Experimental and numerical studies on corrosion-resistant aluminium foam sandwich panel subject to low-velocity impact | Scientific Reports

Nov 04, 2024

Scientific Reports volume 14, Article number: 26611 (2024) Cite this article

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Aluminium foam sandwich panels (AFSPs) have a high impact resistance and are suitable for a wide range of engineering applications. To improve corrosion resistance, this paper proposes an anti-corrosion sandwich panel with stainless steel as the upper sheet. Drop hammer impact tests were performed on a total of ten AFSPs to investigate their dynamic response and failure patterns. To assess the deformation performance of AFSPs, a laser displacement meter was used to obtain the bottom centre displacement. The effects of the impact energy and the thickness of each component of AFSPs on the peak impact force and deformation performance were studied. Test results showed that the thickness of each component had notable effects on the impactor and bottom displacements. In addition, the effect of the unit mass of the components in AFSPs on decreasing the bottom displacement was discussed. Compared to increasing the aluminium foam and lower sheet thicknesses, increasing the upper sheet thickness was more effective in decreasing the bottom displacement. A finite element model of AFSPs was developed to conduct parameter analysis, indicating that impactors with larger diameters resulted in higher peak forces and reduced deformation of AFSPs.

Sandwich panels with aluminium foam as the core and steel plates as the face sheets exhibit excellent energy absorption capacity1,2,3,4 and also possess high strength and stiffness due to the presence of steel plates on both sides5,6,7,8,9. Recently, sandwich panels have been extensively used in various engineering practices, such as bridge piers, marine structures and protection engineering10. In these applications, these panels are often exposed to low-velocity impacts, which can cause significant structural damage or even failure. Therefore, it is of great significance to investigate the load resistance and failure mechanism of AFSPs subjected to low-velocity impacts.

Extensive studies have been carried out on the influence of the core and steel sheets on the impact response of AFSPs11,12,13,14. Compared to polymeric foam, aluminium foam has a higher specific stiffness15,16,17, which makes it widely used as the core material of AFSPs. Moreover, compared with the AFSPs with carbon steel sheets, the AFSPs with stainless-steel sheets have a higher impact resistance17,18. Mohan et al.17 investigated the dynamic mechanical properties of AFSPs with three different sheet materials, namely aluminium, stainless steel, and carbon fibre-reinforced polymer (CFRP). It was found that AFSPs with a stainless-steel sheet could sustain the pre-designed impact force and absorb almost all the impact energy, which proved that stainless steel was the best choice for the sheet. However, in existing studies, alloy steel was often used in AFSPs, which led to a decrease in the impact resistance of AFSPs over time due to the corrosion of the sheets. The AFSPs with a stainless-steel plate as the upper sheet exhibited good corrosion resistance. Considering the high cost of stainless steel, alloy steel is suitable for the lower sheet in AFSPs due to its low cost and high strength.

Several studies have been performed on the dynamic behaviour of AFSPs subjected to low-velocity impact. Kumar et al.19 carried out low-velocity impact tests on AFSPs under different energies. The experimental results showed that as the impact energy increased, the corresponding peak impact force, deformation, and energy absorption also increased. Guo20 conducted impact tests on AFSPs and pure steel plates with the same mass. It was found that the deformation of AFSPs was smaller than that of pure steel plates, which proved that AFSPs have better impact resistance than pure steel plates. Li et al.21conducted experimental studies on the perforation response of AFSPs. The study aimed to investigate the influence of key parameters, including the impact of energy and component thickness, on the energy absorption of AFSPs. It was revealed that the aluminium foam thickness and upper sheet thickness positively affected the energy absorption capacity of AFSPs. Liu et al.22 focused on five groups of AFSPs to study the impact resistance and failure patterns of AFSPs. It was observed that an increase in the aluminium foam thickness caused a slight increase in the energy absorption of AFSPs, whereas the energy absorption capacity increased more significantly with the sheet thickness. Liu et al.23 performed impact tests to explore the influence of the thickness of each component in AFSPs with a stainless-steel upper sheet on its impact response. Test results showed that before the upper sheet cracked, the energy absorption capacity of the AFSPs with the alloy steel upper sheet was lower than that of the AFSP with the stainless-steel upper sheet. Huo et al.24,25 performed drop-weight impact tests to investigate the influence of the core thickness and sheet material on the impact resistance of AFSPs and the interaction between the components. The test results showed that AFSPs with Al6061 sheets developed higher peak impact forces and energy absorptions. Zhao et al.26 investigated the impact behaviour, deformation mechanisms, and energy absorption of AFSPs, founding that the sheet thickness and aluminium foam thickness had obvious influences on the impact response of AFSPs. Nevertheless, in previous studies, the effects of the thicknesses of the upper and lower sheets were analysed together, and the effects of the thicknesses of the upper and lower sheets alone on dynamic behaviour need further investigation. In addition, the deformation mode of AFSPs with composite sheets has been widely studied24,27,28, whereas the investigation on the effect of the impact energy on the deformation mode of AFSPs with steel sheets is still lacking.

This study investigated the impact resistance, deformation, and energy absorption characteristics of an anti-corrosion AFSP under low-velocity impact. A series of drop hammer impact tests were performed on AFSPs, focusing on the effects of impact energy and the thicknesses of each component on their impact behaviour and energy absorption. The influence of the unit mass of the components on the bottom displacement was also discussed. Moreover, a finite element model of AFSPs was developed to conduct parameter analysis. This study provides an important basis for the design of the anti-corrosion AFSP subject to low-velocity impact.

A total of 10 specimens were designed in the test to investigate the dynamic behaviour of sandwich panels. The AFSPs consisted of an aluminium foam as the core, a Grade 304 stainless steel sheet as the upper sheet and a Grade Q460 alloy steel sheet as the lower sheet, as shown in Fig. 1. The stainless-steel upper sheet can improve the corrosion resistance of AFSPs. The steel sheets were bonded to the aluminium foam by using universal epoxy resin adhesive with a shear strength of 12.7 MPa. The manufacturing process included treating the surface of the material, applying epoxy resin adhesive, assembling the sandwich panel, applying pressure and curing. The dimension of specimens was 150 × 150 mm square, and the thickness changed with the component thickness.

Details of stainless steel-aluminium foam-alloy steel sandwich panels.

Table 1 presents the details of specimens used in this study. To study the failure process of AFSPs, four different impact energies were considered in the experimental test, namely, 600 J, 1000 J, 1800 J, and 2000 J. Furthermore, to study the effect of the thickness of the components on the dynamic behaviour of AFSPs, seven AFSPs were designed, which had different aluminium foam thickness and upper and lower sheet thickness. Through experimental impact tests, the impact energy of AFSPs with different thicknesses was determined to be 1000 J. The thickness of the upper sheet varied from 0.8 mm to 2 mm, the thickness of the core varied from 10 mm to 30 mm, and the thickness of the lower sheet varied from 2 mm to 4 mm. The designation of specimens consisted of the upper sheet thickness, core thickness and lower sheet thickness, and the energy of impact. For example, S1.4-20-3-1000 represents the specimen with an upper sheet thickness of 1.4 mm, an aluminium foam thickness of 20 mm, and a lower sheet thick-ness of 3 mm under a 1000 J impact.

Figure 2 shows the DHR940 drop hammer tester, which was utilized to conduct low-velocity impact tests on AFSPs. The impact velocity was varied by adjusting the impactor height. The maximum mass, maximum drop weight effective height and maximum impact velocity were 250 kg, 12.6 m and 15.70 m/s, respectively. In this study, the mass of the impactor and the block was 206.75 kg, and the impact energy was determined as 50% of the product of the mass of the impactor and the square of the impact velocity. AFSPs were clamped by using two 25 mm thick plates with a square opening of 90 × 90 mm in dimensions during the impacting process. The clamps were designed with 12 bolts with a diameter of 12 mm. Twelve holes with a diameter of 12.4 mm were cut in AFSPs by wire cutting technology. The dimension of clamps was 150 × 150 mm, which was the same as the dimension of AFSPs. In the test, a hemispherical impactor with a diameter of 24.7 mm was utilized. A dynamic load cell built into the impactor was adopted to obtain the impact force-time history. In addition, the time histories of velocity, displacement, and energy absorption were obtained based on the impact force-time history. A laser displacement sensor was installed between the ground and AFSPs to measure the centre displacement of the lower sheet.

Drop hammer test setup.

In this study, the average size of the cellular pores and the porosity of the aluminium foam core were 4 mm and 83%, respectively. There were three kinds of aluminium foams with thicknesses of 10 mm, 20 mm, and 30 mm, which corresponded to densities of 0.41 g/cm3, 0.43 g/cm3, and 0.45 g/cm3, respectively. The material characterization of aluminium foam with varying thicknesses was obtained by conducting uniaxial compressive tests. The diameter of the aluminium foam used in the compressive test was 30 mm. The sample was designed to ensure that its diameter was 7-times larger than the average cell size7. Figure 3 displays the stress-strain curve of aluminium foam samples. Table 2 summarizes the material characterization of aluminium foam samples.

Compressive stress-strain curve of aluminium foam.

In this study, stainless steel and alloy steel were used as the face sheets for the AFSPs, and their properties were measured by tensile tests according to China standard GB/T 228–2010 29. Table 3 presents the tensile mechanical characterization of steel sheets. The yield and the ultimate stresses of sheets of the same material with varying thicknesses were roughly equal.

Figure 4 presents the force-displacement curves of AFSPs subjected to various impact energies, namely, 600 J, 1000 J, 1800 J, and 2000 J. The test results demonstrated that for AFSPs with the same dimension under different impact energies, the general trend of force-displacement curves was consistent. It could be seen that the force-displacement curve consisted of four stages, namely, stage I to stage IV, which corresponded to the fracture of the upper sheet, the densification of aluminium foam core, the gradual deformation to fracture of the lower sheet, and the complete penetration of AFSPs, respectively. During stage I, the impact force exhibited a steady increase until it reached its first peak. In this stage, the impactor gradually crushed the aluminium foam and, at the same time, the upper sheet was deformed gradually under impact. The curve of S14.20-3-600 dropped to zero at this stage. When the upper sheet fractured, the first peak value of the impact force at point A was reached. Afterwards, when the curve entered stage II, due to the low plateau stress of aluminium foam, the force dropped to a lower level and fluctuated. In this stage, the aluminium foam mainly sustained the impact force and was gradually densified. With the increasing displacement of AFSPs, the force was transmitted to the lower sheet through the densified aluminium foam, resulting in the increase in the force owing to the hardening of the lower sheet. The curve of S1.4-20-3-1000 ended in stage III. Finally, when the lower sheet fractured, the force attained its second peak at point B and then dropped to zero in the curve of S1.4-20-3-1800. The displacement increased slowly due to the fracture of the lower sheet. In addition, S1.4-20-3-2000 was fully penetrated, and the impact force gradually dropped to a certain value, as the friction force between the lower sheet and the impactor.

Force-displacement curves of specimens under different impact energies.

Figure 5 displays the effect of the thickness of components on the force-displacement curves of AFSPs subjected to a 1000 J impact energy. It was found that the stiffness of AFSPs with a thick upper sheet was increased at stage I, as shown in Fig. 5(a). The curves of S0.8-20-3-1000 and S1.4-20-3-1000 ended at stage III and reached the first peak impact force, but the curve of S2.0-20-3-1000 ended in stage I. The peak impact force increased from 60.0 kN to 87.7 kN, as the upper sheet thickness varied from 1.4 mm to 2.0 mm. AFSPs with a thicker upper sheet had a higher stiffness, which could resist a larger impact force.

Figure 5(b) shows that stage II became longer with increasing aluminium foam core thickness. It should be noted that compared with the stiffness of S1.4-10-3-1000, S1.4-20-3-1000 and S1.4-30-3-1000 were relatively lower after the displacement exceeded 10 mm. The reason was that the foam had been densified prior to the fracture of the upper sheet, which required the lower sheet to provide the stiffness at a smaller displacement. The peak impact forces of S1.4-30-3-1000 and S1.4-20-3-1000 were roughly equal, which were 58.5 kN and 60.0 kN, respectively. However, the peak impact force of S1.4-30-3-1000 and S1.4-20-3-1000 was significantly lower than that of S1.4-10-3-1000. This was because the densification of the foam core prior to the fracture of the upper sheet caused the lower sheet to contribute to the initial stiffness of AFSPs.

Figure 5(c) displays that the influence of the lower sheet on stage I of the curve was relatively negligible. The first peak impact force of the AFSP with lower sheet thicknesses of 2 mm and 3 mm was slightly less than that of the AFSP with lower sheet thickness of 4 mm. This was possibly due to the fact that a 4 mm thick lower sheet increased the stiffness of S1.4-20-4-1000 in stage I. When the lower sheet thickness was increased, the peak impact force had no obvious change. The peak impact forces of AFSPs with lower sheet thickness of 2 mm, 3 mm, and 4 mm were 63.9 kN, 60.0 kN, and 71.6 kN, respectively.

Effect of thicknesses on force-displacement curves of specimens under 1000 J impact.

Figure 6 shows the deformation pattern of the upper and lower sheets subjected to low-velocity impact. Figure 6(a) shows that when the impact energy was low or the upper sheet was thicker, i.e., S1.4-20-3-600 or S2.0-20-3-1000, the upper sheet did not fracture. However, when the impact energy was high, a penetration hole matching the diameter of the impactor became evident in the centre of the upper sheet, as shown in Fig. 6(b). For AFSPs with the upper sheet penetrated, a large deformation appeared on the lower sheet, as shown in Fig. 6(c). When AFSPs failed completely, petal-shaped penetration occurred in the lower sheet, as shown in Fig. 6(d).

Deformation modes of the upper sheet and lower sheet under impact.

Figure 7 displays the failure profiles of AFSPs under different impact energies. Under a 600 J impact energy, the upper sheet remained intact, and the deformation of the lower sheet was neglected. The aluminium foam in the AFSP under a 600 J impact showed obvious compressive deformations, but it was not densified, as shown in Fig. 7(a). When the impact energies were increased to 1000 J, 1800 J, and 2000 J, the upper sheet was penetrated by the impactor. Moreover, the aluminium foam was fully damaged within the impact region while only experiencing limited deformation around the impact region. It was observed from Fig. 7(b and c) that the lower sheet of S1.4-20-3-1000 deformed significantly but did not fracture, whereas a crack was formed in the lower sheet of S1.4-20-3-1800. The lower sheet of S1.4-20-3-2000 was completely penetrated, as shown in Fig. 7(d). Obviously, the deformation of AFSPs increased with the increasing impact energy.

Deformation profiles of specimens under different impact energies.

Figure 8 displays the failure profiles of AFSPs with different thicknesses subjected to an impact energy of 1000 J. Except for S2.0-20-3-1000 and S1.4-10-3-1000, the upper sheet of AFSPs fractured under impact. The upper sheet of S2.0-20-3-1000 did not crack, as a thicker upper sheet could resist a higher impact energy. The aluminium foam had been densified before the fracture of the upper sheet in S1.4-10-3-1000, leading to the lower sheet absorbing energy significantly. Moreover, the aluminium foam in AFSPs was densified except for S2.0-20-3-1000. It can be observed that the lower sheet of all AFSPs did not fracture, and the deformation of the lower sheet decreased with the increasing thickness of the components. Therefore, the increase in the thickness of components could reduce the damage of AFSPs.

Deformation profiles of specimens with different thicknesses.

To quantitatively evaluate the energy absorption capacity for AFSPs, energy absorption (\(\:{E}_{a}\)) and specific energy absorption (SEA) were also calculated. Note that \(\:{E}_{a}\) is obtained from Eq. (1).

where \(\:{D}_{i}\) is the displacement of the impactor.

The shapes of energy absorption-time curves of AFSPs subjected to different impact energies were slightly different, as shown in Fig. 9(a). For S1.4-20-3-2000, initially, the energy absorption and its increasing rate increased with time, mainly due to the aluminium foam and upper sheet. Once the upper sheet fractured, the rate decreased as its energy absorption capacity was exhausted, leaving the aluminium foam to absorb energy through compression. Afterwards, the lower sheet was hardened due to the gradual increase in the deformation, resulting in an increase in the energy absorption rate. When the lower sheet fractured, the energy absorption rate gradually decreased to zero. Finally, the curve tended to be nearly horizontal due to the penetration of S1.4-20-3-2000 by the impactor. The curve of the AFSP subjected to an 1800 J impact energy was similar to that of the AFSP subjected to a 2000 J impact energy, as the deformation mode of S1.4-20-3-1800 was similar to penetration. S1.4-20-3-600 only experienced the initial stage, as its upper sheet did not fracture. Notably, for both S1.4-20-3-600 and S1.4-20-3-1000, the energy absorption decreased to a certain value after rising to the peak value, and then the curve tended to be a horizontal straight line. The reduced energy was transformed into the kinetic energy of the rebound impactor.

It can be seen from Fig. 9(b) that for AFSPs with varying component thicknesses, the increasing trend was different, but the final energy absorption was nearly the same, as the AFSPs did not fail under a 1000 J impact energy. It was found that the energy absorption rate was always higher in AFSPs with thicker upper sheets. After about 0.08 s, the aluminium foam thickness had an obvious effect on the rate of energy absorption, specifically resulting in a smaller increase in the rate for AFSPs with thicker aluminium foam. Under the energy impact of 1000 J, the contribution of the lower sheet to energy absorption was limited, as the energy absorption capacity of the lower sheet did not develop fully.

Energy absorption-time history of specimens.

Figure 10 presents the bottom displacement-time history of AFSPs. For AFSPs subjected to different impact energies, initially, the displacement of the bottom centre in-creased slowly with the increasing time, as shown in Fig. 10(a). This was due to the fact that the force was mainly supported by the upper sheet. After the fracture of the upper sheet, the increasing rate of the bottom displacement increased significantly. The bottom displacement in S1.4-20-3-600, S1.4-20-3-1000, and S1.4-20-3-1800 decreased slightly to a certain value after reaching the peak value, due to the reduction in elastic deformations of the lower sheet. However, for S1.4-20-3-2000, the bottom displacement continuously increased with the increasing time, as the impactor dropped after the penetration of S1.4-20-3-2000.

The bottom displacement of AFSPs with different thicknesses exhibited an initial increasing stage, as shown in Fig. 10(b). It can be clearly seen that the bottom displacement in AFSPs with thinner components increased at a greater rate between about 0.005 s and 0.01 s. Therefore, increasing the upper sheet thickness, lower sheet thickness and aluminium foam thickness could effectively decrease the bottom displacement.

Bottom displacement-time history of specimens.

Table 4 presents the test results, including the peak impact force, energy absorption, impactor displacement, and bottom displacement. To quantitatively evaluate the deformation capacity of AFSPs under impact, impactor displacement (\(\:{D}_{i}\)) and displacement of the bottom centre of AFSPs (\(\:{D}_{b}\)) were adopted.

Figure 11 displays the effect of the impact energy on the impactor and bottom displacements. As the impact energy increased from 600 J to 2000 J, the impactor displacement rose by 143.1%, from 20.9 mm to 50.8 mm, while the bottom displacement surged by 690.5%, from 4.2 mm to 33.2 mm.

Effect of the impact energy on the displacements.

Figure 12 shows the effect of the thickness of components on the impactor and bottom displacements under a 1000 J impact energy. As the thickness of the upper sheet varied from 0.8 mm to 2 mm, the impactor displacement reduced by 46.2% from 39.9 mm to 21.0 mm, and the bottom displacement reduced by 74.0% from 18.4 mm to 4.8 mm.

As the thickness of the aluminium foam varied from 10 mm to 30 mm, the impactor displacement increased by 57.5% from 25.2 mm to 39.7 mm, while the bottom displacement decreased from 14.4 mm to 9.6 mm. The impactor dropped quickly in the aluminium foam core due to the smaller stiffness of aluminium foam, resulting in a larger impactor displacement for AFSPs with the thicker aluminium foam. Nevertheless, the thicker aluminium foam absorbed more impact energy, reducing the energy transmitted to the lower sheet, which in turn resulted in a smaller bottom displacement.

In addition, the impactor displacements of AFSPs with lower sheet thickness of 2 mm, 3 mm, and 4 mm were 33.2 mm, 30.1 mm, and 27.4 mm, respectively, close to one another. However, as the thickness of the lower sheet varied from 2 mm to 4 mm, the bottom displacement reduced by 59.5% from 14.8 mm to 6.0 mm. Therefore, the thickness of the lower sheet had a limited effect on the impactor displacement, but it played a positive role in reducing the bottom displacement.

Effect of the thickness of sandwich components on the displacements.

LS-DYNA software was used to establish a numerical model of AFSPs under impact, ensuring consistency with the dimensions of the test device and specimen, as shown in Fig. 13. Tiwari et al. [14] found that numerical results were significantly affected by boundary restraints, so the real boundary conditions of the steel plates were accurately simulated. To improve efficiency, the keyword *BOUNDARY_SPC_SET was used instead of simulating bolt action, applying restraints on all six degrees of freedom of the fixture. The aluminium foam, impactor, upper steel plate and lower steel plate were modeled using eight-node hexahedral solid elements. To prevent negative volumes, the stiffness control mode IHQ = 6 was applied for hourglass control. The upper and lower sheets were simulated by Belytschko-Tsay shell elements, with five integration points through the thickness. To minimize calculation time, the distance between the impactor and the specimen was set to zero, and the keyword *INITIAL_VELOCITY_GENERATION was used to define the initial velocity of the impactor.

Finite element model of AFSPs.

The interaction between the upper steel plate and the upper sheet, as well as between the lower steel plate and the lower sheet, was modelled by the keyword *AUTOMATIC_SURFACE_TO_SURFACE. In the drop-weight impact test, it was observed that the impactor completely penetrated the AFSP under high-energy impacts. Thus, the contact between the impactor and AFSP components was defined by the keyword *ERODING_SURFACE_TO_SURFACE, allowing material failure to be accounted for during the impact, while ensuring the remaining components continued to interact. Furthermore, since the test showed that the AFSP components detached completely after impact, the contact between the components was modelled using the keyword *TIEBREAK_SURFACE_TO_SURFACE. The failure normal stress (NFLS) and failure shear stress (SFLS) of the interface were both 10 MPa.

In the LS-DYNA model, the keyword *MAT_PLASTIC_KINEMATIC was employed to define the bilinear elastoplastic behaviour of stainless steel and alloy steel sheets, accounting for the strain rate effect. The input parameters for the steel sheets were determined from quasi-static tensile tests and are summarized in Table 3.

To model the behaviour of the aluminium foam, the keyword *MAT_CRUSHABLE_FOAM was used. The material properties are listed in Table 2, and additional parameters, such as the tensile stress cutoff and rate sensitivity, were derived from Xu30. The aluminium foam elements were permanently deleted when the material response met predefined failure criteria, and this was controlled by the keyword *MAT_ADD_EROSION with a shear strain threshold of 0.5. Besides, the keyword *MAT_RIGID was applied to the impactor, upper steel plate, and lower steel plate, as their deformation was negligible during the impact tests.

Figure 14 shows the mesh sensitivity analysis of S1.4-20-3-2000. The force-displacement curve from the numerical simulation using a smaller mesh size closely matched the experimental results. To balance accuracy and computational efficiency, a mesh size of 2 mm was selected for AFSPs in the model. The number of nodes and elements in the model was 87,187 and 11,490, respectively.

Effect of mesh size of the force-displacement curve of S1.4-20-3-2000.

Figure 15 compares the numerical and experimental force-displacement and energy absorption-displacement curves of AFSPs. Table 5 provides a detailed comparison of the results. The results showed that the numerical curves were in good agreement with the experimental curves. The numerical simulations predicted peak forces with an average ratio of 0.93 compared to the experimental values, with a coefficient of variation of 3.2%. The maximum displacement of the impactor showed an average ratio of 1.05 with a coefficient of variation of 6.1%. The numerical peak force was slightly lower, and the maximum displacement was slightly higher. This discrepancy might be due to the fact that the steel sheet experienced multi-directional stretching under impact, while the material properties in the numerical model were based on uniaxial tension tests.

Comparisons of test and numerical force-displacement curve.

Figure 16 shows the comparison between the numerical and experimental failure modes of S1.4-20-3-1000. The numerical model accurately captured the damage of AFSP under impact, including the penetration of the upper sheet, the shear of the aluminium foam and the deformation of the lower sheet.

Comparisons of test and numerical failure mode of S1.4-20-3-1000.

Based on the verified model, the effects of impactor dimensions and shapes on the impact response of AFSPs were investigated. Except for the diameter and shape of the impactor, all other parameters were kept consistent with those of S1.4-20-3-1000. For practical engineering applications, the cracking of the lower sheet was defined as the failure criterion for AFSPs.

Figure 17 demonstrates the effect of impactor diameter on the dynamic response and energy absorption of AFSPs. The diameter of the spherical impactor used were 14.7 mm, 19.7 mm, 24.7 mm and 29.7 mm, respectively. Figure 17(a) presents that a larger impactor diameter increased the contribution of the upper sheet and foam core to resisting the impact, leading to greater energy absorption capacity and stiffness. Specifically, AFSPs with impactor diameters of 14.7 mm and 19.7 mm experienced penetration and cracking of the lower sheet, while those with impactor diameters of 24.7 mm and 29.7 mm exhibited noticeable deformation in the lower sheet without cracking. Therefore, when the impactor diameter increased from 14.7 mm to 29.7 mm, the first peak force increased from 33.5 kN to 68.1 kN, and the maximum displacement of the impactor decreased from 49.6 mm to 27.9 mm, as illustrated in Fig. 17(b). This indicated that a larger impactor diameter led to increased impact resistance and reduced deformation of the AFSPs. Figure 17(c) illustrates that the internal energy absorbed by the upper sheet and aluminium foam increased by 172.9% and 213.5%, respectively, with the increase in impactor diameter. Conversely, the internal energy ratio of the lower sheet reduced from 62.2 to 8.0%, as AFSPs with impactor diameters of 24.7 mm and 29.7 mm did not experience cracking.

Effect of impactor diameter on the dynamic response and energy distribution of AFSPs.

Figure 18 shows the effect of impactor shape on the dynamic response and energy absorption of AFSPs. As shown in Fig. 18(a), under the impact of 1000 J energy, the upper sheet of AFSPs impacted by the spherical, flat, and wedge-shaped impactors all experienced penetration. However, the lower sheet of AFSPs impacted by the wedge impactor cracked, whereas those impacted by the spherical and flat impactors remained intact. Regarding the range of participation of the upper sheet and aluminium foam in resisting impact, the largest area was observed for AFSPs impacted by the flat impactor, while the smallest was with the wedge impactor. Consequently, the AFSP impacted by the flat impactor exhibited the highest peak force, whereas the AFSP impacted by the wedge impactor showed the lowest, as indicated in Fig. 18(b). The maximum displacements for the spherical, flat, and wedge impactors were 36.3 mm, 24.3 mm, and 37.8 mm, respectively, with the wedge impactor causing the greatest displacement. Figure 18(c) shows that the internal energy of the upper sheet and aluminium foam was highest in AFSPs impacted by the flat impactor, while the AFSP impacted by the wedge impactor had the highest internal energy in the lower sheet.

Effect of impactor shape on the dynamic response and energy distribution of AFSP.

This study conducted a series of low-velocity impact tests to investigate the impact resistance of AFSPs. The effects of the impact energy and components thickness on the dynamic behaviour of AFSPs were investigated. A finite element model of AFSPs was developed to conduct parameter analysis. The main findings in this study are summarized as follows.

Both the energy absorption and bottom displacement of AFSPs increased as the impact energy increased. The force-displacement curve of AFSPs exhibited four stages, which corresponded to the fracture of the upper sheet, the densification of the aluminium foam core, the gradual deformation to fracture of the lower sheet, and the penetration of AFSPs.

When subjected to a low impact energy, AFSPs with thicker upper sheets demonstrated higher stiffness, leading to increased first peak force and decreased impactor and bottom displacement. Increasing the thickness of the upper sheet was more effective in reducing deformation compared to increasing the thickness of the lower sheet.

Larger foam thickness resulted in increased impactor displacement and reduced bottom centre displacement. AFSPs with thinner aluminium foam cores exhibited higher peak forces, as the densification of the foam core before the upper sheet fractured allowed the lower sheet to provide stiffness at smaller impactor displacements.

At low impact energies, the contribution of the lower sheet to the impact resistance was mainly reflected after the upper sheet fractured. The thickness of the lower sheet had a limited effect on peak impact force and impactor displacement at low impact energies, though a thicker lower sheet significantly reduced the bottom centre displacement.

The numerical results indicated that impactors with larger diameters resulted in higher peak forces and reduced deformation of AFSPs. Among different impactor shapes, a flat impactor engaged a broader area of the upper sheet and aluminium foam, leading to greater peak force and reduced deformation compared to spherical and wedge-shaped impactors.

The data used to support the findings of this study are available from the corresponding author upon request.

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The authors gratefully acknowledge the financial support provided by the National Natural Science Foundation of China (No. 52278145), the Engineering research (No. JZ2022-002), the Luzhou Science and Technology Program (No. 2022-GYF-2) and Scientific and Technological Research Program of Chongqing Education Commission (Grant No. KJQN202004010 and KJZD-K202204001).

Academy of Combat Support, Rocket Force University of Engineering, Xi’an, 710025, China

Jian Yuan & Cheng-Qiang Gao

Key Laboratory of New Technology for Construction of Cities in Mountain Area (Chongqing University), Ministry of Education, Chongqing, 400045, China

Kun Liu, Zhi-Yue You & Shao-Bo Kang

School of Civil Engineering, Chongqing University, Chongqing, 400045, China

Kun Liu, Zhi-Yue You & Shao-Bo Kang

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J.Y. and K.L. wrote the main manuscript text, C-Q.G. prepared Figs. 4, 5, 6, 7, 8, 9, 10, 11 and 12 and Z-Y.Y. prepared Figs. 13, 14, 15 and 16 and S-B.K. proposed the idea of the paper and checked the manuscript. All authors reviewed the manuscript.

Correspondence to Shao-Bo Kang.

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Yuan, J., Liu, K., Gao, CQ. et al. Experimental and numerical studies on corrosion-resistant aluminium foam sandwich panel subject to low-velocity impact. Sci Rep 14, 26611 (2024). https://doi.org/10.1038/s41598-024-78178-9

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Received: 17 September 2024

Accepted: 29 October 2024

Published: 04 November 2024

DOI: https://doi.org/10.1038/s41598-024-78178-9

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