Failure Mechanism Maps Research Articles

Bending and compressive properties of ultralight carbon fiber honeycomb sandwich beams via stretching process

Due to excellent thermal stability and high specific strength, there are high requirements for all-carbon fiber composite honeycomb sandwich structure (ACFH) in the field of space observation, especially as the support of space telescope and satellite antenna. However, there are few studies on the mechanical properties of ultra-low density ACFH (ρ < 50 kg/m3). Based on the stretching process, the ultra-low density curved-wall ACFH is prepared, and its three-point bending performance and in-plane compression performance are deeply studied by means of theoretical and experimental methods. The interaction and competition mechanism of various failure modes were primarily revealed based on the failure mechanism map. In addition, the mechanical properties of specimens prepared through stretching process were tested and analyzed. The research results shows that the theoretical prediction and experimental testing agree very well in terms of failure modes and ultimate loads. Finally, some suggestions for improving the mechanical properties of ultra-low density ACFH are given, which lays the solid foundation for its application in advanced engineering fields.

Bending behaviors of carbon fiber composite honeycomb cores with various in-plane stiffness

Designing curved surfaces with a traditional straight-walled honeycomb is challenging due to its excessive in-plane stiffness, making it prone to fracturing during bending. The research motivation is overcoming the flexibility limitation of conventional straight-wall honeycombs with the new curved-wall design. Moreover, the three-dimensional failure mechanism map based on the theoretical models is expected to contribute to the design of a carbon fiber composite curved-wall honeycomb. This paper outlines the fabrication process using a modified co-curing method. It also includes theoretical models developed to examine the effect of the center angle of curved walls on the honeycomb’s in-plane stiffness and bending behavior. In-plane tensile and three-point bending tests were conducted to verify the theoretical modes. Finite element model was created to study the stress distribution and damage degree. The study is also aimed at examining the load-bearing capacity of sandwich beams with curved-wall honeycomb cores. A three-dimensional failure mechanism map shows how the failure modes of sandwich structures are affected by the center angle of the curved walls. The study offers a new approach to designing carbon fiber composite honeycombs with flexible bending deformation and high load-bearing capacity. These honeycombs could potentially be used in lightweight launch-vehicle shell structures.

Fabrication and failure mechanisms of ultralight all-CFRP sandwich cylinders under axial compression

Ultralight all-CFRP honeycomb sandwich cylinders were fabricated using a stretching process. Subsequently, critical failure loads corresponding to five typical failure modes of the sandwich cylinders under axial compression were obtained through theoretical derivation. Three-dimensional failure mechanism maps were generated, which intuitively revealed the influence of the dimensionless parameters on structural failure. The panel thickness was selected as a variable, and quasi-static axial compressive tests were performed on the sandwich cylinders. Two failure modes, intracellular buckling and face crushing, were observed, which is consistent with theory. The experimental results were analysed and discussed systematically. The ultralight all-CFRP honeycomb sandwich cylinders were compared with existing cylinders to reveal their bearing advantages. The established failure mechanism maps provide guidance for the preparation and optimisation of honeycomb sandwich cylinders. Compared with the traditional fabrication processes of honeycomb cores, the novel stretching process is expected to achieve mass production, which is helpful to provide technical support for the lightweight manufacturing of aerospace structural components.

Failures of geometrically asymmetric steel-UHPC composite beams

Geometrically asymmetric steel-ultra-high performance concrete (UHPC) composite structures (SUCSs) suffer several typical failure modes during applications in structural engineering. But the competing mechanism of these failure modes remains a challenge to be urgently overcome. In the present paper, the failure modes of the geometrically asymmetric SUCSs under lateral loads are theoretically predicted and numerically studied. Considering both the geometric asymmetry of the structure and the tensile-compressive asymmetry of UHPC, a theoretical model is proposed to predict the critical failure load for each failure mode (e.g., bending and core shear), and then a failure mechanism map is constructed by comparing each critical failure load. The theoretical predictions are in line with the present numerical results and the previous experimental measurements. The results demonstrate that geometric asymmetry, together with some other geometric parameters and material properties, have remarkable influences on the failure modes of structures. This work provides an effective approach for predicting and designing the failure modes of geometrically asymmetric SUCSs in structural engineering applications, such as undersea tunnels, offshore platforms, and nuclear shielding walls.

Fabrication and bending performance of ultra-low-density all-composite honeycomb sandwich shell based on stretching process

A sandwich shell with an ultra-low-density honeycomb core was designed and manufactured from a carbon-fibre prepreg via a stretching process. Subsequently, the bending bearing limits of the sandwich shell corresponding to five possible failure modes (shear buckling, shear fracture, intracellular dimpling, face fracture, and core debonding) were obtained through theoretical predictions. Failure mechanism maps were generated to reflect the possibility of each failure mode intuitively. In addition, three-point bending tests were performed on specimens with different shell thicknesses to acquire as many of these typical failure modes as possible. Moreover, the competition mechanism between different failure modes was revealed. The research results provide theoretical guidance for parameter optimisation and applications in advanced engineering fields for ultra-low-density carbon-fibre honeycomb sandwich shells.

Mechanical properties and failure mechanisms of all-CFRP corrugated sandwich truncated cone

Cone-shaped sandwich structures are extensively employed in various fields due to their excellent bearing efficiency and designability. In this work, the design approach and integrated manufacturing method for the carbon fiber reinforced plastic (CFRP) corrugated sandwich truncated cone (CSTC) are proposed to improve the anti-debonding ability and ensure the reliability of the sandwich cone. First, the theoretical model for the stiffness of the CSTC is derived, in which the conservative prediction and the upper limit considering the fiber orientation of the cone are derived. The multiple failure modes of the CSTC under axial compression are theoretically established. Then, the failure mechanism map of the CSTC is established to forecast the possible failure modes. The typical failure modes of local buckling, face fracture, and core buckling are captured by experiments and finite element analysis (FEA). The theoretical model of the stiffness and failure modes is verified by the experiments and FEA. The effect of the semi-vertex angle and circumferential cell number on the failure modes is revealed. Furthermore, a more comprehensive failure mechanism map is generated by altering the geometric parameters of the CSTC. The failure modes of Euler buckling and global buckling are acquired by the comprehensive failure mechanism map and verified by FEA. Finally, the optimum design of the CSTC structure is performed. The results show that the failure mode of face fracture has the best bearing efficiency. This research provides a solid foundation for designing and applying lightweight CSTCs in constructions, such as the adapter of launch vehicles.

Failure predictions for steel-UHPC-steel sandwich beams under three-point bending

In developing a steel-ultra-high performance concrete (UHPC) -steel sandwich structure (SUSSS) for some emerging applications, attention inevitably falls on the failure of the structure. Some typical failure modes have been summarized based on the experimental observations and numerical results. But the prediction of the failure mode is still a challenge. In the present paper, the failure of SUSSSs under three-point bending is investigated theoretically and numerically. A theoretical model is developed to predict the critical failure load of each failure mode on considering the tension–compression asymmetry of UHPC, and a failure mechanism map is constructed to predict the failure mode. The theoretical predictions are validated by the present numerical results as well as the previous experimental results. Based on the theoretical model, the effects of some geometrical and material parameters on the failure modes are discussed. It is demonstrated that the geometries of the SUSSS and the tensile strength of the UHPC core have remarkable effects on the failure modes of the structure. The present work provides a valid method to predict the failure modes of the SUSSSs.

Failure analysis of sandwich beams under three-point bending based on theoretical and numerical models

Abstract This article presents a comprehensive study on the failure behavior of foam core sandwich beams under three-point bending using theoretical analysis and finite element methods. A displacement formula for the foam sandwich beam is derived, considering the shear deformation of the foam core. Based on this formula, the deflection is obtained using energy and Rayleigh–Ritz methods. The failure loads of face yielding, core shearing, and indentation are combined to construct a failure mechanism map. The proposed theoretical model is then compared with existing theoretical analyses, demonstrating higher prediction accuracy. To investigate nonlinear damage and size effects, a series of finite element analyses is conducted. The results suggest that increasing the face sheet thickness has a greater impact on the ultimate load capacity, while the foam core thickness is more effective in enhancing bending stiffness.

Failure mechanism and size effect of new bioinspired sandwich under quasi-static load

A new additively manufactured bioinspired elytra-like interlocked sandwich (ABEIS) structure is fabricated using selective laser melting three-dimensional (3D)-printing technology. Six specimens of different sizes are designed. Flatwise compression (FC) and three-point bending (3 PB) quasi-static experiments are conducted. A corresponding finite-element model is established using Abaqus software. The Johnson-Cook constitutive model and fracture criteria are introduced. The damage parameters are obtained using dumbbell-shaped specimens. The test results indicate that the ABEIS has excellent mechanical performance, energy absorption, and designability. Analytical models under FC and 3 PB loads are established on the basis of the experimental results. The size effects are analyzed. Additionally, two-dimensional and 3D failure mechanism maps are obtained. Lastly, according to the maximum specific strength and minimum sandwich density, an optimization algorithm is designed for dual working conditions of compression and bending. The corresponding size ratios and specific strengths are determined for different density expectations.

Flexural behavior, failure analysis, and optimization design of a hybrid composite Kagome honeycomb sandwich structure

A carbon fiber-reinforced composite Kagome honeycomb is a new type of structure composed of hexagonal and triangular cells, exhibiting excellent mechanical performance and application potential in the aerospace, automobile, and marine industries. This paper proposes a new hybrid composite Kagome honeycomb sandwich (HCKHS) structure formed using the interlocking method with polymethacrylimide foam sandwich structure as the ribs. The bending characteristics and failure modes were analyzed by conducting three-point bending tests. The experimental results showed excellent flexural bearing and energy absorption capability. Second, analytical models of HCKHS specimens under bending were established. The 1D, 2D, and 3D failure mechanism maps were drawn, and the size effects were analyzed. Based on the principle of minimum specific strength, combined with 3D failure mechanism maps, the optimal design point of the HCKHS structure was obtained through specific strength functions. The proposed method is also applicable to the optimization and design of other 2D composite honeycomb sandwich structures.

Rate capability and Ragone plots for thermal management multifunctional structure designing

With the miniaturization of electronic devices, thermal management has been widely concerned in aerospace engineering. A multifunctional structure with load-bearing and thermal management abilities is proposed and manufactured by combining shape-stabilized phase change material with carbon fiber reinforced plastic (CFRP). The Winkler foundation model is employed to study the load-bearing ability. And corresponding 3D failure mechanism maps are constructed for studying the dominant failure modes. The thermal rate capability and Ragone plots are used for investigating the thermal management ability under different thermal loads. Based on that, the physical properties of phase change materials and geometric parameters influences for thermal management ability are elucidated. Furthermore, the trade-off between load-bearing and thermal management abilities is illustrated by the specific strength – specific energy curves. The appropriate geometric parameters can be selected based on the practical applying conditions through thermal Ragone/structural strength plot. The proposed framework can provide reference for multifunctional structure design.

Failure mechanisms and acoustic emission pattern recognition of all-CFRP cylindrical honeycomb sandwich shell under three-point bending

The winding-based method is used for fabricating all carbon fiber reinforced plastic (CFRP) cylindrical honeycomb sandwich shell. The theoretical model of multi-failure modes of the cylindrical honeycomb sandwich shell is established under three-point bending. The multiple failure mechanisms of the honeycomb sandwich shell under three-point bending are revealed by the established three-dimensional failure mechanism map. The theoretical prediction of multi-failure modes is verified by experiments and finite element method. The acoustic emission (AE) technology is implemented to detect the evolution rule of internal damage of honeycomb sandwich shell. The damage patterns of the acoustic emission signals with different failure modes are identified by the unsupervised k-means clustering algorithm. The meso-damage mechanisms are also disclosed by the digital microscope. It was found that high peak frequency of the AE signals represents the face-core debonding failure. Finally, the optimal geometric design of the honeycomb sandwich shell under the bending load was carried out. The damage characteristics from mesoscale damage to macroscale failure provide a crucial foundation for discriminating multiple damage failure modes of structures.

Fabrication, design, and optimization of hierarchical composite Kagome honeycomb sandwich structure under uniaxial compression

Abstract In this study, a hierarchical composite Kagome honeycomb sandwich (HCKHS) structure was manufactured based on the interlocking method, and its uniaxial compression performance was explored. Through experiments, the compressive strength, stiffness, energy absorption, and failure process of HCKHS specimens of seven different sizes were determined and compared. Mechanical analytical models were established, and the variation trend in the specific strength was predicted and compared with those of other advanced sandwich structures. The size effect of the HCKHS specimens was analyzed. The influence of a single variable on the core modulus, failure strength, and failure modes was discussed, and failure mechanism maps were drawn. The structure was optimized based on the maximum specific strength and engineering application, and the optimal size design ratio was obtained. The results showed that the HCKHS specimens exhibited excellent compressive properties with a convenient manufacturing process, making them suitable for lightweight applications in engineering. The optimization ideas presented herein are also applicable to other two-dimensional hierarchical or normal composite honeycomb sandwich structures with diamond, triangular, and hexagonal shapes.

Four-point bending behaviors of CFRP trapezoidal corrugated sandwich plates

The stiffness, failure load and failure mechanism of carbon fibre reinforced plastic (CFRP) composite trapezoidal corrugated sandwich plates (CTCSPs) subjected to four-point bending load were studied by experiment, modelling prediction and parametric analysis. With orthogonal anisotropic lay-ups containing ± θ plies (θ = 15°, 45° and 90°), three all-CFRP specimens were fabricated by mold hot pressing and secondary bonding. The four-point bending behaviors of specimens were tested and compared, and the analytical expressions of stiffness and failure load were provided. Four buckling failure modes and four strength failure modes were analytically considered. The spatial location and time sequence of eight failure modes were revealed by numerical linear buckling and progressive damage models established in ABAQUS. The modelling stiffness, failure load and failure process agreed with the four-bending experimental results. By increasing θ, the limit load of the specimens first increases and then decreases while the stiffness decrease. Correspondingly, the initial failure modes are shear corrugation fracture, debonding and face fracture. The variations in stiffness parameters and failure mechanism maps were presented; the latter can simultaneously predict the limit load and failure mode. The limit load and stiffness of CTCSPs can be improved more obviously by increasing the number of the face plies than by expanding the core plies.

Failure mechanism map for bending wood-based honeycomb sandwich beams with starch-impregnated core

The research results describing damage to wood-based lightweight panels, in which slender core cells are made of paper impregnated with modified starch, have not been encountered yet. Such solutions can benefit the circular economy era, especially in the automotive and furniture industries. The research aimed to develop failure mechanism maps for thin-walled sandwich panels consisting of wood-based facings separated by a honeycomb core of paper impregnated with modified starch. For this purpose, beams with three different facings and two types of core in two directions of orthotropy were subjected to three-point bending. It was verified that the thickness of the facing determines the strength and stiffness of the honeycomb panels, that the impregnation of the core with modified starch causes a slight deterioration in the strength and stiffness of the beams, and that the dominant type of beam failure is shear damage to the thin-walled core. There were no cases of damage to beams as a result of face indentation or face yielding.

Three-point bending characteristics of all-composite sandwich panels with different core configurations

With cores of the hexagonal honeycomb (HH), staggered corrugated lattice (SCL), bidirectional corrugated lattice (BCL), reinforced hexagonal honeycomb (RHH), and reinforced staggered corrugated lattice (RSCL) made by cutting, bonding, arranging and weaving the trapezoidal corrugation (TC) formed by mold hot pressing, six types of composite sandwich panels of the same macro size were proposed. The failure processes of the six sandwich panels in three-point bending experiments were compared and analyzed, and the effects of core configuration and reinforced stiffener on the bending response were evaluated. A general analytical model was established to predict the bending stiffness and failure mode of six sandwich panels, which was also visually presented by a three-dimensional numerical model. The numerical and experimental results validated the effectiveness of the analytical model. The effects of ply parameters and corrugated sizes on bending responses were studied by a combing application of experiment, analytical and numerical models. The three-dimensional failure mechanism maps were displayed to evaluate the failure mode and failure load. The longitudinal discontinuity of the bonding zone of the core could significantly weaken the bending performance and bonding strength of BCL, SCL, RSCL, and HH. The peak load of SCL and HH was enhanced by 45.97% and 60.29%, respectively, by setting stiffeners. Both RHH and TC could achieve bending stiffness of more than 3.5 kN·mm−1, while the failure load of the latter could be up to 25 kN. The design parameter space of bending stiffness, failure load with respect to ply orientation angle, core wall thickness, corrugated web angle, and horizontal segment length was provided intuitively.

Low-velocity impact response of aluminum alloy corrugated sandwich beams used for high-speed trains

The low-velocity impact response of A6N01S-T5 hollow extruded aluminum alloy corrugated sandwich beams used for the carbody of high-speed trains, under drop-weight impact was investigated in this study. A failure mechanism map of the corrugated sandwich beam under low-velocity impact was obtained by theoretical analysis, which was verified by experimental and finite element simulation results. Typical deformation mode, load-displacement response, and energy absorption of dynamically-loaded corrugated sandwich beams were discussed, and the effects of initial impact energy and impact angle on the impact response of specimens were also explored. The results indicate that there are three initial failure modes of corrugated sandwich beams under the drop-weight impact, namely face-sheet yield, face-sheet buckling, and core buckling, and both initial failure mode and critical load of sandwich specimens are sensitive to the face-sheet thickness and core thickness. The shear deformation of the corrugated core and gradually loading load-displacement response were observed for the case of forward impact, while the compression deformation of the corrugated core and load-displacement response with a larger initial peak were found for the case of reverse impact. Regardless of forward impact or reverse impact, the increase of initial impact energy will lead to the increase of maximum displacement response and structural resistance of sandwich beams. The increase in impact angle leads to the larger values of peak load, deformation resistance, and energy absorption efficiency of specimens for an impact angle less than 60 degrees, while the dynamic response of specimens is not sensitive to the increased impact angle within 75 to 90 degrees.

3D radar stealth composite hierarchical grid structure with extremely broadband absorption performance and effective load bearing

Multifunctional structures with both excellent microwave absorption performance and mechanical properties have attracted great attentions recently due to wide applications in aircraft and ships. In this research, a novel absorption structure was designed and fabricated through molding and interlocking technology by perfectly combining the composite hierarchical grid structure with excellent mechanical properties and extremely broadband 3D absorption metamaterial. The mechanism of structural parameters affecting absorption and mechanical properties of the proposed 3D radar absorption composite hierarchical grid structure (3D-RACHGS) were investigated. The measured result of reflectivity showed that −10 dB absorption bandwidth of 3D-RACHGS achieves 34.8 GHz (2.6–4 GHz, 6.6–40 GHz) with an average reflectivity of −17.4 dB. Further simulation demonstrated that the broadband absorption is attributed to multiple stationary wave modes. The measurement result of out-of-plane compression showed that the specific strength of the 3D-RACHGS achieves 123.5 × 103 m2/s2, which proves its effective load bearing. Failure mechanism map was also constructed to predict the failure mode of the 3D-RACHGS with various structural parameters. The proposed 3D-RACHGS will contribute to the vigorous development of the novel structural absorption materials and have immense potential to be used in new generation multifunctional skin and inlet.

Quasi-static mechanical properties of composite lattice sandwich structures with enhanced face panels

Interface debonding in sandwich structures usually occurs due to the low interfacial bonding strength. To effectively enhance the bonding strength of the interfaces, the quasi-static out-of-plane compressive and shear mechanical properties of composite sandwich structures with four types of enhanced pyramidal configurations are systematically investigated through theoretical and experimental methods. According to the theoretical predictions under two kinds of loads, the 3D failure mechanism maps are generated and the corresponding specimens are designed and fabricated. Based on several necessary assumptions, acceptable error range between the theoretical and experimental results has been achieved, and the 3D failure mechanism maps are well verified. According to the analysis of the shear experimental results, the sandwich structure with enhanced ribs can significantly enhance the adhesive strength of the interface. Besides, except for the enhanced ribs, the vertical struts existed in sandwich structures with both the enhanced pyramidal configurations II and III can also effectively improve the interfacial bonding strength.

The failure behavior of double-layer metal foam sandwich beams under three-point bending

The failure behavior of the double-layer metal foam sandwich beam under three-point bending is investigated experimentally and analytically. Three main failure modes are observed, i.e. indentation, face yield and core shear A-AB. Also, the combined indentation and face yield, and core shear and indentation are observed, respectively. The analytical formulas are given to predict the critical failure loads of double-layer sandwich beams under different failure modes. Analytical results are in good agreement with the experimental ones. The failure mechanism maps of double-layer sandwich beams are constructed, and the minimum mass design of the double-layer metal foam sandwich beam is presented.