractured ribs and to obtain high magnification three-dimensional topography of fractured surfaces after buckling. The effect of moisture content on polyamide reinforced composites and the comparison between 3D printed and traditionally produced isogrid structures will be investigated in future researches.

Isogrid lattice structure for armouring applications

Isogrid structure is a grid stiffening structure formed by partially hollowing out triangular shapes to produce rib features on the surface of the plate. These features are widely used in the aerospace industry for producing lightweight with efficient structures. These structures are usually expensive to manufacture using conventional subtractive manufacturing processes. Therefore, this work involves checking the feasibility of design optimization for additive manufacturing(AM) of Isogrid and Non-Isogrid structure-based structural components subjected to impact loads. Izod impact test, as per ASTM D256, on seven specimens, were performed to check the energy that the material is capable of withstanding for the samples made using various AM parameters(layer height=0.2mm, feed rate 1800mm/min, bed temperature=70◦C, Nozzle temperature= 210 ◦C). Analysing the results of Izod impact test, the projectile velocity of impact for a trivial plate such as of 5mm thickness was used. The results from a trivial case impact test were used to predict the velocity of impact on the identical volume samples. The identical volume samples such as plate, plate stiffened by Isogrid without H-ribs, plate stiffened by Isogrid with H-ribs were used. Also, these results were correlated with simulations, and it was found that Isogrid stiffened plate with H-ribs was more stable.

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.

Analysis of elastic wave propagation characteristics in isogrid structures

Analysis of elastic wave propagation characteristics in isogrid structures