Mechanical characteristics of composite honeycomb sandwich structures under oblique impact

Yuechen Dun, Zhen Cui, Xin Xie, Ying Tie, Ting Zou, Tingting Wng,*

a School of Mechanical and Power Engineering, Zhengzhou University, Zhengzhou 450001, China

b Department of Mechanical Engineering, Memorial University of Newfoundland, St. John’s A1B 3X5, Canada

Keywords:Composite sandwich structures Honeycomb Oblique impact Mechanical characteristics Energy absorption

ABSTRACT Carbon fiber reinforced polymer (CFRP) and CFRP-based composite honeycomb sandwich structures are particularly sensitive to impact. The mechanical characteristics of composite honeycomb sandwich structures under oblique impact are studied by numerical simulation and experiment. The oblique impact model is established, and the reliability of the model is verified by the oblique impact test. To further analyze the influence of structural parameters on energy absorption under oblique impact, the influence of impact angle, face sheet thickness and wall thickness of the honeycomb is numerically studied. The results show that the impact angle has an important effect on energy distribution. The structural parameters also have an effect on the peak contact force, contact time, and energy absorption, and the effect is different from normal impact due to the presence of frictional dissipation energy. Compared with normal impact, the debonding of oblique impact will be reduced, but the buckling range of the honeycomb core will be expanded.

As a result of the constant advancement of lightweight technologies, honeycomb structures are increasingly utilized in the automotive, aerospace, and other fields. Due to their excellent mechanical properties, honeycomb structures have also been intensively studied [1–5]. In addition, a major research direction for honeycomb structures is the formation of sandwich structures with honeycomb and face sheets [6–8]. The study discovered that the honeycomb sandwich structure is extremely sensitive to the impact load and that the low-velocity impact will result in invisible damage, reducing the mechanical properties of the structure [9–11]. Therefore, the mechanical behavior of honeycomb sandwich structures under impact loads has become a problem of increasing attention [12–19].

In the process of impact, the mechanical behavior of the honeycomb sandwich structure mainly depends on the properties of the face sheet and core materials, as well as their structural parameters [17]. Shin et al. [18] examined the impact response and damage characteristics of honeycomb sandwich panels with woven glass fabric/epoxy and aluminum metallic face sheets. The results indicate that woven glass fabric/epoxy skin sandwich panels are more resistant to impact than aluminum skin sandwich panels.In addition, Langdon et al. [19] examined the dynamic response of honeycomb sandwich panels with composite and aluminum alloy faces. The results indicate that the aluminum sandwich panels have greater residual deformation than the composite sandwich panels. Therefore, the combination of composite panels and metal cores can increase the capacity of impact loads to absorb energy.In addition, changing the core of the honeycomb sandwich structure can also increase its resistance to impact. The impact properties of aluminum honeycomb sandwich panels are significantly affected by the size of the honeycomb core [17]. The rigidity and stability of sandwich constructions increase as honeycomb size decreases [20]. The honeycomb core height has little effect on the sandwich structure’s impact response [6].

However, the actual working conditions are not always normal impact, but oblique impact at a certain angle, so the study on the oblique impact of honeycomb sandwich structure is more consistent with the actual situation. Studies [21] have found that for the Nomex honeycomb sandwich structure, the damaged area decreases with the increase in impact angle, the contact area between the impactor and upper face sheet decreases with the increase in inclination angle, and the maximum contact force and energy absorption also decrease with the increase in impact angle.In addition, impact energy has a significant impact on the impact resistance and penetration depth of Nomex honeycomb sandwich structures [22].

Most studies focus on the deformation mode and energy absorption characteristics of the honeycomb sandwich structure under normal impact, while there are few studies on the impact characteristics of the composite honeycomb sandwich structure under oblique impact, and there is little study on the influence of geometric parameters on the structure. More importantly, compared with the normal impact, the sandwich structure will produce different responses to an oblique impact, which will also produce great differences in energy distribution and structural deformation[23].

In this study, the effects of composite honeycomb sandwich structure parameters on peak contact force, contact time, and energy absorption under oblique impact are discussed in detail. The structure’s peak load and energy absorption characteristics are analyzed through experiments and simulations. It is of great engineering importance to find the combination of structural parameters with a smaller peak contact force and more energy absorption from the available structural parameters under low-velocity oblique impact conditions.

To study the energy absorption characteristics of the sandwich structure under oblique impact, the honeycomb sandwich panel in this paper was prepared according to the ASTM D7766/D7766M-16 standard [24]. The sandwich structure is composed of upper and lower skins and core layers, wherein the upper and lower skins use CFRP plates with a size of 150 mm × 100 mm × 2 mm as the face sheets. Woven CFRP laminates are produced by Weihai Guangwei Composite Materials Co., Ltd. The carbon fiber model is T300, the matrix model is 7901, the layering method is [0/90]5,and the nominal thickness of a single layer is 0.2 mm. CFRP lam-inates are made from unidirectional carbon fiber/epoxy prepreg sheets by thermoforming technology. The mechanical properties of carbon fiber and epoxy resin are shown in Table 1, and all mechanical properties are provided by suppliers. The core material is Al3003-H19 aluminum alloy, and Table 2 summarizes the material parameters of the Al3003 aluminum alloy foil [20]. The thickness of the aluminum foil is 0.04 mm, and according to processing technology, the wall thickness of the neighboring unit cell is regarded to be twice that of the other four sides. The height of the aluminum honeycomb core is 15 mm, and its length and width are the same as the skin’s 150 mm × 100 mm dimensions. The facesheet and core are connected by adhesive. The selected adhesive is SY-14, with a nominal thickness of 0.13 mm. When the adhesive is used, it needs high-temperature curing, so the specimen is treated with heat preservation curing for 120 min at 178 °C.Figure 1 shows the schematic diagram of the sandwich structure and the finished product sample.

Table 1 Mechanical parameters of T300/7901 laminates.

Table 2 Mechanical properties of honeycomb core [20].

Fig. 1. Honeycomb sandwich structure: (a) Schematic diagram; (b) Specimen; (c) Honeycomb geometric parameters.

Fig. 2. Impact test platform: (a) test platform; (b) impact fixture.

To meet the requirements of oblique impact, a low-velocity oblique impact experimental platform was established after referring to the ASTM D7136M-15 standard [25], as shown in Fig. 2a.The experimental platform is composed of an impact testing machine and a data acquisition system. The model of the drophammer impact testing machine is XBL-300, which includes a drop hammer tower, a console, and a secondary impact prevention device. A multi-angle impact test fixture is adopted. Figure 2b is the physical drawing of the multi-angle impact test fixture. The fixture consists of three parts: the translation part, the rotation part, and the clamping part. The translation part comprises a base. The base drives the upper structure to move back and forth to realize the impactor is always hitting the center of the specimen. The rotation part’s side panels are moveable. By altering the side plates,the clamp’s inclination can be adjusted. The clamping part comprises a pressure plate, a bottom plate, a fastening bolt, and a limit block. The platen and base plate have rectangular through-holes per ASTM D7136M-15, with dimensions of 125 mm × 75 mm. The specimen with a length and width of 150 mm × 100 mm is placed between the pressing plate and the bottom plate from the side,and the fastening bolts are tightened to achieve the clamping of the specimen. At the same time, a limit block is arranged on the pressure plate and the bottom plate through the hole. The purpose of placing the limit block is to prevent the specimen from sliding out from the side to affect the test results. Because the change of impact angle is realized by the control fixture, the moving direction of the pressure sensor is coincident with the contact direction,which can reflect the total contact force under oblique impact.

The low-velocity oblique impact experimental platform was used to complete the experiment. In this paper, the impact angle is defined as the angle between the impactor axis and the normal line of the honeycomb sandwich structure. In the existing drop hammer impact testing machine, the impactor can only move vertically up and down along the guide column direction, and other degrees of freedom are constrained. The change in impact angle is realized by rotating the honeycomb sandwich structure. When the specimen is placed in a fixed position in the fixture and tilted at a certain angle, the two limit blocks of the fixture will prevent the specimen from slipping out when subjected to oblique impact.The moving fixture makes the impactor always impact the geometric center of the specimen to ensure that the initial impact position is always the same. Calculate the falling height of the hammer and release the impactor from the prefabricated height. During the impact process, the pressure sensor will record the change in the contact force with time.

Based on using a 3 mm cellular core, the sandwich panel with 1 and 5 mm cellular side length was selected for experimental comparison. The impactor of the drop hammer device is hemispheric,with a diameter of 25 mm and a weight of 2.5 kg. Due to equipment limitations, the stud connecting the impactor and the force sensor is rather delicate. When the experiment is conducted at a large impact angle, the impactor will be subjected to a large lateral load, which will cause the stud to break. As a result, the experimental waveform will be distorted, and accurate data is difficult to collect. Therefore, the goal of this study is to validate the model through experiments with several impact angles, and to examine and anticipate the damage of honeycomb sandwich constructions subjected to large impact angles mainly by simulation. The impact angles 0° and 10° were chosen, and the sandwich panel was tested with a 10 J impact energy and a matching impact velocity of 2.82 m/s.

The geometric model was constructed with Abaqus/Explicit using the aforementioned experiments as a guide. The impactor and fixture were considered rigid during the experiment, and the grid was divided by C3D8R solid elements. C3D8R solid elements are used to discretize the laminates, and a COH3D8 element of 0 thickness was inserted into each interlaminar adhesive layer to simulate delamination damage. S4R shell elements are used for grid division in the fine modeling of the honeycomb core layer. At the same time, according to the actual process of the aluminum honeycomb core, the straight-edge thin wall of the cell is given double wall thickness, and the hypotenuse is set as single wall thickness. The binding constraint on the face sheet and the core layer is imposed by a group of non-zero thickness bonding elements. Figure 3 shows the finite element model of the specimen, impactor, and fixture.

According to the impact process test, the impactor only retains the translational DOF in the Z direction, and all DOF of the fixture is restricted. The contact attribute between the impactor and the upper skin is set as face to face, and the “hard” contact model is adopted in the normal direction. Since the impactor will rebound after impact, separation after contact is allowed. The“penalty” function model is adopted in the tangential direction,and the friction coefficient is set as 0.3 according to the relevant settings in Ref. [23]. To prevent element penetration, a general contact model is adopted between other components, with the same specific contact attributes in normal and tangential directions. When modeling, the whole fixture, and the specimen are rotated around the intermediate axis of the specimen (along the Y-axis direction). The impact angle is the included angle between the impactor axis and the plane normal of the specimen, which is also equal to the rotation angle of the honeycomb sandwich structure.

The honeycomb core Refs. [17,20] are established, it is assumed that the core layer is an elastoplastic material, and the material behavior is based on a piecewise linear plastic material model. The Ductile Damage is chosen here to predict the progressive damage and destruction of thin-walled metal sheets due to internal microcrack nucleation, growth and pore aggregation. When the damage state variableωDsatisfies Eq. (1), the damage begins [17].

Fig. 3. The finite element model of specimen, impactor, and fixture.

The equivalent plastic strainis a function of stress triaxialityηand strain rate ˉεpl. Once any point of the material meets the damage initiation criterion, the damage begins to evolve, and then the stiffness of the material degrades according to the exponential criterion. When the stiffness degradation reaches the limit value,the failure element will be deleted from the calculation.

The damage to composite laminates can be divided into intralayer damage and interlayer damage. Therefore, the constitutive model used in this study takes into account the intralaminar and inter-laminar damage models, and the theories of 3D Hashin and the cohesive zone model in Ref. [26] are cited here.

The 3D Hashin damage criterion has been used to predict the progressive failure of composite laminates after the initial repair.On this basis, the residual strength of damaged laminates was calculated by using the continuous damage model (CDM). The 3D Hashin criterion has been implemented using VUMAT user subroutines in Abaqus/Explicit [27] to describe the intralaminar damage behavior of composites. The subprogram includes the damage criterion, damage evolution rule, and element deletion criterion. In a single loading step, this user subroutine is used to calculate the stress state of each integral point in the composite laminate. Damage criteria are then used to determine whether any damage has occurred within the unit, and the elastic properties of the element must be reduced based on the damage pattern. Degradation processes are introduced in user subroutines to reproduce the damage in materials. In addition, when the element is identified as damaged according to the failure criterion, its stiffness will also be reduced. After progressive damage calculation, the damaged element does not contribute to the strength of composite laminates but can converge rapidly in the simulation process.

The cohesive zone model (CZM) is used to describe the interlayer damage in the face sheet. The CZM method follows the law of traction separation in which debonding and delamination damage are determined by the traction force and separation displacement of the nodes on the interaction surface. Before debonding and delamination, the constitutive relationship was considered to be linear elasticity. Similar to intralayer damage, the damage evolution law of interlayer damage is divided into two steps. Before delamination and debonding, the interaction was considered to have linearly elastic behavior. Once the damage criteria are met, the cohesion decreases linearly.

Fig. 4. Stress-strain curves of adhesive SY-14 [29].

Degumming of the face sheet and core is an important failure mode of the sandwich structure under impact load [28]. The degumming phenomenon occurs, and it is one of the most important failure forms under low energy impact, which is more obvious when the unit side length is 1 mm. Figure 4 shows the stressstrain curve of adhesive SY-14 under the tensile test [29]. Among them, point A in the figure represents the starting point of plasticity, point B represents the starting point of damage, and point C represents the endpoint of damage. Based on the stress-strain curve of the tensile test in Fig. 4, the ductile failure model was used to simulate the damage failure behavior of the adhesive. A ductile metal model built into Abaqus is used to determine the initiation of damage, in which the plastic fracture strain is a function of stress triaxiality and strain rate. The plastic fracture strain was set as 0.00325, the stress triaxiality and strain rate were set as 0.3 and 0 [29]. Displacement-based plastic linear degradation was used, and the corresponding displacement for final failure was 0.012 mm.

To verify the 3D finite element model, the simulation and experimental results were compared. At the same time, the effect of certain parameters on the mechanical properties of the honeycomb sandwich structure under oblique impact is further discussed by using a verified accurate finite element method. Verification of the FE model is shown in Table 3, corresponding to E1-E6, respectively. The influence of geometric parameters was divided into three groups, A-C, as shown in Table 3. The impact energy is all set to 10 J.

Figure 5 shows the damaged profile of the upper skin after the experiment. Due to the small impact energy, there is almost no damage on the backside, which is no longer shown here. The surface failure mode of the specimen is the residual depression inthe center, and there is no obvious crack around the pit. Under the condition of a 0° impact, there are only a few visible contact marks between the impactor and the face sheet on the sandwich structure, and the indentation is not obvious. Under the 10° impact condition, the marks left by the impactor’s slippage due to the impact angle after the contact between the impactor and the upper skin can be seen, and the range of scratches is decreasing with the increase of the edge length. This is mainly because the smaller the cell side length is, the greater the stiffness of the honeycomb sandwich structure is, resulting in more severe friction and larger scratches on the surface under oblique impact.

Table 3 Scheme design.

Fig. 5. Frontal damage of face sheet: (a) a=1 mm, θ=0°; (b) a=3 mm, θ=0°; (c) a=5 mm, θ=0°; (d) a=1 mm, θ=10°; (e) a=3 mm, θ=10°; (f) a=5 mm, θ=10°.

Figure 6 shows the simulation and experimental comparison of peak contact force and contact time of a composite honeycomb sandwich structure with different impact angles. The experimental procedure is not ideal, and numerous variables will influence the experimental outcomes. Three of the completed six sets of tests can be observed to oscillate strongly, whereas the other three sets of waves are not apparent. During the experiment, the sensor will capture the vibration’s waveform due to the influence of external vibration on the equipment and the high surface roughness of the specimen. Since the simulation is based on ideal conditions,its curve is smoother than the experimental curve. Simulated data curves can be well fitted to experimental data curves. It can be seen from Table 4 that the relative errors of the contact force peak value and contact time of simulation and test are both within 10%.

Section damage of the honeycomb sandwich structure is shown in Fig. 7. In the impact zone, the upper skin only presents a small degree of bending deformation, while the honeycomb core presents a buckling state. The height of the broken core of the honeycomb is the highest at the center of impact and decreases in an arc to both sides. The comparison of the numerical calculation results of honeycomb core damage with the experimental results is given in the table, and the numerical simulation results are in good agreement with the experimental results. Through numerical analysis, not only the degumming of the honeycomb core layer can be predicted, but also the crushing height of the honeycomb core layer.

Fig. 6. The simulation and experimental comparison of peak contact force and contact time of composite honeycomb sandwich structure with different impact angles: (a)0°, 1 mm; (b) 10°, 1 mm; (c) 0°, 3 mm; (d) 10°, 3 mm; (e) 0°, 5 mm; (f) 10°, 5 mm.

Table 4 Simulation and experimental comparison of peak contact forces and contact times of composite honeycomb sandwich structures with different cell edge lengths.

Fig. 7. Impact damage experiment and simulation comparison of honeycomb sandwich structure profile: (a) 0°, 1 mm; (b) 10 °, 1 mm; (c) 0°, 3 mm; (d) 10°, 3 mm; (e) 0°,5 mm; (f) 10°, 5 mm.

From the results of the experiments and simulations, the debonding and the buckling of the honeycomb core that appeared in the experiments are reflected in the simulations. The experimental and simulated damage cases are approximate, and the results are in good agreement. In conclusion, the established finite element model can correctly predict the dynamic response of a composite honeycomb sandwich structure under low-velocity oblique impact.

To determine the effect of impact angle on honeycomb sandwich structures under the low-velocity oblique impact, the value ofθwas changed in the simulation to explore, and 0°, 15°, 30°,45°, and 60° were used for the calculation and analysis. The impact energy is still 10J, and other parameters are shown in Table 3.

Fig. 8. The relationship between contact force, the kinetic energy of the impactor, frictional energy dissipation, and time or displacement at different impact angles: (a)Contact force history at different impact angles; (b) Contact force-displacement curves at different impact angles; (c) Kinetic energy history of impactor at different impact angles; (d) Friction energy consumption history at different impact angles.

From Figs. 5 and 7, it is found that no matter how the impact angle changes, the structure will always produce pits after being impacted by the impactor, but the center position of pits will change, which is more obvious when the impact angle is larger.As the impact angle increases from 0° (normal impact), the slip becomes more and more, and the center of the pit moves in the slip direction accordingly. The essence of the pit is that the structure absorbs energy by plastic deformation under impact load. The maximum depth of pits decreases gradually with the increase in impact angle, and the decreasing trend is gradually accelerated.In addition, it is obvious that when the impact angle is 0° (i.e.,the normal impact), the concave shape caused by the impactor is round, relatively regular, and symmetrical, which is mainly because the impactor always remains perpendicular to the specimen under the normal impact condition, and almost all the kinetic energy of the impactor is absorbed through the normal deformation and damage of the sandwich structure. It can be seen that the honeycomb core unit near the contact area of the impactor is seriously crushed during normal impact. When the impact angle exists, the impactor loads the normal and tangential directions of the sandwich structure at the same time, and the impact force along the tangential direction increases with the increase in the impact angle. When the impact angle exceeds 45°, the tangential impact force begins to be greater than the normal impact force,and the slip of the impactor becomes easier. When the impactor slips, the clamping structure will change the action position. With the change of the active position, the cellular core units that are far away from the impactor begin to join in the process of resisting the impact of the impactor, and these new units will continue to undergo buckling deformation to absorb the kinetic energy of the impactor. Although the impact angle increases the impactor slip will add new element damage, the honeycomb core but slip more easily, which also means that the friction energy dissipation accordingly, which leads to the impactor a large amount of kinetic energy by sliding friction heat production in the form of dissipation, which is loaded into the sandwich board structure of impact energy is not much, and also causes the structure to only expand the damaged region. And the contact area between impactor and plate increases, so the overall damage degree will be reduced. In addition, it is obvious that, except for the energy consumed by sliding friction, most of the impact energy loaded on the structure is mainly consumed by the plastic deformation of the upper skin and the buckling deformation of the honeycomb core unit, while the deformation of the lower skin is very small under low energy impact and almost does not participate in energy absorption.

Fig. 9. The contact force history and contact force-displacement curves of different face sheet thicknesses: (a) Contact force history of different face sheet thicknesses; (b)Contact force-displacement curves of different face sheet thicknesses.

Figure 8 shows the relationship between contact force, impactor kinetic energy, frictional dissipation energy, and time or displacement for different impact angles. From Fig. 8a and 8b, it can be seen that the contact time between the impactor and the sandwich structure is different. As the impact angle increases, the peak contact force decreases and the contact time between the impactor and the honeycomb structure is prolonged, resulting in a corresponding increase in the damaged area of the honeycomb structure. The initial energy of the whole system composed of the impactor and sandwich structure is the initial kinetic energy of the impactor. Without considering the energy absorption by the rubber layer and the energy exchange with the outside world, the kinetic energy of the impactor will be absorbed by the damaged deformation of the core structure, while part of the energy will be lost by friction, and the remaining energy will be the kinetic energy of the rebound after the impactor is separated from the core structure.For each part of the honeycomb core structure, under different impact angles, as the upper skin is at the forefront of the impactor impact, the damage is the most serious, and the corresponding energy absorption is the most. The honeycomb core is in the middle of the core structure, and it is a thin-walled structure with good energy absorption, so the energy absorption is only second to the upper skin, and under the low energy drop hammer impact,the impactor kinetic energy is too late to cause the lower skin deformation to be exhausted. Therefore, the energy absorbed by the lower skin is almost negligible. Therefore, the energy absorbed by the lower skin is almost negligible. The impactor consumes a lot of energy due to the frictional heat of sliding when impacting at a larger angle, and the kinetic energy of the impactor decreases faster, and only a small part of the kinetic energy of the impactor is used to deform the structure, as shown in Fig. 8c and 8d, and the energy absorption of both the upper skin and the honeycomb core is lower at this time, and the larger the impact angle is, the more serious the situation of low energy absorbed by the honeycomb core. In general, the total energy absorption of the whole honeycomb core structure is negatively correlated with the impact angle, while the energy loss due to frictional heat generated by the impactor sliding is positively correlated with the impact angle, which indicates that part of the energy of the impactor is not absorbed by the core structure during the inclined impact, but is dissipated in the form of frictional heat generated by the impactor sliding on the face sheet of the core structure.

Figure 9 shows the contact force history and contact forcedisplacement curves for different face sheet thicknesses. It can be seen that the larger the face sheet thickness leads to the larger the structural stiffness, and therefore the peak contact force generated by the impact is larger and the contact time decreases accordingly.This is similar to the results of normal impact. Figure 10 shows the energy distribution for different face sheet thicknesses. It can be seen that increasing the face sheet thickness leads to a slow increase in the residual kinetic energy of the impactor under lowvelocity oblique impact conditions. Changing the thickness of the face sheet does not significantly affect the change in frictional energy dissipation. Not only that, but the increase in the face sheet thickness also makes the energy absorption of the honeycomb core decrease, and the total energy absorption of the whole structure slowly decreases.

Figure 11 shows the contact force history and contact forcedisplacement curves for different honeycomb core wall thicknesses.It can be seen that the peak contact force is positively correlated with the honeycomb core wall thickness. Therefore, increasing the honeycomb core wall thickness will make the structure stiffer and lead to an increase in the structure’s ability to resist deformation.It can be seen that the contact time is negatively correlated with the honeycomb core wall thickness. The smaller the honeycomb core wall thickness, the easier it is for the impactor to invade the substrate and cause damage during impact, increasing the contact time. Figure 12 shows the energy distribution of different honeycomb core wall thicknesses. Under the low-velocity oblique impact condition, the larger the wall thickness, the larger the residual kinetic energy of the impactor. There is no clear relationship between the frictional energy dissipation and the wall thickness, but changing the wall thickness can also cause a change in frictional energy dissipation. As the wall thickness goes up, the total amount of energy that the structure takes in slowly goes down.

This paper focuses on the mechanical properties of composite honeycomb structures under oblique impact and further explores the influence of structural parameters on the mechanical properties of honeycomb structures under oblique impact. It is found that the damage to the composite honeycomb sandwich structure under low-velocity impact conditions is mainly in the form of debonding of the upper skin and honeycomb core and flexural deformation of the honeycomb core unit. The impact angle has an important influence on the energy distribution. As the impact angle increases, the frictional energy dissipation due to impactor slip increases, and the total energy absorption of the structure and its components decreases. In addition, the structural parameters also have an effect on the peak contact force, contact time, and energy absorption. Under low-velocity oblique impact conditions, the peak contact force is positively related to face sheet thickness and honeycomb core wall thickness, while the contact time is negatively related to face sheet thickness and honeycomb core wall thickness.This is similar to the case of normal impact. However, the impactor slips during the oblique impact, resulting in a tangential upward component of the contact force, making the contact force smaller and the contact time longer for the oblique impact. Compared with the normal impact, the debonding phenomenon of the oblique impact is reduced, but the flexural range of the honeycomb core will be larger. In the actual working conditions, it is more important to strengthen the stiffness of the sandwich face sheet to mitigate

Fig. 10. Energy distribution of different face sheet thicknesses: (a) Aggregate Chart; (b) Residual kinetic energy of the impactor; (c) Friction energy dissipation; (d) Total energy absorption.

Fig. 11. The contact force history and contact force-displacement curves for different honeycomb core wall thicknesses: (a) Contact force history for different honeycomb core wall thicknesses; (b) Contact force-displacement curves for different honeycomb core wall thicknesses.

Fig. 12. The energy distribution of different honeycomb core wall thicknesses: (a) Aggregate chart; (b) Residual kinetic energy of the impactor; (c) Friction energy dissipation;(d) Total energy absorption.

the buckling. The established finite element model can predict the impact response of the honeycomb sandwich structure under an oblique impact, which facilitates the search for a combination of structural parameters with a smaller contact force peak and more energy absorption from the existing structural parameters and also provides a reference for the study of the low-velocity impact of the honeycomb sandwich structure.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

This research was supported by the National Natural Science Foundations of China (Nos. 52175153, U1833116, 51705468 and 11402234), and the China Scholarship Council (CSC).